Cationic nano-objects produced by polymerization-induced self-assembly using sulfonium-macro chain transfer agents with different counter anions†

Sulfonium cations and sulfonium-based polymers have received increased interest as biomedical and ion-conductive materials because of their unique cationic features. However, the feasible construction of cationic nanostructures via polymerization-induced self-assembly (PISA) remains limited owing to charge repulsion. In this study, we report the efficient synthesis of sulfonium cation-based nano-objects from P(MTEA(S⁺)[R⁻])s with different counter anions (R = bis(trifluoromethylsulfonyl)imide, TFSI; trifluoromethanesulfonate, OTf; and chloride, Cl), which were prepared by reversible addition–fragmentation chain-transfer (RAFT) of 2-(methylthio)ethyl acylate (MTEA) and a subsequent anion exchange reaction. RAFT dispersion copolymerization of styrene (St) and N-phenylmaleimide (PMI) using cationic P(MTEA(S⁺)[R⁻]) macro-chain transfer agents (CTAs) afforded various assembled structures (worms, vesicles, and nanotubes) by tuning the chain lengths of the P(MTEA(S⁺)[R⁻]) and P(St-alt-PMI) blocks and their composition and polymerization conditions (e.g., monomer concentration and solvent polarity). Depending on the three cationic macro-CTAs, the PISA of St and PMI enabled the efficient copolymerization and construction of cationic assemblies, including unique nanotubes. This is the first study demonstrating the successful integration of the sulfonium macro-CTA and PISA, enabling the design and manipulation of cationic nano-objects with various morphologies and unique functionalities originating from sulfonium cations.