Fluoropolymers monomer synthesis

In this entry, the classification, preparation, properties, fabrication, safety considerations, and economics of fluoropolymers are discussed. Monomer synthesis and properties have also been discussed. Increasing the fluorine content of a polymer increases chemical and solvent resistance, flame resistance, and photostability, improves electrical properties, such as dielectric constant, lowers coefficient of friction, raises melting point, increases thermal stability, and weakens mechanical properties. 

All aspects of the fluoropolymers including monomer synthesis, polymerization, properties, applications, part fabrication techniques, safety in handling, and recycling are discussed. Homopolymers and copolymers of vinylidene fluoride, all melt processible, have been covered in Volume Two because of the close... 

Poor solubility in most common organic solvents represents an inherent problem in the synthesis and processing of many high molar mass fluoropolymers. In fact, CFCs and carbon dioxide are the best solvents for amorphous varieties of fluoropolymers. Due to the environmental problems associated with CFCs, the international community is seeking to replace them with more benign compounds such as hydrochlorofluorocarbons and hydrofluorocarbons. However, the environmental problems which will be created by the use of these replacement compounds such as the accumulation of trifluoroacetic acid in the atmosphere clouds this issue [71], Carbon dioxide presents an ideal inert solvent to effect the polymerization of these types of highly fluorinated monomers and obviates the use of solvents that are being phased out because of environmental concerns. 

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... 

Ford, L. A., DesMarteau, D. D. and Smith, D. W., Jr. 2005. Perfluorocyclobutyl (PFCB) aromatic polyethers Synthesis and characterization of new sulfonamide containing monomers and fluoropolymers. Journal of Fluorine Chemistry 126 653-660. 

Like the direct chemical change, the radical coupling mainly concerns fluorinated monomers. Ameduri and Boutevin [238] summarized the different studies concerning the modification of o ,rw-fluoropolymers in a recently published book. They showed, for instance, that extensive research [240] was carried out on the synthesis of diaromatic difunctional compounds linked to fluorinated chains according to the following Ullman coupling reaction ... 

The only way to apply chemically bonded thin perfluorosulfonic acid layer onto the surface of an inert support is to graft perfluorinated functional monomers onto perfluorinated polymers. Some features of radiation-induced graft copolymerization of PFAVESF onto fluoropolymers were investigated. The studies showed that neither irradiation of a fluoropolymer-PFAVESF mixture (direct grafting) or interaction of PFAVESF with previously irradiated fluoropolymers (preirradiation grafting) yielded the grafted copolymers. It was assumed that this is connected with the low activity of PFAVE in radical polymerization. A special method has been developed for the synthesis of grafted copolymer. Previously irradiated fluoropolymer powders were used to prevent waste of PFAVESF. 

Fluorinated surfactants have been used for decades as processing aids during aqueous emulsion polymerization synthesis of fluoropolymers such as poly (tetrafluoroethylene). The function of the fluorosurfactant is to solubilize both the fluorinated monomer(s) as well as the growing fluoropolymer. Historically, the... 

Fluoropolymers have evolved over six decades. New monomers have allowed the synthesis of new polymers with new methods of processing. Most newer perfluoropolymers have the same basic properties as polytetrafluoroethylene (PTFE) but they offer new methods of processing. These new techniques have greatly increased the range of parts that can be fabricated from fluoropolymers at reduced cost. Today, fluoropolymers are processed by methods almost identical to those used a half century ago as well as by state of the art molding technologies. 

The first part of the book deals with definitions and fundamental subjects surrounding the polymerization of fluoropol)miers. Basic subjects such as the identification of fluoropolymers, their key properties, and some of their everyday uses are addressed. The main monomer, tetrafluoroethylene, is extremely flammable and explosive. Consequently, safe polymerization of this monomer requires special equipment and technology. Molecular forces within these polymers are reviewed and coimected to macro properties. Monomer and polymer synthesis techniques and properties are described. Part One ends with a detailed list of advertised commercial grades of fluoroplastics. 

Using the optimal conditions for the radical terpolymerization of 4-[(a,/ ,/ -trifluorovinyl)oxy]bromobenzene with the fluoroalkenes, these authors reported the synthesis of new polymer electrolyte membranes based on fluoropolymers incorporating aromatic perfluorovinyl ether sulfonic acids [85,107]. In fact, a novel synthetic route for the preparation of perfluorovinyl ether monomer containing sulfonic functionalities, 4-[(a,, -trifluorovinyl)oxy]benzenesulfonic acid (TFVOBSA), was proposed. This monomer was synthesized in 72% overall yield. Further, the radical (co)- and terpolymerization of 4-[(a,, -trifluorovinyl)oxy] benzenesulfonyl chloride (TFVOBSC) with VDF, HFP, and PMVE (Fig. 2.25)... 

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