Effect of the polypropylene type on polymer–diluent phase diagrams and membrane structure in membranes formed via the TIPS process: Part I. Metallocene and Ziegler–Natta polypropylenes

Isotactic polypropylene (iPP) samples produced via Ziegler–Natta catalysts (iPPZN) and metallocene catalysts (iPPM) were used to investigate the effects of molecular weight and molecular weight distribution on the phase diagram for iPP–diphenyl ether systems and the morphology of membranes made from these systems. It was found experimentally that the molecular weight and molecular weight distribution influenced the location of the cloud point curve and the morphology of membranes produced via thermally induced phase separation. The influence on the cloud point curve was attributed to entropic and enthalpic considerations. The influence on membrane morphology was attributed to differences in the growth period (resulting from a shift in the cloud point and dynamic crystallization curves) and differences in system viscosity. All of these factors are related to the type of catalyst used to produce the iPP.