An investigation on chain transfer to monomers and initiators, termination of radicals in EVA copolymerization process based on DFT and microkinetic simulation

Abstract

Chain transfer and termination in copolymerization between ethylene and vinyl acetate (VAc) were investigated with DFT method. Chain transfer becomes more active in copolymerization than homopolymerization due to an incorporation between low propagation reactivity of alkyl radical and high chain transfer reactivity of VAc. Competition between combination and disproportionation were detailed for self-termination and cross-termination, and most radical chains terminate through combination. Combination involving alkyl radical or tail radical shows much lower energy barrier than combination involving head radical. Effect of head-to-head defect on termination and chain transfer is also clarified. Chain transfer to initiators and termination of primary radicals were studied for BPO and AIBN. The both, especially AIBN, shows reactivity in direct addition of radicals to initiators, which is revealed by this work at first time. Based on kinetics from DFT, a microkinetic simulation was conducted to extend the research from electron scale to micro scale. Relationship between copolymerization conditions (including temperature, monomer composition and concentration, and initiator concentration) and rates of elemental reactions, radical concentrations, DP and PDI was discussed.