Miscibility level and mechanical characterization of blends of two liquid-crystalline polymers based on p-hydroxybenzoic acid

Injection-molded blends composed of two liquid-crystalline polymers (LCPs) based on 60/40 p-hydroxybenzoic acid/ethylene terephthalate (R3) and 73/27 p-hydroxybenzoic acid/2,6-hydroxynaphthoic acid (VA) copolymers, respectively, were obtained across the whole composition range. The two amorphous phases of the blends contained only slight amounts of the minority component, and the occurrence of some chemical reaction, mainly at high VA contents, was detected by Fourier transform infrared. Synergisms in the modulus of elasticity and in the tensile strength were seen in most of the blend compositions. The largest synergism was in the 50/50 R3/VA blend, which showed a modulus of elasticity 26% higher than that of either of the two components and a 17% positive deviation in the tensile strength with respect to the rule of mixtures. The different orientation of the LCPs in the blends explains the differences in the mechanical behavior. However, contrary to previous works on LCP blends and despite the almost complete immiscibility, the observed negative volume of mixing appears to be the main parameter that determines the synergistic mechanical behavior. (C) 2003 Wiley Periodicals, Inc.