Penultimate effect in radical copolymerization of 2- trifluoromethylacrylates

Abstract

Electron-deficient 2-trifluoromethylacrylates (TFMA) undergo radical copolymerization with electron-rich norbornene derivatives, vinyl ethers, and styrene derivatives, which can be described by the penultimate model much better than by the commonly employed terminal model. In an attempt to directly observe the effect of the CF3 group in the penultimate unit on the radical reactivity, we employed the Giese's mercury method. 4,4,4-Trifluorobutyl and n-butyl radicals produced from respective alkylmercuric chlorides were competitively reacted with t-butyl 2-trifluoromethylacrylate (TBTFMA) and t-butyl methacrylate (TBMA) and the products analyzed with gas chromatography. While TBTFMA has been found to be about 24 times more reactive than TBMA toward the n-butyl radical, the former is about 12 times more reactive than the latter toward the 4,4,4-trifluorobutyl radical. Thus, the reactivity of the propagating radical toward TBTFMA in comparison with TBMA is suppressed by a factor of two when the penultimate unit has the CF3 group. We observed a sextet electron spin resonance of the TFMA propagating radical with a coupling constant of ca. 25 gauss between the β-proton and β-fluorine. © 2008 Wiley Periodicals, Inc.