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R-410A, an azeotropic mixture composed of 50 wt % difluoromethane (HFC-32, CH2F2) and 50 wt % pentafluoroethane (HFC-125, CHF2CF3) used in residential and commercial air-conditioning applications, will be phased down due to the high global warming potential (GWP) of HFC-125. The HFC-32 can be reused in low-GWP blends containing hydrofluoroolefins (HFOs); however, incumbent separation technology, fractional distillation, cannot separate azeotropic mixtures. Membrane technology provides the opportunity to achieve a selective separation of azeotropic HFC refrigerant mixtures with lower energy consumption and capital requirements. This study explores the use of amorphous perfluoropolymers for the separation of R-410A. The permeability, solubility, and diffusivity of HFC-32 and HFC-125 were measured in copolymers of perfluoro(butenyl vinyl ether) (PBVE) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD). Pure gas permeability of HFC-32 and HFC-125 were measured using a static membrane apparatus and the pressure-rise method. Solubility measurements were obtained using a gravimetric microbalance, and diffusivity was calculated using a Fickian model. The results indicate that a high permeability and selectivity of HFC-32/HFC-125 can be obtained with a 50 wt % PBVE and 50 wt % PDD copolymer and that the separation is diffusion-driven over the entire range of compositions tested.

Remarkably low wear rates were observed in PTFE–PEEK and polytetrafluoroethylene (PTFE)-alpha-alumina composites when evaluated in a “self-mated” configuration, where a polymer pin is slid against a polymer countersample of the same composition. Each composite was tested in a controlled humidity environment on a linearly reciprocating tribometer on two different countersamples: a polymer countersample (self-mated) and a stainless steel countersample for comparison. For all the self-mated PTFE–PEEK composites [polyether ether ketone (PEEK) wt % 10, 20, 30, 40, and 50], the average friction coefficient was reduced, and the steady-state and total specific wear rates were improved when compared to testing against stainless steel. Self-mated PTFE–PEEK (wt % 10–40) achieved ultralow wear rates on the order of 10–9mm3/Nm and friction coefficients of 0.08–0.14. When compared with samples slid against stainless steel, IR spectroscopy of the sliding surface showed that the self-mated PTFE–PEEK composites accumulate more PEEK at the sliding interface and more expression of a tribochemical carboxylate species, which have been linked with ultralow wear PTFE materials. The PTFE composites slid on steel rely on the formation of transfer films for ultralow wear performance. This is achieved by unidirectional increasing surface energy gradients from the polymer pin to the steel substrate, which dominate the transport and wear of PTFE composites slid on steel. However, the self-mated ultralow wear PTFE-based composites rely only on the formation and stability of tribofilms that consist of tribochemically altered PTFE with new carboxylate end groups as well as accumulated filler (i.e., PEEK or alumina). These films have self-regulating, minimal differences in surface energy. The close match of these low-energy surfaces contributes to low friction and ultralow wear. The self-mated PEEK-filled PTFE outperforms the alumina-filled PTFE primarily because of the ease at which PEEK accumulates at the surface. Additionally, the reinforcement and anchoring of the surface is better for a polymer blend than a particle-reinforced composite.

The role of water in the tribochemical mechanisms of ultralow wear polytetrafluoroethylene (PTFE) composites was investigated by studying 10 and 20 wt % polyether ether ketone (PEEK)-filled and 5 wt % αAl2O3-filled PTFE composites. These composites were run against stainless-steel substrates in humidity, water, and dry nitrogen environments. The results showed that the wear behavior of both composites was significantly affected by the sliding environment. Both composites achieved remarkably low wear rates in humidity because of tribochemically generated carboxylate end groups that anchored the polymer transfer films to the steel substrate. In nitrogen, PTFE–PEEK outperformed PTFE−αAl2O3because of polar carbonyl groups on PEEK, which increased the surface energy of PEEK, aiding it in adhering to the substrate and resulting in a transfer film. Both composites in water exhibited high wear. The water oversaturated the functional groups at the end of the polymer chains and prevented the formation of a transfer film.

Friction-induced shear stress and wear of poly[tetrafluoroethylene-co-(perfluoroalkyl vinyl ether)], also known as perfluoroalkoxy polymer (PFA), causes microstructural and chemical changes. These changes are essential to understand PFA as a tribological material. Tribological (friction and wear) experimentation coupled with differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy was used to characterize the microstructure and chemical differences in PFA wear debris versus bulk. PFA wear debris transitioned from triclinic to hexagonal crystalline structure at lower temperatures and had increased crystallinity versus bulk PFA. Shear-driven molecular alignment was the likely cause of these microstructural changes. Reduced molecular weight of PFA wear debris was confirmed by the presence of free carboxylic acids. Reduced molecular weight is likely due to shear-driven chain scission of the PFA backbone within the amorphous region of the microstructure. Reduced molecular weight and increased crystallinity are observed in wear of PTFE and support the tribochemically driven mechanism for ultralow wear fluoropolymer–alumina composites.

Twenty-two tricyclo[4.2.1.02,5]non-7-ene (TCN) or 3-oxatricyclononene monomers, having fluorinated or nonfluorinated substituents on the four-membered rings, were prepared by cycloaddition reactions of functionalized olefins with norbornadiene or quadricyclane. Radical polymerizations with tetrafluoroethylene (TFE) and/or TFE and acrylates provided amorphous polymers with high solubility in standard organic solvents. The TFE/TCN dipolymers typically have glass transition temperatures of over 200 °C, substantially higher than TFE copolymers with norbornene. Perfluoroalkyl sulfonyl fluoride groups can be incorporated in the side chains of the TCN monomers giving soluble copolymers. Polymers which also incorporated acrylate monomers were prepared using a semibatch process to control composition. Selected polymers incorporating tertiary alkyl ester groups from the TCN monomer or acrylates have shown good image formation when compounded with a photoacid generator, imaged with 157 or 193 nm light, and developed using aqueous base.

New experimental results are presented for the solubility and diffusivity of difluoromethane in 19 room-temperature ionic liquids (RTILs). In the series of RTILs presented here, eight RTILs with five new fluorocarbon sulfonate anions have been prepared for the first time. The measurements were performed using a gravimetric microbalance at temperatures between (283.15 and 348.15) K and at pressures from (0.01 to 1.0) MPa. Experimental gas solubility data were successfully correlated with the nonrandom two-liquid (NRTL) solution model. The solubility of difluoromethane in RTILs is affected by the choice of both the cation and anion. Diffusivities obtained from the time-dependent absorption data were well analyzed using a model based on a modified Stokes−Einstein equation. The calculated molecular size for difluoromethane is 2 to 3 times larger than the known size.

Synthesized from hexafluorobenzene, the title compound was found to interconvert readily via bond–shift isomerization and electrocyclization with significant amounts of three other valence isomers. The mobile equilibria were revealed by 19F NMR spectroscopy, and spin–saturation transfer experiments played a key role in identifying the isomers, tracing their interconversions, and assigning their spectra. The influence of fluorine substitution on the stability of carbon–carbon double bonds and of 4‐membered rings is discussed in the light of these results.

Linear 1,3‐diketones undergo fluorination with the title α‐fluoroamine.

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