Investigating the influence of solvent quality on RAFT-mediated PISA of sulfonate-functional diblock copolymer nanoparticles

Polymerisation-induced self-assembly (PISA) has become widely recognised as a versatile and efficient strategy to prepare well-defined diblock copolymer nanoparticles in a range of solvents. In this article, we report the synthesis of anionic, sterically-stabilised, sulfonate-functional diblock copolymer nanoparticles via PISA using a reversible addition–fragmentation chain-transfer (RAFT) polymerisation formulation. Anionic poly(potassium 3-sulfopropyl methacrylate) (PKSPMA) macromolecular chain-transfer agents (macro-CTAs) were synthesised via RAFT solution polymerisation followed by chain-extension with benzyl methacrylate (BzMA) in alcohol/water mixtures to form PKSPMA–PBzMA nanoparticles. The influence of solvent quality on the formation of these nanoparticles was investigated by judiciously changing the alcohol/water ratio, the alcohol co-solvent (ethanol or methanol) and relative copolymer composition. The resulting diblock copolymer nanoparticles were analysed by dynamic light scattering (DLS), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and aqueous electrophoresis. The results demonstrated that nanoparticles with controllable diameters for a fixed copolymer composition can be prepared by altering the co-solvent composition. More specifically, when using different ratios of ethanol/water or methanol/water, the nanoparticle diameter can be tuned from approximately 20 to 200 nm with fixed copolymer composition. This indicates that the solvency of both the stabiliser and core-forming block has a marked impact on both the aggregation of polymer chains during self-assembly and the resulting nanoparticles. Additionally, these nanoparticles remain colloidally stable and highly anionic over a wide pH range from 4 to 10, as judged by aqueous electrophoresis.