Microporous membranes based on poly(ether ether ketone) via thermally-induced phase separation

The fabrication of poly(ether ether ketone) based membranes via thermally-induced phase separation has been investigated. Microporous membranes were generated from solid-liquid phase separation of miscible polymer-polymer mixtures comprised of PEEK and polyetherimide, with subsequent extraction of the PEI diluent; the introduction of a high polymer diluent provides a number of advantages in terms of melt processing and ultimate membrane properties. The nature of the solid-liquid phase separation and corresponding PEI segregation was investigated as a function of crystallization temperature and diluent molecular weight using dynamic mechanical thermal analysis. DMTA studies revealed segregation of PEL to both interlamellar and interfibrillar/interspherulitic regions. PEI extraction with liquid dichloromethane was found to be site specific, with diluent removal solely from the interfibrillar and interspherulitic regions; the retention of interlamellar PEI in the final article was reflected in a significant increase in the thermal resistance characteristics of the material. Scanning electron microscopy revealed a microporous morphology comprised of a spherulitic superstructure with two distinct pore size scales corresponding to PEI extraction from between fibrillar bundles and in interspherulitic regions, respectively. The relative morphological distribution could be shifted with variations in initial blend composition.