Abstract
FT-IR spectroscopy was used to examine conformational changes in the quenched Bisphenol A Polycarbonate (BPAPC) films during physical aging. It was observed that the amount of energy favored trans-trans conformers increased, while energy less favored trans-cis conformers decreased upon sub-Tg annealing. Since the trans-trans conformers allow closer local packing of the polymer chains than the trans-cis conformers do, the results may indicate that sub-Tg annealing will lead to closer interchain packing. In situ FT-IR studies on the conformational changes of BPAPC films with different thermal histories, i.e., quenched from the rubbery and sub-Tg annealed for different time, were carried out while increasing the temperature through the glass transition region. The temperature dependencies of the infrared spectra show that incremental changes of the population of trans-cis conformers in the quenched sample are gradual, while rather abrupt changes occur in the sub-Tg annealed samples. The magnitude and temperature of the abrupt changes of trans-cis conformers are related with the time of the sub-Tg annealing. The energy absorbed during the abrupt conformational change represents only part of the energy of the endothermic peak observed by modulated differential scanning calorimetry. The results are explained in terms of the formation of new cohesional entanglements during sub-Tg annealing.
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