Orientation Relaxation of Triblock Copolymer with Cylindrical Microdomain by in situ Stress-Birefringence Measurements

Abstract

The orientation relaxation behavior of polystyrene-block-hydrogenated polyisoprene-block-polystyrene (SEPS) with cylindrical microdomains of polystyrene (PS) dispersed in the rubbery segments was investigated by simultaneous measurements of stress and birefringence, and small angel X-ray scattering (SAXS) measurements. At short relaxation time, the stress σ and the birefringence Δn decreased at almost constant rate with time and temperature. At long relaxation time, however, the σ and Δn decreased steeply with time, and the decrease became larger with increasing time and temperature. The decrease of the Δn stopped and large Δn remained at high temperature, while the σ was close to zero. Such characteristic relaxation behavior is ascribed to the form birefringence induced by the orientation of the parallel arranged cylindrical microdomains and the conformational change of the phenyl ring side group associating with the orientation relaxation of PS. The analysis of these results suggest that the orientation relaxation of the rubbery segments occurs at short relaxation time during the stress relaxation after the uniaxial stretching, and then the orientation relaxation of the PS segments in the cylindrical PS microdomains occurs associating with the conformational change of the phenyl side group at long relaxation time at high temperature while the orientation of the cylindrical domain is not changed.