Segmented Copolymers Synthesized by Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization Using an Asymmetric Difunctional RAFT Agent and the Utilization in RAFT-Mediated Dispersion Polymerization

Abstract

Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) is an in situ growth method of increasing interest for the preparation of block copolymer nano-objects with diverse morphologies at high solids contents (10–50 wt %). Recent reports have shown that structures of multifunctional macro-RAFT agents can significantly affect RAFT-mediated PISA and the formed block copolymer nano-objects, but all these multifunctional macro-RAFT agents are limited to symmetric structures. In this study, we synthesized a novel difunctional RAFT agent with an asymmetric structure and employed in RAFT solution polymerization to prepare segmented macro-RAFT agents. Size exclusion chromatography (SEC) analysis showed that the redistribution of blocks occurred during RAFT polymerization, leading to the formation of segmented copolymers with different blocks (block number up to 4). Control experiments demonstrated that this redistribution process was derived from the unique structure of the asymmetric difunctional RAFT agent rather than monomers. The obtained segmented macro-RAFT agent was then used in RAFT-mediated dispersion polymerization to prepare well-defined block copolymer nano-objects. Owing to the unique structure of segmented block copolymers, shorter micellar nucleation was observed and a certain number of trithiocarbonate groups could be introduced on the surface of block copolymer nano-objects. The trithiocarbonate groups located on the surface of block copolymer nano-objects provide a landscape for further chain extension and functionalization. As a proof-of-concept experiment, vesicles loaded with silver nanoparticles were successfully prepared by in situ reduction of AgNO3 and employed as a catalyst to reduce methylene blue in the presence of NaBH4. We expect that this study will not only provide important mechanistic insights into RAFT polymerization mediated by multifunctional RAFT agents but also enable the preparation of functional block copolymer nano-objects.