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 o xide (PBT/PEO) and the other polybutylene oxide (PBT/PBO), in an oxygen atm osphere at 140 degreesC. The degradation processes were followed by monitor ing the oxygen uptake and CO/CO2 formation during degradation and character izing the degraded samples by GC-MS, FTIR and IH-NMR techniques. The format ion of peroxides was measured titrimetrically. The presence of carboxylic a cids and alcohols was detected by chemical treatment with SF4 and NO, respe ctively. In order to gain more insight into the mechanism of the degradatio n, model compounds of each of these copolymers were used, namely diethylene glycol dibenzoate (DEGDB) and dibutyleneglycol dibenzoate (DBGDB). The resu lts 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 l inkages. Simultaneously carbon-carbon and carbon-oxygen bond cleavage occur s, leading to aliphatic and aromatic carboxylic acids, formates and alcohol s. (C) 2001 Elsevier Science Ltd. All rights reserved.