Poly(acrylonitrile) (PAN)-based co-polymers containing phosphoric acid moiety were synthesized for the dehydration of aqueous pyridine solution. The in situ complex, formed between the phosphoric acid moiety in the membrane and the pyridine in the feed, enhanced the separation capacity of poly(acrylonitrile-co-monoacryloxyethyl phosphate) (PANPH) membranes. All the PAN-based phosphoric acid containing membranes were very selective towards water. The pervaporation performance depended on the content of the phosphoric acid moiety in the membrane, operating temperature, and feed concentrations. The pervaporation separation of water-pyridine mixtures using PANPH membranes exhibited over 97% water concentration in the permeate and a flux of 6-132 g m(-2) h(-1), depending on the content of MAEP and the operating temperature. (C) 2000 Elsevier Science B.V. All rights reserved.