The new amphiphilic triblock copolymers of poly(N-vinyl pyrrolidone-b-methyl methacrylate-b-N-vinyl pyrrolidone) (P(VP-b-MMA-b-VP)) were synthesized via a reversible addition fragmentation chain transfer polymerization route. Using these copolymers as additives in casting solutions, the porous blend membranes of poly (vinylidene fluoride) and P(VP-b-MMA-b-VP) were prepared following a typical nonsolvent induced phase separation process. The influences of P(VP-b-MMA-b-VP) on the morphologies of the blend membranes were observed by scanning electron microscopy. The chemical compositions in membrane surface layers were measured by X-ray photoelectron measurement. Water contact angle and water flux experiments were used to evaluate the hydrophilicity and permeation properties of the blend membranes. It was found that the P(VP-b-MMA-b-VP) copolymers could be retained in membrane stably in membrane formation and application process. The copolymers could enrich in surface layer and endowed the blend membrane with efficient hydrophilicity and higher water permeation flux. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 2953-2960, 2011