Polymethacrylimide foams having a reduced residual monomer content, and production method

A process for producing a poly(meth)acrylimide foam in block or sheet form, the process comprising copolymerizing (meth)acrylic acid and (meth)acrylonitrile with or without further copolymerisable monomers in three process steps of polymerisation;

• and
• tempering and foaming at three respectively higher process temperatures, wherein a polymerisation mixture contains three initiators, in which decomposition temperatures of the three initiators are such that the first initiator has a one hour half-life below 80° C., the second initiator has a one hour half-life between 80 and 110° C. and the third initiator has a one hour half-life above 110° C., and a product directly after foaming has a (meth)acrylonitrile content below 6000 ppm.