Fluorinated peroxy radicals

Fluorinated peroxy radicals. Kinetic, Nitric Oxides, Organic nitrates, UV Spectroscopy... 

Self-Reaction Kinetics. Of all peroxy radical reactions, the self-reaction between two identical peroxy radicals is perhaps the most studied. The measurement of peroxy radical UV absorption cross sections, discussed above, often occurs under the assumption that all the chlorine or fluorine atoms produced by photolysis are converted quantitatively into peroxy radicals however, this assumption must be corrected for by the loss of peroxy radicals from self-reaction. Furthermore, studies of RO2 -b NO or RO2 -f HO2 reactions usually take place at sufficiently high RO2 concentrations to require knowledge of the self-reaction rate constant, in order to interpret the results of the kinetics measurements. Both concerns make laboratory studies of peroxy self-reaction kinetics an important issue. In contrast, the steady-state atmospheric concentrations of HCFC-based peroxy radicals are probably too small for their self-reactions to be relevant to atmospheric chemistry. In this context, the most important peroxy-peroxy radical reactions would be between the HCFC-based peroxy radicals and CH3O2, but such reactions have not been studied to date. 

Since a large body of information is known, it is the purpose of this chapter to review the important structural features of fluorine-containing radicals oriented in irradiated single crystals. It will also be demonstrated that these radicals undergo a dyncimic motion over a wide range of temperatures, that oxygen can diffuse into a number of these irradiated crystals forming peroxy radicals and that a complete radical formation and decay mechanism for oriented fluorinated radicals is not known. 

Mitov, S., Panchenko, A., Roduner, E. (2005) Comparative DPT study of non-fluorinated and perfluorinated alkyl and aUsyl-peroxy radicals. Chem. Phys. Lett. 402,485 90. 

As shown in Figure 1.2, the solvent strength of supercritical carbon dioxide approaches that of hydrocarbons or halocarbons. As a solvent, C02 is often compared to fluorinated solvents. In general, most nonpolar molecules are soluble in C02, while most polar compounds and polymers are insoluble (Hyatt, 1984). High vapor pressure fluids (e.g., acetone, methanol, ethers), many vinyl monomers (e.g., acrylates, styrenics, and olefins), free-radical initiators (e.g., azo- and peroxy-based initiators), and fluorocarbons are soluble in liquid and supercritical C02. Water and highly ionic compounds, however, are fairly insoluble in C02 (King et al., 1992 Lowry and Erickson, 1927). Only two classes of polymers, siloxane-based polymers and amorphous fluoropolymers, are soluble in C02 at relatively mild conditions (T < 100 °C and P < 350 bar) (DeSimone et al., 1992, 1994 McHugh and Krukonis, 1994). 

Essentially, TFE in gaseous state is polymerized via a free radical addition mechanism in aqueous medium with water-soluble free radical initiators, such as peroxy-disulfates, organic peroxides, or reduction-activation systems.15 The additives have to be selected very carefully since they may interfere with the polymerization. They may either inhibit the process or cause chain transfer that leads to inferior products. When producing aqueous dispersions, highly halogenated emulsifiers, such as fully fluorinated acids,16 are used. If the process requires normal emulsifiers, these have to be injected only after the polymerization has started.17 TFE polymerizes readily at moderate temperatures (40 to 80°C) (104 to 176°F) and moderate pressures (0.7 to 2.8 MPa) (102 to 406 psi). The reaction is extremely exothermic (the heat of polymerization is 41 kcal/mol). 

The reaction of perfluoroperoxide macroradicals also yields peroxy nitrate. In this case, the decomposition similar to (Equation 6.21) results in destruction of the macromolecule because the resultant alkoxyl radicals in fluorinated polymers cannot enter into the substitution reaction [18] ... 

However, in PTFE containing end peroxide radicals, no regeneration of these radicals after the removal of NO was observed, though the decomposition temperature was raised to 140 "C. Nevertheless, the reappearance of peroxide radicals in PTFE upon evacuating shows that the product of the R O reaction with NO is peroxy nitrate, and fluorinated compounds also exhibit the reversible reaction ... 

Chemical/electrochemical degradation Trace metal contamination (foreign cations, such as Ca " ", Fe " ", Cu " ", Na" ", K", and Mg " ") radical attack (e.g. peroxy and hydroperoxy). Peroxide radical attack causes membrane polymer chain decomposition and fluorine loss this results in membrane thinning, pinholes, and gas crossover. Note these peroxide radicals are generated by both the fuel cell reaction and the chemical reaction between O2 and H2 within the membrane. 

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