Abstract
New chemistry for grafting maleic anhydride (MAn) and N-aryl maleimides to a propylene homopolymer is described. Whereas conventional peroxide-initiated maleations are accompanied by extensive degradation, formulations containing a small amount of 4-vinyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (VETEMPO) can meet graft content targets while minimizing melt viscosity losses. The first stage of a VETEMPO-mediated process involves alkyl radical trapping by nitroxyl to yield polymer-bound alkoxyamines bearing pendant vinyl ether functionality. Subsequently, copolymerization between vinyl ether and MAn builds polymer molecular weight while offsetting the degradation incurred by the standard MAn grafting mechanism. The result is a lightly branched, maleated product with a melt viscosity close to that of the starting material. This VETEMPO-based copolymerization strategy is adapted to generate thermoset PP derivatives by peroxide-initiated reactions of VETEMPO with an appropriate difunctional monomer such as N,N′-1,3-phenylene dimaleimide (PDM).
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