Relationship between conformation and enthalpy or volume relaxation in polycarbonate

Conformational changes are observed during sub-Tg annealing of solution-cast films of BPA–polycarbonate by following changes in the conformationally sensitive IR aromatic breathing band at 1600 cm−1. The rate of conformational relaxation is compared with published data on enthalpy and volume relaxation on the same polymer. The relaxation rates and timescales converge in the immediate vicinity of Tg, but diverge at temperatures below Tg−15 K and conformational energy only accounts for a very small fraction of observed enthalpy relaxation. The results suggest that a single process is active in volume and conformational relaxation and that at least two processes contribute to enthalpy relaxation.