PET nucleopore membranes with pH value effect were prepared by surface photografting polyacrylic acid with BP as initiator．The grafting degree Dg increased with the rise of monomer concentration and prolongation of irradiation time．With the increase of initiator concentration

the grafting degree has a maximum

which results from the counterbalance between initiating species and self-screening of BP in the reaction solution．Membranes were characterized with XPS

SEM and AFM analysis．The grafted PAA brushes are mainly located on the top surface of the membrane exposed to UV irradiation．No grafting was observed on the back surface and inside the membrane pores．The graft chains around the membrane pores have pore-covering effect．The filtration properties of the membranes are regulated by volume change of the graft brushes that comes from the response to external stimulation of pH value．At low Dg

the permeability of the membranes becomes high as compared to that of the original ungrafted ones because of the improvement in membrane bydrophilicity

but it is not dependent on the pH value of feed solutions．With the increase of Dg

the grafted membrane may act as a pH value．When the pH value varies from 4 to 2

the flux has a leap．The ratio of flux in acidic solution to that in neutral solution rises with the increase of Dg and can be adjusted by controlling Dg values．