Witold Brostow, Michael Hess, and Betty L. López
Departments of Materials Science and Chemistry, University of North Texas, Denton, TX 76203-5308, USA

Tomasz Sterzynski
Ecole Europeénne de Chimie des Polymères et des Matériaux, Louis Pasteur University, 4 rue Boussingault, F-67000 Strasbourg, France

ABSTRACT

This work is aimed at an evaluation of the capability to redict the mechanical behaviour of blends ont he basis of the phase diagram. Connections between phase structures, the phase diagram and mechanical properties were studied for binary blends of polycarbonate (PC) based on bisphenol-A with PET/0.6PHB, where PET = poly(ethylene terephthalate), PHB = p-hydroxybenzoic acid and 0.6 = the mole fraction of PHB with the copolymer. PET/0.6PHB is a longitudinal polymer liquid crystal (PLC) with LC sequences in the backbone along the main-chain direction. The techniques used were differential scanning calorimetry (DSC), thermomechanical analysis (TMA) in the penetration and three-point-bending modes, thermally stimulated depolarization (TSD), and two kinds of dynamic mechanical analysis (DMA) as a function of frequency w and temperature T. The resulting phase diagram is plotted as a quasi-binary one (T versus concentration of PET/0.6PHB or PC) but provides information on miscibilities of all three pairs of constituents; it contains equilibrium as well as long-living non-equilibrium phases, including the quasi-liquid. DSC and DMA results show that glass transition temperatures for the PC-rich phase drop by ~50°C after 1 h of annealing, with evident consequences for mechanical properties. Variations of storage modulus and strain as a function of time are reported for different blend compositions. Isothermal storage moduli and results of three-point bending as a function of compoisition are connected to the phase diagram. Prediction of mechanical behaviour is possible from miscibilities of constituents in specific regions of the diagram.

*Polymer. 1996, 37, 1551.