Recent Advances in the Synthesis and Application of Polymer Compartments for Catalysis.

Catalysis is one of the most important processes in nature, science, and technology, that enables the energy efficient synthesis of essential organic compounds, pharmaceutically active substances, and molecular energy sources. In nature, catalytic reactions typically occur in aqueous environments involving multiple catalytic sites. To prevent the deactivation of catalysts in water or avoid unwanted cross-reactions, catalysts are often site-isolated in nanopockets or separately stored in compartments. These concepts have inspired the design of a range of synthetic nanoreactors that allow otherwise unfeasible catalytic reactions in aqueous environments. Since the field of nanoreactors is evolving rapidly, we here summarize-from a personal perspective-prominent and recent examples for polymer nanoreactors with emphasis on their synthesis and their ability to catalyze reactions in dispersion. Examples comprise the incorporation of catalytic sites into hydrophobic nanodomains of single chain polymer nanoparticles, molecular polymer nanoparticles, and block copolymer micelles and vesicles. We focus on catalytic reactions mediated by transition metal and organocatalysts, and the separate storage of multiple catalysts for one-pot cascade reactions. Efforts devoted to the field of nanoreactors are relevant for catalytic chemistry and nanotechnology, as well as the synthesis of pharmaceutical and natural compounds. Optimized nanoreactors will aid in the development of more potent catalytic systems for green and fast reaction sequences contributing to sustainable chemistry by reducing waste of solvents, reagents, and energy.

pH-Controlled Hierarchical Assembly/Disassembly of Multicompartment Micelles in Water.

Multicompartment micelles (MCMs) have become attractive drug delivery systems as they allow the separate storage of two or more incompatible cargos in their core compartments (e.g., drugs and dyes for imaging). A recent hierarchical self-assembly process for hydrophobic terpolymers in organic solvents showed the ability to form very homogeneous MCM populations, yet the transfer of this process into water requires a better understanding of the formation mechanism and influence of chain mobility during assembly. Here, the synthesis of a linear poly(oligo(ethylene glycol) methacrylate)-block-poly(benzyl acrylate)-block-poly(4-vinylpyridine) (POEGMA-b-PBzA-b-P4VP) triblock terpolymer by reversible addition-fragmentation chain transfer (RAFT) polymerization is reported as well as its step-wise assembly into MCMs in water with POEGMA corona, PBzA patches, and P4VP core. Reversible assembly/disassembly of the MCMs is investigated through protonation/deprotonation of the P4VP core. Interestingly, the low glass transition temperature (Tg ) of the hydrophobic PBzA middle block causes MCMs to directly disassemble into molecularly dissolved chains instead of patchy micelles due to mechanical stress from electrosteric repulsion of the protonated P4VP corona chains. In addition, pH resistant MCMs are created by core-crosslinking and fluorescent properties are added by covalent anchoring of fluorescent dyes via straightforward click chemistry.

Confinement Assembly of ABC Triblock Terpolymers for the High-Yield Synthesis of Janus Nanorings.

Block copolymers are versatile building blocks for the self-assembly of functional nanostructures in bulk and solution. While spheres, cylinders, and bilayer sheets are thermodynamically preferred shapes and frequently observed, ring-shaped nanoparticles are more challenging to realize due to energetic penalties that originate from their anisotropic curvature. Today, a handful of concepts exist that produce core-shell nanorings, while more complex ( e. g., patchy) nanorings are currently out of reach and have only been predicted theoretically. Here, we demonstrate that confinement assembly of properly designed ABC triblock terpolymers is a general route to synthesize Janus nanorings in high purity. The triblock terpolymer self-assembles in the spherical confinement of nanoemulsion droplets into prolate ellipsoidal microparticles with an axially stacked lamellar-ring ( lr)-morphology. We clarified and visualized this complex, yet well-ordered, morphology with transmission electron tomography. Blocks A and C formed stacks of lamellae with the B microdomain sandwiched in-between as nanorings. Cross-linking of the B-rings allowed disassembly of the microparticles into Janus nanorings carrying two strictly separated polymer brushes of A and C on the top and bottom. Decreasing the B volume leads to Janus spheres and rods, while an increase of B results in perforated and filled Janus disks. The confinement assembly of ABC triblock terpolymers is a general process that can be extended to other block chemistries and will allow to synthesize a large variety of complex micro- and nanoparticles that inspire studies in self-assembly, interfacial stabilization, colloidal packing, and nanomedicine.