Synthesis of Self-Healing Syndiotactic Polyolefins by Rare-Earth Catalysts

3,4-Syndiotactic polymerization of 1-(3-/4-methoxy-phenyl or 3,5-dimethoxy-phenyl)-1,3-butadienes (3-/4-MOPB or 3,5-DMOPB) and living copolymerization with 1-phenyl-1,3-butadiene (PB) can be successfully catalyzed by a series of CGC-type rare-earth metal dialkyl complexes at room temperature, affording 3,4-syndiotactic P(3-/4-MOPB or 3,5-DMOPB)s and random P(3-/4-MOPB-co-PB)s having 3-/4-MOPB contents in the range of 13-89 mol%. The research on the mechanism based on DFT suggests that the large steric hindrance around the metal center of the active species originated from the alternating coordination and insertion of MOPB monomers in two different empty coordination sites, respectively, in both cis-1,4-si- and cis-1,4-re-modes as well as the presence of the back-donation coordination of both the anti-η³-π-allyl groups of the two last inserted MOPB units in the polymer chain might be the reason for complete 3,4-syndioselectivity. Significantly, the hydrogenated 3,4-syndiotactic P(3-MOPB)s and P(3-MOPB-co-PB)s exhibit self-healing properties, which is ascribed to the enhanced cohesive energy density and the removal of surface tensions by van der Waals forces through the dipole-dipole interactions of 3-position methoxy substituents of the pendent phenyl groups of adjacent polymer chains to form a “lock key” binding or interdigitated structure.