"HEALABLE AND REPROCESSABLE COMPOSITIONS"

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Australian Provisional Patent Application No. 2021901834 filed on 18 June 2021, the contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure generally relates to healable and reprocessable polymer compositions comprising borate crosslinkers, and to any materials and articles thereof. The present disclosure also relates to the synthesis of the borate crosslinkers and use thereof as monomers in the preparation of the polymer compositions, and materials and articles thereof comprising the borate crosslinkers.

BACKGROUND

Thermoset polymers with individual chains interconnected into a three- dimensional network, account for 15-20% of the global polymer production, and are essential components of adhesives, structural composites, electrical insulation, coatings, sealants etc. ^{1, 2} However, conventional thermosets cannot be re- moulded due to their inability to flow on applying heat — a drawback that hinders recycling or repurposing of components made from these materials. ³

Covalent adaptable networks (CANs) ^4,5 are a new class of thermosets containing dynamic-covalent bonds as exchangeable crosslinks to facilitate damage repair and reprocessing when triggered (commonly by heat), while maintaining high mechanical strength under normal usage conditions. Bond exchange in CANs occurs via either a “ dissociative ” process in which reversible crosslinks are cleaved into the reactive constituents before regeneration, or an “ associative ” pathway involving direct substitution reactions between the dynamic crosslinks and pendant reactive groups in the network. ⁶ Thus, network reshuffling via dissociative bond exchange involves a reversible (or irreversible) reduction in network crosslink density depending on factors such as network microstructure, chain mobility, and the kinetics of bond regeneration. In contrast, associative bond exchange affords malleability (generally thermally induced) without loss of crosslink density — a feature characteristic of the newly introduced subclass of CANs called “vitrimers”. ⁷ ’ ^& Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

SUMMARY

Disclosed herein is the synthesis and utility of trialkylborates, which can be used to provide crosslinking monomers in the preparation of polymer compositions (for example thermoset polymers), materials and articles. Ideally, when incorporated into three-dimensional crosslinked polymer networks, the dynamic trialkylborate junctions can undergo B — O bond exchange reactions via both dissociative and associative mechanisms, enabling damage healing/recyclability in response to stimuli such as moisture and/or heat. The ease of synthesis of functional trialkylborates further allows their use as cost effective building blocks for polymer design via commercially important chemistries, including, but not limited to: photo -initiated free-radical and thiol-ene/yne polymerisation, epoxide ring opening, urethane, and thiol Michael addition, amongst other potential mechanisms.

The present disclosure provides a potential low cost and readily accessible toolbox of building blocks for healable (mendable) and remouldable polymers, materials and/or articles. These materials can provide particular functionality geared to build a circular economy.

The polymers comprising trialkylborate junctions, as described herein, can be classified as covalent adaptable networks, or vitrimers due to their ability to flow and undergo crack repair, in response to heat or moisture. The ability to heal damage is a highly desirable trait of polymers for structural components and protective coatings, especially in service locations where frequent maintenance or replacement is prohibitively costly. Examples include, but are not limited to: space exploration applications, oil rigs and pipelines.

The presence of semi-permanent and/or permanent crosslinks within a dynamic network may also confer shape-memory and can serve to reduce creep within dynamic networks. Shape-memory polymers have potential applications in the design of actuators, sensors, flexible electronics, and biomedical devices. Other interesting applications of dynamic thermoset polymers may include, but are not limited to: adhesives that can ‘debond on demand’, repairable battery electrolytes, three- dimensional printing of strong and recyclable components, energy storage/harvesting devices, wearable electronics etc.

Hydrolysable trialkylborate links may potentially enable close-loop recycling of the polymers. In addition, polymers comprising the borate crosslinkers herein may build upon the fire-resistant properties of boron containing polymers. Therefore the resulting polymers, materials and/or articles, may demonstrate enhanced fire-resistance compared to conventional polymers, for example conventional thermosets.

In a first aspect, disclosed herein is a crosslinkable polymer composition comprising: A. at least one borate crosslinker selected from Formula 1

Formula 1 wherein:

(a) R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

(b) R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of RF and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or (ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group; B. one or more crosslinkable monomers each comprising two or more polymerisable groups; and

C. optionally one or more polymerisable monomers comprising one or more polymerisable groups; wherein one or more monomers selected from the crosslinkable monomers and polymerisable monomers further comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof.

In one embodiment of the first aspect: at least two of R _A , R _B and Rc are the same; or R _A , R _B and Rc are all the same.

In a second aspect, disclosed herein is a method of preparing a polymer composition, the method comprising: a) preparing a mixture comprising: i) at least one borate crosslinker of Formula 1

Formula 1 wherein:

• R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

• R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and - when a is 1 : one of RE, RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of RE, RF and RG are hydrogen; or - when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group; ii) at least one crosslinkable Monomer B, each comprising two or more polymerisable groups; and iii) optionally at least one polymerisable Monomer C, each comprising one or more polymerisable groups, wherein at least one of Monomer B and Monomer C comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof; and b) polymerising the mixture. In a third aspect, disclosed herein is a crosslinked polymer composition produced by the method of the second aspect.

In fourth aspect, disclosed herein is a material comprising a reaction product of the crosslinkable polymer composition of the first aspect or the crosslinked polymer composition of the third aspect. In a fifth aspect, disclosed herein is the use of:

A. at least one borate crosslinker selected from Formula 1

Formula 1 wherein: (a) R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

(b) R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of RE, RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of RE, RF and RG are hydrogen; or when a is 0:

(i) one of RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of RF and RG are hydrogen; or

(ii) RF and RG are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group;

B. one or more crosslinkable monomers each comprising two or more polymerisable groups; and

C. optionally one or more polymerisable monomers comprising one or more polymerisable groups; wherein one or more monomers selected from the crosslinkable monomers and polymerisable monomers further comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof, in the formation of a polymer composition.

In a sixth aspect, disclosed herein is an article comprising or consisting of the polymer composition of the first aspect, the crosslinked polymer composition of the third aspect, or the material of the fourth aspect.

In a seventh aspect, disclosed herein is the use of the composition of the first aspect, the crosslinked polymer composition of the third aspect, or the material of the fourth aspect, in the manufacture of an article.

In an eighth aspect, disclosed herein is a method of repairing an article comprising or consisting of the polymer composition of the first aspect, the crosslinked polymer composition of the third aspect, or the material of the fourth aspect, the method comprising subjecting a defect in or on the article to heat, moisture, compression force, or a mixture thereof.

In a ninth aspect, disclosed herein is a borate compound for crosslinking a polymer composition, having a structure of Formula 1

Formula 1 wherein:

(a) R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

(b) R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group. In a tenth aspect, disclosed herein is a method of synthesising the borate compound of the ninth aspect, the method comprising the step of exposing a borate to an alcohol, wherein the alcohol comprises a polymerisable group.

Any embodiment herein shall be taken to apply mutatis mutandis to any other embodiment unless specifically stated otherwise.

The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally- equivalent products, compositions and methods are clearly within the scope of the disclosure, as described herein.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the present disclosure will be further described and illustrated, by way of example only, with reference to the accompanying drawings in which: Figure 1 Stacked ¹ H NMR (A), ¹³ C NMR (B), and FTIR (C) spectra overlays of 2-allyloxyethanol and tris(2-(allyloxy)ethyl) borate (Bl). Figure 2 Stacked Ή NMR (A), ¹³ C NMR (B), and FTIR (C) spectra of 2- hydroxyethyl methacrylate and tris(2-(allyloxy)ethyl) borate (B2). Figure 3 Image A) shows the synthesis of dynamic thermoset networks via photo- initiated thiol-ene, and thiol-ene-methacrylate hybrid polymerization. Image B) shows hydrolysis/re-esterification, and image C) shows transesterification with the dissociative and associative pathways.

Figure 4 ¹ H NMR spectra of tris(2-(allyloxy)ethyl) borate (A), and a mixture of tris(2-(allyloxy)ethyl) borate and D2O before (B), and after overnight stirring in presence of molecular sieves (C).

Figure 5 IR spectra analyses for network 6.

Figure 6 IR spectra analyses for network 1.

Figure 7 IR spectra analyses for network 9.

Figure 8 Digital images of: A) reversible depolymerisation; B) reversible softening; and C) a swelling study of network 3.

Figure 9 Influence of Bl loading on T _g , and tensile properties of the thiol-ene networks. Figure 10 Image A) shows digital images of moisture assisted healing of network 1. Image B) shows representative tensile stress vs strain curves for uncut (solid) and re-joined (dashed) specimens of networks 2-6 after annealing (the numbers above the curves denote the equivalents of B1 in the network). Image C) shows the healing efficiency of networks 2-6 as a function of B1 loading.

Figure 11 Digital images for network swelling studies in different solvents for network 11.

Figure 12 Image A) shows the influence of B2 loading on mechanical properties, and healing efficiency of thiol-ene-methacrylate networks. Image B) provides representative stress vs strain curves for uncut (solid), and healed (dashed) specimens of networks 7, 9, and 11 after annealing. Image C) shows photographs of pulverised and reprocessed samples of network 11. Figure 13 Image A) shows the influence of TDAE loading (free hydroxyl groups) on mechanical properties, and healing efficiency of the thiol-ene- methacrylate networks. Image B) provides representative stress vs strain curves for uncut (solid) and healed (dashed) specimens of thiol-ene- methacrylate networks containing varying amounts of TDAE, after annealing.

Figure 14 Image A) shows digital photographs of the dogbone specimen of network 11 before (left), and after (right) overnight incubation at 75% relative humidity. Image B) shows digital photographs demonstrating the load bearing ability of the exposed dogbone specimen that can support a load of 280 g without buckling.

DESCRIPTION OF EMBODIMENTS

The present disclosure describes the following various non-limiting examples, which relate to investigations undertaken to identify alternative and improved polymer compositions, and to any formulations, coatings, and methods of making and use thereof.

General Definitions and Terms

In the following description, reference is made to the accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be utilised and structural changes may be made without departing from the scope of the present disclosure.

With regards to the definitions provided herein, unless stated otherwise, or implicit from context, the defined terms and phrases include the provided meanings. In addition, unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

All publications discussed and/or referenced herein are incorporated herein in their entirety.

Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, compositions, coatings, processes, and coated substrates, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

The term “and/or”, e.g. “X and/or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower-numbered item (e.g. a “first” item) and/or a higher-numbered item (e.g. a “third” item).

As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub combination.

Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 4.5, and 5, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

Herein, suitable alkyl chains, which may or may not be substituted with one or more substituents, may comprise 1 to 20 carbon atoms (i.e. C1-C20), or 1 to 15 carbon atoms (i.e. C1-C15), or 1 to 10 carbon atoms (i.e. C1-C10), or 1 to 5 carbon atoms (i.e. C1-C5). A Ci-20 alkyl chain may comprise 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15 or 16 or 17 or 18 or 19 or 20 carbon atoms. Examples of suitable alkyl groups which may or may not be substituted, or optionally interrupted include, but are not limited to: methyl, ethyl, «-propyl, isopropyl, «-butyl, isobutyl, sec-butyl and ieri-butyl, «-pentyl, terf-pentyl, neopentyl, isopentyl, 1 -methylbutyl and 1-ethylpropyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosanyl, isomers thereof, and mixtures thereof. The alkyl chains may optionally interrupted, for example with one or more groups selected from, but not limited to: cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl-O-aryl, amine, amide, and alkyl-amine, and mixtures thereof. Alternatively the alkyl chain may be interrupted with an oxygen atom.

As used herein, the phrase “optionally substituted” means that substitution is optional and therefore includes both unsubstituted and substituted atoms and moieties. A “substituted” atom or moiety indicates that any hydrogen on the designated atom or moiety can be replaced with a selection from the indicated substituent groups, provided that the normal valency of the designated atom or moiety is not exceeded, and that the substitution results in a stable compound. For example, if a methyl group is optionally substituted, then 3 hydrogen atoms on the carbon atom can be replaced with substituent groups. Suitable substituents include, but are not limited to: a Ci-io acyl derivative, an aldehyde moiety (-C(O)H), a C _2-10 alkene, a Ci- ₁₀ alkoxy, a Ci- ₁₀ alkyl, a Ci- ₁₀ alkyl alcohol, a C _2-10 alkene, a C _2-10 alkyne, a Ci- ₁₀ alkyl amide, a Ci- ₁₀ alkyl amine, a Ci- ₁₀ alkyl azide, a Ci- ₁₀ alkyl diol, a Ci- ₁₀ alkyl ester, a C _2-10 alkyl ether, a Ci- ₁₀ alkyl nitrile, a Ci- ₁₀ alkyl thiol, an allyl, a Ci- ₁₀ allyl, a -C(0)NH ₂ moiety, a -NH ₂ moiety, a Ci- ₁₀ amine, a Ci- ₁₀ amino-nitrile, an aryl, an aryl ether, an aryl fused heterocycle, a -N ₃ moiety, a Ci- ₁₀ carbamate, a carbonyl moiety (-C(O)), a carboxylic acid, a Ci- ₁₀ carboxylic acid, a cyano group (-CN), a C ₂ -7 cyclic ether, a C3-7 cycloalkyl, a Ci- ₁₀ dialkyl amine, an epoxide, a formate group, a Ci- ₁₀ halo alkyl, a halogen (“halo”), chlorine, fluorine, bromine, iodine, a heteroaryl, a heterocycle, a hydroxide group (- OH), a Ci- ₁₀ isocyanate, a ketal, a C _3-7 lactam, a C _3-7 lactone, a Ci- ₁₀ nitrile, a nitro moiety (-NO ₂ ), a Ci- ₁₀ nitro, an oxime, a Ci- ₁₀ oxime ether, a Ci- ₁₀ sulfate, a Ci- ₁₀ sulfite, a C _4-7 sulfone, a Ci- ₁₀ sulfoxide, a Ci- ₁₀ thiocyanate, a Ci- ₁₀ thioester, a Ci- ₁₀ thionoester, a Ci- ₁₀ thioether or a thiol moiety (-SH), or mixtures thereof.

Herein “capable of forming hydroxyl groups on reaction thereof’ would be understood to include the removal of a protecting groups present on one or more hydroxyl groups, the introduction of the hydroxyl group following a reaction on a compound and/or monomer, or the conversion of a functional group already present on the compound and/or monomer. Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Throughout this specification, the term "consisting essentially of" is intended to exclude elements which would materially affect the properties of the claimed composition.

The terms "comprising", "comprise" and "comprises" herein are intended to be optionally substitutable with the terms "consisting essentially of", "consist essentially of", "consists essentially of", "consisting of", "consist of" and "consists of", respectively, in every instance.

Herein the term “about” encompasses a 10% tolerance in any value or values connected to the term.

Herein “weight maybe abbreviated to as “wt%”.

Compositions

Disclosed herein is a crosslinkable composition (for example polymer composition) comprising:

A. at least one borate crosslinker selected from Formula 1

Formula 1 wherein:

• R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

• R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and

- when a is 1 : one of RE, RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of RE, RF and RG are hydrogen; or

- when a is 0:

(i) one of RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of RF and RG are hydrogen; or

(ii) RF and RG are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group;

B. one or more crosslinkable monomers each comprising two or more polymerisable groups; and

C. optionally one or more polymerisable monomers comprising one or more polymerisable groups; wherein one or more monomers selected from the crosslinkable monomers and polymerisable monomers further comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof.

It will be appreciated that the compositions disclosed herein may comprise or may consist of a thermoset polymer. It will also be appreciated that the compositions disclosed herein may be used in the formation of a thermoset polymer.

Borate Crosslinkers Disclosed herein is borate compound for crosslinking a polymer composition, having a structure of Formula 1

Formula 1 wherein: · R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

• R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and - when a is 1 : one of RE, RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of RE, RF and RG are hydrogen; or - when a is 0: (i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or (ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group.

Herein R _A , R _B and Rc each of may be independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprises a polymerisable group. In one embodiment each alkyl group is an optionally substituted Ci-20, Ci-15, Ci-10, or C1-5, alkyl group which is optionally interrupted and optionally comprises a polymerisable group.

In one embodiment, at least two of R _A , R _B and Rc are the same. In another embodiment, R _A , RB and Rc are all the same.

In one embodiment the borate compound is not at least one of:

In one embodiment at least one of R _A , R _B and Rc is an optionally substituted alkyl group which is optionally interrupted, and optionally comprises a polymerisable group. In one embodiment at least one of R _A , R _B and Rc is an optionally substituted alkyl group which is not interrupted, and optionally comprises a polymerisable group.

In one embodiment at least one of R _A , R _B and Rc is an optionally substituted alkyl group that comprises a polymerisable group, and is optionally interrupted. In one embodiment at least one of R _A , R _B and Rc is an optionally substituted alkyl group which is not interrupted, and comprises a polymerisable group.

In one embodiment, the optional interruption in the alkyl group of at least one of R _A , R _B and Rc _, is selected from, but not limited to: an oxygen atom, cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl- O- aryl, amine, amide, and alkyl-amine. In another embodiment, the alkyl group of at least one of R _A , R _B and Rc _, is substituted. In yet another embodiment, the alkyl group of at least one of R _A , R _B and Rc _, is not substituted.

In yet another embodiment at least one of R _A , R _B and Rc is an alkyl group comprising at least a hydroxyl group. Herein R _A and R _B may be joined to form a five or six membered ring of Formula la:

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of RE, RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group;

In one embodiment R _A and R _B are joined to form a five membered ring. In another embodiment R _A and R _B are joined to form a six membered ring.

In one embodiment a is 0. In another embodiment a is 1.

In one embodiment: a is 1 ; one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and the other two of R _E , R _F and R _G are hydrogen. In another embodiment: a is 0; either R _F or R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and the other group is hydrogen. In yet another embodiment, a is 0 and R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group. Herein, the borate crosslinker may be a compound of: Formula 2, Formula 3, Formula 4, Formula 5, or Formula 6: Formula 4 Formula 5

Formula 6 wherein:

Ri, R ₂ , R3, R ₄ , R5, R6, R7 and Rs, are each independently selected from an alkyl group, each of which are optionally substituted and optionally interrupted;

RT, RU, RV, RW, RX, RY and Rz, are each independently selected as a polymerisable group; and b is 0 or 1. Integer b in Formula 4 is 0 or 1. In one embodiment, integer b is 0. In another embodiment integer b is 1.

In embodiment the borate crosslinker is a compound of Formula 2. In another embodiment the borate crosslinker is a compound of Formula 3. In another embodiment the borate crosslinker is a compound of Formula 4. In another embodiment the borate crosslinker is a compound of Formula 5. In another embodiment the borate crosslinker is a compound of Formula 6.

In one embodiment the borate crosslinker is a compound of Formula 3, and R2 is an optionally substituted alkyl group selected from optionally substituted: methyl, ethyl, isopropyl, n-butyl, and t-butyl groups. Herein, mixtures of borate crosslinkers may be used. For example, at least two borate crosslinkers may be used, wherein at least one borate crosslinker is a compound of Formula 1, Formula la, Formula 2, Formula 3, Formula 4, Formula 5, and Formula 6. In one embodiment, at least one of Ri, R ₂ , R ₃ , R ₄ , Rs, R ₆ , R ₇ and Rs is an optionally substituted alkyl group which is interrupted. In one embodiment at least one of Ri, R ₂ , R ₃ , R ₄ , Rs, R ₆ , R ₇ and Rs is an optionally substituted alkyl group which is not interrupted. In another embodiment, at least one of Ri, R2, R3, R4, Rs, R6, R7 and Rs is an optionally substituted alkyl group which is optionally interrupted, and comprises at least one hydroxyl group. In one embodiment each alkyl group is an optionally substituted Ci- ₂₀ , Ci- ₁₅ , Ci- ₁₀ , or C _1-5 , alkyl group which is optionally interrupted.

In one embodiment, the optional interruption in the alkyl group of at least one of Ri, R ₂ , R3, R ₄ , Rs, R6, R7 and Rs, is selected from, but not limited to: an oxygen atom, cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl-O-aryl, amine, amide, and alkyl-amine.

In another embodiment, the alkyl group of at least one of Ri, R ₂ , R3, R ₄ , Rs, R6, R ₇ and Rs _, is substituted. In yet another embodiment, the alkyl group of at least one of Ri, R2, R3, R4, Rs, R6, R7 and Rs, is not substituted.

In yet another embodiment, for any one of the Ri, R ₂ , R3, R ₄ , Rs, R6, R7 and Rs groups, the optional substitution or optional interruption is selected from: an oxygen atom, cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl-O-aryl, amine, amide, and alkyl- amine.

In yet another embodiment at least one of Ri, R ₂ , R3, R ₄ , Rs, R6, R7 and Rs comprises at least a hydroxyl group. Herein, any one of the Ri, R ₂ , R3, R ₄ , Rs, R6, R7 and Rs groups may be independently selected from the group consisting of, but not limited to: attachment to one of the borate oxygen groups and ^# represents attachment to R _T , R _U , Rv, Rw, Rx, RY, RZ, hydrogen or alkyl. In one embodiment R3 and R4 are the same. In another embodiment R3 and R4 are different.

In one embodiment R ₅ and R ₆ are the same. In another embodiment R ₅ and R ₆ are different. In one embodiment R ₇ and Rs are the same. In another embodiment R ₇ and Rs are different.

Groups R _T , R _U , R _V , R _W , R _X , R _Y and Rz may be a functional group, independently selected from the group consisting of, but not limited to: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, cycloalkyl, maleic anhydride, phthalic anhydride, maleimide, o o mixtures thereof. In one embodiment any one of the RT, RU, RV, RW, RX, RY, RZ groups is selected from the group consisting of, but not limited to: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate or methacrylate.

In one embodiment Ru and Rv are the same. In another embodiment Ru and Rv are different.

In one embodiment Rw and Rx are the same. In another embodiment Rw and Rx are different. In one embodiment RY and Rz are the same. In another embodiment RY and Rz are different.

In one embodiment, the borate crosslinker may be a compound the borate crosslinker is selected from:

wherein:

X and Y are each independently integers in a range of 1 to 15; and R9 is an optionally substituted alkyl group.

In one embodiment X is an integer of 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15. In another embodiment, Y is an integer of 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15.

In one embodiment, R9 is an optionally substituted Ci-20, Ci-15, Ci-10, or C1-5, alkyl group.

Examples of borate crosslinkers include, but are not limited to at least one of: In one embodiment, a borate as disclosed herein (for example a borate crosslinker of Formula 1, Formula la, Formula 2, Formula 3, Formula 4, Formula 5 and/or Formula 6), is incorporated into a crosslinkable polymer composition and/or polymer composition as defined herein. Also disclosed herein is a method of synthesising the borate compound as disclosed herein (for example a borate crosslinker of Formula 1, Formula la, Formula 2, Formula 3, Formula 4, Formula 5 and/or Formula 6). In one embodiment, the method comprises the step of exposing a borate to an alcohol, wherein the alcohol comprises a polymerisable group. Exemplary polymerisable groups include, but are not limited to: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, siloxane, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic method may also involve the removal of by-products. In one embodiment, the method comprises the removal of volatile alcohols (for example the removal of methanol, ethanol, isopropanol, amongst other alcohols that may be utilised in the synthesis steps).

Crosslinkable Monomer

One or more monomers deemed a “crosslinkable monomer” may be present in the compositions, methods and/or uses disclosed herein.

In one embodiment at least one crosslinkable monomer is present, wherein each crosslinkable monomer comprises two or more polymerisable groups. In another embodiment, one crosslinkable monomer is present. In yet another embodiment, at least two crosslinkable monomers are present. In one embodiment, at least one crosslinkable monomer is a compound selected from, but not limited to, the group consisting of: alkyl, alkene, aryl, polyaryl, cycloalkyl, heterocyclyl, polycyclic, heteroaryl, bridged bicylclo, allyl ether, phthalate, norbomene, cyanuric acid, polysiloxane, branched allylic, polyalcohol, sulfone, and mixtures thereof. The compound may comprise at least one functional group selected from, but not limited to, the group consisting of: allyl, vinyl, hydroxyl, epoxide, methacrylate, acrylate, amide, amine, acrylamide, methacrylamide, thiol, malemide, isocyanate, and mixtures thereof.

The polymerisable groups may be the same or different. The polymerisable groups may be each independently selected from, but not limited to the group consisting of: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, siloxane, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic o o anhydride, maleimide, mixtures thereof. In one embodiment, the polymerisable groups may be each independently selected from, but not limited to the group consisting of: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate, methacrylate, and mixtures thereof.

The crosslinkable monomer may comprise: at least one polymerisable RR group; at least two polymerisable Rs groups; or a mixture thereof.

The crosslinkable monomer may comprise one or more polymerisable RR groups. The RR groups may be selected from, but not limited to, the group consisting of: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, siloxane, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, o o maleimide, and mixtures thereof. In one embodiment, one or more R _R groups may be selected from, but not limited to the group consisting of: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate and methacrylate. At least one of RT, RU, RV, RW, RX, RY or Rz may be the same as RR.

The crosslinkable monomer may comprise two or more polymerisable Rs groups. The Rs groups may be selected from, but not limited to, the group consisting of: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, siloxane, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, o o maleimide, and mixtures thereof. In one embodiment, the Rs groups may be selected from, but not limited to the group consisting of: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate and methacrylate. At least one of RT, RU, RV, RW, RX, RY or Rz may be the same as Rs.

In yet another embodiment, the polymerisable groups on the crosslinkable monomer may be the same, or there may be a mixture of polymerisable groups present.

In yet another embodiment at least one crosslinkable monomer comprises at least one hydroxyl group and/or at least one group capable of forming a hydroxyl group on reaction thereof. In yet another embodiment at least one crosslinkable monomer comprises a plurality of hydroxyl groups and/or a plurality of groups capable of forming hydroxyl groups on reaction thereof.

At least one crosslinkable monomer may be selected from, but not limited to, the group consisting of: mixtures thereof.

In one embodiment, “Monomer B” is a “crosslinkable monomer” as defined herein.

Polymerisable Monomer

One or more monomers deemed a “polymerisable monomer” may be present in the compositions, methods and/or uses disclosed herein. In one embodiment at least one polymerisable monomer is present, wherein each polymerisable monomer comprises one or more polymerisable groups. The one or more polymerisable groups may be RR groups as defined herein. In another embodiment at least one of the polymerisable monomers comprises a single polymerisable group. In another embodiment, at least one of the polymerisable monomer comprises at least two polymerisable groups, which may be the same or different.

In yet another embodiment, one polymerisable monomer is present. In yet another embodiment, at least two polymerisable monomers are present.

In one embodiment, the polymerisable monomer is a crosslinkable monomer, optionally a crosslinkable monomer as defined herein.

In yet another embodiment at least one polymerisable monomer comprises at least one hydroxyl group and/or at least one group capable of forming a hydroxyl group on reaction thereof. In another embodiment, at least one polymerisable monomer comprises a plurality of hydroxyl groups and/or a plurality of groups capable of forming hydroxyl groups on reaction thereof. In one embodiment the polymerisable monomer comprises at least one polymerisable group selected from, but not limited to, the group consisting of: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, maleimide,

Examples of polymerisable monomers include, but are not limited to: thereof.

At least one polymerisable monomer may be a macromonomer, for example a macromonomer in the form of an oligomer or a polymer. In one embodiment at least one polymerisable monomer is an oligomer or polymer comprising at least one polymerisable group. At least one polymerisable group on the oligomer or polymer may be a R _R group as defined herein. The oligomer or polymer may comprise at least one hydroxyl group, or at least one group capable of forming a hydroxyl group on reaction thereof. In one embodiment the polymerisable monomer is an oligomer or polymer comprising at least one polymerisable group selected from, but not limited to, the group consisting of: thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride,

The oligomer or polymer may take any form known in the art. Examples include, but are not limited to: linear, branched, hyperbranched, dendrimer, or comb materials, or a mixture thereof. The oligomer or polymer may be based on a single monomer (for example a homopolymer), or a plurality of different monomers (for example a copolymer such as a statistical, alternating, gradient or block copolymers). The oligomer or polymer may be composed of any monomer known in the art, for example, the oligomer or polymer may comprise: styrenics, polyolefins, poly(meth)acrylates, poly(meth)acrylamides, polyethers, silicones, polyesters, polyurethanes, and mixtures thereof.

In one embodiment, “Monomer C” is a “polymerisable monomer” as defined herein.

Further monomer

For the compositions, methods and uses defined herein, in addition to the crosslinkable monomer, polymerisable monomer, Monomer B and/or Monomer C, at least one additional monomer “further monomer” may be present.

In one embodiment a composition as defined herein comprises at least one further monomer. At least one further monomer may be selected from, but not limited to: methacrylate-based, acrylate-based, olefin-based, carbonate-based, acrylamide- based, methacrylamide -based, styrene-based, or epoxide-based monomers, or a mixture thereof.

At least one monomer may be selected from the group consisting of: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, hexyl acrylate, 2- ethylhexyl acrylate, octyl acrylate, tert-octyl acrylate, 2-chloroethyl acrylate, 2- bromoethyl acrylate, 4-chlorobutyl acrylate, cyanoethyl acrylate, 2-acetoxyethyl acrylate, dimethylaminoethyl acrylate, benzyl acrylate, methoxybenzyl acrylate, 2- chlorocyclohexyl acrylate, cyclohexyl acrylate, furfuryl acrylate, tetrahydrofurfuryl acrylate, phenyl acrylate, 5-hydroxypentyl acrylate, 2-methoxyethyl acrylate, 3- methoxybutyl acrylate, 2-ethoxybutyl acrylate, 2-ethoxyethyl acrylate, 2-isopropoxy acrylate, 2-butoxyethyl acrylate, 2-(2-methoxyethoxy)ethyl acrylate, 2-(2- methoxyethoxy)ethyl acrylate, 2-(2-butoxyethoxy) ethyl acrylate, co- methoxypolyethylene glycol acrylate, l-bromo-2-methoxyethyl acrylate, and 1 ,1- dichloro-2-ethoxyethyl acrylate; methacrylic esters, optionally: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butylmethacrylate, tert-butylmethacrylate, amylmethacrylate, hexylmethacrylate, cyclohexylmethacrylate, benzyl methacrylate, chlorobenzyl methacrylate, octyl methacrylate, stearylmethacrylate, sulfopropylmethacrylate, N-ethyl-N-phenylaminoethyl methacrylate, 2-(3- phenylpropyloxy)ethyl methacrylate, dimethylaminophenoxyethyl methacrylate, furfuryl methacrylate, tetrahydrofurfuryl methacrylate, phenyl methacrylate, cresyl methacrylate, naphthyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate, triethylene glycol monomethacrylate, dipropylene glycol monomethacrylate, 2-methoxyethyl methacrylate, 3-methoxybutyl methacrylate, 2- acetoxyethyl methacrylate, 2-acetoacetoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-isopropoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2-(2- methoxyethoxy)ethyl methacrylate, 2-(2-ethoxyethoxy)ethyl methacrylate, 2-(2- butoxyethoxy)ethyl methacrylate, co-methoxypolyethylene glycol methacrylate (addition mol number: 6), acryl methacrylate, and methacrylic acid dimethylaminoethylmethyl chloride salt; vinylesters, optionally: vinylacetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl chloroacetate, vinylmethoxy acetate, vinylphenyl acetate, vinyl benzoate and vinyl salicylate; acrylamides, optionally: acrylamide, ethylacrylamide, propylacrylamide, isopropylacrylamide, n-butylacrylamide, sec-butylacrylamide, tert-butylacrylamide, cyclohexylacrylamide, benzylacrylamide, hydroxymethylacrylamide, methoxyethylacrylamide, dimethylaminoethylacrylamide, phenylacrylamide, dimethylacrylamide, diethylacrylamide, b-cyanoethylacrylamide, N-(2- acetoacetoxyethyl)acrylamide, and diacetoneacrylamide; methacrylamides, optionally: methacrylamide, methylmethacrylamide, ethylmethacrylamide, propylmethacrylamide, isopropylmethacrylamide, n-butylmethacrylamide, sec-butylmethacrylamide, tert- butylmethacrylamide, cyclohexylmethacrylamide, benzylmethacrylamide, hydroxymethacrylamide, chlorobenzylmethacrylamide, octylmethacrylamide, stearylmethacrylamide, sulfopropylmethacrylamide, N-ethyl-N- phenylaminoethylmethacrylamide, 2-(3-phenylpropyloxy)ethylmethacrylamide, dimethylaminophenoxyethylmethacrylamide, furfurylmethacrylamide, tetrahydrofurfurylmethacrylamide, phenylmethacrylamide, cresylmethacrylamide, naphthylmethacrylamide, 2-hydroxyethylmethacrylamide, 4- hydroxybutylmethacrylamide, triethylene glycol monomethacrylamide, dipropylene glycol monomethacrylamide, 2-methoxyethylmethacrylamide, 3- methoxybutylmethacrylamide, 2-acetoxyethylmethacrylamide, 2- acetoacetoxyethylmethacrylamide, 2-ethoxyethylmethacrylamide, 2- isopropoxyethylmethacrylamide, 2-butoxyethylmethacrylamide, 2-(2-methoxyethoxy) ethylmethacrylamide, 2-(2-ethoxyethoxy) ethylmethacrylamide, 2-(2- butoxyethoxy)ethylmethacrylamide, co-methoxypolyethylene glycol methacrylamide (addition mol number: 6), acrylmethacrylamide, dimethylaminomethacrylamide, diethylaminomethacrylamide, cyanoethylmethacrylamide, and N-(2- acetoacetoxyethyl)methacrylamide; olefins, optionally: dicyclopentadiene, ethylene, propylene, 1 -butene, 1-pentene, vinyl chloride, vinylidene chloride, isoprene, chloroprene, butadiene, and 2,3-dimethylbutadiene; styrenes, optionally: styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, isopropylstyrene, chloromethylstyrene, methoxystyrene, acetoxystyrene, chlorostyrene, dichlorostyrene, bromostyrene, and vinylbenzoic acid methyl ester; vinyl ethers, optionally: methylvinyl ether, butylvinyl ether, hexylvinyl ether, methoxyethylvinyl ether and dimethylaminoethylvinyl ether; butyl crotonate; hexyl crotonate; dibutyl itaconate; dimethyl maleate; dibutyl maleate; dimethyl fumarate; dibutyl fumarate; methyl vinyl ketone; phenyl vinyl ketone; methoxyethyl vinyl ketone; glycidyl acrylate; glycidyl methacrylate; N-vinyloxazolidone; N-vinylpyrrolidone; acrylonitrile; methacrylonitrile; methylene moronnitrile; vinylidene; and mixtures thereof.

Additives

The compositions, materials and/or articles disclosed herein may comprise one or more additional additives, such as, but not limited to: rheology modifiers, fillers, tougheners, thermal or UV stabilizers, fire retardants, lubricants, surface active agents. One or more additives may be present in an amount of about, or at least about: 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or 85 wt%, based on the total weight of the material and/or article. Examples of optional additives includes, but is not limited to: rheology modifiers; film formers; wetting agents; surfactants; dispersants; anti-foaming agents; anti-corrosion reagents; stabilizers; levelling agents; pigments or dyes; organic and inorganic dyes; suitable flame retardants which retard flame propagation, heat release and/or smoke generation; and/or mixtures thereof.

Methods of Synthesis

Disclosed herein is a method of preparing a polymer composition, the method comprising: a) preparing a mixture comprising: i) at least one borate crosslinker of Formula 1 Formula 1 wherein:

• R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

• R _A and R _B are joined to form a five or six membered ring of Formula 1 a

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group; ii) at least one crosslinkable Monomer B, each comprising two or more polymerisable groups; and iii) optionally at least one polymerisable Monomer C, each comprising one or more polymerisable groups, wherein at least one of Monomer B and Monomer C comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof; and b) polymerising the mixture.

In one embodiment, the method comprises at least one compound of Formula 2, Formula 3, Formula 4, Formula 5 or Formula 6, as defined herein.

In another embodiment, Monomer B is a crosslinkable monomer as defined herein.

In yet another embodiment, Monomer C is a polymerisable monomer as defined herein.

The polymer composition may be formed from any polymerisation procedure known in the art. The polymer composition may be formed using a single process, or a plurality of processes (which may be the same or different). At least one polymerisation procedure may selected from, but not limited to, the group consisting of: free radical or controlled-radical polymerisation; thiol-Michael addition; thiol-ene reactions, optionally with a methacrylate, acrylate, acrylamide and/or methacrylamide; thiol- yne reactions; thio-urethane formation; thiol-epoxide ring opening polymerisation; thiol-isocyanate (thiourethane formation); hydrosilylation; ROMP; Diels-Alder; epoxy-amine ring opening polymerisation; amidation; amine/hydroxyl- isocyanate (poly urea/urethane); aza- Michael addition; azide-alkyne reaction; imide formation, optionally with anhydrides; acyclic diene metathesis (ADMET) polymerisation; free-radical photocuring; radical addition reaction with maleimides; and mixtures thereof.

In one embodiment, a crosslinked polymer composition is produced by a method as disclosed herein.

Also disclosed herein is method of repairing an article comprising or consisting of a composition (for example polymer composition) and/or material as disclosed herein. In one embodiment, the method comprises subjecting a defect in or on the article to heat, moisture, a compression force, or a mixture thereof.

Materials and Articles

Also disclosed herein is a material comprising a reaction product of a crosslinkable polymer composition as defined herein, or the product of a method as disclosed herein. For example, the material is based on the reaction product of a mixture comprising:

• at least one borate crosslinker of: Formula 1, Formula la, Formula 2, Formula 3, Formula 4, Formula 5 or Formula 6;

• optionally at least one crosslinkable monomer; and

• optionally at least one polymerisable monomer.

It will be appreciated that the material may be or comprises a thermoplastic polymer.

The materials disclosed herein preferably comprise a plurality of static junctions and a plurality of dynamic junctions. The term “static junction” or grammatical variations thereof, may be used interchangeably with “static bonds”, and refers to irreversible covalent bonding. The term “dynamic junction” or grammatical variations thereof, may be used interchangeably with “reversible bonding” or “reversible crosslinking”.

At least a portion of the static junctions may be derived from reaction between two or more monomers selected from the crosslinkable monomers and polymerisable monomers. A plurality of the dynamic junctions may be derived from a reaction between a borate crosslinker and one or more monomers optionally selected from the crosslinkable monomers and polymerisable monomers.

In one embodiment the material is self-healing. The terms "healing," "self- healing" and grammatical variants thereof, relate to the application of a stimulus, such as elevated temperatures, the introduction or removal of moisture and/or the application or removal of pressure, to activate the components of the material or polymer composition and heal a portion of said material or polymer composition. For example, to re-join surfaces of a fracture that has formed within and/or on the material. In one embodiment, healing of such fractures does not substantially change the mechanical properties of the material, for example the adhesive and/or tensile strength of the material.

In one embodiment the material is re-mouldable. For example, under appropriate conditions, the material or an article comprising a material or composition as defined herein, may be changed from an initial form to a secondary form, such as by changing the size and or shape of the initial form. The ability to remould an article may be advantageous. For example, the remoulding of a material and/or article, may allow for the reduction in post-manufacturing waste and/or allow for post-consumer recycling of objects made from these materials.

The material may be healed and/or remoulded at a temperature that does not decompose the material or a portion thereof. One or more components of the polymer composition or material may be selected to enable curing of the polymer composition and/or material at a temperature substantially less than the melt temperature (T _m ) for the polymer composition or material. The components for the material and or polymer composition can also be selected to have a T _m to promote the flow or movement of components present in the polymer composition and/or material into an interstitial gap if present in the self-healing material.

It will be appreciated that the healing and/or remoulding conditions will depend on the nature of material or polymer composition, for example the specific borate cross! inker. The healing and/or remoulding process may comprise external or internal processes. For example, the self-healing material may be heated by applying an external temperature to the surroundings of the material thereby raising the internal temperature of the polymer. An internal process may involve resistive heating, ultrasound, or other molecular motion process, whereby heat is generated internally in the material. Resistive heating may involve applying a current across a composite material having a particular resistance and thereby causing internal heating in the component and material.

In one embodiment, the material or polymer composition, can be healed and/or remoulded at relatively low temperatures and pressures, for example, by having a T _m generally below about 100 °C, for example, less than about: 95 °C, 90 °C, 85 °C, 80 °C, 75 °C, or 70 °C. It will also be appreciated that the healing or remoulding conditions will need to be lower than the temperature at which the polymer composition and/or material will decompose. It will also be appreciated that lower temperatures may require longer healing times to achieve similar strength recovery rates available at higher temperatures.

It will be appreciated that the optimal healing and/or remoulding conditions (for example temperature, pressure and/or the specific amount of water present), will vary depending on, amongst other factors: the nature of the polymer composition and/or material, degree of healing and/or remoulding required; and/or the duration and cycles of healing and/or remoulding. In one embodiment, the polymer compositions and/or materials may be healed and/or remoulded more than once. For example the polymer compositions or materials described herein, may be healed multiple times over a duration of many years. Partially or previously healed materials may be further healed, for example by applying further heating and/or pressure.

In one embodiment the healing of a polymer composition and/or material in conducted is in accordance with a known standard or procedure. In another embodiment the remoulding of a polymer composition and/or material is in conducted in accordance with a known standard or procedure.

In another embodiment, the healing of the polymer composition and/or material is conducted in a single process or a single cycle of a procedure. In yet another embodiment, the healing of the composition and/or materials comprises multiple cycles (for example at least 2, 3, 4 or 5) of a process and/or a plurahty of different processes.

In another embodiment, the remoulding of the polymer composition and/or material is conducted in a single process or a single cycle of a procedure. In yet another embodiment, the remoulding of the composition and/or materials comprises multiple cycles (for example at least 2, 3, 4 or 5) of a process and/or a plurahty of different processes.

Also disclosed herein is article comprising or consisting of a composition (e.g. a polymer composition), as defined herein, a crossl inked polymer composition produced by a method disclosed herein, or a material disclosed herein. The article may take any form known in the art, for example, the article may be in the form of: a coating, a portion of a laminate an adhesive, a composite, a moulded compound, a casting and optionally an electrical casting, 3D printing ink, or an additive for polymer waste recycling.

In one embodiment, at least a portion of the article is self-healing. In another embodiment, at least a portion of the article is capable of being remoulded. In yet another embodiment, the healing and/or recycling is performed in the absence of a catalyst.

Uses

Also disclosed herein is use of:

A. at least one borate crosslinker selected from Formula 1 Formula 1 wherein:

(a) R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

(b) R _A and R _B are joined to form a five or six membered ring of Formula la

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group; one or more crosslinkable monomers each comprising two or more polymerisable groups; and optionally one or more polymerisable monomers comprising one or more polymerisable groups; wherein one or more monomers selected from the crosslinkable monomers and polymerisable monomers further comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof, in the formation of a polymer composition, material and/or article as disclosed herein. In one embodiment, the use comprises at least one compound of Formula 2,

Formula 3, Formula 4, Formula 5 or Formula 6, as defined herein.

A composition or material as disclosed herein, may be used in the manufacture of at least a portion of an article. In one embodiment, a composition or material as disclosed herein may be used in the manufacture of at least a portion of a coating for an article.

EXAMPLE EMBODIMENTS

The present disclosure may encompass one or more of the following example embodiments. 1. A crosslinkable polymer composition comprising:

A. at least one borate crosslinker selected from Formula 1

Formula 1 wherein:

(a) R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; and optionally wherein 2 or 3 of R _A , R _B and Rc are the same or

(b) R _A and R _B are joined to form a five or six membered ring of Formula la

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group ;

B. one or more crosslinkable monomers each comprising two or more polymerisable groups; and

C. optionally one or more polymerisable monomers comprising one or more polymerisable groups; wherein: one or more monomers selected from the crosslinkable monomers and polymerisable monomers further comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof, and wherein:

- the optional interruption is optionally independently selected from: an oxygen atom, cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl-O-aryl, amine, amide, alkyl-amine, and mixtures thereof; and

- the optional polymerisable group is optionally independently selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, cycloalkyl, maleic anhydride, phthalic anhydride, maleimide, mixtures thereof. 2. The crosslinkable polymer composition of example embodiment 1, wherein the borate crosslinker is a compound of Formula 2, Formula 3, Formula 4, Formula 5 or Formula 6:

Formula 4 Formula 5

Formula 6 wherein:

Ri, R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ and Rs, are each independently selected from an alkyl group, each of which are optionally substituted and optionally interrupted;

R _T , R _U , R _V , R _W , R _X , R _Y and Rz, are each independently selected as a polymerisable group; and b is 0 or 1.

3. The composition of example embodiment 2, wherein for any one of the Ri, R2, R3, R4, R5, R6, R7 and Re groups the optional substitution or optional interruption is selected from: an oxygen atom, cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl-O-aryl, amine, amide, and alkyl-amine.

4. The composition of example embodiment 2 or example embodiment 3, wherein any one of polymerisable groups R _T , R _U , R _V , R _W , R _X , R _Y and Rz is independently selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, cycloalkyl, maleic anhydride, phthalic anhydride, maleimide, mixtures thereof.

5. The composition of any one of the preceding example embodiments, wherein any one of the Ri, R ₂ , R3, R ₄ , Rs, R6, R7 and Rs groups is independently selected from: wherein m, n and p are each independently an integer in range of 1 to 12; and * represents attachment to one of the borate oxygen groups and ^# represents attachment to RT, RU, RV, RW, RX, RY, RZ, hydrogen or alkyl. 6. The composition of any one of the preceding example embodiments, wherein any one of the RT, RU, RV, RW, RX, RY, RZ groups is selected from: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate or methacrylate.

7. The composition of any one of the preceding example embodiments, wherein the borate crosslinker is selected from:

wherein:

X and Y are each independently integers in a range of 1 to 15; and R ₉ is an optionally substituted alkyl group.

8. The composition of any one of the preceding example embodiments, wherein the borate crosslinker is selected from: 9. The composition of any one of the preceding example embodiments, wherein the borate crosslinker is a compound of Formula 3

Formula 3 wherein R2 is an optionally substituted alkyl group.

10. The composition of example embodiment 9, wherein R2 is an optionally substituted methyl, ethyl, isopropyl, n-butyl, or t-butyl group. 11. The composition of any one of the preceding example embodiments, wherein the crosslinkable monomer comprises two or more polymerisable Rs groups selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, siloxane, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, maleimide, mixtures thereof.

12. The composition of example embodiment 11 , wherein the Rs groups are selected from: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate or methacrylate.

13. The composition of any one of the preceding example embodiments, wherein at least one crosslinkable monomer is a compound selected from: alkyl, alkene, aryl, polyaryl, cycloalkyl, heterocyclyl, polycyclic, heteroaryl, bridged bicylclo, allyl ether, phthalate, norbornene, cyanuric acid, polysiloxane, branched allylic, polyalcohol, sulfone, and mixtures thereof, and optionally comprises at least one functional group selected from: allyl, vinyl, hydroxyl, epoxide, methacrylate, acrylate, amide, amine, acrylamide, methacrylamide, thiol, malemide, isocyanate, and mixtures thereof.

14. The composition of any one of the preceding example embodiments, wherein at least one crosslinkable monomer is selected from: mixtures thereof.

15. The composition of any one of the preceding example embodiments, wherein the polymerisable monomer comprises one or more RR groups selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, maleimide, o o 16. The composition of example embodiment 15, wherein at least one R _R group is selected from: thiol, primary amine, secondary amine, allyl, vinyl, propargyl, acrylate or methacrylate.

17. The composition of example embodiment 15 or example embodiment 16, wherein at least one of: RT, RU, RV, RW, RX, RY or Rz is the same as RR.

18. The composition of any one of example embodiments 15 to 17, wherein the polymerisable monomer comprises one or more hydroxyl groups or groups capable of forming hydroxyl groups on reaction thereof.

19. The composition of any one of example embodiments 15 to 18, wherein the polymerisable monomer comprises a plurality of hydroxyl groups, a plurality of groups capable of forming hydroxyl groups, or a combination thereof. 20. The composition of any one of example embodiments 15 to 19, wherein the polymerisable monomer is an oligomer or polymer comprising at least one hydroxyl group and at least one RR group selected from: thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic o o anhydride, phthalic anhydride, maleimide, mixtures thereof. 21. The composition of any one of example embodiments 15 to 20, wherein the polymerisable monomer is a linear polymer, branched polymer, hyperbranched polymer, dendrimer, comb polymer, or a mixture thereof. 22. The composition of any one of example embodiments 15 to 21, wherein the polymerisable monomer is a polymer or oligomer selected from: styrenics, polyolefins, poly(meth)acrylates, poly(meth)acrylamides, polyethers, silicones, polyesters, polyurethanes, and mixtures thereof.

23. The composition of any one of the preceding example embodiments, wherein the polymerisable monomer is selected from: 24. The composition of any one of the preceding example embodiments, wherein at least one further monomer is present wherein the monomer is: methacrylate-based, acrylate based, olefin-based, carbonate-based, acrylamide-based, methacrylamide- based, styrene-based, epoxide-based, or a mixture thereof. 25. The composition of any one of the preceding example embodiments, wherein at least one further monomer is present, and is selected from: acrylic esters, optionally: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, tert-octyl acrylate, 2-chloroethyl acrylate, 2- bromoethyl acrylate, 4-chlorobutyl acrylate, cyanoethyl acrylate, 2-acetoxyethyl acrylate, dimethylaminoethyl acrylate, benzyl acrylate, methoxybenzyl acrylate, 2- chlorocyclohexyl acrylate, cyclohexyl acrylate, furfuryl acrylate, tetrahydrofurfuryl acrylate, phenyl acrylate, 5-hydroxypentyl acrylate, 2-methoxyethyl acrylate, 3- methoxybutyl acrylate, 2-ethoxybutyl acrylate, 2-ethoxyethyl acrylate, 2-isopropoxy acrylate, 2-butoxyethyl acrylate, 2-(2-methoxyethoxy)ethyl acrylate, 2-(2- methoxyethoxy)ethyl acrylate, 2-(2-butoxyethoxy) ethyl acrylate, co- methoxypolyethylene glycol acrylate, l-bromo-2 -methoxyethyl acrylate, and 1,1- dichloro-2-ethoxyethyl acrylate; methacrylic esters, optionally: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butylmethacrylate, tert-butylmethacrylate, amylmethacrylate, hexylmethacrylate, cyclohexylmethacrylate, benzyl methacrylate, chlorobenzyl methacrylate, octyl methacrylate, stearylmethacrylate, sulfopropylmethacrylate, N-ethyl-N-phenylaminoethyl methacrylate, 2-(3- phenylpropyloxy)ethyl methacrylate, dimethylaminophenoxyethyl methacrylate, furfuryl methacrylate, tetrahydrofurfuryl methacrylate, phenyl methacrylate, cresyl methacrylate, naphthyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate, triethylene glycol monomethacrylate, dipropylene glycol monomethacrylate, 2-methoxyethyl methacrylate, 3-methoxybutyl methacrylate, 2- acetoxyethyl methacrylate, 2-acetoacetoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-isopropoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2-(2- methoxyethoxy)ethyl methacrylate, 2-(2-ethoxyethoxy)ethyl methacrylate, 2-(2- butoxyethoxy)ethyl methacrylate, co-methoxypolyethylene glycol methacrylate (addition mol number: 6), acryl methacrylate, and methacrylic acid dimethylaminoethylmethyl chloride salt; vinylesters, optionally: vinylacetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl chloroacetate, vinylmethoxy acetate, vinylphenyl acetate, vinyl benzoate and vinyl salicylate; acrylamides, optionally: acrylamide, ethylacrylamide, propylacrylamide, isopropylacrylamide, n-butylacrylamide, sec-butylacrylamide, tert-butylacrylamide, cyclohexylacrylamide, benzylacrylamide, hydroxymethylacrylamide, methoxyethylacrylamide, dimethylaminoethylacrylamide, phenylacrylamide, dimethylacrylamide, diethylacrylamide, b-cyanoethylacrylamide, N-(2- acetoacetoxyethyl)acrylamide, and diacetoneacrylamide; methacrylamides, optionally: methacrylamide, methylmethacrylamide, ethylmethacrylamide, propylmethacrylamide, isopropylmethacrylamide, n-butylmethacrylamide, sec-butylmethacrylamide, tert- butylmethacrylamide, cyclohexylmethacrylamide, benzylmethacrylamide, hydroxymethacrylamide, chlorobenzylmethacrylamide, octylmethacrylamide, stearylmethacrylamide, sulfopropylmethacrylamide, N-ethyl-N- phenylaminoethylmethacrylamide, 2-(3-phenylpropyloxy)ethylmethacrylamide, dimethylaminophenoxyethylmethacrylamide, furfurylmethacrylamide, tetrahydrofurfurylmethacrylamide, phenylmethacrylamide, cresylmethacrylamide, naphthylmethacrylamide, 2-hydroxyethylmethacrylamide, 4- hydroxybutylmethacrylamide, triethylene glycol monomethacrylamide, dipropylene glycol monomethacrylamide, 2-methoxyethylmethacrylamide, 3- methoxybutylmethacrylamide, 2-acetoxyethylmethacrylamide, 2- acetoacetoxyethylmethacrylamide, 2-ethoxyethylmethacrylamide, 2- isopropoxyethylmethacrylamide, 2-butoxyethylmethacrylamide, 2-(2-methoxyethoxy) ethylmethacrylamide, 2-(2-ethoxyethoxy) ethylmethacrylamide, 2-(2- butoxyethoxy)ethylmethacrylamide, co-methoxypolyethylene glycol methacrylamide (addition mol number: 6), acrylmethacrylamide, dimethylaminomethacrylamide, diethylaminomethacrylamide, b-cyanoethylmethacrylamide, and N-(2- acetoacetoxyethyl)methacrylamide; olefins, optionally: dicyclopentadiene, ethylene, propylene, 1 -butene, 1-pentene, vinyl chloride, vinylidene chloride, isoprene, chloroprene, butadiene, and 2,3-dimethylbutadiene; styrenes, optionally: styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, isopropylstyrene, chloromethylstyrene, methoxystyrene, acetoxystyrene, chlorostyrene, dichlorostyrene, bromostyrene, and vinylbenzoic acid methyl ester; vinyl ethers, optionally: methylvinyl ether, butylvinyl ether, hexylvinyl ether, methoxyethylvinyl ether and dimethylaminoethylvinyl ether; butyl crotonate; hexyl crotonate; dibutyl itaconate; dimethyl maleate; dibutyl maleate; dimethyl fumarate; dibutyl fumarate; methyl vinyl ketone; phenyl vinyl ketone; methoxyethyl vinyl ketone; glycidyl acrylate; glycidyl methacrylate; N-vinyloxazolidone; N-vinylpyrrolidone; acrylonitrile; methacrylonitrile; methylene moronnitrile; vinylidene; and mixtures thereof.

26. A method of preparing a polymer composition, the method comprising: a) preparing a mixture comprising: i) at least one borate crosslinker of Formula 1

Formula 1 wherein:

• R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

• R _A and R _B are joined to form a five or six membered ring of Formula la Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of R _F and R _G are hydrogen; or

(ii) R _F and R _G are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group; ii) at least one crosslinkable Monomer B, each comprising two or more polymerisable groups; and iii) optionally at least one polymerisable Monomer C, each comprising one or more polymerisable groups, wherein at least one of Monomer B and Monomer C comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof; and b) polymerising the mixture.

27. The method of example embodiment 26, wherein the borate crosslinker is a compound of Formula 2, Formula 3, Formula 4, Formula 5 or Formula 6:

Formula 4 Formula 5

Formula 6 wherein:

Ri, R2, R3, R4, R5, R6, R7 and Rs, are each independently selected from an alkyl group, each of which are optionally substituted and optionally interrupted;

RT, RU, RV, RW, RX, RY and Rz, are each independently selected as a polymerisable group; and b is 0 or 1.

28. The method of example embodiment 27, wherein for any one of the Ri, R2, R ₃ , R4, Rs, R6, R7 and Rs groups the optional substitution or optional interruption is selected from: an oxygen atom, cyclyl, aryl, aralkyl, heterocyclyl, herteroaryl, alkoxy, alkyl-O-aryl, amine, amide, and alkyl-amine.

29. The method of example embodiment 27 or example embodiment 28, wherein any one of polymerisable groups RT, RU, RV, RW, RX, RY and Rz is independently selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, cycloalkyl, maleic anhydride, phthalic anhydride, maleimide, mixtures thereof.

30. The method of any one of example embodiments 26 to 29, wherein Monomer B comprises one or more Rs groups and at least one Rs group is selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, maleimide, o o mixtures thereof. 31. The method of any one of example embodiments 26 to 30, wherein Monomer C comprises one or more R _R groups and at least one R _R group is selected from: hydroxyl, thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, maleimide, o o mixtures thereof.

32. The method of any one of example embodiments 26 to 31, wherein Monomer C comprises at least one hydroxyl group and at least one R _R group selected from: thiol, epoxide, primary amine, secondary amine, isocyanate, silane, glycidyl, alkene, diene, alkyne, allyl, vinyl, propargyl, acrylate, methacrylate, acrylamide, methacrylamide, a cycloalkane, maleic anhydride, phthalic anhydride, maleimide, o mixtures thereof.

33. The method of any one of example embodiments 26 to 32, wherein Monomer C is an oligomer or polymer.

34. The method of any one of example embodiments 26 to 33, wherein the polymer composition is prepared via at least one process selected from: free radical or controlled-radical polymerisation; thiol-Michael addition; thiol-ene reactions, optionally with a methacrylate, acrylate, acrylamide and/or methacrylamide; thiol- yne reactions; thio-urethane formation; thiol-epoxide ring opening polymerisation; thiol- isocyanate (thiourethane formation); hydrosilylation; ROMP; Diels-Alder; epoxy amine ring opening polymerisation; amidation; amine/hydroxyl-isocyanate (poly urea/urethane); aza-Michael addition; azide-alkyne reaction; imide formation, optionally with anhydrides; acyclic diene metathesis (ADMET) polymerisation; free- radical photocuring; radical addition reaction with maleimides; and mixtures thereof.

35. A cross! inked polymer composition produced by the method of any one of example embodiments 26 to 34.

36. A material comprising a reaction product of the crosslinkable polymer composition of any one of example embodiments 1 to 25, or the crosslinked polymer composition of example embodiment 35. 37. The material of example embodiment 36, wherein the material is self-healing.

38. The material of example embodiment 36, or example embodiment 37, wherein the material is capable of being remoulded. 39. The material of any one of example embodiments 36 to 38, wherein the material comprises a plurality of static junctions and a plurality of dynamic junctions, wherein the plurality of static junctions are each derived from reaction between two or more monomers selected from the crosslinkable monomers and polymerisable monomers, and wherein the plurality of dynamic junctions are each derived from reaction between the borate crosslinker and one or more monomers selected from the crosslinkable monomers and polymerisable monomers.

40. Use of:

A. at least one borate crosslinker selected from Formula 1

Formula 1 wherein:

(a) R _A , R _B and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

(b) R _A and R _B are joined to form a five or six membered ring of Formula la

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of R _E , R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of R _E , R _F and R _G are hydrogen; or when a is 0:

(i) one of R _F and R _G is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of RF and RG are hydrogen; or

(ii) RF and RG are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group ;

B. one or more crosslinkable monomers each comprising two or more polymerisable groups; and C. optionally one or more polymerisable monomers comprising one or more polymerisable groups; wherein one or more monomers selected from the crosslinkable monomers and polymerisable monomers further comprise one or more hydroxyl groups or one or more groups capable of forming a hydroxyl group on reaction thereof, in the formation of a polymer composition.

41. The use of example embodiment 40, wherein the borate crosslinker is a compound of Formula 2, Formula 3, Formula 4, Formula 5 or Formula 6:

Formula 6 wherein:

Ri, R ₂ , R3, R ₄ , R5, R6, R7 and Rs, are each independently selected from an alkyl group, each of which are optionally substituted and optionally interrupted; RT, RU, RV, RW, RX, RY and Rz, are each independently selected as a polymerisable group; and b is 0 or 1.

42. An article comprising or consisting of the polymer composition of any one of example embodiments 1 to 25, the crosslinked polymer composition of example embodiment 35, or the material of any one of example embodiments 36 to 39.

43. The article of example embodiment 42, wherein the article is in the form of: a coating, an adhesive, a composite, a moulded compound, a casting and optionally an electrical casting, 3D printing ink, or an additive for polymer waste recycling.

44. The article of example embodiment 42 or example embodiment 43, wherein at least a portion of the article is self-healing.

45. The article of any one of example embodiments 42 to 44, wherein at least a portion of the article is capable of being remoulded.

46. Use of the composition of any one of example embodiments 1 to 25, the crosslinked polymer composition of example embodiment 35, or the material of any one of example embodiments 36 to 39, in the manufacture of an article.

47. The use of example embodiment 46, wherein at least a portion of the article is self-healing.

48. The use of example embodiment 46 or example embodiment 47, wherein at least a portion of the article is capable of being remoulded.

49. A method of repairing an article comprising or consisting of the polymer composition of any one of example embodiments 1 to 25, the crosslinked polymer composition of example embodiment 35, or the material of any one of example embodiments 36 to 39, the method comprising subjecting a defect in or on the article to heat, moisture, compression force, or a mixture thereof.

50. A borate compound for crosslinking a polymer composition, having a structure of Formula 1

Formula 1 wherein:

(a) RA, RB and Rc are each independently selected from an alkyl group, each of which are optionally substituted, optionally interrupted, and optionally comprise a polymerisable group; or

(b) RA and RB are joined to form a five or six membered ring of Formula la

Formula la wherein: a is 0 or 1 ; and when a is 1 : one of RE, RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and two of RE, RF and RG are hydrogen; or when a is 0:

(i) one of RF and RG is an alkyl group which is optionally substituted, optionally interrupted, and comprises a polymerisable group; and one of RF and RG are hydrogen; or

(ii) RF and RG are joined to form a six membered cyclic or aryl ring, wherein the cyclic or aryl ring comprises an alkyl group, the alkyl group being optionally substituted, optionally interrupted, and comprises a polymerisable group . 51. The borate compound of example embodiment 50, wherein the borate crosslinker is a compound of Formula 2, Formula 3, Formula 4, Formula 5 or Formula

6:

Formula 4 Formula 5

Formula 6 wherein:

Ri, R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ and Rs, are each independently selected from an alkyl group, each of which are optionally substituted and optionally interrupted;

R _T , R _U , R _V , R _W , R _X , R _Y and Rz, are each independently selected as a polymerisable group; and b is 0 or 1.

52. A method of synthesising the borate compound of example embodiment 50 or example embodiment 51, the method comprising the step of exposing a borate to an alcohol, wherein the alcohol comprises a polymerisable group.

EXAMPLES

The present disclosure will now be described with reference to the following non-limiting examples and with reference to the accompanying Figures.

Materials

2-Allyloxyethanol (Sigma Aldrich, 98%), 2-hydroxyethyl methacrylate (Sigma Aldrich, 98%), diallyl phthalate (DAP, Sigma Aldrich, 97%), trimethylolpropane diallyl ether (TDAE, Sigma Aldrich, 90%), pentaerythritol tetrakis(3- mercaptopropionate) (PTMP, Sigma Aldrich, >95%), 2,2-dimethoxy-2- phenylacetophenone (Sigma Aldrich, 99%), and deuterium oxide (D2O, Cambridge Isotopes, 99.8%) were used as obtained. N,N-dimethylformamide (DMF, Sigma Aldrich), ethyl acetate (Sigma Aldrich), deuterated chloroform (CDCb, Cambridge Isotopes, 99.8%) were dried over activated molecular sieves (4 A) before use.

Methods

Network healing

Standard dog bone specimens of post cured networks were cut in to two halves using a sharp razor knife. The cut pieces of the dog bone specimen were immediately re-joined and gently pressed together for 1 minute. The re-joined specimen was placed into the silicone dog bone mould. The mould was covered with a high temperature resistant plastic film, followed by an 8 mm thick glass plate and placed in the preheated oven at 120 °C along with a beaker filled with activated silica gel desiccant. After annealing for 16 hours at 120 °C, the mould was allowed to cool to room temperature, and placed in an airtight container containing silica gel desiccant. Samples were tested for tensile properties within 3 hours after removal from the oven. The healing efficiency was calculated using Equation 1.

% Healing efficiency

Equation 1 - Ouncut, and Ore-joined are the average values of peak tensile stress obtained for the uncut, and the re-joined samples, respectively.

Network reprocessabilitv

Following tensile testing, broken dogbone specimens of network 11 were pulverised into millimetre sized pieces. The polymer pieces were poured into a 2 mm thick rectangular trough created on a steel plate using high temperature-resistant tape and rectangular metal strips. The plate was placed on the bottom platen of a hot press machine preheated to 120 °C, and covered with another steel plate. After equilibration at 120 °C for 15 minutes, the material was hot pressed under a pressure of 1 tonne for 10 minutes, allowed to cool to room temperature, and the remoulded polymer film was removed. Digital images were acquired to record the homogeneity and appearance of the re-moulded network film. Instrumentation and Analysis

Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR spectra were recorded on a Bruker AVANCE III 500 MHz Standard Bore spectrometer at 295K. ¹ H NMR spectra were acquired at 500 MHz, while ¹³ C NMR spectra were recorded at 125 MHz. Chemical shifts were referenced to residual solvent peaks and are quoted in terms of parts per million (ppm), relative to tetramethylsilane.

Fourier transform infrared (FTIR1 spectroscopy

Measurements on both liquid and solid samples were recorded in the attenuated total reflectance (ATR) mode on a Bruker Vertex 70 spectrophotometer. The data was plotted in the absorbance mode using the OriginPro 2018 graphing software. Relevant absorbance peaks for thiol and vinyl groups were compared after normalisation of the spectra using the ester carbonyl absorbance (1718-1737 cm ¹ ) as a reference.

Dynamic scanning calorimetry (DSC)

DSC measurements were performed on a TA Instruments Q200 equipped with a liquid nitrogen cooling accessory and calibrated using sapphire and high-purity indium metal. The samples (4-12 mg) were placed in aluminium pans sealed with aluminium lids, and referenced to an empty aluminium pan. Analysis was performed using a heat- cool-heat cycle at a scan rate of 10 °C/min as follows. The sample was heated from 25 °C to 120 °C, cooled to -60 °C, and heated again from -60°C to 120 °C. Glass transition temperatures were evaluated as the midpoint of a step change in heat capacity for the second heating curve.

Tensile testing

Stress/strain properties of all network compositions were measured on a standard Instron testing machine using test specimens in the form of dog bones according to ASTM standard and procedure (D 638-14, type V). The gauge length was 7.62 (±0.25) mm, and the thickness was 3.18 ( 0.5) mm. The crosshead speed was 10 mm/min at 25 °C. Data reported are the averages of at least three measurements, except when less number of specimens for self-healing studies could be tested due to premature separation of re-joined pieces due to poor healing. Synthesis

Synthesis of trialkylb orate monomers with allyl and methacrylate functionality

In order to demonstrate the utility of trialkylborates as dynamic crosslinks in bulk polymer networks, the photoinitiated copolymerization of binary (thiol-ene), ^{9, 10} and ternary (thiol-ene-methacrylate) ^{11 14} monomer mixtures for network synthesis at room temperature. The ready availability of multifunctional thiol and vinyl monomers, the scope for excluding solvents, and the rapid and near-quantitative monomer conversion at room temperature in presence of oxygen are some of the advantages of these techniques. The thiol-ene photopolymerisation is a free -radical step-growth process, while the thiol-ene-methacrylate ternary copolymerisation involves network formation through both step-growth, and chain-growth mechanisms. Consequently, polymer networks obtained by the two types of polymerization are expected to have significantly different mechanical properties, enabling assessment of possible effects of building block choice, and network microstructure on the final material properties.

A selection of trialkylborate monomers were synthesised using the thermally assisted transesterification process. ^{15 16} The exemplary synthesis of tris(2- (allyloxy)ethyl) borate and tris(2-(methacryloyloxy)ethyl) is shown in Scheme 1.

Scheme 1 - Synthesis of functional trialkylborate monomers using a thermal transesterification protocol. The synthesis of tris(2-(allyloxy)ethyl) borate (Bl) is described as a typical example.

2-Allyloxyethanol (56.00 mL, 53.48 g, 5.24 x 10 ¹ mol), and trimethyl borate (21.00 mL, 19.57 g, 1.88 x 10 ¹ mol) were heated at 55 °C under magnetic stirring with a continued flux of dry nitrogen gas, in a two-necked reaction flask for 2 hours to allow equilibration. The temperature was then raised to 75 °C and heating continued overnight under nitrogen flux. The temperature was further raised to 90 °C and heating continued under nitrogen flux for a further 2 hours. The product was cooled to room temperature to obtain a colourless liquid which was stored in a tightly sealed amber glass bottle with the headspace flushed with dry nitrogen (46.22 g, yield = 83.84%). ¹ H NMR [500 MHz, CDCb, 5(ppm)]: 5.87 (CH ₂ =C H, 1H), 5.25 & 5.14 (CH ₂ =CU, 2H), 3.99 (CH ₂ =CH-0-C¾, 2H), 3.93 (B-O-CH2, 2H), 3.52 (B-0-CH ₂ -O¾, 2H). ¹³ C NMR [125 MHz, CDCb, 5(ppm)]: 134.93 (CH ₂ =CH), 116.85 (CH ₂ =CH), 72.04 (B-O- CH ₂ -CH ₂ ), 70.54 (CH ₂ =CH-0-CH ₂ ), 62.83 (B-0-CH ₂ ).

Tris(2-(methacryloyloxy)ethyl) borate (B2) was synthesised following a similar procedure to Bl. Ή NMR [500 MHz, CDCls, 5(ppm)]: 6.48 & 6.40 (C// ₂ =C(CH ₃ )- COO, 2H), 4.22 (B-0-CH ₂ -C H ₂ , 2H), 4.00 (B-O-C H ₂ , 2H), 1.93 (CH ₂ =C(C H ₃ ) COO, 3H). ¹³ C NMR [125 MHz, CDCls, 5(ppm)]: 167.38 (C=0), 136.30 (CH ₂ =C(CH _S )-COO), 125.72 (CH ₂ =C(CH ₃ )-COO), 64.77 (B-0-CH ₂ -CH ₂ ), 61.68 (B-0-CH ₂ ), 18.37 (CH ₂ =C(CH ₃ )-COO).

Characterisation data, including stacked ¹ H NMR (A), ¹³ C NMR (B), and FTIR (C) spectra overlays of: 2-hydroxyethyl methacrylate and tris(2-(allyloxy)ethyl) borate (Bl); and 2-hydroxyethyl methacrylate and tris(2-(allyloxy)ethyl) borate (B2), are shown in Figure 1 and Figure 2, respectively. The NMR spectra were obtained in CDCls.

Trialkylborate monomers with allyl (Bl) and methacrylate (B2) functionality were readily obtained in good yields via the thermally facilitated transesterification of the corresponding alcohol with trimethyl borate in absence of organic solvents. Figure 3 shows the exemplary synthesis of dynamic thermoset networks via photoinitiated thiol-ene, and thiol-ene-methacrylate hybrid polymerisation (image A). B — O bond exchange in the dynamic thermosets is shown in: image B) with the hydrolysis/re esterification; and image C) with the transesterification as the dissociative and associative pathways.

Both Bl and B2 were transparent, water-white liquids that were stable at room temperature when stored in a dry environment. Additionally, they were readily miscible with common thiol-ene reagents, DAP, TDAE, PTMP, and the photoinitiator used in this example.

¹ H NMR study of the reversible hydrolysis of tris(2-(allyloxy)ethyl) borate

The self-healing ability, and the reprocessability of dynamic polymer networks are dependent on the reversible bond exchange between polymeric strands. The successful synthesis of monomers Bl and B2 from trimethyl borate and the corresponding alcohols indirectly serves to establish transesterification as a potential pathway for associative B — O bond exchange in resulting polymer networks. The reversible hydrolysis of Bl as a model compound was studied using 1H NMR spectroscopy under wet and dry conditions to observe the extreme shifts in equilibrium. A stock solution of tris(2-(allyloxy)ethyl) borate (0.400 mL, 0.360 g, 1.15 x 10 ³ mol, 3.45 equivalents B — O bonds) in dry CDCb (4 mL) was prepared in a 4 mL glass vial and ¹ H NMR spectra of the mixture were recorded. To this stock solution, D2O (65 pL, 0.072 g, 3.59 x 10 ³ mol, 3.59 equivalents) was added at once and the contents were mixed vigorously for 1 minute. A white, fine particulate precipitate of boric acid was observed instantaneously. ¹ H NMR spectra of the supernatant solution were recorded to confirm hydrolysis of tris(2-(allyloxy)ethyl) borate. A small amount of freshly activated molecular sieves was added to the mixture, and the contents were mixed overnight on a rotary mixer. ¹ H NMR spectra of the mixture were recorded to confirm re-formation of tris(2-(allyloxy)ethyl) borate.

Figure 4 shows the ¹ H NMR spectra of tris(2-(allyloxy)ethyl) borate (A), and a mixture of tris(2-(allyloxy)ethyl) borate and D2O before (B), and after overnight stirring in presence of molecular sieves (C).

Addition of water to a solution of B1 in dry CDCL resulted in the instantaneous formation of a finely dispersed white precipitate of boric acid. The ¹ H NMR spectra of the supernatant solution shows a peak corresponding to the a-methylene protons of 2- allyloxyethanol (d ~ 3.72 ppm) as the hydrolysis product (Figure 4). Notably, the equilibrium could be shifted to favour the re-formation of B1 by addition of molecular sieves and gentle overnight mixing to exclude water. This was confirmed by the significant reduction in the peak intensity of the a-methylene proton (d ~ 3.72 ppm) corresponding to the free alcohol, and an increase in the relative peak intensity for the a-methylene protons (d ~ 3.94 ppm) corresponding to the ester, in the dry sample. These results indicate that polymer networks containing trialkylborate junctions can likely demonstrate healing and reprocessing abilities via B — O bond exchange through both associative and dissociative pathways.

Preparation of polymer networks by photo initiated thiol-ene/thiol-ene-methacrylate polymerisation

Multiple variants of two types of bulk polymer networks were prepared by photoinitiated curing at room temperature.

Ah the network samples were prepared by pouring a homogeneous solution of 2,2-dimethoxy-2-phenylacetophenone (1 wt.%) as a photoinitiator in the monomer mix (allyl, methacrylate, and thiol) in dogbone shaped silicone moulds or disk shaped polypropylene moulds. The moulds were placed on a lab jack within an opaque enclosure housed in a fume hood, with the UV lamp (Thermo Fischer, 3UV lamp, 8 Watt) directly above it at a distance of approximately 3 cm. The opaque enclosure, although not air tight, was maintained under continuous nitrogen gas flux to minimise exposure to ambient moisture. The samples were irradiated for 2 hours (l = 365 nm), followed by thermal post curing at 150 °C for 2 hours in the presence of silica gel desiccant. The cooled samples were stored in an air tight container with silica gel desiccator beads until further analysis.

Exemplified compositions are shown in Table 1.

Table 1 - Composition of bulk polymer networks prepared via thiol-ene and thiol-ene- methacrylate photopolymerisation.

Networks 1-6 are thiol-ene type networks obtained via photoinitiated copolymerisation of varying proportions of allyl monomers Bl, DAP, and TDAE and stoichiometric amounts of the tetrafunctional thiol monomer PTMP. Readily available allyl monomers DAP, and TDAE were chosen as the static crosslinkers to suppress any potential creep associated with B — O bond exchange or hydrolysis by ambient moisture.

TDAE with a pendant hydroxyl group was specifically chosen to facilitate transesterification with trialkylborate junctions during network healing and reprocessing. A network without any B1 or B2 was prepared as a negative control for comparison of healing behaviour (Table 1, entry 6). Networks 7-11 were obtained by ternary thiol-ene-methacrylate copolymerisation of the methacrylate functional trialkylborate monomer B2, the allyl (DAP, and TDAE) monomers, and PTMP.

B2 is expected to react predominantly via free radical polymerisation pathway while the allyl monomers participate in the thiol-ene reaction with PTMP, during the photocuring of the ternary monomer mixtures. Consequently, networks 7-11 are expected to have a different microstructure compared to the thiol-ene networks, with high molecular weight polymer strands densely crosslinked via dynamic trialkylborate junctions. Additionally, the concurrent step-growth thiol-ene polymerisation between the allyl monomers (DAP, and TDAE) and PTMP arguably results in an interpenetrating network like microstructure that confers superior mechanical properties relative to the thiol-ene networks.

In order to prevent retention of residual thiol groups upon photocuring, the ratio of thiol groups to allyl groups in both type of networks was maintained at 1 : 1 equivalents, while the ratio of thiol groups to methacrylate was maintained at 0 : 1 equivalents.

Figure 5 shows stacked IR spectra of the monomer mixture for the control network 6 before irradiation, after UV irradiation (l = 365 nm, 2 hours), and post curing (150 °C, 2hours) (A), and overlays of zoomed regions of the IR spectra for the monomer mixture before irradiation, after UV irradiation, and post curing showing the near-quantitative disappearance of characteristic peaks for thiol (2573 cm ¹ ) (B), and allyl groups (932 cm ¹ , and 1649 cm ¹ ) (C & D).

Figure 6 shows stacked IR spectra of the monomer mixture for the network 1 before, and after UV irradiation (l = 365 nm, 2 hours) (A), and overlays of zoomed regions of the IR spectra for the monomer mixture before and after UV irradiation showing the near-quantitative disappearance of characteristic peaks for thiol (2569 cm ') (B), and allyl groups (924 cm ¹ , and 1645 cm ¹ ) (C & D).

Figure 7 shows stacked IR spectra of the monomer mixture for the control network 9 before irradiation, after UV irradiation (l = 365 nm, 2 hours), and post curing (150 °C, 2 hours) (A), and overlays of zoomed regions of the IR spectra for the monomer mixture before irradiation, after UV irradiation, and post curing showing the near-quantitative disappearance of characteristic peaks for thiol (2573 cm ¹ ) (B), and allyl groups (932 cm ¹ , and 1649 cm ¹ ) (C and D).

Near-quantitative consumption of all the monomers during photocuring is essential to ensure maximum crosslink density and to exclude any contribution to the network dynamics from residual thiol groups in the resulting polymer networks. Given the susceptibility of trialkylborates to hydrolysis on contact with ambient moisture during photocuring and subsequent handling, the photocured networks were also subjected to thermal post curing to minimise dangling chain ends arising from B — O bond hydrolysis. The thermal annealing could also serve to drive the thiol-ene reaction of any residual thiol and alkene groups. Near-quantitative monomer consumption was confirmed by the disappearance of characteristic absorbance peaks of thiol (2569-2573 cm ¹ ), and alkenes (overlapping peaks from allyl and methacrylate groups: stretching = 1637-1649 cm ¹ , and bending = 924-937 cm ¹ ) in the ATR-FTIR spectra of the monomer mixtures after photocuring, and subsequent thermal annealing (Figures 5-7). It is important to highlight that while ATR-FTIR spectra indicated near-quantitative thiol consumption, undetected traces of residual thiol are not expected to contribute significantly to network dynamics.

Network characterisation

All the thiol-ene networks containing B1 (Table 1, entries 1-5), are moisture sensitive and display reduced stiffness and transparency on exposure to ambient humidity. The reduced transparency of the samples on overnight exposure to ambient air can be attributed to the finely dispersed boric acid formed as a result of trialkylborate hydrolysis. In contrast, the control network (Table 1, entry 6), shows no apparent change even on prolonged exposure to ambient humidity. Network integrity on exposure to ambient humidity improved with increasing amounts of static crosslinks. For example, network 1 (0.9 equivalents Bl) was a soft, rubbery solid that became tacky within minutes and transformed into a highly viscous syrup on overnight exposure to ambient air (-60% RH), indicating depolymerisation via trialkylborate hydrolysis (Figure 8, image A). Notably, the viscous syrup could be restored to the original rubbery network upon overnight heating at 80 °C in a vacuum oven to shift the equilibrium in favour of re-formation of the trialkylborate crosslinks. In contrast, network 5 (0.4 equivalents Bl) retained its dimensional stability, albeit becoming slightly tacky and hazy on overnight exposure to ambient air (-75% RH) (Figure 8, image B). Notably, networks 1-6 did not dissolve in dry DMF, ethyl acetate, or THF — good solvents for the precursor monomer compounds, confirming their three dimensionally crosslinked structure (Figure 8, image C).

Networks 1-6 were all rubbery at room temperature, with glass transition temperature (T _g ) values decreasing from 7 °C to -36 °C with increasing ratio of B1 to the static crosslinkers. This is counterintuitive, since the higher functionality of B1 compared to DAP, and TDAE is expected to yield networks with increased crosslink density, and hence higher T _g values as the ratio of B1 to static monomers increases. The reduced network T _g with increasing amounts of B1 is likely due to a combination of the reduced rigidity of the alkyl ether chains in B1 compared to DAP (an aromatic ether), and the rapid B — O bond exchange between network strands via transesterification even below room temperature. However, the possibility of partial B — O bond hydrolysis through inadvertently introduced moisture during handling and storage of the network samples cannot be completely ruled out.

While the tensile properties of networks 2-6 could be measured reliably, network 1 was too hygroscopic and tacky for reliable tensile testing. The average peak tensile stress of the thiol-ene networks reduced almost linearly from 1.89 MPa for network 6 (0 equivalents Bl) to 0.114 MPa for network 2 (0.55 equivalents Bl) with increasing amounts of Bl (Figure 9). Similarly, the Young’s modulus decreased from 3.33 MPa for network 6 to 0.41 MPa for network 2. The concomitant increase in elongation to break values from 78% for network 6, to 830% for network 2, is commensurate with the increased network mobility owing to the lower rigidity of Bl, and the B — O bond exchange via transesterification at room temperature. Additionally, the average toughness of the networks dropped initially on addition of Bl, but recovered steadily on further increasing Bl. These results indicate that the initial loss in network rigidity on introduction of Bl, was gradually compensated by the increased crosslink density offered by the highly transient trialkylborate junctions that allowed for enhanced stress dissipation through B — O bond exchange between network strands.

To study damage repair or healing qualitatively, a circular disc of network 1 was cut into two halves (Figure 10). The cut surfaces were gently dabbed with water, and the two pieces were re-joined and placed in a vacuum desiccator. The wetting of the cut surfaces with water should cleave the exposed trialkylborate junctions to yield free hydroxyl groups and boric acid (Figure 10, image A). Subsequent recombination of boric acid and the pendent hydroxyl groups on network strands across the cut interface should facilitate healing via formation of new trialkylborate junctions. The possibility of trialkylborate exchange between strands across the cut interface via transesterification (Figure 10, image B) with free hydroxyl groups present in the network cannot be completely excluded, given the low T _g of network 1. Strong adhesion between the re-joined pieces was evident within 5 minutes, and the original scar had significantly faded in 1 day. After 4 days, the scar had further diminished, and the re-joined sample could be manually stretched to nearly twice the original length without fracturing.

Arguably, networks 1-5 could also undergo damage healing through B — O bond exchange via the associative pathway, involving the thermally assisted transesterification between trialkylborate junctions and excess pendant hydroxyl groups (Figure 10, image B). To test this hypothesis, the recovery of peak tensile stress of dog bone shaped specimens that were cut, re-joined, and annealed at 120 °C for 16 hours was quantified for networks 2-6. Notably, despite the low T _g values for networks 2-6, the high annealing temperature was chosen to exclude the possibility of moisture induced healing via dissociative bond exchange, given the moisture sensitivity of these materials. The high annealing temperature may also help counter the likely reduction in chain mobility caused by the presence of static crosslinks in the networks by promoting rapid B — O bond exchange. Network 6 (0 equivalents Bl) showed no healing as the re-joined dogbone pieces readily separated during removal from the mould excluding the need for tensile testing. Networks 4 (0.40 equivalents Bl), and 5 (0.45 equivalents Bl) showed less than 30% recovery in peak tensile stress after annealing. Networks 3 (0.50 equivalents Bl), and 2 (0.55 equivalents Bl) demonstrated excellent healing behaviour with near-quantitative recovery in peak tensile stress values, post annealing. These results indicate that networks containing a threshold proportion of dynamic trialkylborate junctions to static junctions, can undergo damage healing via transesterification with pendant hydroxyl groups dispersed throughout the network.

Networks containing >0.50 equivalents B2 copolymerised with DAP, TDAE, and PTMP were prepared via photoinitiated thiol-ene-methacrylate copolymerisation for comparison of mechanical properties and healing (Table 1, entries 7-11). The thiol- ene-methacrylate networks display significantly reduced moisture sensitivity compared to the thiol-ene networks

In swelling studies on network 11, a small piece of the polymer network sample (0.1 - 0.3 g) was placed in a clean dry glass vial, and digital images were acquired. Dry solvent (DMF or ethyl acetate or THF) (6 mL) was added, the vial was sealed with a screw cap. After 16 hours, the solvent was carefully decanted and digital images of the swollen polymer residue were acquired. Figure 11 shows digital images of pieces of network 11 before and after overnight immersion in organic solvents, indicating an insoluble 3D crosslinked structure.

A dog bone shaped sample of network 11 (0.65 equivalents B2) exposed to ambient air (-75% RH) overnight, had very slight surface tack and retained its optical clarity, dimensional stability, and apparent stiffness. Networks 7-11 did not dissolve in dry DMF, ethyl acetate, or THF — good solvents for the precursor monomer compounds, confirming their three dimensionally crosslinked structure.

Networks 7-11 were significantly stiffer materials compared to the thiol-ene networks, with T _g values ranging from 2 °C to 24 °C. Notably, in contrast to the thiol- ene networks, the T _g values for the thiol-ene-methacrylate networks increased with increasing ratio of B2 to the static crosslinkers, despite the lower rigidity of the alkyl ether chains in B2 compared to the aryl ether in DAP. This can be attributed to the tendency of methacrylates to polymerise predominantly via the free radical chain- growth pathway in thiol-ene-methacrylate copolymerisations, resulting in high molecular weight strands that improve mechanical properties through chain entanglement and multiple weak intermolecular interactions, in addition to the dynamic trialkylborate crosslinks. Consequently, the resulting thiol-ene-methacrylate network is expected to be an interpenetrating mesh comprising a densely crosslinked network of high molecular weight strands interconnected via dynamic trialkylborate junctions, interspersed with a dense network of shorter chains interconnected via static junctions contributed by the thiol-ene reaction.

The different microstructure of the thiol-ene-methacrylate networks also leads to a significant improvement in their mechanical properties with increasing B2 loading. For instance, the peak tensile stress increased sharply from 3.35 MPa for network 9 (0.55 equivalents B2) to 23 MPa for network 11 (0.65 equivalents B2) (Figure 12, image A). Similarly, the Young’s modulus increased from 7.1 MPa for network 9 to 194.7 MPa for network 11. The concomitant decrease in elongation to break values from 714% for network 9, to 67% for network 11, is commensurate with the increased chain entanglement and crosslink density with increasing B2 loading. Notably, the material toughness only decreased slightly from 15.55 MJ/m ³ for network 9 (0.55 equivalents B2) to 11.87 MJ/m ³ for network 11 (0.65 equivalents B2), likely due to the efficient stress relaxation provided by the B — O bond exchange via transesterification even at room temperature. To assess the ability of the thiol-ene-methacrylate networks to heal damage via trialkylborate transesterification, dog bone shaped specimens of networks 7-11 were cut, re-joined, annealed at 120 °C for 16 hours, and subjected to tensile testing. Networks 9, 10, and 11 with B2 loading >0.55 equivalents demonstrated high healing efficiencies (> 84%), based on peak tensile strength recovery (Figure 12, images A and

B). These results further support the hypothesis that the thermally assisted transesterification between trialkylborate junctions and excess pendant hydroxyl groups enables damage repair in these networks.

Based on the results for trialkylborate network healing via thermally assisted B — O bond exchange, the thermal reprocessability of network 11 was also evaluated as a representative example. Dog bone specimens of network 11 were pulverised into small millimetre sized pieces and hot pressed at 120 °C under a force of 1 tonne for 10 minutes to yield a homogeneous, clear and intact rectangular strip (Figure 12, image

C). The apparent material stiffness was similar to that of the pristine dogbone specimen.

The role of free hydroxyl groups in the B — O bond exchange via thermally assisted transesterification with trialkylborate junctions was investigated by varying the amount of TDAE in the thiol-ene-methacrylate networks. Networks 8-10 were prepared with the same B2 loading (0.55 equivalents), but varying amounts of TDAE (0, 0.1, and 0.2 equivalents), to explore the effect of free hydroxyl group content on network properties and healing behaviour (Table 1). Networks 8-10 had similar T _g values of 16 to 17 °C. However, network 8 (0 equivalents TDAE) was significantly stronger, with peak tensile stress (10.93 MPa), and Young’s modulus (23 MPa) — over three times the values for networks 9 (0.10 equivalents TDAE), and 10 (0.20 equivalents TDAE) (Figure 13, images A and B). The thermally assisted healing efficiency of network 8 (36%) was less than half that of networks 9 (87%), and 10 (86%). The lowered healing efficiency in the absence of free hydroxyl groups, confirms that thermally assisted healing occurs predominantly via associative B — O bond exchange between trialkylborate junctions and free hydroxyl groups. The decrease in peak tensile stress with increasing TDAE loading can be attributed, in part, to the lower rigidity of the TDAE monomer compared to DAP. However, since replacing DAP with TDAE does not theoretically alter the crosslink density of the networks, we reason that the pendant hydroxyl groups on TDAE promote B — O bond exchange even at room temperature, resulting in increased material creep. Consequently, there is a trade-off between mechanical strength, and network dynamics depending on the amount of free hydroxyl groups in the network.

Moisture sensitivity studies in a humidity chamber

A standard 75% relative humidity chamber was prepared using a saturated sodium chloride solution. Polymer network samples were placed overnight, either in the humidity chamber, or left out on a benchtop (humidity monitored using a portable hygrometer) and qualitatively compared to dry samples for changes in appearance and stiffness. For network 11, the exposed sample was also subjected to a load bearing ability test on a digital laboratory scale as shown in Figure 14. In Figure 14, image A) shows digital photographs of the dogbone specimen of network 11 before (left), and after (right) overnight incubation at 75% relative humidity. Image B) shows digital photographs demonstrating the load bearing ability of the exposed dogbone specimen that can support a load of 280 g (140 times its own weight) without buckling.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

REFERENCES 1. Fortman, D. J.; Brutman, J. P.; De Hoe, G. X.; Snyder, R. L.; Dichtel, W. R.;

Hillmyer, M. A., Approaches to Sustainable and Continually Recyclable Cross- Linked Polymers. ACS Sustainable Chemistry & Engineering 2018, 6 (9), 11145 - 11159.

2. Helms, B. A.; Russell, T. P., Reaction: Polymer Chemistries Enabling Cradle-to- Cradle Life Cycles for Plastics. Chem 2016, 1 (6), 816-818.

3. Morales Ibarra, R., Chapter 20 - Recycling of thermosets and their composites. In Thermosets (Second Edition), Guo, Q., Ed. Elsevier: 2018; pp 639-666.4.

5. Kloxin, C. J.; Scott, T. F.; Adzima, B. J.; Bowman, C. N., Covalent Adaptable Networks (CANs): A Unique Paradigm in Cross-Linked Polymers. Macromolecules 2010, 43 (6), 2643-2653. 6. Scheutz, G. M.; Lessard, J. J.; Sims, M. B.; Sumerlin, B. S., Adaptable Crosslinks in Polymeric Materials: Resolving the Intersection of Thermoplastics and Thermosets. Journal of the American Chemical Society 2019.

7. Montarnal, D.; Capelot, M.; Tournilhac, F.; Leibler, L., Silica-Like Malleable Materials from Permanent Organic Networks. Science 2011, 334 (6058), 965.

8. Denissen, W.; Winne, J. M.; Du Prez, F. E., Vitrimers: permanent organic networks with glass-like fluidity. Chemical Science 2016, 7 (1), 30-38.

9. Hoyle, C. E.; Bowman, C. N., Thiol-Ene Click Chemistry. Angewandte Chemie International Edition 2010, 49 (9), 1540-1573.

10. Lowe, A. B., Thiol-ene “click” reactions and recent applications in polymer and materials synthesis. Polymer Chemistry 2010, 1 (1), 17-36.

11 Lee, T. Y.; Carioscia, J.; Smith, Z.; Bowman, C. N., Thiol-Allyl Ether-Methacrylate Ternary Systems. Evolution Mechanism of Polymerization- Induced Shrinkage Stress and Mechanical Properties. Macromolecules 2007, 40 (5), 1473-1479.

12. Cramer, N. B.; Couch, C. L.; Schreck, K. M.; Carioscia, J. A.; Boulden, J. E.; Stansbury, J. W.; Bowman, C. N., Investigation of thiol-ene and thiol-ene- methacrylate based resins as dental restorative materials. Dental Materials 2010, 26 (1), 21-28.

13. Beigi Burujeny, S.; Atai, M.; Yeganeh, H., Assessments of antibacterial and physico-mechanical properties for dental materials with chemically anchored quaternary ammonium moieties: Thiol-ene-methacrylate vs. conventional methacrylate system. Dental Materials 2015, 31 (3), 244-261.

14. Lecamp, L.; Houllier, F.; Youssef, B.; Bunel, C., Photoinitiated cross-linking of a thiol-methacrylate system. Polymer 2001, 42 (7), 2727-2736.

15. Shim, J.; Lee, J. S.; Lee, J. H.; Kim, H. J.; Lee, J.-C., Gel Polymer Electrolytes Containing Anion-Trapping Boron Moieties for Lithium-Ion Battery Applications. Applied Materials & Interfaces 2016, 8 (41), 27740-27752.

16. U.S. patent No. 2987537 A.