Tetrafluoroethylene molecular structure

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. ... 

It is well known that the morphological and molecular structures of polymers play an important role in their wear behavior. It seems that the degree of crystallinity is also a structural factor of semicrystalline polymers important to their wear. Lontz et al. ( ) reported that the wear of poly(tetrafluoroethylene),(PTFE) decreased with the increase in crystallinity. Tanaka et al. (2 ) studied the wear of heat-treated PTFE specimens and concluded that the wear rate was affected by the width of the band in the fine structure rather than crystallinity. Recently, Hu et al. ( 3) have studied the effect of crystallinity on wear of PTFE using various heat-treated specimens. They have shown that the wear decreases with the increase in crystallinity, when molecular weight is constant. Eiss et al. ( ) reported that poly(chlorotrifluoroethylene) of a crystallinity of 65% exhib-ted higher wear than that of 45%. The results obtained by the authors mentioned above indicate that the effect of crystallinity on the wear of polymers is somewhat complicated and further investigation is needed to clarify the effect of crystallinity on polymer wear. 

Figure 4.1 Molecular structure of Hyflon AD60X (x = 0.6) and Hyflon AD80X (x = 0.8), poly(2,2,4-trlfluoro-5-trifluoromethoxy-l,3-dioxole-co-tetrafluoroethylene)...

Isomerism is a term covering different molecular conformation effects. We will not speak here again on the type of information that can be gained on the alternating or block structure of copolymers, as was explained above for an ethylene-tetrafluoroethylene copolymer. For homopolymers, we will distinguish various categories ... 

Polymers are widely used as implant materials because they have physical properties that are similar to those of natural tissues. Examples are long-term and shortterm implants such as blood vessels, heart valves, membranes, mesh prostheses, corneas, tracheal prostheses, dental materials, parts of the nose and ear, knee and hip joints, and others. The synthetic polymers used include polyethylene (PE), particularly ultrahigh molecular weight PE (UHMWPE), poly(ethylene terephthal-ate) (PET), poly(tetrafluoroethylene) (PTFE), polyurethane (PU), and poly(methyl methacrylate) (PMMA). The necessary sterilization before implantation can be performed by y-irradiation, heat (steam), or chemical treatment (ethylene oxide), which should not cause any structural degradation of the polymers. Current challenges in research include the development of biomimetic materials that match both the mechanical and biological properties of their natural counterparts. 

Polymer destruction initiated by ionizing radiation is accompanied by the formation of double bonds and by the evolution of gaseous products (hydrogen, low-molecular-weight hydrocarbons, hydrochloric acid, tetrafluoroethylene, etc.). In the presence of oxygen, oxidized structures such as hydroperoxides. 

---