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

Thermo-responsive poly(N-isopropylacrylamide, NIPAAm) was grafted onto etchedtrack copolymer films with cylindrical pores of diameter 2.5 μm by means of post-polymerization at 60°C for 30 min after pre-irradiation of 30 kGy, using γ-rays from a60Co source to obtain a layer with a surface graft yield of 0.18 mg/cm2. The permeation of p-nitrophenol (PNP) through NIPAAm-grafted etched-track films, when measured at 30°C, was markedly depressed, to 7.12 × 10−5 cm/min, compared with those measured below and above this temperature, e.g. 3.84 × 10−3 cm/min at 29°C and 2.46 × 10−3 cm/min at 31°C. This phenomenon can be explained by the existence of a theta-point (⊝) 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.