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 RAFTmediated 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 AgNO 3 and employed as a catalyst to reduce methylene blue in the presence of NaBH 4 . 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 nanoobjects.

Efficient Synthesis and Self-Assembly of Segmented Hyperbranched Block Copolymers via RAFT-Mediated Dispersion Polymerization Using Segmented Hyperbranched Macro-RAFT Agents

“…Recently, polymerization-induced self-assembly (PISA) based on RDRP has become a well-established method for the efficient synthesis of block copolymers and block copolymer assemblies at high solids (10–50 wt %). − In a typical PISA system, a macromolecular chain-transfer agent (macro-CTA) dissolved in the reaction medium is chain extended with a core-forming monomer. As the molar mass of the second block increases to a critical value, the formed block copolymer self-assembles into micelles with a variety of morphologies.…”

Combining Green Light-Activated Photoiniferter RAFT Polymerization and RAFT Dispersion Polymerization for Graft Copolymer Assemblies

“…Moreover, the obtained block copolymers would self-assemble into colloidally stable polymer assemblies via a polymerization-induced self-assembly (PISA) mechanism. Since 2009, RAFT-PISA has become an emerging approach to produce block copolymer assemblies with diverse morphologies under concentrated conditions (solids content of 10–50% w/w). − …”

“…Since the RAFT-PISA involves the chain extension from a macro-RAFT agent, the structure and composition of the macro-RAFT agent should have a great impact on the nature of RAFT-PISA as well as the obtained block copolymer assemblies. ,,− Currently, the utilization of linear monofunctional or difunctional macro-RAFT agents dominates the research of RAFT-PISA, , and linear block copolymer assemblies are mainly formed. In contrast, the preparation of graft copolymer assemblies via RAFT-PISA mediated by a multifunctional macro-RAFT agent has rarely been reported.…”

Organic–inorganic hybrid nanomaterials prepared via polymerization-induced self-assembly: recent developments and future opportunities

“…Very recently, we synthesized segmented macro-RAFT agents using an asymmetric difunctional small molecular RAFT agent. 136 These segmented macro-RAFT agents were used to mediate the RAFT dispersion polymerization of St and various block copolymer nano-objects were obtained. Due to the unique structure of the segmented macro-RAFT agent, a certain number of RAFT groups could be introduced to the surfaces of block copolymer nano-objects.…”