| 摘要 |
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 to 260 .degree.C; and then heat treating the sheet in two steps, at a first step of 2-6 hours at 100-130 .degree.C and a second step of 32-64 hours at 180-220 .degree.C.
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