IMIDE TYPE PREPOLYMER COMPOSITIONS AND PROCESSES FOR PREPARING SAME

Abstract: Compositions containing an unsaturated bisimide component (A) and a diamine component (B) at the (A)/(B) molar ratio of 0.9-1.5 and (C) 0.01-4.0% by weight, based on the sum of (A) and (B), of at least one compound selected from radical polymerization inhibitors, carboxylic acids and acid anhydrides provide, upon heating, imide type prepolymer compositions which can be cured to provide products which are tough and have excellent adhesive strength to glass cloths and metals and heat resistance.

Description: This invention relates to imide type prepolymer compositions from which tough cured products are obtained, said cured products having excellent adhesive strength to glass cloths and metals, flexibility and heat resistance, and to processes for preparing said prepolymer compositions. US-A-3878172 describes the preparation of curable prepolymers intended for use as solutions or in the fused state by reacting a bisimide with a diamine in the presence of an inhibitor of free radicals. The inhibitors mentioned are hydroquinone, picric acid and N,N-diphenyl-N′-picrylhydrazine. JP-B-7875/1973 discloses that imide type prepolymers can be prepared by reacting a bisimide with a diamine in a solution state using a high boiling solvent such as N-methylpyrrolidone, or heating the reactants to yield a molten mixture which is allowed to undergo reaction. When the imide type prepolymers thus obtained are cured by heating, cured products having excellent heat resistance are obtained. However, the cured products obtained are not always satisfactory in respect of tensile strength, tensile elongation and Izod impact strength. The present invention seeks to provide imide type prepolymer compositions and processes for preparing the same, which imide type prepolymer compositions are capable of providing heat-cured products which are tough, have excellent adhesive strength to glass cloths or metals such as copper and good heat resistance. The invention accordingly provides a curable composition characterised by containing (A) an unsaturated bisimide of general formula (I) wherein D represents a divalent group containing a carbon-carbon double bond, and A represents a divalent group containing at least 2 carbon atoms; (B) a diamine of formula H₂N-B-NH₂ wherein B represents a divalent group containing less than 30 carbon atoms, the molar ratio (A)/(B) being 0.9/1 to 1.5/1; (C) 0.01-5.0% by weight, based on the total weight of (A) and (B), of at least one radical polymerization inhibitor selected from 2,5-di-t-butylhydroquinone, and t-butylhydroquinone; and optionally (D) at least one compound selected from carboxylic acids and acid anhydrides, the total amount of (C) and (D) not exceeding 5% by weight based on the total weight of (A) and (B). The invention also provides a process for preparing an imide type prepolymer composition of the present invention which comprises heating the curable composition of the invention to initiate a prepolymerization reaction. The unsaturated bisimide (A) represented by formula (I), which is used as one of the components of the imide type prepolymer composition of the present invention, includes such compounds, for example, as; N,N′-ethylenebismaleimide, N,N′-hexamethylenebismaleimide, N,N′-m-phenylenebismaleimide, N,N′-p-phenylenebismaleimide, N,N′-4,4′-diphenylmethanebismaleimide, N,N′-4,4′-diphenyl ether bismaleimide, N,N′-3,4′-diphenyl ether bismaleimide, N,N′-4,4′-diphenylsulfonebismaleimide, N,N′-m-xylenebismaleimide, N,N′-4,4′-cyclohexanebismaleimide and N,N′-4,4′-diphenylmethanebiscitraconimide. The diamine (B) mentioned above, which is used as another component of the imide type prepolymer composition of the present invention, includes such compounds, for example, as; 4,4′-diaminodicyclohexylmethane,1,4′-diaminocyclohexane, m-phenylene diamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ehter, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfide, m-xylenediamine, p-xylenediamine, 1,3-bis(p-aminocumyl) benzene, 1,4-bis-(p-aminocumyl) benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2′-bis[4-(4-aminophenoxy)phenyl]propane and hexamethylenediamine. The radical polymerization inhibitor (C) used in the curable composition of the present invention is 2,5-di-t-butylhydroquinone or t-butylhydroquinone. These radical polymerization inhibitors are used to improve brittleness and adhesive properties to glass cloths or the like of cured products obtained by heating imide type prepolymers. By incorporating these radical polymerization inhibitors in the above-mentioned range into imide type prepolymer compositions, tensile strength, tensile elongation or Izod impact strength of cured products obtained therefrom is improved. The carboxylic acid (D) which may be used in the compositions of the present invention includes such compounds as enumerated below. Aromatic monocarboxylic acids such as benzoic acid, o-toluic acid and its isomers, o-tert-butylbenzoic acid and its isomers, o-nitrobenzoic acid and its isomers, o-dichlorobenzoic acid and its isomers, o-bromobenzoic acid and its isomers, o-nitobenzoic acid and its isomers, o-hydroxybenzoic acid and its isomers, o-methoxybenzoic acid and its isomers, o-aminobenzoic acid and its isomers. Aromatic dicarboxylic acids such as phthalic acid and its isomers. Aromatic tricarboxylic acids such as trimellitic acid, and aromatic tetracarboxylic acids such as pyromellitic acid and benzophenonecarboxylic acid. Aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, phenylacetic acid, gluconic acid, lactic acid and tartaric acid. Aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, maleic acid and fumaric acid. The acid anhydride (D) which may be used in the compsitions of the present invention includes such compounds as listed below. Acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, tetrahydroxyphthalic anhydride, tetrahydroxymethyl phthalic anhydride, nadic anhydride, trimellitic acid anhydride, pyromellitic acid anhydride, and 3,3′, -4,4′-benzophenonetetracarboxylic acid anhydride. In order to prepare the imide type prepolymers of the present invention, the aforementioned starting materials must be heated to undergo reaction. This reaction is carried out usually by heating for several minutes to several hours at a suitable temperature of from 100° up to 200°C. In carrying out this reaction, the aforementioned component (B) is first fused by heating, and then the afrementioned component (A) is added thereto and the two components in a molten state is heated undergo reaction, whereupon the reaction proceeds smoothly. Since the imide type prepolymers of the present invention dissolve in inert polar solvents such as dimethylformamide, N-methylpyrrolidone and dimethylacetamide, when the aforementioned starting materials are heated to undergo reaction in these solvents, the reaction proceeds smoothly and imide type prepolymers having excellent characteristics are obtained. The imide type prepolymers obtained in the manner as mentioned above dissolve in polar solvents such as dimethylformamide, N-methylpyrrolidone and dimethylacetamide, and hence a solution of imide type prepolymer in said solvent is particularly useful as a laminating varnish for preparing laminate sheets. The thus prepared prepolymers may be used in the form of a solvent solution as aforesaid, or may be used in the form of a powder. The thus obtained imide type prepolymers may be cured directly by heating them at a temperature of 180-250°C, if desired, under pressure for 10 minutes to 2 hours. In order that a cured product of this imide type prepolymer exhibits its inherent physical properties, the cured product must be subjected to postcuring treatment for 4-48 hours at a temperature of 180-250°C. The imide type prepolymer of the present invention may be mixed, if necessary, with lubricants or mold release agents as enumerated below. Fatty acid esters such as carnauba wax, beeswax, rice wax, stearic esters and butyl esters, fatty acid amides such as ethylenebisstearoamide, fatty acids such as montanic acid and stearic acid, and metal salts thereof, petroleum wax, polyethylene wax, polypropylene wax and oxidates thereof, and silicone oil such as polymethylsiloxane and polymethylphenylsiloxane. The amount of these lubricants or mold release agents is preferably 0.1-5.0% by weight based on the sum (total amount) of the unsaturated bisimide and diamine. The imide type prepolymer of the present invention may also be mixed, if necessary, with rubber components such as amine-terminated butadiene nitrile rubber (ATBN), polytetrafluoroethylene, silicone resins, phenol resins or aniline resins. The amount of these additives is preferably 10-200% by weight based on the sum (total amount) of the unsaturated bisimide and diamine. Further, the imide type prepolymers of the present invention may be mixed, if necessary, with the following inorganic or organic substances as filler components. Silica powder, alumina powder, glass powder, mica, talc, barium sulfate, titanium oxide, molybdenum disulfide, aluminum powder, iron powder, copper powder, metallic hydroxides such as aluminum hydroxide and magnesium hydroxide, microfine hollow bodies of silica, alumina, glass or phenol resins, and reinforcing fibers such as glass fiber, alumina fiber, carbon fiber, Aramide fiber, silicon carbide fiber, aluminum fiber and copper fiber. The amount of these filler components is preferably 50-500% by weight based on the sum (total amount) of the unsaturated bisimide and diamine. The imide type prepolymers of the present invention have such a feature that when they are dissolved in inert polar solvents such as dimethylformamide, N-methylpyrrolidone and dimethylacetamide, the portion thereof which remains undissolved is very small in comparison with that of imide type prepolymers prepared by conventional processes. On that account, in preparing the prepolymers of the present invention, it becomes possible to adopt such a process wherein the starting materials dissolved in these solvents are heated to undergo reaction. Further, even resins having high softening points can easily processed to varnish. By utilization of such properties of the present prepolymers as mentioned above, it is possible to provide cured products high in flexibility as well as of excellent heat resistance. The cured products thus obtained can be used for various purposes such as anti-friction materials, bearings, gearings, laminate sheets, adhesives and insulating varnishes. The cured products obtained by heat curing the imide type prepolymers of the present invention have good tensile stength, tensile elongation and Izod impact strength as compared with cured products obtained by heat curing prepolymers obtained by conventional processes. Furthermore, when the imide type prepolymers of the present invention are used as adhesives for laminate sheets, there is observed such an effect that T-peel peeling strength of copper foils or T-peel peeling strength between laminates becomes high. The present invention is illustrated below with reference to Examples and Comparative Examples. Example 1 Into a separable flask were charged 35.6 g of 4,4′-diaminodiphenylmethane, 1.0 g of t-butylhydroquinone and 0.5 g of p-hydroxybenzoic acid, and the flask was immersed in an oil bath kept at 150°C. At the time when the 4,4′-diaminodiphenylmethane dissolved to form a homogeneous solution, to the resulting solution was added with strring in 2 minutes 64.4 g of N,N′-4,4′-diphenylmethanebismaleimide. The resulting mixture was allowed to undergo reaction with stirring for 15 minutes, and then drawn from the flask into a vat. This vat was placed into an air oven kept at 160°C, aged therein for 45 minutes and then pulverized to obtain an imide type prepolymer. It was found that the imide type prepolymer thus obtained dissolves in its entity in dimethylformamide. This prepolymer was molded according to compression molding into a flat plate of 2 mm in thickness and a square bar having a sectional area of 12.7 mm × 12.7 mm under the conditions of 200°C, 30 minutes and 150 kgf/cm², and the moldings obtained were then subjected to postcuring treatment at 200°C for 24 hours to obtain molded articles. Physical properties of the molded articles thus obtained are shown in Table 1. Comparative Example 1 Molded articles of imide type prepolymer similar to those of Example 1 were obtained by repeating Example 1 except that the t-butylhydroquinone was not used. Physical properties of the molded articles thus obtained shown in Table 1. Comparative Example 2 Molded articles of imide type prepolymer similar to those of Example 1 were obtained by repeating Example 1 except that in place of 1.0 g of the t-butylhydroquinone and 0.5 g of the p-hydroxybenzoic acid, there was used 0.5 g of benzoic acid. Physical properties of the molded articles thus obtained are shown in Table 1. Comparative Example 3 Molded articles similar to those of Example 1 were obtained according to compression molding under the same conditions as in Example 1 using only a commercially available polyimide resin (a product of Nippon Polyimide K.K. sold under a trade name of Chelimide 1000). Physical properties of the molded articles thus obtained are shown in Table 1. Example 2 Into a separable flask was charged 33.4 g of 4,4′-diaminodiphenylmethane, and the flask was immersed in an oil bath kept at 150°C. After the 4,4′-diaminodiphenylmethane dissolved, 0.5 g of 3,3′, 4,4′-benzophenonetetracarboxylic acid dianhydride was dissolved in the solution, and the mixed solution was allowed to undergo reaction. Subsequently, in this solution was dissolved with stirring 1.0 g of t-butylhydroquinone and thereto was added in 2 minutes 66.6 g of N,N′-4,4′-diphenylmethanebismaleimide. This mixture was allowed to undergo reaction with stirring for 20 minutes, and the reaction mixture was then drawn from the flask into a vat. Then, this vat was placed in an oven kept at 160°C, and the reaction product was aged for 60 minutes and then pulverized to obtain an imide type prepolymer. From the prepolymer thus obtained, molded articles similar to those of Example 1 were obtained according to compression molding under the same conditions as in Example 1. Physical properties of the molded articles thus obtained are shown in Table 1 Comparative Example 4 Into a separable flask was charged 35.6 g of 4,4′-diaminodiphenylmethane, and the flask was immersed in an oil bath kept at 150°C. After the 4,4′-diaminodiphenylmethane dissolved, 1 g of 3,3′, 4,4′-benzophenonetetracarboxylic acid dianhydride was dissolved with stirring in this solution. To the resulting solution was added with stirring 64.4 g ot N,N′-4,4′-diphenylmethanebismaleimide for 2 minutes. The resulting mixture was allowed to undergo reaction with stirring for 15 minutes, and the reaction product was drawn from the flask into a vat. Following the same procedure as in Example 1, there were obtained molded articles of imide type prepolymer similar to those of Example 1. Physical properties of the molded articles thus obtained are shown in Table 1. Comparative Example 5 Molded articles of imide type prepolymer were obtained by repeating Example 1 except that in place of 1.0 g of the t-butylhydroquinone and 0.5 g of p-hydroxybenzoic acid, there was used 0.5 g of hydroquinone, and the compression molding time was changed to 20 minutes. Physical properties of the molded articles thus obtained are shown in Table 1. Comparative Example 6 Molded articles of imide type prepolymer similar to those of Example 1 were obtained by repeating Example 1 except that the t-butylhydroquinone and p-hydroxybenzoic acid were not used, and the compression molding time was changed to 20 minutes. Physical properties of the molded articles thus obtained are shown in Table 1. Example 3 Molded articles of imide type prepolymer similar to those of Example 1 were obtained by repeating Example 1 except that in place of 1.0 g of the t-butylhydroquinone and 0.5 g of the p-hydroxybenzoic acid, there was used 0.25 g of 2,5-di-t-butylhydroquinone, the ageing time was changed to 50 minutues, and the compression molding time was changed to 20 minutes. Physical properties of the molded articles thus obtained are shown in Table 1. comparative Example 7 Molded articles of imide type prepolymer similar to those of Example 1 were obtained by repeating Example 1 except that in place of 1.0 g of the t-butylhydroquinone and 0.5 g of the p-hydroxybenzoic acid, there was used 0.5 g of 1,1-diphenyl-2-picrylhydrazyl, and the compression molding time was changed to 20 minutes. Physical properties of the molded articles thus obtained are shown in Table 1. Example 4 A separable flask charged with 150 g of dimethylformamide, 50.2 g of 4,4′-diaminodiphenylmethane and 0.75 g of 3,3′, 4,4′-benzophenonetetracarboxylic acid was immersed in an oil bath. At the time when the temperature of the liquid in the flask reached 100°C, 1.5 g of t-butylhydroquinone and 99.8 g of N,N′-4,4′-diphenylmethanebismaleimide were added to the contents of the flask, and the mixture was maintained at 100°C with stirring and allowed to undergo reaction for 3 hours. A glass cloth was impregnated with the thus obtained varnish, and the impregnated glass cloth was dried at 160°C for 5 minutes to prepare a prepreg. Nine sheets of this prepreg were laminated together to form a laminate, a copper foil of 28 g (one ounce) was placed on both the top and bottom of the laminate, the resulting laminate was compression molded at 180°C for 60 minutes and then subjected to postcuring treatment at 200°C for 24 hours, whereby a copper-clad laminate sheet was prepared. The laminate sheet thus obtained was measured for T-peel peeling strength of the copper foils and that of the lamination layers. The results of measurement are shown in Table 2. Comparative Example 8 Using a commercially available polyimide resin (a product of Nippon Polyimide K.K. sold under a trade name of Chelimide 601), prepregs were prepared and therefrom a copper-clad laminate sheet was prepared under the same conditions as in Example 4. Physical properties of the thus prepared copper-clad laminate sheet were measured. The results obtained are shown in Table 2. Comparative Example 9 To a separable flask charged with 150 g of dimethylformamide were added 53.4 g of 4,4′-diaminodiphenylmethane, 96.6 g of N,N′-4,4′-diphenylmethanebismaleimide and 0.75 g of p-hydroxybenzoic acid. The mixture in the flask was stirred and the temperature of the liquid was maintained at 100°C to undergo reaction for 3 hours. A copper-clad laminate sheet was prepared as described in Example 4. The laminate sheet thus obtained was measured for T-peel peeling strength of the copper foils and that of the lamination layers The results of measurement are shown in Table 2. Comparative Example 10 Using commercially available polyimide resin (a product of Nippon Polyimide K.K. sold under a trade name of Chelimide 601), prepregs were prepared and therefrom a copper-clad laminate sheet was prepared under the same conditions as in Comparative Example 9. Physical properties of the copper-clad laminate sheet thus obtained were measured. The result obtained are shown in Table 2. Comparative Example 11 A copper-clad laminate sheet was prepared by repeating Comparative Example 9 except that in place of 0.75 g of the p-hydroxybenzoic acid, there was used 0.75 g of hydroquinone, and the compression molding time was changed to 30 minutes. The copper-clad laminate sheet thus obtained was measured for T-peel peeling strength of the copper foils and that of the lamination layers. The results of measurement obtained are shown in Table 2. Comparative Example 12 A copper-clad laminate sheet was prepared by repeating Comparative Example 9 except that in place of the varnish used therein, there was used a commercially available polyimide resin (a product of Nippon Polymide K.K. sold under a trade name of Chelimide 601). The copper-clad laminate sheet thus obtained was measured for T-peel peeling strength of the copper foils and that of the lamination layers. The results of measurement obtained are shown in Table 2.

Claims: 1. A curable composition containing (A) an unsaturated bisimide of general formula (I) wherein D represents a divalent group containing a carbon-carbon double bond, and A represents a divalent group containing at least 2 carbon atoms; (B) a diamine of formula H₂N-B-NH₂ wherein B represents a divalent group containing less than 30 carbon atoms, the molar ratio (A)/(B) being 0.9/1 to 1.5/1; (C) 0.01-5.0% by weight, based on the total weight of (A) and (B), of at least one radical polymerization inhibitor characterised in that said inhibitor is selected from 2,5-di-t-butylhydroquinone and t-butylhydroquinone; and optionally (D) at least one compound selected from carboxylic acids and acid anhydrides, the total amount of (C) and (D) not exceeding 5% by weight based on the total weight of (A) and (B). 2. A composition according to claim 1 wherein (A) is N,N′-ethylenebismaleimide, N,N′-hexamethylenebismaleimide, N,N′-m-phenylenebismaleimide, N,N′-p-phenylenebismaleimide, N,N′-4,4′-diphenylmethanebismaleimide, N,N′-4,4′-diphenyl ether bismaleimide, N,N′-3,4′-diphenyl ether bismaleimide, N,N′-diphenylsulfonebismaleimide, N,N′-m-xylenebismaleimide, N,N′-4,4′cyclohexanebismaleimide or N,N′-4,4′-diphenylmethanebiscitraconimide. 3. A composition according to claim 1 or 2 wherein (B) is 4,4′-diaminodicyclohexymethane, 1,4′-diaminocyclohexane, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, 4,4′diaminodiphenylsulfide, m-xylenediamine, p-xylenediamine, 1,3-bis(p-aminocumyl) benzene, 1,4-bis(p-aminocumyl) benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis (4-aminophenoxy)benzene, 2,2-bis [4-(4-aminophenoxy) phenyl] propane or hexamethylenediamine. 4. A composition according to claim 1, 2 or 3 wherein (D) is a carboxylic acid selected from benzoic acid, o-toluic acid or its isomer, o-tert-butylbenzoic acid or its isomer, o-chlorobenzoic acid or its isomer, o-hydrozybenzoic acid or its isomer, o-methoxybenzoic acid or its isomer, o-aminobenzoic acid or its isomer, phthalic acid or its isomer, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, formic acid, acetic acid, propionic acid, phenylacetic acid, gluconic acid, lactic acid, tartaric acid, malonic acid, succinic acid, glutaric acid, maleic acid and fumaric acid. 5. A composition according to claim 1, 2 or 3 wherein (D) is an acid anhydride selected from acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, tetrahydroxyphthalic anhydride, tetrahydroxymethylphthalic anhydride, nadic anhydride, trimellitic acid anhydride, pyromellitic acid dianhydride and 3,3′, 4,4′-benzophenonetracarboxylic acid dianhydride. 6. A process for preparing an imide type prepolymer composition which comprises heating a composition as claimed in any one of the preceding claims to initiate a prepolymerization reaction. 7. A process according to claim 6 wherein component (B) is fused by heating, component (A) is then added thereto, and a mixture of (A), (B) and (C) is heated at 100 to 200°C. 8. A process according to claim 7 wherein the mixture is heated in an inert polar solvent. 9. A process according to claim 8 wherein the inert polar solvent is dimethylformamide, N-methylpyrrolidone or dimethylacetamide. 10. A process according to any one of claims 6 to 9 which comprises the additional step of curing the imide-type prepolymer by heating at 180 to 250°C, and optionally post-curing the resulting cured product.

Inventors: AOKI, HIDEYA, KAN, KOJIRO, TOMOSHIGE, TORU
Applicants: MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1988
Main classification: C08G73
IPC codes: H05K3, C08G73, H05K1