Organocatalyzed atom transfer radical polymerization (O-ATRP) has emerged as a metal-free variant of historically transition-metal reliant atom transfer radical polymerization. Strongly reducing organic photoredox catalysts have proven capable of mediating O-ATRP. To date, operation of photoinduced O-ATRP has been demonstrated in batch reactions. However, continuous flow approaches can provide efficient irradiation reaction conditions and thus enable increased polymerization performance. Herein, the adaptation of O-ATRP to a continuous flow approach has been performed with multiple visible-light absorbing photoredox catalysts. Using continuous flow conditions, improved polymerization results were achieved, consisting of narrow molecular weight distributions as low as 1.05 and quantitative initiator efficiencies. This system demonstrated success with 0.01% photocatalyst loadings and a diverse methacrylate monomer scope. Additionally, successful chain-extension polymerizations using 0.01 mol % photocatalyst...

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Photoinduced Organocatalyzed Atom Transfer Radical Polymerization Using Continuous Flow

Polymer Synthesis in Continuous Flow Reactors

Photoinduced controlled radical polymerizations (CRPs) have provided a variety of approaches for the synthesis of polymers possessing targeted structures, compositions, and functionalities with the added capability for spatial and temporal control, presenting the potential for new materials development. However, the scalability and reliability of these systems can be limited as a consequence of dependence on uniform irradiation of the reaction to produce well-defined products. In this perspective, we highlight the utility and promise of photo-CRP approaches through an overview of the adaptation of these methodologies to photo-flow reactor systems. Special emphasis is placed on the current state-of-the-art in polymerization scalability, reactor design, and polymer scope.

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Photoinduced Controlled Radical Polymerizations Performed in Flow: Methods, Products, and Opportunities†

Microreaction Technology for Synthetic Chemistry

Continuous flow copper-mediated reversible deactivation radical polymerizations

We report on the synthesis of 2-(dimethylamino)ethyl methacrylate by atom transfer radical polymerization (ATRP) in tubular microreactors. Different process parameters, temperature, pressure, and shear rate, were considered to accelerate the reaction. Increase in temperature induced a faster reaction, but controlled nature of ATRP decreased past a threshold value that can be increased up to 95 °C by reducing the residence time. Positive effect of pressure was observed since significant increases in monomer conversion (+12.5 %) and molecular weight (+5,000 g/mol) were obtained. Moreover, polydispersity index was found to decrease from 1.52 at normal pressure to 1.44 at 100 bars. Benefit of pressure was more visible in smaller reaction space (smaller tube diameter). Finally, shear rate has quite an influence on the early stage of the polymerization and is expressed by an increase in the reaction rate. However, the effect was dimed for long residence times.

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Atom Transfer Radical Polymerization in Continuous Microflow Effect of Process Parameters

Performances of a newly developed microprocess in producing size-controlled nanoemulsions in the lower nanometer range are assessed. The microprocess comprises an elongational-flow micromixer with a bore size of either 150, 250, or 500 μm. By inducing a reciprocating flow through the restriction of the micromixer, methyl methacrylate (MMA)-based nanoemulsions with controlled sizes in the range 50–300 nm are successfully prepared at low pressures (ca. 2.5 bars) in laminar to intermediate hydrodynamic flow regimes. Effect of process parameters (flow rate through the restriction, number of cycles), micromixer parameters (angle, bore size), and finally composition parameters (weight content of MMA and surfactant, dispersed to continuous phase viscosity ratio) on nanodroplet size and size distribution is thoroughly studied. A unique empirical correlation is extracted from the experimental results and is found to fairly well model the variations of the nanodroplet size with aforementioned parameters.

Rigoberto Ibarra Gomez

Papers

Atom Transfer Radical Polymerization in Continuous Microflow Effect of Process Parameters

Development of an Elongational-Flow Microprocess for the Production of Size-Controlled Nanoemulsions: Batch Operation