Control of degradation of Polypropylene during the radical functionalization with furan and thiophene derivatives

The traditional melt radical functionalisation of isotactic polypropylene (iPP) with maleic anhydride (MAH)
and peroxide affords functionalized samples with a severe decrease of the average molecular weight (MW)
due to the b-scission reaction. In this work new push-pull unsaturated molecules were investigated,
consisting of a heterocyclic ring conjugated with a double bond bearing an electron attracting group. These
molecules were specifically designed as MAH substitute able to limit the iPP degradation, while providing
functionalisation through grafting. Butyl 3-(2-furanyl) propenoate (BFA) and butyl 3-(2-thienyl) propenoate
(BTA) were comparatively tested. The analysis of the reaction products indicated that both molecules
are able to graft onto the iPP backbone by prompt reaction with the macro-radicals formed through
H-abstraction from iPP chains, thereby significantly limiting theMWdecrease, as the functionalized macroradicals
are stabilized by resonance. Nonetheless, some of iPP macro-radicals can give a parallel chain
scission before reacting with the newmolecules. In the case of BFA, coupling reactions of the formed macroradicals
can lead to the formation of branched highMWarchitectures, whereas in the case of the thiophene
derivative (BTA) only a partial retaining of polymer chain fragmentationwas observed due to the reduction
of b-scission