A “click” approach to facile synthesis of long-chain highly branched ROMP polymers

Abstract

The click chemistry strategy was successfully applied for the preparation of long-chain highly branched ring-opening metathesis polymers (LCHBPs). The hydroxyl-functionalized monotelechelic polymers with various molecular weights were synthesized first via ring-opening metathesis polymerization of N-azidopentyl oxanorbornene imide in the presence of a symmetrical functional terminating agent, and then transformed into alkynyl-monotelechelic polymers, which acted as AB_n-type macromonomers for subsequent click reaction to finally produce LCHBPs as the reaction time prolonged. All intermediates, macromonomer, and the resultant LCHBPs were characterized in detail by mass spectroscopy, elemental analysis, FTIR, GPC, and NMR measurements. The experimental results showed that polymerization has a two-step feature, that is, a fast and a slow increase of the average degree of polymerization at the initial and the subsequent stages, respectively. The final LCHBPs have high molecular weight up to M_n,NMR = 210 600, and relatively moderate molecular weight distributions (M_w/M_n = 2.12–1.67).