Quantum Chemistry Study On The Mechanism Of Short Chain Branching In HPPE

ABSTRACT The mechanism of short chain branching in ethylene high-pressure free-radical polymerization has been studied using density functional theory (DFT) and ab initio methods at B3LYP/6-31G (d) and HF/6-31G(d) levels respectively. The geometries of the reactants, transition structures and products have been optimized, the transition structures have been verified by frequency analysis and the IRC calculation. The reaction barriers were also evaluated at the same levels. The results show that the reaction proceeds via backbiting. The reaction barriers of three-carbon, six-carbon , four-carbon , two-carbon-, five-carbon chain branching reactions calculated at B3LYP/6-31G (d) level are 84.82, 66.94, 48.49, 44.54, 34.69 kJ/mol, while the relative results calculated at HF/6-31G (d) level show the same regulation that is Ea(C-3)> Ea(C-6) Ea(C-4)> Ea(C-2)> Ea(C-5). The calculated results are in good agreement with the actual production observed results. The results also demonstrate that all the reactions are exothermic reactions.