Robust Miniemulsion PhotoATRP Driven by Red and Near-Infrared Light

Abstract

Photoinduced polymerization techniques have gathered significant attention due to their mild conditions, spatiotemporal control, and simple setup. In addition to homogeneous media, efforts have been made to implement photopolymerization in emulsions as a practical and greener process. However, previous photoinduced reversible deactivation radical polymerization (RDRP) in heterogeneous media has relied on short-wavelength lights, which have limited penetration depth, resulting in slow polymerization and relatively poor control. In this study, we demonstrate the first example of a highly efficient photoinduced miniemulsion ATRP in the open air driven by red or near-infrared (NIR) light. This was facilitated by the utilization of a water-soluble photocatalyst, methylene blue (MB + ). Irradiation by red/NIR light allowed for efficient excitation of MB + and subsequent photoreduction of the ATRP deactivator in the presence of water-soluble electron donors to initiate and mediate the polymerization process. The NIR light-driven miniemulsion photoATRP provided a successful synthesis of polymers with low dispersity (1.09 ≤ Đ ≤ 1.29) and quantitative conversion within an hour. This study further explored the impact of light penetration on polymerization kinetics in reactors of varying sizes and a large-scale reaction (250 mL), highlighting the advantages of longer-wavelength light, particularly NIR light, for large-scale polymerization in dispersed media owing to its superior penetration. This work opens new avenues for robust emulsion photopolymerization techniques, offering a greener and more practical approach with improved control and efficiency.

Highly efficient dual photoredox/copper catalyzed atom transfer radical polymerization achieved through mechanism-driven photocatalyst design

“…ATRP with dual photoredox/copper catalysis has recently been proposed by the groups of Yagci 48 – 50 , Strehmel 50 – 52 , and Matyjaszewski 53 – 60 . This approach combines the advantages of both photo-ATRP and photoredox-mediated ATRP.…”

“…In the other mechanism, PC in the photoexcited state is initially reduced via ET process with the ligand, forming the PC radical anion (PC •– ) (Fig. 1a , Mechanism III) 59 , 60 . Subsequently, the PC •– facilitates the reduction of Cu(II)Br 2 /L to Cu(I)Br/L, simultaneously regenerating the ground state of PC.…”

“…The mechanism for remarkable oxygen tolerance is believed to rely on the oxygen scavenging ability of Cu(I)Br/L and/or the lowest triplet excited (T 1 ) state of PC 55 , 59 . This leads to substantial improvements in the practical utility of ATRP 59 , 60 , 63 – 65 .…”