Birefringence in polycarbonate: Molecular orientation induced by cooling stresses. I. Free quenching

The residual birefringence distributions in polycarbonate disks quenched in a liquid bath under various conditions are determined. Unbalanced distributions of approximately parabolic shape are obtained in the cross‐sections in general. A systematic influence of the initial quench temperature on the imblance of the birefringence distributions is observed, with higher initial temperatures leading to a strong shift of birefringence in the positive direction. The systematic variation of the birefringence distribution with quenching conditions is interpreted in terms of a stress and an orientation contribution. The distributions are predicted correctly by a numerical program making use of the linear stress‐optical rule with a different stress‐optical coefficient above and below the glass‐transition temperature. The contribution of molecular orientation is distinguished experimentally from the stress contribution by annealing experiments.