Selective permeation across a blend film of cellulose acetate and polymer or copolymer of c-( Nε-AcrLys-Sar)

Abstract

A blend film of cellulose acetate and the homopolymer (PCP) or the copolymer with styrene [P(CP_ST)] or 4-vinylpyridine [P(CP_VP)] of cyclo(N ε- acryloyl- l-lysylsarcosyl ) [c-( N ε -AcrLys_Sar)], which is a vinyl compound carrying a cyclic dipeptide in the side chain, was prepared and investigated as a selectively permeable film for ions and polar substances. For the permeation of alkali metal chlorides, the solubility coefficient S increased in proportion to the content of PCP in the blend film, whereas the diffusion constant D s increased up to 20 wt% of PCP content and levelled off beyond it. D s of Rb + was greatest for any blend film regardless of the composition. It was considered that the hydrophilic PCP forms water channels in the blend film and metal salts diffuse by coordination with cyclic dipeptide ligand groups which are arrayed along the water channels. In this process, the cooperative interaction of the ligand groups with a metal ion along the flexible polymer chain should work most efficiently with Rb +, leading to the Rb + selectivity in the permeation. A similar ion selectivity was observed with the blend film of P(CP_ST). For the blend film of P(CP_VP), S increased in proportion to the content of P(CP_VP), where D s was a minimum at 20 wt% of P(CP_VP) content. The ion selectivity was not observed with either S or D s. For the permeation of alkali metal salts across the blend film of PCP, D s and the ion selectivities were compared for chlorides and thiocyanates, and no remarkable difference was observed. D s for the permeation of alkaline earth metal salts across various blend films were smaller than those for alkali metal salts. A blend film containing 20 wt% of PCP was found to permeate l-phenylalanine about three times as fast as d-phenylalanine. The optical resolution of racemic phenylalanine by the permeation across the blend film was possible. With increasing content of PCP in the blend film, the urea permeability increased but the oxygen permeability decreased.