Synthesis and Thermotropic Liquid Crystalline Behavior of Copolymers Containing Ether Ketone and Ester Links

Copolymers containing ether ketone and ester links were synthesized by high temperature solution condensation and were characterized by Fourier transform infrared (FT/IR) spectroscopy, differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized light microscopy (PLM). The melting behavior and liquid crystalline transition temperatures of the homopolymers and copolymers were dependent on the composition of trimer content. The transition temperatures could be observed to decrease at first and increase subsequently; i.e. surpass a minimum, with the increment of trimer content. Thermotropic liquid crystalline behaviors were observed in the copolymers containing 20, 40, 50 and 60 mol % trimer. But the further addition of the trimer content resulted in the gradual loss of liquid crystallinity. The crystalline to liquid crystalline transition (Tm) and liquid crystalline to isotropic transition (Ti) appeared in the DSC curves, whereas the trimer-based homopolymer had only a melting transition. The polymers were thermally stable up to 400 °C. WAXD results indicated that the copolymers showed a continuous change of the diffraction peaks from sharp main crystalline reflections for crystalline Homo-C to strong broad dispersed peak for liquid crystalline TLCP.