Polymerization of Tetrafluoroethylene

Essentially, TFE in its gaseous state is polymerized via a free radical addition mechanism in aqueous medium with water-soluble free radical initiators, such as per-oxydisulfates, organic peroxides, or reduction-activation systems [16]. The additives have to be selected very carefully since they may interfere with the polymerization. They may either inhibit the process or cause a chain transfer that leads to inferior products. When producing aqueous dispersions, highly halogenated emulsifiers, such as fully fluorinated acids [17], are used. If the process requires normal emulsifiers, these have to be injected only after the polymerization has started [18]. TFE polymerizes readily at moderate temperatures (40°C to 80°C, or 104°F to 176°F) and moderate pressnres (0.7 to 2.8 MPa, or 102 to 406 psi). The reaction is extremely exothermic (the heat of polymerization is 41 kcal/mol). 

Granular PTFE resins are produced by polymerizing tetrafluoroethylene alone or with a trace of comonomers [19,20] with initiator and sometimes in the presence of an alkaline buffer in aqueous suspension medium. The product from the autoclave can consist of a mixture of water with particles of polymer of variable size and irregular shape. After the water is removed from the mixture, the polymer is dried. 

FIGURE 2.1 Granular, fine powder, and dispersion PTFE products. (From Gangal, S. V. in Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 11, 3rd ed., 1980, John Wiley Sons. With permission.) 

Fine-cut granular resins resnlting from size redaction of the snspension polymer have a typical average particle size 20 pm to 40 pm. The small particle size of hne-cnt PTFE imparts the highest possible mechanical properties to articles made from grannlar resins. Fine-cnt resins (powders) have poor flow and low apparent density 

Pelletized granular resins can be obtained by agglomeration of fine-cut resins. The agglomeration process increases the powder flow and apparent density. The goal of this process is to make the small PTFE particles adhere together. Essentially, there are two processes of agglomeration namely, dry and wet techniques [24]. 

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The first report of the polymerization of tetrafluoroethylene was by Plunkett in 1941, who had a cylinder of tetrafluoroethylene cut open to see why the expected amount of gas was not released when the valve was opened. His perspicacity led to the discovery of an inert, white, opaque solid with a waxy feel. Various methods of polymerization were tried after the adventitious discovery and the preferred methods for polymerization now involve aqueous media and super-atmospheric pressures. Suitable initiators (Hanford and Joyce) include ammonium, sodium, or potassium persulfate, hydrogen peroxide, oxygen, and some organic peroxy compounds. Oxidation-reduction initiation systems involving the use of persulfate with either ferrous ion or bisulfite or the use of bisulfite with ferric ion are also useful and have been discussed by Berry and Peterson. 

Bryant has calculated the changes in free energy for various reaction steps of the polymerization of tetrafluoroethylene. He concluded (1) that the initiation and propagation are about twice as favorable for tetrafluoroethylene as the analogous reactions for ethylene, (2) that termination by combination is more favorable than disproportionation, and (3) that chain-transfer to monomer and to polymer are less likely than the combination of radicals. 

Polymerization of tetrafluoroethylene with dibasic acid peroxide catalysts. U. S. Patent 2,534,058 (Dec. 12, 1950). 

Figure 2.1 Perfluoropolyether (PFPE) carboxylate compounds used as stabilizers in the polymerization of tetrafluoroethylene in scC02.

Romack, T. J. Kipp, B. E. DeSimone, J. M. Polymerization of Tetrafluoroethylene in a Hybrid Carbon Dioxide/Aqueous Medium. Macromolecules 1995b, 28, 8432-8434. 

A unique polymer is formed by the radical polymerization of tetrafluoroethylene and is called PTFE or Teflon. The outside of the polymer consists of a layer of fluorine atoms which repel all other molecules. It is used as the coating in nonstick pans and as a bearing that needs no lubrication. Two F pieces of Teflon slide across one another almost without friction. 

Ishigure e al. (1964) reported that the radiation-induced polymerization of tetrafluoroethylene and propylene in the liquid phase produced an essentially alternating rubbery copolymer. Ito et al. (1974a) and Matsuda et al. (1974a) studied the same system in emulsion using a variety of mixed and pure emulsifiers. The experiments were conducted in a stirred 200-ml... 

Write a balanced chemical equation to represent the addition polymerization of tetrafluoroethylene. The product of this reaction is Teflon. 

PTFE is produced by free-radical polymerization mechanism in an aqueous media via addition polymerization of tetrafluoroethylene in a batch process. The initiator for the polymerization is usually a water-soluble peroxide, such as ammonium persulfate or disuccinic peroxide. A redox catalyst is used for low temperature polymerization. PTFE is produced by suspension (or slurry) polymerization without a surfactant to obtain granular resins or with a perfluori-nated surfactant emulsion polymerization) to produce fine powder and dispersion products. Polymerization temperature and pressure usually range from 0 to 100°C and 0.7 to 3.5 MPa. 

Plasma Polymerization of Tetrafluoroethylene in a Capacitively Coupled Discharge with Internal Electrodes... 

A capacitively coupled reactor designed to permit continuous coating of a moving substrate with plasma polymer has been described [ 1 ]. In this paper the results of a study of the plasma polymerization of tetrafluoroethylene in such a reactor presented. Plasma polymer has been deposited on aluminum electrodes as well as on an aluminum foil substrate placed midway between electrodes. The study particularly explores conditions in which deposition is minimized on the electrode. For this reason the chemical nature of the polymer formed in a low flow rate (F = 2 cm (S.T.P.)/min) and low pressure (p = 60 mlllltorr) plasma has been analyzed by the use of ESCA (electron spectroscopy for chemical analysis) and deposition rate determinations. This method combined with the unusual characteristics of TFE plasma polymerization (described below) has yielded Information concerning the distribution of power in the inter-electrode gap. The effects of frequency (13.56 MHz, 10 KHz and 60 Hz), power and magnetic field have been elucidated. The properties of the TFE plasma polymer prepared in this apparatus are compared to those of the plasma polymer deposited in an inductively coupled apparatus [2,3]. 

The plasma polymerization of tetrafluoroethylene has also been studied in a straight tube reactor. Deposition rates and ESCA results were obtained as a function of location upstream from, within, and downstream from the induction coll [ ]. It was found that fluorine poor polymer was formed downstream fr m the coil even at the relatively low power level of 1.9 x 10 Joules/kg. Fluorine poor pol3rmer was formed at all locations at 7.7 X 10 Joules/kg. 

The close similarity of the spectra for these three examples (Figure 2) suggests that in all cases, irrespective of the mechanism of removal of material from the cathode or the nature of the cathode material, the polymer matrix formed at the film forming electrode is essentially the same. Furthermore, the overall band profile of the Cis spectra and fluorine/carbon stoichiometries are strikingly similar to those which have previously been reported in the literature for the polymer produced in the plasma polymerization of tetrafluoroethylene ( ). 

Studies of the plasma polymerization of tetrafluoroethylene in such a capacltively coupled system are described in another paper presented at this symposium [ 9]. The apparatus has been used to coat polysulfone hollow fibers with pyridine and acetylene + nitrogen plasma polymer to form a composite reverse osmosis desalination membrane. Salt rejections of 90-93% have been achieved at fluxes of 1.5-2.0 g.f.d with a fiber take up rate of 50-100 cm/min. 

For polymerization of tetrafluoroethylene, and A5 values at 25°C are given as —37 kcal/mol and —26.8 cal/°K-mol. Calculate the ceiling temperature (Tc) from these two values. Account for the fact that in practice poly(tetrafluoroethylene) is found to undergo fragmentation well below the calculated Tc-... 

Polytetrafluoroethylene is a completely fluorinated polymer manufactured by free-radical polymerization of tetrafluoroethylene. With a linear molecular structure of repeating -CF2—CF2- units, PTFE is a crystalline polymer with a melting point of 326.7°C. Its specific gravity is 2.13—2.19. Polytetrafluoroethylene has exceptional resistance to chemicals. Its dielectric constant (2.1) and loss factor are low and stable across a wide range of temperature. It has useful mechanical properties from myogenic temperatures to 260°C. In the United States, PTFE is sold as Halon, Algoflon, Teflon, Fluon, Hostaflon, and Polyflon. ... 

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