Simultaneous Click Coupling Reaction and Declick Cyclization Reaction in the Synthesis of Degradable Polymers

Abstract

The development of degradable polymers with desirable functionalities and chemical structures is a challenging goal in the field of polymer chemistry. Central to the challenge are the applications of new chemical reactions in the polymerization and degradation processes. In this research, a method based on a simultaneous click coupling reaction and declick cyclization reaction is applied in the synthesis of degradable polymers. Base-catalyzed thiol-phenylsulfone click reactions among small monomer molecules containing a phenylsulfonyl group and a thiol group on each structure lead to the growth of polymer chains. Meanwhile, thiolate anions generated at the ends of polymer chains have a nucleophilic substitution reaction with heteroaromatic thioethers in the backbones, leading to the degradation of the formed polymer chains and the generation of a cyclic compound. The chain growth and degradation processes can be tuned by controlling the concentrations of monomer and polymer chains. The click polymerization is dominant in the initial stage, and with an increase in polymer concentration, the declick reaction is dominant. The declick reaction and degradation of polymer chains are inhibited at a low temperature. Both click and declick reactions can be terminated by adding acids, and stable polymers are synthesized. Through a coupling reaction between the degradable homopolymer and pyridyl disulfide terminated poly(ethylene glycol) monomethyl ether, a degradable triblock copolymer is synthesized. Degradable diblock copolymers are synthesized by reversible addition–fragmentation chain transfer polymerizations using a degradable macro chain transfer agent.