Oxygen‐Demanding Photocontrolled RAFT Polymerization Under Ambient Conditions

Abstract

A photocontrolled reversible addition−fragmentation chain transfer (RAFT) process is developed by initiating polymerization through a 1,3‐diaminopropane‐triethylborane (DAPTB)−diphenyl iodonium salt (Ph2I+) complex (DAPTB/Ph2I+) under ambient temperature and atmospheric conditions. Upon demand, this air‐stable DAPTB/Ph2I+ complex is photolyzed to liberate a reactive triethylborane that consumes atmospheric oxygen and generates ethyl radicals, which initiate and mediate RAFT polymerization. Controlled RAFT polymerization is thus achieved without any prior deoxygenation using a novel RAFT chain transfer agent, BP‐FSBC, which contains both benzophenone and sulfonyl fluoride moieties. Furthermore, the kinetics of polymerization reveal that the reaction process is rapid, and well‐defined polymers are produced by a 61% conversion of 2‐hydroxyethyl acrylate (HEA) within 7 min and 77% conversion of N,N‐dimethylacrylamide (DMA) within 10.5 min. The temporal and spatial control of this photopolymerization is also demonstrated by an “on/off” switch of UV irradiation and a painting‐on‐a‐surface approach, respectively. In addition, active chain ends are demonstrated by preparing block copolymers by chain extension and click sulfur(VI)‐fluoride exchange postreaction using RAFT‐derived macrochain transfer agents.

Photocontrolled RAFT polymerization: past, present, and future

“…178 Wu and coworkers reported both oxygen-demanding and photocontrolled polymerization based on light-induced decomplexation of the alkylborane complex. 179 Upon UV light irradiation, the photoacid in the triethylborane-amine/photoacid complex 1,3-diaminopropane-triethylborane (DAPTB)/Ph 2 I + generated a proton which subsequently released ethylborane to consecutively initiate polymerization (Scheme 17b).…”

“…ZnTPP demonstrated a wide absorption profile, so PET-RAFT polymerization could be performed under blue, green, Scheme 17 Mechanism of (a) oxygen-mediated generation of an initiating radical from triethylborane 177 and (b) photomediated decomplexation of 1,3-diaminopropane-triethlyborane (DAPTB) to triethylborane. 179 This journal is © The Royal Society of Chemistry 2023 Chem. Soc.…”

N-Coordinated Organoboron in Polymer Synthesis and Material Science

“…However, alkylboranes were pyrophoric species, which limited their use under ambient conditions. An electron-donating ligand (L) was used to stabilize alkylborane via the N→B dative bond, thereby forming air-stable initiators (Figure b). − It was deblocked with carboxylic acid, isocyanate, or a photocatalyst to in situ release the alkylborane that initiated controlled radical polymerization (the structures of the synthesized polymers summarized in Figure d) or drove thiol–ene polymerization in the presence of oxygen. More stable N-coordinated alkylboranes were suitable for preservation and wide applications.…”

Alkylborane initiated RAFT polymerization: impact of carboxylic acid deblockers

“…18 Most recently, in 2022, Peng et al reported a photo-controlled alkylborane RAFT process allowing the release of alkylborane using a photo-acid and UV trigger for spatiotemporal control of polymerization. 19 Beyond RAFT, alkylboranes are also being explored in combination with other mechanisms of reversible deactivation radical polymerization. 10,20,21 While alkylborane chemistry has shown great versatility and utility in RAFT, many aspects remain unexplored.…”