Thermal degradation of poly(ethyleneglycol)

The thermal degradation of poly(ethyleneglycol) (PEG) with an average molecular weight of 4000 has been investigated from the point of view of developing PEG as a phase change material in thermal energy storage. The PEG was maintained at 80 °C for 1000 h in air and in vacuo. It was severely degraded in air; the melting point and heat of fusion were reduced by as much as 13 °C and 32 kJ/kg, respectively. In vacuo, however, almost no degradation was observed. Both the fresh and degraded PEG samples were examined by thermal and spectroscopic methods. The results suggest that the thermal degradation of PEG in air follows a random chain scission oxidation mechanism. This was confirmed by adding an antioxidant which successfully suppressed the degradation.