Polyesters based on hydroxyl-containing prepolymers of olefinically unsaturated monomers and their use as binders for electrophotographic toners

A process for the preparation of polyester resin based on hydroxyl-containing prepolymers of olefinically unsaturated monomers, comprising

• (1) polymerizing a mixture of
• (a) from 60 to 90% by weight of styrene or of a styrene derivative of the formula I ##STR4## where R.sup.1, R.sup.2 and R.sup.3 are each hydrogen, methyl or ethyl and n is 1 or 2, or of a C.sub.2 -C.sub.10 -olefin having one or two conjugated double bonds, or of a mixture thereof,
• (b) from 0 to 40% by weight of a C.sub.1 -C.sub.12 -alkyl ester of acrylic or methacrylic acid, acrylonitrile or methacrylonitrile, acrylamide or methacrylamide which may be substituted by one or two C.sub.1 -C.sub.4 -alkyl groups on the amide nitrogen, maleic anhydride or maleimide which may be substituted by C.sub.1 -C.sub.4 -alkyl on the imide nitrogen, or a mixture thereof,
• (c) from 0 to 20% by weight of one or more monomers selected from the group consisting of hydroxy-C.sub.2 -C.sub.4 -alkyl acrylates and methacrylates, N-(hydroxy-C.sub.2 -C.sub.4 -alkyl)-acrylamides and methacrylamides, N-(hydroxy-C.sub.2 -C.sub.4 -alkyl)maleimides, o-, m- and p-hydroxystyrene, o-, m- and p-(hydroxymethyl)-styrene, alkenols and mixtures thereof, and
• (d) from 0 to 2% by weight of one or more polyolefinically unsaturated monomers, to give a prepolymer A, having hydroxyalkyl hydroxyphenyl or hydroxyalkenyl groups incorporated therein by using a hydroxyl-containing regulator if the monomer component (c) is absent, and subsequently
• (2) polycondensation of a mixture of
• A) from 5 to 95% by weight of the prepolymer A,
• B) from 0 to 95% by weight of a further polyol, of a polyester or of a polyamide or a mixture thereof and
• C) from 5 to 70% by weight of one or more aliphatic or aromatic dicarboxylic acids C or C.sub.1 -C.sub.4 -alkyl esters thereof,
• where A and B together account for from 30 to 95% by weight of this mixture, and, wherein optionally carboxylic acids or C.sub.1 -C.sub.4 -alkyl esters thereof having more than two carboxyl groups in the molecule or monocarboxylic acids or C.sub.1 -C.sub.4 -alkyl esters thereof or hydroxymonocarboxylic acids, or C.sub.1 -C.sub.4 -alkyl esters thereof, waxes, or a mixture thereof are present in the polycondensation.