Acyloxyimide derivatives as efficient promoters of polyolefin C–H functionalization: application in the melt grafting of maleic anhydride onto polyethylene

Abstract

Acyloxyimides as a new H-abstracting agent have been developed for the radical grafting of maleic anhydride (MA) onto polyethylene in the melt state. Their model decomposition in DMSO-d6 as well as in tetradecane that mimics polyolefins was performed. These studies confirmed first the complete decomposition of N-acetoxyphthalimide (NAPI) in 1 hour at 180 °C by a N–O bond dissociation mechanism and also the patching of the produced macroradicals by the phthalimide group. The reaction was then performed in a mini-extruder at 190–250 °C and the hydrogen abstraction ability of N-acyloxyphthalimide (NAP)-, N-acyloxynaphthalimide (NANP)- and N-acyloxysuccinimide (NAS)-based derivatives was demonstrated. Optimal experimental conditions were determined by varying the initial MA content and the degree of grafting of MA was quantified by infrared spectroscopy. The MA grafting degree was as high as 2.98 wt% when using tBu-NAP as the H-abstracting agent at 230 °C with only a slight modification of the PE chain structures as proved by rheological experiments while the use of a peroxide (L101) led to a lower grafting degree (1.9 wt%) and a cross-linking of the polymer chains, confirmed by the three–five fold higher complex viscosity.