Patent Publication Number: US-4546168-A

Title: Thermosetting resin composition comprising (1) dicyanamide, (2) polyvalent imide and (3) polymerizable compound

Description:
This is a division of application Ser. No. 435,766, filed Oct. 20, 1982, now U.S. Pat. No. 4,482,703. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a thermosetting resin composition, a prepolymer thereof and a cured product thereof, said composition undergoing curing reaction by heating to proceed stage changes from A stage to B stage and then to C stage and particularly gives a cured product excellent in heat resistance and flexibility. 
     2. Description of the Prior Art 
     As resin molding materials having heat resistance of class H, addition polymerization type polyimides such as bismaleimide and the like are well known. This maleimide is often used in combination with a diamine or an epoxy resin. According to the specification of British Pat. No. 1,322,332, a heat-resistant polymer having isomelamine rings was provided by polymerizing a dicyanamide compound, in order to further improve the heat resistance. However, a defect of this polymer is that it is difficult to subject to molding using a usual mold or laminate molding because the polymerization reaction proceeds relatively rapidly. This is because the production of a prepolymer itself is difficult or because even if a prepolymer can be produced, no sufficient fluidity can be retained for the time required for molding because the curing reaction proceeds rapidly. 
     SUMMARY OF THE INVENTION 
     Objects of this invention are to provide a thermosetting resin composition giving a cured product having heat resistace of class C or more and excellent flexibility, a prepolymer thereof and a cured product thereof. 
     This invention provides a thermosetting resin composition comprising (A) at least one dicyanamide compound represented by the formula: 
     
         NCHN--Y--NHCN                                              (I) 
    
     wherein Y is a divalent organic group having an aromatic ring, and (B) at least one polyvalent imide having one or more unsaturated bonds. 
     In this invention, the reaction of the aforesaid dicyanamide compound with the aforesaid polyvalent imide yields a prepolymer and a final cured product which contain structural units having isomelamine rings and imide rings represented by the following formulas (II) and (III). That is to say, there are produced a prepolymer and a cured product having a repeating unit in which an isomelamine ring and an imide ring are directly combined and represented by the formula: ##STR1## wherein R 1  and R 2  are independently hydrogen, an alkyl group or a halogen atom, and a repeating unit in which an isomelamine ring formed by radical polymerization of a dicyanamide compound and a polyvalent imide is not directly combined with an imide ring and represented by the formula: ##STR2## wherein R 2  is hydrogen, an alkyl group or a halogen atom. 
     As the dicyanamide compound represented by the above general formula and used in this invention, there may be used alone or as a mixture thereof, for example, 4,4&#39;-dicyanamidodicyclohexylmethane, 1,4-dicyanamidocyclohexane, 2,6-dicyanamidopyridine, m-phenylene dicyanamide, p-phenylene dicyanamide, 4,4&#39;-dicyanamidodiphenylmethane, 2,2&#39;-bis(4-cyanamidophenyl)propane, 4,4&#39;-dicyanamidophenyloxide, 4,4&#39;-dicyanamidodiphenylsulfone, bis(4-cyanamidophenyl)phosphine oxide, bis(4-cyanamidophenyl)phenylphosphine oxide, bis(4-cyanamidophenyl)methylamine, 1,5-dicyanamidonaphthalene, m-xylylene dicyanamide, p-xylene dicyanamide, hexamethylene dicyanamide, 6,6&#39;-dicyanamido-2,2&#39;-dipyridyl, 4,4&#39;-dicyanamidobenzophenone, 4,4&#39;-dicyanamidoazobenzene, bis(4-cyanamidophenyl)phenylmethane, 1,1-bis(4-cyanamidophenyl)cyclohexane, 1,1-bis(4-cyanamido-3-methylphenyl)-1,3,4-oxadiazol, 4,4&#39;-dicyanamidodiphenylether, 4,4&#39;-bis(p-cyanamidophenyl)-2,2&#39;-dithiazol, m-bis(4-p-cyanamidophenyl-2-thiazolyl)benzene, 4,4&#39;-dicyanamidobenzanilide, 4,4&#39;-dicyanamidophenyl benzoate, 2,2&#39;-bis[4-(4-cyanamidophenoxy)phenyl]propane, 2,2&#39;-bis[3-methyl-4-(4-cyanamidophenoxy)phenyl]propane, 2,2-bis[3-ethyl-4-(4-cyanamidophenoxy)phenyl]propane, 2,2-bis[3-propyl-4-(4-cyanamidophenoxy)phenyl]propane, 2,2-bis[3-isopropyl-4-(4-cyanamidophenoxy)phenyl]propane, bis[4-(4-cyanamidophenoxy)phenyl]methane, and cyanamide-terminated sulfone ether oligomers represented by the following formula: ##STR3## wherein n is zero to 3. Dicyanamide compounds having an aromatic ring as Y in the above formula (I) are particularly preferred from the viewpoint of the heat resistance. 
     As the polyvalent imide having one or more unsaturated bonds, there may be used, for example, bisimides such as bismaleimides obtained by reacting an acid anhydride such as maleic anhydride, citraconic anhydride, itaconic anhydride, pyrocinchonic anhydride, dichloromaleic anhydride, or Diels-Alder adducts of any of the above-mentioned acid anhydride with a dicyclodiene, with a diamine, for example, N,N&#39;-methylene bismaleimide, N,N&#39;-ethylene bismaleimide, N,N&#39;-hexamethylene bismaleimide, N,N&#39;-trimethylene bismaleimide, N,N&#39;-m-phenylene bismaleimide, N,N&#39;-p-phenylene bismaleimide, N,N&#39;-4,4&#39;-diphenylmethane bismaleimide, N,N&#39;-4,4&#39;-diphenylether bismaleimide, N,N&#39;-methylenebis(3-chloro-p-phenylene)bismaleimide, N,N&#39;-4,4&#39;-diphenylsulfone bismaleimide, N,N&#39;-4,4&#39;-dicyclohexylmethane bismaleimide, N,N&#39;-α,α&#39;-4,4&#39;-dimethylenecyclohexane bismaleimide, N,N&#39;-m-xylene bismaleimide, N,N&#39;-4,4&#39;-diphenylcyclohexane bismaleimide and the like, and polyvalent maleimides obtained by reacting maleic anhydride with a condensate of aniline with formaldehyde and represented by the following formula: ##STR4## wherein m is zero to 3. 
     In this invention, the following monomaleimide compounds may be co-used. For example, there may be co-used at least one of monomaleimide compounds such as N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-butylmaleimide, N-allylmaleimide, N-vinylmaleimide, N-phenylmaleimide, N-3-chlorophenylmaleimide, N-o-tolylmaleimide, N-m-tolylmaleimide, N-p-tolylmaleimide, N-o-methoxyphenylmaleimide, N-m-methoxyphenylmaleimide, N-p-methoxyphenylmaleimide, N-benzylmaleimide, N-pyridylmaleimide, N-hydroxyphenylmaleimide, N-acetoxyphenylmaleimide, N-dichlorophenylmaleimide, N-benzophenone maleimide, N-diphenylethermaleimide, N-acetylphenylmaleimide, N-cyclohexylmaleimide and the like. 
     Further, the following polyvalent imide prepolymers may also be used. That is to say, there may be used prepolymers obtained by reacting any of the polyvalent imides described above with a diamine, an epoxy compound, a phenolic compound or triallyl isocyanurate. Here, as the epoxy compound, there is used at least one of, for example, bifunctional epoxy compounds such a diglycidyl ether of bisphenol A, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 4,4&#39;-(1,2-epoxyethyl)biphenyl, 4,4&#39;-di(1,2-epoxyethyl)diphenylether, resorcin diglycidyl ether, bis(2,3-epoxycyclopentyl)ether, N,N&#39;-m-phenylenebis(4,5-epoxy-1,2-cyclohexanedicarbodiimide and the like; tri- or higher functional epoxy compounds such as 1,3,5-tri(1,2-epoxyethyl)benzene, tetraglycidoxytetraphenylethane, polyglycidyl ether of phenol-formaldehyde novolak resin, and the like; epoxy compounds having a hydrantoin skeleton; and epoxy compounds containing one or more halogen atoms, such as brominated epoxy compounds and the like. As the phenolic compound, there may be used liquid or resinous condensates obtained by reacting at least one of phenol, cresol, m-cresol, p-cresol, 2,5-xylenol, 2,6-xylenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, o-phenylphenol, m-phenylphenol, p-phenylphenol, saligenin, bisphenol A and the like with formalin or parafolmaldehyde in the presence of an acidic or alkaline catalyst, diphenyl ether resins, xylene-modified phenolic resins, parahydroxypolystyrene resins, brominated parahydroxypolystyrene resins, bisphenol A-furfural resins, etc. There may be used besides them prepolymers obtained by directly reacting bisphenol A, resorcinol, catechol, hydroquinone, pyrogallol or the like with a polyvalent maleimide. 
     Even if the mixing proportion of the dicyanamide compound to the polyvalent imide is varied over a relatively wide range, a cured product good in heat resistance can be obtained. The flexibility of the resulting cured product tends to be lowered when the ratio between the dicyanamide compound and the polyvalent imide each other is extremely high. From the viewpoint of the solubility of the prepolymer of the dicyanamide compound and the polyvalent imide in solvents, it is preferable to increase the amount of the dicyanamide compound. In general, the amount of the polyvalent imide is suitably in the range from 10 to 1 mole per 1 to 10 moles of the dicyanamide compound. It is more preferable to use the polyvalent imide in the range from 3 to 7 moles per 7 to 3 moles of the dicyanamide compound. 
     The resin composition of this invention can react by heating to be cured as a solution or varnish in an organic solvent or in the absence of any solvent. The latter reaction is a so-called melt reaction. The reaction using a solvent can preferably be effected by heating at about 50°-150° C., followed by raising the temperature to about 150°-220° C. On the other hand, the melt reaction can be effected by heating at a relatively high temperature, namely, about 150°-220° C. When the prepolymer is obtained, heating is stopped at the time when the reactants are in B stage. In the case of the reaction in a solvent, heating is stopped before a solid (a cured product) deposits. In this invention, the cured product may directly be produced without once stopping the reaction at B stage. As the solvent, there may be used, for example, methyl ethyl ketone, methyl acetyl ketone, 2-methoxyethanol, 2-(methoxymethoxy)ethanol, 2-isoproxyethanol, 2-(ethoxyethoxy)ethanol, dioxane, dimethyldioxane, monopropylene glycol methyl ether, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. These solvents may be used alone or as a mixture thereof. Particularly preferable are methyl ethyl ketone, 2-methoxyethanol, N,N-dimethylformamide, N-methyl-2-pyrrolidone and dioxane. 
     In this invention, the curing properties and flexibility of the cured product can be improved by co-using a diamine. The diamine may be mixed directly with a system consisting of a dicyanamide compound and a polyvalent imide or used as a mixture prepared by mixing a dicyanamide compound with a product of the preliminary reaction of the diamine with a polyvalent imide or a polyvalent imide prepolymer. Here, the preliminary reaction is, in general, sufficiently be effected by heating at 50°-180° C. for about 10-120 minutes in a solvent or in the absence of any solvent. A ternary prepolymer may also be produced by adding a diamine in synthesizing a polyvalent imide prepolymer. As the diamine, there may be used at least one of 4,4&#39;-diaminodicyclohexylmethane, 1,4-diaminocyclohexane, 2,6-diaminopyridine, m-phenylenediamine, p-phenylenediamine, 4,4&#39;-diaminodiphenylmethane, 2,2&#39;-bis(4-aminophenyl)propane, benzidine, 4,4&#39;-diaminophenyloxide, 4,4&#39;-diaminophenylsulfone, bis(4-aminophenyl)methylphosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, bis(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, m-xylylenediamine, p-xylylenediamine, hexamethylenediamine, 6,6&#39;-diamino-2,2&#39;-dipyridyl, 4,4&#39;-diaminobenzophenone, 4,4&#39;-diaminoazobenzene, bis(4-aminophenyl)phenylmethane, 1,1-bis(4-aminophenyl)cyclohexane, 1,1-bis(4-amino-3-methylphenyl)cyclohexane, 2,5-bis(m-aminophenyl)-1,3,4-oxadiazole, 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, 2,5-bis(m-aminophenyl)thiazolo(4,5-d)-thiazole, 5,5-di(m-aminophenyl)-(2,2&#39;)bis(1,3,4-oxadiazolyl), 4,4&#39;-diaminodiphenyl ether, 4,4&#39;-bis(p-aminophenyl)-2,2&#39;-dithiazole, m-bis(4-p-aminophenyl-2-thiazolyl)benzene, 4,4&#39;-diaminobenzanilide, 4,4&#39;-diaminophenyl benzoate, N,N&#39;-bis(4-aminobenzyl)-p-phenylenediamine, 4,4&#39;-methylene-bis(2-dichloroaniline), benzoguanamine, methylguanamine and the like. The mixed amount of the diamine is, in general, suitably in the range from 1.0 to 30% by weight, preferably 3.0 to 20% by weight based on the weight of the composition. 
     In this invention, curing catalysts such as conventional curing catalysts for maleimides or curing catalysts for epoxy resins may also be used in order to accelerate the reaction. Concrete examples of the curing catalysts include imidazole series compounds such as tetramethylbutanediamine, benzyldimethylamine, 2,4,6-tris(dimethylaminophenol), tetramethylguanidine, guanidine, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2,4&#39;-dimethylimidazole and the like; azine derivatives, onium salts, trimellitates and nitrylethyl derivatives of the above-mentioned imidazole compounds; tetraphenylphosphonium tetraphenylborate; tetraphenylammonium tetraphenylborate; tetrabutylammonium tetraphenylborate; tetramethylammonium fluoride; etc. The using amount of these curing catalysts is generally suitably 0.1 to 5% by weight based on the weight of the composition. 
     The resin composition of this invention may contain one or more conventional inorganic fillers, fire retardants, flexibility-imparting agents, antioxidants, pigments, coupling reagents, mold-releasing agents, and the like. 
     At least one polymerizable compound selected from epoxy compounds, phenolic compounds and triallyl isocyanurate series compounds may additionally be used in combination with the resin composition of this invention described above in detail. Concrete examples of the polymerizable compound include the same compounds as described earlier. Its mixing proportion is suitably 2 to 50% by weight in usual. 
     The resin composition of this invention can be made useful as a varnish for impregnation, lamination, adhesion, coating films, films and prepregs by making it into a solution (varnish) in an organic solvent. On the other hand, in a form containing no solvent, said resin composition can be used as powder for molding. As the organic solvent, there may be used many solvents such as acetone, methyl ethyl ketone, methyl cellosolve, N-methyl-2-pyrrolidone, N,N&#39;-dimethylformamide, N,N-dimethylacetamide and the like. The resin composition can be retained at the B stage by a preliminary reaction. The B stage resin is a so-called prepolymer which is advantageous in that it has a further improved solubility in organic solvents and is readily soluble even in a low boiling solvent. 
    
    
     EXAMPLE 1 
     
         ______________________________________                                    
(A)    4,4&#39;-Dicyanamidodiphenyl-                                          
                         60 parts by weight                               
       methane           (0.24 mole)                                      
(B)    N,N&#39;--4,4&#39;-Diphenylmethane                                         
                         40 parts by weight                               
       bismaleimide      (0.11 mole)                                      
______________________________________                                    
 
    
     The above-mentioned two components were dissolved (solid content: 50% by weight) in methyl Cellosolve and reacted at 70° to 110° C. for about 40 minutes to obtain a prepolymer which was soluble in methyl ethyl ketone and methyl Cellosolve even at ordinary temperatures. The infrared absorption spectrum of the prepolymer was measured to show an absorption due to the isomelamine ring at 1620 cm -1  and an absorption due to the maleimide ring at 1780 cm -1 . 
     Next, 0.2 part by weight of 2-ethyl-4-methylimidazole was added to the prepolymer, and the methyl Cellosolve was removed at 120° C., after which the residue was allowed to react at 170° to 200° C. for 80 minutes to obtain an insoluble and infusible cured product. 
     EXAMPLE 2 
     
         ______________________________________                                    
(A)   4,4&#39; -Dicyanamidodiphenylether                                      
                           50 parts by weight                             
                           (0.2 mole)                                     
(B)   N,N&#39;--Diphenylether bismaleimide                                    
                           50 parts by weight                             
                           (0.14 mole)                                    
______________________________________                                    
 
    
     The above-mentioned two components were mixed at 140° C. and then reacted at 170° to 200° C. for 120 minutes to obtain an insoluble and infusible cured product directly. The infrared absorption spectrum of the cured product was measured to show an absorption due to the isomelamine ring at 1620 cm -1  and an absorption due to the maleimide ring at 1780 cm -1 . 
     EXAMPLE 3 
     
         ______________________________________                                    
(A)  2,2&#39;-Bis[4-(4-cyanamidophenoxy)-                                     
                            70 parts by weight                            
     phenyl]propane         (0.1 mole)                                    
(B)  N,N&#39;--Diphenylmethane bismaleimide                                   
                            30 parts by weight                            
                            (0.08 mole)                                   
______________________________________                                    
 
    
     The above-mentioned two components were dissolved (solid content: 50% by weight) in methyl Cellosolve and reacted at 80° to 110° C. for 30 minutes to obtain a prepolymer which was soluble in methyl ethyl ketone, methyl Cellosolve, dimethylformamide even at ordinary temperatures. 
     For the prepolymer, absorptions due to the isomelamine ring and the maleimide ring, respectively were confirmed by its infrared absorption spectrum, as in Example 1. 
     Next, 2 parts by weight of the azine derivative of 2-methyl-imidazole was added to the prepolymer, and the metnyl Cellosolve was removed at 120° C., after which the residue was allowed to react at 170° to 200° C. for 80 minutes to obtain an insoluble and infusible cured product. 
     EXAMPLE 4 
     
         ______________________________________                                    
(A)   2,2&#39; -Bis[4-(4-cyanamidophenoxy)-                                   
                           60 parts by weight                             
      phenyl]propane       (0.08 mole)                                    
(B)   Polyphenylmethylene polymale-                                       
                           40 parts by weight                             
      imide represented by the above                                      
                           (0.08 mole)                                    
      general formula (V) (in which                                       
      n has a value of 0.8)                                               
______________________________________                                    
 
    
     To the above-mentioned components (A) and (B) was added 0.2 part by weight of benzyldimethylamine, and the resulting mixture was mixed at 140° C. and then allowed to react at 170° to 200° C. for 80 minutes to obtain an insoluble and infusible cured product. For the cured product, absorptions due to the isomelamine ring and the maleimide ring respectively were confirmed by its IR spectrum. 
     EXAMPLE 5 
     
         ______________________________________                                    
(A)   4,4&#39; -Dicyanamidodiphenylmethane                                    
                           30 parts by weight                             
                           (0.084 mole)                                   
(B)   2,2-Bis[4-(4-maleimidophenoxy)-                                     
                           70 parts by weight                             
      phenyl]propane       (0.084 mole)                                   
______________________________________                                    
 
    
     The above-mentioned two components were dissolved (solid content: 50% by weight) in methyl ethyl ketone and reacted at 60° to 80° C. for about 40 minutes to obtain a prepolymer which was soluble in methyl ethyl ketone, methyl Cellosolve, dimethylformamide and the like even at ordinary temperatures. Next, 0.3 part by weight of 2-ethyl-4-methylimidazole was added to the prepolymer, and the methyl Cellosolve was removed at 90° C., after which the residue was allowed to react at 170° to 200° C. for 80 minutes to obtain an insoluble and infusible cured product having isomelamine rings and maleimide rings. 
     Subsequently, each of the prepolymers obtained in Examples 1, 3 and 5 was dissolved in a mixed solvent of methyl ethyl ketone and methyl Cellosolve (1:1) to prepare a varnish having a concentration of 50% by weight, and each of the resin compositions in Examples 2 and 4 was dissolved in a mixed solvent of methyl ethyl ketone and N,N&#39;-dimethylformamide (1:1) to prepare a varnish having a concentration of 50% by weight. 
     A glass cloth of 0.18 mm in thickness subjected to aminosilane treatment was impregnated with each of the varnishes prepared in the manner described above, and dried at 120° to 160° C. for 10 minutes to prepare a coated cloth having a resin content of about 40% by weight. Subsequently, eight plies of each of the thus prepared coated cloths were placed one on another and then laminated and attached to one another at a predetermined temperature to produce a laminated plate of about 1.6 mm in thickness. 
     As a comparative example, a conventional varnish having 50% by weight solids was prepared by dissolving aminobismaleimide prepolymer (m.p. 80°-90° C.) in N-methyl-2-pyrrolidone (b.p. 202° C.). Subsequently, coated cloths and a laminate were produced in the same manner as described above. As to the lamination conditions, the cure was conducted at a pressure of 80 Kg/cm 2  at 180° C. for 90 minutes and post-cure was then conducted at 220° C. for 180 minutes. 
     There are shown in Table 1 the results of measuring various characteristics of the respective resins collected from the thus prepared coated cloths and of the laminated plates. In Table 1, the initial weight loss temperature is a temperature at which weight loss began when each sample was heated in air at a heating rate of 4° C./min and its weight loss characteristics was measured. The weight loss at 500° C. is a weight loss percentage at the time when the temperature reached 500° C. The flexural strength is a retention of flexural strength at each temperature based on the flexural strength at 20° C., and the flexural strength after deterioration is a retention of flexural strength after heating and deterioration in air at 220° C. for a predetermined time, based on the initial value. The measurement temperature was room temperature (20° C.). 
     
                                           TABLE 1                                 
__________________________________________________________________________
                                   Conven-                                
Molding and post-cure conditions,                                         
                    Example        tional                                 
and characteristics 1  2  3  4  5  Example                                
__________________________________________________________________________
Molding conditions                                                        
          Temperature (°C.)                                        
                    170                                                   
                       170                                                
                          170                                             
                             170                                          
                                170                                       
                                   180                                    
          Time (min)                                                      
                    40 40 40 40 40 90                                     
Post-cure conditions                                                      
          Temperature (°C.)                                        
                    200                                                   
                       200                                                
                          200                                             
                             200                                          
                                200                                       
                                   220                                    
          Time (min)                                                      
                    40 100                                                
                          40 40 40 180                                    
Initial weight loss temperature (°C.)                              
                    482                                                   
                       485                                                
                          470                                             
                             465                                          
                                470                                       
                                   395                                    
Weight loss at 500° C. (%)                                         
                     6  5  8 10  7 23                                     
Glass transition temperature (°C.)                                 
                    280                                                   
                       285                                                
                          260                                             
                             255                                          
                                265                                       
                                   220                                    
Flexural strength                                                         
          100° C.                                                  
                    95 96 95 94 95 95                                     
(%)       150° C.                                                  
                    94 94 94 93 94 90                                     
          200° C.                                                  
                    92 92 90 90 91 82                                     
          250° C.                                                  
                    88 90 87 88 89 81                                     
Flexural strength                                                         
            500 hrs 100                                                   
                       100                                                
                          100                                             
                             100                                          
                                100                                       
                                   100                                    
after deterioration                                                       
          1,000 hrs 100                                                   
                       100                                                
                          98 100                                          
                                97 90                                     
(%)       1,500 hrs 97 98 97 98 95 80                                     
          2,000 hrs 89 90 90 91 87 70                                     
__________________________________________________________________________
 
    
     EXAMPLE 6 
     
         ______________________________________                                    
(A)   4,4&#39; -Dicyanamidodiphenylmethane                                    
                           50 parts by weight                             
                           (0.20 mole)                                    
(B)   N,N&#39;--4,4&#39;-Diphenylmethane                                          
                           42 parts by weight                             
      bismaleimide         (0.12 mole)                                    
______________________________________                                    
 
    
     To the above-mentioned components (A) and (B) was added 8 parts by weight (0.04 mole) of 4,4&#39;-diaminodiphenylmethane, and the resulting mixture was allowed to react at 90° C. to 150° C. for 10 minutes to obtain a prepolymer which was soluble in methyl ethyl ketone, methyl Cellosolve, N,N&#39;-dimethylformamide and the like. The infrared absorption spectrum of the prepolymer was measured to show an absorption due to the isomelamine ring at 1620 cm -1  and an absorption due to the maleimide ring at 1780 cm -1 . 
     Next, 0.2 parts by weight of 2-ethyl-4-methylimidazole was added to the prepolymer to prepare a resin composition. 
     EXAMPLE 7 
     A composition prepared by adding 60 parts by weight (0.24 mole) of 4,4&#39;-dicyanamidodiphenylphenylether to a prepolymer obtained by reacting 32 parts by weight (0.09 mole) of N,N&#39;-4,4&#39;-diphenylmethane bismaleimide with 8 parts by weight (0.04 mole) of 4,4&#39;-diaminodiphenylmethane at 100° to 140° C. for 30 minutes, was reacted at 170° to 200° C. for 80 minutes to obtain an insoluble and infusible cured product. The infrared absorption spectrum of the cured product was measured to show an absorption due to the isomelamine ring at 1620 cm -1  and an absorption due to the maleimide ring at 1780 cm -1 . 
     EXAMPLE 8 
     
         ______________________________________                                    
(A)   2,2&#39;-Bis[4-(4-cyanamido-                                            
                           60 parts by weight                             
      phenoxy)phenyl]propane                                              
                           (0.08 mole)                                    
(B)   N,N&#39;--Diphenylether bismaleimide                                    
                           30 parts by weight                             
                           (0.08 mole)                                    
______________________________________                                    
 
    
     To the above-mentioned components (A) and (B) was added 10 parts by weight (0.02 mole) of 2,2&#39;-bis[4-(4-aminophenoxy)phenyl]propane, and these were further dissolved (solid content: 50% by weight) in methyl Cellosolve and reacted at 60° to 100° C. for about 40 minutes to obtain a prepolymer having isomelamine rings and maleimide rings, as in Example 6. 
     Next, 0.5 parts by weight of the azine derivative of 2-methyl-imidazole was added to the prepolymer to prepare a resin composition. 
     EXAMPLE 9 
     
         ______________________________________                                    
(A)   4,4&#39;-Dicyanamidodiphenylmethane                                     
                           40 parts by weight                             
                           (0.16 mole)                                    
(B)   2,2-Bis[4-(4-maleimidophenoxy)-                                     
                           50 parts by weight                             
      phenyl]propane       (0.06 mole)                                    
______________________________________                                    
 
    
     To the above-mentioned components (A) and (B) was added 10 parts by weight (0.05 mole) of 4,4&#39;-diaminodiphenylmethane, and the resulting mixture was mixed at 140° C. and further allowed to react at 170° to 200° C. for 120 minutes to obtain an insoluble and infusible cured product. The infrared absorption spectrum of the cured product was measured to show, as in Example 7, an absorption due to the isomelamine ring and an absorption due to the maleimide ring. 
     EXAMPLE 10 
     
         ______________________________________                                    
(A)     2,2&#39;-Bis[4-(4-cyanamido-                                          
                        40 parts by weight                                
        phenoxy)phenyl]propane                                            
                        (0.06 mole)                                       
(B)     Polyphenylmethylenepolymaleimide represented                      
        by the above general formula (V) (in which n has                  
        a value of 0.8), 52 parts by weight (0.1 mole)                    
______________________________________                                    
 
    
     To the above-mentioned components (A) and (B) was added 8 parts by weight (0.04 mole) of 4,4&#39;-diaminodiphenylmethane, and the resulting mixture was mixed at 140° C. and then allowed to react at 170° to 200° C. for 120 minutes to obtain an insoluble and infusible cured product. 
     Next, each of the prepolymers obtained in Examples 6 to 8 was dissolved in a mixed solvent of methyl ethyl ketone and methyl Cellosolve (1:1) to prepare a varnish, and each of the resin compositions in Examples 9 and 10 was dissolved in a mixed solvent of methyl ethyl ketone and N,N-dimethylformamide (1:1) to prepare a varnish. The concentration of each of the thus obtained varnishes was 50% by weight. 
     By use of the aforesaid varnishes, laminated plates were produced in the same manner as described in Examples 1 to 5. 
     The characteristics of the thus obtained laminated plates were shown in Table 2. 
     
                       TABLE 2                                                     
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Molding and post-cure                                                     
                  Example                                                 
conditions, and characteristics                                           
                  6      7      8    9    10                              
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Molding    Temperature                                                    
                      180    170  180  170  170                           
conditions (°C.)                                                   
           Time (min) 90     40   90   60   60                            
Post-cure  Temperature                                                    
                      --     200  --   200  200                           
conditions (°C.)                                                   
           Time (min) --     40   --   60   60                            
Initial weight loss temperature                                           
                  450    455    445  440  445                             
(°C.)                                                              
Weight loss at 500° C. (%)                                         
                  13     10     15   14   15                              
Glass transition temperature                                              
                  260    255    250  245  255                             
(°C.)                                                              
Flexural strength                                                         
           100° C.                                                 
                      95     96   94   94   93                            
(%)        150° C.                                                 
                      92     92   91   90   91                            
           200° C.                                                 
                      88     90   87   87   88                            
           250° C.                                                 
                      86     87   85   83   84                            
Flexural strength                                                         
             500 hrs  100    100  100  100  100                           
after deterioration                                                       
           1,000 hrs  97     98   97   96   97                            
(%)        1,500 hrs  90     92   91   90   91                            
           2,000 hrs  80     83   83   81   82                            
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     EXAMPLE 11 
     With 16 parts by weight (0.05 mole) of N,N&#39;-4,4&#39;-diphenylmethane bismaleimide was reacted 4 parts by weight (0.02 mole) of 4,4&#39;-diaminodiphenylmethane at 100° to 140° C. for 30 minutes, after which 30 parts by weight of a phenol novolak type epoxy resin (DEN-438, a trade name, epoxy equivalent 176-178; manufactured by Dow Chemical Co., U.S.A) was further added, and the resulting mixture was allowed to react at 90° C. for 30 minutes. Next, the reaction mixture was cooled to room temperature, after which 50 parts by weight (0.20 mole) of 4,4&#39;-dicyanamidodiphenylether was added thereto to prepare a resin composition. 
     The procedure described above was carried out in 2-methoxyethanol. Next, the aforesaid composition was heated at 100° to 140° C. to be freed from the solvent and subjected to preliminary reaction at the same time, whereby a prepolymer was prepared. Thereafter, the prepolymer was further subjected to reaction at 170° to 200° C. for 60 minutes to obtain an insoluble and infusible cured product. 
     EXAMPLE 12 
     
         ______________________________________                                    
(A)   4,4&#39;-Dicyanamidodiphenylmethane                                     
                           40 parts by weight                             
                           (0.11 mole)                                    
(B)   2,2-Bis[4-(4-maleimidophenoxy)-                                     
                           35 parts by weight                             
      phenyl]propane       (0.04 mole)                                    
(C)   Phenol novolak resin (softening point: 75° C.,               
      the active hydrogen equivalent of phenol group:                     
      about 100), 25 parts by weight                                      
(D)   2-Methylimidazole    0.3 part by weight                             
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     The above-mentioned four components were subjected to solid blending, and then reacted at 170° to 200° C. for 120 minutes to obtain an insoluble and infusible cured product. 
     EXAMPLE 13 
     
         ______________________________________                                    
(A)   4,4&#39;-Dicyanamidodiphenylether                                       
                         40 parts by weight                               
                         (0.16 mole)                                      
(B)   N,N&#39;--Diphenylmethane                                               
                         40 parts by weight                               
      bismaleimide       (0.11 mole)                                      
(C)   Triallyl isocyanurate                                               
                         20 parts by weight                               
                         (0.08 mole)                                      
(D)   Dicumyl peroxide   0.6 part by weight                               
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     The above-mentioned four components were dissolved in N-methyl-2-pyrrolidone and mixed, after which the solvent was removed by drying at 100° to 150° C., and the residue was reacted at 170° to 200° C. for 80 minutes to obtain an insoluble and infusible cured product. 
     EXAMPLE 14 
     With 60 parts by weight of the resin composition in Example 11 were uniformly mixed 20 parts by weight of the phenol novolak resin described above, 20 parts by weight of triallyl isocyanurate, 0.2 part by weight of 2-methyl-4-methylimidazole and 0.3 part by weight of benzoyl peroxide, after which the resulting mixture was reacted at 170° to 200° C. for 60 minutes to obtain an insoluble and infusible cured product. 
     The characteristics of the obtained cured product are shown in Table 3. 
     
                       TABLE 3                                                     
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           Example                                                        
           11     12       13       14                                    
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Cure   Temper-   170-200  170-200                                         
                                 170-200                                  
                                        170-200                           
conditions                                                                
       ature (°C.)                                                 
       Time (min)                                                         
                 60       120    80     60                                
Initial weight loss                                                       
             425      430      420    415                                 
temperature (°C.)                                                  
Weight loss at                                                            
             18        16      18     20                                  
500° C. (%)                                                        
Glass transition                                                          
             235      230      260    235                                 
temperature (°C.)                                                  
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