Patent ID: 7169339

Claim:
A method for production of polymethylacrylimide foamed materials in the form of blocks or plates, comprising: copolymerizing methacrylic acid and methacrylonitrile and optionally a copolymerizable monomer and additive in the presence of a radical-forming initiator, thereby obtaining a copolymer; postpolymerizing and cyclizing said copolymer to said polymethylacrylimide, and transforming said polymethylacrylimide to a foamed material, in a two-stage process step, wherein a first stage of said two-stage process step comprises preheating of the polymethylacrylimide to be foamed in a first hot-air oven or hot air oven section at a heating rate used to raise the temperature of between 0.001 K/min and 10 K/min, while foaming of the preheated polymethylacrylimide takes place in a second stage of said two-stage process, in a second hot-air oven or hot-air ovens or hot air oven section.