From quantum mechanics to viscoelasticity: A multiscale modeling and characterization of radical initiated modification of polyolefin in molten state

Multiscale approaches for peroxide-initiated grafting of vinyl silane monomers to polyolefins have been investigated with the intention of the development of a mechanistic model for the synthesis of functional copolymers by melt phase processing. A comprehensive mechanistic view of the complex radical mediated reactions is achieved by determining the reaction kinetics through both quantum theory and model compound study. Our results clearly show that the overall mechanism is dominated by grafting single monomer of vinyl silane to hydrocarbon substrates, rather than forming localized or homopolymer grafts, and this occurs at the expense of polymer crosslinking due to the termination of radicals via combination. A fundamental kinetic model is therefore established to depict the general chemistry involving all the critical reactions in modification of molten polymer and their relationships to processing conditions. Combined Fourier transformation infrared spectroscopy with gel permeation chromatography, the further implement of this kinetic model to our recently-developed topology-based viscoelastic model allows, for the first time, to estimate both the yield of graft content and the change of rheological properties during the synthesis of polyolefin graft copolymer in molten state.