Morphology of thermotropic polyesters with azoxybenzene moiety examined by optical microscopy.

Abstract

ABSTRACT:Morphological observation of the texture of thermotropic polyester, poly(4,4'-dioxy-2,2'-dimethylazoxy benzene alkanedioyl) has been performed by using a polarized microscope equiped with a hot stage. The observation showed that the oily streak texture of the nematic phase changes dramatically in the nematic-isotropic biphasic region.Thermotropic liquid crystalline polymers have been intensively studied from both theoretical and practical points of view. Blumstein et al.(1-4) described the synthesis and thermal properties of main-chain nematic polyesters of poly(4,4'-dioxy-2,2'-dimethylazoxybenzene alkanedioyl). The polymer consists of a regular sequence of rigid azoxybenzene mesogenic core (mesogen 9) and flexible alkanedioate "spacer" group as shown below.The polyesters show a remarkable odd-even effect in both transition temperature and entropy of nematic (N) -isotropic (1) transition (2). Such polyesters are characterized by random coil conformation and high flexibility in the melt well above the isotropisation temperature. On cooling from the melt, the polymer can transit through a nematic mesophase before crystallizing or vitrification. In this paper, we present preliminary results on the temperature dependence of morphological texture of the thermotropic polyesters by polarizing microscopy.The synthesis and properties of the thermotropic polyesters were described elsewhere (2-4). The num ber-average molecular weights M" of DDA-9 and AZA-9 were 20,000 and 36,000, respectively. The