Thermostable vinylchloride mixed polymers

A process for the preparation of vinyl chloride copolymers involves free radical suspension polymerization or emulsion polymerization of a mixture of vinyl chloride, epoxide-containing vinyl monomers and further comonomers copolymerizable therewith, wherein a) from 49.5 to 90% by weight of vinyl chloride, b) from 0.01 to 0.7% by weight of epoxide-containing vinyl monomers and c) from 9.5 to 50% by weight of further comonomers copolymerizable with a) and b) are polymerized, the data in % by weight totaling 100% by weight, and from 0.001 to 0.1% by weight of one or more aliphatic or alicyclic, saturated or unsaturated dicarboxylic acids having 1 to 10 carbon atoms, or aliphatic and alicyclic, saturated and unsaturated hydroxymono-, hydroxydi- and hydroxytricarboxylic acids having 3 to 10 carbon atoms and 1 to 4 hydroxyl groups are added during or after the polymerization, and the vinyl chloride copolymer is isolated as a solid resin.