抄録
The dynamic mechanical properties of bisphenol A polycarbonate (BPA-PC: poly (oxycarbonyloxy-1, 4-phenyleneisopropylidene-1, 4-phenylene)) and bisphenol AP polycarbonate (BPAP-PC: poly (oxycarbonyloxy-1, 4-phenylene-1-phenyl-1, 1-ethylidene-1, 4-phenylene)) were measured, and the differences in their dynamic mechanical relaxation were analyzed based on the conformational changes and subunit rotations estimated by MM2. The results indicated that the partial rotations of the carbonate and oxycarbonyl groups have low energy barrier and are reasonably ascribed to the major modes of the γ relaxation of both BPA-PC and BPAP-PC. In BPA-PC these rotations should be conjugated with the rotation of the phenylene groups to allow the low temperature relaxation which follows the γ relaxation. The correlated double rotations and flip-flop rotations of the phenylene groups as well as the full rotations of the carbonate may be responsible for the β relaxations of both polycarbonates which may lead to the α relaxations at higher temperature. The excellent toughness of BPA-PC is ascribed to these various modes of partial rotations of the carbonate and the phenylene groups by which the occurring inner stress can be diffused.
