Effect of leaving group in dithiocarbamates on mediating melt radical reaction during preparing long chain branched polypropylene

The effectiveness of dithiocarbamates in mediating melt radical reaction during preparing long chain branched polypropylene (LCB-PP) was studied. 1H NMR, FTIR, GPC-TALLS and rheological measurements were used to characterize the structure of the resultant LCB-PP. The results showed that adding dithiocarbamates could help forming more long chain branches on PP, and furthermore the chemical structure of the leaving group (R) of dithiocarbamates played a key role in adjusting melt reaction of PP in the presence of peroxide and multifunctional monomer. When the R formed a stable radical (compared to PP macroradicals) after leaving from the dithiocarbamate, such as allyl or benzyl radicals, the presence of dithiocarbamates could reduce the chain scission of PP due to the formation of dormant state species. In this case, the polymerization degree of grafted monomer was also reduced comparing with conventional radical polymerization under the same conditions. Thus more multifunctional monomer could react with PP macroradical to form more branching points and then more uniformly distributed LCB structure on the PP backbone. The reaction mechanism was investigated through model reactions.