May Trifluoromethylation and Polymerization of Styrene Occur from a Perfluorinated Persistent Radical (PPFR)?

The radical polymerization of styrene (St) initiated by a trifluoromethyl radical generated from a perfluorinated highly branched persistent radical (PPFR) is presented with an isolated yield above 70 %. The release of (CF3)-C-. radical occurred from a temperature above 85 degrees C. Deeper H-1 and F-19 NMR spectroscopies of the resulting fluorinated polystyrenes (CF3-PSts) evidenced the presence of both CF3 end-group of the PSt chain and the trifluoromethylation of the phenyl ring (in meta-position mainly). [PPFR](0)/[St](0) initial molar ratios of 3:1, 3:10 and 3:100 led to various molar masses ranging from 1750 to 5400 g mol(-1) in 70-86 % yields. MALDI-TOF spectrometry of such CF3-PSts highlighted polymeric distributions which evidenced differences between m/z fragments of 104 and 172 corresponding to styrene and trifluoromethyl styrene units, respectively. Such CF3-PSt polymers were also compared to conventional PSts produced from the radical polymerization of St initiated by a peroxydicarbonate initiator. A mechanism of the polymerization is presented showing the formation of a trifluoromethyl styrene first, followed by its radical (co)polymerization with styrene. The thermal properties (thermal stability and glass transition temperature, T-g) of these polymers were also compared and revealed a much better thermal stability of the CF3-PSt (10 % weight loss at 356-376 degrees C) and a T-g of around 70 degrees C.