Thermo-sensitive switching membranes regulated by pore-covering polymer brushes

Novel thermo-sensitive switching membrane regulated by pore-covering polymer brushes was prepared by photografting N-isopropylacrylamide (NIPAAm) onto the polyethylene terephthalate (PET) track membranes with benzophenone (BP) as initiator. The influence of solvent, initiator concentration and temperature on photografting has been investigated. ATR-FTIR and SEM confirmed that poly-NIPAAm brushes were immobilized on the membranes surface exposed to the UV light instead of inside the pores. The thickness of grafted layer can be adjusted by grafting reaction parameters via grafting degree. The membrane flux is regulated by pore-covering effect that comes from the grafted chains' stretching into the membrane pores. Responding to the change of the temperature, the pore size varied with the swelling and shrinkage of poly-NIPAAm brushes and accordingly adjusted the membranes flux. The 0.2 mum-grafted membranes do not show a remarkable thermo-sensitive valve effect near the range of 30-35 degreesC until the grafting degree exceeds 1%. To 0.4 mum membrane, the grafted brushes are not long enough to cover the membrane pores and thus crosslink agent is necessary. The crosslink network limit the free movement of grafted polymer brushes and thus the critical temperature has a shift to high temperature. (C) 2003 Elsevier Science B.V. All rights reserved.