Most polymerizations achieve molecular weight control by reducing the relative rate of propagation to termination. In metal-free ring-opening metathesis polymerization (MF-ROMP), the propagating chain ends continuously undergo deactivation and reactivation. This activation equilibrium makes it difficult to directly measure the population of propagating chain ends. This study probes the rates of activation and deactivation of MF-ROMP chain ends through the use of quench labeling, a method first used by the Landis group to determine active site counts on metal catalysts in olefin polymerizations. In this method, a UV-active quench is added to the polymerization such that it quickly and irreversibly binds and deactivates the active chain end, thus quenching the polymerization. The result is a population of labeled and unlabeled polymers, both of which are visible via gel permeation chromatography (GPC). From these GPC results, we can then calculate, along with other kinetic information, the equilibrium of active to inactive chain ends. Here, we look at a variety of chromophoric quenchers and MF-ROMP reaction conditions, and how these variables affect the chain end equilibrium and control over MF-ROMP.

Determining active chain end distribution of MF-ROMP via quench labeling

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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