Study on the influence of metal residue on thermal degradation of poly(cyclohexene carbonate)

Poly(cyclohexene carbonate) (PCHC) is an alternative copolymer of carbon dioxide and cyclohexene oxide. Severe thermal decomposition occurs during melt processing of PCHC, thus, it is important to find the reason for thermal decomposition and raise its thermal stability. In this report, as-polymerized PCHC was obtained under Y(CCl₃COO)₃-ZnEt₂-glycerin rare earth coordination ternary catalyst. The pyrolysis gas chromatography with mass spectrometry analysis disclosed that chain unzipping depolymerization dominated the thermal decomposition process. The residue metal (mainly ZnO in this catalyst system) was important in PCHC degradation, and the onset decomposition temperature of PCHC containing 5 ppm zinc was 56 °C higher than that of PCHC containing 4,400 ppm Zn, corresponding to apparent activation energy change from 190 KJ/mol to 146 KJ/mol. When PCHC was subjected to melt processing, its average molecular weight decreased more rapidly, as it contained more catalyst residue, indicating metal residue in PCHC could accelerate the decomposition process, and removing the metal residue should be effective in raising its thermal stability.