Microporous membranes prepared via thermally induced phase separation from metallocenic syndiotactic polypropylenes

Microporous membranes were prepared by thermally induced phase separation (TIPS) using different tailor-made syndiotactic polypropylenes (sPP) synthesized by metallocene catalysts. The phase diagrams of sPP samples in diphenyl ether (DPE) were determined. The polymer microstructure effect on the thermodynamic and kinetic properties of the sPP-DPE systems were also determined and correlated with membrane pore size. The crystal structure which developed in the matrix of the porous membranes was investigated by wide-angle X-ray diffraction (WXRD). The cloud points were found to be slightly affected by molecular weight (M_w) and the influence of syndiotacticy was negligible. The dynamic crystallization curves depended solely on the syndiotacticity of the samples, shifting to lower temperatures as the stereoregularity of the sPP decreased, and no relation with M_w was found. The viscosity of sPP-DPE solutions increased with M_w and stereoregularity of the sPP. Membrane pore sizes were correlated with droplet growth period, crystallization behaviour, and sample viscosity, the latter being an important parameter for low polymer solution concentration (15 wt%) but not so at higher concentration (40 wt%). The results showed that by controlling polymer microstructure it is possible to control membrane pore size.