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 -hydroxybenzoic acid, and 0.6 is the mole fraction of PHB in the copolymer, were studied along with their blends from the PC side up to 20 wt % PLC. Dielectric relaxation in the range 10 -2 −10 6 Hz and dynamic mechanical behavior at 1.0 Hz were determined, both as a function of temperature T . Broad relaxations (β of PC, β of the PLC), seen by earlier investigators who covered narrower frequency ranges, result in fact each from two or three distinct processes. Earlier assignments of the main β peak of PC are discussed and found to contain a common denominator. The results are interpreted in terms of multiphase hierarchical structures contributed by the PLC related to the morphology as a function of composition and the macromolecular dynamics of the blend components. As compared to pure PET, copolymerization with PHB results in competition of increased chain stiffness with plasticization resulting from added free volume. Pertubations in the structure of the PC matrix increase up to 15 wt % of the PLC, but then they decrease because of crossing the θ LC limit at which islands of the LC-rich (PHB-rich) phase separate from the matrix; the effect is seen in several properties, both mechanical and dielectric.