Synthesis and liquid crystalline properties of thermotropic homo- and copolycarbonates

Nondirect-type thermotropic homo- and copolycarbonates which have flexible spacers between mesogens and carbonate linkages (-mesogenic unit-flexible spacer-carbonate link-flexible spacer-) were derived from dihydroxyalkyleneoxy derivatives containing biphenyl, i.e., 4,4′-bis (ω-hydroxyalkyleneoxy)biphenyl (Ia and Ib), as mesogens and the structure-liquid crystallinity relationships were evaluated by thermal analysis and with polarizing microscope. Homopolycarbonates with high molecular weight were prepared from (Ia) and (Ib), and alkylene diphenyl dicarbonates (II) by melt polycondensation. The polymers form mesomorphic phases and exhibit linear decrease of phase-transition temperatures with increment of alkylene spacer lengths without displaying odd-even number fluctuations. They show lower phase-transition temperatures and narrower mesomorphic temperature ranges than analogous direct-type (-mesogenic unit-functional group-flexible spacer-) biphenyl-containing polycarbonates documentclass{article}pagestyle{empty}begin{document}$ rlap{--} ({rm OMOC}({rm O}){rm O}({rm CH}_2)_m {rm OC}({rm O})rlap{--})_x $end{document} and polyesters documentclass{article}pagestyle{empty}begin{document}$ rlap{--} ({rm OMOC}({rm O})({rm CH}_2)_m {rm C}({rm O})rlap{--})_x $end{document}, but have wider temperature ranges than nondirect-type (-mesogenic unit-flexible spacer-functional group-flexible spacer-) biphenyl-containing polyesters documentclass{article}pagestyle{empty}begin{document}$ rlap{--} ({rm O}({rm CH}_2)_n {rm OMO}({rm CH}_2)_n {rm OC}({rm O})({rm CH}_2)_m {rm C}({rm O})rlap{--})_x $end{document}. These results indicate that by the incorporation of alkylene segments between mesogens and carbonate linkages the polymers having reasonable phase-transition temperatures and wider mesophasic temperature ranges can be obtained. Copolycarbonates were prepared from mixtures of (Ib) and 1,4-bis(2-hydroxyethyleneoxy)benzene (IV), nonmesogenic moiety, taken in definite molar ratio in feed and (II) (m = 2 and 4). These copolymers except polymers having only nonmesogenic moiety show liquid crystalline mesophases and have wider phase-transition temperature ranges than the homopolymers. Maximum temperature ranges are observed in the copolymers of composition ratio of 1 : 1. Stable mesophases can be obtained over the entire range of compositions, even though the copolymers contain nonmesogenic units in the backbones.