A ring-closure method for preparing cyclic polymers from unconjugated vinyl monomers

Abstract

A unique ring-closure method was developed specifically focusing on the preparation of cyclic polymers derived from unconjugated vinyl monomers, which was established on the combination of reversible addition–fragmentation chain transfer polymerization (RAFT)/macromolecular design via the interchange of xanthate (MADIX) and light-induced strain promoted azide–alkyne cycloaddition (SPAAC) reaction. By virtue of a specifically designed xanthate agent 1 as the reversible chain transfer agent to polymerize the unconjugated vinyl monomers, well-defined telechelic polymers were produced by the RAFT/MADIX polymerization technique bearing the cyclopropenone-masked dibenzocyclooctyne and azide end groups. Under UV irradiation on a highly diluted solution of the resultant linear polymer precursors, the dibenzocyclooctyne end group was quantitatively released from cyclopropenone-masked dibenzocyclooctyne, which intramolecularly reacted with the azide end group in situ to ring-close the linear polymers and produce the corresponding cyclic polymers based on the SPAAC click reaction. In addition, this novel ring-closure method produced the cyclic polymer chain with a cleavable S–C(S)O bond within the xanthate group, which facilitated the resultant cyclic polymers to be efficiently cleaved back to their linear counterparts under mild aminolysis or reduction reaction conditions.