Molecular Order, Phase Transitions and Chain Mobility in Liquid Crystalline Copolyesters

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Abstract
Poly (ethylene naphthalene-2,6-dicarboxylate) (PEN) and copolyesters of PEN and p-hydroxybenzoic acid (PHB) containing different amounts of PHB ranging from 10 to 90 mole-% were synthesized and studied by wide angle X-ray scattering employing synchrotron radiation, by DSC and microscopically. The copolyesters form liquid crystalline states if their content of PHB exceeds 30 %. In the materials containing up to 50 % PHB, crystals of PEN are formed, in those containing 80 and 90 % PHB, crystals of poly-PHB are found. The influence of the PHB content on the melting point and on the kinetics of crystallization is investigated. In addition, copolyesters of poly(ethylene terephthalate) (PET) and different amounts of PHB were synthesized. By means of deuteron NMR it has been found, that the PHB groups decrease the mobility of the PET groups considerably. Small angle neutron scattering experiments show that in the liquid crystalline state, the molecules are far away from being extended.