Abstract
In addition to the homopolyesters, poly(4-hydroxybenzoate) and poly(4-phenylene terephthalate), two series of copolyesters have been prepared with a systematic variation of the molar ratio. The first series was prepared by polycondensation of 4-acetoxybenzoic acid, terephthalic acid and acetylated hydroquinone in a liquid inert reaction medium at 400 °C. The second series was prepared under the same reaction conditions but from silylated 4-acetoxybenzoic acid and silylated terephthalic acid and showed a considerably higher 4-hydroxybenzoate/terephthalate ratio than expected from the feed ratio. The composition of these copolyesters was checked by 1H NMR spectroscopy after hydrolysis. All copolyesters proved to be highly crystalline regardless of the molar composition. WAXS measurements were conducted with synchrotron radiation up to 450 °C. These WAXS patterns indicate a gradual phase transition between 150 and 300 °C which is not detectable in the DSC curves. For the copolyesters containing > 50 mol% or 4-Hybe (4-hydrobenzoic acid) units one or two reversible first-order phase transitions were found in the DSC traces. Electron microscopy revealed that all these copolyesters are crystal powders consisting of particles of irregular shape. However, copolycondensations of silylated 4-acetoxybenzoic acid with silylated terephthalic acid and acetylated hydroquinone yielded copolyesters with a ‘potato-chip morphology’.
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