Liquid fluorinated pitch

As mentioned in the last section, three types of fluorinated pitches, yellowish white powdery solid (S-type), colorless transparent resin (R-type) and liquid (L-type),... 

Heat treatment of the S-type fluoride in a fluorine atmosphere Based on the results above mentioned, Fujimoto et al. developed a new fluorination procedure in order to prepare the perfluorinated pitch, and obtained two types of other fluorinated pitches [23,24], The new process is by the heat treatment at 200-400°C of S-type of fluorinated pitch prepared at relatively low temperature in a fluorine atmosphere. They firstly fluorinated the mesophase pitch at 70°C for 10 h (first step for the preparation of S-type fluorinated pitch) and then heated up to a selected temperature between 200°C and 400°C, and maintained this temperature for 12 h (second step for the heat-treatment of fluorinated pitch). Thus, they obtained two kinds of fluorocarbons, a transparent resin (R-type) and a liquid (L-type). L-type is a viscous fluid containing some volatile materials and the viscosity gradually becomes higher when it is kept for a few weeks in an air atmosphere even at ambient temperature. They reported that the R-type was obtained in the nickel boat in the heating zone and L-type at the bottom of the vertical reaction vessel which was cooled down by the water. Therefore, it is likely that the liquid fluorocarbon is formed by the vaporization of some component contained in the S-type fluoride or decomposition reaction during the heat treatment of the S-type fluoride. The yields of these compounds depends on the heat treatment temperature. In Fig. 3, the yields of the R-type and L-type fluorocarbons are plotted as a function of the heat treatment temperature of the S-type fluoride. The yield of the former decreases with increase of the heat treatment temperature and finally, at 400 C, it can not be obtained at all. On the other hand, the yield of the latter increases with increase of temperature and it is selectively obtained at 400°C. 

Fig. 8. The l9FNMR spectra of liquid and resin type fluorinated pitches prepared by the heat treatment at 210=C together with the original fluorinated pitch (A) Liquid type fluorinated pitch (B) Resin type fluorinated pitch (C) Solid type fluorinated pitch prepared at 70°C. (Quoted from H. Fujimoto, M. Yoshikawa, A. Mabuchi, T. Maeda, J. Fluorine Chem., 57 (1992) 65, with permission).

The characteristics of fluorinated pitch (Pitch Fluoride) [20-25,38-44] include high water repellency, high solubility in fluorine-containing solvents and ease of micronization. We examined the characteristics of solid, glassy and liquid... 

This partial fluorination has a number of interesting and even surprising effects [181]. First, it almost always totally suppresses the nematic phase and strongly enhances the smectic phases, in general both smectic A and smectic C. Moreover, it lowers the birefringence of the liquid crystal An may go from typically 0.20 to 0.07 or 0.10. It also makes the smectic C phase less hardtwisted the helical pitch may increase from about 2 pm to 5 -10 pm. 

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