On the strain-induced birefringence of glassy polymers

The strain-induced birefringence of glassy polymers is due not only to the contribution from the polymer chain orientation but to an additional contribution of a different origin. Two methods have been proposed to separately evaluate these contributions; T. Inoue et al., Macromolecules, 24, 5670 (1991) and A. Fujita ei al., Polymer Preprints, Japan, 41, 4451 (1992). The former employs the data of dynamic birefringence in oscillatory elongation and the latter the birefringence in simple elongation at various temperatures. In the present study these methods were revealed to be equivalent under certain conditions. The parameters involved in these analyses were examined in details and a new simple method was proposed for evaluation of the intrinsic birefringence from the data of dynamic birefringence.