Process for preparing isocyanic acid - methyl methacrylate copolymers

A process for preparing a copolymer of isocyanic acid and methyl methacrylate comprises irradiating a homogeneous mixture thereof dissolved in a solvent, e.g. tetrahydrofuran, with gamma-rays at 0 to -780C in the presence or absence of zinc chloride as a catalyst. In one example, a homogeneous mixture of isocyanic acid (4.0 ml), methyl methacrylate (2.0 ml) and tetrahydrofuran (2.0 ml) is sealed into a glass ampoule, which is then irradiated with Co-60 gamma rays at the dose rate of 1 x 105r/hr for 16 hr at -210C. Treatment of the content with methanol gives a crude copolymer (A) in 91% yield. (A) can be fractionated into an acetone-soluble fraction (B) and an acetone-insoluble fraction (C). (B) is soluble in many polar solvents, while (C) is soluble only in sulfuric acid. (B): yield from (A) 40% by wt., molar composition (isocyanic acid/methyl methacrylate) 1/3.1, reduced viscosity (0.1% solution in trifluoroacetic acid at 300C) 0.12, softening temperature 1600C, and melting point 2100C. (C): yield from (A) 60% by wt., molar composition 1/0.15, decomposition temp. 2500C. If the polymerization is carried out in the presence of zinc chloride catalyst, the ratio (B)/(C) increases. (Kaichi, S.)