Secondary relaxation processes in bisphenol-A polysulphone

Dynamic mechanical spectra of bisphenol-A polysulphone in torsional deformation have been obtained as a function of frequency and thermal history. Results indicate a major low-temperature γ peak at 166 K and a broad, low-intensity β peak near 352 K at 10 rad s^-1 for quenched samples. Activation energies have been estimated to be 10.7 and 67.3 kcal mol^-1, respectively. Annealing eliminates the β peak and intensifies the shoulder of the γ peak. Geometry-optimized CNDO/2 (complete neglect of differential overlap) molecular-orbital calculations for the diphenyl ether and isopropylidene units of polysulphone and use of molecular-mechanical calculations for diphenylsulphone indicate intramolecular conformational energies in the range from 5 to 10.6 kcal mol^-1. Comparison of these calculated energy barriers to torsional motions with experimentally determined activation energies from dynamic mechanical measurements suggests that phenyl and methyl group rotations in the isopropylidene unit, possibly phenyl ring rotation in the diphenyl sulphone unit, and phenyl group rotations in the diphenyl ether unit may all contribute to the γ transition. The higher-energy β transition is most probably due to intra- or interchain cooperative motions involving motions of several groups along the chain.