Deciphering the Mechanism of Coordinative Chain Transfer Polymerization of Ethylene Using Neodymocene Catalysts and Dialkylmagnesium

Ethylene polymerizations were performed in toluene using the neodymocene complex (C5Me5)(2)NdCl2Li(OEt2)(2) or {(Me2Si(C13H8)(2))Nd(mu-BH4)[(mu-BH4)Li(THF)]}(2) in combination with n-butyl-n-octylmagnesium used as both alkylating and chain transfer agent. The kinetics were followed for various [Mg]/[Nd] ratios, at different polymerization temperatures, with or without ether as a cosolvent. These systems allowed us to (i) efficiently obtain narrowly distributed and targeted molar masses, (ii) characterize three phases during the course of polymerization, (iii) estimate the propagation activation energy (17 kcal mol(-1)), (iv) identify the parameters that control chain transfer, and (v) demonstrate enhanced polymerization rates and molar mass distribution control in the presence of ether as cosolvent. This experimental set of data is supported by a computational investigation at the DFT level that rationalizes the chain transfer mechanism and the specific microsolvation effects in the presence of cosolvents at the molecular scale. This joint experimental/computational investigation offers the basis for further catalyst developments in the field of coordinative chain transfer polymerization (CCTP).