Process for bulk copolymerization of vinyl esters

In a process for the preparation of copolymers of monoethylenically unsaturated compounds in the presence of a free-radical forming initiator by bulk copolymerization of

• A. 1-50 parts by weight of vinyl esters of alpha-branched saturated aliphatic monocarboxylic acids having from 5 to 22 carbon atoms per acid molecule;
• B. 1-60 parts by weight of a vinyl aromatic hydrocarbon;
• C. 0-50 parts by weight of an ester, amide, and/or nitrile of an ethylenically unsaturated monocarboxylic acid having 3 to 4 carbon atoms per molecule;
• D. 0-30 parts by weight of an ester of an ethylenically unsaturated dicarboxylic acid having 4-5 carbon atoms per molecule:
• E. 0-20 parts by weight of an ethylenically unsaturated mono-or dicarboxylic acid, or anhydride thereof, having 3 to 5 carbon atoms per molecule, and
• F. 1-20 parts by weight of a polyisobutylene having a molecular weight;
• of from 2,000 to 15,000 the total amount of ethylenically unsaturated monomers being 100 parts by weight, the improvement which comprises first adding component (F) and optionally a part of the initiator, to the reactor and heating to at least 150.degree. C and then gradually adding the other monethylenically unsaturated components and remaining initiator during a period from about 3 to about 24 hours at a reaction temperature between 150.degree. C and 200.degree. C in two stages, the first stage comprising gradual addition of component (A), at least part of component (B), initiator, and optionally part of components (C), (D), and (E), the second stage comprising gradual addition of the remainder of component (B), initiator, and optionally the remainder of components (C), (D), and (E).