Curable Resin Composition Comprising Cyanate Ester and Acrylic Alkenyl Ester

This invention relates to a curable resin composition comprising a mixture and/or a preliminary reaction product of (a) a polyfunctional cyanate ester, prepolymer of the cyanate ester or coprepolymer of the cyanate ester and an amine (sometimes hereinunder referred to as component (a) and (b) at least one compound selected from the group consisting of alkenyl acrylic esters, alkenyl methacrylic esters, prepolymers of alkenyl acrylic esters, prepolymers of alkenyl methacrylic esters, coprepolymers of alkenyl acrylic esters and alkenyl methacrylic esters and mixtures thereof (sometimes hereinunder referred to as component (b)) and also relates to a curable resin composition comprising a mixture and/or a preliminary reaction product of (a) a polyfunctional cyanate ester, prepolymer of the cyanate ester or coprepolymer of the cyanate ester and an amine, (b) at least one compound selected from the group consisting of alkenyl acrylic esters, alkenyl methacrylic esters, prepolymers of alkenyl acrylic esters, prepolymers of alkenyl methacrylic esters, coprepolymers of alkenyl acrylic esters and alkenyl methacrylic esters and mixtures thereof, and (c) a polyfunctional maleimide, prepolymer of the maleimide or coprepolymer of the maleimide and an amine (sometimes hereinunder referred to as component (c)). Cured resin obtained by curing each of the resin compositions has excellent impact-resistance, adhesive power, heat-resistance and chemical resistance.

In the prior art, the cured resin obtained by cast-molding a composition containing a polyfunctional maleimide and a polyfunctional cyanate ester has low impact resistance. Similarly, the cured resin obtained by cast-molding cyclopentadiene resin is fragile.

The present inventors carried out research for obtaining a cured resin having excellent impact resistance and excellent adherence to the substrate. As a result it was found that when a curable resin composition comprising a mixture and/or a preliminary reaction product of (a) a polyfunctional cyanate ester, prepolymer of the cyanate ester or coprepolymer of the cyanate ester and an amine, and an alkenyl acrylic ester or its prepolymer, a alkenyl methacrylic ester or its prepolymer, or coprepolymer of the alkenyl acrylic ester and the alkenyl methacrylic ester or a curable resin composition comprising a mixture and/or a preliminary reaction product of above component (a), above component (b) and (c) a polyfunctional maleimide, prepolymer of the maleimide or coprepolymer of the maleimide and an amine is cured, a cured resin having the above-mentioned desirable properties can be obtained. This invention is based on this discovery.

By polyfunctional cyanate ester is meant a compound having at least two cyanate groups in its molecule. The polyfunctional cyanate ester is represented by the formula ##STR1## wherein R is an aromatic nucleus-containing residue which is selected from the group consisting of a residue derived from an aromatic hydrocarbon selected from the group consisting of benzene, biphenyl and naphthalene, a residue derived from a compound in which at least two benzene rings are bonded to each other by a bridging member selected from the group consisting of ##STR2## wherein R.sup.1 and R.sup.2 are the same or different and each represents a hydrogen atom or an alkyl group containing 1 to 4 carbon atoms, ##STR3## said aromatic nucleus is optionally substituted by a substituent selected from the group consisting of alkyl groups containing 1 to 4 carbon atoms, alkoxy groups containing 1 to 4 carbon atoms, chlorine and bromine; m is an integer of 2 to 5, and the cyanate group is always directly bonded to the aromatic nucleus.

Examples of the polyfunctional cyanate ester include dicyanatobenzene; 1,3,5-tricyanatobenzene; 1,3-, 1,4-, 1,6-, 1,8-, 2,6- or 2,7-dicyanatonaphthalene; 1,3,6-tricyanatonaphthalene; 4,4'-dicyanatobiphenyl; bis(4-cyanatophenyl)methane; 2,2-bis(4-cyanatophenyl)propane, 2,2-bis(3,5-dichloro-4-cyanatophenyl)propane, 2,2-bis-(3,5-diblomo-4-dicyanatophenyl)propane; bis(4-cyanatophenyl) ether; bis(4-cyanatophenyl)thioether; bis(4-cyanatophenyl)sulfone; tris(4-cyanatophenyl)phosphite; tris(4-cyanatophenyl)phosphate; bis(3-chloro-4-cyanatophenyl)methane; cyanated novolak derived from novolak cyanated bisphenol type polycarbonate oligomer derived from bisphenol type polycarbonate oligomer and mixture thereof. Other cyanate esters employed in the practice of this invention are given in Japanese Patent Publication Nos. 1928/1966, 4791/1969, 11712/1970 and 41112/1971 and Japanese Patent Publication (laid open) No. 63149/1976 which are incorporated herein for references. The above-mentioned cyanate esters may be used as mixtures.

Prepolymers may be used containing a sym-triazine ring which is prepared by the trimerization of the cyanate groups of the cyanate ester, and which have an average molecular weight of at least 400 but no more than 6,000. Such prepolymers can be prepared by polymerizing the above cyanate esters in the presence of, as a catalyst, an acid such as a mineral acid or a Lewis acid, a base such as sodium hydroxide, a sodium alcoholate or a tertiary amine, or a salt such as sodium carbonate or lithium chloride.

The polyfunctional cyanate ester can be used in the form of a mixture of the monomer and the prepolymer. For example, many of the commercially available cyanate esters derived from bisphenol A and cyanogen halide are in the form of mixtures of cyanate monomers and prepolymers, and such materials can also be used in the present invention.

A coprepolymer of the cyanate ester and an amine may be used as the cyanate ester component. Examples of the amines include meta- or para-phenylenediamine, meta- or para-xylylenediamine, 1,4- or 1,3-cyclohexanediamine, hexahydroxylylenediamine, 4,4'-diaminobiphenyl, bis(4-aminophenyl)methane, bis(4-aminophenyl)ether, bis(4-aminophenyl)sulfone, bis(4-amino-3-methylphenyl)methane, bis(3-chloro-4-aminophenyl) methane, bis(4-amino-3,5-dimethylphenyl)methane, bis(4-aminophenyl)cyclohexane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-amino-3-methylphenyl)propane, 2,2-bis(3,5-dibromo-4-aminophenyl)propane, bis(4-aminophenyl)phenylmethane, 3,4-diaminophenyl-4'-aminophenylmethane and 1,1-bis(4-aminophenyl)-1-phenylethane.

A mixture of prepolymer of the cyanate ester and coprepolymer of the cyanate ester and an amine may be used as component (a) of this invention.

The alkenyl acrylic ester or alkenyl methacrylic ester is represented by the formula ##STR4## wherein each of X.sup.1, X.sup.2 and X.sup.3 is hydrogen, methyl, ethyl or halogen; and R is hydrocarbon or substituted hydrocarbon having 1-16 carbon atoms. Profitably R group in the compound represented by the above formula I or II may be ##STR5## wherein both of Y.sup.1 and Y.sup.2 are hydrogen, or one of them is hydrogen and the other is methyl, and p is integer of 1-7. The alkenyl acrylic ester or alkenyl methacrylic ester may be prepolymerized by means of an organic peroxide, an ionic polymerization catalyst, heat or ultraviolet rediation. Prepolymer of the alkenyl acrylic ester or the alkenyl methacrylic ester or coprepolymer of the alkenyl acrylic ester and the alkenyl methacrylic ester may be used as component (b).

The ratio of component (a) and component (b) is not critical. The ratio by weight of component (a) to component (b) may be in the range of from 99:1 to 1:99, preferably from 95:5 to 35:65. For example, when it is necessary for a cured resin to have heat resistance, more component (a) is used than component (b).

When component (c) is used with components (a) and (b), the heat resistance of the cured resin is further improved.

The polyfunctional maleimides employed in the present invention are organic compounds having two or more maleimide groups derived from maleic anhydride and a polyamine and are represented by the following general formula ##STR6## wherein R represents divalent to pentavalent aromatic or alicyclic organic group, each of X.sup.1 and X.sup.2 represent a hydrogen atom, halogen atom or alkyl group, and n represent integer of 2-5.

The maleimides represented by the above formula can be produced by a method known per se which involves reacting maleic anhydride with polyamine to form a maleamide acid, and then dehydro-cyclizing the maleamide acid.

Aromatic amines are preferable as the starting polyamines. The reason is that the resulting object resin has excellent properties, such as heat-resistance, etc. When the resulting object resins have desirable flexibility and pliability, alicyclic amine alone or combination of the alicyclic amines and other amines may be used. Though secondary amines can be used as the starting amine, the primary amines are preferable.

Amines employed in reaction with cyanate esters for preparing coprepolymers of the cyanate ester and the amine may be profitably used as the amine component for preparing maleimides. In addition to the above-mentioned amines, melamine having s-triazine ring and polyamines obtained by reaction aniline with formaldehyde, in which two or more benzene rings are bonded through methylene bond, may also be used.

The functional maleimides as mentioned above may be used alone or as a mixture. Also the prepolymer of the maleimide obtained by heating the maleimide in the presence or absence of a catalyst may be used. In addition, coprepolymers of the maleimide and the amine employed for synthesizing the polyfunctional maleimide may be used.

The curable composition of this invention may be prepared by merely mixing the above-mentioned components (a) and (b) or components (a), (b) and (c) or by using the product of preliminary reaction of these components.

The curable composition of this invention comprises a mixture and/or a preliminary reaction product of (a) at least one compound selected from the group consisting of polyfunctional cyanate esters, prepolymers of the cyanates esters or coprepolymers of the cyanate esters and an amine and (b) at least one compound selected from the group consisting of acrylic alkenyl esters, methacrylic alkenyl esters, prepolymers of acrylic alkenyl esters, prepolymers of methacrylic alkenyl esters, coprepolymers of acrylic alkenyl esters and methacrylic alkenyl esters and mixtures thereof and optionally (c) at least one compound selected from the group consisting of polyfunctional maleimides, prepolymers of the maleimides and coprepolymers of the maleimides and an amine and/or (d) other component. The composition may be a mixture of components (a) and (b) and optionally (c) and/or (d); a preliminary reaction product of components (a) and (b), components (a), (b) and (c) or components (a), (b), (c) and (d); a mixture of preliminary reaction product of two or three of components (a), (b), (c) and (d) and the remainder thereof. Other components (d) include epoxy resins; (meth)acrylates, such as methacrylates, acrylates, methacrylic epoxy esters, acrylic epoxy esters, its prepolymers; polyallyl compounds, such as diallyl phthalate, divinylbenzene, diallylbenzene, trialkenyl isocyanurates or its prepolymers; phenol resins; polyvinyl acetal resins, such as polyvinyl formal, polyvinyl acetal, or polyvinyl butyral; acrylic resins, silicone resins, or alkyd resins having OH group or COOH group; and liquid or elastic rubbers, such as polybutadiene, butadiene-acrylonitrile copolymer, polychloroprene, butadiene-styrene copolymer, polyisoprene or natural rubbers.

The curable composition of this invention may be reticulated by heating it alone to form a cured resin having heat resistance. In general, a catalyst may be used in order to promote crosslinking reaction of the components in the composition.

Examples of the catalysts include imidazoles, such as 2-methylimidazole, 2-undecylimidazole, 2-heptadecyl imidazole, 2-phenylimidazole, 2-ethyl 4-methylimidazole, 1-benzyl-2-methylimidazole, 1-propyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-guanaminoethyl-2-methylimidazole and addition product of an imidazole and trimellitic acid; tertiary amines, such as N,N-dimethyl benzylamine, N,N-dimethylaniline, N,N-dimethyltoluidine, N,N-dimethyl-p-anisidine, p-halogeno-N,N-dimethylaniline, 2-N-ethylanilino ethanol, tri-n-butylamine, pyridine, quinoline, N-methylmorpholine, triethanolamine, triethylenediamine, N,N,N'N'-tetramethylbutanediamine, N-methylpiperidine; phenols, such as phenol, cresol, xylenol, resorcine, and phloroglucin; organic metal salts, such as lead naphthenate, lead stearate, zinc naphthenate, zinc octylate, tin oleate, dibutyl tin maleate, manganese naphthenate, cobalt naphthenate, and acetyl acetone iron; and inorganic metal salts, such as stannic chloride, zinc chloride and aluminum chloride; peroxides, such as benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, acetyl peroxide, para-chlorobenzoyl peroxide and di-t-butyl diperphthalate; acid anhydrides, such as maleic anhydride, phthalic anhydride, lauric anhydride, pyromellitic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, hexa hydropyromellitic anhydride and hexahydrotrimellitic anhydride; azo compounds, such as azoisobutylonitrile, 2,2'-azobispropane, m,m'-azoxystyrene, hydrozones, and mixtures thereof.

In addition to the above-mentioned catalysts, a curing agent for epoxy resin and a curing catalyst for epoxy resin may be used as a catalyst of this invention.

The amount of the catalyst employed may be less than 5% by weight of total composition.

A variety of additives may be added to the curable composition to impact specific properties provided that they do not impair the essential properties of the resulting resin. Examples of the additives include natural or synthetic resins, fibrous reinforcement, fillers, pigments, dyestuffs, thickening agents, lubricants, flame-retardants and the like.

The curable compositions of this invention are present in a wide range of forms from liquid to solid at room temperature, depending on the natures of the components constituting the composition, and the preliminary reaction conditions. Solid curable composition, liquid curable composition or solution of the composition in solvent may be used according to the use purpose.

The curing conditions of the curable composition of this invention depend on proportion of components constituting the composition and the nature of the components employed. In general, the composition of this invention may be cured by heating it at a temperature within the range of 100.degree.-250.degree. C.

When the curable composition of this invention is used for preparing molding, laminate, adhesive-assembly, press means is preferably applied to the molding, laminate or adhesive-assembly in the heat curing step. In general, these products may be pressed at a superpressure of 10-500 Kg/cm.sup.2.

The composition of this invention is rapidly curable and is cured even under mild conditions, so is especially suitable when quantity production and ease of workability are desired. The cured resin made from the composition not only has excellent adhesive force, bond strength, heat resistance, and electric properties, but also is excellent in mechanical properties, such as impact resistance, chemical resistance, moisture resistance and the like. The composition of this invention has a variety of uses as a coating material for rust prevention, flame resistance, flame retardance and the like; as electrical insulating varnish; as adhesive; in laminates to be used for furnitures, building materials, sheathing materials, electrical insulating materials, and the like; and in a variety of moldings.

The present invention is further illustrated by the following non-limiting Examples and Comparative Examples. Percent and parts are by weight, unless otherwise specified.

0.4 (grams) of benzoyl peroxide was added to 300 grs of allyl methacrylate. The allyl methacrylate was prepolymerized at 100.degree. C. for 95 minutes.

To the resulting prepolymer were added prepolymer obtained by prepolymerizing 900 grs of 2,2-bis(cyanatophenyl)propane at 160.degree. C. for 3 hours, 0.3 grs of zinc octylate and 0.3 grs of triethylene diamine. 2500 grs of active silica and 3 grs of carbon black were added to the mixture; and the resulting mixture was uniformly milled to form molding material. The molding material was molded at 30 Kg/cm.sup.2 at 150.degree. C. for 120 minutes. The resulting molded product was cured at 185.degree. C. for 30 hours. The physical data on the product are shown in Table 1.

The procedure of Example 1 was repeated except that allyl methacrylate was not used. The physical data are also shown in Table 1.

200 grs of allyl methacrylate prepolymer prepared in the same way as in Example 1 was mixed with prepolymer obtained by preliminarily reacting 700 grs of 1,4-dicyanatobenzene, 240 grs of bis(4-maleimidophenyl)methane and 60 grs of 4-maleimidophenyl-3',4'-dimaleimidophenyl methane and 4-maleimidophenyl-2',4'-dimaleimidophenyl methane at 160.degree. C. for 90 minutes. 0.3 grs of zinc octylate and 0.3 grs of triethylene diamine as catalytic composite were added to the mixture. The mixture was uniformly milled and poured into a mold and then cured at 190.degree. C. for 10 hours in the mold, thereby obtaining dark brown plate. The physical data on the plate are shown in Table 2.

The procedure of Example 2 was repeated except that allyl methacrylate was not used. The physical data on the resulting plate are shown in Table 2.

A plate was prepared from allyl methacrylate in the way as in Example.

Spherical iron weighing 1000 grs was dropped from height of 3 m on a 10 cm.times.10 cm plate 3 mm thick. Symbol "O" shows that the plate was not cracked, whereas symbol "X" shows that the plate was cracked.

200 grs of monomer represented by the formula ##STR7## was preliminarily polymerized at 80.degree. C. for 150 minutes in the present of 0.2 grs of benzoyl peroxide. To the resulting prepolymer was added prepolymer obtained by preliminarily polymerizing 900 grs of 2,2-bis(4-cyanatophenyl)propane 100 grs of bis(4-maleimidophenyl)ether at 160.degree. C. for 180 minutes. The resulting mixture was uniformly milled. Thereafter, 100 grs of Epikote 828 (Shell Chemical Co.), 0.3 grs of zinc octylate, 0.3 grs of triethylene diamine and 0.1 gr of 2-ethylimidazole were added to the mixture, and the mixture was uniformly milled. The mixture was coated on a metal surface and baked at 170.degree. C. for 120 minutes to obtain a good coating having surface gloss. The coating had a pencil hardness of 3H.

800 grs of monomer represented by the formula ##STR8## was preliminarily polymerized at 70.degree. C. for 45 minutes in the presence of 2,2'-azobis (isobutylonitrile). The prepolymer was dissolved in methyl ethyl ketone (Solution A). Prepolymer obtained by preliminarily reacting 50 grs of 2,2-bis(4-cyanatophenyl)propane and 150 grs of bis(4-maleimidophenyl)sulfone at 165.degree. C. for 45 minutes was mixed with solution A. The mixture was uniformly milled. 0.03 grs of zinc octylate and 0.02 grs of triethylene diamine were added to the mixture, and the mixture was uniformly milled. The mixture was coated on a metal surface and baked at 120.degree. C. for 100 minutes to obtain good coating having surface gloss. The coating had a pencil hardness of 2H.

Preliminary reaction was effected at 110.degree. C. under super pressure for 2 hours with stirring. The catalytic composite employed was 0.08 grs of zinc octylate and 0.07 grs of triethylene diamine. The resulting solution was coated on 25 mm.times.125 mm.times.0.4 mm test pieces composed of glass cloth. It was heated to form B stage product. Two test pieces were placed one on the other by facing the B staged surfaces so that their longitudinal ends overlapped by 10 mm. The B-staged product was cured at 120.degree. C. for 10 hours, and cured at 150.degree. C. for another 3 hours. Thickness of the overlapped portion was 1.57 mm and adhesive strength under shear thereof was 119 Kg/cm.sup.2.