"Pulsed" Chain Transfer Anionic Polymerization: A Green and Cost-Effective Approach for Controlled Polymer Synthesis

Herein, we report a method that significantly enhances the atom economy of catalysts in living polymerization. By introducing intermittent, switchable chain-transfer reactions during the polymerization process, multiple regenerations of the catalyst are achieved while preserving the "living"/controlled characteristics. The specially designed catalytic system, composed of 1,2-dipyrrolidinoethane/n-butyllithium/n-butylpotassium/toluene, exhibits a chain-transfer rate that is highly sensitive to temperature. It enables living polymerization at low temperatures, while at high temperatures, rapid chain transfer to toluene occurs. Utilizing this characteristic, polymerization is initially carried out at low temperatures; once the monomer is consumed, increasing the temperature promotes chain transfer, resulting in initiator regeneration. The regenerated initiator can then initiate new cycles of living polymerization upon the addition of fresh monomers. This process was repeated for more than a dozen cycles, achieving an initiator efficiency of up to 1500%. Using this method, we successfully synthesized polybutadiene and styrene-butadiene copolymer with an extremely narrow molecular weight distribution (Đ = 1.1). The mechanism was investigated by in situ NMR spectroscopy, MALDI-TOF-MS, and DFT calculations. This approach is particularly well-suited for the controllable, green, and cost-effective production of low- to medium-molecular-weight polymers and block copolymers.