Studies on sequence distribution of aliphatic/aromatic copolyesters by high-resolution C-13 nuclear magnetic resonance spectroscopy for evaluation of biodegradability

Copolyesters with different stoichiometric compositions, obtained from 1,4-butanediol, adipic acid, and terephthalic acid by molten-state polycondensation, are studied by means of high resolution C-13 NMR spectroscopy with respect to copolymer composition and block length distribution. The ratio of aliphatic and aromatic dicarboxylic acids in the polymer, which sensitively influences the biodegradability of the polymers, reflects the initial monomer composition during polycondensation. This indicates that under the conditions applied for polycondensation no loss for example of terephthalic acid due to sublimation occurs. It was found that the aliphatic and aromatic repeating units are randomly distributed within the polymer chain. The experimentally determined average sequence length distribution dependence on stoichiometric copolymer compositions are in accord with ideal polycondensation statistics. In combination with the results of the degradability of aromatic oligomers, predictions about the degradation characteristics of the aliphatic/aromatic copolymers can be made.