Abstract: A process for preparing microporous membranes by coextruding a melt of a plurality of interdigitated layers of at least two polymers, one having preferential solubility over the other, dividing and reorienting the layers of said melt into discrete domains of random orientation, forming a thin membrane or like article and leaching the preferentially soluble polymer out of the resulting article.

Abstract: A method for preparing porous membranes containing a homogeneous microporous structure and narrow pore size distribution which are useful for ultrafiltration, distillation and substrates for composite membranes, including preparing films, pellets or sheets containing alternating microlayers of high density polyethylene and polystyrene, recoextruding these films, pellets or sheets, pulverizing into fine granules or powder, compression molding or sintering into thin films, immersing these films in a solvent bath into which one component is selectively dissolved and separating the resultant porous membrane from the solvent.

Abstract: A method for preparing an asymmetric, semi-permeable membrane containing a uniform microporous structure for gas and liquid separation, including forming a dense separation on one major surface of a microporous support structure. The microporous support structure is initially formed as a solid unitary film, fiber or sheet by the simultaneous extrusion of at least two streams of heat-plastified polymeric materials including at least two differentially soluble polymeric materials. The separation layer can be formed on the support structure prior to or after the soluble polymeric material has been dissolved out of, as by leaching from the solid support structure to form the microporous support for the separation layer. Preparation in this manner greatly reduces the tendency to form undesiralbe pinholes in the membrane.