Calcium–Lithium Systems as Innovative Bimetallic Initiators for the Anionic Polymerization of Butadiene: Toward Control and High 1,4-trans Microstructure

Polybutadiene architecture and microstructure are key parameters for the mechanical and viscoelastic properties of rubber materials. The versatility of anionic polymerization can supply a variety of polymers with different architectures and chain end functionalization, but few reports show the ability to increase 1,4-trans units of polybutadiene. Herein, we report the first controlled anionic polymerization of butadiene using an innovative bimetallic Ca:Li initiator. [(THF)2Ca(HMDS)2]:[n-BuLi] in situ prepared allowed the polymerization of butadiene in apolar medium, with the control of molar masses, a low dispersity (below 1.2), a living character, and the modulation of 1,4-trans units between 55 and 80% while maintaining a low vinyl content (below 10%). The influence of the [Ca]/[Li] ratio on the polybutadiene microstructure, kinetics, control, and living character of the polymerization are investigated and discussed.