Manufacture of aqueous polymer dispersions and coating compositions derived from them

Claim 1

A process for the production of a sterically stabilised dispersion of polymer particles of a size in the range of 0.01 to 10 microns in an aqueous medium, the process comprising the polymerisation in the aqueous medium of one or more ethylenically unsaturated monomers at a temperature which is at least 10° C. higher than the glass transition temperature of the polymer which is formed, in the presence of a free radical initiator which is soluble in the said monomer or monomers and also in the presence of a stabiliser precursor compound which is soluble in the aqueous medium and which contains in the molecule a polymeric component of molecular weight at least 1000 which is solvatable by the aqueous medium and an unsaturated grouping which is capable of copolymerising with the said monomer or monomers, the aqueous medium being a mixture comprising (a) at least 30% by weight of water and (b) not more than 70% by weight of a second constituent which is miscible with water, the nature and proportion of the second constituent being such that the mixture as a whole is capable of dissolving the monomer or monomers being polymerised to the extent of at least 3% by weight but is a non-solvent for the polymer formed, the concentration of free monomer in the polymerisation mixture being maintained throughout the process at a level such that at no time does the free monomer form a separate phase and the total amount of monomer polymerised being such that the resulting dispersion contains at least 20% by weight of polymer.