EP2324077A1

EP2324077A1 - Epoxy-based composition containing copolymer

Info

Publication number: EP2324077A1
Application number: EP09782801A
Authority: EP
Inventors: Stefan Kreiling; Rainer SCHÖNFELD; Metin Hayri Acar; Artun Zorvaryan
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2008-09-12
Filing date: 2009-09-09
Publication date: 2011-05-25
Also published as: WO2010029096A1

Abstract

The invention relates to a curable composition, comprising: (a) at least one epoxy resin; and (b) at least one copolymer selected from copolymers, comprising M-B, M-B-M and/or M-B-C blocks, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the A block, B is a polymer block having a glass transition temperature below 10°C, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B. The invention further relates to a cured product made from the curable compositions, such as prepregs and towpregs.

Description

EPOXY-BASED COMPOSITION CONTAINING COPOLYMER

BACKGROUND OF THE INVENTION

Field of the invention

The invention relates to a curable composition, comprising: (a) at least one epoxy resin; and (b) at least one copolymer selected from copolymers, comprising M-B, M-B-M and/or M-B-C blocks, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the A block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B.. The invention further relates to a cured product made from the curable compositions, such as prepregs and towpregs.

Brief description of related technology

Thermoset resins such as epoxy resins are commonly used, for example, in the microelectronic and aircraft industries. Epoxy resins in general are known to be very difficult to toughen and some epoxies are too brittle to toughen effectively. Moreover, increasing the fracture toughness of brittle epoxies often comes at the expense of modulus and use temperature, creating unacceptable limits on the applicability of these resins. Numerous solutions have been developed to attempt to respond to this problem.

In this regard WO 2007/025007 A1 teaches epoxy compositions having improved impact resistance, comprising at least one epoxy resin; rubber particles having a core-shell structure; at least one auxiliary impact modifier/toughening agent; and at least one heat-activated latent curing agent. The addition of specific block copolymers to epoxy resins is also known to increasing the fracture toughness.

In this regard Hillmyer et al. describes the addition of a A-B diblock copolymers to thermosetting epoxy/phthalic anhydride systems, wherein A is poly(ethylene oxide) and B is poly(ethylethylene) (Journal of the American Chemical Society, 1997, 1 19, 2749-2750)).

The addition of a Polysiloxane-Polycaprolactone block copolymer has also been described: PCL-b-PDMS-b-PCL and (PCL)₂-b-PDMS-b-(PCL)₂. Koenczol et al. (Journal of Applied Polymer Science, vol. 54, pages 815-826, 1994) have studied blends between an epoxy/an hydride system and a PCL-b-PDMS-b-PCL or (PCL)₂-b-PDMS-b-(PCL)₂ multiblock copolymer, where PCL denotes polycaprolactone and PDMS polydimethylsiloxane. The authors show that the material obtained is transparent and that the addition of 5% to 15% of copolymer makes possible a significant improvement in the impact strength of the epoxy material.

US patent US 6,887,574 B2 discloses curable flame retardant epoxy compositions with increased toughness, comprising an amphiphilic block copolymer in an amount such that said amphiphilic block copolymer self assembles into micellar morphologies and such that the fracture resistance of the cured product increases.

Patent application WO 2001/92415 teaches thermoset materials with improved impact resistance, comprising diblock and triblock copolymers. The therein disclosed block copolymers have to contain blocks made from at least 50 % polymethylmethacrylate.

Patent application WO 2006/077153 describes thermoset materials with improved impact resistance, comprising 1 to 80% of an impact modifier comprising at least one copolymer chosen from copolymer comprising diblock or triblock structures. Each block structure contains a copolymer of methyl methacrylate and of at least one water-soluble monomer. The addition of block copolymers having at least one block predominantly composed of methyl methacrylate units to thermoset materials results in thermoset materials with improved impact resistance.

However, it has been found that the modification of epoxy resins as thermoset materials with block copolymers having at least one block predominantly composed of methyl methacrylate often significantly increases the viscosity of said epoxy resins.

Epoxy resins of low viscosity are desirable, because these kinds of materials can easily be handled in simple and low-cost processes.

Therefore, it would be desirable to find another way to further increase fracture toughness of cured epoxy resins without sacrificing other properties of the epoxy resins such as simple and low-cost processability.

SUMMARY OF THE INVENTION

The authors of the present invention found that by adding block copolymers, having at least one block predominantly composed of methyl acrylate, to epoxy resins, the fracture resistance of the cured epoxy resins can be increased without sacrificing other properties of the epoxy resins such as simple and low-cost processability. The compositions according to the present invention are curable, in particular heat curable and include broadly the combination of (a) at least one epoxy resin, and (b) at least one copolymer selected from copolymers, comprising at least one M-B, M-B-M and/or M-B-C block, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the M block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B.

The curable compositions are in particular suitable as coatings, adhesives, sealants and matrices for the preparation of reinforced material such as prepregs and towpregs and/or can be used in injection molding or extrusion.

Therefore it is another object of the invention to provide an adhesive, sealant or coating, comprising the curable composition of the present invention and a cured reaction product of the curable composition of the present invention, in particular a cured reaction product containing bundles or layers of fibers. It is further provided a method of preparing such material.

In another object of the present invention the at least one copolymer selected from copolymers, comprising at least one M-B, M-B-M and/or M-B-C block, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the M block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B, is used as a toughening agent for epoxy resins.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention provides a curable composition comprising (a) at least one epoxy resin, and (b) at least one copolymer selected from copolymers, comprising at least one M-B, M-B-M and/or M-B-C block, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the A block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B.

The term "comprising at least one M-B, M-B-M and/or M-B-C block" means that said copolymers can only comprise one or several M-B block(s) or can only comprise one or several M-B-M block(s) or can only comprise one or several M-B-C block(s) or said copolymer can comprise at least two different blocks, such as at least one M-B block and at least one M-B-M block. (a) Epoxy resin

The term "epoxy resin", as used in the present invention, refers to any organic compound having at least two functional groups of oxirane type which can be polymerized by ring opening.

The term "epoxy resins" preferably denotes any conventional epoxy resin which is liquid at room temperature (23°C) or at a higher temperature. These epoxy resins can be monomeric or polymeric, on the one hand, aliphatic, cycloaliphatic, heterocyclic or aromatic, on the other hand.

The epoxy resins used in the present invention may include multifunctional epoxy- containing compounds, such as C₁-C₂₈ alkyl-, poly-phenol glycidyl ethers; polyglycidyl ethers of pyrocatechol, resorcinol, hydroquinone, 4,4'-dihydroxydiphenyl methane (or bisphenol F, such as RE-303-S or RE-404-S available commercially from Nippon Kayuku, Japan), 4,4'-dihydroxy- 3,3'-dimethyldiphenyl methane, 4,4'-dihydroxydiphenyl dimethyl methane (or bisphenol A), 4,4'- dihydroxydiphenyl methyl methane, 4,4'-dihydroxydiphenyl cyclohexane, 4,4'-dihydroxy-3,3'- dimethyldiphenyl propane, 4,4'-dihydroxydiphenyl sulfone, and tris(4-hydroxyphenyl) methane; polyglycidyl ethers of transition metal complexes; chlorination and bromination products of the above-mentioned diphenols; polyglycidyl ethers of novolacs; polyglycidyl ethers of diphenols obtained by esterifying ethers of diphenols obtained by esterifying salts of an aromatic hydrocarboxylic acid with a dihaloalkane or dihalogen dialkyl ether; polyglycidyl ethers of polyphenols obtained by condensing phenols and long-chain halogen paraffins containing at least two halogen atoms; phenol novolac epoxy; cresol novolac epoxy; and combinations thereof.

Among the commercially available epoxy resins suitable for use in the present invention are polyglycidyl derivatives of phenolic compounds, such as those available under the tradenames EPON 825, EPON 826, EPON 828, EPON 1001 , EPON 1007 and EPON 1009, cycloaliphatic epoxy-containing compounds such as Araldite CY179 from Huntsman or waterborne dispersions under the tradenames EPI-REZ 3510, EPI-REZ 3515, EPI-REZ 3520, EPI-REZ 3522, EPI-REZ 3540 or EPI-REZ 3546 from Hexion; DER 331 , DER 332, DER 383, DER 354, and DER 542 from Dow Chemical Co.; GY285 from Huntsman, Inc.; and BREN-S from Nippon Kayaku, Japan. Other suitable epoxy-containing compounds include polyepoxides prepared from polyols and the like and polyglycidyl derivatives of phenol-formaldehyde novolacs, the latter of which are available commercially under the tradenames DEN 431 , DEN 438, and DEN 439 from Dow Chemical Company and a waterborne dispersion ARALDITE PZ 323 from Huntsman. Cresol analogs are also available commercially such as ECN 1273, ECN 1280, ECN 1285, and ECN 1299 or waterborne dispersions ARALDITE ECN 1400 from Huntsman, Inc. SU-8 and EPI- REZ 5003 are bisphenol A-type epoxy novolacs available from Hexion. Epoxy or phenoxy functional modifiers to improve adhesion, flexibility and toughness, such as the HELOXY brand epoxy modifiers 67, 71 , 84, and 505. When used, the epoxy or phenoxy functional modifiers may be used in an amount of about 1 :1 to about 5:1 with regard to the heat curable resin.

Of course, combinations of different epoxy resins are also desirable for use herein.

The epoxy resin is preferably the only curable ingredient in the curable compositions of the present invention. However other curable ingredients or resins can be included, if desired.

If the epoxy resin is the only curable ingredient in the curable compositions of the present invention it is preferred that the amount of the at least one epoxy resin in the curable composition of the present invention is in the range of about 20 to about 99 percent by weight, such as about 60 to about 95 percent by weight, desirably about 70 to about 90 percent by weight, based on the total weight of the curable composition.

If the epoxy resin is not the only curable ingredient in the curable compositions of the present invention it is preferred that the amount of the at least one epoxy resin in the curable composition of the present invention is in the range of about 20 to about 95 percent by weight, such as about 60 to about 90 percent by weight, desirably about 70 to about 85 percent by weight, based on the total weight of the curable composition.

(b) Copolymer

The copolymer (b) used in the curable compositions of the present invention is a thermoplastic polymer, comprising at least one M-B, M-B-M and/or M-B-C block, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the A block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B.

The polymer blocks M, B and C are independently from a single monomer or a mixture of two or more monomers. Each block can independently be a statistically polymerized copolymer block or a gradient copolymer block. Each block is preferably connected to the other by means of a covalent bond or of an intermediate molecule connected to one of the blocks via a covalent bond and to the other block via another covalent bond.

In a preferred embodiment of the present invention, the at least one copolymer is a M-B diblock copolymer.

Preferably, the number average molecular weight of the M-B diblock copolymer is in the range of 5,000 g/mol to 500,000 g/mol, preferably in the range of 15,000 g/mol to 200,000 g/mol.

The M-B diblock copolymer is advantageously composed of a fraction by mass of M of between 5 and 95% and preferably between 15 and 85%.

In another preferred embodiment of the present invention, the at least one copolymer is a M-[B- M]_n block copolymer and n is an integer having the values 1 to 4. Preferably n is 1 (triblock copolymer), 2 (pentablock copolymer), or 3 (heptablock copolymer).

If the at least one copolymer of the present invention is a M-B-M triblock copolymer, it is preferred that the number average molecular weight of said copolymer is in the range of 5,000 g/mol to 500,000 g/mol, preferably in the range of 15,000 g/mol to 200,000 g/mol.

Advantageously, the M-B-M triblock copolymer is composed of a fraction by mass of M of between 5 and 95% and preferably between 15 and 85%, and of B of between 5 and 95% and preferably between 15 and 85%.

In a further preferred embodiment of the present invention, the at least one copolymer is a M-[B- C]₀ block copolymer and o is an integer having the values 1 to 4. Preferably o is 1 (triblock copolymer), 2 (pentablock copolymer), or 3 (heptablock copolymer).

If the at least one copolymer of the present invention is a M-B-C triblock copolymer, it is preferred that said copolymer has a number average molecular weight in the range of 5,000 g/mol to 500,000 g/mol, preferably in the range of 15,000 g/mol to 200,000 g/mol.

Advantageously, the M-B-C triblock copolymer has the following compositions, expressed as fraction by mass, the total being 100%: M+C: between 10 and 80% and preferably between 15 and 70%; B: between 20 and 90% and preferably between 30 and 85%.

Without wishing to be bound to theory, it is believed that the M polymer block has to contain the methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the M block, to render the at least one copolymer compatible with the epoxy resin (a). In case block M is not completely build of methyl acrylate, the methyl acrylate should preferably be present in an amount which renders the copolymer (b) compatible with the epoxy resin (a). "Compatibility" means that preferably no macroscopic phase separation of the curable composition, visible with the naked eye, occurs. Preferably the amount of methyl acrylate in block M is from 50 to 100 mol-% or from 60 to 100 mol-%, more preferably from 70 to 100 mol- % or from 80 to 100 mol% and most preferably from 90 to 100 mol-%, based on the total amount of monomers used to build block M.

In a preferred embodiment of the present invention the M block can consist of or contain only methyl acrylate monomer in polymerized form.

Although it is preferred that the M block contains the before mentioned amounts of methyl acrylate monomer, other ethylenically unsaturated monomers can be used as co-monomers to build the M block.

By "ethylenically unsaturated" is meant monomers that contain at least one polymerizable carbon-carbon double bond (which can be mono-, di-, tri-or tetra-substituted). Either a single monomer or a combination of two or more monomers can be utilized.

Such ethylenically unsaturated co-monomers are not specifically limited. However they should preferably not interfere with the compatibilising effect of the methyl acrylate. Such co-monomers which are different from methyl acrylate are preferably present in the M polymer block, in an amount of 0 to 49 mol-%, more preferably 0 to 30 mol-% and most preferably 0 to 10 mol-%, based on the total number of monomers used to build block M. In an especially preferred embodiment of the at least one copolymer (b), the number of co-monomers, which are different from methyl acrylate monomers, is essentially zero in the M block.

Examples of ethylenically unsaturated (co)monomers which can be used in the preparation of the (co)polymers apart from methyl acrylate are: (i) styrene and its derivatives as e.g. alpha-alkylstyrenes, like alpha-methylstyrene; vinyltoluene, phenoxyalkyl acrylates and methacrylates, like phenoxyethyl acrylate or phenoxy ethyl methacrylate, phenylalkyl acrylate and methacrylate, such as phenylethyl methacrylate, phenyl acrylate and phenyl methacrylate, benzyl acrylate and benzyl methacrylate.

(ii) esters of ethylenically unsaturated acids, such as alkyl or cycloalkyl esters having up to 20 carbon atoms in the alkyl radical, especially ethyl, propyl, n-butyl, sec-butyl, tert-butyl, hexyl, ethylhexyl, stearyl, and lauryl esters of acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, vinylphosphonic acid or vinylsulfonic acid; cycloaliphatic esters of acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, vinylphosphonic acid or vinylsulfonic acid, especially cyclohexyl, isobornyl, dicyclopentadienyl or tert-butylcyclohexyl esters of acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, vinylphosphonic acid or vinylsulfonic acid.

(iii) monomers which carry at least one hydroxyl group or hydroxymethylamino group per molecule, such as hydroxyalkyl esters of alpha, beta-ethylenically unsaturated carboxylic acids, such as hydroxyalkyl esters of acrylic acid, methacrylic acid and ethacrylic acid in which the hydroxyalkyl group contains up to 20 carbon atoms, such as 2-hydroxyethyl, 2-hydroxypropyl, 3- hydroxypropyl, 3-hydroxybutyl, 4-hydroxybutyl acrylate, methacrylate or ethacrylate; olefinically unsaturated alcohols such as allyl alcohol; reaction products of ethylenically unsaturated carboxylic acids with glycidyl esters of an alpha-branched monocarboxylic acid having from 5 to 18 carbon atoms in the molecule; olefinically unsaturated monomers containing acryloxysilane groups and hydroxyl groups, preparable by reacting hydroxy-functional silanes with epichlorohydrin and then reacting the intermediate with an ethylenically unsaturated carboxylic acid, especially acrylic acid and methacrylic acid, or hydroxyalkyl esters thereof;

(iv) vinyl esters of alpha-branched monocarboxylic acids having from 5 to 18 carbon atoms in the molecule, such as the vinyl esters of Versatic® acid;

(v) cyclic and/or acyclic olefins, such as ethylene, propylene, but-1-ene, pent-1-ene, hex-1-ene, cyclohexene, cyclopentene, norbornene, butadiene, isoprene, cyclopentadiene and/or dicyclopentadiene;

(vi) amides of alpha, beta-olefinically unsaturated carboxylic acids, such as (meth)acrylamide, N- methyl-, N,N-dimethyl-, N-ethyl-, N,N-diethyl-, N-propyl-, N,N-dipropyl-, N-butyl-, N,N-dibutyl- and/or N,N-cyclohexyl-methyl (meth)acrylamide; (vii) monomers containing epoxide groups, such as the glycidyl ester of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid and/or itaconic acid;

(viii) nitriles, such as acrylonitrile or methacrylonitrile;

(ix) vinyl compounds, selected from the group consisting of vinyl halides such as vinyl chloride, vinyl fluoride, vinylidene dichloride, and vinylidene difluoride; vinylamides, such as N- vinylpyrrolidone; vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, and vinyl cyclohexyl ether; and also vinyl esters such as vinyl acetate, vinyl propionate, and vinyl butyrate; and

(x) allyl compounds selected from the group consisting of allyl ethers and allyl esters, such as propyl allyl ether, butyl allyl ether, and allyl acetate and allyl propionate.

None of the before-mentioned comonomer groups (i) to (x) should contain the methyl acrylate monomers, which are essential to build polymer block M.

The weight average molecular weight of each M preferably ranges from 2,000 to 300,000 g/mol, more preferably 6,000 to 80,000 g/mol and most preferably 10,000 to 40,000 g/mol. The weight average molecular weight - as used in the description- is determined by gel permeation chromatography (GPC) using a styrene standard.

Without wishing to be bound to theory, it is believed that the B polymer block, is apt to enhance flexibility and toughness of the at least one copolymer (b).

The B block of the at least one copolymer (b) used in the curable compositions of the present invention is characterized by its glass transition temperature. If synthesized separately, the B block has a glass transition temperature of below 10 ºC, preferably below 0 ºC, more preferably below -10 ºC and most preferably below -20 ºC as determined by differential scanning calorimetry (DSC). In a preferred embodiment of the present invention the glass transition temperature is determined by DSC at a heating rate of 10°C/min.

The preferably elastomeric block B can be prepared from the ethylenically unsaturated monomers of the above-mentioned groups (i) to (ix) with the same polymerization techniques as the M block, as will be described below. Examples of such B blocks include, but are not limited to polyalkylenes, such as polybutadiene or polyisoprene, polyalkyl acrylates and polyalkyl methacrylates, such as poly(n-butyl acrylate) or poly(2-ethylhexyl acrylate), polyethers, such as poly(tetrahydrofurane), polyesters or polyurethanes or polymers containing ester and ether or ester and urethane groups. The B Block can contain only one type of monomers or mixtures of two or more types of monomers.

The B block can also be prepared by ring-opening polymerization of lactones, e.g. ε- caprolactone and/or δ-valerolactone, i.e. the B block can essentially be a poly(ε-caprolactone) modified with a terminal group at one or both terminal positions of the poly(ε-caprolactone), the terminal group allowing the connection to the A and/or A' block.

Moreover the B block can for example also consist of or contain a (linear) polysiloxane macromonomer, such as a polydimethylsiloxane, e.g. carrying the above mentioned terminal groups at one or both of its two terminal positions.

Another possible structure for a B block can be build by a polyaddition reaction, such as a diisocyanate/diol reaction forming a linear polyurethane, both terminal ends of which can be modified similar as described above.

In a particular preferred embodiment of the present invention, polymer block B is prepared from monomers selected from the group consisting of butyl acrylate, 2-ethylhexyl acrylate, butadiene, and dimethylsiloxane.

The weight average molecular weight of the B block preferably ranges from 1 ,000 to 200,000 g/mol, more preferably 2,000 to 80,000 g/mol and most preferably 8,000 to 40,000 g/mol.

If present, the C block of the at least one copolymer (b) used in the curable compositions of the present invention is characterized by its glass transition temperature. If synthesized separately, the C block has a higher glass transition temperature than the glass transition temperature of polymer block B.

Preferably, the glass transition temperature of polymer block C and polymer block B can be determined by differential scanning calorimetry (DSC) at a heating rate of 10°C/min.

The C block is a homo or copolymer which can preferably be prepared from ethylenically unsaturated monomers. The ethylenically unsaturated monomers of the C block are chosen from the same family of monomers as those of the M block. However, the presence of methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the C block is not obligatory.

In a preferred embodiment of the present invention vinylaromatic compounds, such as styrene, alpha-methylstyrene or vinyltoluene, and those which derive from alkyl esters of acrylic and/or methacrylic acids having from 1 to 18 carbon atoms in the alkyl chain can be used in the preparation of polymer block C.

The M and C block of the M-B-C triblock structures are different. They may be composed of different monomers or may also be different in their molar masses but composed of the same monomers.

The weight average molecular weight of the C block preferably ranges from 1 ,000 to 200,000 g/mol, more preferably 2,000 to 80,000 g/mol and most preferably 8,000 to 40,000 g/mol. In a preferred embodiment of the present invention polymer block B is incompatible with the epoxy resin (a) and/or polymer block C, if present, is incompatible with polymer block B.

The term "incompatible" is used to refer to the relationship of one polymer block to another or refers to the relationship of one polymer block to the epoxy resin (a). To be incompatible, a mixture of two different and separately synthesized polymer blocks or a mixture of one separately synthesized polymer block and epoxy resin (a) exhibits a phase separation of the two components at 22 ºC.

The at least one copolymers (b) used in the curable composition of the present invention can for example be prepared by conventional ionic or radical polymerization techniques, in which a first block of the copolymer is formed, and, upon completion of the first block a second monomer stream is started to form a subsequent block of the polymer and optionally a third or additional monomer stream(s) is/are started to subsequently form a third or additional block(s) of the polymer. However, using the anionic polymerization techniques the reaction temperatures using such techniques should be maintained at a low level, for example, 0 to -40 ºC, so that side reactions are minimized and the desired blocks, of the specified molecular weights, are obtained.

To attain the desired weight average molecular weight of each block as well as uniformity in the blocks, "living" free radical polymerization techniques such as nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT) and catalytic chain transfer (CCT) are advantageously, and preferably, used. One preferred polymerization route for the at least one copolymer (b) used in the curable composition of the present invention are nitroxide-mediated polymerizations. Thus, a nitroxide initiator may be employed to produce well-defined copolymers, such as M-B-M block copolymers. The process comprises two steps. In the first step, a core polymer of a defined length is synthesized with the bis-nitroxide initiator at the "centre" of the core polymer. This involves the living polymerization of the monomer or monomers with a bis-nitroxide initiator. After this first stage is complete, the core polymer is optionally purified or used without purification. A second step involves the introduction of the flanking polymer(s) using the same technique.

Nitroxide-mediated polymerizations (NMP) are disclosed for example in U.S. Pat. No. 4,581 ,429. A comprehensive review of NMP is provided by Hawker et al., Chem. Rev. 2001 , 101 , pp. 3661- 3688.

Another preferred polymerization route for the at least one copolymer (b) used in the curable composition of the present invention are atom transfer radical polymerizations.

Atom transfer radical polymerizations are based on the combination of a transition metal halide and an alkyl halide. The term "atom transfer" refers to the transfer of the halogen atom between the transition metal and the polymer chain. For example, K. Matyjaszewski, ( Macromolecules, vol. 28, 1995, pp. 7901-7910 and WO 96/30421 ) describes the use of CuX (where X=CI, Br) in conjunction with bipyridine and an alkyl halide to give polymers of narrow molecular weight distribution and controlled molecular weight. Comprehensive reviews of ATRP are provided by Matyjaszewski and Xia, Chem. Rev., vol. 101 , pp. 2921-2990, 2001 and by Braunecker and Matyjaszewski, Prog. Polym. ScL, vol. 32, pp. 93-146, 2007.

The physical characteristics of the at least one copolymer (b) of the present invention obtained for example by any of the above-mentioned "living" free radical polymerization techniques can be confirmed by conventional analytical techniques, including differential scanning calorimetry, matrix assisted laser desorption mass spectrometry (MALDI), nuclear magnetic resonance, chromatography and infrared analysis. For example, the chemical composition of the blocks can be determined by proton nuclear magnetic resonance or infrared analysis, or by pyrolysis and gas chromatographic analysis. The block arrangement and sizes in the copolymers can be determined by nuclear magnetic resonance, GPC or MALDI, and the glass transition temperature by DMTA. Even though the at least one copolymer (b) of the present invention comprises a linear polymer backbone, each block can independently comprise one or more side chains to create a comb- like structure. However polymers without such side chains are preferred.

In the curable compositions of the present invention only one copolymer (b) or a mixture of such copolymers can be used.

The amount of the at least one copolymer (b) in the curable composition of the present invention is preferably from 1 to 60 % by weight, more preferably from 3 to 30 % by weight and most preferably from 4 to 10 % by weight based on the total weight of the curable composition.

The curable compositions of the present invention can be obtained by simply mixing components (a) and (b) and optionally further ingredients, such as curing agents. However, it might be preferable to facilitate the mixing step by heating, e.g. to temperatures of 40 to 180 ºC, preferably 60 to 100 ºC. It may also be advisable to apply a vacuum to the composition while heating and mixing to 5-200 mbar. Therefore a further object of the present invention is a method of producing the curable composition of the present invention by mixing the ingredients.

Other additives

In a particular preferred embodiment of the present invention the curable composition further contains at least one curing agent.

The curing agent for the curable composition of the present invention may be chosen from a host of classes of nitrogen-containing compounds. One such class of nitrogen-containing compounds includes those having at least two amine functional groups available for reaction. For instance, a nitrogen-containing compound having at least two primary and/or secondary amines may be represented as being within the following structure C-I:

R, R¹, R², and R³ may be the same or different and may be selected from hydrogen, C_{1 -12} alkyl, C _{1 -12} alkenyl, C_5-12 cyclo or bicycloalkyl, C_6-18 aryl, and derivatives thereof, and is C_6-i β arylene, and derivatives thereof, and oxidized versions thereof. Preferably, at least one of R, R¹, R², and R³ is hydrogen.

Within structure C-I are a variety of materials that may be used herein, for instance, the aromatic diamines represented by structures C-Il:

C-Il where X is CH₂, CR₂, NH, NR, O, S, or SO₂; and R, R¹, R², and R³ are as described above.

Within structure C-Il are those compounds within structure C-III:

C-III where R is as defined above.

More specific materials within structure C-I further include those within structure C-IV where R⁴ and R⁵ are hydrogen, C_5-12 alkyl, C_5-8 cycloalkyl, C_7-15 phenylalkyl, or C_6-1O aryl, with or without substitution by one or two C_1-4 groups.

The commercially available phenylene diamines may be obtained under one or more of the following tradenames: SUMILIZER from Sumitomo, such as BPA, BPA-M1 , 4A, and 4M, and UOP from Crompton, such as UOP 12, UOP 5, UOP 788, UOP 288, UOP 88, UOP 26, UOP 388, UOP 588, UOP 36 and UOP 688.

Other diamines includes aromatic diamines, such as trialkyl substituted benzene diamines, such as diethyl toluene diamines (CAS No. 68479-98-1 ), available commercially under the tradename ETHACURE 100 from Albemarle Corporation.

The nitrogen-containing compounds also include aza compounds (such as di-aza compounds or tri-aza compounds). The nitrogen-containing compounds further include the aliphatic polyamines: diethylenetriamine, triethylenetetraamine, diethylaminopropylamine; the aromatic polyamines: benzyl dimethylamine, m-xylenediamine, diaminodiphenylamine and quinoxaline; and the alicyclic polyamines: isophoronediamine and menthenediamine. Examples of still other nitrogen-containing compounds include imidazoles, such as isoimidazole, imidazole, alkyl substituted imidazoles, such as 2-ethyl-4-methylimidazole, 2,4- dimethylimidazole, butylimidazole, 2-heptadecenyl-4-methylimidazole, 2-methylimidazole, 2- undecenylimidazole, 1-vinyl-2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2- phenylimidazole, 1-benzyl-2-methylimidazole, 1-propyl-2-methylimidazole, 1-cyanoethyl-2- methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1- cyanoethyl-2-phenylimidazole, 1-guanaminoethyl-2-methylimidazole and addition products of an imidazole and methylimidazole and addition products of an imidazole and trimellitic acid, 2-n- heptadecyl-4-methylimidazole and the like, generally where each alkyl substituent contains up to about 17 carbon atoms and desirably up to about 6 carbon atoms, aryl substituted imidazoles, such as phenylimidazole, benzylimidazole, 2-methyl-4,5-diphenylimidazole, 2,3,5- triphenylimidazole, 2-styrylimidazole, 1-(dodecyl benzyl)-2-methylimidazole, 2-(2-hydroxyl-4-t- butylphenyl)-4,5-diphenylimidazole, 2-(2-methoxyphenyl)-4,5-diphenylimidazole, 2-(3- hydroxyphenyl)-4,5-diphenylimidazole, 2-(p-dimethylaminophenyl)-4,5-diphenylimidazole, 2-(2- hydroxyphenyl)-4,5-diphenylimidazole, di(4,5-diphenyl-2-imidazole)-benzene-1 ,4, 2-naphthyl- 4,5-diphenylimidazole, 1-benzyl-2-methylimidazole, 2-p-methoxystyrylimidazole, and the like generally where each aryl substituent contains up to about 10 carbon atoms and desirably up to about 8 carbon atoms. Commercially available examples include EPI-CURE P-101 , EPI-CURE P-104 and EPI-CURE P-301 , all of which are available commercially from Resolution Performance Products, or AJICURE PN-23 and AJICURE MY-24, each of which is available commercially from Ajinomoto Fine Chemicals, Tokyo, Japan, which of course can be used. Bis(para-amino-cyclohexyl)methane is a particularly desirable nitrogen-containing compound for use herein [(PACM) CAS No. 1761-71-3, available commercially from Air Products], and OMICURE 33DDS, 3,3'-diaminodiphenylsulfone, CAS No. 599-61-1 , commercially available from CVC Specialty Chemical.

Other desirable nitrogen-containing compounds for use herein include 4,4'- diaminodiphenylsulfone, dicyandiamide, and 4,4'-methylenebis(cyclohexylamine) and melamine-formaldehyde polymers including the commercially available ones RESIMENE 745, RESIMENE 747 and RESIMENE AQ 7550 from Solutia, St. Louis, Missouri.

Of course, combinations of these various nitrogen-containing compounds are also desirable for use in the curable compositions of the present invention. The curing agent for the curable composition may typically be used in an amount that yields about 25 to about 100% amine equivalents compared to the epoxy equivalents, with about 65 to about 100% amine equivalents compared to the epoxy equivalents being particularly desirable.

In one embodiment the amount of the at least one curing agent in the curable composition of the present invention is in the range of 0.01 to 10 % by weight, more preferably from 0.1 to 8 % by weight and most preferably from 1 to 7 % by weight based on the total weight of the curable composition.

A catalyst, such as a urea-based one, may be included to promote the cure of the at least one epoxy resin of the present invention, preferably in an amount from 0.01 to 10 % by weight, more preferably from 0.1 to 8 % by weight and most preferably from 1 to 7 % by weight based on the total weight of the curable composition.

Other useful catalysts include amine-blocked toluenesulfonic acids, such as the amine-blocked p-toluenesulfonic acids available commercially under the tradenames NACURE 2500, NACURE 2547 and NACURE XC-221 1 from King Industries.

In a further particular preferred embodiment of the present invention the curable composition further contains at least one benzoxazine component.

The benzoxazine component can be any curable monomer, oligomer or polymer comprising at least one benzoxazine moiety. Preferably monomers containing up to four benzoxazine moieties are employed as the benzoxazine component in form of single compounds or mixtures of two or more different benzoxazines.

In the following a broad spectrum of different suitable benzoxazines containing one to four benzoxazine moieties are presented.

One possible benzoxazine may be embraced by the following structure B-I:

B-I where o is 1-4, X is selected from a direct bond (when o is 2), alkyl (when o is 1 ), alkylene (when o is 2-4), carbonyl (when o is 2), oxygen (when o is 2), sulfur (when o is 1 ), thioether (when o is 2), sulfoxide (when o is 2), and sulfone (when o is 2) , R¹ is selected from hydrogen, alkyl, alkenyl and aryl, and R⁴ is selected from hydrogen, halogen, alkyl and alkenyl, or R⁴ is a divalent residue creating a naphthoxazine residue out of the benzoxazine structure.

More specifically, within structure B-I the benzoxazine may be embraced by the following structure B-Il:

B-I where X is selected from a direct bond, CH₂, C(CH₃)₂, C=O, O, S, S=O and O=S=O, R¹ and R² are the same or different and are selected from hydrogen, alkyl, such as methyl, ethyl, propyls and butyls, alkenyl, such as allyl, and aryl, and R⁴ are the same or different and defined as above.

Representative benzoxazines within structure B-Il include:

where R ¹, R2 and R⁴ are as defined above. Alternatively, the benzoxazine may be embraced by the following structure B-VII:

B-VII

where p is 2, Y is selected from biphenyl (when p is 2) , diphenyl methane (when p is 2), diphenyl isopropane (when p is 2), diphenyl sulfide (when p is 2), diphenyl sulfoxide (when p is 2), diphenyl sulfone (when p is 2), and diphenyl ketone (when p is 2) , and R⁴ is selected from hydrogen, halogen, alkyl and alkenyl.

Though not embraced by structures B-I or B-VII additional benzoxazines are within the following structures:

B-VIII

B-IX

where R¹, R² and R⁴ are as defined above, and R³ is defined as R¹, R² or R⁴.

The benzoxazine component may include the combination of multifunctional benzoxazines and monofunctional benzoxazines, or may be the combination of one or more multifunctional benzoxazines or one or more monofunctional benzoxazines.

Examples of monofunctional benzoxazines may be embraced by the following structure XIX:

where R is alkyl, such as methyl, ethyl, propyl and butyl, alkenyl or aryl with or without substitution on one, some or all of the available substitutable sites, and R⁴ is selected from hydrogen, halogen, alkyl and alkenyl, or R⁴ is a divalent residue creating a naphthoxazine residue out of the benzoxazine structure

Benzoxazines are presently available commercially from several sources, including Huntsman Advanced Materials; Georgia-Pacific Resins, Inc.; and Shikoku Chemicals Corporation, Chiba, Japan, the last of which offers among others Bisphenol A-aniline, Bisphenol A-methylamin, Bisphenol F-aniline benzoxazine resins.

In a particularly preferred embodiment of the present invention the benzoxazine compound is an "aliphatic benzoxazine", i.e. a benzoxazine having aliphatic residues bound to the nitrogen atoms of the benzoxazine residue.

However in another preferred embodiment it can be desirable to use "aromatic benzoxazines", i.e. benzoxazines having aromatic residues bound to the nitrogen atoms of the benzoxazine residues. In some other preferred embodiments mixtures of the before-mentioned benzoxazines are advantageously employed.

If desired, however, instead of using commercially available sources, the benzoxazine may typically be prepared by reacting a phenolic compound, such as a bisphenol A, bisphenol F, bisphenol S or thiodiphenol, with an aldehyde and an alkyl or aryl amine. U.S. Patent No. 5,543,516, hereby expressly incorporated herein by reference, describes a method of forming benzoxazines, where the reaction time can vary from a few minutes to a few hours, depending on reactant concentration, reactivity and temperature. See generally U.S. Patent Nos. 4,607,091 (Schreiber), 5,021 ,484 (Schreiber), 5,200,452 (Schreiber) and 5,443,911 (Schreiber).

Any of the before-mentioned benzoxazines may contain partially ring-opened benzoxazine structures.

However, for the purpose of this invention those structures are still considered to be benzoxazine moieties, in particular ring-opened benzoxazine moieties.

The inventive compositions may also include a further toughener component, examples of which include poly(phenylene) oxide, polyethersulfones; amine-terminated polyethylene sulfide, such as PES 5003P, available commercially from Sumitomo Chemical Company, Japan; acrylonitrile-butadiene co-polymer having secondary amine terminal groups ("ATBN"), core shell polymers, such as PS 1700, available commercially from Union Carbide Corporation, Danbury, Connecticut; and BLENDEX 338, SILTEM STM 1500 and ULTEM 2000, which are available commercially from General Electric Company. ULTEM 2000 (CAS Reg. No. 61128-46-9) is a polyetherimide having a weight average molecular weight ("M_w") of about 30,000 ± 10,000 g/mol;

Curable Compositions of the present invention may ordinarily be cured by heating to a temperature in the range of about 120 to about 240 ºC for a period of time of about 30 minutes to 4 hours.

Preferably, the said compositions are cured in the presence of a curing agent, preferably selected from the group of nitrogen-containing compounds.

If desired, reactive diluents, for example styrene oxide, butyl glycidyl ether, 2,2,4-trimethylpentyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ether or glycidyl esters of synthetic, highly branched, mainly tertiary, aliphatic monocarboxylic acids, may be added to the curable compositions to reduce their viscosity.

The inventive compositions can include further additives preferably selected from plasticizers, extenders, microspheres, fillers and reinforcing agents, for example coal tar, bitumen, textile fibres, glass fibres, asbestos fibres, boron fibres, carbon fibres, mineral silicates, mica, powdered quartz, hydrated aluminum oxide, bentonite, wollastonite, kaolin, silica, aerogel or metal powders, for example aluminium powder or iron powder, and also pigments and dyes, such as carbon black, oxide colors and titanium dioxide, fire-retarding agents, thixotropic agents, flow control agents, such as silicones, waxes and stearates, which can, in part, also be used as mold release agents, adhesion promoters, antioxidants and light stabilizers, the particle size and distribution of many of which may be controlled to vary the physical properties and performance of the inventive compositions.

When used, fillers are used in an amount sufficient to provide the desired rheological properties. Fillers may be used in an amount up to about 50 percent by weight, such as about 5 to about 32 percent by weight, for instance about 10 to about 25 percent by weight. Properties of the curable compositions of the present invention As noted, the curable compositions of the present invention are in particular suitable as coatings, adhesives, sealants and matrices for the preparation of reinforced material such as prepregs and towpregs and/or can be used in injection molding or extrusion.

Therefore it is another object of the invention to provide an adhesive, sealant or coating comprising the curable composition of the present invention.

Suitable substrates on which the curable compositions of the present invention can be applied are metals such as steel, aluminum, titanium, magnesium, brass, stainless steel, galvanized steel, like HDG-steel and EG-steel; silicates such as glass and quartz; metal oxides; concrete; wood; electronic chip material, for instance semiconductor chip material; or polymers such as polyimide films and polycarbonate.

The invention also provides a cured reaction product of the curable composition, in particular cured reaction products containing bundles or layers of fibers infused with the curable composition, and a method of preparing such material.

In this regard, the invention relates to processes for producing a prepreg or a towpregs. One such process includes the steps of (a) providing a layer or bundle of fibers; (b) providing a curable composition of the present invention; (c) joining said curable composition and the layer or bundle of fibers to form a prepreg or a towpreg assembly; and (d) optionally removing excess curable composition from the prepreg or towpreg assembly, and exposing the resulting prepreg or towpreg assembly to elevated temperature and pressure conditions sufficient to infuse the layer or bundle of fibers with the polymerizable composition to form a prepreg or a towpregs assembly as the cured reaction product.

Another such process for producing a prepreg or towpreg, includes the steps of (a) providing a layer or bundle of fibers; (b) providing curable composition of the present invention in liquid form; (c) passing the layer or bundle of fibers through said curable composition to infuse the layer or bundle of fibers with said curable composition; and (d) removing excess of said curable composition from the prepreg or towpreg assembly, and exposing the resulting prepreg or towpreg assembly to elevated temperature and pressure conditions sufficient to infuse the layer or bundle of fibers with the curable composition to form a prepreg or a towpregs assembly as the cured reaction product.

Generally, the fiber layer or bundle may be constructed from unidirectional fibers, woven fibers, chopped fibers, non-woven fibers or long, discontinuous fibers. The fiber chosen may be selected from carbon, glass, aramid, boron, polyalkylene, quartz, polybenzimidazole, polyetheretherketone, polyphenylene sulfide, poly p-phenylene benzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate and napthenoate.

The carbon is selected from polyacrylonitrile, pitch and acrylic, and the glass is selected from S glass, S2 glass, E glass, R glass, A glass, AR glass, C glass, D glass, ECR glass, glass filament, staple glass, T glass and zirconium oxide glass.

The inventive curable composition (and prepregs and towpregs prepared therefrom) is particularly useful in the manufacture and assembly of composite parts for aerospace and industrial end uses, bonding of composite and metal parts, core and core-fill for sandwich structures and composite surfacing.

Preferably the curable compositions of the present invention are cured to obtain cured reaction products having a flexural modulus and flexural strength being about the same or even higher than said values for a composition not containing the at least one copolymer (b). Moreover the toughness "indicators" - K₁₀ and dc values (K₁₀ is standing for critical stress intensity factor and Gic is standing for critical energy release rate) - should be increased compared to compositions not containing the at least one copolymer (b).

One aim of the present invention is to provide a curable composition, which exhibit G₁₀ and K₁₀ values at least 10 %, more preferably at least 20 % and most preferably at least 30 % higher than the same cured composition without the at least one copolymer (b), while still maintaining a relatively low viscosity of the curable composition.

The cured reaction products of the present invention obtained from the curable compositions of the present invention preferably exhibit a flexural modulus of about 1000 to about 5000 MPa, a flexural strength of about 50 to about 200 MPa, a critical stress intensity factor (K1 c) of about 0.5 to about 4.0 MPa/m², a critical energy release rate (G1c) of about 100 to about 600 J/m².

Although a flexural modulus of 2000 to 5000 MPa usually forms the technically relevant range, it is preferred that the cured reaction products have a flexural modulus of at least 2500 MPa, more preferably 3500 MPa and most preferably 4000 MPa. The target range of flexural strength for most applications is 50 to 200 MPa, however it is preferably at least 60 MPa, more preferably 70 MPa and even more preferable at least 90 MPa. The target range of the critical stress intensity factor (K1c) is 0.5 to about 4.0 MPa/m², however it is preferred that the cured reaction products have a critical stress intensity factor (K1 c) of at least about 0.9 MPa/m². The target range of critical energy release rate (G 1c) is 100 to about 600 J/m², however it is preferred that the cured reaction products have a critical energy release rate (G1 c) of at least about 180 J/m².

The flexural strength and the flexural modulus of the cured reaction products of the curable compositions of the present invention can be determined according to ASTM D790, using samples of 90 mm x 12.7 mm x 3.2 mm size (span 50.8 mm; test speed: 1.27 mm/min).

The critical energy release rate (G 1 c) and critical stress intensity factor (K1c) of the cured reaction products of the curable compositions of the present invention can be determined according ASTM D5045-96 using so-called "Single-Edge Notch Bending (SENB)"-test using samples having the dimensions 56 mm x 12.7 mm x 3.2 mm.

As noted above one aim of the present invention is to increase the fracture toughness of cured epoxy resins without sacrificing other properties of the epoxy resins such as simple and low- cost processability.

In order to ensure simple and low-cost processability it is preferred that the viscosity of the curable composition of the present invention is in the range of 3000 to 20000 mPas, preferably in the range of 5000 to 16000 mPas, and more preferably in the range of 6500 to 15000 mPas, preferably measured with a Brookfield-Viskosimeter DV Il at 30° C, 20 rpm, spindel 3.

Another object of the present invention is the use of at least one copolymer of the present invention, selected from copolymers, comprising at least one M-B, M-B-M and/or M-B-C block, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the A block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B, as a toughening agent for epoxy resins.

A further object of the present invention is a method to increase the fracture toughness of at least one epoxy resin of the present invention by adding at least one copolymer selected from copolymers, comprising at least one M-B, M-B-M and/or M-B-C block, in which M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the M block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B to at least one epoxy resin of the present invention.

This invention is further illustrated by the following representative examples.

EXAMPLES

1. Preparation of copolymers (b) comprising at least one M-B-M block,

The copolymers (b) comprising at least one M-B-M block can be prepared according to any method as e.g. the method disclosed in J. Am. Chem. Soc, vol. 121 , pp. 3904-3920, 1999 for A- B block copolymers, which likewise can be carried out to obtain M-B-M or higher-order block copolymers and homopolymers. Alternatively, a further method for preparing the polymers of the present invention is disclosed in J. Polym. Sci: Part A: Polym. Chem, vol. 38, pp. 2023- 2031 , 2000.

Different copolymers of the present invetion, which were prepared according to one of the methods described above, are shown in Table 1.

Table 1

^*molar ratio = (x mol monomers in M) : (y mol monomers in B) PMA = poly(methyl acrylate) PMMA = poly(methyl methacrylate) PBA = poly(butyl acrylate)

The number average molecular weight was determined by gel permeation chromatography (GPC) using a styrene standard

2. Preparation of curable compositions

For the preparation of the curable compositions the following materials were used:

Epoxy resin DER 331 ; epoxy resin based on Bisphenol-A and epichlorohydrin commercially available from Dow Copolymer as described above

Curing agent Dicyandiamide

Catalyst Phenyl dimethyl urea [CAS 5 101-42-8]

Adhesion Promoter Mesamoll; C10-21 alkylsulfonic acid phenyl es available from Lanxess

Curable composition A

E poxy resin DER 331 82.4 wt.-%

Copolymer Copolymer No. 1 5.3 wt.-%

Curing agent Dicyandiamide 6.0 wt.-%

Catalyst Phenyl dimethyl urea 0.3 wt.-%

Adhesion Promoter Mesamoll 6.0 wt.-%

Curable composition B

Epoxy Resin DER 331 83.3 wt.-%

Copolymer Copolymer No. 2 4.4 wt.-%

Curing agent Dicyandiamide 6.0 wt.-%

Catalyst Phenyl dimethyl urea 0.3 wt.-%

Adhesion Promoter Mesamoll 6.0 wt.-%

Curable composition C

Epoxy Resin DER 331 83.3 wt.-%

Copolymer Copolymer No. 3 4.4 wt.-%

Curing agent Dicyandiamide 6.0 wt.-%

Catalyst Phenyl dimethyl urea 0.3 wt.-%

Adhesion Promoter Mesamoll 6.0 wt.-%

Curable composition D

Epoxy Resin DER 331 78.9 wt.-%

Copolymer Copolymer No. 3 8.8 wt.-%

Curing agent Dicyandiamide 6.0 wt.-%

Catalyst Phenyl dimethyl urea 0.3 wt.-% Adhesion Promoter Mesamoll 6.0 wt.-%

Curable composition E

Epoxy Resin DER 331 83.3 wt.-%

Copolymer Copolymer No. 4 4.4 wt.-%

Curing agent Dicyandiamide 6.0 wt.-%

Catalyst Phenyl dimethyl urea 0.3 wt.-%

Adhesion Promoter Mesamoll 6.0 wt.-%

Curable composition F (Reference)

Epoxy Resin DER 331 83.3 wt.-%

Copolymer Copolymer No. 5 4.4 wt.-%

Curing agent Dicyandiamide 6.0 wt.-%

Catalyst Phenyl dimethyl urea 0.3 wt.-%

Adhesion Promoter Mesamoll 6.0 wt.-%

The curable compositions A, B, C, D and F were prepared by mixing all components at elevated temperature. The viscosity of the curable compositions was measured with a Brookfield- Viskosimeter DV Il at 30° C, 20 rpm, spindel 3.

Viscosity of the curable compositions

Curable composition A n.d.

Curable composition B 1 1200 mPas

Curable composition C n.d.

Curable composition D n.d.

Curable composition E 6700 mPas

Curable composition F 9900 mPas

The curable compositions of the present invention are of low viscosity and therefore can easily be handled in simple and low-cost processes such as resin transfer molding (RTM). For curable compositions E and F, which contain block copolymers of identical molecular weight, it is clearly shown that poly(methyl acrylate)-based block copolymers (curable composition E, copolymer No. 4) lead to significantly lower formulation viscosities compared to poly(methyl methacrylate)- based block copolymers (curable composition F, reference copolymer No. 5). 3. Curing and testing of the curable compositions

The curable compositions A, B, C, D and F were cured in sealed containers in a circulating air drying for 30 min at 130ºC and 60 min at 180ºC. Subsequently the cured reaction products of the curable compositions were taken out of the drying oven, removed from the container and cooled to room temperature.

The cured reaction products were characterized using the following analytical methods:

Flexural Strength and Flexural Modulus

Flexural strength and flexural modulus were determined according to ASTM D790. The Samples were cut into pieces of 90 mm x 12.7 mm x 3.2 mm size (span 50.8 mm; test speed: 1.27 mm/min).

Critical Energy Release Rate (G1 c) and Critical Stress Intensity Factor (K1 c) Critical Energy Release Rate (G 1c) and Critical Stress Intensity Factor (K1 c) were determined according ASTM D5045-96 using so-called "Single-Edge Notch Bending (SENB)"-test pieces having the dimensions 56 mm x 12.7 mm x 3.2 mm.

Table 2 shows the properties of the cured samples tested according to the above procedures.

Table 2

CRP: Cured reaction product comp.: composition

The material testing results show that even at a content of 4 to 6% by weight of poly(methyl acrylate)-based block copolymers as toughening agents, the cured reaction products of the curable compositions of the present invention exhibit a relatively high fracture resistance.

Claims

1. A curable composition, comprising:

(a) at least one epoxy resin; and

(b) at least one copolymer selected from copolymers, comprising at least one M-B, M-B-M and/or M-B-C block, in which:

M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the M block,

B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B.

2. The curable composition according to claim 1 , wherein the at least one copolymer is a M-B block copolymer

3. The curable composition according to claim 1 , wherein the at least one copolymer is a M-[B- M]_n block copolymer and n is an integer having the values 1 to 4.

4. The curable composition according to claim 1 , wherein the at least one copolymer is a M-[B- C]₀ block copolymer and o is an integer having the values 1 to 4.

5. The curable composition according to any one of claims 1 to 4, wherein the amount of methyl acrylate in polymer block M is from 70 to 100 mol-% based on the total amount of monomers used to build block M.

6. The curable composition according to any one of claims 1 to 5, wherein the glass transition temperature of polymer block B is less than 0 ºC, preferably less than -10 ºC, and most preferably less than - 20 ºC.

7. The curable composition according to any one of claims 1 to 6, wherein the polymer block B includes polyalkylenes, poly(alkyl acrylates), poly(alkyl methacrylates), polyethers, polyesters, polyurethanes and/or polymers containing ester and ether or ester and urethane groups.

8. The curable composition according to any one of claims 1 to 7, wherein polymer block B is incompatible with the epoxy resin and/or polymer block C, if present, is incompatible with polymer block B.

9. The curable composition according to any one of claims 1 to 8, further containing at least one curing agent.

10. The curable composition according to any one of claims 1 to 9, further containing at least one benzoxazine component.

11. A cured reaction product of the curable composition according to any one of claims 1 to 10.

12. The cured reaction product according to claim 1 1 comprising a layer or bundle of fibers infused with the curable composition of any one of claims 1 to 10 before curing.

13. A process for producing the cured reaction product of claim 12, steps of which comprise: a) providing a layer or bundle of fibers; b) providing the curable composition of any one of claims 1 to 10; c) joining the composition and the layer or bundle of fibers to form an assembly, d) optionally removing excess curable composition from the assembly, and exposing the resulting assembly to elevated temperature and pressure conditions sufficient to infuse the layer or bundle of fibers with the curable composition to form the cured reaction product.

14. An adhesive, sealant or coating composition comprising the curable composition according to any one of claims 1 to 10.

15. Use of at least one copolymer selected from copolymers, comprising at least one M-B, M-B- M and/or M-B-C block, in which:

M is a polymer block which contains in polymerized form methyl acrylate in an amount of at least 50 mol-%, based on the total amount of monomers used to build the A block, B is a polymer block having a glass transition temperature below 10 ºC, and C is a polymer block having a higher glass transition temperature than the glass transition temperature of polymer block B, as a toughening agent for epoxy resins.