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 [(CpPh4H)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 (rVBCB/rSt = 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.