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.

Urea and poly(ethylene glycol) (PEG)-functionalized amphiphilic random copolymers served as self-folding polymers in both water and chloroform via hydrophobic and/or hydrogenbonding interactions. For this, a urea-bearing methacrylate (BPUMA) was newly designed as a trigger monomer. Various random, gradient, and block copolymers were synthesized by living radical copolymerization of PEG methyl ether methacrylate (PEGMA) and BPUMA to systematically survey folding/association properties. Importantly, self-folding in both water and chloroform requires the random incorporation of BPUMA along a chain and the control of its composition, while gradient or block counterparts tend to induce multichain aggregation. Typically, 30−40 mol % BPUMA random copolymers effectively fold in water to form compact globular unimer micelles with hydrophobic/hydrogen-bonding core covered by multiple PEG arm chains. The dual functionalization of polymers with hydrophilic PEG and hydrophobic/hydrogen-bonding urea units afforded singlechain compartmentalized polymers in both aqueous and organic media.

Single-chain crosslinked star polymers with hydrophilic multiple short arms and a hydrophobic core were created as novel microgel star polymers of single polymer chains. The synthetic process involves the intramolecular crosslinking of self-folding amphiphilic random copolymers in water. For this, amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic olefin pendants were synthesized by ruthenium-catalyzed living radical copolymerization of PEG methyl ether methacrylate, dodecyl methacrylate, and hydroxyl-functionalized methacrylates, and the in-situ or post esterification of the hydroxyl pendants of the resulting copolymers with methacryloyl chloride. The olefin-bearing copolymers with 20-40 mol% hydrophobic units efficiently self-folded with hydrophobic interaction in water and were crosslinked intramolecularly using a free radical initiator or a ruthenium catalyst to selectively provide single-chain crosslinked star polymers, while a counterpart with 50 mol% hydrophobic units induced bimolecular aggregation in water to give double-chain crosslinked star polymers. Primary structure of the star polymers can be precisely controlled with random copolymer precursors. Owing to PEG arm units, the star polymers further showed thermosensitive solubility in water.

Summary: Amphiphilic three-armed star random copolymers were synthesized by ruthenium-catalyzed living radical copolymerization of hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) and hydrophobic dodecyl methacrylate (DMA). Their amphiphilic star random copolymers with 10-50 mol% DMA efficiently self-folded in water with intramolecular hydrophobic interaction to form compact unimolecular micelles. Owing to PEG segments, star copolymers were thermoresponsive to induce lower critical solution temperature-type phase separation in water.