Mn2(CO)10-promoted cationic polymerization of isobutylene upon visible light irradiation
Trofimuk D.1,2, Hulnik M.1,Kostjuk S. 3
1 Research Institute for Physical Chemical Problems of the Belarusian State University, 220006 Minsk, Belarus
2 Department of Chemistry, Belarusian State University, 220006 Minsk, Belarus
3Sorbonne Universite, CNRS, Institut Parisien de Chimie Moleculaire, Equipe Chimie des Polymeres, 4 place Jussieu, 75252 Paris Cedex 05, France
Photocatalysis in polymer synthesis has rapidly advanced recently with significant progress in photocontrolled cationic polymerization [1]. The most promising approach to perform photocontrolled cationic polymerization involves using a suitable photoredox catalyst (PC) paired with a chain transfer agent (CTA), capable of mediating the polymerization via reversible-deactivation mechanism. However, despite the wide range of PCs and CTAs reported, this field remains limited to polymerization of highly reactive monomers such as vinyl ethers [2]. Recently, Yagci et al. developed alternative approach using a benzyl bromide/Mn₂(CO)₁₀/diphenyliodonium salt catalytic system for visible-light-induced living cationic polymerization of vinyl ethers [3]. The reaction occurs via radical oxidation/addition/deactivation mechanism, which can be potentially applied for the polymerization of less reactive monomers.
In this study, the visible-light-induced cationic polymerization of isobutylene using photoinitiating system PhCH₂Br/Mn₂(CO)₁₀/Ph₂IPF₆ was investigated in a mixture of CH₂Cl₂/n-hexane at −30°C [4]. Polyisobutylenes with a number-average molecular weight up to 3000g·mol⁻¹, relatively low polydispersity (Đ<1.7), and high content of exo-olefin end groups (>90%) were obtained. The possibility of controlling the molecular weight of synthesized polymers in the range of 2000 to 12,000g·mol⁻¹ by varying the concentration of diphenyliodonium salts was demonstrated. The influence of the oxidizing agent nature was investigated in detail. It was shown that substituents in the benzene ring of the diaryliodonium salt affect the rate of polymerization, while the nature of counterion influences significantly the molecular weight of polyisobutylene.
This work was supported by State Program for Scientific Research of Belarus “Chemical processes, reagents and technologies, bioregulators and bioorganic chemistry” (project 2.1.01.03).
References
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[3] Ciftci, M.; Yoshikawa, Y.; Yagci, Y.; Living Cationic Polymerization of Vinyl Ethers through a Photoinduced Radical Oxidation/Addition/Deactivation Sequence. Angew. Chem., 2016, 129 (2), 534-538. DOI: 10.1002/ange.201609357
[4] Hulnik, M.; Trofimuk, D.; Nikishau, P.A.; Kiliclar, H.C.; Kiskan, B.; Kostjuk, S.V. Visible-Light-Induced Cationic Polymerization of Isobutylene: A Route toward the Synthesis of End-Functional Polyisobutylene. ACS Macro Lett., 2023, 12 (8), 1125-1131. DOI: 10.1021/acsmacrolett.3c00384.