Two types of resins (F401 and PPH) were selected to develop microporous membranes using cast film extrusion followed by stretching.The roles of the molecular weight and molecular weight distribution on the row-nucleated lamellar crystallization and micropore formation were investigated.The relaxation spectra of the resins were examined by dynamic rheology.The content of high molecular weight component (Mw 106) for PPH was 1.5 times larger than that of that for F401. Under the same temperature

the relaxation time of PPH was much longer than of F401.The crystalline orientation was measured by Fourier transform infrared spectroscopy (FTIR).At the same draw ratio (DR)

the crystalline orientation of the precursor film for PPH was higher than that of F401.Scanning electron microscopy (SEM) images of the membrane surface showed the high molecular weight component or long chains played a remarkable role in the formation of mircopores and were included in the part of bridging structure as tie chains.Under the same processing condition

the pore structure of microporous membrane for PPH was more regular and uniform.The porosities of the microsporous membranes were tested by the liquid absorption method.For both resins

the porosities of the microporous membranes increased with DR.The content of high molecular weight component of the resins primarily influenced the pore structure of the microporous membranes.