Influence of residual impurities on ring-opening metathesis polymerization after copper(I)-catalyzed alkyne-azide cycloaddition click reaction

Abstract

Bottlebrush polymers (BBPs) are three-dimensional polymers with great academic and industrial potential owing to their highly tunable and intricate architecture. The most popular method to synthesize BBPs is ring-opening metathesis polymerization (ROMP) with Grubbs' catalyst, allowing living grafting-through polymerization of macromonomers of up to ultrahigh molecular weights with narrow molecular weight distribution. In this case, it has been well recognized that the purity of macromonomers (MMs) is critical for a successful ROMP reaction. For MMs synthesized from reversible-deactivation radical polymerization, Grubbs and Xia demonstrated that the better control of ROMP reaction can be achieved when they are prepared via "growth-then-coupling" method that is coupling a norbornenyl group to end-functionalized prepolymers. However, these MMs can also contain various residual impurities from previous synthetic steps, which can potentially poison the catalyst and hamper the ROMP reaction. Herein, we intentionally doped possible impurities into purified MMs to identify the most poisoning species. As a result, it was found that alkyne-functionalized norbornene most significantly retarded the ROMP reaction due to a formation of Ru-vinyl-carbene intermediates having low catalytic reactivity, whereas the other reagents such as solvent, Cu-catalyst, ligands, and azido-terminated prepolymers were relatively inert. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 726-737