A Robust and Versatile Photoinduced Living Polymerization of Conjugated and Unconjugated Monomers and Its Oxygen Tolerance

TLDR

Controlled/living radical polymerization has enabled precise polymer synthesis but lacks external stimulus control and remains sensitive to trace oxygen. This study introduces a photoinduced living polymerization that uses ultralow concentrations of an iridium photoredox catalyst and a low‑energy visible LED to polymerize a wide range of conjugated and unconjugated monomers. The method allows chain extensions of poly(methacrylate), poly(styrene), poly(N‑vinyl pyrrolidinone), poly(vinyl ester), and poly(acrylate) homopolymers to form diblock copolymers. The approach yields homopolymers from 1,000 to 2,000,000 g mol⁻¹ with narrow dispersities (M_w/M_n < 1.3), enables decablock copolymer synthesis, and functions effectively in the presence of air.

Abstract

Controlled/living radical polymerization techniques have transformed polymer chemistry in the last few decades, affording the production of polymers with precise control over both molecular weights and architectures. It is now possible to synthesize almost an infinite variety of macromolecules using nonspecialized equipment, finding applications in high-tech industry. However, they have several shortcomings. Until recently, living radical polymerizations could not be controlled by an external stimulus, such as visible light, pH, mechanical, chemical, etc. Moreover, they are usually sensitive to trace amounts of oxygen in the system. In this Article, we report a photoinduced living polymerization technique, which is able to polymerize a large range of monomers, including conjugated and unconjugated monomers, using ultralow concentrations of an iridium-based photoredox catalyst (typically 1 ppm to monomers) and a low energy visible LED as the light source (1-4.8 W, λ(max) = 435 nm). The synthesis of homopolymers with molecular weights ranging from 1000 to 2,000,000 g/mol was successfully achieved with narrow molecular weight distributions (M(w)/M(n) < 1.3). In addition, chain extensions of poly(methacrylate)s, poly(styrene), poly(N-vinyl pyrrolidinone), poly(vinyl ester)s, and poly(acrylate)s were performed to prepare diblock copolymers. The reusability of the catalyst was demonstrated by the synthesis of a decablock polymer by multiple chain extensions. Most importantly, this process was employed to prepare well-defined polymers and multiblock copolymers in the presence of air.