Porous polymeric structures and a method of making such structures by means of heat-induced phase separation

A process for making microporous polymeric structure having pores of an average size between about 0.05 and 10 micrometers which comprises:

• a) preparing a homogeneous solution of a polymer composition consisting of at lease one polymer in a solvent system, said solvent system consisting of at least one component which is solvent for said polymer composition, and containing zero, one or more components which are non-solvents for said polymer composition, said homogeneous solution exhibiting a lower critical solution temperature,
• b) forming the polymeric solution into a desired shape,
• c) heating the shaped polymeric solution until it phase separates and becomes cloudy, wherein the heating is effected during or after forming the desired shape, and
• d) removing the components of the solvent system from said at least one polymer wherein the removing is effected when said solution is cloudy and either by immersing the shaped, phase-separated polymeric solution in at least one liquid bath comprising at least one non-solvent for the polymer which is miscible with at least one of the components of the solvent system, or by evaporating the components of the solvent system.