Multimode self-folding polymers were created via the reversible and thermoresponsive self-assembly of amphiphilic/fluorous random copolymers bearing poly-(ethylene glycol) (PEG) and perfluoroalkyl pendants in water, N,N-dimethylformamide (DMF), and 2H,3H-perfluoropentane (2HPFP). The random copolymers with precision primary structure were synthesized by ruthenium-catalyzed living radical copolymerization of PEG methyl ether methacrylates and perfluoroalkyl methacrylates. Owing to three distinct properties of the hydrophobic backbone, hydrophilic PEG chains, and fluorous perfluorinated pendants, the random copolymers allowed various self-assembly modes for different folded structures by changing solvents. Namely, they form self-folding polymers of fluorous and/or hydrophobic cores in water or DMF, while they in turn provide reverse self-folding polymers of hydrophilic PEG cores in 2HPFP. The reverse folding in 2HPFP was further promoted by lower critical solution temperature-type phase separation of the PEG units upon heating. ■ INTRODUCTIONSingle-chain folding (self-folding) of polymers has attracted attention as a promising approach to create functional polymeric nanomaterials with globular three-dimensional architectures and precision nanocompartments. 1−24 Selective self-folding involves the precision design of polymeric precursors generally based on functional and/or amphiphilic random copolymers with well-controlled primary structure. Such random copolymers effectively allow the intramolecular association of the functional pendants (side chains) via physical interactions (e.g., hydrophobic, 8−11 hydrogen bonding, 12−15,16a host−guest, 16b,23 and coordination 16c ) by selecting solvents, adding molecules, and/or giving stimuli (e.g., temperature), while they can also undergo the intramolecular cross-linking of the pendants via covalent bond formation. 11b,17−22 Particularly interesting, the former self-folding system can provide reversibly folded/unfolded polymers with "dynamic" singlechain nanospaces that directly reflect the precision primary structure of the precursor polymers. Self-folding functional polymers have been also employed as novel functional nanospaces for unique catalysis. 15 Recently, we have created self-folding polymers in water with amphiphilic random copolymers bearing hydrophilic poly-(ethylene glycol) (PEG) and hydrophobic alkyl pendants. 11 This is one of the simplest systems of self-folding polymers (i.e., unimer micelles) via hydrophobic interaction in water. The random copolymers were efficiently synthesized by rutheniumcatalyzed living radical polymerization 25 of PEG methyl ether methacrylate (PEGMA) and alkyl methacrylates (RMA) including dodecyl methacrylate (DMA) and octadecyl methacrylate. By the optimization of the primary structure in terms of degree of polymerization (DP) and monomer composition, we typically found that PEGMA/DMA random copolymers with 20−40 mol % DMA (DP ∼ 200) self-folded in water with the hydrophobic interaction of the backbone and the multiple dodecyl...

Sequence regulation of monomers is undoubtedly a challenging issue as an ultimate goal in polymer science. To efficiently produce sequence-controlled copolymers, we herein developed the versatile tandem catalysis, which concurrently and/or sequentially involved ruthenium-catalyzed living radical polymerization and in situ transesterification of methacrylates (monomers: RMA) with metal alkoxides (catalysts) and alcohols (ROH). Typically, gradient copolymers were directly obtained from the synchronization of the two reactions: the instantaneous monomer composition in feed gradually changed via the transesterification of R(1)MA into R(2)MA in the presence of R(2)OH during living polymerization to give R(1)MA/R(2)MA gradient copolymers. The gradient sequence of monomers along a chain was catalytically controlled by the reaction conditions such as temperature, concentration and/or species of catalysts, alcohols, and monomers. The sequence regulation of multimonomer units was also successfully achieved in one-pot by monomer-selective transesterification in concurrent tandem catalysis and iterative tandem catalysis, providing random-gradient copolymers and gradient-block counterparts, respectively. In contrast, sequential tandem catalysis via the variable initiation of either polymerization or in situ transesterification led to random or block copolymers. Due to the versatile adaptability of common and commercially available reagents (monomers, alcohols, catalysts), this tandem catalysis is one of the most efficient, convenient, and powerful tools to design tailor-made sequence-regulated copolymers.

Immiscible with either hydrophobic or hydrophilic solvents, polyfluorinated compounds (PFCs) are generally "fluorous", some of which have widely been employed as surfactants and water/oil repellents. Given the prevailing concern about the environmental pollution and the biocontamination by PFCs, their efficient removal and recycle from industrial wastewater and products are critically required. This paper demonstrates that fluorous-core star polymers consisting of a polyfluorinated microgel core and hydrophilic PEG-functionalized arms efficiently and selectively capture PFCs in water into the cores by fluorous interaction. For example, with over 10 000 fluorine atoms in the core and approximately 100 hydrophilic arms, the fluorous stars remove perfluorooctanoic acid (PFOA) and related PFCs in water from 10 ppm to as low as a parts per billion (ppb) level, or an over 98% removal. Dually functionalized microgel-core star polymers with perfluorinated alkanes and additional amino (or ammonium) groups cooperatively recognize PFOA or its ammonium salt and, in addition, release the guests upon external stimuli. The "smart" performance shows that the fluorous-core star polymers are promising PFC separation, recovery, and recycle materials for water purification toward sustainable society.

Herein, amphiphilic/fluorous random copolymers bearing poly(ethylene glycol) (PEG) chains and perfluorinated alkane pendants were developed as novel non-cytotoxic polymers for protein conjugation. Three kinds of random copolymers with different initiating terminals (carboxylic acid, pyridyl disulfide, N-hydroxysuccinimide ester) were prepared by reversible addition-fragmentation chain transfer (RAFT) copolymerization of a PEG methyl ether methacrylate and a perfluorinated alkane methacrylate with corresponding functional chain transfer agents. All of the polymers were soluble in water to form nanostructures with perfluorinated compartments via fluorous interaction: large aggregates from the intermolecular multi-chain association and compact unimer micelles from the intramolecular single-chain folding. Such a PEGylated and perfluorinated random copolymer was non-cytotoxic to NIH 3T3 mouse embryonic fibroblast cells and human umbilical vein endothelial cells (HUVECs). Additionally, a random copolymer with a pyridyl disulfide terminal was also successfully conjugated with a thiolated lysozyme.