Identification of a Transient but Key Motif in the Living Coordinative Chain Transfer Cyclocopolymerization of Ethylene with Butadiene

Copolymers of ethylene and butadiene were prepared using the ansa-bisfluorenyl complex Me2Si-(C1(3)H(8))(2)NdR in combination with dialkylmagnesium as a chain transfer agent. Thorough kinetic studies and computational mechanistic investigations of this copolymerization reaction were performed. In combination with detailed analyses of the polymer microstructure and chain ends, these studies demonstrate that the title copolymerization operates according to a living coordinative chain transfer copolymerization of ethylene and butadiene. In addition to the formation of the previously described 1,2-cyclohexane inner chain cyclic motif, the presence of bicyclic 1,5-decalin units via the formation of transient (vinylcyclohexyl)methyl chain ends is discussed in the present communication. The nonaccumulation of the vinylcyclohexane motif within the chains is explained by the reversibility of its formation, as interpreted with the help of DFT calculations, or by its rapid conversion into decalin motif after one ethylene insertion. Finally, this study also illustrates the ability of the fluorenyl ligand to adjust its binding mode on demand in order to avoid inhibition of the catalyst.