Permeation of p-nitrophenol through N-isopropylacrylamide-grafted etched-track membrane close to theta-point temperature

Thermo-responsive poly(N-isopropylacrylamidel NIPAAm) was grafted onto etched track copolymer films with cylindrical pores of diameter 2.5 mu m by means of post-polymerization at 60 degrees C for 30 min after pre-irradiation of 30 kGy, using gamma-rays from a Co-60 source to obtain a layer with a surface graft yield of 0.18 mg/cm(2). The permeation of p-nitrophenol (PNP) through NIPAAm-grafted etched-track films, when measured at 30 degrees C, was markedly depressed, to 7.12 x 10(-5) cm/min, compared with those measured below and above this temperature, e.g. 3.84 x 10(-3) cm/min at 29 degrees C and 2.46 x 10(-3) cm/min at 31 degrees C. This phenomenon can be explained by the existence of a theta-point (Theta) temperature, at which the hydrophilic interaction between the linear polymer of NIPAAm and water apparently disappears, resulting in permeation retardation of the water soluble PNP.