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

Abstract

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 π-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 13C 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.

Coordinative Chain Transfer and Chain Shuttling Polymerization

“…The above-mentioned strategy was later extended to 1,3-butadiene using the in situ formed π- allyl nickel trifluoroacetate catalyst 38b, as represented in Scheme 25. 37 It was proposed that the Ni catalyst can play both roles, i.e., CCTP and displacement catalysis. Consequently, a significant amount of macromonomer is formed, a part of which is reinserted into the growing polybutadiene chain, leading to branched polybutadiene in a one-pot process.…”

“…The above-mentioned strategy was later extended to 1,3-butadiene using the in situ formed π-allyl nickel trifluoroacetate catalyst 38b , as represented in Scheme . It was proposed that the Ni catalyst can play both roles, i.e., CCTP and displacement catalysis.…”

“…36 In situ formed π-allyl nickel trifluoroacetate complex (38b, Figure 11 and Scheme 25) allowed 1,3-butadiene CCTP in the presence of magnesium and aluminum alkyls, leading to the formation of branched polybutadiene (see chapter 2.6.1.2). 37 Stereoregular polyisoprenes containing ∼ 96% of 1,4-cis units were synthesized by various neodymium chloride hydroxyquinolines (24, Figure 7) in good yields. 38 Polymerizations were activated by i-Bu 3 Al and MAO, while MAO offered only negligible activity in standard polymerization conditions (50 °C, hexane, Al/Nd = 40).…”

Recent Advances in Controlled Production of Long‐Chain Branched Polyolefins

“…In another recent study, Zinck et al applied the same approach for the polymerization of a conjugated diene monomer and reported on the one-pot synthesis of branched polybutadiene. [97] They used an 𝜋-allyl nickel(II) (TFA) catalyst resulting from Ni(COD) 2 and trifluoroacetic acid, which functions simultaneously as the polymerization and the displacement catalysts along with AlEt 3 or Mg n BuEt as the CTA. The initiation of the chain transfer occurs via 𝛽-hydride elimination of the Ni-alkyl moieties and/or transfer to the monomer, which leads to the growth of additional chains.…”

“…Bimetallic catalysts PE [78] Tree-like Need for novel catalyst design Tandem CCTP PE [94,96] Poly(1-hexene) [ 93] Polybutadiene [ 97] LLDPE [98] Tree-like Incompatibility of catalyst components toward in situ chemical methods. Significant progress ensued by single, tandem, and bimetallic catalytic systems operating under controlled conditions.…”