Characterisation of polypropylene peroxides; Their thermo-oxidative stability and reactivity towards dimethylsulfide

Exposure to dimethylsulfide (DMS) has previously been presented as a tool to distinguish between different types of polypropylene (PP) peroxides. The reasons for the differences in peroxide reactivity towards DMS are investigated for PP peroxides. This was accomplished using iodometry, infrared spectroscopy, measurements of total emitted chemiluminescence, chemiluminescence imaging and measurements of glass transition and melting temperatures. On the basis of our results, we propose that DMS reacts preferentially with peroxides which are adjacent to each other, rather than with isolated peroxides. The higher reactivity of adjacent peroxides towards DMS is believed to be due to a catalytic action of protic species. An increase in glass transition temperature during oxidation was observed, which indicates an increasingly restricted segmental mobility. Furthermore. changes in concentration of DMS-resistant peroxides during oxidation were found to correlate with the changes in glass transition and melting temperatures. Consequently, we propose that the segmental mobility in the polymer affects the reactivity of the isolated peroxides towards DMS. (C) 1996 Elsevier Science Limited