Star polymerization of norbornene derivatives using a tri-functionalized Blechert's olefin metathesis catalyst†
Blechert's catalyst (III), one of the powerful olefin metathesis catalysts in ring closing metathesis (RCM), was demonstrated to show living ROMP characteristics towards conventional norbornene derivatives. The obtained homopolymers and block copolymers have very narrow Đ and controlled molecular weights. The tri-functionalized ROMP initiator (IV) based on Blechert's catalyst was isolated in good yield, and showed highly efficient activity in the star polymerization of norbornene derivatives, including bulky fourth generation dendrons, to afford tri-arm star polymers with a precise molecular weight and narrow Đ. The difference in the solution properties between tri-arm star polymers and linear polymers with similar molecular weights was studied by tandem GPC/light scattering.