The use of light to mediate controlled radical polymerization has emerged as a powerful strategy for rational polymer synthesis and advanced materials fabrication. This review provides a comprehensive survey of photocontrolled, living radical polymerizations (photo-CRPs). From the perspective of mechanism, all known photo-CRPs are divided into either (1) intramolecular photochemical processes or (2) photoredox processes. Within these mechanistic regimes, a large number of methods are summarized and further classified into subcategories based on the specific reagents, catalysts, etc., involved. To provide a clear understanding of each subcategory, reaction mechanisms are discussed. In addition, applications of photo-CRP reported so far, which include surface fabrication, particle preparation, photoresponsive gel design, and continuous flow technology, are summarized. We hope this review will not only provide informative knowledge to researchers in this field but also stimulate new ideas and applications to further advance photocontrolled reactions.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00671

Light-Controlled Radical Polymerization: Mechanisms, Methods, and Applications

Having control over an entity or even an entire process is arguably the ultimate demonstration of its understanding and it will enable its potential to be fully exploited. With this in mind, chemists have not only been creating and optimizing a myriad of different catalysts for most (relevant) chemical reactions over the past decades, but have recently started to implement controlling elements into the catalyst design. These incorporated gates operate upon exposure to suitable control stimuli, and light represents perhaps the scientifically and technologically most attractive stimulus. In principle, irradiation can thereby induce activity and selectivity in a given catalyst system with high spatial and temporal control, leading to an overall localization and amplification of an optical signal and translation into chemical action. While nature has developed and utilized this concept, in particular in the processes of vision and photomovement, such artificial photocontrolled catalyst systems offer unique opportunities and have high potential for future applications. In this Review, we outline the general concept of light-gated catalysis based on photocaged and also photoswitchable systems, and discuss relevant examples of the past and recent literature.

Artificial light-gated catalyst systems.

NHC–Ru complexes—Friendly catalytic tools for manifold chemical transformations

Ruthenium complexes bearing bidentate Schiff base ligands as efficient catalysts for organic and polymer syntheses

Upon UV irradiation, the complexes [(η6-arene1)Ru(η6-arene2)]2+ (toluene-4-sulfonate or trifluormethane-sulfonate as counter ion; examples for arene: benzene, toluene, mesitylene, hexamethylbenzene, anisole, biphenyl, naphthalene) and [Ru(NC-R)6]2+ (tosylate or triflate as counter iron; R = methyl, ethyl, phenyl) are transformed into active catalysts for ring opening metathesis polymerization (ROMP) of strained bicyclic olefins. The photoinduced ring opening metathesis polymerization (PROMP) is most efficient with sandwich complexes having high quantum yields for the photochemically induced solvation of [(η6-arene1)Ru(η6-arene2)]2+ to [Ru(solvent)6]2+. With most of the complexes no (or only low) catalytic activity is observed in the absence of light. After the photolysis step, the mechanism of the polymerzation is identical to ROMP reactions with thermally activated ruthenium catalysts. Good yields and high molecular weights are obtained with a catalyst concentration of 0.1–1%. A mechanistic model for the initiation is presented. © 1995 John Wiley & Sons, Inc.

Photoinduced ring opening metathesis polymerization (PROMP) of strained bicyclic olefins with ruthenium complexes of the type [(η6‐arene1)Ru(η6‐arene2)]2+ and [Ru(Nc‐R)6]2+

Ring opening metathesis polymerization of bicyclo [2.2.1] hept-2-ene (2-norbornene) and exo,exo-5,6-bis (methoxycarbonyl)-7-oxabicyclo [2.2.1]hept-2-ene using Ru(II) and Ru(III) complexes: Polymerization kinetics and ruthenium content in polymers

P. Bernhard

Papers

Photoinduced ring opening metathesis polymerization (PROMP) of strained bicyclic olefins with ruthenium complexes of the type [(η6‐arene1)Ru(η6‐arene2)]2+ and [Ru(Nc‐R)6]2+

Ring opening metathesis polymerization of bicyclo [2.2.1] hept-2-ene (2-norbornene) and exo,exo-5,6-bis (methoxycarbonyl)-7-oxabicyclo [2.2.1]hept-2-ene using Ru(II) and Ru(III) complexes: Polymerization kinetics and ruthenium content in polymers