SCHEDULED MAINTENANCE
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 ((POOMe,OMe)PdMe, POOMe,OMe = {2(2-MeOC6H4)(2-SO3-5-MeC6H3)P}) and A′ ((POBp,OMe)PdMe, POBp,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.
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