Subject fluoropolymers

In this chaper, the two principal methods for their synthesis and some of the main applications of functional fluoropolymers will be reviewed. However, as there are many patents and papers as well as several reviews on these subjects, the review will be brief and the primary focus will be on selected applications and specific properties of functional fluoropolymers that can be achieved in highly ordered Langmuir-Blodgett (LB) films of these polymers. 

While on the subject of fluoroorganic compounds, one cannot overstate the importance of fluoropolymers in modem industry and science. There is hardly anyone around today who has never heard of polytetrafluoroethylene (PTFE) [CF2—CF2] . Housewives who know nothing about fluorine use PTFE-coated frying pans or pots, and know that PTFE makes washing up easier, because virtually nothing sticks to a PTFE-coated utensil. 

Arguments similar to those stated above can be used to explain the relative chemical inertness of fluoropolymers. Consider the reactivity of alkanes vs. perfluoroalkanes as shown in Table 4.2 (abstracted from Sheppard and Sharts Statistically, FA based materials will have many more types of bonds, in addition to C—F, than fluoropolymers. These bonds will be subject to the same chemical fate during assault by aggressive reagents as bonds in their hydrocarbon counterparts. Similar reasoning can be used to explain the relative thermal stability of FAs compared to fluoropolymers. Thus, incorporation of perfluoroalkyl groups will not make the modified material less stable than the native one. 

Indeed, free radical polymerization of fluoroolefins continues to be the only method which will produce high-molecular weight fluoropolymers. High molecular weight homopolymers of TFE, CFC1 = CF2, CH2CF2, and CH2=CHF are prepared by current commercial processes, but homopolymers of hexafluoro-propylene or longer-chain fluoroolefins require extreme conditions and such polymerizations are not practiced commercially. Copolymerization of fluoroolefins has also led to a wide variety of useful fluoropolymers. Further discussion of the subject of fluoroolefin polymerization may be found elsewhere and is beyond the scope of this review [213-215]. 

The subject of fluorinated polyurethanes is covered extensively by R. F. Brady, Jr. in Modern Fluoropolymers (Schiers, J., Ed.), John Wiley Sons, New York, 1997, Chapter 6, pp. 125-163. 

Coatings and sealants for varied industrial applications are made by dissolving compounds of low-viscosity FKM elastomers (e.g., Viton C-10, Viton A-35, Dyneon 2145) in methyl ethyl ketone, ethyl acetate, methyl isobutyl ketone, amyl acetate, or other related ketones [68], Such products have typical useful storage life of 7 days at 24°C (75°F) and cure within 2 weeks [80], This subject is covered in more detail in Modern Fluoropolymers (Scheirs, J Ed.), Chapter 23 (Ross, E. W. Jr. and Hoover, G. S.), John Wiley Sons, New York (1997). 

A major environmental and health issue is currently the toxicity of PFOA and its salts used in the polymerization process and in processing of the majority of fluoropolymers [27,28] and issues involving the use of PTFE coating on cookware and its thermal degradation [29-32]. More on this subject is in Appendix 1. 

Abrasion Resistance Testing. In the chemical process industry, fluoropolymers are typically subjected to abrasive slurries. However, there is no standardized test for slurry abrasion. The Tabor abrader test (ASTM D3884), which measures the weight loss for a certain time using a grinding wheel, is done for comparison purpose only. 

Fluoropolymers, as well as other thermoplastics, exhibit a complicated nonlinear response when subjected to loads. The behavior is characterized by initial linear viscoelasticity at small deformations, followed by distributed yielding, viscoplastic flow, and material stiffening at large deformations until ultimate failure occurs. The response is further complicated by a strong dependence on strain rate and temperature, as illustrated in Fig. 11.1. It is clear that higher deformation rates and lower temperatures increase the stiffness of the material. 

In electronic applications, wires are commonly stripped by heat and soldered for hookup of circuits. Fluoropolymer insulation is subjected to heat and decomposition occurs. It is important to remove the fumes by local ventilation to avoid exposure to gases. 

None of fluoropolymers or their decomposition products poses any threats to the ozone layer. None are subject to any restrictive regulations under the Montreal Protocol and the US Clean Air Act. Reacting HF with chloroform produces the main fluori-nated ingredient of tetrafluoroethylene synthesis CHCIF2. It has a small ozone depleting potential but is excluded from the Montreal Protocol regulation... 

In recent years, we have explored the application of low-temperature atmospheric pressure helium plasma sources to activate polymer surfaces for grafting of various monomers. For laboratory experiments with fluoropolymers such as ETFE as the substrate, the application of the handheld plasma source proved to be very efficient because surface areas of a few square centimeters could be activated in approximately 1 min by sweeping the plasma jet over the surface. Samples were reacted with ambient air to enable the formation of (hydro)peroxides and subsequently subjected to grafting. Successful... 

Ruorine-contaimng polymers, commonly known as fluoropolymers, constitute a class of materials with a combination of a unique set of properties that have attracted the considerable attention of material chemists over the past few decades [9,27-29] and which is still a field of continuous research. Incorporation of fluorine into polymers is a subject of intense research because it affects many of the physical properties of the polymers. In this context, trifluoromethyl (-CF3) and hexafluoroisopropyli-dene (6F) groups were most widely used to structurally modify different high-performance polymers, leading to considerable property improvement. Ru-orine as -CF3 or 6F groups in a polymer affects the following properties ... 

There has been a slight increase in activity in this area compared with that in the previous two year period. For the polymeric esters of acrylic, methacrylic acids, and related polymers the simplest reaction, apart from thermal depolymerization, is hydrolysis, and one or two papers on this subject have appeared. One of these concerns a comparison of the kinetics of hydrolysis of a number of methacrylate esters and a further two deal with the formation of copolymers containing carboxylic acid functions. Methyl trifluoroacrylate forms alternating copolymers with cE-olefins (ethylene, propylene, isobutylene) and these are readily hydrolysed in boiling aqueous methanolic sodium hydroxide to yield hydrophilic fluoropolymers. Hydrolysis is reported to be nearly quantitative with no chain scission. An alternating copolymer is also formed by radical polymerization of maleic anhydride with A-vinyl succinimide. On hydrolysis this copolymer is... 

PVDP Is a crystalline polymer that has offered interesting and fruitful subjects for analysis to many scientists in the entire domain on engineering plastics since about 1975, Both crystallization and morphology of the polymer are Important features for the polymer properties and the richness of the morphological behavior is not surpassed by any other polymer (3). It has the characteristic stability of fluoropolymers when exposed to harsh thermal, chemical, and ultraviolet environments. The alternating CH and CF groups in the chain contributes to the unique polarity that influences its solubility and electric properties. 

The span of this text has earned the designation as a handbook in that it covers comprehensively the subject of fluoropolymers Irom synthesis to properties to copolymers, to composites to processing to applications, even to decomposition, all sorely needed and wisely included herein. 

A link between the relatively good processability of low density polyethylene (LDPE) and the excellent toughness of linear low density polyethylene (LLDPE) has been a key subject for many researchers. Fluoropolymer-based additives provide this link. Today, the use of fluoropolymer processing additives has expanded greatly, from an early way of minimizing melt defects, to improving the throughput rates and properties of LLDPE. These additives now provide benefits in a host of polyolefin extrusion applications. 

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