LOCAL CONFORMATIONS IN THE GLASSY POLYCARBONATE OF 2,2-BIS(4-HYDROXYPHENYL)PROPANE (BISPHENOL-A)

NMR experiments were carried out on glassy samples containing C-13-lab eled bisphenol-A polycarbonate with isolated C(carbonate)-O-C*(phenyl ene) arrangements in the chains. The dihedral angle distributions in t he C-O-C moieties were determined by fitting simulated spectra to the experimental data. It was found that the O-C-phenylene torsion angle i s widely distributed with population maxima where the C-O-C plane form s an angle of ca. 55 degrees with the phenylene ring. The carbonate un its assume trans conformations at 135 K (torsion angle around C(carbo nate)-O < 10% cis). Three different molecular packings obtained by com puter simulation with different construction methods and two different force fields yielded considerably higher cis contents; this discrepan cy is currently still unresolved. From comparison of the data to those for single-chain models (rotational-isomeric-state models) it is conc luded that considerable conformational change could be possible far be low T-g.