Liquid-crystalline polyethers based on conformational isomerism: 12. Molecular engineering of phase transitions in copolyethers based on 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane and multiple combinations of flexible spacers

Abstract

This paper describes the synthesis and characterization of copolyethers based on 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane (MBPE) and various combinations of from three to eight α,ω-dibromoalkanes. Copolymers containing spacers with an odd number of methylene units display a uniaxial nematic mesophase and a second unidentified mesophase. Copolymers containing spacers with odd and even or only even numbers of methylene units display a uniaxial nematic mesophase. The parameters of the mesomorphic phase transitions of all copolymers represent weight-averaged values of the corresponding parameters of the parent homopolymers. This proves that the structural units of these copolymers are isomorphic within their mesophase. These results also demonstrate that the parameters of the mesomorphic phases can be engineered by copolymerization. All MBPE copolymers are crystallizable. Their crystallizability decreases by increasing the number of flexible spacers and decreasing their length, and by using an odd rather than an even number of methylenic units in the spacer.