Synthesis and characterization of thermotropic liquid crystalline poly(aryl ether ketone) copolymers with pendant 3‐(trifluoromethyl) phenyl groups

Novel poly(aryl ether ketone) copolymers with pendant 3‐(trifluoromethyl)phenyl groups were synthesized by the reaction of a crystal‐disrupting monomer, 3‐(trifluoromethyl)phenylhydroquinone (FH) and a mesogenic monomer, 4,4′‐biphenol (BP) with 1,4‐bis( p ‐fluorobenzoyl)benzene (BF). Thermotropic liquid crystalline behavior of the copolymers was investigated by means of differential scanning calorimetry, polarized optical microscope and wide‐angle X‐ray diffraction. As a result, the copolymers with the respective molar ratios of FH/BP/BF of 0/100/100–10/90/100 and 80/20/100–100/0/100 were semi‐crystalline without liquid crystalline properties, and amorphous polymers, respectively. In contrast, copolymers with the molar ratio of FH/BP/BF of 20/80/100–70/30/100 had liquid crystalline characteristics. Interestingly, the formation of a highly ordered smectic phase was confirmed for copolymers with the molar ratio of FH/BP/BF of 20/80/100–50/50/100, respectively. All the liquid crystalline copolymers had a wide liquid crystalline temperature range (57–75 °C).