| Abstract: | The effect of orientation on the low-strain mechanical properties, dielectric relaxation, and thermal expansivity of poly(butylene terephthalate) has been studied. The α relaxation at 50°C (1 Hz), which involves large-scale chain motion in the amorphous regions, is reduced in magnitude and shifted to higher temperature after drawing. In contrast, the localized motions of the carbonyl and glycol groups associated with the β process at ?90°C (1 Hz) is not much affected by orientation. At low temperature, a large difference along and normal to the draw direction is observed for both Young's modulus and thermal expansivity. The anisotropy, however, diminishes with increasing temperature and becomes nearly zero above the α relaxation. This feature can be understood on the basis of the Takayanagi model. |
