| 摘要 |
Thermoplastic synthetic resins which will foam when heated are prepared by copolymerizing a mixture of (A) methacrylonitrile; (B) acrylic and/or methacrylic acid; and, if desired, (C) at least one further copolymerizable monomer; the proportions of A, B and C being from 20-60- by weight, from 10-60% by weight and not greater than 60% by weight respectively of the total weight of polymerizable monomer in A, B and C; and the said mixture containing (1) from 3 to 20 % by weight (based upon the total weight of polymerizable monomer in A, B and C) of urea or N,N1-dimethyl urea, and (2) highly dispersed silica and/or asbestos flour, whereby the said mixture prior to copolymerization is in the form of a substantially uniform paste (bulk polymerization process). The resin prepared by this process may be foamed in bulk or may be foamed after granulation by heating to a temperature above 180 DEG C. Component C may be methyl or butyl methacrylate or styrene. The copolymerization may be effected in the presence of free radical accelerators, e.g. azodiisobutyronitrile or benzoyl peroxide. |
