Control of Polymer Morphology for Biomedical Applications. I. Hydrophilic Polycarbonate Membranes for Dialysis

The control of polymer morphology for biomedical applications is discussed by a detailed reference to the tailormaking of polycarbonates for hemodialysis membranes, a case in which control was necessary on molecular, microcrystalline, and colloidal levels.

On the molecular level, the hydrophilicity of the parent polymer, bisphenol-A polycarbonate, was increased with the introduction of aliphatic ether groups by the copolymerization of bisphenol-A and the polyethylene glycols. On the microcrystalline level it was found that the bisphenol-A polycarbonate blocks formed crystallites within the amorphous matrix composed of the polyethylene oxide blocks. Because of this the modified polymer retained most of the strength of the parent bisphenold polycarbonate. Another striking property exhibited by the copolymer is that the tensile strength of the wet material was in excess of that of the dry. This has been attributed to plasticization and realignment of the polyethylene oxide blocks by water molecules. Finally, morphology on the colloidal level was controlled by the preparation of asymmetric membranes possessing a skin layer and a substructure whose void volume, and hence resistance to material transport, could be varied at will.