WO2009071991A2

WO2009071991A2 - Nanoparticle silica filled benzoxazine compositions

Info

Publication number: WO2009071991A2
Application number: PCT/IB2008/003474
Authority: WO
Inventors: Andreas Taden; Stefan Kreiling; Elmar Hecht; Oliver Bedford; Christine Mohr
Original assignee: Henkel Ag & Co. Kgaa; Sustech Gmbh & Co. Kg
Priority date: 2007-12-06
Filing date: 2008-12-05
Publication date: 2009-06-11
Also published as: WO2009071991A3

Abstract

The invention relates to a curable composition comprising: (A) a benzoxazine component; and (B) silica particles dispersed therein, the silica particles having a maximum length in any direction of space in the range of about 2 to 200 nm determined by transmission electron microscopy, and an amino benzene, phenol or thiophenol being bound to the surface of said silica particles. The invention further relates silica particle dispersions and cured product made from the curable compositions, such as prepregs and towpreg.

Description

NANOPARTICLE SILICA FILLED BENZOXAZINE COMPOSITIONS

BACKGROUND OF THE INVENTION

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 is filled with surface modified dispersed silica nanoparticles.

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), 5,200,452 (Schreiber), and 5,445,911

(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 e.g. U.S. Patent No. 6,207,786 (Ishida).

[0006] U.S. Patent No. 6,323,270 (Ishida) discloses a nanocomposite composition of clay and a benzoxazine monomer, oligomer, and/or polymer in amount effective to form a nanocomposite. The clay is described as a silicate comprised of multiple platelets, or a hydrated aluminum silicate comprised of multiple platelets. Clay, according to U.S. Patent

No. 6,323,270, is a component of soils typically derived from the weathering of rocks that can be an aggregate having particle sizes of less than about 50 microns, examples of which being montmorillonite, atapulgite, illite, bentonite, and halloysite.

[0007] EP 0 875 531 A2 (Ishida) also discloses the use of fused or crystalline silica based fillers in benzoxazine based curable compositions.

[0008] WO 2006/062891 discloses a heat curable composition based on the combination of one or more benzoxazines and silicas having a mean particle diameter in the order of 10^~9 meters. See also European Patent Application No. 1734069 A1. [0009] Notwithstanding the state of the technology, there has been no disclosure, teaching or suggestion to prepare a heat curable composition based on the combination of one or more benzoxazines and a surface-modified silica component having a maximum length in any direction of space in the range of about 2 to 200 nm, determined by transmission electron microscopy (TEM), where an amino benzene, phenol or thiophenol is bound to said silica particles, and which can be pre-dispersed in a resin-free or substantially resin-free medium.

SUMMARY OF THE INVENTION

[0010] The compositions according to the present invention are heat curable and include broadly the combination of (a) a benzoxazine component and (b) silica particles. The silica particles are dispersed throughout the benzoxazine component. The silica particles have a maximum length in any direction of space in the range of about 2 to 200 nm, as determined by TEM, and an amino benzene, phenol or thiophenol is bond to the surface of the silica particles.

[0011] The invention further provides cured products of the heat curable compositons of the present invention, a process for producing the cured product and adhesives, sealants and coating compositions comprising or consisting of the heat curable compositions.

[0012] The invention further provides silica particle dispersions, the silica particles having a maximum length in any direction of space in the range of about 2 to 200 nm, determined by TEM, and wherein an amino benzene, phenol or thiophenol is bound to said silica particles.

DETAILED DESCRIPTION OF THE INVENTION

[0013] As noted above, the present invention provides a heat curable composition comprising the combination of (a) a benzoxazine component and (b) silica particles dispersed therein, the silica particles having a maximum length in any direction of space in the range of about 2 to 200 nm, determined by TEM, and wherein an amino benzene, phenol or thiophenol is bound to said silica particles.

The Benzoxazine Component (A)

[0014] 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. [0015] n one embodiment of the present invention 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.

[0016] In the following a broad spectrum of different suitable benzoxazines containing one to four benzoxazine moieties are presented.

[0017] 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. [0018] 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, O, C=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. [0019] Representative benzoxazines within structure Il include:

where R , R and R⁴ are as defined above.

[0020] 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.

[0021] Though not embraced by structures I or VII additional benzoxazines are within the following structures:

VIII

X where R¹, R² and R⁴ are as defined above, and R³ is defined as R¹, R² or R⁴. [0022] Specific examples of the above generically described benzoxazines include:

XVII

XVIII

[0023] 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. [0024] Examples of monofunctional benzoxazines may be embraced by the following structure XIX:

XIX where R is alkyl, such as methyl, ethyl, propyls and butyls, 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.

[0025] 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 interupted by one or more O, N, S, C=O, COO, and NHC=O, and aryl; m is O to 4; and R¹¹, R¹", R^ιv, R^v and R^vl are independently selected from hydrogen, alkyl, alkenyl, each of which being optionally substituted or interrupted by one or more O, N, S, C=O, COOH₁ and NHC=O, and aryl. [0026] Specific examples of such a monofunctional benzoxazine are:

XXI where R¹ is as defined above; or

XXII

[0027] 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. [0028] 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).

[0029] Any of the before-mentioned benzoxazines may contain partially ring-opened benzoxazine structures.

[0030] However, for the purpose of this invention those structures are still considered to be benzoxazine moieties, in particular ring-opened benzoxazine moieties. [0031] 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.

[0032] In one preferred embodiment of the present invention the amount of the curable benzoxazine component of the heat 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.

[0033] 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 imidizaoles, may be used to initiate polymerization. Silica nanoparticles of the heat curable composition (B) [0034] Conventional silica nanoparticles are obtainable as aqueous dispersions, dispersions in alcohol such as isopropanol or pre-dispersed in resins, such as epoxy-resins. However, dispersions in resins are not desirable since they limit the applicability to a small range of compositions. On the other hand aqueous dispersion cannot be mixed into organic resin components such as the benzoxazine component of the present invention. Finally, dispersions of nanoparticles in alcohols such as isopropanol tend to agglomerate if mixed into organic resins, at least after removing the solvent from the curable composition. [0035] The drawbacks of the before-mentioned compositions can be overcome by the silica nanoparticles of the present invention, having a maximum length in any direction of space in the range of about 2 to 200 nm, preferably 5 to 100nm, more preferably 5 to 50 nm and most preferably 10 to 40 nm, as determined by TEM.

[0036] The present invention provides silica nanoparticles whose surface has been modified by a functionalized benzene, such as amino benzene, phenol or thiophenol. The surface modification of the silica nanoparticles may be a chemical or physical modification, with covalent or non-covalent bonds oftentimes being formed. At present, covalent bonding is a desirable way in which to achieve such surface modification.

[0037] Depending on the kind of silica nanoparticles employed a direct or indirect bonding can occur. If plain silica nanoparticles are to be treated with the amino benzene, phenol or thiophenol, a surface modification before treatment with the amino benzene, phenol or thiophenol is preferred.

[0038] The surface of plain un-modified silica nanoparticles should be prepared to exhibit binding sites for amino, hydroxy or thiol groups, in particular binding sites for the amino, hydroxy or thiol groups of the amino benzenes, phenols or thiophenols, respectively. [0039] In one particularly preferred embodiment such binding sites to amino, hydroxy or thiol groups are introduced to the nanosilica surface by reacting the nanosilica particles with an organo-silane preferably comprising an amino, hydroxy or thiol reactive functional group.

[0040] Organo-silanes satisfying this criterion contain at least one hydrolysable group bound to the silane silicon atom. Examples for such hydrolysable groups are alkoxy groups or acetoxy groups.

[0041] A particularly preferred organo-silane can be described by the following general structure:

X-R-Si(OR^u)_n(R^v)₃-n wherein

X is a group which is reactive towards amino, hydroxy and/or thiol groups, R is an alkylene group having 1 to 6 carbon atoms, OR¹ is a hydrolysable group, wherein R^u is a straight-chain or branched alkyl group with 1 to

4 carbon atoms or a -CO-R^W group, wherein R^w independently has the same meaning as R^u,

R^v is a straight-chain or branched alkyl group with 1 to 4 carbon atoms, and n is 1 , 2 or 3.

[0042] Residue X can be any group that is reactive towards amino, hydroxy and/or thiol groups, such alpha, beta-unsaturated carbonyl groups, imino groups and particularly preferred glycidoxy or isocyanato groups.

[0043] Most preferably the X group is also reactive towards the benzoxazine component of the curable composition under curing conditions.

[0044] Residue R can be any alkylene group, even being interrupted by hetero atoms or functional groups such as urethane, ether or ester groups. Most preferred is that R is a methylene, ethylene or propylene group.

[0045] Residue OR^U can be any hydrolysable residue such as an alkoxy residue or an alkoxy residue. However methoxy, ethoxy or acetoxy residues are preferred.

[0046] Residue R^v is most preferably methyl or ethyl and n is preferably 2 or 3, most preferably 3.

[0047] Examples of suitable organo-silanes are glycidoxyalkyl silanes and isocyanatoalkyl silanes with one, two or three hydrolysable groups chosen from the group consisting of methoxy, ethoxy, propoxy, butoxy and acetoxy. Particularly preferred are the glycidoxyalkyl silanes such as glycidoxypropyl silane, containing two or three methoxy and/or ethoxy groups. Most preferred is glycidoxypropyl trimethoxysilane.

[0048] The amino benzene, phenol or thiophenol for use in the present invention can be any benzene comprising a primary or secondary, preferably a primary amino group, a hydroxy group or thiol group. Most preferably used in the present invention are amino benzenes and amongst those the primary amino benzenes.

[0049] In a particularly preferred embodiment the amino benzene, phenol or thiophenol for use in the present invention can be described by the following general formula

wherein Y is a primary or secondary amino group, OH or SH. [0050] Although it is possible that the amino benzene, phenol or thiophenol of the present invention can be bound to the silica surface by physisorption or ionic bonding, it is most preferred that the amino benzene, phenol or thiophenol is covalently bound by reaction between the amino, OH or SH group of the amino benzene, phenol or thiophenol and die X group of the organo-silane.

[0051] For that reason it is particularly preferred that in the above general formula of the amino benzene, Y stands for NHR^a, wherein R^a is H or an straight-chain or branched alkyl group with 1 to 6 carbon atoms, and R^b, R^c, R^d, R^e and R^f independently are H, a residue selected from the group consisting of straight-chain or branched alkyl groups with 1 to 6 carbon atoms, alkoxy groups with 1 to 6 carbon atoms, aryl groups with 6 to 12 carbon atoms, halo groups, carbonyl groups or alkenyl groups with 2 to 10 carbon atoms. [0052 ] Desirably Y is NH₂ and one of R^b, R^c, R^d, R^e and R^f is a methoxy group and another one of R^b, R°, R^d, R^e and R^f is an methyl group such as in 2-methoxy-5- methylaniline.

[0053] Nanosilica dispersions, wherein the nanosilica is surface-modified with silanes as described above exhibiting a binding site towards the amino, OH or SH function of the amino benzene, phenol or thiophenol and will readily react with the amino benzene, phenol or thiophenol, preferably at temperatures in the range of about 40 ⁰C to about 100 ⁰C, more preferably in the range of about 40 to about 100 ⁰C and most preferably in the range of about 60 to about 95 ⁰C.

[0054] It was surprisingly found that the modification of the nanosilica surface with the amino benzene, phenol or thiophenol is able to prevent nanosilica agglomeration, in particular if the silica nanoparticles of the present invention being dispersed in an organic solvent such as isopropanol and are incorporated into a resin composition, preferably into a heat curable composition comprising at least one benzoxazine component. [0055] Since the preferably substantially resin-free silica dispersion in water or an organic solvent is useful to be incorporated into various different heat curable resins, it is a valuable object of the present invention to be claimed separately.

[0056] Further object of the present invention is the preparation of silica nanoparticles and silica nanoparticle dispersions, respectively, involving the steps of (a) providing a silica nanoparticle dispersion in aqueous medium optionally containing an organic solvent, (b) reacting the silica nanoparticle dispersion with a hydrolysable silane, the hydrolysable silane comprising an amino, OH or SH reactive group, such as a glycidoxy or isocyanato group, to obtain a silane-modifϊed silica nanoparticle dispersion (c) exchanging the aqueous medium with an organic solvent and (d) reacting an amino benzene, phenol or thiophenol with the silane-modified silica nanoparticle dispersion. This ready-to-use dispersion can be combined with the resin phase and excessive solvent is optionally to be evaporated depending on the application, before cure. However, after the modification step with the amino benzene, phenol or thiophenol, the organic solvent can be exchanged for water or mixtures of water with organic solvents if desired.

[0057] Preferred organic solvent for steps (a) and (c) is isopropanol. However other alcohols, which are fluid at room temperature, diethyl ether, tetrahydrofuran, toluene or benzene and other organic solvents, which allow an azeotropic distillation with water can also be employed.

[0058] The silica component of the present invention should be present in the curable composition of the present invention an amount of about 1 to about 50 percent by weight, such as about 3 to about 25 percent by weight, desirably about 4 to about 15 percent by weight, based on the total weight of the composition. The weight of the silica component is defined as the sum of the weight of employed unmodified silica plus the weight of employed amino benzene, phenol and/or thiophenyl plus the weight of employed bridging molecule such as silane, if present.

Tougheners

[0059] The inventive compositions may also include a toughener component, examples of which include poly(phenylene) oxide; 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.

Other Additives

[0060] 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, a thermoplastic additive, a reactive or non-reactive diluent, and a thixotrope may be included. 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.

[0061] The invention also provides cured reaction products of the adhesives.

[0062] 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, potyphenylene sulfide, poly p-phenylene benzobisoaxazole, silicon carbide, phenoiformaldehyde, phthalate and napthenoate.

[0063] Of course, the invention provides cured reaction products of the adhesive film.

[0064] Compositions of the present invention may ordinarily be cured by heating to a temperature in the range of about 120 to about 180 ⁰C for a period of time of about 30 minutes to 4 hours.

[0065] 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.

[0066] 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.

[0067] Other additives which the inventive compositions can include tougheners, 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.

[0068] 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

[0069] Preferably the curable compositions of the present invention are cured to obtain cured products having a flexural modulus and flexural strength being the same or higher than said values for a composition not containing component (B), in particular in formulations that do not need to contain epoxy resins. Moreover the toughness "indicators" - K-ic and Gic values (K-ι_C is standing for critical stress intensity factor and G₁C is standing for critical energy release rate) - should be increased compared to compositions not containing component B).

[0070] One aim of the present invention is to provide curable coating composition, which comprise after curing an increased flexural and exhibit G-ic values at least 10 %, more preferably at least 20 % and most preferably at least 30 % higher than the same cured composition without component b), i. e. the surface-modified nanosilica, while still maintaining flexural modulus and an almost as high glass transition temperature as for the silica free composition.

[0071] 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 heat curable composition.

[0072] 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 heat curable composition; and (c) joining the heat curable composition and the layer or bundle of fibers to form a prepreg or a towpreg assembly, respectively, 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 heat curable composition to form a prepreg or towpreg, respectively.

[0073] 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 heat curable composition in liquid form; (c) passing the layer or bundle of fibers through the liquid heat curable composition to infuse the layer or bundle of fibers with the heat curable composition; and (d) removing excess heat curable composition from the prepreg or towpreg assembly. [0074] The fiber layer or bundle may be constructed from unidirectional fibers, woven fibers, chopped fibers, non-woven fibers or long, discontinuous fibers. [0075] 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.

[0076] 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. [0077] 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. [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 (such as the inorganic filler noted above, or a different one), 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.

[0079] 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 20⁰C to about 65°C and nozzle diameter of about 0.5 to about 1.5 mm. [0080] This invention is further illustrated by the following representative examples.

EXAMPLES A. Preparation of a silica dispersion (SD)

DOWEX HCR-W2 ion exchanger (available from Dow, Merck) is dried on a frit using a suction pump. The ion exchanger is rinsed with water until the filtrate is colourless. To 43 g of the ion exchanger, 110 ml of a colloidal silica dispersion ("Bindzil 30NH₃/220", from Akzo Nobel; colloidal solution of discrete, dense and spherical SiO₂ particles (30 % by weight) in weakly alkaline water; mean particle diameter = 15 nm; specific area (220 g/m²)) are added within 15 minutes while stirring. After an additional 15 minutes of stirring, the ion exchanger is recovered by filtering the mixture on a glass frit using a vacuum pump. During the procedure, it is important that the pH value of the solution remains above 3. Subsequently 87.56 g of isopropanol and 87.56 g of the acidic colloidal silica dispersion are heated in a 500 ml round bottom flask to 60⁰C (T = 60°C +/- 3⁰C) while stirring. Within 2 hours, 52.25 g (49.10 ml) of 3-glycidoxypropyltrimethoxysilane are added using a piston pump (0.4378 g/min, 0.4092 ml/h), and the mixture is stirred over night at 60°C. After an additional 2 hours of stirring, the mixture is concentrated using a rotary evaporator with the bath temperature set at 6O⁰C. Subsequently a first distillation step is carried out at 200 mbar, evaporating about 48% of the total weight, while the remaining reaction liquid turns hazy and milky, lsopropanol (about 60% (w/w)) of the remaining liquid is added. During the following second distillation step, the pressure is slowly adapted to 100 mbar. The reaction yields about 100 g of a slightly hazy, bluishly shimmering product. To remove traces of water remaining in the product, 30 g of isopropanol is added distillation at 100 mbar is repeated to yield a clear, slightly yellow product.

B. Preparation of heat curable compositions

B.1. Preparation of a benzoxazine mixture (a)

150 ml of 1-methoxy-2-propanol and 30 ml of toluene are added to 150 g of melted B-Mix 6/4 (structures see below) in a 500 ml one-necked round bottom flask. The mixture is stirred at 90°C with a magnetic stirrer bar until dissolved.

B-Mix 6/4 is a 60/40 mixture of the following two benzoxazines:

60 parts by weight

40 parts by weight

B.2. Preparation of a silica dispersion (b) containing a substituted amino benzene In a 100 ml beaker, 17 g of SD (preparation see above) are dissolved in 80 ml of 1-methoxy- 2-propanol. Then, 1.5 g of 2-methoxy-5-methylaniline are added and the mixture is stirred for 30 minutes at 85°C.

B.3. Preparation of a Masterbatch of (a) and (b) Dispersion (b) is added dropwise to mixture (a). The resulting mixture is stirred for 10 minutes and solvents are removed by distillation (120⁰C at the still head) at ambient atmospheric pressure until almost no more solvents are evaporated. The remaining solvents are removed by vacuum distillation (800 Pa; 60°C) using a rotary evaporator. After removal of the volatile compounds as described, a yellow, almost transparent, highly viscous material is obtained that is solid at room temperature. The masterbatch contains 10.2 % by weight of the organo-silica component (sum of the employed unmodified silica, the employed 3- glycidoxy propyl trimethoxy silane and the employed 2-methoxy-5-methylamidine), which is equivalent to approximately 6.3 wt.-% of unmodified (employed) silica particles.

This masterbatch is already a curable composition of the present invention. However it is also used to supplement different further curable compositions as lined out in Table 1 below (all amounts are in parts by weight):

Table 1

^*Sample 4 is a comparative Example, which is identical to Example 11 (Table 6) in WO

2006/062891

B-m: benzoxazine resin of the following structure, commercially available from Shikoku

Chemicals Corporation (Chiba, Japan)

Nanopox XP 0317: silica nanoparticles contained in a cycloaliphatic epoxy resin matrix (40-50 wt.-% nanoparticles in epoxy resin matrix), commercially available from Hanse Chemie (Geesthacht, Germany)

N/A: does not apply, since no silica modified according to the present invention is employed; however, according to the above specifications approximately 10-12.5 wt.-% silica nanoparticles are contained ¹based on the weight of the total composition

Remark: A likewise produced masterbatch without the use of 2-methoxy-5-methylaniline as dispersant in dispersion (b) resulted in a yellow, turbid, non-transparent, highly viscous material that is solid at room temperature. The turbidity and non-transparency is the result of agglomeration of silica in the preparation, which is deteriorating the properties of the product and finally of the cured product.

C. Curing and testing of the curable compositions

The curable formulations according to Table 1 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 test by the following procedures:

C.1. Glass Transition Temperature (T_fl) 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 10 °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.

C.2. 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).

C.3. Critical Energy Release Rate (G1c)

Critical Energy Release Rate (G1c) was determined according ASTM D5045-96 using so- called "Single Etch 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 test pieces tested according to the above procedures.

Table 2

*Sample 4 is a comparative Example, which is identical to Example 11 (Table 6) in WO 2006/062891 N/D: not determined

[0081] The material testing results show that even a content of approximately 5 % by weight of the surface-modified silica incorporated as dispersion according to the present invention into the benzoxazine resin system enhances the critical energy release rate G1c by approximately 40 %. Simultaneously flexural modulus is almost unaffected. Increasing the amount of silica to about 10 % by weight has no further influence on the critical energy release rate G 1c. However, flexural strength is further enhanced.

Claims

1. A curable composition comprising:

(A) a benzoxazine component; and

(B) silica particles dispersed therein, the silica particles having a maximum length in any direction of space in the range of about 2 to 200 nm determined by transmission electron microscopy, and an amino benzene, phenol or thiophenol being bound to the surface of said silica particles.

2. The curable composition according to claim 1 , wherein the silica particles (b) dispersed therein, are surface-modified with an organo-silane, to which the amino benzene, phenol and/or thiophenol is bound.

3. The curable composition according to claim 2, wherein the organo-silane has the following general structure:

wherein

X is a group which is reactive towards amino, OH and/or SH groups, R is an alkylene group having 1 to 6 carbon atoms,

OR^U is a hydrolysable group, wherein R^u is a straight-chain or branched alkyl group with 1 to 4 carbon atoms or a -CO-R^W group, wherein R^w independently has the same meaning as R^u, R^v is a straight-chain or branched alkyl group with 1 to 4 carbon atoms, and n is 1 , 2 or 3.

4. The curable composition according to claim 3, wherein X is a glycidoxy or an isocyanato group, R is a methylene, ethylene or propylene group, OR^U is methoxy, ethoxy or acetoxy, R^v is methyl or ethyl and n is 2 or 3.

5. The curable composition according to any of claims 1 to 4, to which an amino benzene, phenol and/or thiophenol of the following general formula

is covalently bound by reaction between the donor group Y of the amino benzene, phenol or thiophenol and the X group of the organo-silane, and wherein Y is OH, SH or NHR^a and R^a is H or a straight-chain or branched alkyl group with 1 to 6 carbon atoms, R^b, R^c, R^d, R^e and R^f independently are a residue selected from the group consisting of straight-chain or branched alkyl groups with 1 to 6 carbon atoms, aikoxy groups with 1 to 6 carbon atoms, aryl groups with 6 to 12 carbon atoms, halo groups, carbonyl groups or alkenyl groups with 2 to 10 carbon atoms.

6. A silica particle dispersion, the silica particles having a maximum length in any direction of space in the range of about 2 to 200 nm determined by transmission electron microscopy, and an amino benzene, phenol and/or thiophenol being bound to the surface of said silica particles.

7. The silica particle dispersion according to claim 6, wherein the silica particles dispersed therein, are surface-modified with an organo-silane, to which the amino benzene, phenol and/or thiophenol is bound.

8. The silica particle dispersion according to claim 7, wherein the organo-silane has the following general structure:

wherein

OR^υ is a hydrolysable group, wherein R^u is a straight-chain or branched alkyl group with 1 to 4 carbon atoms or a -CO-R^W group, wherein R^w independently has the same meaning as R^u, R^v is a straight-chain or branched alkyl group with 1 to 4 carbon atoms, and n is 1 , 2 or 3.

9. The silica particle dispersion according to claim 8, wherein X is a glycidoxy or an isocyanato group, R is a methylene, ethylene or propylene group, OR^U is methoxy, ethoxy or acetoxy, R^v is methyl or ethyl and n is 2 or 3.

10. The silica particle dispersion according to any of claims 6 to 9, to which an amino benzene, phenol and/or thiophenol of the following general formula

is covalently bound by reaction between the donor group Y of the amino benzene, phenol or thiophenol and the X group of the organo-silane, and wherein Y is OH, SH or NHR^a and R^a is H or an straight-chain or branched alkyl group with 1 to 6 carbon atoms, R^b, R°, R^d, R^e and R^f independently are a residue selected from the group consisting of straight-chain or branched alkyl groups with 1 to 6 carbon atoms, alkoxy groups with 1 to 6 carbon atoms, aryl groups with 6 to 12 carbon atoms, halo groups, carbonyl groups or alkenyl groups with 2 to 10 carbon atoms.

11. The silica particle dispersion according to any of claims 6 to 10, where the medium in which the silica particles are dispersed is water, an organic solvent or a mixture of both.

12. A cured reaction product of the composition according to any of claims 1 to 5.

13. The cured reaction product according to claim 12 comprising a layer or bundle of fibers infused with the composition of any of claims 1 to 5 before curing.

14. A process for producing the cured reaction product of claim 13, steps of which comprise:

A) providing a layer or bundle of fibers;

B) providing the composition according to any of claims 1 to 5;

C) joining the composition and the layer or bundle of fibers to form an assembly,

D) optionally removing excess heat 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 heat curable composition to form the cured reaction product.

15. An adhesive, sealant or coating composition comprising or consisting of the composition according to any of claims 1 to 5.