Perfluorocarbons properties

The reactivity of fluorine compounds varies from extremely stable, eg, compounds such as sulfur hexafluoride [2551-62 ] nitrogen trifluoride [7783-54-2] and the perfluorocarbons (see Fluorine compounds, organic) to extremely reactive, eg, the halogen fluorides. Another unique property of nonionic metal fluorides is great volatiUty. Volatile compounds such as tungsten hexafluoride [7783-82-6] molybdenum hexafluoride [7783-77-9] ... 

The extremely nonpolar character of PFCs and very low forces of attraction between PFC molecules account for their special properties. Perfluorocarbons bod only slightly higher than noble gases of similar molecular weight, and their solvent properties are much more like those of argon and krypton than hydrocarbons (2). The physical properties of some PFCs are Hsted in Table 1. 

Table 1. Physical Properties of Aliphatic Perfluorocarbons (PFCs) ...

Although the gas-phase hydrogen-bonded dimer (MeF)2H" is held by a strong hydrogen bond (McMahon and Kebarle, 1986) this is a rare exception to the previous statement regarding covalently bonded fluoride. More typical are the perfluorocarbons, which are among the weakest hydrogenbonding substances known, as their physical properties and uses clearly demonstrate. 

The first heavier than water internal tamponade was introduced in 1987 by Chang with LPFC [1]. The two perfluorocarbons most used are perfluorooctane and perfluorodecaline. Perfluorotributylamine, perfluoropolyether, perfluorooctyl-bromide and perfluorophenanthrene are less used. LPFC are transparent fluids and are not miscible in water and their main characteristic is their high density (1.76-2.03) [2], Their properties are summarised in Table 1. 

Brief reminder of basic properties of perfluorocarbons relevant to biomedical uses... 

Highly fluorinated molecules have a nonpolar character and an extremely low polarizability, inducing only weak intra- and intermolecular interactions. As a consequence, perfluorocarbons behave almost like ideal liquids they are very compressible and have very high vapor pressure. For example, the physical properties of perfluoro-hexane, heptafluorohexane, and hexane are reported in Table 1.2 The effect of the polar character of the hemifluorinated compound (heptafluorohexane) on the dielectric constant value is remarkable. 

This very specific ability of perfluorinated compounds to dissolve gases has found an application in oxygen carrier liquids (short-time blood substitutes). A perfluorocarbon dissolves three times more oxygen than the corresponding hydrocarbon, and ten times more than water. This property can be explained by the presence of large cavities in the liquid and by the weak intermolecular interactions of the medium, and not by specific interactions. 

Perfluorocarbons are a class of organic compounds in which all of the hydrogen atoms are replaced with fluorine atoms. They possess unique properties that make them very useful as dispersants, carrier solvents, and processing solvent additives. Their lack of chlorine or bromine atoms results in zero-ozone-depletion potential. 

Perfluorocarbon fluids possess a unique combination of physical properties which have been exploited in a wide range of applications where the effects provided can justify their relatively high cost. Table 7 lists a selection of illustrative examples. 

Under appropriate conditions, the perfluorocarbon (CF3)3CCF2CF2-C(CF3)3is obtained in 89%yield (70b). As may be seen from the reaction scheme, a number of partially fluorinated products are also isolable and it is clear that the protons are readily accessible to fluorine. The physical properties of highly branched fluorocarbons (see Table IX) are most unusual. 

Liquid fluorocarbon was used as continuous phase by Perez-Moral and Mayes [19] as well. They proposed a new method for rapid synthesis of MIP beads, in that they prepared 36 polymers imprinted for propranolol and morphine with different amounts of EDMA as a cross-linker and different functional monomers (MAA, acrylic acid, hydroxyethyl methacrylate, 4-vinylpyridine) directly in SPE cartridges. The properties of MIP microspheres prepared by this method were very similar in terms of size, morphology and extent of rebinding to microspheres prepared by conventional suspension polymerisation in perfluorocarbons as well as to bulk polymers prepared in the same solvent. The most notable advantages of this method are no waste production (no transfer of beads during washing steps) and possible direct use for a variety of screening, evaluation and optimisation experiments. 

Some researchers are exploring a totally different approach to the production of artificial blood that focuses on the synthesis of nonnatural substances with bloodlike properties. This approach has the advantage of avoiding the use of human or animal blood or any of its components. One line of research makes use of a class of chemicals known as the perfluorocarbons (PFCs), hydrocarbons in which all hydrogens have been replaced by fluorine atoms. The first PFC to be marketed commercially was called Fluosol-DA, manufactured by the Green Cross Corporation of Japan. Fluosol-DA was a mixture of perfluorodecalin (C10F18) and perfluorotripropylamine (CgF21N) emulsified with Pluronic F-68, a copolymer of oxyethylene and oxy-propylene. 

Symmetry is another factor to affect Tm. The salts with symmetric ions generally show higher Tm than those with asymmetric ones. For example, 1,3-dimethylimidazolium tetrafluoroborate showed higher Tm than 1-methylimi-dazolium or l-ethyl-3-methylimidazolium salts, as shown in Figure 3.1. In the case of tetraalkylammonium salts, their Tm also increased with increasing symmetry of the cation structure [18]. This tendency is understood to relate to the structural effect on crystallinity [19], i.e., highly symmetric ions are more efficiently packed into the crystalline structure than unsymmetric ones. Other kinds of chain structures such as polyether [20], perfluorocarbon [21], etc. [22] are obviously also effective in influencing thermal properties. 

The properties of perfluorocarbons can be exploited to provide reaction media for organic and inorganic synthesis, where their attractions include their low reactivity, easy phase separation from organic reaction products without purification, their low toxicity and their broad liquid ranges. 

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