WO2009133011A1

WO2009133011A1 - Benzoxazine compositions containing (co)polymer

Info

Publication number: WO2009133011A1
Application number: PCT/EP2009/054865
Authority: WO
Inventors: Stefan Kreiling; Rainer SCHÖNFELD; Andreas Taden; Claudia Mai; Harald KÜSTER; Michael Kux; Stanley Leroy Lehmann
Original assignee: Henkel Ag & Co. Kgaa
Priority date: 2008-05-02
Filing date: 2009-04-23
Publication date: 2009-11-05

Abstract

The invention relates to a curable composition comprising: (a) at least one benzoxazine component; and (b) at least one (co)polymer of general formula A-(B)_m-(A')_n-[B-C]_O, wherein A and A' are polymer blocks which independently are same or different and A contains in polymerized form at least one ethylenically unsaturated aromatic monomer, A' contains in polymerized form at least one ethylenically unsaturated monomer, C is A or A' and B is a polymer block having a glass transition temperature below 20 °C, and m and n independently are 0 or 1, and o is an integer having the values 0 to 4. The invention further relates to a cured product made from the curable compositions, such as prepregs and towpregs.

Description

BENZOXAZINE COMPOSITIONS CONTAINING (CO)POLYMER

FIELD OF THE INVENTION

[0001] Curable benzoxazine-based compositions are useful in applications within the aerospace industry, such as for example as a heat curable composition for use as a matrix resin or an adhesive, and form the basis of the present invention, in which the curable composition contains specific (co)polymers.

BRIEF DESCRIPTION OF RELATED TECHNOLOGY

[0002] Epoxy resins with various hardeners have been used extensively in the aerospace and electronics industries both as adhesives and as matrix resins for use in prepreg assembly with a variety of substrates.

[0003] Benzoxazines themselves have been reported in the literature as generally having a high glass transition temperature, good electrical properties (e.g., dielectric constant), and low flammability. [0004] Blends of epoxy resins and benzoxazines are known. See e.g. U.S. Patent Nos.

4,607,091 (Schreiber), 5,021 ,484 (Schreiber), and 5,200,452 (Schreiber). These blends appear to be potentially useful in the electronics industry, as the epoxy resins can reduce the melt viscosity of benzoxazines allowing for the use of higher filler loading while maintaining a processable viscosity. However, epoxy resins oftentimes undesirably increase the temperature at which benzoxazines polymerize.

[0005] Ternary blends of epoxy resins, benzoxazine and phenolic resins are also known. See

U.S. Patent No. 6,207,786 (Ishida), and S. Rimdusit and H. Ishida, "Development of new class of electronic packaging materials based on ternary system of benzoxazine, epoxy, and phenolic resin," Polymer, 41 , 7941-49 (2000). WO-A2-2006/077153 describes benzoxazine-free systems exhibiting an improved impact resistance containing diblock and triblock copolymers. Benzoxazine-free curable compositions containing block copolymers are also disclosed in W0-A1 -2001/92415. The therein disclosed block copolymers have to contain blocks made from at least 50 % polymethylmethacrylate. [0006] However none of the before-mentioned documents discloses a suitable teaching on how to provide benzoxazine-based compositions with a high critical energy release rate (G 1c) and a high critical stress intensity factor (K1c) and therefore improved fracture toughness without deterioration the cured compositions further properties such as flexural strength, flexural modulus and glass transition temperature and without the need to incorporate epoxy resins.

SUMMARY OF THE INVENTION

[0007] The compositions according to the present invention are curable, in particular heat curable and include broadly the combination of (a) at least one benzoxazine component and (b) at least one (co)polymer of general formula A-(B)_m-(A')_n-[B-C]₀, wherein A and A' are polymer blocks which independently are same or different and A contains in polymerized form at least one ethylenically unsaturated aromatic monomer, A' contains in polymerized form at least one ethylenically unsaturated monomer, C is A or A' and B is a polymer block having a glass transition temperature below 20 ⁰C, and m and n independently are 0 or 1 , and o is an integer having the values 0 to 4. [0008] The invention further provides cured reaction products of the curable compositions of the present invention, a process for producing the cured reaction product and adhesives, sealants and coating compositions comprising the curable compositions.

DETAILED DESCRIPTION OF THE INVENTION

[0009] As noted above, the present invention provides a curable, in particular heat curable composition comprising the combination of (a) one or more benzoxazine components and (b) one or more (co)polymers of general formula A-(B)_m-(A')_n-[B-C]₀, wherein A and A' are polymer blocks which independently are same or different and A contains in polymerized form at least one ethylenically unsaturated aromatic monomer, A' contains in polymerized form at least one ethylenically unsaturated monomer, C is A or A', and B is a polymer block having a glass transition temperature below 20 ⁰C, and m and n independently are 0 or 1 , and o is an integer having the values 0 to 4.

(a) Benzoxazine Component

[0010] 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.

[0011] In the following a broad spectrum of different suitable benzoxazines containing one to four benzoxazine moieties are presented.

[0012] One possible benzoxazine may be embraced by the following structure I:

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), thiol (when o is 1 ), sulfur (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.

[0013] More specifically, within structure I the benzoxazine may be embraced by the following structure II:

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. [0014] Representative benzoxazines within structure Il include:

Vl where R¹, R² and R⁴ are as defined above. [0015] Alternatively, the benzoxazine may be embraced by the following structure VII:

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.

[0016] Though not embraced by structures I or VII additional benzoxazines are within the following structures:

VIII

where R , R and R are as defined above, and R is defined as R 1 , r R-,2 or r R-,4^' [0017] Specific examples of the above generically described benzoxazines include:

XVII

XVIII

[0018] 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.

[0019] Examples of monofunctional benzoxazines may be embraced by the following structure

XIX:

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. [0020] For instance, monofunctional benzoxazines may be embraced by general structure XX:

XX

where in this case R¹ is selected from alkyl, alkenyl, each of which being optionally substituted or interrupted by one or more O, N, S, C=O, COO, and NHC=O, and aryl; m is 0 to 4; and R", R¹", R^IV, R^V and R^vι are independently selected from hydrogen, alkyl, alkenyl, each of which being optionally substituted or interrupted by one or more O, N, S, C=O, COOH, and NHC=O, and aryl. [0021] Specific examples of such a monofunctional benzoxazine are:

XXI where R is as defined above; or

[0022] 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.

[0023] 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, such as the compound of formula Xl above. 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 such as the compounds of formulas XV or XX. In some other preferred embodiments mixtures of the before- mentioned benzoxazines are advantageously employed.

[0024] 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 also Burke et al., J. Org. Chem., 30(10), 3423 (1965); see generally U.S. Patent Nos. 4,607,091 (Schreiber), 5,021 ,484 (Schreiber), 5,200,452 (Schreiber) and 5,443,911 (Schreiber).

[0025] Any of the before-mentioned benzoxazines may contain partially ring-opened benzoxazine structures.

[0026] However, for the purpose of this invention those structures are still considered to be benzoxazine moieties, in particular ring-opened benzoxazine moieties.

[0027] The benzoxazine component 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.

[0028] In one preferred embodiment of the present invention the amount of the curable benzoxazine component of the curable composition of the present invention is in the range of about 20 to about 99 percent by weight, such as about 40 to about 98 percent by weight, desirably about 50 to about 95 percent by weight, based on the total weight of the composition.

[0029] Benzoxazine polymerization can be self-initiated under elevated temperature conditions and also by inclusion of cationic initiators, such as Lewis acids, and other known cationic initiators, such as metal halides; organometallic derivatives; metallophorphyrin compounds such as aluminum phthalocyanine chloride; methyl tosylate, methyl triflate, and triflic acid; and oxyhalides. Likewise, basic materials, such as imidazoles, may be used to initiate polymerization.

(b) (Co)polymer A-(BV(A¹J_n-[B-C]₀

[0030] The term (co)polymer as used in the present invention comprises homopolymers as well as copolymers. The (co)polymer (b) used in the curable compositions of the present invention is a thermoplastic polymer being defined by general formula A-(B)_m-(A')_n-[B-C]₀, wherein C is A or A', m and n independently of each other are 0 or 1 , and o is an integer having the values 0 to 4 and A, B and A' are polymer blocks built of at least 5 monomers per block.

[0031] The polymer blocks A, A' and B 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.

[0032] In case of the homopolymer o, m and n = 0 and polymer block A is made of one type of monomer only. A homopolymer is also defined for o = 0, m = 0 and n = 1 , if A and A' are made of the same one type of monomer.

[0033] In case of the copolymers o, m and n may be 0, if polymer block A is made of at least two types of monomers. However a copolymer is also formed for o = 0, if m and/or n are 1 , and if m = 0 and n = 1 , polymer blocks A and A' differ in the monomer composition.

[0034] Preferably, the term (co)polymer as used in the present invention also comprises higher- order copolymers, such as penta-block or hepta-block copolymers. For example, if m, n and o are 1 a penta-block copolymer is formed and if m and n are 1 and if o = 2 a hepta-block copolymer is formed. [0035] In a preferred embodiment of the present invention copolymer (b) is a penta-block or hepta-block copolymer.

[0036] Polymer blocks A and A' independently are same or different. They may differ in weight average molecular weight and/or the kind of monomers used to form blocks A and A', respectively, and/or the ratio of monomers used in blocks A and A'.

[0037] However, blocks A and A' have in common that they are made of a monomer or monomer mixture containing at least one ethylenically unsaturated monomer.

[0038] 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.

[0039] Therefore, polymer block A' contains in polymerized form at least one ethylenically unsaturated monomer. Said monomer may be selected from aromatic and non-aromatic ethylenically unsaturated monomers.

[0040] Additionally, block A is made of a monomer or monomer mixture containing at least one ethylenically unsaturated aromatic monomer. In a preferred embodiment of the invention block A' is also made of a monomer or monomer mixture containing at least one ethylenically unsaturated aromatic monomer. [0041] Preferred ethylenically unsaturated aromatic monomers are vinyl group containing aromatic or heteroaromatic hydrocarbons, wherein the aromatic or heteroaromatic hydrocarbon ring contains 5 to 10 carbon atoms. Other preferred ethylenically unsaturated aromatic monomers are aromatic esters of acrylic acid or methacrylic acid. The aromatic esters of acrylic acid or methacrylic acid preferably contain an aromatic or heteroaromatic hydrocarbon residue, wherein the aromatic or heteroaromatic hydrocarbon ring contains 5 to 10 carbon atoms and is part of the alcohol component used to esterify the acrylic acid or methacrylic acid. The most preferred aromatic alcohol to form an ester with acrylic acid or methacrylic acid is benzyl alcohol. In general the aromatic or heteroaromatic ring can be directly bound to the ester oxygen (-O-) of the ester group (-C(=O)-O-), however it is preferred that the aromatic or heteroaromatic ring is bound to the ester oxygen via a saturated aliphatic residue containing 1 to 8 carbon atoms and optionally one or more heteroatoms as for example oxygen or sulfur. [0042] Particularly preferred ethylenically unsaturated aromatic monomers of which the A polymer block, and preferably the A and A' polymer blocks, is/are made or which are contained in the A polymer block, and preferably in the A and A' polymer blocks, is 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. Most preferred are styrene and benzyl methacrylate.

[0043] Without wishing to be bound to theory, it is believed that the A polymer block has to contain the ethylenically unsaturated aromatic monomer to render the (co)polymer compatible with the benzoxazine component (a). In case block A, is not completely build of the ethylenically unsaturated aromatic monomer, the ethylenically unsaturated aromatic monomer should preferably be present in an amount which renders the (co)polymer (b) compatible with the benzoxazine component (a). "Compatibility" means that preferably no macroscopic phase separation of the curable composition, visible with the naked eye, occurs. Preferably the amount of the ethylenically unsaturated aromatic monomer in block A is from 10 to 100 mol-%, more preferably 40 to 100 mol-% and most preferably 75 to 100 mol-% based on the total amount of monomers used to build block A. Preferably, the same applies to block A'.

[0044] In a preferred embodiment of the present invention the A block and if present the A' block can consist of or contain only one kind of the ethylenically unsaturated aromatic monomer in polymerized form. However it can be advantageous to use two or more different ethylenically unsaturated aromatic monomers.

[0045] Although it is preferred that the A block and/or A' block contain the before mentioned amounts of the ethylenically unsaturated aromatic monomers and although it is most preferred that the A and/or A' block essentially consist of one or more ethylenically unsaturated aromatic monomers, as is the case for the most preferred A and A' polymer blocks, which consist of poly(benzylmethacrylate) only, other ethylenically unsaturated non-aromatic monomers can be used as monomers to build the A' block and/or as co-monomers to build the A block. [0046] Such (co)mononners are not specifically limited. However they should preferably not interfere with the compatibilising effect of the ethylenically unsaturated aromatic monomers. Such (co)monomers which are different from the ethylenically unsaturated aromatic monomers in that they are non-aromatic, are preferably present in the A polymer block, in an amount of 0 to 90 mol-%, more preferably 0 to 60 mol-% and most preferably 0 to 25 mol-% and in the A' polymer block, in an amount of 0 to 100 mol-%, more preferably 0 to 60 mol-% and most preferably 0 to 25 mol-% based on the total number of monomers used to build block A. In an especially preferred embodiment of the (co)polymer (b), the number of (co)monomers, which are different from the ethylenically unsaturated aromatic monomers, is essentially zero in the A and/or A' block.

[0047] In another preferred embodiment of the present invention the amount of the ethylenically unsaturated non-aromatic monomer in block A' is 100 mol-% based on the total amount of monomers used to build block A\

[0048] Examples of non-aromatic ethylenically unsaturated (co)monomers which can be used in the preparation of the (co)polymers apart from the ethylenically unsaturated aromatic monomers are: (i) esters of ethylenically unsaturated acids, such as alkyl or cycloalkyl esters having up to 20 carbon atoms in the alkyl radical, especially methyl, 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.

(ii) 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 hydroxyl-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; (iii) 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;

(iv) 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; (v) 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-m ethyl (meth)acrylamide; (vi) monomers containing epoxide groups, such as the glycidyl ester of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fu marie acid and/or itaconic acid; (vii) nitriles, such as acrylonitrile or methacrylonitrile;

(viii) 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

(ix) 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.

[0049] None of the before-mentioned comonomer groups (i) to (ix) should contain the ethylenically unsaturated aromatic monomers, which are essential to build blocks A and A', if present. [0050] All of the monomers forming the A and A' block, if present, should preferably contain only one polymerizable carbon-carbon double bond, i.e. one ethylenically unsaturated group per molecule. This should apply to ethylenically unsaturated aromatic monomer(s) and non-aromatic monomer(s) as well as to the (co)monomers of groups (i) to (ix).

[0051] The weight average molecular weight of each A and A' block 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. In case the (co)polymer consists of an A block only, the weight average molecular can preferably even range from 2,000 to 2,000,000 g/mol, with the same more preferred ranges as mentioned before. The weight average molecular weight - as used in the description - is determined by gel permeation chromatography (GPC) using a styrene standard.

[0052] Without wishing to be bound to theory, it is believed that the B polymer block, if present

(i.e. m = 1 ), is apt to enhance flexibility and toughness of the (co)polymer.

[0053] The B block of the (co)polymers (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 20 ⁰C, preferably below 0 ⁰C, most preferably below -20 ⁰C 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. [0054] The B block can be prepared from the ethylenically unsaturated monomers of the above- mentioned groups (i) to (ix) with the same polymerization techniques as the A and/or A' 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. [0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The (co)polymers (b) used in the curable compositions of the present invention can for example be prepared by conventional ionic or radical polymerization techniques, in which a first block of the (co)polymer is formed, and, upon completion of the first block, optionally 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 ⁰C, so that side reactions are minimized and the desired blocks, of the specified molecular weights, are obtained.

[0060] 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.

[0061] One preferred polymerization route for the (co)polymers (b) used in the curable compositions of the present invention are nitroxide-mediated polymerizations. Thus, a nitroxide initiator may be employed to produce well-defined (co)polymers, such as ABA 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. Optionally, a second step involves the introduction of the flanking polymer(s) using the same technique.

[0062] 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.

[0063] Another preferred polymerization route for the (co)polymers (b) used in the curable compositions of the present invention are atom transfer radical polymerizations.

[0064] 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.

[0065] The physical characteristics of the (co)polymers (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.

[0066] Even though the (co)polymer A-(B)_m-(A')_n-[B-C]₀ 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.

[0067] In the curable compositions of the present invention a single (co)polymer (b) or a mixture of such copolymers can be used.

[0068] The amount of (co)polymer(s) (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

5 to 20 % by weight based on the total weight of the curable composition.

[0069] The curable compositions of the present invention can be obtained by simply mixing components (a) and (b) and optionally further ingredients. However it might be preferable to facilitate the mixing step by heating, e.g. to temperatures of 40 to 180 ⁰C, preferably 60 to 100 ⁰C. 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 compositions by mixing the ingredients.

Other resins

[0070] The curable compositions of the present invention may further comprise other resin components apart from the benzoxazine component (a) and the (co)polymer component (b). Although not particularly preferred, at least one epoxy resins may be present for some applications were the disadvantages of the use of epoxy resins are not crucial. However the amount of epoxy resins should not exceed 70 % by weight, more preferably 50 % by weight and most preferably 25 % by weight of the total weight of the curable composition of the present invention.

[0071] The epoxy resins used in the present invention may include multifunctional epoxy- containing compounds, such as C₁-C_2S alkyl- or 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.

[0072] 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.

[0073] 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.

[0074] Of course, combinations of different epoxy resins are also desirable for use herein.

[0075] As further resin components contained in the curable compositions of the present invention polyoxazolines, polyisocyanates and their blocked derivatives may be additionally introduced. The amount of those components should not exceed 70% by weight, more preferably not exceed 40 % by weight, based on the total amount of the curable compositions.

Tougheners

[0076] The inventive compositions may also include a 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 copolymer 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;

[0077] Additionally, the curable composition may also comprise a toughener component, selected from benzoxazine-based thermoplastic tougheners, polyurethane-based thermoplastic tougheners and/or silica nanoparticles and/or mixtures thereof.

Other Additives

[0078] The inventive composition may be in the form of an adhesive, in which case one or more of an adhesion promoter, a flame retardant, a filler, nanoparticles, a thermoplastic additive, a reactive or non-reactive diluent, and a thixotrope may be included.

[0079] In addition, the inventive adhesive may be placed in film form, in which case a support constructed from nylon, glass, carbon, polyester, polyalkylene, quartz, polybenzimidazole, polyetheretherketone, polyphenylene sulfide, poly p-phenylene benzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate and naphthenoate should be included.

[0080] The invention also provides cured reaction products of the compositions, such as adhesives.

[0081] The invention also provides the adhesive in the form of a film, in which case the film may further include a support therefore selected from nylon, glass, carbon, polyester, polyalkylene, quartz, polybenzimidazole, polyetheretherketone, polyphenylene sulfide, poly p-phenylene benzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate and napthenoate.

[0082] Of course, the invention provides cured reaction products of the adhesive film.

[0083] Compositions of the present invention may ordinarily be cured by heating to a temperature in the range of about 120 to about 240 ⁰C for a period of time of about 30 minutes to 4 hours. [0084] The curing can if desired be conducted in two stages, for example, by interrupting the curing process or, if a curing agent is employed for elevated temperatures, by allowing the curable composition to cure partially at lower temperatures.

[0085] 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.

[0086] Other additives which the inventive compositions can include 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. [0087] 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. Fillers may also include core- shell-particles as for example disclosed in International Patent Application Publication No. WO 2007/064801 A1 (Li) the disclosure of which is incorporated herein by reference.

Properties of the curable compositions of the present invention

[0088] Preferably the curable compositions of the present invention are cured to obtain cured products having a flexural modulus and flexural strength being about the same or even higher than said values for a composition not containing (co)polymer (b), in particular in formulations that do not need to contain epoxy resins. Moreover the toughness "indicators" - K₁₀ and G_1C values (K₁₀ is standing for critical stress intensity factor and G_1C is standing for critical energy release rate) - should be increased compared to compositions not containing (co)polymer (b).

[0089] One aim of the present invention is to provide a curable composition, which exhibit G₁₀ and K_1C values at least 10 %, more preferably at least 20 % and most preferably at least 30 % higher than the same cured composition without (co)polymer (b), i.e. the A-(B)_m-(A')_n-[B-C]₀ polymer, while still maintaining flexural modulus and an almost as high glass transition temperature as for the composition not comprising (co)polymer (b).

[0090] 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 glass transition temperature of about 120 to about 300 ⁰C, a critical stress intensity factor (K1c) of about 0.5 to about 4.0 MPa/m², a critical energy release rate (G1c) of about 100 to about 600 J/m².

[0091] 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 (K1c) of at least about 0.9 MPa/m². The target range of critical energy release rate (G1 c) is 100 to about 600 J/m², however it is preferred that the cured reaction products have a critical energy release rate (G 1c) of at least about 180 J/m².

[0092] The glass transition temperature of the cured reaction products of the present invention given in the Example section is the glass transition temperature derived from the most prominent maximum of the loss modulus-temperature graph in the measured DMTA thermogram. As noted, the glass transition temperature should preferably be in the range of 120 to 300 ⁰C, more preferably in the range of 160 to 240 ⁰C, however it is preferred that the cured reaction products have a glass transition temperature of at least about 140 ⁰C. [0093] As noted, the invention relates also to the use of the curable compositions in the formation of prepregs or towpregs formed from a layer or bundle of fibers infused with the inventive curable composition.

[0094] In this regard, the invention relates to processes for producing a prepreg or a towpreg.

One such process includes the steps of (a) providing a layer or bundle of fibers; (b) providing the inventive curable composition; and (c) joining the curable composition and the layer or bundle of fibers to form a prepreg or a towpreg assembly, respectively, and optionally (d) 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 curable composition to form a prepreg or towpreg, respectively.

[0095] Another such process for producing a prepreg or towpreg, includes the steps of (a) providing a layer or bundle of fibers; (b) providing the inventive curable composition in liquid form; (c) passing the layer or bundle of fibers through the liquid curable composition to infuse the layer or bundle of fibers with the curable composition; and (d) removing excess curable composition from the prepreg or towpreg assembly.

[0096] The fiber layer or bundle may be constructed from unidirectional fibers, woven fibers, chopped fibers, non-woven fibers or long, discontinuous fibers.

[0097] 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.

[0098] 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.

[0099] The inventive compositions (and prepregs and towpregs prepared therefrom) are 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.

[00100] The inventive composition may be in the form of an adhesive, in which case one or more of an adhesion promoter, a flame retardant, a filler (such as the inorganic filler noted above, or a different one), nanoparticles, a thermoplastic additive, a reactive or non-reactive diluent, and a thixotrope may be included. In addition, the inventive compositions in adhesive form may be placed in film form, in which case a support e.g. constructed from nylon, glass, carbon, polyester, polyalkylene, quartz, polybenzimidazole, polyetheretherketone, polyphenylene sulfide, poly p-phenylene benzobisoaxazole, silicon carbide, phenolformaldehyde, phthalate and naphthenoate may be included.

[00101] The inventive compositions can be applied by any techniques well known in the art, such as from a robot into bead form on the substrate, using mechanical application methods such as a caulking gun, or any other manual application means, using a swirl technique employing pumps, control systems, dosing gun assemblies, remote dosing devices or application guns, or using a streaming process, where a bead is sprayed distance, nozzle to substrate, of about 3 to about 10 mm, using pressures of about 50 to about 300 bar, speeds of about 200 to about 500 mm/s, application temperatures from about 20 ⁰C to about 65 ⁰C and nozzle diameter of about 0.5 to about 1.5 mm. [00102] This invention is further illustrated by the following representative examples.

EXAMPLES

Preparation of A-(BL-(AVfB-CIn polymers (b)

[00103] The A-(B)_m-(A')_n-[B-C]₀ polymers prepared in the present invention 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 A-B-A' 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 (co)polymers are shown in Table 1 :

Table 1 : (Co)polymers comprising in polymerized form at least one ethylenically aromatic monomer

*molar ratio = (x mol monomers in A) : (y mol monomers in B)

** molar ratio = ( x mol monomers BMA) : (y mol monomers BA) in block A

PBMA = poly(benzylmethacrylate)

PBA = poly(butylacrylate)

BMA = benzylmethacrylate

BA = butylacrylate

PB = poly(butadiene)

PS = poly(styrene) Preparation of curable compositions

[00104] The curable compositions described in the following examples contain the following benzoxazines:

Benzoxazine A

Benzoxazine B

[00105] To 160 g of the above shown benzoxazine component (a) (Benzoxazine A or

Benzoxazine B) the respective amount of (co)polymer (b), according to Table 2 or Table 3, is added. The mixtures of components (a) and (b) are stirred under vacuo (< 1 mbar) for 15 to 30 minutes at a temperature of 105 to 115 ⁰C until the (co)polymer (b) is homogeneously dissolved in the benzoxazine component (a). The thus prepared composition was stored at room temperature in a sealed container.

Table 2: Samples based on Benzoxazine A

K) K)

Table 3: Samples based on Benzoxazine B

Curing and testing of the curable compositions

[00106] The curable formulations according to Table 2 and Table 3 were cured in sealed molds in an air-circulating drying oven at a temperature of 180 ⁰C for 3 hours. Subsequently the cured material was removed from the molds and cooled to room temperature.

The cured material was tested by the following procedures:

[00107] Glass Transition Temperature (T_g) by Dynamic Mechanical Thermal Analysis (DMTA):

The Samples were cut into pieces of 35 mm x 10 mm x 3.2 mm size. The samples were heated from 25

⁰C with a heating rate of 3 °C/min to a final temperature of 250 ⁰C. The glass transition temperature values were obtained from the maximum of the loss-modulus/temperature profile.

[00108] 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).

[00109] Critical Energy Release Rate (G 1c) and Critical Stress Intensity Factor (K1c): Critical

Energy Release Rate (G1c) 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.

[00110] Table 4 shows the properties of the test pieces tested according to the above procedures.

Table 4: Physical and mechanical properties of the cured compositions

K)

[00111] The material testing results show that even a content of 5 % by weight of the (co)polymer

(b) (Sample 3; A-B-A block copolymer) incorporated into the benzoxazine system enhances the critical energy release rate G1c and the critical stress intensity factor (K1c) to a great extend. Simultaneously flexural modulus is only slightly decreased.

[00112] The incorporation of the homopolymer (Sample 2; polymer consisting of block A only) in an amount of 10 % by weight gives an increase in critical energy release rate Gi c and a critical stress intensity factor K1c to the cured composition. However, flexural strength and glass transition temperatures are not as high as compared to the block copolymer tougheners. However for application were flexural strength is not the limiting parameter, but a high critical energy release rate G1c and a high critical stress intensity factor K1c are desired the homopolymer is still of high value. [00113] Sample 5, containing the A-B block copolymer ranges inbetween the homopolymer A and the triblock copolymer A-B-A containing cured compositions and is a good choice for applications, where particularly high critical energy release rates G1c and high critical stress intensity factors K1c are desired without affecting the flexural strength as much as for the homopolymer containing cured compositions. [00114] A comparison of Samples 6 and 3 shows how flexural strength can be affected by the choice of different B blocks in A-B-A block copolymers.

[00115] Finally, a comparison of Samples 12 and 11 shows that an ABA block copolymer in an amount of 5 % by weight gives an increase in critical energy release rate G1 c and a critical stress intensity factor K1c to the cured composition, which are based on benzoxazines of type B.

Claims

1. A curable composition comprising:

(a) one or more benzoxazine components; and

(b) one or more (co)polymers of general formula (I)

A-(BV(A¹J_n-[B-C]₀ (I), wherein

A and A' are polymer blocks which independently are same or different and A contains in polymerized form at least one ethylenically unsaturated aromatic monomer and A' contains in polymerized form at least one ethylenically unsaturated monomer and C is A or A', and

B is a polymer block having a glass transition temperature below 20 ⁰C, and m and n independently are 0 or 1 and o is an integer having the values 0 to 4.

2. The curable composition according to Claim 1 , wherein the benzoxazine component (a) comprises at least one benzoxazine of the group consisting of benzoxazines having one benzoxazine ring and benzoxazines having at least two benzoxazine rings.

3. The curable composition according to Claim 1 and/or 2, wherein m, n and o are 0.

4. The curable composition according to Claim 1 and/or 2, wherein m is 1 and n is 0 or 1 and o is 0.

5. The curable composition according to Claim 4, wherein n is 1 and blocks A and A' are same regarding the kind and ratio of monomers in each block.

6. The curable composition according to Claim 1 or 2, wherein o is 2 or 3.

7. The curable composition according to any of Claims 1 to 6, wherein the ethylenically unsaturated aromatic monomer, which is contained in the A block and A' block, if present, is selected from the group consisting of styrene and its derivatives, vinyltoluene, phenoxyalkyl acrylates and methacrylates, phenylalkyl acrylates and methacrylates, benzyl acrylate and benzyl methacrylate.

8. The curable composition according to any of Claims 1 to 7, wherein the ethylenically unsaturated aromatic monomer is contained in the A block and the A' block, if present, in an amount of 10 to 100 mol- % based on the total amount of monomers used to build the A block and the A' block, respectively.

9. The curable composition according to any of Claims 1 , 2 and 4 to 8, wherein the polymer block B, if present, includes polyalkylenes, polyalkyl acrylates, polyalkyl methacrylates, polyethers, polyesters, polysiloxanes, polyurethanes and/or polymers containing ester and ether or ester and urethane groups.

10. The curable composition according to any of Claims 1 to 9, further containing at least one epoxy resin.

11. A cured reaction product of the composition according to any of Claims 1 to 10.

12. The cured reaction product according to claim 11 comprising a layer or bundle of fibers infused with the composition of any 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 according to any 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 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 composition according to any of Claims 1 to 10.

15. The adhesive, sealant or coating composition of claim 14, further comprising one or more of a toughener, an adhesion promoter, a flame retardant, nanoparticles, a filler, a thermoplastic additive, an reactive or unreactive diluent, and a thixotrope.