Grafting From Polymerization of Vinylidene Fluoride (VDF) from Silica to Achieve Original Silica-PVDF Core-Shells

A new method of surface modification based on the grafting from polymerization process enabled to prepare original silica nanoparticles covered with PDVF hair. This strategy involved two steps: (i) the radical addition of 1,4-diiodoperfluorobutane initiated by tert-butylperoxypivalate onto the double bonds of silica nanoparticles (specific area of 150 m(2) g(-1)) led to silica that bore C4F8I end-groups on its surface, and (ii) its use as original macrochain transfer agent in the grafting from polymerization of vinylidene fluoride (VDF) initiated by bis(4-tert-butylcyclohexyl) peroxydicarbonate. The characterizations of both modified silica were achieved by elemental analysis, H-1 and F-19 magic angle spinning solid state rotational-echo double resonance NMR spectroscopy, thermogravimetry, and water contact angle (WCA) assessments. The grafting efficiency was confirmed by three features: (i) the increase of weight percentage of fluorine atom (that ranged from 0 for the starting unsaturated silica to 2.50% for silica-bearing -C4F8I end-group and to 3.32% for original silica-PVDF core-shells), (ii) a high thermostability (that reached more than 400 degrees C under air), and (iii) a good hydrophobicity: the WCA values were ranging from 84 degrees to 109 degrees and to 126 degrees for vinyl silica, for silica coated with -C4F8I, and for PVDF-covered silica nanoparticles, respectively.