Process for the polymerization of acrylonitrile

A process for the catalytic polymerization of acrylonitrile or a monomer mixture containing above 75% by weight of the mixture of acrylonitrile and at least one other ethylenically unsaturated compound, characterized in that the polymerization is conducted at a temperature above 120.degree. C. under the internal pressure generated in a closed polymerization system or under external pressure above the vapor pressure generated in the polymerization system under such polymerization conditions wherein water is present in the system in a range of 5 to 20 percent by weight based on the total weight of the monomer(s) and water to produce an acrylonitrile polymer in a substantially molten state, said polymerization being conducted in the presence of an oil-soluble radical generating agent as a catalyst whose decomposing temperature to obtain a half-life period of 10 hours is about 80.degree. C. selected from the group consisting of di-tert-butyl diperoxyphthalate, tert-butyl hydroperoxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexine, 4-azobis-4-cyanopentanoic amide and 1-azobis-1-cyclohexanecarbonitrile.