Cross‐Linked Polymeric Micelles as Catalytic Nanoreactors

Abstract

Cross-linked micelles have emerged as promising catalyst supports over the past two decades due to their improved structural stability, chemical diversity in multiple domains, and catalyst recovery compared to their uncross-linked analogues. We highlight the different physicochemical properties that arise by cross-linking the shell or core-domain and the subsequent impact on catalysis. Both, shell cross-linked micelles (SCMs) and core cross-linked micelles (CCMs) were initially designed to include one catalytic entity. Later on, SCMs were used to compartmentalize catalysts for non-orthogonal tandem catalysis while CCMs were investigated as phase transfer agents in biphasic catalysis. Current challenges in this field and new design trends for advanced micellar nanoreactors are discussed.

Core-crosslinked micelles with a poly-anionic poly(styrene sulfonate)-based outer shell made by RAFT polymerization

“…Crosslinking, which may be realized either on the shell, in the core, or at an intermediate corona level for multiblock copolymer micelles, removes the dynamic equilibrium between the micellar objects and the free arm constituents, thus improving properties such as drug loading capacity, stability, and confinement in the aqueous medium. [1][2][3][4][5][6][7][8] Controlled radical polymerizations are compatible with water as reaction medium, in addition to being applicable to a wide range of monomers and can be implemented under less stringent conditions relative to the non-radical methods. Among the various possible techniques, reversible addition-fragmentation chain-transfer (RAFT) polymerization has been very successful, 9,10 particularly when combined with "polymerization-induced self-assembly" (PISA), [11][12][13][14][15] directly leading to crosslinked particles in a one-pot process in water.…”

Cascade Processes with Micellar Reaction Media: Recent Advances and Future Directions

“…Notably, for hydrogenation, the catalytic performance was dependent on the size of the substrate. Whereas 3-buten-2-ol and 2-methyl-3-buten-2-ol did not react, hydrogenation of 1-hexene was observed under the same conditions, with 82% yield [ 96 , 97 ]. Clusters (0.7 nm, approximately seven atoms) of Pd atoms could also be incorporated into shell-crosslinked micelles using ligand exchange with Pd(PPh 3 ) 4 .…”

“…Heck reactions could also be performed at low Pd loadings (0.001 mol%). Low leaching confirmed that the Pd was encapsulated within the hydrophobic core of the micelles [ 97 ].…”

“…The carboxylic acid functionalities of the intermediate shell were crosslinked via amidation chemistry following self-assembly in water. The resulting copper complex containing micelles was used to catalyze the 1,3-dipolar cycloaddition of azido- and alkynyl-functionalized small molecules [ 97 , 101 ].…”

“…To date, the block copolymer micelle platform has been based on a single type of block copolymer. Scale up and the cost of block copolymer synthesis must also be carefully considered [ 97 ].…”