Krytox polymer

In their pioneering work on CO2 thickeners. Hoefling et al. studied the solubility of different Krytox-class compounds [23], At a constant temperature of 295 K (i.e., 22° C), a Krytox polymer having an M. of 13,000 g/mol exhibited cloud points at around 75, 125, and 150 bar for respective polymer contents of 1, 5, and 10 wt%. Another Krytox polymer having a carboxylic acid chain end and an of 2500 g/mol... 

FIGURE 13.6 Pressure-composition phase diagram at 40°C for binary mixtures of COj and sodium carboxylate-Krytox polymers with an of (A) 2500 g/mol, ( ) 5000 g/mol, and (O)... 

The high solubility of Krytox polymers in SC-CO2 was attributed to their weak polymer-polymer interactions, which is illustrated by their low surface tension in the range of 16-20 mN/m [25]. Interestingly, the second virial coefficient was also determined by neutron scattering experiments for a Krytox polymer with an of 16,000 g/mol [26]. A value of 0 0.2 x 10 mol.cm /g was found, which suggested that the polymer chain adopted an unperturbed chain dimension in SC-CO2. 

In addition to the fluoroplastics and fluororubbers already described other fluoropolymers have been marketed. Polymers of hexafluoropropylene oxide are marketed by Du Pont (Krytox). These materials have a low molecular weight (2000-7000) and are either oils or greases. The oils are uses as lubricants, heat transfer fluids and non-flammable oils for diffusion pumps. The greases are also used as lubricants. They have good heat and oil resistance but it is said that explosions may result from contact with the surfaces aluminium or magnesium cuttings. 

Perfluoro polyethers (Fomblin) (Krytox ) (3 x IO 8) If exposed to too much heat, decomposes to a gas rather than breaking down. Is resistant to oxidation and chemically resistant with few exceptions. No polymers are formed under energetic particle bombardment. Can be regenerated for reuse. Provides somewhat lower pumping speeds than other oils. High initial cost. Above 300 - 350°C, breaks down into aggressive and toxic compounds. To effectively remove it, chlorofluorocarbons must be used. 

Figure 8.46 shows a segment of the high-mass, positive-ion, TOF SIMS spectrum of Krytox AD. Similar spectra were reported later/ in addition, SIMS and PDMS measurements have been compared for PFPEs and other polymers. The earliest study reported more peaks in the Krytox spectra than later results, due primarily to differences in experimental conditions. To further complicate matters, the nomenclature used also changed. In all studies, however, the same major peaks were observed and the origin of these peaks is indicated in Table 8.13. We will adopt the nomenclature used in the latest study. ... 

There are also a few reports of interfacial tension of polymers with simpler liquids. Water is the most important of these liquids, e.g., the interfacial tension between water and poly(oxyhexafluoropropylene) is 53.1 mN/m at 25°C (Krytox AX, 300 cS viscosity [17]) and between water and poly(dimethylsiloxane) is 42.7 mN/m at 24°C at (Mn 1,000[18]). Interfacial tensions with liquids can also be calculated from the equations discussed in Section 59.4 [Eqs. (59.6), (59.7), or (59.8)]. For example, King et al. [19] have calculated using the harmonic mean equation [Eq. (59.8)] that the interfacial tension with water of poly... 

Peifluoropolyethers Similarly to fluorinated olefins, the introduction of fluorine atoms onto the poly(ethylene oxide) (PEO) backbone has been explored through the family of perfluoropolyethers (sometimes coined perfluoroalkylethers or perfluoropolyalkylethers). Functionalized poly(hexafluoropropylene oxides) are representative perfluoropolyethers that actually attracted early attention for their solubility in SC-CO2 (see Figure 13.5). These polymers are produced by anionic ringopening polymerization of HFP oxide and commercialized as industrial lubricants by Dupont under the name of Krytox . 

While the stabilization of W/C microemulsions with Krytox-type polymers or molecular surfactants has been largely reported [66, 67], examples implying amphiphilic copolymers are scarce in literature. These examples—described below— are exclusively based on fluorinated poly((meth)acrylates) as a consequence of their lower surface tension compared to hydrocarbons and poly(siloxanes). 

Modeling of polymer membrane structure through dynamics simulations is generally coupled with the water/proton-transfer properties. Yana et al. conducted molecular dynamics (MD) simulations of Krytox-Silica-Nafion composite membranes in comparison to the pure Nation. A 5 wt% of carboxylic acid terminated perfluoropolyether hybrid with silica (Krytox-Silica) in Nation composite polymer was used in the modification of a PEM in order to improve its efficiency at high operating temperatures. MD simulations were carried out in order to understand the microscopic properties of two systems, Krytox-Silica in Nation and pure... 

FIGURE 9.20 Initial structures of (a) Krytox-Silica molecule and charges, (b) 5% wt of Krytox-Silica in Nafion system, and (c) pure Nafion system. (From Yana, J. et al.. Polymer, 51,4632, 2010.)... 

Nafion. Models of the initial structure of Krytox-Silica as shown in Figure 9.20a and of a composition structure incorporating 5 wt% Krytox-Silica in a Nafion composite polymer consisting of 15 Nafion side chains, 15 hydronium ions, and 1 of Krytox-Silica, as shown in Figure 9.20b, were established. In another system, pure Nafion was modeled without Krytox-Silica (model structure shown in Figure 9.20c). 

Yana, J., Nimmanpipug, R, Chirachanchai, S., Gosalawit, R., Dokmaisrijan, S., Vannarat, S., Vilaithong, T., Lee, V.S., Molecular dynamics simulations of Krytox-Silica-Nafion composite for high temperature fuel cell electrolyte membranes. Polymer, 2010, 51, 4632-4638. 

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