The different molecular weight Polyethylene glycol (PEG) was chosen to be the nucleating agent to investigate the effects of nucleating agents on the porous structure of polyphenylene sulfide (PPS) via thermally induced phase separation (TIPS). The pore structures were changed with the addition of PEG, due to the different mechanism on pattern formation. Moreover, some effecting factors, such as the molecular weight and concentration of PEG, were used to control the pore structure and size. With addition of nucleating agent, it can be estimated that the pore size (radius) should be about 0.5 similar to 0.05 mu m and the porosity should be above 70%. (c) 2007 Wiley Periodicals, Inc.