Multimode Self-Folding Polymers via Reversible and Thermoresponsive Self-Assembly of Amphiphilic/Fluorous Random Copolymers

Abstract

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...

Prolate and Temperature‐Responsive Self‐Assemblies of Amphiphilic Random Copolymers with Perfluoroalkyl and Polyoxyethylene Side Chains in Solution

“…The size distribution in water solutions was stably centered at ≈8 nm (≈0.4 PDI), independent of the concentration (0.5–5.0 mg mL −1 ) and type of solvent investigated (Figures S1, S2, Supporting Information). These nanostructures were identified as nanoassemblies of single‐chain folded copolymer, consistent with previous results on structurally analogous PEGMA‐ co ‐FMA copolymers . The hydrophobic interactions among the FA side chains induced self‐folding in an inner, core structure of a single‐chain nanoassembly, whereas the hydrophilic PEGMA side chains were exposed to contact with water in a outer, shell structure.…”

“…Typical precursors of the hydrophilic component of single‐chain nanoassemblies have been reported to be either ionic monomers, such as 2‐acrylamido‐2‐methylpropanesulfonate, or non‐ionic monomers, such as poly(ethylene glycol) methyl ether methacrylate (PEGMA) or acrylamide (PEGAAm) . Random copolymers based on the latter type of monomers have the advantage to be soluble in both water and organic solvents and to be thermally responsive in water solution, due to the occurrence of a lower critical solution temperature‐type (LCST) transition .…”

“…The introduction of fluorinated comonomer units is known to drastically affect both bulk and surface properties of a copolymer, enhancing for example its ability to spontaneously organize at low energy surfaces and interfaces, both phenomena being driven by the lowest surface energy perfluorinated moieties . Amphiphilic random copolymers of PEGMA with fluoroalkyl methacrylates (FMA) were recently synthesized by ruthenium‐catalyzed living radical polymerization and shown to give rise to single‐chain self‐assemblies, referred to as unimer micelles, in water and 2 H ,3 H ‐perfluoropentane solutions …”

Optical and Magnetic Resonance Imaging Using Fluorous Colloidal Nanoparticles

“…59,56,55 The self-assembly of the polymer in water was probed using DLS. The copolymer was dispersed in ultrapure water and vigorously vortexed to form a stable colloidal dispersion.…”

Base-catalyzed diastereoselective trimerization of trifluoroacetone

“…The hydrophilic nature of the oxygen rich face coupled with the hydrophobic fluorous plane is a feature that has been recognized and exploited in a number of systems. These include the syntheses of multicompartment 29 and thermoresponsive 30 micelles, Janus dendrimers, 31 and gels 32 (among many other fluorous constructs) that enjoy a wide range of biomedical applications. 33,34 …”