Mesogenic random copolymers. II. Copolymers with one flexible and two rigid segments

Abstract

AbstractWe have investigated copolyesters based on a single aliphatic dibasic acid flexible segment and two rigid segments arising from 4,4′‐dihydroxybiphenyl (PB) and 2,6‐dihydroxynaphthalene (PN). Homopolyesters based on the latter rigid segment exhibit no enantiotropic mesophase for 5 ≤ n ≤ 8. The copolymers are designated PBN‐n where n is the number of methylene units in the dibasic acid. From the temperature–composition phase diagram, the odd‐membered PBN‐5 and PBN‐7 exhibit only a nematic phase. The temperature range of the nematic phase decreases progressively with increasing mole fraction of naphthalene units. The even‐membered PBN‐6 and PBN‐8 exhibit a smectic SH mesophase and a newly induced nematic phase. Comparison with a previous study of copolymers involving a single rigid segment and two flexible segments reveals that the smectic SH phase is more easily disrupted, and converted to a less ordered nematic phase, by different rigid segments than by different flexible segments. The isotropization entropy of a series of nematogenic equimolar copolymers exhibits a marked odd–even effect, with the observed ΔSNI values being quite large for the even‐membered copolymers.