Fluorine-containing polymers polytetrafluoroethylene

Polytetrafluoroethylene contains only C—C and C—F bonds. These are both very stable and the polymer is exceptionally inert. A number of other fluorine-containing polymers cU e available which may contain in addition C—H and C—Cl bonds. These are somewhat more reactive and those containing C—H bonds may be cross-linked by peroxides and certain diamines and di-isocyanates. 

The high thermal stability of the carbon-fluorine bond has led to considerable interest in fluorine-containing polymers as heat-resistant plastics and rubbers. The first patents, taken out by IG Farben in 1934, related to polychlorotri-fluoroethylene (PCTFE) (Figure 13.1 (a)), these materials being subsequently manufactured in Germany and the United States. PCTFE has been of limited application and it was the discovery of polytetrafluoroethylene (PTFE) (Figure... 

Fluorinated polymers, especially polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene (TFE) with hexafluoropropylene (HFP) and perfluorinated alkyl vinyl ethers (PFAVE) as well as other fluorine-containing polymers are well known as materials with unique inertness. However, fluorinated polymers with functional groups are of much more interest because they combine the merits of pefluorinated materials and functional polymers (the terms functional monomer/ polymer will be used in this chapter to mean monomer/polymer containing functional groups, respectively). Such materials can be used, e.g., as ion exchange membranes for chlorine-alkali and fuel cells, gas separation membranes, solid polymeric superacid catalysts and polymeric reagents for various organic reactions, and chemical sensors. Of course, fully fluorinated materials are exceptionally inert, but at the same time are the most complicated to produce. 

Polytetrafluoroethylene and other fluorine-containing polymers for water repellency. 

Sperati CA, Starkweather, Jr. HW (1961) Fluorine-containing Polymers. II. Polytetrafluoroethylene. Adv Polymer Sci 2 465-495. 

Sperati, C. A., Starkweather. H. W., Jr. Fluorine-containing polymers. II. Polytetrafluoroethylene. Fortschr. Hochpolymer.-Forsch. 2, 465 (1961). Starkweather, H. W., Jr., Boyd, R. H. The entropy of melting of some linear polymers. J. Phys. Chem. 64, 410 (I960). 

The serendipitous discovery of polytetrafluoroethylene (PTFE) in 1938 by Roy J. Plunkett [82] and his co-workers at DuPont research laboratories has spurred the development of a variety of fluorine containing polymers, which include fluorosilicones, fluorinated polyurethanes, fluorinated thermoplastic elastomers, etc.. Many of the commercial fluoropolymers are suitable for melt processing via conventional injection molding, screw extrusion and blown film extrusion techniques. 

The perfluorohydrocarbon polymers are among the most thermally resistant organic polymers. Polytetrafluoroethylene (PTFE), polytrifluoroethylene and various copolymers of fluorine-containing monomers are the most important among them. 

Teflon is the brand name for the chemical compound called polytetrafluoroethylene (PTFE). One molecule of PTFE contains two carbon atoms bonded to four fluorine atoms. Many molecules of PTEE can form polymer chains known as fluoropolymers. 

Fluorocarbon elastomers represent the largest group of fluoroelastomers. They have carbon-to-carbon linkages in the polymer backbone and a varied amount of fluorine in the molecule. In general, they may consist of several types of monomers poly-vinylidene fluoride (VDF), hexafluoropropylene (HFP), trifluorochloroethylene (CTFE), polytetrafluoroethylene (TFE), perfluoromethylvinyl ether (PMVE), ethylene or propylene.212 Other types may contain other comonomers, e.g., 1,2,3,3,3-pentafluropropylene instead of HFP.213 Fluorocarbon elastomers exhibit good chemical and thermal stability and good resistance to oxidation. 

Perfluorinated fluoroplastics have higher creep tendency than partially fluorinated fluoropol5miers. Polytetrafluoroethylene, comprised of 100% tet-rafluoroethylene monomer, has the highest tendency to exhibit cold flow. Copolymers of tetrafluoroeth-ylene containing small amounts (0.1% by weight) of certain other fluorinated monomers, also referred to as modifiers, have significantly lower creep. These modifiers form pendent groups in the polymer chain. 

The best known fluorocarbon polymer is polytetrafluoroethylene (PTFE), commonly known as Teflon (DuPont). Other polymers containing fluorine are polytrifluorochloroethylene (PTFCE), polyvinylfluor-ide (PVF), and fluorinated ethylene propylene (FEP). Only PTFE will be discussed here since the others have rather inferior chemical and physical properties and are rarely used for implant fabrication. 

The arrangement of elements in the molecule, the symmetry of the structure, and the polymer chains degree of branching are as important as the specific elements contained in the molecule. Polymers containing the carbon-hydrogen bonds such as pol5 ropylene and polyethylene, and the carbon-chlorine bonds such as PVC and ethylene chlorotrifluoroethylene are different in the important property of chemical resistance from a fully fluorinated pol)nner such as polytetrafluoroethylene. The latter has a much wider range of corrosion resistance. 

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