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

摘要

NMR experiments were carried out on glassy samples containing C-13-labeled bisphenol-A polycarbonate with isolated C*(carbonate)-O-C*(phenylene) arrangements in the chains. The dihedral angle distributions in the C-O-C moieties were determined by fitting simulated spectra to the experimental data. It was found that the O-C-phenylene torsion angle is widely distributed with population maxima where the C-O-C plane forms an angle of ca. 55 degrees with the phenylene ring. The carbonate units assume trans conformations at 135 K (torsion angle around C*(carbonate)-O < 10% cis). Three different molecular packings obtained by computer simulation with different construction methods and two different force fields yielded considerably higher cis contents; this discrepancy is currently still unresolved. From comparison of the data to those for single-chain models (rotational-isomeric-state models) it is concluded that considerable conformational change could be possible far below T-g. [References: 42]