Polimerização Radical por Transferência de Átomos de Monômeros Vinílicos Funcionalizados Usando Perileno como Fotocatalisador de Luz Visível

The synthesis of technologically advanced polymers requires precise control over polymer molecular weight, dispersity (Ð), composition, and architecture.^1,2 Controlled radical polymerizations (CRPs)^3-8 have revolutionized the synthesis of well-defined polymers, with atom transfer radical polymerization (ATRP) being the most used CRP, largely due to operational simplicity and synthetic versatility.^9-14 The crux of ATRP is the ability to reversibly deactivate the polymerization, controlling the equilibrium between a propagating radical and a dormant species. Enforcing a low concentration of active radicals greatly minimizes bimolecular termination pathways and allows for the synthesis of well-defined polymers.

Traditional ATRP relies on a transition metal catalyst to mediate this equilibrium.³ These metal catalysts contaminate the polymer product and impede implementation in biomedical or electronic applications while also raising environmental concerns. Although significant strides have been made to reduce the catalyst concentration to ppm levels, these methodologies require more demanding experimental conditions and metal contamination is still not entirely eliminated.^15,16

Reversible addition-fragmentation transfer^17,18 and nitroxide-mediated polymerizations^19,20 are CRPs that do not require metal catalysts, although they have been used less often than ATRP.³ Recently, reversible chain-transfer²¹ and reversible complexation^22,23 variants of ATRP that can use organic catalysts were reported. However, these methodologies require the use of alkyl iodide initiators and are not effective with the alkyl bromides commonly employed in ATRP. A highly desirable CRP would match the performance, feasibility, and robustness of traditional ATRP while being catalyzed by an organic catalyst under mild conditions.

Here, we describe a methodology for the radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst. Through optimization of parameters such as stoichiometry, concentration, time, and light flux, the molecular weight of the polymers can be controlled.^{24, 25} Similar methodologies have been recently introduced using phenothiazine derivatives as photocatalysts for metal-free ATRP.^{26, 27} Because researchers in the field of polymerization catalysis are constantly developing new catalytic systems, the ability to compare catalyst performance across a number of metrics is vital. This ability to make comparisons relies heavily upon procedural consistency and clarity on the part of the researchers performing the experiments. As such, it is our goal that this video will be used to help precisely communicate the methods by which these polymers are synthesized and characterized.