Liquid‐crystalline polyethers and copolyethers based on conformational isomerism, 4. Thermotropic polyethers and copolyethers based on 1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane and flexible spacers containing an even number of methylene units

Abstract

AbstractThe synthesis and characterization of thermotropic main‐chain liquid‐crystalline polyethers MBPE‐X and copolyethers MBPE‐X/Y based on 3‐methyl‐4,4′‐ethylenediphenol [1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane (MBPE)], which is flexible rod‐like mesogenic unit or a rod‐like mesogenic unit based on conformational isomerism, and flexible spacers containing an even number of methylene units, X, Y, are described. The particular examples presented in this paper refer to polyethers MBPE‐4, MBPE‐6, MBPE‐8, MBPE‐10, and MBPE‐12, and copolyethers MBPE‐X/Y; where X,Y = 4, 6, 8, 10, 12. MBPE‐4, MBPE‐6, MBPE‐10 and MBPE‐12 are crystalline. MBPE‐8 displays an enantiotropic nematic mesophase. Copolymerization of MBPE with different pairs of spacers containing even numbers of methylene units leads to MBPE‐X/Y copolymers displaying monotropic or enantiotropic nematic mesophases. Both liquid‐crystalline transition temperatures and the corresponding enthalpy changes of the copolymers represent weight‐averaged values of the similar parameters of the parent homopolymers. Extrapolation of the isotropic‐nematic and nematic‐isotropic transition temperatures and their corresponding enthalpy changes demonstrated that all homopolymers containing an even number of methylene units in the flexible spacer exhibit virtual nematic mesophases. The virtual isotropic‐nematic transition temperatures and the corresponding enthalpy changes were determined for MBPE‐4, MBPE‐6, MBPE‐10 and MBPE‐12. The virtual nematic‐isotropic transition and the corresponding enthalpy changes could be determined only for MBPE‐10 and MBPE‐12.