DIELECTRIC AND MECHANICAL RELAXATION IN THE BLENDS OF A POLYMER LIQUID-CRYSTAL WITH POLYCARBONATE

Bisphenol A polycarbonate (PC) and PET/0.6PHB polymer liquid crystal ( PLC), where PET is poly(ethylene terephthalate), PHB is p-hydroxybenzo ic acid, and 0.6 is the mole fraction of PHB in the copolymer, were st udied along with their blends from the PC side up to 20 wt% PLC. Diele ctric relaxation in the range 10(-2)-10(6) Hz and dynamic mechanical b ehavior at 1.0 Hz were determined, both as a function of temperature T . Broad relaxations (beta of beta C, beta of the PLC), seen by earlier investigators who covered narrower frequency ranges, result in fact e ach from two or three distinct processes. Earlier assignments of the m ain beta peak of PC are discussed and found to contain a common denomi nator. The results are interpreted in terms of multiphase hierarchical structures contributed by the PLC related to the morphology as a func tion of composition and the macromolecular dynamics of the blend compo nents. As compared to pure PET, copolymerization with PHB results in c ompetition of increased chain stiffness with plasticization resulting from added free volume. Pertubations in the structure of the PC matrix increase up to 1.5 wt% of the PLC, but then they decrease because of crossing the theta(LC limit) at which islands of the LC-rich (PHB-rich ) phase separate from the matrix; the effect is seen in several proper ties, both mechanical anti dielectric.