Facile graft polymerization of methacrylic acid (MAA) onto polyethersulfone (PES) using benzoyl peroxide (BPO) as chemical initiator had been developed. The polymerization was carried out in a heterogeneous polymer-monomer reaction system using water as reaction medium. The crucial parameters affecting the graft yield, such as monomer concentration, reaction time and temperature, were studied. The amount of grafted PMAA on PES was increased with increasing monomer concentration and reaction time. The optimum temperature for the grafting was around 75 C. The graft polymers produced herein were cast into ultrafiltration membranes via phase inversion process. The cross-sectional morphology and surface composition of the membranes were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. Remarkable surface enrichment of the hydrophilic MAA segment in the membrane was revealed by XPS analysis. Due to the pH-induced conformational transition of the PMAA chains, the permeability of the membranes cast from the grafted polymers displayed pronounced pH dependence, which was large under low pH values and small under high pH values. (C) 2009 Elsevier B.V. All rights reserved.