Liquid Crystalline Polyethers and Copolyethers of 4-Hydroxyacetophenone Azine with a Homologous Series of Flexible Methylene Spacers
The synthesis of high-molecular-weight polyethers and copolyethers based on 4-hydroxyacetophenone azine and α,ω-dibromoalkanes was carried out in N-methyl-2-pyrrolidone via Williamson etherification using the caesium salt of the diol. Polyethers were composed of a homologous series of flexible methylene spacers with m = 5−12, while the copolyethers contained a 1:1 mole ratio of two different spacers with m = 5/7, 6/8, 7/9, 8/10, 9/11 and 10/12. Polymers with relatively short spacers (m = 5−8 methylene groups) exhibit enantiotropic mesomorphism, whereas those having m = 8−11 are tentatively identified to be monotropic. The polyether with m = 12 is crystalline. Copolyethers are enantiotropic and their mesophase ranges are considerably wider than those of the homopolyethers. The mesophases were identified to be nematic by polarised light microscopy. The transition temperatures of both the homopolymers and copolymers show classical even-odd variations as a function of the spacer length.