Polyacrylonitrile (PAN)-based copolymers containing phosphonic acid moiety were synthesized for dehydration of aqueous pyridine solution. The in, situ complex, formed between the vinylphosphonic acid (VP) moiety in the membrane and the pyridine in the feed, enhanced separation capacity of poly(acrylonitrile-co-vinylphosphonic acid) (PANVP) membranes. All the PAN-based membranes containing phosphonic acid were very selective toward water. The pervaporation performances of PANVP membranes depended on the content of the phosphonic acid moiety in the membrane and operating temperature. The pervaporation separation of water/pyridine mixtures using PANVP membranes exhibited over 99.8% water concentration in permeate and flux of 4-120 g/m(2)/h depending on the content of vinylphosphonic acid and operating temperature.