The yttrium-catalyzed heteroatom-assisted terpolymerization of ortho-alkoxystyrene, isoprene and butadiene with high regio- and stereoselectivity

The use of coordination polymerization to synthesize functional styrene-isoprene-butadiene rubber (SIBR) is a theoretical challenge in the field of polymer science, since functional monomers are usually poisonous to the employed catalysts. Herein, we report the coordination terpolymerization of polar ortho-alkoxystyrene (oAOS), isoprene (IP), and butadiene (BD) via pyridyl-functionalized tetramethylcyclopentadiene-ligated rare-earth-metal bis(allyl) complexes [(C5Me4C5H4N)Ln(η3-C3H5)2] [(Ln = Sc (1); Ln = Y (2)]. Complex 1 was poisoned by polar groups, while complex 2 realized the first successful terpolymerization of ortho-methoxystyrene (oMOS), IP, and BD with high syndio- and cis-1,4-regioselectivity via a heteroatom-assisted olefin polymerization strategy. We were able to tune the concentration of inserted oMOS in a wide range, specifically 5.6–50.7 mol%, via changing the feed ratios. The gradient microstructure of the resultant poly(oMOS-IP-BD)s was confirmed from the results of NMR measurements and a kinetics study. By switching to ortho-ethoxystyrene (oEOS), random poly(oEOS-IP-BD)s with a single Tg could be afforded, and it exhibited remarkable elasticity.