Patent ID: 8501870

Claim:
A process for manufacturing a thermosetting resin composition comprising a polyphenylene ether-modified butadiene prepolymer that includes a polyphenylene ether (A) and a butadiene polymer, wherein: the butadiene polymer has a crosslinking structure; the process has a step (1) in which a butadiene polymer (B) crosslinks with a crosslinking agent (C) (excluding the butadiene polymer (B)) in the presence of the polyphenylene ether (A) in a medium to obtain the polyphenylene ether-modified butadiene prepolymer; the number average molecular weight of the polyphenylene ether (A) is in a range of 7,000 to 30,000; the butadiene polymer (B) molecule contains 40% or more of a 1,2-butadiene unit having a 1,2-vinyl group in a side chain; the butadiene polymer (B) is not a modified polybutadiene in which the 1,2-vinyl group in the side chain, or one or both of the terminals in the molecule is/are chemically modified by converting into epoxy, glycol, phenol, maleic acid, (meth)acryl, or urethane; and the crosslinking agent (C) is at least one maleimide compound including 2,2-bis (4-(4-maleimidophenoxy)phenyl)propane, or the crosslinking agent (C) is at least one maleimide compound including bis(3-ethyl-5-methyl-4-maleimidophenyl)methane, and with the proviso that the polyphenylene ether (A) which is a modified phenol product so preferred by redistribution reaction of a polyphenylene ether resin having a number average molecular weight of 10,000-30,000 with a phenolic compound in the presence of a reaction initiator that the number average molecular weight of the product becomes 5 to 70% of that of the used polyphenylene ether resin is excluded.