Coordinative Chain Transfer Polymerization of Butadiene Using Nickel(II) Allyl Systems: A Straightforward Route to Branched Polybutadiene

Nickel allyl complexes are catalysts for the 1,4-regioselective polymerization of butadiene (BD). Coordinative chain transfer polymerization (CCTP) was not yet assessed by using these systems. We report in this work the polymerization of butadiene in the presence of pi-allyl Nickel(II) trifluoroacetate (TFA) and MgnBuEt or AlEt3 as chain transfer agent (CTA) case studies. The reaction follows a first-order kinetic versus the monomer. Chain transfer is evidenced in the presence of CTAs, together with the formation of polybutadiene bearing a conjugated diene moiety. This allows one-pot access to branched polybutadiene by reinsertion of the chains. The branching is quantitatively analyzed by C-13 NMR after hydrogenation of the polybutadiene, and its impact on the thermal properties of the hydrogenated samples is assessed, in particular for low degrees of branching that cannot be quantitatively determined. A full description of the catalytic cycle is tentatively provided. If similar tandem processes were described in the literature in the course of the polymerization of ethylene, it is, as far as we know, the only system reported so far for a conjugated diene leading to branched polybutadiene thus extending the range of application of CCTP processes.