Perfluoropolyether Oligomers Research Articles

Testing organic and organic–inorganic fluorinated hybrid coatings as protective materials for clay bricks

The durability of brickworks, used as facing bricks, parapets, or chimneys, is a crucial aspect of the maintenance of buildings. Water absorption and penetration due to wind-driven rain, water rundown, and capillary rising can cause serious damages and a premature deterioration of porous clay bricks, and a significant increase in their thermal conductivity. Protective coatings for brickwork must provide enhanced hydrophobic properties without affecting moisture regulation and breathability of masonry. In the present work, a standardized type of facing clay brick was treated with two types of hydrophobic coatings based on a commercial perfluoropolyether oligomer containing alkoxysilane terminal groups, respectively, with or without an inorganic precursor, tetraethoxysilane, to generate in situ silica nanoparticles. The performance of the coating was assessed by multiple indicators, such as wetting delay, water absorption coefficient, protection degree by capillarity, contact angle, roughness and gloss, as a function of the amount of coating. Uncertainties analysis of indicators was carried out. Coating performance was assessed at different exposure times comparable to in situ real ones. Optimal amounts of coating were established to maximize the protection with the minimum quantity of polymer. As a result, a square meter of brick surface exposed to water for 2–4 h can absorb about 7–8 L of water. Very small amounts of PFPE coatings change the brick surface/water interactions, more than halving the absorbed water (0.5–2 l) and increasing the protection degree up to 80–100%. After longer exposure times, the reduction in absorbed water is basically higher when brick specimens are treated with organic/inorganic nanostructured hybrid PFPE coatings.

Morphology-induced percolation in crosslinked AMPS/Fluorolink for fuel cell membrane application

New proton-conducting co-networks were synthesized, characterized and tested as Polymer Exchange Membranes for Fuel Cells application. The membranes were obtained from 2-acrylamido-2-methylpropane sulfonic acid (AMPS) copolymerized with a perfluoropolyether oligomer used as crosslinker (Fluorolink® FMD700). The structure, the thermo-mechanical behavior, the transport properties and the stability were examined in function of the co-network composition, e.g. increasing amount of conductive AMPS. High proton conductivity (1.10–3–5.10−3Scm−1) was reached at a threshold composition of 10wt% AMPS, which also corresponds to a significant increase in water sorption. The efficiency of proton transfer was shown to directly correlate to the phase-separated nanostructures. On increasing the AMPS content, hydrophilic clusters embedded in the mechanically-robust FMD700 percolate and a co-continuous 3D morphology is formed. Fuel cells tests performed using the high-AMPS content crosslinked membranes showed behaviors comparable to benchmark Nafion® under similar conditions, with performances significantly improved when the temperature is increased.

Experimental study on fluid phase equilibria of hydroxyl-terminated perfluoropolyether oligomers and supercritical carbon dioxide

Dew and bubble point pressures for bifunctional hydroxyl-terminated perfluoropolyether oligomers and supercritical carbon dioxide (SCCO2) were measured in the range (50–80)°C. The oligomers used in the measurements were purified for the present work in order to obtain four fractions with molar mass (Mn) in the range (598–4391)g/mol and dispersity close to one. The maximum pressures for the existence of phase split increase from approximately (12–13)MPa at 50°C to (17–20)MPa at 80°C, with increasing values, at given temperature, with Mn. Over the investigated ranges, the solubility of the oligomers in SCCO2 varies substantially (from 23g/kg to 318g/kg), increasing with pressure and decreasing with temperature. For Mn≥1140, the solubility monotonically decreases with Mn. In this range, the experimental data indicate that SCCO2 is a viable solvent for the fractionation of these oligomers on the basis of Mn.

Photochemical synthesis of perfluoropolyether (PFPE) nanocomposites containing PFPE oligomer stabilized magnetite nanoparticles

Magnetite nanoparticles were synthesized and their post-synthesis surface modification was carried out with triethoxy terminated perfluoropolyether (PFPE) oligomers. The surface-treated nanoparticles were then dispersed in a UV-curable difunctional methacrylic PFPE oligomer. Thin films prepared from the resulting stable suspensions were photopolymerized. The obtained nanocomposites showed good distribution of the surface-treated magnetite nanoparticles in the polymer matrix. The surface treatment of magnetite nanoparticles with perfluoropolyether oligomers thus was found to be effective in preventing nanoparticle segregation and aggregation, ensuring therefore an increased compatibility with the PFPE matrix.

UV Curing of Perfluoropolyether Oligomers Containing Graphene Nanosheets to Enhance Water‐Vapor Barrier Properties

Recently, graphene and its derivative nanosheets have been considered as potential candidates for gas barrier membranes. Here, the effect on the water‐vapor barrier properties of incorporating graphene nanoplatelets into a UV‐curable perfluoropolyether methacrylic oligo­mer is investigated. By combining the hydrophobicity of the highly fluorinated polymer with the tortuous path induced by the graphene sheets, the barrier properties of the crosslinked films are further enhanced, acting both on the thermodynamic (low solubility) and kinetic (longer diffusion path) contribution of the water‐vapor diffusion through the polymeric films. Good performance in increasing water‐vapor barrier properties at a very low filler loading is obtained: the permeability is halved in the presence of only 0.3 wt% graphene. image

Photopolymerization of a perfluoropolyether oligomer and photolithographic processes for the fabrication of microfluidic devices

A perfluoropolyether based photocured polymer is proposed as structural material for the fabrication and easy prototyping of microfluidic devices. The kinetics of photopolymerization and the fluoropolymer characterization is reported, assessing the suitability of the material: it results transparent, thermally resistant, with a good dimensional stability and a chemical resistance much higher than polydimethylsiloxane, material currently used in microfluidics. The direct fabrication of microchannels is finally presented by direct photopolymerization under UV light irradiation through photomasks: the transfer of micropatterns was successful.

Hydrophobic and oleophobic coatings based on perfluoropolyether/silica hybrids by the sol‐gel method

AbstractGlass substrates were spin‐coated with a perfluoropolyether oligomer based organic‐inorganic hybrid material, and prepared by the sol‐gel process. Contact angle analysis and atomic force microscopic analysis were carried out to characterize the surface of the prepared coatings. All systems exhibited strong hydrophobic and oleopophobic characteristics. The wettability behavior was found to be almost independent of both molecular weight and functionality of the fluorinated oligomer. The low values obtained for the contact angle and surface tension indicate that surface segregation of perfluoropolyether segments is likely to take place within the network. On the basis of these results and the high quality of the obtained coatings, these materials could be used as functional coatings to impart water and oleo‐repellent characteristics to glasses and other similar substrates. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:182–190, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20098

Catalyst effect on the crosslinking kinetics of a fluorine containing polyurethane network

A bicomponent fluorinated polyurethane coating was obtained by crosslinking a bifunctional, OH terminated perfluoropolyether oligomer with a fluorinated polyisocyanate based on the isophorone diisocyanate (IPDI) cyclic trimer. Three different tin containing catalysts (dibutylin dilaurate (DBTDL), dibutyltin dimercaptide (DBTDM), tin octoate (TO)) were evaluated during the crosslinking reaction through gel time measurements and IR spectroscopy at various temperatures from +15 to +45°C. Both the methods showed a substantial higher activity of the first two catalysts, tin octoate being almost ineffective (latent) at ambient temperature. The spectroscopic measurements allowed the determination of apparent second-order kinetic constant (k) of the crosslinking reaction. The activation energies E a in the temperature range considered were obtained from the corresponding Arrhenius plot, showing a temperature dependence higher for DBTDM than DBTDL (8.5 vs. 7.0 kcal/mol). Finally, the conversion of the crosslinking reaction on the dry polymer film was estimated to be around 60-80% after 8h at ambient temperature for DBTDM and DBTDL, but only 20-25% for TO catalyzed reactions. The formation of a hard urethane phase having a glass transition temperature T g higher than the crosslinking temperature was considered as the main limiting factor of the overall reaction rate.

Catalyst effect on the crosslinking kinetics of a fluorine containing polyurethane network

A bicomponent fluorinated polyurethane coating was obtained by crosslinking a bifunctional, OH terminated perfluoropolyether oligomer with a fluorinated polyisocyanate based on the isophorone diisocyanate (IPDI) cyclic trimer. Three different tin containing catalysts (dibutyltin dilaurate (DBTDL), dibutyltin dimercaptide (DBTDM), tin octoate (TO)) were evaluated during the crosslinking reaction through gel time measurements and IR spectroscopy at various temperatures from +15 to +45°C. Both the methods showed a substantial higher activity of the first two catalysts, tin octoate being almost ineffective (latent) at ambient temperature. The spectroscopic measurements allowed the determination of apparent second-order kinetic constants (k) of the crosslinking reaction. The activation energies Ea in the temperature range considered were obtained from the corresponding Arrhenius plot, showing a temperature dependence higher for DBTDM than DBTDL (8.5 vs. 7.0 kcal/mol). Finally, the conversion of the crosslinking reaction on the dry polymer film was estimated to be around 60–80% after 8 h at ambient temperature for DBTDM and DBTDL, but only 20–25% for TO catalyzed reactions. The formation of a hard urethane phase having a glass transition temperature Tg higher than the crosslinking temperature was considered as the main limiting factor of the overall reaction rate.

Linear perfluoropolyether difunctional oligomers: chemistry, properties and applications

The synthesis of telechelic perfluoropolyether oligomers (PFPE) is described. The preparation of these fluorinated derivatives of the structure R h–CF 2(OCF 2) q (OCF 2CF 2) p OCF 2–R h was performed by condensation or nucleophilic reactions starting from PFPE precursors bearing carboxylic or alcoholic functional groups. A large variety of selective synthetic routes have been explored, differences in comparison with conventional hydrogenated molecules emphasized, and the related mechanisms elucidated. High yields and selectivities were generally observed, this enables to isolate oligomers of high purity, whose properties can be easily fine-tuned by varying the structural parameters. Some interesting chemical and physical properties are shown; and potential, highly innovative applications briefly discussed.

A facile synthesis for functional perfluoropolyether oligomers, diacids, diesters, and surfactants

AbstractLinear polyester precursors provide a convenient low cost synthesis for flurocarbon surfactants, diacids, diesters, and intermediates. A reaction scheme starting with hydrocarbon linear polysters followed by conversion of the ester to a perfluoro ester by direct fluorination and subsequent treatment with nonstoichiometric amount of sulfur tetrafluoride produce upon hydrolysis of ester units remaining in the polymer, low molecular weight perfluropolyether diacids. Alternatively, this technique can be altered slightly to produce diesters and other functional perfluorocarbon intermediates.