Origin of different chain-end microstructures in ethylene/vinyl halide copolymerization catalysed by phosphine–sulfonate palladium complexes

Abstract

Ethylene and vinyl halide (VX, X = F or Cl) copolymerization mechanism in the presence of catalysts A ((PO^OMe,OMe)PdMe, PO^OMe,OMe = {2(2-MeOC₆H₄)(2-SO₃-5-MeC₆H₃)P}) and A′ ((PO^Bp,OMe)PdMe, PO^Bp,OMe = {(2-MeOC₆H₄)(2-{2,6-(MeO)₂C₆H₃}C₆H₄)(2-SO₃-5-MeC₆H₃)P}) has been comparatively studied via density functional theory (DFT) calculations. The origin of different chain-end microstructures produced by A and A′ and the discrepancy due to VX insertion into Pd–X (X = F and Cl) species are disclosed. It is found that β-F elimination does not result in catalytic deactivation. –CH₂–CHF₂ as a major copolymer unit generated from catalyst A′ was mainly ascribed to a more positive charge of metal Pd assisting the β-F elimination and stronger H⋯OMe and C–H⋯π interactions. However, in the catalysis with A′, the same chain-end unit –CH₂–CHCl₂ was difficult to be generated with a high energy barrier and an apparent endergonic character, which was mainly attributed to the strong Pd–Cl bond and the higher tendency for the reversible β-Cl elimination.