Quenching of metal-catalyzed living radical polymerization with silyl enol ethers

✍ Scribed by Kazuki Tokuchi; Tsuyoshi Ando; Masami Kamigaito; Mitsuo Sawamoto

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 325 KB
• Volume: 38
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/1099-0518(200012)38:1+<4735::aid-pola130>3.0.co;2-l

✦ Synopsis

Various silyl enol ethers were employed as quenchers for the living radical polymerization of methyl methacrylate with the ROCl/RuCl 2 (PPh 3 ) 3 /Al(Oi-Pr) 3 initiating system. The most effective quencher was a silyl enol ether with an electrondonating phenyl group conjugated with its double bond [CH 2 AC(OSiMe 3 )(4-MeOPh) (2a)] that afforded a halogen-free polymer with a ketone terminal at a high end functionality [F n ϳ 1]. Such silyl compounds reacted with the growing radical generated from the dormant chloride terminal and the ruthenium complex to give the ketone terminal via the release of the silyl group along with the chlorine that originated from the dormant terminal. In contrast, less conjugated silyl enol ethers such as CH 2 AC(OSiMe 3 )Me were less effective in quenching the polymerization. The reactivity of the silyl compounds to the poly(methyl methacrylate) radical can be explained by the reactivity of their double bonds, namely, the monomer reactivity ratios of their model vinyl monomers without the silyloxyl groups. The lifetime of the living polymer terminal was also estimated by the quenching reaction mediated with 2a.