Compositions comprising a supramolecular polymer and a resin

Cross reference to related applications

[0001] This application claims priority to Indian provisional patent application No.

201821037163 filed on October 1 , 2018 and to European patent application No. 18208773.4 filed on November 28, 2018, the whole content of each of these applications being incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention relates to a composition comprising a

supramolecular polymer and a resin. In particular, said supramolecular polymer is obtained by reacting carboxylic- and amine-terminated polyethers.

Background Art

[0003] Supramolecular polymers consist of polymeric units held together via

reversible non-covalent associations, such as ionic interactions, hydrogen bonds and metal-ligand coordination. Said polymeric units typically have low glass-transition temperature (T _g ) to impart self-healing (self-repairing) properties to supramolecular polymers. Self-healing is understood as the ability of supramolecular polymers to break and revert to their original state with full or partial recovery of mechanical strength. Thanks to their self- healing properties, supramolecular polymers hold great promise to extend the lifetime of polymeric products in many fields, such as aerospace, automotive, civil and medical engineering.

[0004] However, self-healing supramolecular polymers suffer from low stiffness and low dimensional stability. Further, they are mechanically weak as their mechanical integrity is held together by supramolecular bonds, which are intrinsically weaker than covalent bonds. As a consequence, their mechanical properties are insufficient for many applications of rubbers. In particular, they exhibit low tensile strength, low elongation at break and slow elastic springbacks after strain.

[0005] Efforts have been notably made to balance between the requirements of high stiffness and good mechanical properties and the self-healing properties.

[0006] Some strategies involved adding fillers (e.g. calcium carbonate, silica, carbon black), plasticizers, oils and the like. For instance, WO

2006/087475 (ARKEMA FRANCE) discloses using dodecane as plasticizer. Other strategies involved chemically cross-linking the self- healing polymers, for example with peroxides.

[0007] However, the formulation (fillers, plasticizers, oils and the like) and the chemical cross-linking of said polymers have their limits and are generally reflected by a notable loss of properties, for instance the self-repairing ability. Thus, although it is possible to increase the tensile strength of a self-healing supramolecular polymer by adding fillers, this increase in tensile strength remains modest owing to a low filler content necessary in order to preserve optimum self-repair. In addition, using flammable and volatile additives like dodecane strongly limits possible applications of supramolecular polymers.

[0008] Therefore, there is still the need to provide supramolecular polymers with an optimum combination of toughness and self-healing ability.

Summary of invention

[0009] In a first aspect, the present invention relates to a composition comprising: a) at least one supramolecular polymer obtained by reacting:

- a first polymer [polymer (P1)] comprising a polyoxyalkylene chain [chain (ROA)] consisting of a plurality of recurring units [units (UOA)] , equal to or different from each other, of formula:

-OR*OA- (UOA) wherein R*OA is a straight or branched alkylene divalent group, said polymer (P1) having two chain ends (E1 , E1’), each end comprising at least two ionisable acid groups, and

- a second polymer [polymer (P2)] comprising a polyoxyalkylene chain [chain (ROA)] consisting of a plurality of recurring units [units (UOA)] , said chain (R _s ) being equal to or different from that of polymer (P1), and said polymer (P2) having two chain ends (E2, E2’), each end comprising at least two ionisable amino groups, and

b) at least one resin selected among: phenol-formaldehyde resins,

melamine-formaldehyde resins, epoxy resins and epoxidised novolacs.

[0010] In a second aspect, the present invention relates to sealing agents,

gaskets, membranes or coatings comprising the above composition.

[0011] In a third aspect, the present invention relates to a method for repairing a damage in said sealing agents, gaskets, membranes or coatings, said method comprising bringing the composition to a temperature of 50 °C or below.

[0012] The Applicant has surprisingly found that the composition according to the invention exhibits an excellent balance of properties. In particular, the Applicant has surprisingly found that said resin makes it possible to notably improve the properties of the supramolecular polymer, i.e. to increase its tensile strength and speed of recovery from strain when mechanically stressed, while retaining its self-repairing properties.

Accordingly, it is herewith provided a composition able to exhibit both self- repairing properties and mechanical properties which are significantly improved compared with those of the supramolecular polymers used alone.

Detailed Description of the Invention

[0013] In the present description, unless otherwise indicated, the following terms are to be meant as follows. [0014] A“trivalent hydrocarbon group” is a trivalent radical derived from a hydrocarbon by removal of three atoms of hydrogen from carbon atoms; a trivalent hydrocarbon group thus comprises three ends, each end being able to form a linkage with another chemical group.

[0015] An“alicyclic group” is an aliphatic cyclic group consisting of one or more all-carbon rings which may be either saturated or unsaturated.

[0016] The adjective“aromatic” denotes any mono- or polynuclear cyclic group (or moiety) having a number of p electrons equal to 4n+2, wherein n is 0 or any positive integer; an aromatic group (or moiety) can be an aryl or an arylene group (or moiety).

[0017] An“aromatic group” consists of one core composed of one benzenic ring or of a plurality of benzenic rings fused together by sharing two or more neighboring ring carbon atoms. Non limitative examples are benzene, naphthalene, anthracene, phenanthrene, tetracene, triphenylene, pyrene, perylene.

[0018] Alicyclic and aromatic groups can be substituted with one or more straight or branched alkyl or alkoxy groups and/or halogen atoms and/or can comprise one or more heteroatoms, like nitrogen, oxygen and sulfur, in the ring.

[0019] The use of parentheses“(...)” before and after the names of compounds, symbols or numbers identifying formulae or parts of formulae like, for example“polymer (P1)”, has the mere purpose of better distinguishing those names, symbols or numbers from the remaining text; thus, said parentheses could also be omitted.

[0020] When ranges are indicated, range ends are included.

[0021] The expressions“ionisable amino groups” and“ionisable acid groups” identify amino or acid groups able to form ionic groups, namely cationic and anionic groups respectively. In greater detail, an ionisable amino group identifies a primary, secondary or tertiary amino group, while an ionisable acid group identifies an acid group comprising at least one hydroxyl function in its protonated form, i.e. a protic acid group. POLYMER (P1 )

[0022] Polymer (P1) can be represented with formula (P1) here below:

(P1 ) E1 -R _OA -E1’

wherein ROA is a polyoxyalkylene chain [chain (ROA)] , as detailed above, and E1 and E1’, equal to or different from one another, are end groups each comprising at least two ionisable acid groups.

[0023] Polyoxyalkylene chain (RO _A )

[0024] As said, chain (ROA) consists of a plurality of recurring units [units (UOA)] , as detailed above.

[0025] Said chain (RO _A ) has a number average molecular weight (M _n ) preferably ranging from 500 to 10,000, more preferably from 500 to 5,000.

[0026] Preferably, said chain (ROA) comprises, preferably essentially consists of, oxypropylene or oxytetramethylene recurring units or a mixture thereof. Accordingly, in formula (UOA), each R*OA, equal to or different from each other, is independently selected among propylene groups of formulae (R*OA-I) - (R*oA-ii) and a tetramethylene group of formula (R*OA-IV):

-CH2CH2CH2- (R*OA-I)

-CH ₂ CH(CH ₃ )- (R*OA-M)

-CH(CH ₃ )CH ₂ - (R*oA-iii)

-CH2CH2CH2CH2- (R*OA- iv)

[0027] Minor amounts (i.e. < 1 % in moles) of groups R*OA other than those

specified may be present as impurities, defects or spurious components without this affecting chemical properties of the chain (RO _A ).

[0028] In a preferred embodiment, said chain (ROA) is a polyoxypropylene chain and each R*OA is independently selected among propylene groups of formulae (R*OA-I) - (R*oA-iii) above.

[0029] In another preferred embodiment, said chain (ROA) is a polytetramethylene glicole chain and each R*OA is a tetramethylene group of formula (R*OA- iv) above.

[0030] Groups E1 and EV

[0031] End groups E1 and E1’ typically comprise at least two ionisable acid

groups selected among carboxylic acid groups, phosphonic acid groups and sulfonic acid groups. Each of said ionisable acid groups is able to form an anionic group via acid/base reaction with one of the at least two ionisable amino groups at one end of polymer (P2).

[0032] Preferably, groups E1 and E1’ comply with formula (E1-A) here below:

(E1-A) -B1-(EA) ₂

wherein:

B1 is a trivalent hydrocarbon group preferably comprising from 1 to 20 carbon atoms and possibly comprising one or more than one heteroatom, said heteroatom(s) being preferably selected among N, S and O; and EA represents a -COOH, a -P(0)(OREA)2 or a -S(0) ₂ 0H group, wherein one of REA is hydrogen and the other one is hydrogen or straight or branched alkyl, preferably Ci-C ₄ alkyl. In one preferred embodiment, EA is a -COOH group.

[0033] B1 may comprise one or more of the groups selected from: -O-, -S-, -

0C(0)0-, -OC(0)NH-, -NH-C(O)-, OC(0)S-, -SC(0)S-, -NHC(0)NH-, -NH- C(=S) and -NHC(S)NH-.

[0034] Preferably, B1 comprises one or more than one cyclic hydrocarbon group, which may be alicyclic group(s), aromatic group(s), heterocyclic group(s) comprising one or more than one heteroatom, and heteroaromatic group(s) comprising one or more than one heteroatom, the heteroatom(s) being preferably selected from N, S and O. Each of said cyclic

hydrocarbon groups may comprise one or more substituents. In case B1 comprises more than one cyclic group, i.e. at least two cyclic gropus, said cyclic groups may be condensed or may be connected through a bond or through any (hydro)carbon divalent group optionally comprising one or more than one heteroatom, said heteroatom(s) being preferably selected from N, S and O.

[0035] According to an embodiment, polymer (P1) complies with the following formula (P1-A):

(P1-A) (E _A )2RB1 -(OR*OA)n*OA-0-RBl (E _A )2

wherein RBI is a trivalent C1-C10 straight or branched aliphatic group, a trivalent C ₄ -C6 alicyclic group or heterocyclic group, a trivalent C5-C6 aromatic group or heteroaromatic group; P*OA is a positive number selected in such a way that the number average molecular weight (M _n ) of the chain ROA preferably ranges from 500 to 10,000, more preferably from 500 to 5,000; R*OA and EA are as defined above.

[0036] According to another embodiment, polymer (P1) complies with the

following formula (P1-B):

(P1-B) (E _A )2RB1-C(0)-(OR*OA)n*OA-0-C(0)-RBl(E _A )2

wherein RBI , P*OA, R*OA and EA are as defined above with respect to polymer (P1-A). Preferably, RBI is an aromatic group. More preferably, RBI is a C6 aromatic group. According to different embodiments, each ionisable acid group may be in ortho, meta, para positions with respect to — C(O)— . According to different embodiments, each ionisable acid group may be in ortho, meta, para positions with respect to each other.

Preferably, EA is COOH.

POLYMER (P2)

[0037] Polymer (P2) can be represented with formula (P2) here below:

(P2) E2-ROA-E2’

wherein ROA is a polyoxyalkylene chain [chain (ROA)] as defined above, and E2 and E2’, equal to or different from one another, are end groups each comprising at least one ionisable amino groups.

[0038] Said chain (ROA) of polymer (P2) can be equal to or different from the

chain (ROA) of polymer (P1).

[0039] Groups E2 and E2’

[0040] End groups E2 and E2’ typically comprise at least two ionisable amino groups selected among primary, secondary or tertiary amino groups. The term“ionisable” is understood as meaning that the amino group is in its free form, so that it is capable to form a cationic group via acid/base reaction with one of the at least two ionisable acid groups at one end of polymer (P1).

[0041] Preferably, groups E2 and E2’ comply with formula (E2-A) here below:

(E2-A) -B2-(N(RP ₂ ) ₂ )2

wherein: B2 is a trivalent hydrocarbon group preferably comprising from 1 to 20 carbon atoms and possibly comprising one or more than one heteroatom, said heteroatom(s) being preferably selected among N, S and O; and each of R _P 2, equal to or different from each other at each occurrence, is hydrogen or straight or branched alkyl, preferably Ci-C ₄ alkyl.

[0042] B2 may comprise one or more than one group selected from the following:

-O-, -S-, -0C(0)0-, -OC(0)NH-, -NH-C(O)-, OC(0)S-, -SC(0)S-, - NHC(0)NH-, -NHC(S)NH-, -N(R _P 2 _* )- wherein R _P 2 _* represents hydrogen or straight or branched alkyl, preferably Ci-C ₄ alkyl, more preferably methyl.

[0043] Preferably, B2 comprises one or more than one cyclic hydrocarbon group, which may be alicyclic group(s), aromatic group(s), heterocyclic group(s) comprising one or more than one heteroatom, and heteroaromatic group(s) comprising one or more than one heteroatom, the heteroatom(s) being preferably selected from N, S and O. Each of said cyclic

hydrocarbon groups may comprise one or more substituents. In case B2 comprises more than one cyclic group, i.e. at least two cyclic gropus, said cyclic groups may be condensed or may be connected through a bond or through any (hydro)carobn divalent group possibly comprising one or more than one heteroatom, said heteroatom(s) being preferably selected from N, S and O.

[0044] According to an embodiment, polymer (P2) complies with the following formula (P2-A):

(P2-A) ((Rp2)2N)2RB2-(OR*OA)n*OA-R*OA-RB2(N(Rp2)2)2

wherein R _B 2 is a trivalent a C1-C10 straight or branched aliphatic group, a trivalent C ₄ -C6 alicyclic group or heterocyclic group, a trivalent C5-C6 aromatic group or heteroaromatic group; P*OA is a positive number selected in such a way that the number average molecular weight (M _n ) of the chain ROA preferably ranges from 500 to 10,000, more preferably from 500 to 5,000; R*OA and RP2 are as defined above.

[0045] According to a particular embodiment, polymer (P2) complies with the following formula (P2-B):

(P2-B) ((Rp2)2N) ₂ RB2-NH-(OR*OA)n*OA-R*OA-NH-RB2(N(Rp2)2)2 wherein RB2 is a triazine, preferably a 1 ,3,5-triazine, and P*OA, R*OA , RP2 are as defined above with respect to polymer (P2-A). Preferably, each R _P 2 is hydrogen.

SUPRAMOLECULAR POLYMER

[0046] The supramolecular polymer can be prepared by mixing polymer (P1) and polymer (P2) according to conventional mixing techniques at an equivalent ratio between polymer (P1) and polymer (P2) ranging from 1.1 to 0.9. Mixing is advantageously carried out without solvents. For the avoidance of doubt, the ratio between the equivalents of polymer (P1) and the equivalents of polymer (P2) is referred to the acid/base reaction between the at least two ionisable acid groups in each end group of polymer (P1) and the at least two ionisable amino groups in each end of polymer (P2).

[0047] One or more polymers (P1) can be used in the manufacture of the

supramolecular polymer.“More polymers” means that polymers (P1) can be used which differ from one another in the kind of recurring units (UOA) of the chain (ROA), in the kind of end groups (E1) and (ET) or both, or in the number average molecular weight.

[0048] One or more polymers (P2) can also be used in the manufacture of the supramolecular polymer.’’More polymers” means that polymers (P2) can be used which differ from one another in the kind of recurring units (UO _A ) of the chain (RO _A ), in the kind of end groups (E2) and (E2’) or both, or in the number average molecular weight.

[0049] According to a preferred embodiment, one polymer (P1) and one polymer (P2) are used in the manufacture of supramolecular polymer; the chain (ROA) of polymer (P1) can be equal to or different from the chain (ROA) of polymer (P2).

[0050] Without being bound to theory, it is believed that, when a polymer (P1) and a polymer (P2) are mixed in the above equivalent ratio, the ionisable acid groups at each end of polymer (P1) undergo acid/base reaction with the ionisable amino groups at each end of polymer (P2). RESIN

[0051] As said, composition (C) comprises at least one resin selected among phenol-formaldehyde resins, melamine-formaldehyde resins, epoxy resins and epoxidised novolacs.

[0052] The phenol-formaldehyde resins as intended herein comprise both

Novolacs, which have a formaldehyde to phenol molar ratio of less than 1 , and Resoles, which have a formaldehyde to phenol ratio greater than 1 , preferably around 1.5 (also known as).

[0053] Preferably, the epoxy resins are selected among those produced starting from Bisphenol A, for example bisphenol A diglycidyl ethers obtained by combining epichlorohydrin and bisphenol A.

[0054] The epoxidised novolacs as intended herein are obtained by reaction of phenols with formaldehyde and subsequent glycidylation with

epichlorohydrin. Examples of epoxidised novolacs are epoxy phenol novolacs (EPN) and epoxy cresol novolacs (ECN).

[0055] Said resins have the advantage of being relatively low-cost.

[0056] Preferably, said at least one resin is present in the composition (C) in an amount of at least 50 %(wt), more preferably of about 50 %(wt), based on the combined weight of polymer (P1 ), polymer (P2) and resin(s).

[0057] Without being bound by theory, it is believed that, when said

seupramolecular polymer and said resin are mixed together, an

interpenetrating polymer network (IPN) is formed.

[0058] Should the disclosure of any patents, patent applications and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0059] The invention is described in greater detail in the following experimental section by means of non-limiting examples.

Experimental section

[0060] Materials [0061] Novolac resin was purchased from LERG S.A. and used as received.

[0062] Trimellitic anhydride, 2-chloro-4,6-diamino-1 ,3,5 triazine, potassium

hydrogen carbonate, 2-propanol (IPA), toluene, dichloromethane were purchased from Aldrich® and used as received.

[0063] Poly(propyleneglycol) (Mn 2000) [herein after (PPG-diol)] was purchased from Aldrich ^® and was used as received.

[0064] Poly(propyleneglycol)-bis(2-aminopropylether) (Mn 2000) [herein after (PPG-diamine)] was purchased from Aldrich® and was used as received. It is a low viscous liquid characterized by a T _g of -70°C, it contains two amine groups per molecule, and complies with formula:

with n being an integer so as to provide for the Mn as detailed above.

[0065] Methods

[0066] Preparation of samples

[0067] The composition (C) obtained as a viscous liquid according to the

procedure described below was poured into molds and casted into specific shapes. The resulting samples were kept at room temperature for about 60 min, thus reaching thermal equilibrium and relaxation of the mechanical stresses. Samples were obtained with the following dimensions: 40 mm x 10.5 mm x 2.8 mm. A sample of Novolac resin was obtained in the same manner.

[0068] Tensile properties

[0069] The tensile properties were measured using UTM (Zwick Roell, UTM-030) by application of strain at the rate of 1 mm/min.

[0070] Self-healing properties

[0071] After measurement of the tensile properties, which was performed till the breakage of the sample, the broken pieces were reattached by hand, pressed for 2 minutes and subsequently kept for other 30 min at 25 °C and 50 °C, respectively, without any extra pressure.

[0072] Viscosity [0073] Rheological measurements of the supremolecular polymer were carried out with a rotational rheometer“ARES G2 from TA Instruments”. Said measurements were performed after keeping the supramolecular polymer for 24 hours at 25 °C.

[0074] ¹³ C and ¹ H NMR

[0075] NMR analyses were performed on a Bruker Avance™ 400 MHz

spectrometer with a 5 mm probe and the obtained spectra were processed using Bruker’s TopSpin™ software (3.2 ver.).

[0076] The polymer structures were determined by ¹ H or ¹³ C NMR analyses. The weight average molecular weight (M _n ) of the polymers (P1) and (P2) were estimated by polymer and group analysis (using ¹ H NMR spectra).

[0077] Synthesis examples

[0078] Synthesis of polymer PPG-tetraacid [herein after (PPG-Tac)] of formula:

A glass reactor was charged with trimellitic anhydride (144.1 g, 750 mmol) dissolved in dehydrated DMF (100 ml) under nitrogen atmosphere.

Triethylamine (165 ml) and DMAP (9.16 g, 75 mmol) were introduced to the solution and the mixture was stirred for 30 min at room temperature (25°C). Poly(propyleneglycol) (PPG-diol), as specified above, (250 g, 125 mmol) was dissolved in DMF (100ml) and added dropwise to the mixture over a period of 30 min. The mixture was stirred continuously at 80 °C for 48 hours, until complete conversion of hydroxyl groups of (PPG-diol), which was monitored by NMR. Then the reaction mixture was cooled at room temperature, diluted with dichloromethane and washed with an aqueous 1 N HCI solution (thrice) followed by brine (twice), and finally with water (once). The organic phase was separated and concentrated to give the target product in 100% yield. ¹ H-NMR analysis confirmed the obtainment of the title product, Mw 2300 (acid equivalent weight 575). [0079] Synthesis of polymer PPG-tetraamine [herein after (PPG-Tam)] of formula:

2-chloro-4,6-diamino-1 ,3,5-triazine (21.83 g, 150 mmol) was dispersed in a mixture of 2-propanol and water (450 ml, 2:1 v/v ratio).

Poly(propyleneglycol)-bis(2-aminopropylether) (PPG-diamine) (100 g, 50 mmol) and K2CO3 (27.6 g, 200 mmol) were added to the mixture and stirred continuously at 90 °C for 48 hours. Then, the solvent was

evaporated under reduced pressure and dissolved in toluene. The insoluble material was filtered off and the filtrate was washed with water (twice). The organic phase was separated, filtered and concentrated to give the target product in 100% yield. ¹ H-NMR analysis confirmed the obtainment of the title product, Mw 2220 (amine equivalent weight 550).

[0080] Preparation of supramolecular polymer from PPG-Tac and PPG-Tam

[0081] PPG-Tac (5.75 g) and PPG-Tam (5.5 g) were manually mixed at room

temperature in an equivalent ratio of 1 [i.e. nr acidic groups of PPG-Tac = nr basic groups of polymer PPG-Tam] and the resulting mixture was kept at room temperature (25 °C) for 24 hours.

[0082] Preparation of composition (C) comprising the supramolecular polymer and Novolac resin

The Novolac resin (2 g) and the supramolecular polymer (2 g) obtained as described above were taken in an aluminium sheet and were heated to about 120 °C on a hot plate. The resulting composition was mixed with a spatula for about 5-7 min till formation of a viscous liquid.

[0083] Mechanical characterization

[0084] Table 1 reports the mechanical properties, namely the modulus, the tensile strength and the elongation at break, of the composition (C) before breakage and after healing of a broken sample at 25 °C and 50 °C, respectively, in order to observe the extent of the self-healing. Table 1

[0085] The data reported in the table above demonstrate the self-healing

properties of the composition (C) according to the invention. It is observed that the tensile properties of the sample after healing at 25 °C are slightly lower than those of the sample before breakage. It is also observed that the modulus of the sample after healing at 50 °C is the same as that of the sample before breakage, while the tensile strength and the elongation at break are even higher.

[0086] On the contrary, the Novolac sample was found to be too brittle for an effective measurement of the tensile properties and, therefore, did not provide any healing ability. The supramolecular polymer resulted instead to behave like a viscous amorphous liquid with a complex viscosity of 200 Pa-s and a G”/G’ ratio ranging from 100 to 1000 depending of the frequency and, therefore, not even in this case mechanical measurements were applicable.