CHARACTERIZATION OF POLYPROPYLENE PEROXIDES - THEIR THERMOOXIDATIVE STABILITY AND REACTIVITY TOWARDS DIMETHYLSULFIDE

Exposure to dimethylsulfide (DMS) has previously been presented as a t ool to distinguish between different types of polypropylene (PP) perox ides. The reasons for the differences in peroxide reactivity towards D MS are investigated for PP peroxides. This was accomplished using iodo metry, infrared spectroscopy, measurements of total emitted chemilumin escence, chemiluminescence imaging and measurements of glass transitio n and melting temperatures. On the basis of our results, we propose th at 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 ac tion of protic species. An increase in glass transition temperature du ring oxidation was observed, which indicates an increasingly restricte d segmental mobility. Furthermore. changes in concentration of DMS-res istant peroxides during oxidation were found to correlate with the cha nges in glass transition and melting temperatures. Consequently, we pr opose that the segmental mobility in the polymer affects the reactivit y of the isolated peroxides towards DMS. (C) 1996 Elsevier Science Lim ited