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The production is described of a dispersion of polymer microparticles, which may optionally be crosslinked, by dispersion polymerisation in aliphatic hydrocarbon liquid under specified conditions of a monomer mixture which comprises up to 50% of styrene or a substituted derivative thereof and up to

The production is described of a dispersion of polymer microparticles, which may optionally be crosslinked, by dispersion polymerisation in aliphatic hydrocarbon liquid under specified conditions of a monomer mixture which comprises up to 50% of styrene or a substituted derivative thereof and up to 50% by weight of a derivative of maleic acid or fumaric acid which is soluble in the hydrocarbon liquid at the polymerization temperature. The microparticles have a size in the range 100-400 nm and a high refractive index, and are suitable for incorporation in coating compositions which are based on a film-forming polymer, such as a thermosetting acrylic resin or an alkyd resin, containing a significant proportion of aromatic residues, and which are intended to be used either unpigmented or when containing only light-absorbing pigments.

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A process for the production of a dispersion of addition polymer microparticles, of a size in the range 100-400 nm, the process comprising the dispersion polymerization in an aliphatic hydrocarbon liquid of an ethylenically unsaturated monomer mixture which gives rise to a copolymer insoluble in the

A process for the production of a dispersion of addition polymer microparticles, of a size in the range 100-400 nm, the process comprising the dispersion polymerization in an aliphatic hydrocarbon liquid of an ethylenically unsaturated monomer mixture which gives rise to a copolymer insoluble in the hydrocarbon liquid and which comprises (i) up to 50% by weight of styrene or a substituted derivative thereof and (ii) up to 50% by weight of a derivative of maleic acid or fumaric acid which is per se soluble in the hydrocarbon liquid at the temperature of polymerization, said derivative being selected from the group consisting of an N-aryl-substituted maleimide of the general formula [Figure] where Ar is an aromatic radical which may contain a single benzene nucleus or two or more connected or fused benzene nuclei, a diester of maleic acid or fumaric acid of the structure [Figure] where either X or Y, or both, is an aromatic radical which may contain a single benzene nucleus or two or more connected or fused benzene nuclei, and a monoester of maleic acid or fumaric acid of the structure [Figure] where X is an aromatic radical which may contain a single benzene nucleus or two or more connected or fused benzene nuclei, the polymerization being carried out in the presence in the hydrocarbon liquid of a steric dispersion stabilizer the molecule of which comprises at least one polymeric component which is solvated by the hydrocarbon liquid and at least one other component which is not solvated by the liquid and is capable of associating with the copolymer produced, and the concentration of unpolymerized monomer in the hydrocarbon liquid being regulated so that throughout the polymerization the reaction medium remains a non-solvent for the copolymer formed.