Patent ID: 7696273

Claim:
A method for increasing a mechanical hardness of polymer particles, the polymer particles comprising hydrophilic groups and hydrophobic groups, the method comprising the step of: subjecting the polymer particles to a thermal cycle comprising at least one heating step followed by at least one cooling step, wherein the polymer particles are contained in a polar solvent, whereby a mechanical hardness of the polymer particles is increased, wherein the polymer particles are subjected to a temperature of up to 300° C. during the heating step, and wherein the polymer particles are subjected to a temperature down to 10° C. during the cooling step wherein the polymer particles comprise at least one polymer selected from the group consisting of poly(methyl methacrylate), polystyrene, polypropylene, polyvinylchloride, polyisobutylene, acrylate, methoxypolyethylene glycol methacrylate and 4-vinylpyridine.