Structure and properties of injection molded blends of poly(ether imide) and a thermotropic copolyester

The phase structure and mechanical properties of blends composed of poly(ether imide) and a thermotropic liquid-crystalline copolyester, Rodrun LC-5000, processed by injection molding were studied in the PEI-rich region. The addition of Rodrun to PEI produces fully immiscible blends and strongly improves the processability of PEI. Injection molding gave rise in very poor LCP blends to fine dispersed phases; in the rest of compositions it gave rise to coarse structures. This was probably due to the very large viscosity difference between the components of the blends. An increase in the melt temperature led to a smaller viscosity difference and as a consequence dispersed phase dispersion improved. The Young's modulus clearly increased with the Rodrun content. The tensile strength was maintained up to a LCP content of 5% but decreased at higher contents because of the coarse morphologies obtained. The overall mechanical behavior was a main consequence of the lack of fibrillation and of the LCP dispersion level in the matrix.