Syndiotactic (Co)polymerization of 4-Vinylbenzocyclobutene Catalyzed by Rare-Earth Metal Complex

Recent years have witnessed great achievements in the coordination polymerization of various olefins catalyzed by rare-earth metal catalysts. However, the ubiquitous monomers containing a benzocyclobutene (BCB) group, which have excellent thermal properties, remain unexplored yet. Here, we report the coordination (co)polymerization of 4-vinylbenzocyclobutene (4-VBCB) by using tetraphenylcyclopentadienyl supported scandium alkyl complex [(Cp^Ph4H)Sc(CH₂SiMe₃)₂(THF)] (1) as a precatalyst. The high syndioselectivity (rrrr > 99%) was observed in both the resultant poly(4-VBCB)s and poly(St-co-VBCB)s, which are soluble in most common solvents, sharply in contrast to the typical sPS. Copolymerization of 4-VBCB with styrene afforded a gradient copolymer due to the dramatically different reactivity of the two monomers (r_VBCB/r_St = 84.3). Moreover, copolymerization of 4-VBCB with ethylene (2 atm) proceeded smoothly to yield ethylene-VBCB random copolymers with a variety of VBCB contents (5.2–22.7%). In the presence of maleimide, cross-linked functional polyethylene was obtained through the Diels–Alder reaction and intermolecular cross-link. More interestingly, nanoparticles based on polyethylene were successfully synthesized under ultralow concentration via intramolecular cross-linking of the ethylene-VBCB copolymer.