Fluoropolymer Monomer Synthesis: Tetrafluoroethylene;Hexafluoropropylene;Perfluoroalkyl Vinyl Ethers;Chlorotrifluoroethylene;Vinylidene Fluoride;Vinyl Fluoride.
Properties of Tetrafluoroethylene
Tetrafluoroethylene is a colorless, odorless, tasteless,nontoxic gas which boils at 76.3 C and melts at 142.5 C. The critical temperature and pressure of TFE are 33.3 C and 3.92 MPa. TFE is stored as a liquid; vapor pressure at 20 C is 1 MPa. Its heat of formation is reported to be 151.9 kcal/mole. Polymerization of TFE is highly exothermic and generates 41.12 kcal/mole heatdthe extent of which can be compared with the heats of polymerization of vinyl chloride and styrene, at 23-26 kcal/mole and 16.7 kcal/mole, respectively.
Safe storage of TFE requires its oxygen content to be less than 20 ppm. Temperature and pressure should be controlled during its storage. Increasing the temperature, particularly at high pressures, can initiate deflagration in the absence of air (TFE degrades into carbon tetrafluoride). In the presence of air or oxygen, TFE forms explosive mixtures in the molar percentage range of 14-43%. Detonation of a mixture of TFE and oxygen can increase the maximum pressure to 100 times the initial pressure.
Properties of Hexafluoropropylene
Hexafluoropropylene is a colorless, odorless, tasteless, and relatively low toxicity gas, which boils at 29.4 C and freezes at 156.2 C. In a 4-hour exposure, a concentration of 3000 ppm corresponded to LC50 in rats. Critical temperature and pressure of HFP are 85 C and 3254 MPa. Unlike TFE, HFP is extremely stable with respect to autopolymerization and may be stored in liquid state without the addition of telogen. HFP is thermally stable up to 400e500 C. At about 600 C under vacuum, it decomposes and produces octafluoro-2-butene (CF3CF¼CFCF3) and octa-fluoroisobutylene.
Properties of Perfluoroalkyl Vinyl Ethers
Perfluoroalkyl vinyl ethers (PAVE) form an important class of monomers in that they are comonomers of choice for the “modification” of the properties of homofluoropolymers in additionto broad use inthe structure of copolymers of TFE. The madvantage of PAVEs as modifiers over HFP is their remarkable thermal stability. A commercially significant example is per-fluoropropyl vinyl ether (PPVE). PPVE is an odorless, colorless liquid at room temperature. It is extremely flammable and burns with a colorless flame. It is less toxic than HFP.
Properties of Chlorotrifluoroethylene
Chlorotrifluoroethylene is a colorless gas at room temperature and pressure. It is fairly toxic with an LC50 (rat) at 4-hour exposure and a concentration of 4000 ppm. It has a critical temperature and pressure of 105.8 C and 4.03 MPa. Oxygen and liquid CTFE react and form peroxides at fairly low temperatures. A number of oxygenated products, such as chlorodifluoroacetylfluoride, are generated by oxidation of CTFE. The same reaction can occur photochemically in the vapor phase. Chlorotrifluoroethylene oxide is a by-product of this reaction. The peroxides act as initiators for the polymerization of CTFE, which can occur violently.
Properties of Vinylidene Fluoride
Vinylidene fluoride, (CH2¼CF2), is  flammable and is a gas at room temperature. It is colorless and almost odorless and boils at 84 C. VDF can form explosive mixtures with air. Polymerization of this gas is highly exothermic and takes place above its critical temperature and pressure.
Properties of Vinyl Fluoride
Vinyl fluoride (75-02-5) (fluoroethene) is a colorless gas at ambient conditions. It is flammable in air between the limits of 2.6 and 22% by volume. Minimum ignition temperature for VF and air mixtures is 400 C. Adding a trace amount (<0.2%) of terpenes is effective to prevent spontaneous polymerization of VF. Inhibited VF has been classified as a flammable gas by the U.S. Department of Transportation.