Intrinsic birefringence of amorphous poly(bisphenol‐A carbonate)

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Abstract
The birefringence of uniaxially oriented poly(bisphenol‐A carbonate) (PC) samples stretched over a wide range of temperatures has been measured accurately with a combination of the compensator and the wedge methods. The Hermans' orientation function of anisotropic PC was calculated from the measured dichroic ratio of the infrared absorption band at 1364 cm‐1. Measurements using differential scanning calorimetry, X‐ray diffraction, or infrared spectroscopy indicated no stress‐induced crystallinity in stretched amorphous PC. At each state having a defined molecular orientation, samples stretched below the glass transition temperature (Tg) always exhibited excess birefringence and slightly higher density. This phenomenon is attributed to bond distortion during stretching, a result of the suppression of large‐scale segmental motions of polymer chains below the Tg. The birefringence of samples stretched above the Tg arises exclusively from the orientation effect as a result of greater chain mobility. These measured birefringence values are proportional to Hermans' orientation functions, yielding a linear relationship which allows precise determination of the intrinsic birefringence of amorphous PC as 0.192 ± 0.006.