Abstract
A series of copolyesters were prepared from p-hydroxybenzoic acid (HBA), hydroquinone (HQ), terephthalic acid (TPA) and poly(ethylene terephthalate) (PET) by an acidolysis reaction and subsequent polycondensation. On the basis of viscosity measurements, these copolyesters have the same level of intrinsic viscosity as the original PET, and 1H-NMR analyses indicated the total insertion of comonomers. They exhibit a nematic phase above melting temperature, as observed by polarized light microscopy. Their crystallization and melting behavior were studied with differential scanning calorimetry and wide angle X-ray diffraction. It was found that these copolyesters are more crystalline than poly[(p-hydroxybenzoic acid)-co-(ethylene terephthalate)] (PET/HBA). Introduction of HQ/TPA disrupts longer rigid-rod sequences formed by HBA, and thus enhances molecular motion and increases crystallization rate and crystallinity. Isothermal crystallization under solid phase polymerization conditions (up to 24 hours at 200°C) resulted in increased randomness of the copolymer (by 1H-NMR) and increased melting point and crystallinity, the latter attributed to structural annealing.
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