Synthesis and characterization of a novel polyfluorinated silsesquioxane polymer as a promising material for creating hydrophobic coatings and proton-conducting membranes

The demand for original fluorine-containing organosilicon polymer materials is constantly growing, which is associated with their unique properties, such as chemical and thermal stability, hydro- and oleophobicity, optical clarity, mechanical strength, and others, which open up new opportunities for the creation of innovative technologies and materials. In this regard, it is necessary to create new materials with a set of high performance characteristics that meet the increased requirements placed on them. In this study, we report the synthesis of a previously unknown poly[3-(2,2,3,3-tetrafluoropropoxy)propyl]silsesquioxane (F-PSQ) by a facile and efficient hydrolytic polycondensation reaction of triethoxy[3-(2,2,3,3-tetrafluoropropoxy)propyl]silane (F-TES) monomer in ethanol using sodium hydroxide as a catalyst. The structure of the target polymer was characterized by 1H, 13C, 19F, and 29Si multinuclear NMR spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography and powder X-ray diffraction, and its thermal stability was analyzed by thermogravimetric analysis and differential scanning calorimetry. It has been established that F-PSQ is characterized by the high weight average molecular weight of 16800 Da and a low polydispersity index  and has a ladder-like structure. The possibility of using the synthesized polyfluorosilsesquioxane as a promising functional hydrophobic material and component of proton-conducting membranes is shown. The values of water contact angles for film coatings obtained on the basis of synthesized fluorine-containing triethoxysilane and polysilsesquioxane, depending on the surface structure, varied from 92° to 115°. A hybrid composite membrane based on fluorinated polysilsesquioxane and poly(1-vinyl-1,2,4-triazole) doped with phosphoric acid has a proton conductivity of 5.3⋅10-4 S/cm to 1.2⋅10-2 S/cm in the temperature range from 25°C to 150°C in anhydrous state.