PERMEATION CONTROL THROUGH POROUS MEMBRANES IMMOBILIZED WITH THERMOSENSITIVE POLYMER

Permeation through a porous polycarbonate membrane, on which a thermos ensitive polymer, poly(N-isopropylacrylamide), was immobilized, was in vestigated. For photoimmobilization of poly(N-isopropylacrylamide), ph otoreactive azidophenyl group was connected to the polymer either at a chain terminal or in side chains. The two types of derivatized polyme rs had different lower critical solution temperature (LCST). Prescribe d amounts of the derivatized polymer were cast on the polycarbonate me mbrane and photoirradiated, When a small amount of polymer was used, a thin layer of immobilized polymer was not enough to cover pores of th e polycarbonate membrane, while a thick gel layer of immobilized polym er was for med on the polycarbonate membrane to cover pores when a lar ge amount of polymer was used. The former is represented by ''porous m embrane'', and the tatter by ''nonporous membrane''. The rate of water permeation through the porous membranes changed at different temperat ures, although permeation through nonimmobilized membrane was independ ent of temperature. Water permeation through the porous membrane incre ased above the LCST of graft polymers. Hydraulic permeation through th e nonporous membrane was not observed at agv temperature. On the other hand, tryptophan permeation through the polymer-immobilized porous me mbrane became slower above the LCST, whereas that through the nonporou s membrane became faster above the LCST. The permeation rate through t he porous membrane was much higher than that through the nonporous mem brane. The different temperature dependences of permeation can be expl ained as follows. In the case of the porous membrane, the graft chains expand below the LCST to close pores but contract at above the LCST t o open pores. On the other hand, the nonporous membrane swells below t he LCST to enhance diffusion of tryptophan and deswells above the LCST to reduce the diffusion. The present study demonstrated that the sign al responsiveness of intelligent membrane can be controlled by the mod e of device fabrication as well as by the nature of the sensoring unit .