Mechanism of Janus Polymerization: A DFT Study

Janus polymerization is featured as a combination of cationic and anionic growing ends in one living polymer chain. In the copolymerization of THF and CL catalyzed by lutetium triflates and initiated by propylene oxide, three stages are identified by kinetic study including (1) fast cationic polymerization with slow anionic one, (2) fast anionic polymerization with dormant cationic one, and (3) reactivation of cationic polymerization with coupling of anionic and cationic chain ends. In this work, density functional theory (DFT) calculation is employed to investigate the reaction details of ionic polymerization and dormancy. A "tripedal crow" configuration is proposed to illustrate the unique high-coordinated ligand exchange configuration in anionic polymerization in different stages. The trigger of dormancy is determined as chain structures rather than concentration of triflate anion according to both calculation and experimental results.