(413g) Microenvironment Effect on Reaction Kinetics within Self-Assembled Polymer Nanoreactors

Confining catalyzed reactions to the hydrophobic core of micellar nanoreactors can facilitate organic phase reactions in a bulk aqueous environment. We are confining catalyzed reactions to the hydrophobic core of kinetically-trapped polymer nanoreactor to achieve reaction and separation. Flash NanoPrecipitation is a rapid, scalable, and modular method capable of continuously producing inorganic-polymer hybrid particles. In this work, we explore the use of Flash NanoPrecipitation (FNP) as a platform technology to produce core-shell polymer nanoreactors that encapsulate catalytic gold nanoparticles within tunable hydrophobic microenvironments. In FNP, amphiphilic block copolymers direct molecular self-assembly of catalytic nanoparticles and co-precipitant(s). Adsorption of the hydrophobic block encapsulates the catalyst while the hydrophilic block sterically stabilizes the nanoreactor. The precipitation process is controlled by carefully tuning the time scales of micromixing, self-assembly, and nucleation and growth. The focus of this work is (1) formulation of nanoreactors with tunable size, catalyst loading, and hydrophobic microenvironment and (2) evaluation of the reaction kinetics of the encapsulated catalyst.

Using the FNP platform and polystyrene as a model co-precipitant, the process parameters to tune the nanoreactor size and catalyst loading independently were determined. Nanoreactors with tunable microenvironments have also been achieved. In addition to polystyrene (solid), nanoreactors with liquid microenvironments (Dodecane, Vitamin E) have been fabricated. We have systematically varied microenvironment-catalyst interactions from no interactions (Dodecane, Vitamin E-gold), intermediate interaction (gold-amine), and strong interactions (gold-thiol).

The reaction kinetics of the encapsulated catalyst were evaluated using reduction of 4-nitrophenol as a model reaction. To determine the effect of the microenvironment on apparent reaction kinetics, the induction time and apparent rate constants will be compared. Microenvironment-catalyst interactions significantly impacted the reaction kinetics; presence of dodecanethiol or dodecylamine in the nanoreactor core inhibited the reaction. This result confirms that the reaction occurs at the surface of the gold nanoparticle. Overall, nanoreactors with inert microenvironments enhanced the apparent reaction when compared to the unencapsulated gold nanoparticle catalysts.