Diffusion of p-aminoazobenzene in SBS block copolymer

Abstract

The temperature dependence of p-aminoazobenzene diffusion in a styrene–butadiene–styrene (SBS) triblock copolymer film, prepared from a toluene or ethyl acetate solution, was investigated in the temperature region from 40° to 110°C by using a sublimative desorption method. Parallel studies on the mechanical relaxations of this copolymer were carried out in the same temperature range to be compared with the diffusion data. The penetrant-diffusion characteristics were interpreted in terms of Fujita's free-volume theory with due consideration of the different SBS domain morphology. The value of Bd, defined as the diffusional volume ratio of a penetrant molecule to a segment, was then estimated as 0.45–0.55 above the Tg of the polystyrene phase or 0.7 below that temperature. Interestingly, sigmoidal desorption appeared in the range under the Tg of the polystyrene phase for film cast from ethyl acetate; the anomalous behavior was considered to reflect the slow relaxation process of the copolymer chain ascribable to the predominant exposure of the polystyrene phase on the film surface.