By grafting reaction of poly(ethylene glycol monomethyl ether) (MPEG) and poly(ethylene-co-acrylic acid) (EAA), the MPEG-grafted EAA (EAA-g-MPEG) was obtained. The effect of MPEG on the phase diagram of EAA-g-MPEG/MPEG/di-n-octyl phthalate (DOP) system was investigated by varying the composition of MPEG and DOP via thermally induced phase separation (TIPS). The binodal temperature originally shifted to lower temperature as the proportion of MPEG increased, then increased remarkably when the ratio of MPEG to DOP was more than 1/6. The domain growth kinetics of EAA/DOP, EAA-g-MPEG/DOP and EAA-g-MPEG/MPEG/DOP systems was studied by light scattering method. It was found that the domain growth rate of EAA-g-MPEG/MPEG/DOP system was lower than EAA/DOP and EAA-g-MPEG/DOP systems at a certain quench temperature. Moreover, the membrane morphologies were compared, indicating that the pore size became smaller when MPEG was added as a component of diluent. Furthermore, the distribution of the grafted MPEG chains on the imitated interphase was investigated by energy-dispersive X-ray (EDX) analysis. Results showed that more hydrophilic MPEG chains existed on the interphase when MPEG was contained in the solvent. (c) 2006 Elsevier B.V. All rights reserved.