| abstract |
Polymethacrylimide foams are prepared by a method, comprising: preparing a mixture consisting of (a) a monomer mixture of 40-60 wt. % methacrylonitrile, 60-40 wt. % methacrylic acid, and, optionally, up to 20 wt. %, based on the sum of methacrylic acid and methacrylonitrile, of other monofunctional, vinyl-unsaturated monomers, (b) 0.5-8 wt. % of a propellant mixture of formamide or monomethyl formamide and a univalent C3-8-aliphatic alcohol, (c) a cross-linking agent system, which consists of (c.1) 0.005-5 wt. % of a vinyl-unsaturated compound which can be radically polymerized, with at least two double bonds in the molecule, and (c.2) 1-5 wt. % magnesium oxide, dissolved in the monomer mixture, and at least one radical initiators and optionally at least one additive, shaped in the form of a sheet; polymerizing the monomers in the sheet; subsequently foaming the polymerizate sheet at temperatures from 200-260 DEG C.; and then heat treating the sheet in two steps, at a first step of 2-6 hours at 100-130 DEG C. and a second step of 32-64 hours at 180-220 DEG C. |