Amine-Containing Monomers for Ring-Opening Metathesis Polymerization: Understanding Chelate Effects in Aryl- and Alkylamine-Functionalized Polyolefins

Abstract

Ring-opening metathesis polymerization (ROMP) of two different types of amine-functionalized monomers, aminonorbornenes (ANs) and aminocyclooctenes (ACs), has been studied using [(H2IMes)(PCy3)(Cl)2Ru = CHPh] Grubbs second generation catalyst, G2, and [(H2IMes)(pyr)2(Cl)2Ru = CHPh] Grubbs third generation catalyst, G3. Despite the known detrimental effects of unprotected amine functionalities on Ru-based ROMP catalysts, aminopolyolefins can be readily prepared using G2 and G3. The influence of the amine substituent of the monomer on the polymerization process, as probed by monitoring reaction kinetics, confirmed that the basicity/nucleophilicity of the amine group has a detrimental influence on the ROMP process. Reaction kinetics of homopolymerization of both these classes of monomers revealed faster polymerization of ACs than the more strained AN counterpart, which has been attributed to the favored chelated catalyst resting states in the case of ANs. Hammett studies show increased polymerization rates in the presence of electron-withdrawing aryl amine-containing monomers. These observed kinetic effects were used to advantage in the copolymerization of AN and AC monomers to access a gradient polymer. Polymerization kinetics of combined monomers displayed different reactivity profiles than observed during homopolymerization. Polyolefins with unprotected secondary alkyl amines could be synthesized by leveraging the unfavorable chelate formation in the case of AC monomers. The strategic selection of cyclic alkene and relative positioning of amine substituent allows for the diverse incorporation of secondary amines into polymers by ROMP.