Self-Assembled Thermoresponsive Molecular Brushes as Nanoreactors for Asymmetric Aldol Addition in Water

Abstract

The manipulation and tunability of self-assembled block copolymers through external stimuli present an attractive strategy to develop smart polymer-based nanoreactors as supports for non-orthogonal tandem catalysis. We report on thermoresponsive core−shell micelles based on poly[norbornene-poly(2-methyl-2-oxazoline-block-2-propyl-2-oxazoline)]-graf tpoly[norbornene L-proline] (P[NB-P(MeOx-b-PropOx)]-graft-P[NB-L-proline]) as catalyst supports for L-proline. These molecular brushes exhibit large differences in lower critical solution temperature behavior and nanostructure size in water, depending on chain lengths and proline connectivity. L-Proline-mediated aldol reactions expose the efficiency by which the molecular brushes selfassemble into micelles. Molecular brushes with an extended backbone show higher activity and selectivity, suggesting better core− shell segregation of the micelles and exclusion of water from the catalytic site. Catalytic efficiencies are not improved above the cloud point temperature, and the catalytic behavior is rather sensitive to conformational changes of the polymer chains.

Near-Infrared Fluorescent Micelles from Poly(norbornene) Brush Triblock Copolymers for Nanotheranostics

“…Living ring-opening metathesis polymerization (ROMP) is one of the most powerful methods for synthesizing well-defined amphiphilic block polymers with controlled molecular weights (MW) and low dispersities ( Đ ). , The sequential ROMP of norbornene-based monomers following the “grafting-through” strategy is an effective methodology for the preparation of highly branched amphiphilic brush copolymers (also known as molecular brushes or bottlebrush copolymers) with unique self-assembly, drug delivery, and imaging capabilities. ,− This is possible due to the exceptional functional group tolerance of highly active Grubbs initiators and the mild reaction conditions required …”

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

“…This was attributed to enhance hydrophobic effect of the norbornene backbone. 96 On the contrary, it was also demonstrated that increasing molecular weight of poly(N,N 0 -dimethyl(methacryloylethyl) ammonium propanesulfonate) (PDAMPS) gives rise to higher UCST. This could be explained by considering the increasing inter-chain interactions due to the increasing number of charged pendants.…”

“…22a). 96 Furthermore, instillation of the nanoreactors could enable temperatureassisted recyclability to soluble catalysts. Two works published in 2019 illustrated that providing ethylene glycol-based polymers as scaffolds maintained high catalytic activity, in comparison to soluble catalysts, while became recoverable simply by precipitation using additional heat.…”

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

“…The yield decreased with every reuse, and selectivity decreased after the third reuse. The apparent decrease in catalytic efficiency and selectivity was attributed to the loss of micelles and disruption of the micelle structure during extraction [ 85 ]. The performance of micellized block copolymers was compared to that of random copolymers that to did not form micelles.…”