Synthesis and thermal behavior of polyesters derived from 1,3-propanediol and various aromatic dicarboxylic acids

Seven aromatic dicarboxylic acids were esterified by melt polycondensation in two steps with 1,3-propanediol (1,3-PDO) in the presence of tetrabutoxytitanium as catalyst. The acids used were: terephthalic (TPA), isophthalic (IPA), naphthalene-2,6-dicarboxylic (2,6-NDA), naphthalene-1,4-dicarboxylic (1,4-NDA), biphenyl-4,4'-dicarboxylic (4,4'-BPDA), diphenylsulfone-4,4'-dicarboxylic (4,4'-DPSDA), and pyridine-2,6-dicarboxylic acid (2,6-PDA). In the first step, the esterification reaction was monitored, by measuring the distilled water. The prepared oligomers were polycondensated in a second step under high vacuum using the same catalyst as before. The received poly(propylene dicarboxylate)s were characterized by viscometry, carboxyl end-group content (CC), color measurement, and were studied by differential scanning calorimetry (DSC). From this study, the above polyesters could be classified to three classes: (a) easily crystallizing polyesters derived from TPA and 2,6-PDA, (b) slow crystallizing polyesters derived from IPA and 2,6-NDA, and (c) amorphous polyesters derived from 1,4-NDA, 4,4'-BPDA, and 4,4'-DPSDA.