Modification of cation exchange membrane by grafted poly(4-vinyl-N-methylpyridinium-iodide)

Abstract It is well known that cation exchange membranes, having a very thin layer of a cationic polyelectrolyte on the membrane surface, have preferential permselectivity for monovalent cations in a monovelent‐divalent cations system. We studied the relationship between preferential permselectivity and molecular structure of the cationic polyelectrolyte. Grafted poly(4‐vinyl‐ N ‐methylpyridinium‐iodide) was used and was compared with poly(4‐vinyl‐ N ‐methylpyridiniumiodide). The backbone polymers were poly(styrene‐co‐p‐benzylstyrene) and poly(benzyl), onto which 4‐vinylpyridine was grafted by anionic polymerization and then quaternized with CH 3 I. The grafted poly(4‐vinyl‐ N ‐methylpyridinium‐iodide) is effective in making the cation exchange membrane preferentially permselevtive for Na + ‐ Ca 2+ system and is more preferable than poly(4‐vinyl‐ N ‐methylpyridinium‐iodide) in terms of electric resistance of the membrane. However, the relationship between the molecular structure of the cationic polyelectrolyte and the durability of the preferential permselectivity is not clear.