Polychlorotrifluoroethylene

The other chain scissions are accompanied by chlorine-atom transfer to the break site to form two fragments (by disproportionation) of lower molecular mass than the original polymer. Trifluoronitrosomethane copolymers are the least thermally stable. Trifluorochloroethylene copolymers occupy an intermediate position, while polyvinylidene fluoride and polytetrafluoroethylene are the most thermally stable. 

The isothermal decomposition of Teflon in vacuum was reported by Madorsky and co-workers [26] to involve first-order kinetics. However, Wall and Michaelsen [27] later indicated, by the use of isothermal methods in a nitrogen atmosphere, that first-order kinetics apply above about 510 C, whereas below 480 C the polymer degrades by a zero-order law. Subsequently, Madorsky and Straus [28] carried out another series of isothermal experiments under vacuum at lower temperatures than they had previously employed (below 485 °C). They concluded that the degradation 

Anderson [29] studied the pyrolysis of Teflon under vacuum, using TGA techniques, over the temperature range of 450 to 550 C. He found that, based upon 11 replicate TGA experiments, the values of and n were 74.8 3.9 kcal/mole, and 1.02 0.07, respectively. 

The monomer can be prepared by dechlorination of trichlorotrifluoroethane with zinc dust and ethanol. 

It is a toxic gas that boils at -26.8 C. Polymerization of chlorotrifluoroethylene is usually carried out commercially by free-radical suspension polymerization. Reaction temperatures are kept between 0-40 C to obtain a high molecular weight product. A redox initiation based on reactions of persulfate, bisulfite, and ferrous ions is often used. Commercial polymers range in molecular weights fiom 50,000-500,000. 

Many challenging industrial and military applications utilize polychlorotriduoroethylene [9002-83-9] (PCTFE) where, ia addition to thermal and chemical resistance, other unique properties are requited ia a thermoplastic polymer. Such has been the destiny of the polymer siace PCTFE was initially synthesized and disclosed ia 1937 (1). The synthesis and characterization of this high molecular weight thermoplastic were researched and utilized duting the Manhattan Project (2). The unique comhination of chemical iaertness, radiation resistance, low vapor permeabiUty, electrical iasulation properties, and thermal stabiUty of this polymer filled an urgent need for a thermoplastic material for use ia the gaseous UF diffusion process for the separation of uranium isotopes (see Diffusion separation methods). 

The typical mechanical properties that qualify PCTFE as a unique engineering thermoplastic are provided ia Table 1 the cryogenic mechanical properties are recorded ia Table 2. Other unique aspects of PCTFE are resistance to cold flow due to high compressive strength, and low coefficient of thermal expansion over a wide temperature range. 

The high fluorine content contributes to resistance to attack by essentially all chemicals and oxidizing agents however, PCTFE does swell slightly ia halogenated compounds, ethers, esters, and selected aromatic solvents. Specific solvents should be tested. PCTFE has the lowest water-vapor transmission rate of any plastic (14,15), is impermeable to gases (see also Barrierpolymers), and does not carbonize or support combustion. 

PCTFE plastic is compatible withHquid oxygen, remains ductile at cryogenic temperatures (16—22), and retains its properties when exposed to either uv or gamma radiation. PCTFE exhibits a refractive iadex of 1.43 (ASTM D542) and an amorphous sheet can provide over 90% transmittance. 

PCTFE exhibits very good electrical properties ia terms of high iasulation resistance, minimal trackiag, corona formation, and surface flashover due to the polymer s nonwettable surface and ultralow moisture absorption (Table 3). 

---

Cm.OROCARBONSANDCm.OROHYDROCARBONS - RDIG-Cm.ORINATED TOLUENES] (Vol 6) PCTFE. See Polychlorotrifluoroethylene. 

Figure 13.1. (a) Polychlorotrifluoroethylene (PCTFE). (b) Polytetrafluoreoethylene (PTFE). (c) Poly(vinyl fluoride), (d) Poly(vinylidene fluoride)... 

POLYCHLOROTRIFLUOROETHYLENE POLYMERS (PCTFE) AND COPOLYMERS WITH ETHYLENE (ECTFE)... 

Polychlorotrifluoroethylene was the first fluorinated polymer to be produced on an experimental scale and polymers were used in Germany and in the United States early in World War II. PCTFE was used, in particular, in connection with the atomic bomb project in the handling of corrosive materials such as uranium hexafluoride. 

The Kel-F polychlorotrifluoroethylene view ports let us see what is happening on the hydrogen side of the screen (see later discussion). If it were really necessary to view the fluorine side, sapphire or diamond windows could probably be used. It is difficult to see below the electrolyte level of an operating cell because of gas bubbles. 

Materials compatibility. We use scrupulously clean and scratch-free FEP (FEP is the acronym for the copolymer of tetrafluoroethylene and hexafluoropropylene) tubing for handling our mixtures of fluorine and nitrogen at ambient temperature. Corrugated FEP tubing is convenient for making strain-free assemblies. We have found that Monel is excellent for use with dry molten KF-2HF. Mild steel corrodes slowly and stainless steels corrode rapidly. Kel-F polychlorotrifluoroethylene is satisfactory for use with HF and with KF-2HF polypropylene and polymethylpentene are not satisfactory. 

It is considerably more reactive than perchloryl fluoride, and attacks glass and the usually inert polytetrafluoroethylene and polychlorotrifluoroethylene. 

Bulk surfaces of polytetrafluoroethylene or polychlorotrifluoroethylene are resistant to the liquid or vapour under static conditions, but breakdown and ignition may occur under flow conditions. 

Polychlorotrifluoroethylene (PCTFE) is ordinarily prepared by emulsion polymerization. A polymer suitable for thermal processing requires coagulation, extensive washing, and postpolymerization workup. Coagulation to provide a filterable and washable solid is a slow, difficult process and removal of surfactant is an important part of it. Complete removal may be extremely difficult depending on the extent of adsorption to the polymer particles. Consequently we set out to develop a suspension polymerization process, which would be surfactant-free and afford an easily isolated product requiring a minimum of postreaction workup. 

The substances generally used as osmotic membranes include collodion (nitrocellulose of 11-13.5 per cent nitrogen) regenerated cellulose, obtained by denitration of collodion gel cellophane that has never permitted to dry after manufacture bacterial cellulose, obtained by the action of certain strains of bacteria rubber, poly (vinyl alcohol) polyurethances poly (vinyl butyral) and polychlorotrifluoroethylene. At present gel cellophane is most widely used. 

---