FIELD OF THE INVENTION

[0001 ] The present invention generally relates to toughened thermoset compositions. In particular, the invention relates to thermoset compositions toughened by block copolymer ionomers. The invention also relates to a process for the preparation of toughened thermoset compositions.

BACKGROUND

[0002] Thermoset resins, such as epoxy resins, are one class of the most important synthetic resins. Compared with thermoplastic resins, thermoset resins exhibit numerous excellent properties including good heat resistance, high hardness, and excellent electric performances which allow them to be used as structural adhesives or as a matrix for composite materials or in applications for protecting electronic components. However, they are usually highly cross-linked and thus inherent brittle having poor resistance to crack propagation, which largely inhibits various applications. Therefore, considerable efforts have been devoted to toughen thermosetting resins so that they have more excellently balanced physical as well as mechanical properties.

[0003] Numerous methods have been employed to improve the toughness of thermoset resins, and one of the most successful strategies is to incorporate a second phase of either elastomers or thermoplastics into the thermoset matrix. In these systems, the fracture resistance can be increased by forming multiphase morphology able to initiate various toughening mechanisms during crack growth. A well-established factor responsible for the final mechanical properties of these hybrid materials, aside from the intrinsic properties of the composite materials themselves, is the resultant morphology of the material. Control over this morphology is critical for the fabrication of modified toughened thermosets composites with target end-use properties. Traditional additives generally form micro-sized morphology in the thermoset matrix and usually lead to opaque appearance, i.e., loss of transparency.

[0004] Recently, attempts have been made to toughen thermosets by nanostructures, i.e., nano-sized inclusions are employed to toughen thermosets. Experiments have shown that compared to micro-sized inclusions, nano-sized inclusions confer some unique features to thermosets. Block copolymers, especially amphiphilic block copolymers, have been studied as possible tougheners, which are able to form nanostructures in thermoset matrix. Examples of toughened thermosets, particularly epoxies, with block copolymers are disclosed in U.S. Pat. Nos. 7670649 B2; 7923073 B2; 8021586 B2; Publication Nos. 20040034124; 20070265373; 20080260955; 20080287595; 20090084286 and 20090123759; as well as International Patent with Publication Nos. WO2005/097893; WO2006/052727; WO2006/052728 and WO 2006/052729.

[0005] Much of the previous work relating to toughened thermosets with block copolymers is focused on the use of amphiphilic block copolymers which consist of an epoxy miscible segment as well as an immiscible segment. The miscible blocks most widely used are poly(ethylene oxide) (PEO) and polycaprolactone (PCL). Amphiphilic block copolymers containing poly(methyl methacrylate) (PMMA) has also been disclosed (U.S. Pub. No. 20040034124). Aside from block copolymers containing aforementioned miscible blocks, reactive block copolymers such as those containing poly (epoxyisoprene) or poly(glycidyl methacrylate) (PGMA) have also been studied. For example, Soft Matter, 2010, 6, 61 1 9-6129 disclosed that reactive block copolymer poly(dimethyl siloxane)-poly(glycidyl methacrylate) (PDMS-PGMA) form highly ordered nanostructures in the cured epoxy systems and improve the tensile strength as well as tensile ductility at low addition content.

[0006] Although amphiphilic block copolymers have shown some efficiency at providing nanostructured thermosets with appealing properties, the block copolymers are mostly too expensive to be used in some applications and the process can be costly and difficult to carry out on industrial scale.

[0007] It would be desirable to develop alternative approaches for improving the toughness of thermoset resins that address or at least ameliorate one or more disadvantages associated with the prior art.

[0008] The discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

SUMMARY

[0009] The present invention is directed to toughened thermosets comprising block copolymer ionomers. The block copolymer ionomers used herein may be prepared by polymerising appropriately functionalised monomers, or by modification of commercially available block copolymers. It has been found that block copolymer ionomers can effectively toughen thermosets by forming nanostructures in the thermosetting matrix, preferably without loss of transparency.

[0010] In one aspect, the present invention provides a toughened thermoset composition comprising:

(a) a thermoset polymer; and

(b) a block copolymer ionomer dispersed in the thermoset polymer, wherein the block copolymer ionomer comprises at least one charged block comprising a plurality of ionic groups and at least one polymer immiscible block that is substantially immiscible with the thermoset polymer, and wherein the quantity of charged block in the block copolymer ionomer is at least 30 mol%.

[001 1 ] In embodiments of a toughened thermoset composition the quantity of charged block in the block copolymer ionomer is at least 40 mol%, at least 50 mol%, or at least 60 mol%.

[0012] In some embodiments, the block copolymer ionomer comprises a plurality of charged blocks, wherein each charged block comprises a plurality of ionic groups.

[0013] In one set of embodiments each charged block comprises a plurality of anionic groups.

[0014] Each charged block present in the block copolymer ionomer may comprise from about 0.5 mol% to about 100 mol% of anionic groups. In some embodiments, each charged block comprises from about 5 mol% to about 50 mol%, or from about 10 mol% to about 30 mol% of anionic groups.

[0015] When present in a charged block, the anionic groups may suitably be derived from a free acid selected from the group consisting of sulfonic acid and carboxylic acid.

[0016] In some embodiments, a portion of the anionic groups present in the block copolymer ionomer may be neutralised with a counterion. For example, up to 25%, up to 50%, or up to 80% of the anionic groups may be neutralised with a counterion.

[0017] When present, the counterion may be selected from the group consisting of an inorganic counterion, an organic counterion, and mixtures thereof.

[0018] In some embodiments, anionic groups present in a block copolymer ionomer may be neutralised with an inorganic counterion derived from an alkali salt, an alkaline earth salt, a transition metal salt, a rare earth metal salt, or mixtures thereof.

[0019] In some embodiments, anionic groups present in a block copolymer ionomer may be neutralised with an organic counterion is derived from an organic amine.

[0020] In embodiments of a toughened thermoset composition at least one polymer immiscible block of the block copolymer ionomer comprises an elastomeric polymer. The elastomeric polymer may be selected from the group consisting of hydrogenated poly (conjugated dienes), poly(olefins), organosilicon polymers, polyethers and mixtures thereof.

[0021 ] Block copolymer ionomers employed in the toughened thermoset composition may be di-blocks, tri-blocks or multiblocks or have a structure selected from the group consisting of linear, graft, branched or star. In some embodiments, the block copolymer ionomer has a structure ABA, wherein A is a charged block and B is a polymer immiscible block. [0022] In some embodiments of a toughened thermoset composition of the invention the composition comprises from about 0.1 % to about 80% (w/w), from 0.1 % to about 70% (w/w), from about 0.1 % to about 50% (w/w), from about 1 % to about 30% (w/w), or from about 2% to about 20% (w/w) of block copolymer ionomer.

[0023] The toughened thermoset composition also comprises a thermoset polymer. In some embodiments the thermoset polymer may be selected from the group consisting of alkyd resins, allyl diglyol carbonate resins, diallyl isophthalate resins, diallyl phthalate resins, melamine resins, melanime/phenolic resins, phenolic resins, vinyl ester resins, epoxy resins, unsaturated polyester resins, cyanoacrylate resins, melamine-formaldehyde resins, polyurethane resins, polyimide resins, polyphenol resins, and mixtures thereof, preferably phenolic resins, epoxy resins, epoxy vinyl ester resin, an unsaturated polyester resin and mixtures thereof, and most preferably epoxy resin.

[0024] In embodiments of a toughened thermoset composition of the present invention, the block copolymer ionomer is dispersed in the thermoset polymer, forming a second phase morphology at nano-scale that imparts remarkable improvements in toughness with minor effects on other properties.

[0025] In another aspect the present invention provides a process for the preparation of a toughened thermoset composition comprising the steps of:

(a) mixing a thermosettable composition with a block copolymer ionomer, and

(b) curing the thermosettable composition in the presence of the block copolymer ionomer to form a thermoset polymer comprising block copolymer ionomer dispersed in the thermoset polymer,

wherein the block copolymer ionomer comprises at least one charged block comprising a plurality of ionic groups and at least one polymer immiscible block that is substantially immiscible with the thermoset polymer, and wherein the quantity of charged block in the block copolymer ionomer is at least 30 mol%. [0026] According to a further aspect of the present invention, there is provided also a method of manufacturing a toughened thermoset comprising forming a mixture comprising a block copolymer ionomer as described herein, a thermosettable resin and a curing agent, introducing the mixture into a preheated mould, and subjecting the mixture to cure conditions to fully cure the components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0028] Figure 1 shows SAXS (small angle X-ray scattering) profiles of MDA- cured epoxy blends with 2.5, 5, 10, 15 and 20 wt% SSEBS with a sulfonation degree of 21 .9mol% in accordance with embodiments of the invention, indicating the blends exhibit a nano-scaled structure and may contain long-range ordered nanostructures.

[0029] Figure 2 presents TEM images of MDA-cured epoxy blends with (a) 2.5 wt%, (b) 5 wt%, (c) 10 wt%, (d) 15 wt% and (e) 20 wt% SSEBS with a sulfonation degree of 21 .9mol% in accordance with embodiments of the invention which show that nano-scaled heterogeneous morphology was observed for all these blends, consistent with the transparent appearance.

[0030] Figure 3 shows the storage modulus and tan δ versus temperature curves of (a) neat epoxy and epoxy blends with (b) 2.5 wt%, (c) 5 wt%, (d) 10 wt%, (e) 15 wt% and (f) 20 wt% SSEBS with a sulfonation degree of 21 .9mol% in accordance with embodiments of the invention tested at different frequencies, (0.1 , 0.4, 1 , 2, and 4 Hz).

[0031 ] Figure 4 is a graph showing DSC curves of the second scan of neat SEBS, neat SSEBS, and epoxy blends with 0, 2.5, 5, 10, 15 and 20 wt% SSEBS with a sulfonation degree of 21 .9mol% in accordance with embodiments of the invention at a heating rate of 20 ^< C/min. DETAILED DESCRIPTION

[0032] The present invention relates to toughened thermosets prepared with a block copolymer ionomer as a toughening agent.

[0033] Thermoset polymers are generally formed when thermosettable resins are polymerised and irreversibly cured. When forming toughened thermoset compositions it is desirable that the mechanical properties of the thermoset is improved, while other properties of the thermoset, such as appearance, modulus and glass transition temperature are not significantly altered. The present invention has found that the use of block copolymer ionomers as toughening agents in thermosets can provide one or more advantages over the prior art.

[0034] In one aspect, the present invention provides a toughened thermoset composition comprising:

(a) a thermoset polymer; and

(b) a block copolymer ionomer dispersed in the thermoset polymer, wherein the block copolymer ionomer comprises at least one charged block comprising a plurality of ionic groups and at least one polymer immiscible block that is substantially immiscible with the thermoset polymer, and wherein the quantity of charged block in the block copolymer ionomer is at least 30 mol%.

[0035] The block copolymer ionomer employed in the toughened thermoset composition comprises at least one charged block. The term "charged block" as used herein refers to a block segment of the block copolymer ionomer that comprises a plurality of ionic (charged) groups. The charged block may therefore carry a net charge and may also impart a net charge to the block copolymer ionomer.

[0036] In some embodiments, the block copolymer ionomer comprises a plurality of charged blocks. For example, the block copolymer ionomer may comprise two, three, four, or more charged blocks. When the block copolymer ionomer comprises a plurality of charged blocks, each charged block comprises a plurality of ionic groups. Where the block copolymer ionomer comprises a plurality of charged blocks, the composition of each charged block may be independently selected at each occurrence.

[0037] The block copolymer ionomer employed in the toughened thermoset composition comprises at least 30 mol% of charged blocks. When the block copolymer comprises a plurality of charged blocks, the quantity of such charged blocks as a proportion of the total number of moles of monomer units in the copolymer is at least 30 mol%. In one set of embodiments, the quantity of charged block in the block copolymer ionomer is at least 40 mol%. In another set of embodiments, the quantity of charged block in the block copolymer ionomer is at least 50 mol%. In another set of embodiments, the quantity of charged block in the block copolymer ionomer is at least 60 mol%.

[0038] The quantity of charged blocks in the block copolymer ionomer may influence the miscibility of the block copolymer ionomer with thermosettable resins that are used to form the thermoset polymer. For instance, the inventors have found that it can be difficult to mix block copolymer ionomers comprising less than 30 mol% of charged blocks with a thermosettable resin to prepare thermoset compositions with nanoscaled dispersed phase. However, it has been found that block copolymer ionomers comprising at least 30 mol%, and in some embodiments, at least 40 mol%, at least 50 mol%, or at least 60 mol%, of charged blocks are miscible with, and can be homogeneously dispersed in thermosettable resins and be used to form nanostructured thermoset compositions showing improvements in mechanical properties such as toughness. As used herein, miscibility of the block copolymer ionomer may be defined as being soluble in the thermosettable resin prior to cure. Accordingly, the block copolymer and thermosettable resin are able to form homogeneous mixtures before cure. Miscibility of the block copolymer ionomer in the uncured resin is such that preferably no macroscopic phase separation of the block copolymer ionomer takes place in the course of curing and network formation of the thermosets, or at least up to high conversions.

[0039] The mol% of charged blocks in the block copolymer ionomer may be determined on the basis of the number of moles of monomer units in the charged block or blocks as a proportion of the total number of moles of monomer units in the ionomer.

[0040] In some embodiments, each charged block of the block copolymer ionomer comprises a plurality of anionic groups. The molar percentage of the anionic groups in each charged block present in the block copolymer ionomer may vary from as little as 0.5 mol%, to as high as up to about 100 mol%. A skilled person would appreciate that a charged block having 100 mol% of anionic groups would contain a plurality of monomeric units and that each of the monomeric units would carry an anionic group (i.e. all of the monomeric units have an anionic group). In some embodiments, each charged block may comprise from about 1 mol% to about 80 mol% of anionic groups, or from about 5 mol% to about 50 mol% of anionic groups, or from about 10 mol% to about 30 mol% of anionic groups. In such embodiments it would be understood that only a portion of the monomeric units present in the charged block carries an anionic group.

[0041 ] Without wishing to be limited by theory, it is believed that anionic groups present in the charged blocks of the block copolymer ionomer may have a role in influencing the miscibility of the ionomer with thermosettable resins. The anionic groups may also promote non-covalent bonding interactions between the block copolymer ionomer and the cured thermoset polymers, leading to favourable mechanical properties in the toughened thermosets. The block copolymer ionomer may therefore be regarded as a modifier, due to its ability to modify the mechanical properties of the thermoset polymer in which it is dispersed.

[0042] In one set of embodiments, anionic groups present in each charged block of the block copolymer ionomer are derived from a free acid. The free acid may be selected from the group consisting of sulfonic acid, carboxylic acid, and mixtures thereof.

[0043] The mol% of anionic groups in the ionomer can be calculated on the basis of the number of moles of anionic groups relative to the number of moles of monomer units present in the charged blocks. For example, where the anionic groups are derived from sulfonic acid, the mol% of anionic groups may be expressed as a sulfonation degree, which can be determined as follows: moles of sulfonic acid

sulfonation degree = X 100%

moles of monomer units in charged blocks

[0044] The content of sulfonic acid groups in the ionomer may be measured by several ways. For instance, infrared analysis or elemental analysis may be used to determine the sulfonation degree. Alternatively, titration of a solution of the block copolymer ionomer with a strong base may be employed to determine the sulfonation degree.

[0045] It has been found that block copolymer ionomers having at least 30 mol% charged blocks are miscible with, and are capable of being homogeneously mixed in thermosettable resins to form toughened thermoset compositions. Miscibility can be obtained even when the ionic groups present in the charged blocks of the ionomer are each free charged groups, such as for example, free acid groups.

[0046] Block copolymer ionomers employed in the toughened thermoset compositions can be obtained through the functionalization of a pre-formed polymer, or by polymerization of one or more monomers with suitable ionic groups. The functionalization of a pre-formed block copolymer with ionic groups may provide an attractive route for the synthesis of block copolymer ionomers on a large scale.

[0047] Block copolymer ionomers which are suitable for the preparation of toughened thermosets of this invention may be sulfonated block copolymer ionomers or carboxylic acid block copolymer ionomers, which are divided into their broad categories according to the ionic groups.

I. Sulfonated Block Copolymer lonomers

[0048] Block copolymers having sulfonic acid groups may be prepared by polymerizing a monomer with a free sulfonic acid group or salt thereof. For example, block copolymers having sulfonic acid groups may contain a block segment prepared from the polymerisation of a monomer selected from the group consisting of vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-allyl oxyethane sulfonic acid, styrene sulfonic acid, and mixtures thereof. Conventional polymerisation processes, such as free radical polymerisation, may be employed to form a charged polymer block from sulfonic acid containing monomers. The resulting charged polymer block may then be conjugated with one or more other polymer blocks to provide a block copolymer ionomer containing sulfonic acid groups. In one set of embodiments, the charged polymer block is conjugated with at least one polymer immiscible block that is substantially immiscible with the thermoset polymer matrix. Examples of polymer immiscible blocks are described herein.

[0049] Block copolymers having sulfonic acid groups covalently bonded to the carbon atoms forming the backbone of the copolymer may also be prepared by modification of a suitable pre-formed block copolymer by sulfonation or grafting reagents. Modification of the pre-formed block copolymer leads to the grafting of sulfonic acid groups to one or more blocks of the copolymer, and conversion of those blocks into charged blocks bearing pendant sulfonic acid groups.

[0050] Sulfonation of hydrocarbon polymers is a conventional process. Generally, polymers suitable for grafting with sulfonic acid groups are: (a) essentially free of olefinic unsaturation except for chain-end unsaturation, or (b) possess a measureable degree of olefinic unsaturation which may be in the polymer backbone chain of carbon atoms or is in an acyclic alkenyl or alkylidene radical or alicyclic radical which is pendant to the backbone chain of carbon atoms, or (c) possess aryl or arylene radicals which comprise the backbone chain of carbon atoms or are pendant to the backbone chain of carbon atoms. Provided that at least one unsaturated bond is present in the block copolymer (i.e. as a terminal group, as a part of the polymer backbone and/or as a pendant group), the polymer may undergo sulfonation to graft sulfonic acid groups to the block copolymer. In some embodiments, it is preferred that pre-formed block copolymers comprising either olefinic unsaturation in the polymer backbone or unsaturated bonds pendant to the polymer backbone are used to form block copolymer ionomers comprising sulfonic acid groups. [0051 ] Pre-formed block copolymers that may be modified to form block copolymer ionomers preferably comprise at least one block segment comprising an olefinic unsaturation in the polymer backbone, or an unsaturated group (for example, an aryl group) pendant to the polymer backbone. The unsaturation may be reactive to the reagent used to graft sulfonic acid groups to the block segment and thereby forms a charged block in the block copolymer. Examples of sulfonation reagents that may be useful for preparing the sulfonated block copolymers described herein include "acryl sulfate", more preferably, acetyl sulfate (CH ₃ -CO-O-SO ₃ H) as disclosed in U.S. Pat. Nos. 3870841 , 383651 1 , and 5239010 incorporated herein by reference. The acryl sulfate can be formed in situ in the reaction medium or prepared freshly before its addition to the reaction medium.

[0052] Pre-formed block copolymers used to form the block copolymer ionomers may also comprise at least one block segment that is free of unsaturation and which would be inert to or unreactive with the sulfonation reagent. The blocks "free of unsaturation" are preferably elastomeric blocks that are incompatible or substantially immiscible with the thermoset polymer matrix and which might be capable of contributing to the improvement in the toughness of the thermoset polymer. Non- limiting examples of blocks free of unsaturation are hydrogenated poly (conjugated dienes) and the monomers used to form the blocks include: 1 ,3-butadiene (butadiene), 2-methyl-1 ,3-butadiene (isoprene), 2, 3-dimethyl-1 ,3-butadiene, piperylene, and mixtures thereof, preferably, butadiene and isoprene. Blocks obtained from olefins, such as ethylene, butylene, isobutylene, pentene and its homologs are also suitable examples for the present invention.

[0053] In some embodiments, at least one charged block of the block copolymer ionomer comprises sulfonated poly(alkyl arene). In such embodiments, sulfonic acid groups may be grafted onto pendant arene groups of a pre-formed poly(alkyl arene). The poly(alkyl arene) may be obtained from the polymerisation of an alkylene arene monomer, such as monoalkenyl arene monomer. The poly(alkyl arene) may be obtained from the polymerisation of styrene and its analogs and homologs including alpha-methylstyrene and ring alkylated styrene. II. Carboxylic Block Copolymer lonomers

[0054] A wide range of block copolymers having carboxylic acid groups primarily in one block may be used for the preparation of toughened thermosets of this invention. Non-limiting examples include diblock, triblock or star-block copolymers composed of poly(styrene) and poly(acrylic acid) or poly(methacrylic acid) blocks.

[0055] Similar to sulfonated block copolymer ionomers, block copolymers having carboxylic acid groups may be obtained through modification of a pre-formed block copolymer with carboxylic acid groups. Alternatively, carboxylic block copolymer ionomers may be obtained by synthesising carboxylic acid containing block segments from carboxylic acid containing monomers, then conjugating one or more of the carboxylic acid containing block segments with at least one block segment that is substantially immiscible with the thermoset polymer matrix.

[0056] In some embodiments it may be desirable for ionomers used in the toughened thermosets of the invention to comprise no more than about 30 mol% of ionic groups (such as free acid groups), as a high concentration of such groups may adversely affect one or more physical properties of the thermoset polymer (for example, 7 _g ) due to the high level of non-covalent bonding interaction between the ionomer and the polymer which introduces high level of penetration of soft polymer chains (block copolymer ionomer) into crosslinked network of thermoset polymer.

[0057] Without wishing to be limited by theory, it is believed that interactions between ionic groups (such as sulfonic acid groups) present in an ionomer and the thermoset polymer may be the main driving force that effectively avoids macroscopic phase separation. Thus, the concentration of ionic groups in the ionomer (which may be reflected by sulfonation degree) is thought to have an impact on the formation of nano or microstructures, which can influence the mechanical properties of the thermoset composition.

[0058] In one set of embodiments, the toughened thermoset composition comprises a sulfonated block copolymer ionomer, wherein the sulfonated block copolymer ionomer has a sulfonation degree of no more than about 30 mol%. In some embodiments, the sulfonated block copolymer ionomer has a sulfonation degree in the range of about 0.5 mol% to about 30 mol%, preferably in the range of about 2 mol% to about 20 mol%, more preferably in the range of about 3 mol% to about 15 mol%, most preferably in the range of about 5 mol% to about 1 1 mol%.

[0059] Ionic groups present in one or more charged blocks of the block copolymer ionomer may be partially neutralised. Accordingly, charged blocks in the block copolymer ionomer may comprise free ionic groups and/or salts of the ionic groups.

[0060] In embodiments where the ionic groups are anionic groups, a portion of the anionic groups, such a sulfonic acid groups or carboxylic acid groups, in a block copolymer ionomer may be optionally neutralised with a counterion. In some embodiments, up to 25%, up to 50%, or up to 80% of the anionic groups may be neutralised with a counterion. It is preferable that at least some of the ionic groups are not neutralised, but remain as free charged groups. It is believed that free charged groups can help to promote non-covalent bonding interactions between the ionomer and the cured thermoset polymer matrix and may assist in the formation of nanostructures in the cured thermoset.

[0061 ] Counterions that may be used to neutralise anionic groups present in the charged blocks may be selected from the group consisting of inorganic counterions, organic counterions, and mixtures thereof. When a counterion is used, it is preferred that the counterion does not adversely affect the miscibility of the block copolymer ionomer in the thermosettable resin to a significant degree.

[0062] Inorganic counterions may be derived from an alkali salt, an alkaline earth salt, a transition metal salt, a rare earth metal salt, or mixtures thereof. Examples of salts that may provide inorganic counterions include sodium and magnesium salts.

[0063] Organic counterions may be derived from an organic amine. Organic amines can form ionic interactions with acid groups to generate block copolymer ionomers in the form of organic amine salts. Organic amines useful in the practice of the invention can be derived from mono-amines or polyamines. The amines can be primary, secondary, or tertiary amines. The organic amine may be substituted with one or more substituents selected from the group consisting of alkyl, aryl, alkaryl, and aralkyl. Examples of suitable organic amines include pyridine and alkylamines. The amines can be derived from mono-amines or polyamines.

[0064] In one aspect, the present invention provides a toughened thermoset composition comprising:

(a) a thermoset polymer; and

(b) a block copolymer ionomer or salt thereof dispersed in the thermoset polymer,

wherein the block copolymer ionomer comprises at least one charged block comprising a plurality of ionic groups and at least one polymer immiscible block that is substantially immiscible with the thermoset polymer, and wherein the quantity of charged block in the block copolymer ionomer is at least 30 mol%.

[0065] The block copolymer ionomer also comprises at least one polymer immiscible block. The term "polymer immiscible block" as used herein refers to a block segment of the block copolymer ionomer that is substantially immiscible with the cured thermoset polymer. By being "substantially immiscible", the polymer immiscible block may be susceptible to phase separate from the thermoset polymer before and/or during cure. The phase separation can lead to multi-phase morphology being formed in the thermoset polymer matrix. Immiscibility of the polymer immiscible block may be ascertained by determining whether a corresponding homopolymer of similar molecular weight and composed of the same monomer units as that of the polymer immiscible block would be able to be homogeneously mixed with a thermosettable resin. If the homopolymer is unable to form a single phase with the uncured thermosettable resin, or in the alternative, if the homopolymer can be mixed with the thermosettable resin but macroscopically phase separates from the cured resin, resulting in the formation of an opaque thermoset polymer, then this is an indication of the immiscibility of the polymer block.

[0066] In some embodiments, the block copolymer ionomer comprises a plurality of polymer immiscible blocks. For example, the block copolymer ionomer may comprise two, three, four, or more polymer immiscible blocks. Where the block copolymer ionomer comprises a plurality of polymer immiscible blocks, the composition of each polymer immiscible block may be independently selected at each occurrence.

[0067] In one set of embodiments, at least one polymer immiscible in the block copolymer ionomer comprises an elastomeric polymer. The elastomeric polymer may provide a "soft" or "rubbery" block in the block copolymer ionomer, which provides an immiscible phase, resulting in multi-phase morphology in the thermoset polymer. In some embodiments, the elastomeric polymer is selected from the group consisting of hydrogenated poly (conjugated dienes) formed from monomers such as 1 ,3-butadiene (butadiene), 2-methyl-1 ,3-butadiene (isoprene), 2,3-dimethyl-1 ,3- butadiene, piperylene, and mixtures thereof, poly(olefins) derived from one or more olefinic monomers such as ethylene, butylene, isobutylene and pentene and its homologs, organosilicon polymers such as poly(dimethyl siloxane) and poly(methyl siloxane), and polyethers such as poly(butylene oxide), poly(hexylene oxide) and poly(dodecylene oxide), and mixtures thereof. In one set of embodiments, the polymer immiscible block may be derived from at least one monomer selected from the group consisting of 1 ,3-butadiene (butadiene), 2-methyl-1 ,3-butadiene (isoprene), 2, 3-dimethyl-1 ,3-butadiene, piperylene, ethylene, butylene, isobutylene, pentene, and mixtures thereof. In one embodiment, the polymer immiscible block is derived from ethylene, butylene or mixtures thereof.

[0068] Block copolymer ionomers employed in toughened thermoset compositions of the invention may be derived from di-blocks, tri-blocks, or multiblocks, or graft, branched, hyperbranched or star block copolymers. It is a requirement that the ionomers comprise at least one charged block and at least one polymer immiscible block that is incompatible or at least partially incompatible with the cured thermoset polymer matrix so as to form multiphase morphology in the thermoset matrix.

[0069] In some embodiments, the block copolymer ionomer employed in the toughened thermoset compositions has a structure ABA, where A is a charged block and B is a polymer immiscible block. An exemplary block copolymer is sulfonated poly(styrene)-block-(ethylene-ran-butylene)-block-poly(styre ne) (SSEBS). In the case of SSEBS, each poly(styrene) block comprises a plurality of sulfonic acid groups.

[0070] In one set of embodiments, a toughened thermoset composition of the invention comprises SSEBS as a block copolymer ionomer. In some embodiments, the SSEBS ionomer has a sulfonation degree of no more than about 30 mol%. In some embodiments, the SSEBS ionomer may have a sulfonation degree in a range selected from the group consisting of about 0.5 mol% to about 30 mol%, about 2 mol% to about 20 mol%, about 3 mol% to about 15 mol%, and about 5 mol% to about 1 1 mol%.

[0071 ] The amount of block copolymer ionomer that may be employed in the toughened thermoset composition depends on several factors, such as the equivalent weight of the polymers as well as the desired properties of the products. Generally, the amount of block copolymer ionomer present in the toughened thermoset composition may be from about 0.1 wt% to about 30 wt%, preferably from about 1 wt% to about 20 wt%, more preferably from about 5 wt% to about 10 wt%. One advantage of the use of block copolymer ionomers is that enhanced toughness of the thermoset can be achieved at lower loading levels of the modifier, compared with other types modifiers reported in the prior art.

[0072] The toughened thermoset compositions of the present invention may contain at least one block copolymer ionomer dispersed in a thermoset polymer. Moreover, more than one type of block copolymer ionomer may also be used, i.e., a mixture of two or more different types of block copolymer ionomer may be blended together to make up the modifier component used to toughen the thermosets. In such embodiments, the total amount of the two or more block copolymer ionomers in the toughened thermoset composition may be in the range of from about 0.1 wt% to about 30 wt%.

[0073] The toughened thermoset compositions of the present invention also comprise a thermoset polymer. The thermoset polymer comprises a plurality of polymer chains of variable length bonded to one another via covalent bonds, providing a three-dimensional network. The thermoset polymer forms a continuous phase of the toughened thermoset composition. The block copolymer ionomer is dispersed in the thermoset polymer and forms a nano-structured phase within the polymer.

[0074] Thermoset polymers are derived from a thermosettable resin and are generally formed when polymer precursors in the thermosettable resin react or polymerise in the presence of a hardener (curing agent).

[0075] As used herein, the terms "thermosettable resin" and "thermosettable composition" are used interchangeably and refer to a composition comprising thermosetting polymer precursors that are generally of low molecular weight and which are capable of undergoing a curing process to form a high molecular weight, often crosslinked, thermoset polymer. The thermosettable resin may be a pourable liquid, yet has the capability of being transformed into a polymer that is no longer a liquid. The cured polymer is permanently set, and cannot be converted to a fluid melt by heating and mixing.

[0076] A variety of thermosettable resins are commercially available, and these thermosettable resins may be combined with at least one block copolymer ionomer and subsequently polymerised or cured in the presence of the block copolymer ionomer to provide a toughened thermoset composition. Examples of thermosettable resins that may be used to form a thermoset polymer include: alkyd resins, allyl diglyol carbonate resins, diallyl isophthalate resins, diallyl phthalate resins, melamine resins, melamine/phenolic resins, phenolic resins, vinyl ester resins, epoxy resins, unsaturated polyester resins, cyanoacrylate resins, melamine-formaldehyde resins, polyurethane resins, polyimide resins, polyphenol resins, and combinations thereof. Though any commercially available thermosettable resin can be toughened by the block copolymer ionomers, the block copolymer ionomers are particularly effective in toughening thermoset polymers obtained from phenolic resins, unsaturated polyester resins, vinyl ester resins, epoxy resins, and most preferably phenolic resins and epoxy resins. In some embodiments, the thermoset polymer may be derived from a mixture of thermosettable resins for example, a mixture of phenolic resin and epoxide resin. [0077] Thermosettable epoxy resins that can be used in the practice of the present invention contain epoxy compounds having at least one terminal 1 ,2-epoxy group per molecule. The epoxy resins can contain monomeric polyepoxy compounds. Examples of epoxy resins with monomeric polyepoxy compounds include the diglycidyl ether of bisphenol A, novolac based epoxy resins, and tris- epoxy resins. Other epoxy resin, such as advanced epoxy resins with higher molecular weight, for instance, the diglycidyl ether of bisphenol A advanced with bisphenol A, or epoxy resins comprising polymerized unsaturated monoepoxides, or polyepoxide homopolymers or copolymers (e.g., glycidyl acrylates, glycidyl methacrylate, allyl glycidyl ether, etc.), may also be used to provide a thermoset polymer.

[0078] The toughened thermoset composition of the invention may be prepared by dispersing a block copolymer ionomer in a thermosettable resin, then curing the thermosettable resin to form a thermoset polymer. The cured thermoset polymer would form a continuous phase of the thermoset composition, while the block copolymer ionomer would be retained within the thermoset polymer as a discrete phase on the nano-scale.

[0079] In another aspect, the present invention provides a process for the preparation of a toughened thermoset composition comprising the steps of:

(a) mixing a block copolymer ionomer with a thermosettable resin, and

(b) curing the thermosettable resin in the presence of the block copolymer ionomer to form a thermoset polymer comprising block copolymer ionomer dispersed in the polymer,

wherein the block copolymer ionomer comprises at least one charged block comprising a plurality of ionic groups and at least one polymer immiscible block that is substantially immiscible with the thermoset polymer, and wherein the quantity of charged block in the block copolymer ionomer is at least 30 mol%.

[0080] In another aspect, the present invention provides a process for the preparation of a toughened thermoset composition comprising the steps of:

(a) mixing a block copolymer ionomer or salt thereof with a thermosettable resin, and (b) curing the thermosettable resin in the presence of the block copolymer ionomer or salt thereof to form a thermoset polymer comprising block copolymer ionomer dispersed in the polymer,

wherein the block copolymer ionomer comprises at least one charged block comprising a plurality of ionic groups and at least one polymer immiscible block that is substantially immiscible with the thermoset polymer, and wherein the quantity of charged block in the block copolymer ionomer is at least 30 mol%.

[0081 ] It is preferred that the block copolymer ionomer is miscible with the thermosettable resin, so that upon mixing with the resin, the ionomer is homogeneously dispersed in the uncured resin. The mixture generally appears as a single phase composition, although the block copolymer ionomer may form a dispersed microscopic phase in the thermosettable resin.

[0082] Various processes are capable of providing a composition comprising a thermosettable resin and block copolymer ionomer. For example, the thermosettable resin (not yet cured), and the block copolymer ionomer can be blended together through several ways, such as melting blending and solution blending. The choice of processing conditions may depend on the physical properties of the uncured thermosettable resin and the selected block copolymer ionomer. The principle is to make sure components are fluid so as to obtain a homogeneous blend.

[0083] Solution blending of thermosettable resin comprising thermoset polymer precursors with a certain amount of block copolymer ionomer can be achieved with assistance of solvents. For example, a block copolymer ionomer can be dissolved in a solvent (A) leading to a solution containing block copolymer ionomer at a concentration ranging from 0.1 wt% to 30 wt%, preferably from 1 wt% to 20 wt%, more preferably from 5 wt% to 10 wt%. It may be beneficial to ensure that the solution is not too viscous. While the block copolymer ionomer solution is prepared, the thermosettable resin (polymer precursor) used for forming the thermoset polymer are dissolved in a solvent B. The concentration of polymer precursor solution is not critical, but generally a solution with relatively low viscosity is preferred. Solvent A and B are good solvents for the block copolymer ionomer and the thermosettable resin respectively. Moreover, solvent A and B should be solvents that are miscible with each other. Time and temperature of the process of preparing single phase uncured thermoset compositions is not critical, but generally the components solutions are mixed at a temperature and a period of time long enough so as to form a homogeneous mixture. The solvents are then removed leading to a homogeneous mixture of block copolymer ionomer and uncured thermosettable resin.

[0084] To form the toughened thermoset composition, a curing agent is then added to the mixture and blending is carried out at a temperature sufficient to be fluid in order to obtain a homogeneous blend. The crosslinking reaction that forms the thermoset polymer starts once the curing agent is added and care should be taken that the blending must be carried out for a time period as short as possible. If desired, the blends may be subsequently cast and cured in a preheated mould.

[0085] The curing agent component (also referred to as a hardener or cross- linking agent) that may be used to form the toughened thermoset composition may be selected from any one of those conventionally used in the art. The curing agent may contain active groups that are reactive with functional groups present on the polymer precursors in the thermosettable resin. For example, for an epoxy resin, the curing agent may contain active groups that are capable of reacting with an epoxy group of the epoxy resin, allowing crosslinking reactions between the polymer precursors to occur and the formation of a three-dimensional network.

[0086] Curing agents that may be suitable to initiate cure of a thermosettable resin include those react with thermoset polymer precursors at room temperature and at higher temperature. For epoxy resins, suitable curing agents may include, but not limited to:

• acid anhydrides;

• aromatic or aliphatic polyamines including diaminodiphenyl sulfone (DDS), methylenedianiline (MDA), 4,4'-Methylene-bis(3-chloro-2,6-diethylaniline) (MCDEA), 4,4'-Methylene-bis(2,6- diethylaniline) (MDEA);

• dicyandiamide (DICY) and derivatives thereof;

• imidazoles;

• polycarboxylic acids; • polyphenols.

[0087] The curing, or setting, of a thermosettable resin to form a thermoset polymer may be accomplished using conventional processing steps and conditions known in the art. For example, the thermosettable resin may be cured in the presence of the block copolymer ionomer at a temperature ranging from ambient temperature (e.g. 15 to 40 ^< C) to elevated temperat ure (e.g. 50 to 200 ^< €-), and by using thermal, radiation or a combination of energy sources. In addition, the time used for complete curing can range from seconds to several hours or days depending on the nature of the curing agent and the thermosettable resin components. In addition, the curable composition can be cured in one step or in multiple steps, or the curable composition can be post-cured at a different temperature or with different energy source after the initial cure cycle.

[0088] Without wishing to be limited by theory, it is believed that the increase in toughness or fracture resistance is due to the block copolymer ionomer self- assembling into nano-scale morphologies, such as worm-like, vesicle or spherical nanostructures within the continuous phase of the thermoset polymer. The self- assembly of the block copolymer ionomer occurs before and/or during curing of the thermosettable resin to form the thermoset polymer. This results in the ionomer forming a second phase morphology on a nanometer length scale within the thermoset polymer matrix.

[0089] As the block copolymer ionomer is miscible in the uncured thermosettable resin, and forms a second phase morphology on a nano-scale in the cured thermoset polymer, properties such the appearance (optical transparency), glass transition temperature ( 7 _g ) and thermal resistance of the cured thermoset polymer do not significantly differ from that of the thermoset polymer without the modifier. However, it has been observed that the formation of a second phase morphology by the block copolymer ionomer in the thermoset polymer imparts remarkable improvements in mechanical properties, such as toughness. Accordingly, one advantage of the invention is that an improvement in mechanical properties can be achieved without compromising other important properties of the thermoset polymer. [0090] Toughened thermoset compositions of embodiments of the invention preferably exhibit an increase in toughness or fracture resistance. The increase in toughness can be achieved with relatively low concentrations of block copolymer ionomer. In some embodiments, when 5-10 wt% of block copolymer ionomers are employed, toughness of the thermosets may increase by a factor from 2 times to up to around 6 times that of a control thermoset that does not contain a block copolymer ionomer.

[0091 ] The miscibility between the block copolymer ionomer, the thermosettable resin and the curing agent may play an important role in determination of the scale of the phase separation morphology in thermoset blends. It has been found that block copolymer ionomers comprising at least 30 mol% charged blocks can be mixed with thermosettable resins homogeneously. In comparison, block copolymers that are not miscible with the uncured thermosettable resin are not able to form nano-scale morphologies due to macro-scale phase separation from the resin. In addition, the miscibility of the block copolymer ionomer in the thermosettable resin can help to ensure that the ionomer is uniformly dispersed in the thermoset polymer that forms upon curing of the resin.

[0092] The ionic groups (such as sulfonic acid or carboxylic acid based groups) in the block copolymer ionomer may also have a role in promoting sufficient miscibility of the ionomer with a thermosettable resin, to allow formation of the nano- scaled phase-separated morphologies in the thermoset polymer. The nano-scaled phase-separated morphology in turn, is believed to make it possible to achieve the toughness improvement observed.

[0093] For instance, the ionic groups of the ionomer may have interactions, such as covalent bonding interactions and non-covalent bonding interactions, particularly ionic interactions and hydrogen bonds, with the polymer precursors in the uncured thermosettable resin. Additionally, the ionic groups may form specific interactions with the curing agent, especially an amine-type curing agent. The interaction may contribute to the ability of the block copolymer ionomer to be incorporated into the thermoset polymer network. Chemical bonding the block copolymer ionomer to the matrix of the thermoset polymer could also contribute to the improvement in mechanical properties and formation of a toughened thermoset.

[0094] The ability of the block copolymer ionomer to mix with and be homogeneously dispersed in the thermosettable resin, then self-assemble into nanoscale morphologies may be influenced by the chemical composition, degree of asymmetry of the block copolymer ionomer; the composition of the thermoset polymer, and/or the choice of curing agent for the forming the thermosets. For instance, it is believed that the miscibility between block copolymer ionomers and thermosettable resin is an important factor in determining the scale of phase separation (either macroscopic or microscopic) forming dispersed phases at micron- scale or nano-scale respectively, in the cured thermoset polymer.

[0095] The choice of curing agent may also have an influence on the properties of the thermosets if the curing agent is capable of interacting with the block copolymer ionomer. For example, amine containing curing agents may be capable of participating in non-covalent bonding interactions with ionic groups present in the block copolymer ionomer, and may have an impact on the self-assembly of the ionomer. This may provide a further avenue for adjusting the properties of the cured thermoset composition.

[0096] According to a further aspect of the present invention, there is provided a method of manufacturing a toughened thermoset material, the method comprising forming a mixture comprising a block copolymer ionomer as described herein, a thermosettable resin and a curing agent, introducing the mixture into a preheated mould, and subjecting the mixture to cure conditions to fully cure the components.

[0097] As used herein, the term "alkyl", used either alone or in compound words denotes straight chain, branched or cyclic alkyl (or "cycloalkyl"), for example Ci _-40 alkyl, or Ci _-2 o or Ci _-10 - Examples of straight chain and branched alkyl include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, f-butyl, n-pentyl, 1 ,2-dimethylpropyl, 1 ,1 - dimethyl-propyl, hexyl, 4-methylpentyl, 1 -methylpentyl, 2-methylpentyl, 3- methylpentyl, 1 ,1 -dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1 ,2- dimethylbutyl, 1 ,3-dimethylbutyl, 1 ,2,2-trimethylpropyl, 1 ,1 ,2-trimethylpropyl, heptyl, 5-methylhexyl, 1 -methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4- dimethylpentyl, 1 ,2-dimethylpentyl, 1 ,3-dimethylpentyl, 1 ,4-dimethyl-pentyl, 1 ,2,3- trimethylbutyl, 1 ,1 ,2-trimethylbutyl, 1 ,1 ,3-trimethylbutyl, octyl, 6-methylheptyl, 1 - methylheptyl, 1 ,1 ,3,3-tetramethylbutyl, nonyl, 1 -, 2-, 3-, 4-, 5-, 6- or 7-methyloctyl, 1 -, 2-, 3-, 4- or 5-ethylheptyl, 1 -, 2- or 3-propylhexyl, decyl, 1 -, 2-, 3-, 4-, 5-, 6-, 7- and 8- methylnonyl, 1 -, 2-, 3-, 4-, 5- or 6-ethyloctyl, 1 -, 2-, 3- or 4-propylheptyl, undecyl, 1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-methyldecyl, 1 -, 2-, 3-, 4-, 5-, 6- or 7-ethylnonyl, 1 -, 2-, 3-, 4- or 5-propyloctyl, 1 -, 2- or 3-butylheptyl, 1 -pentylhexyl, dodecyl, 1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8-, 9- or 10-methylundecyl, 1 -, 2-, 3-, 4-, 5-, 6-, 7- or 8-ethyldecyl, 1 -, 2-, 3-, 4-, 5- or 6-propylnonyl, 1 -, 2-, 3- or 4-butyloctyl, 1 -2-pentylheptyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonoadecyl, eicosyl and the like. Examples of cyclic alkyl include mono- or polycyclic alkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl and the like. Where an alkyl group is referred to generally as "propyl", butyl" etc., it will be understood that this can refer to any of straight, branched and cyclic isomers where appropriate. An alkyl group may be optionally substituted by one or more optional substituents as herein defined.

[0098] As used herein, the term "aryl" (or "carboaryl") denotes any of single, polynuclear, conjugated and fused residues of aromatic hydrocarbon ring systems. Examples of aryl include phenyl, biphenyl, terphenyl, quaterphenyl, naphthyl, tetrahydronaphthyl, anthracenyl, dihydroanthracenyl, benzanthracenyl, dibenzanthracenyl, phenanthrenyl, fluorenyl, pyrenyl, idenyl, azulenyl, chrysenyl. Preferred aryl include phenyl and naphthyl. An aryl group may be optionally substituted by one or more optional substituents as herein defined.

EXAMPLES

[0099] The following examples illustrate the present invention in further detail however the examples should by no means be construed as limiting the scope of the invention as described herein.

Materials

[0100] A thermosettable resin (epoxy resin) which is diglycidyl ether of bisphenol A (DGEBA) with an epoxide equivalent weight of 172-176, a molar mass of 340 g/mol, sold by the Sigma-Aldrich Co. with the trademark D.E.R. 332 was used in the following examples. The hardener (curing agent) used to cure the epoxy resin was an amine hardener, 4, 4'-methylenedianiline (MDA), purchased from Sigma- Aldrich Co. This product is characterized by a melting point of 89-91 ^< C and a molar mass of 198 g/mol.

Characterisation Methods

[0101 ] Prepared thermoset blends containing block copolymer ionomer were characterised using the following methods:

Transmission Electron Microscopy

[0102] TEM experiments were conducted on a JEOL JEM-2100 transmission electron microscope at an acceleration voltage of 100 kV. The samples were cut into ultrathin sections of -70 nm thick, collected on 400 mesh copper grids and stained with ruthenium tetroxide (RuO ₄ ) for TEM examination.

Small-Angle X-Rav Scattering (SAXS)

[0103] SAXS experiments were conducted at the Australian Synchrotron on the small/wide angle X-ray scattering beamline utilising an undulator source that allowed measurement at a very high flux to moderate scattering angles and a good flux at the minimum q limit (0.012 nm ^"1 ). The intensity profiles were interpreted as the plot of scattering intensity (I) versus scattering vector, q = (4/λ) sin (θ/2) (Θ = scattering angle, the wavelength A was 0.062 nm.).

Scanning Electron Microscopy (SEM)

[0104] The multiphase structures of the epoxy blends were studied by SEM on the fracture surface of specimens broken under cryogenic conditions using liquid nitrogen. The fracture surface was immersed in the THF at room temperature for 24 h. The block ionomer phase and/or the sol fraction of the epoxy network were preferentially etched by the solvent whereas the cured epoxy phase remained relatively unaffected. The etched samples were dried in a vacuum oven to remove the solvent. The phase structure was observed using a field emission gun SEM (Zeiss, Supra 55 VP). Fracture surfaces were coated with a thin gold layer to avoid charging the samples. Images were obtained under an accelerating voltage of 5 kV with a working distance of 1 0 mm.

Dynamic Mechanical Thermal Analysis (DMTA)

[01 05] Rectangular specimens with dimension of 30x5.0x2.0 mm ³ were cut for dynamic mechanical thermal analyzer (DMTA) test. Five different frequencies (0.1 , 0.4, 1 , 2 and 4 Hz) with single-cantilever mode experiments were run by first cooling the samples down to -1 00 ^Q C under liquid nitrogen and applying a steady temperature ramp of 3.0 ^Q C/min to 250 ^Q C. The storage modulus (G), loss modulus (G'), and tan δ were measured from -1 00 to 250 ^< C. The T _g was taken at the maximum of the tan δ curve (1 Hz frequency) in the glass transition region.

Mechanical and Fracture Toughness Tests

[01 06] The fracture toughness of the blends based on the plane strain energy release rate (Gic) was computed from the plane strain critical stress intensity factor ( ic) which in turn, was calculated according to ASTM D5045 standard using a three- point-bend (SEN-3PB) single-edge-notch specimen. Specimens with a sharp notch were prepared by using a mould designed with a sharp tip. Subsequently, a sharp crack tip was initiated by tapping a fresh razor blade. Care was taken to avoid forming a long crack or breaking the specimen. Samples were then gripped and tested in accordance with ASTM D 5045 test standard.

[01 07] Tensile tests were performed using an Instron 30 kN screw driven tensile tester equipped with a non-contact video extensometer. The dumbbell specimens with a 1 6.0x3.5 x2.5 mm ³ neck were used. Tests were performed at room temperature and at a constant crosshead speed of 5 mm/min. At least five samples were tested to get the average values of tensile properties for all blends and neat epoxy.

Example 1. Preparation of Block Copolymer lonomer SSEBS

[01 08] The block copolymer ionomer was prepared by sulfonation of commercially available polystyrene- :/oc -poly(ethylene-co-butylene)-ib/oc - polystyrene (SEBS, Tuftec™ H1 043) supplied by Asahi Kasei Chemicals Corporation, Tokyo, Japan. The SEBS consisted of 67 wt% polystyrene, with the average molecular weight M _w of 40,000 and M _w /M _n = 1 .05 measured by GPC in tetrahydrofuran (THF) relative to polystyrene standard.

[0109] Sulfonation of SEBS was carried out according to the procedure of U.S. Pat. No 3,836,51 1 . Specifically, the sulfonation was conducted in 1 ,2-dichloroethane (DCE) at 50-55 ^< C by reacting with acetyl sulphate in a nitrogen atmosphere. The acetyl sulfate was freshly prepared from acetic anhydride and concentrated sulfuric acid. The quantity of sulfonated polystyrene blocks in the resulting sulfonated polystyrene-ib/oc -poly(ethylene-co-butylene)-ib/oc -polystyrene copolymer ionomer (SSEBS) was determined to be approximately 62 mol%. The sulfonation degree of SSEBS, i.e., the molar percentage of styrene in SEBS which was grafted with sulfonic acid was determined by titration with standard sodium hydroxide solution (0.1 N) using phenolphthalein as the indicator.

[01 10] Using the above method, SSEBS ionomers with sulfonation degrees of 0.9%, 5.8%, 10.8% and 21 .9% were prepared from the SEBS copolymer. These are denoted 0.9SSEBS, 5.8SSEBS, 10.8SSEBS and 21 .9SSEBS, respectively.

[01 1 1 ] The SSEBS ionomers were used in the preparation of toughened thermosets according to the method described below.

Example 2. Preparation of metal salts of SSEBS

[01 12] Metals salts (magnesium and sodium salts) of SSEBS were prepared through neutralization of SSEBS in methanol solution of magnesium acetate or sodium hydroxide. A stoichiometric amount of the alkaline solution was used. Magnesium and sodium metal salts of 10.8SSEBS were found to be miscible with epoxy resin with degrees of neutralization of up to 80%.

[01 13] 10.8SSEBS with 80% of the sulfonic acid groups neutralized with either magnesium salt (Mg-SSEBS) or sodium salt (Na-SSEBS) were used in the preparation of toughened thermosets according to the method described below. General Method for preparing thermoset polymer with block copolymer ionomer

[01 14] A desired quantity of the block copolymer ionomer (was blended with epoxy resin by means of solution blending. The epoxy precursor DGEBA and the block copolymer ionomer was separately dissolved in THF. Then, individual THF solutions of DGEBA and block copolymer ionomer were mixed and acutely stirred. Meanwhile, a stoichiometric amount of curing agent MDA was added and stirred to form a homogeneous mixture. The solvent was evaporated at room temperature in the fume hood first and the vacuum oven next. The mixture was then poured into a preheated mould and cured to obtain cured thermoset blends. Curing reactions were carried out at 120 ^< C for 17 h firstly and then a successi ve post-cure at 180 for 2 h.

Epoxy thermoset with various quantities of 21.9SSEBS block copolymer ionomer

[01 15] Using the general method described above, 21 .9SSEBS block copolymer ionomer was blended with epoxy resin in quantities of 2.5wt%, 5wt%, 10wt%, 15wt% and 20wt% in order to form thermoset polymers having various concentrations of ionomer. The blends are denoted 97.5/2.5, 95/5, 90.10, 85/15 and 80/20, respectively, reflecting the epoxy/ionomer ratio.

[01 16] Figure 1 shows (small angle X-ray scattering) SAXS profiles of epoxy/21 .9SSEBS blends with various concentrations of 21 .9SSEBS. Well-defined scattering peaks are observed for all the studied blends except the 97.5/2.5 epoxy/21 .9SSEBS blend, indicating the blends exhibit a nano-scaled structure and may contain long-range ordered nanostructures. It should be noted that no pronounced scattering peak is observed for the 97.5/2.5 epoxy/SSEBS blend, which might be due to the very low content of the epoxy immiscible block at this composition in the blend.

[01 17] Figure 2 presents TEM images of MDA-cured epoxy blends with 2.5wt%, 5wt%, 10 wt%, 15wt% and 20wt% 21 .9SSEBS. Nanoscaled heterogeneous morphology was observed for all these blends, consistent with the SAXS investigation. It should be mentioned that all the epoxy blends were transparent before and after curing, indicative of macroscopic homogeneity of the various epoxy/SSEBS blends.

[01 18] Figure 3 shows the storage modulus and tan δ versus temperature curves of neat epoxy and epoxy blends with 2.5wt%, 5wt%, 10 wt%, 15wt% and 20wt% 21 .9SSEBS, tested at different frequencies, i.e., 0.1 , 0.4, 1 , 2, and 4 Hz.

[01 19] Table 1 gives the mechanical properties of the MDA-cured epoxy blends with various amounts of 21 .9SSEBS.

Table 1. Mechanical Properties of Nanostructured Epoxy/21 .9SSEBS Blends

[0120] The toughness of the thermoset compositions comprising the ionomer 21 .9SSEBS was compared to that of the pure epoxy resin (without ionomer) can be expressed as a ratio G\c _/ G\c ( _pur e epoxy)- The ratio provides an indication of the improvement in toughness obtained with the blended materials comprising the ionomer, compared to the neat thermoset without ionomer. Fracture toughness of the epoxy blends with block copolymer ionomer was found to be improved dramatically. [01 21 ] Figure 4 shows DSC curves of the second scan of SEBS, 21 .9SSEBS and epoxy blends with 2.5wt%, 5wt%, 1 0 wt%, 1 5wt% and 20wt% 21 .9SSEBS at a heating rate of 20 ^< C/min. The DSC thermograms show t hat T _g decreases with increasing wt% of 21 .9SSEBS. This may be due to the penetration of soft chains into the epoxy network (plasticisation effect).

Epoxy thermoset with metal salt of block copolymer ionomer

[01 22] Using the general method described above, Mg or Na metal salts of 1 0.8SSEBS block copolymer ionomer was blended with epoxy resin in quantities of 2.5wt%, 5wt% or 1 0wt%.

[01 23] Table 2 gives the mechanical properties of the MDA-cured epoxy blends with Mg-1 0.8SSEBS or Na-1 0.8SSEBS.

Table 2. Mechanical Properties of Nanostructured Epoxy/Epoxy/M-10.8SSEBS Blends

Na-10.8

10 SSEBS 2.43±0.1 1 43.23±1 .84 170 1 .42±0.07 0.73±0.03 3.47 (5wt%)

Na-10.8

1 1 SSEBS 2.26±0.05 40.50±2.61 157 1 .59±0.09 0.98±0.09 4.67 (10wt%)

[0124] As shown by the ratio of G\c _/ G\c ( _pur e epoxy), thermoset compositions containing metal salts of SSEBS exhibit improved toughness.

Epoxy thermoset with 10wt% SSEBS block copolymer ionomer having different degrees of sulfonation

[0125] Using the general method described above, SEBS block copolymer ionomer with different degrees of sulfonation was blended with epoxy resin in a quantity of 10wt%. The sulfonation degrees were 0 mol% (SEBS), 0.9 mol%, 5.8 mol%, 10.8 mol% and 21 .9 mol%. The sulfonated block copolymer ionomers (SSEBS) were denoted 0.9SSEBS, 5.8SSEBS, 10.8SSEBs and 21 .9SSBS, respectively.

[0126] Cured thermoset compositions containing SEBS and 0.9SSEBS were opaque, indicating macrophase separation, while the thermoset composition containing 5.8SSEBS was translucent. The thermoset composition containing 10.8SSEBS was transparent with no discernible macroscopic separation.

[0127] The different thermoset compositions were subject to DSC tests, which showed that T _g of the thermosets decreased when SSEBS with higher sulfonation degrees were incorporated. The decrease in T _g may indcate that SSEBS with higher sulfonation degrees having better miscibility with the thermoset matrix, leading to a more pronounced plasticisation effect.

[0128] Table 3 gives the mechanical properties of the MDA-cured epoxy thermosets prepared with 10wt% of SEBS, 0.9SSEBS, 5.8SSEBS, 10.8SSEBS or 21 .9SSEBS. Table 3. Effect of Sulfonation Degree of SSEBS on Mechanical Properties of Epoxy Thermosets

[0129] Fracture toughness of the epoxy blends with block copolymer ionomer was found to be improved with the incorporation of SSEBS and appears to optimum when SSEBS having sulfonation degrees of 5.8 mol% and 10.8 mol% are used.

[0130] It is to be understood that various other modifications and/or alternations may be made without departing from the spirit of the present invention as outlined herein.

[0131 ] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.