Tetrafluoroethylene, monomers

Pure tetrafluoroethylene monomer under ambient conditions is an odorless, colorless, tasteless gas with low toxicity. It may be polymerized by either suspension or emulsion techniques. Both procedures require use of high pressures in an autoclave in order to maintain the monomer in liquid form. These techniques produce chemically identical product, the first a granular resin, and the second a fine powder (Eq. 23.7). 

Tetrafluoroethylene monomer, polyvinyl chloride Vinyl chloride... 

The preparation of a new class of processable heavily fluorinated aciylic resins with veiy low dielectric constants is described. The title compounds 2 and 5 were prepared through the condensation of the respective aicohols 1 and 4 with aciyloyl chloride. Unlike tetrafluoroethylene, monomers 2 and 5 are ea to process into polymers under normal conditions due to their liquid or semisolid nature. Radical polymerization of the title compounds with a trace amount of azobisisobutyronitrile or methyl ethyl ketone peroxide at 85-100 leads to homopolymers 3 and 6 and copolymer 7. All polymers exhibit dielectric constants around 2.10-2.24 over a frequency region of 500 MHz to 18.5 GHz the variation of dielectric constant values over the measured frequency region is within 0.03 for each polymer. These values are very close to the minimum known dielectric constants of 2.0-2.08 for poly(tetrafluoroeth-ylene) and 1.89-1.93 for a terpolymer of 2,2-bis-(trifluoromethyl)-4,5-difluoro-1,3-dioxole 8, perfluoropropylene and tetrafluoroethylene 9. The dielectric constants for poly(tetraf1uoroethylene) measured with the same method are observed to be around 1.96-1.99 in order to validate the accuracy of our measurement. 

Of course, polymer structures having other chemistries are possible. For example, the tetrafluoroethylene monomer, CF2=CF2, can polymerize to form polytetrafluor-oethylene (PTFE) as follows ... 

Tetrafluoroethylene, perfluoromethyl vinyl ether cure site monomer... 

Perfluoroepoxid.es were first prepared ia the late 1950s by Du Pont Co. Subsequent work on these compounds has taken place throughout the world and is the subject of a number of reviews (1 5). The main use of these epoxides is as intermediates in the preparation of other fluorinated monomers. Although the polymerisation of the epoxides has been described (6—12), the resulting homopolymers and their derivatives are not significant commercial products. Almost all the work on perfluoroepoxides has been with three compounds tetrafluoroethylene oxide (TFEO), hexafluoropropylene oxide (HFPO), and perfluoroisobutylene oxide (PIBO). Most of this work has dealt with HFPO, the most versatile and by far the most valuable of this class of materials (4). 

Tetrafluoroethylene was first synthesized in 1933 from tetrafluoromethane, CF, in an electric arc furnace (11). Since then, a number of routes have been developed (12—18). Depolymerization of PTFE by heating at ca 600°C is probably the preferred method for obtaining small amounts of 97% pure monomer on a laboratory scale (19,20). Depolymerization products contain highly toxic perfluoroisobutylene and should be handled with care. 

Alternation is usually above 90%. Nearly perfect alternation of isomeric units in a ca 1 1 monomer ratio has been confirmed by infrared spectroscopy. Bands at 733 and 721 cm have an intensity proportional to the concentration of (CH2) groups (n = 4 and <6, respectively) present in a copolymer containing 46 mol % tetrafluoroethylene intensity decreases with increasing concentration of fluorinated monomer. 

Uses. Vinyhdene fluoride is used for the manufacture of PVDF and for copolymerization with many fluorinated monomers. One commercially significant use is the manufacture of high performance fluoroelastomers that include copolymers of VDF with hexafluoropropylene (HFP) (62) or chlorotrifluoroethylene (CTFE) (63) and terpolymers with HEP and tetrafluoroethylene (TEE) (64) (see Elastomers, synthetic-fluorocarbon elastomers). There is intense commercial interest in thermoplastic copolymers of VDE with HEP (65,66), CTEE (67), or TEE (68). Less common are copolymers with trifluoroethene (69), 3,3,3-trifluoro-2-trifluoromethylpropene (70), or hexafluoroacetone (71). Thermoplastic terpolymers of VDE, HEP, and TEE are also of interest as coatings and film. A thermoplastic elastomer that has an elastomeric VDE copolymer chain as backbone and a grafted PVDE side chain has been developed (72). 

In the late 1950s, the copolymers of vinyUdene fluoride and hexafluoropropylene, CF2=CFCF3, were developed on a commercial scale by 3M (Fluorel) and by Du Pont (Viton) (5—8). In the 1960s, terpolymers of vinyUdene fluoride, hexafluoropropylene, and tetrafluoroethylene, CF2=CF2, were developed (9) and were commercialized by Du Pont as Viton B. At about the same time, Montedison developed copolymers of vinyUdene fluoride and 1-hydropentafluoropropylene as well as terpolymers of these monomers with tetrafluoroethylene, marketed as Tecnoflon polymers (10,11). 

Fig. 3. The percent volume swell in benzene after seven days at 21°C compared with the wt % of fluorine on standard recommended compounds. A, copolymers of vinyUdene fluoride—hexafluoropropylene B, terpolymers of vinyUdene fluoride—hexafluoropropylene—tetrafluoroethylene C, terpolymers of vinyhdene fluoride—hexafluoropropylene—tetrafluoroethylene-cure site monomer D, copolymer of tetrafluoroethylene—perfluoro(methyl vinyl ether)-cure...

Pure uninhibited tetrafluoroethylene can polymerise with violence, even at temperatures initially below that of room temperature. There is little published information concerning details of commercial polymerisation. In one patent example a silver-plated reactor was quarter-filled with a solution consisting of 0.2 parts ammonium persulphate, 1.5 parts borax and 100 parts water, and with a pH of 9.2. The reactor was closed and evacuated, and 30 parts of monomer... 

In attempts to further improve the stability of fluorine-containing elastomers Du Pont developed a polymer with no C—H groups. This material is a terpolymer of tetrafluoroethylene, perfluoro(methyl vinyl ether) and, in small amounts, a cure site monomer of undisclosed composition. Marketed as Kalrez in 1975 the polymer withstands air oxidation up to 290-315°C and has an extremely low volume swell in a wide range of solvents, properties unmatched by any other commercial fluoroelastomer. This rubber is, however, very expensive, about 20 times the cost of the FKM rubbers and quoted at 1500/kg in 1990, and production is only of the order of 1 t.p.a. In 1992 Du Pont offered a material costing about 75% as much as Kalrez and marketed as Zalak. Structurally, it differs mainly from Kalrez in the choice of cure-site monomer. 

Free radical polymerization is a key method used by the polymer industry to produce a wide range of polymers [37]. It is used for the addition polymerization of vinyl monomers including styrene, vinyl acetate, tetrafluoroethylene, methacrylates, acrylates, (meth)acrylonitrile, (meth)acrylamides, etc. in bulk, solution, and aqueous processes. The chemistry is easy to exploit and is tolerant to many functional groups and impurities. 

PTEE is a linear polymer of the addition type, formed by polymerisation of the unsaturated monomer tetrafluoroethylene, CF2=Cp2. Despite the fact... 

The influence of polyfunctional monomers—tripropyleneglycol diacrylate (TPGDA), TMPTA, TMPTMA, TMMT, and TAG on the stmctural changes of fluorocarbon terpolymer poly(vinylide-nefluoride-co-hexafluoropropylene-co-tetrafluoroethylene) has been investigated [425]. The ATR-IR studies show that the absorbance due to the double bond at 1632 cm decreases both in the... 

In solution polymerization, monomers mix and react while dissolved in a suitable solvent or a liquid monomer under high pressure (as in the case of the manufacture of polypropylene). The solvent dilutes the monomers which helps control the polymerization rate through concentration effects. The solvent also acts as a heat sink and heat transfer agent which helps cool the locale in which polymerization occurs. A drawback to solution processes is that the solvent can sometimes be incorporated into the growing chain if it participates in a chain transfer reaction. Polymer engineers optimize the solvent to avoid this effect. An example of a polymer made via solution polymerization is poly(tetrafluoroethylene), which is better knoivn by its trade name Teflon . This commonly used commercial polymer utilizes water as the solvent during the polymerization process,... 

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