Facile synthesis of highly pure block copolymers by combination of RAFT polymerization, click reaction and de-grafting process

Abstract

A facile strategy for synthesizing highly pure block copolymers with polymeric segments such as polystyrene, polyacrylamides and polyacrylates was described. The methodology involves a grafting reaction by tandem RAFT polymerization and azide–alkyne cycloaddition reaction and a subsequent de-grafting reaction via aminolysis or radical-induced addition-fragmentation reaction. S-methoxycarbonylphenylmethyl S′-propynyloxycarbonylethyltrithiocarbonate was used to synthesize Z-alkyne-functionalized macro chain transfer agents, and silica particles grafted with well-defined “living” block copolymers were obtained by simultaneous RAFT process and click reaction using clickable RAFT agents and azido-functionalized silica particles as raw materials. This approach afforded grafted polymers with polydispersity typically lower than 1.2 and silica–polymer hybrids with grafting density in the range of 0.020–0.091 chains nm⁻² as the grafted chains had molecular weights between 4920 and 26 300 g mol⁻¹. Highly pure block copolymers with terminal functionalities such as thiol, methyldithio, carboxyl, hydroxyl and halogen were obtained by a de-grafting process and postmodification, and azido-functionalized silica particles were efficiently recovered. The cycles of grafting and de-grafting reactions could be applied many times, and no significant decrease in grafting density was noted, indicating the versatility and generality of this approach for surface modification, synthesis of high-purity block copolymers and recycling of clickable solid substrate.