Perfluorinated fluoropolymers

The era of fluoropolymers began with the serendipitous discovery of PTFE by Roy Plunkett of DuPont Companywhile conducting research to find new refrigerants. A number of fluoroplastics have been developed since the discovery of PTFE. They are divided into two classes of perfluorinated and partially fluorinated polymers. Perfluorinated fluoropolymers... 

Perfluorinated Fluoropolymers - These are polymers consisting of only carbon and fluorine (and an occasional oxygen atom) atoms. 

In some cases, used perfluorinated fluoropolymers (e.g., PTFE, PFA) are recycled by special cleaning processes and are ending up in the Repro-PTFE or micropowder-PTFE-market. Perfluorinated thermoplasts (e.g., PFA) are reused in applications where the quality requirements (e.g., lot traceability) are much lower. Overall, the lion s share of used fluoropolymers is, however, ending up in landfills, in incineration plants, or in blast furnaces. Communal waste incinerators can tolerate only very limited amounts of fluoropolymers due to the high corrosion due to hydrofluoric acid formed in the process. 

The serendipitous discovery of polytetrafluoro-ethylene (PTFE) in 1938 by Roy Plunkett, a DuPont Company chemist, [4] began the era of fluoropolymers. PTFE has been used in thousands of applications because of its unique properties. Numerous flu-oroplastics (Fig. 3.1) have been developed since the discovery of FI FE. These plastics are produced by several companies in the US, Europe, Japan, China, India, and Russia. Ruoropolymers are divided into two classes of perfluorinated and partially fluorinated polymers. Perfluorinated fluoropolymers are homopolymers and copolymers of Tre. Some of the comonomers may contain a small amount of elements other than C or F. 

The main driver for fluoroplastic foams has been the insulation for data transmission cables. An example is coaxial cables that have relatively thick insulation. Its low dielectric constant and dissipation factor are desirable electrical properties. Air has the ideal dielectric constant (1.0). The ideal dissipation factor for data-cable insulation is zero. Perfluoropolymers have low dielectric constant and dissipation factor values (Table 11.2, see Ch. 6 for additional data). Foaming perfluorinated fluoropolymers further reduces the dielectric constants toward 1.0 and moves the dissipation factors closer to zero because the resin is replaced with air-filled cells in the insulation. The decrease in the dielectric constant is proportional for example, FEP insulation with 60% void content had a dielectric constant of More uniform foam cell size and smaller cells yield foams with the best electrical properties. 

Perfluoropolymers bum, but do not continue to bum when the flame is removed. All perfluorinated fluoropolymers pass a UL 83 vertical flame test and are classified 94 V-0 according to Underwriters Laboratory (UL) in their burning test classification for polymeric materials. Limiting oxygen index (LOI) by ASTM D2863 is 95% or higher for PTFE, PFA, FEP, and PCTFE. Partially fluorinated fluoropolymers are more flame resistant than other thermoplastics but not quite as resistant as the perfluorinated fluoropolymers, as evidenced by their lower EOI values. PVDF, ETFE, and ECTFE meet UE 94 V-0. Table 13.48 lists the EOI of various fluoropolymers. 

Limited solubility in selected perfluorinated solvents (unique amongst commercial fluoropolymers), enabling solution-cast ultra-thin coatings in the submicrometre thickness range. 

Since PTFE was first synthesized more than 50 years ago, fluoropolymers have been produced by radical polymerization and copolymerizaton processes, but without any functional groups, for several reasons. First, the synthesis of functional vinyl compounds suitable for radical polymerization is much more complicated and expensive in comparison with common fluoroolefins. In radical polymerization of one of the simplest possible candidates—perfluorovinyl sulfonic acid (or sulfonyl fluoride—there was not enough reactivity to provide high-molecular-weight polymers or even perfluorinated copolymers with considerable functional comonomer content. Several methods for the synthesis of the other simplest monomer—trifluoroacrylic acid or its esters—were reported,1 but convenient improved synthesis of these compounds as well as radical copolymerization with TFE induced by y-irradiation were not described until 1980.2... 

We are going to discuss the syntheses of fluoropolymers, poly(carbon monofluoride), perfluoropolyethers, perfluorinated nitrogen-containing ladder polymers, and surface fluorination of polymers by direct fluorination. 

For instance, the Dow experimental membrane and the recently introduced Hyflon Ion E83 membrane by Solvay-Solexis are "short side chain" (SSC) fluoropolymers, which exhibit increased water uptake, significantly enhanced proton conductivity, and better stability at T > 100°C due to higher glass transition temperatures in comparison to Nafion. The membrane morphology and the basic mechanisms of proton transport are, however, similar for all PFSA ionomers mentioned. The base polymer of Nation, depicted schematically in Figure 6.3, consists of a copolymer of tetrafluoro-ethylene, forming the backbone, and randomly attached pendant side chains of perfluorinated vinyl ethers, terminated by sulfonic acid head groups. °... 

With values in the range of about 10-18 mN m 1 perfluorinated liquids have the lowest surface tensions among the known organic liquids, and will completely wet any solid surface. Increasing amounts of hydrogen in the molecule increase the surface tension. Fluorinated solid surfaces, e.g. fluoropolymers, possess very low critical surface tensions yc, which relates to their antistick and low frictional properties, whereas hydrocarbon polymers have substantially higher values (PTFE yc = 16.0 mN m-1 PE yc = 31.0 mN m-1).7... 

Diethyl phenylmalonate and its sodium salt undergo substitutive fluorination by perfluoro-1-fluoropiperidinc (1) and perfluorinated polymers. The fluorination product is diethyl fluoro(phenyl)malonate, perfluoro-l-fluoropiperidine being a more efficient fluorinating agent than the N-F containing fluoropolymers 5. 

TFE — Tetrafluoroethylene, a perfluorinated monomer used as a feedstock for the production of PTFE and as a comonomer for the production of a variety of other fluoropolymers. 

Currently, there is concern about the use of ammonium perfluorooctanoate (APFO), also known as C8 , which is necessary for the manufacture of fluorinated plastics and elastomers in water. C8 is a perfluorinated anionic surfactant used as a dispersing agent in the polymerization and copolymerization of many fluoropolymers, including poly(tetrafluoroethylene) (PTFE), poly(vinylidene... 

Similar to other fluoropolymers and fluoroelasto-mers, such as PTFE, FEP, PFA, etc., low-level perfluorinated surfactants or chemicals, such as ammonium perfluoro-octanoate (APFO), etc. may be used in some fluoropolymer production as an emulsifier. These perfluorinated compounds are mostly extremely stable, degrade slowly, and therefore persist in the environment. These surfactants have varying ecotoxicity profiles, and users should contact their supplier for a more detailed ecotox information for their particular product.Industrial efforts are being made to reduce or even eliminate the use of such perfluorinated surfactants in their products and/or manufacturing processes. 

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