Thermally induced phase separation (TIPS) is one of the most important methods to prepare micro-porous polymer membranes.In this paper

isotactic polypropylene (iPP) was dissolved in diamylphthalate (DAP)

and the effects of polymer molecular weight on their phase diagram and micro-structure of membranes prepared are studied.Different iPPs and DAP were mixed in a Haake torque rheometer to obtain homogeneous solution.To determine the phase diagram

the cloud points (liquid-liquid phase separation temperatures) and the crystallization temperatures of the iPP/DAP system were examined by microscope with a heating device and DSC

respectively.The micro-structures of the films prepared by TIPS were observed under SEM.The results showed that the liquid-liquid separation temperatures of the solution shifted to higher temperatures when the molecular weight of polypropylene increased.On the other hand

their crystallization temperature curves changed little.These phenomena are interpreted by using Flory-Huggins theory.The molecular weight of polypropylene has a great effect on the resulting average pore size and pore shape in the film via influencing not only the droplet growth time but also the super-cooling temperature range and the coarsening rate.