Amphiphilic random methacrylate copolymers, consisting of poly(ethylene glycol) (PEG) and alkyl pendent groups, undergo reversible single-chain self-folding in water via intramolecular hydrophobic interaction, to generate a dynamic unimolecular hydrophobic nanospace, similar in shape but structurally different relative to micelles and microgel star polymers. These copolymers were prepared by the ruthenium-catalyzed living radical copolymerization of a PEG methacrylate (PEGMA) and an alkyl methacrylate (RMA; R, −C n H2n+1, n = 1–18), where copolymer composition, degree of polymerization, and hydrophobic R moiety were varied. Detailed structural and chain-folding characterization has revealed: single-chain folding is favored with the RMA content 20–40 mol % per chain; the hydrophobic inner compartment (or the self-folded structure) is stable even at a high polymer concentration (up to ∼6 wt %); and folded–unfolded transition occurs on addition of methanol or by elevating solution temperature, finally to phase-separation above a lower critical solution temperature.
Cation-condensed microgel-core star polymers with poly(ethylene glycol) (PEG)-based arms were designed as unimolecular polycationic nanocapsules (hosts) to encapsulate and stimuli-responsively release hydrophilic and anionic dyes (guests) in water. Typically, a cation-condensed star polymer (core cations: ∼670/star) was directly synthesized in high yield (>90%) by the linking reaction of a PEG macroinitiator (1) with a quaternary ammonium cation-carrying linking agent (2) in ruthenium-catalyzed living radical polymerization. Analyzed by UV–vis spectroscopy, the star polymer efficiently encapsulated various hydrophilic dyes carrying sulfonate anions (methyl orange: MO; orange G: OG; methyl blue: MB) in water (UV–vis: ∼400 OG per a single star). The efficient dye encapsulation is due to the high concentration of quaternary ammonium cations in the core. The number of core-bound dyes increased with increasing the number of core-bound cations. The ligation structure of dyes within the core was proposed: the immobilization of one OG molecule involves two in-core ammonium cations. Additionally, stimuli-responsive release of dyes from cation-condensed star polymers was successfully achieved via ion exchange with NaCl aqueous solution.
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