Abstract
We investigated the stress and birefringence Δn during stress relaxation in poly(styrene-co-acrylonitrile). The Δn changed its sign from positive to negative during the stress relaxation with increasing relaxation time and temperature in the glassy region. The negative Δn was found to increase when the stress was released and the specimen was cooled to room temperature. Such characteristic Δn behavior is ascribed to three relaxation mechanisms consisting of distortion, orientation, and conformational change of the phenyl ring side group. The master curve of the Δn was nicely explained by assuming that the distortion relaxation is expressed by Kohlrausch−Williams−Watts equation, the orientation relaxation by modified Rouse equation, and the conformational change by a stretched exponential relaxation function. The curve fitting procedures of the master curves revealed that the conformational change of the side group is much slower than the phenyl ring vibration (β relaxation); i.e., the rotational angle of ...
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