Trifluoromethyl radicals reaction with fluoro-olefins

The fraction of head-to-head linkages in the poly(fluoro-olefms) increases in the series PVF2 < PVF PVF3 (Tabic 4.2). This can be rationalized in terms of the propensity of electrophilic radicals to add preferentially to the more electron rich end of monomers (i.e, that with the lowest number of fluorines). This trend is also seen in the reactions of trifluoromethyl radicals wilh the fluoro-olefins (see 2.3). 

The behavior of methyl and halomethyl radicals in their reactions with the fluoro-olefins (Table 1.2), can thus be rationalized hi terms of a more dominant role of polar factors and the nucleophilic or electrophilic character of the radicals involved. Methyl radicals are usually considered to be slightly nucleophilic, trifluoromethyl and trichloromcthyl radicals arc electrophilic (Tabic 1.4). 

It is apparent that substitution of fluorine for hydrogen initially causes a reduction in reactivity towards the electrophilic oxy n atom, but tetra-fluoroethylene is anomalous. A further study has indicated that substitution by trifluoromethyl has a strong deactivating effect compared with methyl, which has an activating effect. A study of the reactions of nearly thermal i F atoms, produced by F(n,2n) F and moderated by collisions with an excess of sulphur hexafluoride, with fluoro-oleflns (modes of addition were identified by scavenging the radicals produced with hydrogen iodide) has indicated that F atoms react preferentially with less-fluorinated olefins, and at the less-fluorinated end of a particular olefin. ... 

---