Plasma graft polymerization of N,N‐dimethylaminoethyl methacrylate and water–ethanol separation by pervaporation through the grafted membranes

N,N‐dimethylaminoethyl methacrylate was graft‐polymerized onto the porous polypropylene films of Celgard 2400 and 2500 which have been previously surface‐activated by glow discharge plasmas. The grafting was dependent on various factors both in the plasma pretreatment and the post‐polymerization with the monomer. The reaction was discussed from the aspects of the dependences of graft polymerization on discharge power, plasma pretreatment period, etc. When the grafting exceeded a critical amount depending on the size of pores on the substrate film, pervaporation of water‐ethanol separation functioned through these grafted membranes. The water permselectivity was improved by the ammonium ionization of the pendant N,N‐dimethylamino group using dimethyl sulfate or chloroacetic acid, although the increase of prevaporation performance was not so high as those previously obtained by the grafted poly(sodium acrylate) ‐type membranes. Pervaporation characteristics of these membranes were discussed from the ionized states of the permselective layers analyzed by IR and ESCA.