AbstractWater–ethanol permselectivity was investigated by pervaporation through composite membranes which were prepared by coating photocrosslinkable poly(vinyl alcohol) containing pendant styrylpyridinium group (0.86–3.93 mol ) on porous films. These membranes were water‐permselective, and the selectivity was dependent on the state of membranes; namely, incorporation ratio of styrylpyridinium group on poly(vinyl alcohol), molecular weight of the base polymer, coating thickness of a photopolymer, etc. Photocrosslinkable styrylpyridinium group showed, of course, the ionic character by a pyridinium moiety to work on permseparation of water effectively as well as preventing the dissolution of membranes by crosslinking. Membranes based on the higher molecular weight poly(vinyl alcohol) (P= 1700) gave the higher permselectivity of water in general than those of lower molecular weight (P= 500) one. Swelling of the polymers reached 160, and permeation rate through the membranes increased with the increase of swelling. Selective diffusion of water was found to take place in swelling, and to play a part in the water‐permseparation through the me
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