Thermosetting prepolymer from polyfunctional maleimide and bis maleimide

A process for preparing a thermosetting maleimide prepolymer, which comprises reacting (A) a polyfunctional maleimide compound obtained by the dehydration reaction of an amide acid formed from maleic anhydride and a polyamine prepared by the condensation of aniline with formaldehyde and represented by the formula (1) ##STR7## wherein n is in the range of from 0.1 to 3.0, (B) at least one bis-maleimide selected from the group consisting of N,N'-m-phenylene-bis-maleimide, N,N'-p-phenylene-bis-maleimide, N,N'-4,4'-diphenylmethane-bis-maleimide, N,N'-4,4'-diphenyl-ether-bis-maleimide, N,N'-methylene-bis(3-chloro-p-phenylene)-bis-maleimide, N,N'-4,4'-diphenylsulfone-bis-maleimide, N,N'-m-xylene-bis-maleimide and N,N'-4,4'-diphenylcyclohexane-bis-maleimide, (C) at least one diamine selected from the group consisting of m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 2,2'-bis(4-aminophenyl)propane, benzidine, 4,4'-diaminodiphenylsulfone, bis(4-aminophenyl)methylphosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, bis(4-aminophenyl)methylamine, 1,5-diaminonaphthalene, m-xylylenediamine, p-xylylenediamine, 4,4'-diaminobenzophenone, 4,4'-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'-bis(1,3,4-oxadiazolyl), 4,4'-diaminodiphenyl ether, 4,4'-bis(p-aminophenyl)-2,2'-dithiazole, m-bis(4-p-aminophenyl-2-thiazolyl)benzene, 4,4'-diaminobenzanilide, 4,4'-diaminophenyl benzoate, N,N'-bis(4-aminobenzyl)-p-phenylenediamine and 4,4'-methylenebis(2-chloroaniline), wherein the weight proportion of said polyfunctional maleimide compound (A) relative to the total of said polyfunctional maleimide compound (A) and said at least one bis-maleimide (B) is 3 to 80%, and the molar ratio of the total of said polyfunctional maleimide compound (A) and said at least one bis-maleimide (B) relative to said at least one diamine (C) is 1:2 to 1:0.1, said process further comprising a reaction with (D) at least one 1,2-epoxy compound which, when polymeric, has a weight average molecular weight of up to 5,000, and the process comprising the reaction between (A), (B), (C) and (D) being performed in one or more stages, provided that in any stage involving a reaction in which said at least one 1,2-epoxy compound (D) participates, the reaction is effected at a temperature of 50.degree. to 145.degree. C. for a period of time of 5 to 240 minutes and that in any stage involving a reaction in which said at least one 1,2-epoxy compound (D) does not participate, the reaction is effected at a temperature of 70.degree. to 180.degree. C. for a period of time of 5 to 240 minutes, and wherein the weight proportion of said at least one 1,2-epoxy compound (D) relative to the total of said polyfunctional maleimide compound (A), said at least one bis-maleimide (B), said at least one diamine (C) and said at least one 1,2-epoxy compound (D) is 5 to 80%.