Frédéric Boschet

Novel source of trifluoromethyl radical as efficient initiator for the polymerization of vinylidene fluoride.

A persistent perfluoroalkyl radical (PPFR), perfluoro-3-ethyl-2,4-dimethyl-3-pentyl, is shown to be a good source of •CF(3) radicals and a useful radical capable of initiating the polymerization of vinylidene fluoride (VDF). NMR characterizations of the resulting PVDF homopolymers showed that polymerization of VDF was exclusively initiated by •CF(3) radicals. The addition of •CF(3) radical onto VDF was regioselective leading to CF(3) -CH(2) -CF(2) -PVDF and the CF(3) end-group acted as an efficient label to assess the molecular weights by (19) F NMR spectroscopy. Various [PPFR](0) /[VDF](0) initial molar ratios lead to CF(3) -PVDF-CF(3) of different molecular weights. When that ratio decreased, both the molecular weights and the thermostability of these PVDFs increased, showing less defects of chaining and higher crystallinity.

Synthesis of 3,3,3-trifluoropropene telomers and their modification into fluorosurfactants

Original fluorinated surfactants based on 3,3,3-trifluoropropene (TFP) as alternatives to perfluorooctanoic acid (PFOA) were synthesized in three to five straightforward steps in good overall yields. First, the radical or thermal telomerization of TFP in the presence of perfluoroisopropyl iodide as the chain transfer agent led to various TFP telomers of different molecular weights. They were further chemically modified into various ionic and non-ionic surfactants. To obtain anionic surfactants, TFP telomers bearing iodine end-group was converted into allylic group on which thioglycolic acid was added under a radical or photochemical process. Non-ionic surfactants were obtained by esterification of the anionic acid with poly(ethylene glycol) monomethylether. Cationic surfactants were obtained by ethylene end-capping of the TFP telomers followed by a nucleophilic substitution by either triethylamine or pyridine. All surfactants showed good inertness to bases and acids, and satisfactory surface properties. They exhibit interesting critical micellar concentration values comparable to that of PFOA (0.06, 4.10, and 3.20 versus 3.00 g L−1).

Direct surface modification of poly(VDF-co-TrFE) films by surface-initiated ATRP without pretreatment

The direct surface modification of poly(vinylidene fluoride-co-trifluoroethylene) (VDF-co-TrFE) copolymer films via surface-initiated atom transfer radical polymerization (ATRP) is presented. The surface-initiated ATRP of tert-butyl acrylate (tBA) and styrene was carried out on poly(VDF-co-TrFE) films containing 75 mol% VDF at 383 K. Such a reaction was monitored by 1H and 19F NMR, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and by water contact angle measurements. First, the 19F NMR spectra of poly(VDF-co-TrFE)-g-poly(tBA) graft copolymers revealed a reduction in the signal intensity at −123 ppm compared with that of the poly(VDF-co-TrFE) copolymer, indicating that the polymerization of tBA occurred exclusively by fluorine abstraction from the TrFE units. ATR-FTIR spectra of the resulting poly(VDF-co-TrFE)-g-poly(tBA) and poly(VDF-co-TrFE)-g-polystyrene (PS) films evidenced the characteristic absorption frequencies assigned to carbonyl and aromatic C–H stretching. The atomic ratio on the surface of polymer-grafted poly(VDF-co-TrFE) film observed by XPS well agreed with theoretical value of poly(tBA) and PS hompolymers. These results indicated that poly(tBA) and PS were successfully grafted onto the poly(VDF-co-TrFE) film surfaces forming grafting layers, the thickness of which was over 10 nm. The poly(VDF-co-TrFE)-g-poly(tBA) film was subsequently treated with p-toluenesulfonic acid and sodium hydrogen carbonate to modify the grafted chains into poly(acrylic acid sodium salt). Surface-grafted polystyrene was also converted to poly(styrene sulfonic acid sodium salt) by treatment with sulfonic acid. Each reaction step was characterized by ATR-IR and XPS. The static water contact angle of poly(VDF-co-TrFE) copolymer was remarkably reduced from 91 to 15° by hydrolysis of the tBA chains, sulfonation of the styrene chains and their neutralization. A hydrophilic surface was successfully achieved on the poly(VDF-co-TrFE) film by direct surface-initiated polymerization from the outermost surface of the TrFE unit without any change in the bulk physical properties.