Activation and Deactivation of Chain-transfer Agent in Controlled Radical Polymerization by Oxygen Initiation and Regula
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ARTICLE
POLYMER SCIENCE
https://doi.org/10.1007/s10118-020-2441-7 Chinese J. Polym. Sci.
Activation and Deactivation of Chain-transfer Agent in Controlled Radical Polymerization by Oxygen Initiation and Regulation Chun-Na Lv, Ning Li, Yu-Xuan Du, Jia-Hua Li, and Xiang-Cheng Pan* State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200438, China
Electronic Supplementary Information Abstract The activation and deactivation of the chain-transfer agent were achieved by oxygen initiation and regulation with triethylborane under ambient temperature and atmosphere. The autoxidation of triethylborane overcame the oxygen inhibition and produced initiating radicals that selectively activate the chain-transfer agent for the chain growth or deactivate the active chain-end of polymer in controlled radical polymerization. Both activation and deactivation were highly efficient with broad scope for various polymers with different chain-transfer agents in both organic and aqueous systems. Oxygen molecule was particularly used as an external regulator to initiate and achieve the temporal control of both activation and deactivation by simply feeding the air. Keywords RAFT; Oxygen; Borane Citation: Lv, C. N.; Li, N.; Du, Y. X.; Li, J. H.; Pan, X. C. Activation and deactivation of chain-transfer agent in controlled radical polymerization by oxygen initiation and regulation. Chinese J. Polym. Sci. https://doi.org/10.1007/s10118-020-2441-7
INTRODUCTION Controlled radical polymerization (CRP) was recognized as the most important breakthrough in macromolecular science during the last half-century that provided practical routes for synthesizing polymers with precisely defined molecular weights, molecular weight distributions, and architectures.[1−3] Atom transfer radical polymerization (ATRP)[4−6] and reversible addition-fragmentation chain transfer (RAFT)[7,8] polymerization were extensively investigated and commonly used CRP methods. Compared to the utilization of alkyl bromides or chlorides as ATRP initiators, chain-transfer agents (CTAs) were responsible for the controlled polymerization in RAFT process, such as dithioesters, trithiocarbonates, dithiocarbamates, and xanthates.[9,10] The sulfur-containing CTAs could be activated to generate initiating or propagating radicals by conventional radical initiators[11,12] and photoredox catalysts via photoinduced electron/energy transfer (PET) process.[13−18] However, sulfurcontaining groups left in synthetic polymers were undesirable due to their heavy odor, color, toxicity, and reactivity, limiting the practical application and commercialization.[19] Additional methods such as deactivations or transformations of CTAs were required to solve these problems.[20−22] Oxygen molecule was considered as a radical inhibitor in almost all the radical reactions including controlled radical polymerization at low temperature. To overcome this limita
* Corresponding author, E-mail: [email protected] Received March
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