A comparative study on the thermo-oxidative degradation of poly(ether-esters)

A comparison is made between the thermo-oxidative degradation processes in two copolymers of polybutylene terephthalate, one containing polyethylene oxide (PBT/PEO) and the other polybutylene oxide (PBT/PBO), in an oxygen atmosphere at 140 degreesC. The degradation processes were followed by monitoring the oxygen uptake and CO/CO2 formation during degradation and characterizing the degraded samples by GC-MS, FTIR and IH-NMR techniques. The formation of peroxides was measured titrimetrically. The presence of carboxylic acids and alcohols was detected by chemical treatment with SF4 and NO, respectively. In order to gain more insight into the mechanism of the degradation, model compounds of each of these copolymers were used, namely diethyleneglycol dibenzoate (DEGDB) and dibutyleneglycol dibenzoate (DBGDB). The results are explained in terms of the initiation of oxidation at the methylene carbon vicinal to the oxygen ether, leading to the formation of new ester linkages. Simultaneously carbon-carbon and carbon-oxygen bond cleavage occurs, leading to aliphatic and aromatic carboxylic acids, formates and alcohols. (C) 2001 Elsevier Science Ltd. All rights reserved.