Quenching of metal-catalyzed living radical polymerization with silyl enolethers

Various silyl enol ethers were employed as quenchers for the living radical polymerization of methyl methacrylate with the R-Cl/RuCl2(PPh3)(3)/Al(Oi-P r)(3) initiating system. The most effective quencher was a silyl enol ether with an electron-donating phenyl group conjugated with its double bond [CH 2=C(OSiMe3)(4-MeOPh) (2a)] that afforded a halogen-fi ee polymer with a ket one terminal at a high end functionality [(F) over bar (n) similar to 1]. S uch silyl compounds reacted with the growing radical generated from the dor mant chloride terminal and the ruthenium complex to give the ketone termina l via the release of the silyl group along with the chlorine that originate d from the dormant terminal. In contrast, less conjugated silyl enol ethers such as CH2=C(OSiMe3)Me were less effective in quenching the polymerizatio n. The reactivity of the silyl compounds to the poly(methyl methacrylate) r adical can be explained by the reactivity of their double bonds, namely, th e monomer reactivity ratios of their model vinyl monomers without the silyl oxyl groups. The lifetime of the living polymer terminal was also estimated by the quenching reaction mediated with 2a. (C) 2000 John Wiley & Sons, In c.