Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Copolyesters of terephthalic acid, p-hydroxybenzoic acid and ethylene glycol were prepared by high-temperature melt polycondensation, starting from different hydroxybenzoic acid derivatives. Methyl p-hydroxybenzoate monomers having the hydroxyl either free, etherified with ethylene glycol or esterified with terephthalic acid were used. The chemical structure of the copolyesters obtained was characterized by means of 13C NMR spectroscopy, and chemical shifts were assigned to the respective carbons. The investigation clearly indicates that oxybenzoate units are quantitatively present in the polymer as etherified (on the hydroxyl group) and esterified (on the carboxylic group) with ethylene glycol. Similar analyses were performed on intermediate products formed after the transesterification stage. They point out that at this stage the hydroxyl group is free when starting from methyl p-hydroxybenzoate, while a noticeable amount of ether is already present when starting from the monomer esterified with terephthalic acid. A reaction scheme encompassing these results and based on the competition between esterification and etherification process of the phenolic hydroxyl is put forward.
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