SECONDARY RELAXATION MOTION IN BISPHENOL-A POLYCARBONATE

The nature of the molecular motion responsible for the mechanical secondary relaxation process of bisphenol A polycarbonate (BPA-PC) was studied. To characterize the secondary relaxation motion, dynamic mechanical behaviors of an alternating copolymer and alternating multiblock copolymers of BPA-PC and tetramethylbisphenol A polycarbonate (TMBPA-PC) were investigated. The dynamic mechanical spectrum of the alternating copolymer showed only one secondary relaxation peak at an intermediate temperature, indicating that more than one repeating unit is needed for the motion of BPA-PC. With systematically increasing block lengths from one repeating unit, multiple peaks reemerged. At a block length of nine units for each type of comonomer, two secondary relaxation peaks for each component were restored at their corresponding temperatures. In addition, a third peak at an intermediate temperature was observed, which is thought to be due to the motion of the interlinking part of the two blocks. These results suggest that the secondary relaxation of BPA-PC is due to the cooperative motion of several repeating units along the chain. The results of dynamic mechanical analyses of the blends of BPA-PC and TMBPA-PC indicate that the molecular motion has contributions from intermolecular interactions.