Carbon-13 NMR study of the conformation and dynamics of bisphenol A polycarbonate

The line widths of the protonated aromatic carbons depended strongly on temperature. A motion that could cause such temperature-dependent line widths is ring flipping. The results are consistent with an activation energy of 8-9 kcal/mol. Three-fold rotation of the methyl groups is adequate to explain the width of the signals from the methyl carbon at low temperature. However, isotropic motion of the methyls with a temperature-dependent amplitude, in addition to methyl rotation, is not ruled out