Unprecedented Reactivity of Terminal Olefins in Ring-Opening Metathesis Polymerization

The use of aliphatic terminal olefins is ubiquitous in metal-catalyzed olefin metathesis reactions. Therefore, a great deal of mechanistic and kinetic studies have been performed regarding the reactivity of such olefins over the years. But when it comes to ring-opening metathesis polymerization (ROMP) chemistry, the use of such olefins as an effective and regioselective chain transfer agent (CTA) has never been realized. Here, we investigated the unexpectedly high, albeit very controlled, reactivity of terminal olefins in traditional ROMP employing popular norbornene-imide-based monomers. ¹H NMR spectroscopy and MALDI-ToF mass spectrometry analyses strongly suggested the desired regioselectivity as well as the chemoselectivity of such olefins in ROMP. Both electronic and steric parameters of the olefin CTAs are also investigated. Kinetic measurements revealed the highest chain transfer rate constants among the reported CTAs to this date. Moreover, an unusual independence of the terminal olefin concentration on the polymerization rate was observed, which was attributed to the higher rates of both chain transfer and reinitiation steps. This approach describes inexpensive, functional, and abundant terminal olefins as surprisingly better CTAs for a ROMP process that utilizes substoichiometric amounts of metal catalyst with respect to the number of polymer chains formed.