SYNTHESIS AND CHARACTERIZATION OF COPOLYESTERS BASED ON POLY(TETRAMETHYLENE TEREPHTHALATE) AND P-HYDROXYBENZOIC ACID

Copolyesters of poly(tetramethylene terephthalate) (PTMT) and p-hydrox ybenzoic acid (PHB) are obtained by means of transesterification in th e molten state using different ratios of the starting reagents. After treatment with trifluoroacetic acid, the total reaction product could be divided into a soluble part and an insoluble one, differing in the tetramethylene terephthalate/oxybenzoate (TMT/OB) units ratio. It was proved by H-1 NMR that the fraction of OB units in the soluble part of the copolyester varies from 3 to 12 mol-% for PHB feed contents of 10 - 80 mol-%. There is no systematic influence of the PHB feed content on the copolyester composition. The maximum OB content was achieved at 20 mol-% PHB in the starting mixture. The results from C-13 NMR, DSC, WAXS and crystallization kinetics measurements suggest the presence o f blocks of TMT units in the macrochains. The observed thermal propert ies and crystalline structure are explained in terms of the inhomogene ity of both chemical composition and units sequence in the total react ion products. This leads to the coexistence of at least two phases dif fering mainly in their content of OB units.