Relative permittivity fluorination

An additional benefit of fluorination is an increase in hydrophobicity through the effect of the highly polar C-F groups. This means that the level of absorbed water in the polymer at typical ambient humidity is much reduced. Water has a very high relative permittivity, so that its presence can significantly increase the relative permittivity of a material, and the level will also be liable to vary with ambient conditions, bringing uncertainty into design considerations for electronic systems. 

Adopting the fluorination approach in polyimides, relative permittivities can be reduced from 3.4 to 2.8, a common structure incorporating the hexafluoroLsopropylydene moiety (6F) ... 

This section mainly reviews the papers on the novel fluorinated organic solvents, which were investigated for lithium batteries in the past decade. Although their chemical structures were drawn in Schemes, it was difficult to include all detailed data on physical and electrochemical properties of fluorinated solvents. The physical properties of typical fluorinated compounds and non-fluorinated counterparts were summarized in Tables 2.3 and 2.4, respectively [4,5], where FW, d, e t, Ehomo. and fiium, are formula weight, density, relative permittivity, viscosity, and frontier orbital energies, respectively. The frontier orbital energies were recalculated by RFtF/6-311 H-G(2d,p) with stracture optimization. 

Ethylene carbonate (EC) and propylene carbonate (PC) have favorable physical and electrochemical properties such as high relative permittivity, high donicity, and relatively wide potential window. The direct fluorination of EC was successfully carried out to provide 4-fluoro-l,3-dioxolan-2-one (fluoroethylene carbonate, FEC) as shown in Scheme 2.3 [20], The fluorination of EC was strongly dependent on a choice of a reaction medium and no solvent was preferred from the viewpoint of conversion. FEC was further fluorinated to give three di-fluorinated derivatives. On the other hand, FEC was also prepared from 4-chloroethylene carbonate by exchange with KF [21], FEC was tested as an electrolyte additive for rechargeable lithium cells [21, 22] and is now practically used [23, 24],... 

The relative permittivities and viscosities of these fluorinated linear carbonates were higher than those of EMC and DEC, respectively. The relative permittivity and viscosity were in the order DEC < EMC FDEC, DFDEC < TFEMC, TFDEC, FEMC DFEMC and EMC [Pg.111]

Fig. 2.7 Properties of diethyl carbonates and its fluorinated derivatives, (a) relative permittivity (b) viscosity (c) electrolytic conductivity (d) oxidation potentitil...

The direct fluorination of A -methylpyrrolidinone (NMP) was also carried out to afford a-fluoro-A -methylpyrrolidinone (a-F-NMP). Its relative permittivity (70) and viscosity (3.6) were almost doubled those of NMP (32, 1.7), respectively. The electrolytic conductivity of 1 moldm" LiPF6/a-F-NMP solution at 25 °C was 2.5 mScm less than half of that of NMP (6.1) [58]. 

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