Synthesis of Polyisobutylene Bottlebrush Polymers via Ring-Opening Metathesis Polymerization

Polyisobutylene (PIB)-based bottlebrush polymers were synthesized via ring-opening metathesis polymerization (ROMP) of norbornene- and oxanorbornene-terminated PIB macromonomers (MM) initiated by Grubbs third-generation catalyst ((H₂IMes₂)­(pyr)₂(Cl)₂RuCHPh) (G3). While both MMs reached greater than 97% conversion as measured by ¹H NMR, the rate of propagation of PIB norbornene was measured to be 2.9 times greater than that of PIB oxanorbornene MMs of similar molecular weight (MW). The slower rate of propagation of the oxanorbornene MM was attributed to interaction between the electron-rich oxygen bridge and the metal center of G3, which slowed but did not inhibit polymerization. Both types of MMs demonstrated controlled/“living” polymerization behavior, and brush polymers with MWs up to ∼700 kg/mol with narrow dispersity (Đ ≤ 1.04) were achieved.