Patent ID: 8722751

Claim:
A process for producing a foamable crosslinked polymer, comprising: polymerizing a mixture comprising (A) 30-70 parts by weight of methacrylic acid, 30-60 parts by weight of methacrylonitrile, 0-30 parts by weight of other monomers having vinyl unsaturation, (B) 0.01-4.99 parts by weight of tert-butyl methacrylate, (C) 0.01-10 parts by weight of a blowing agent, (D) 0.01-10 parts by weight of a crosslinking agent, (E) 0.01 to 2 parts by weight of a polymerization initiator, and (F) 0 to 20 parts by weight of a conventional additive, in bulk to give a polymer in the form of a sheet; wherein said sheet is optionally subjected to the following treatment: heat-conditioning and then foaming at temperatures of from 150 to 250° C.; foaming to obtain a foam having extremely fine and uniform pore structure having a pore size of 10-35 μm.