Fluoroolefins copolymerization

Bromine- and iodine-containing fluoroolefins have been copolymerized with the above monomers in order to allow peroxide cure (14—21). The peroxide cure system does not requite dehydrofluorination of the polymer backbone, resulting in an elastomer that shows improved properties after heat and fluid aging. 

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... 

As was noted above, functional fluoropolymers produced by copolymerization of fluoroolefins with functional PFAVE have several unique properties, with the main disadvantage of these materials being the extremely high cost of functional monomers and the resulting high cost of the functional polymers produced from them. The fact that they are so expensive limits their wider industrial application in other fields such as catalysis and membrane separation, except for chlorine-alkali electrolysis and fuel cells, where the only suitable materials are fully fluorinated polymers because of the extreme conditions associated with those processes. 

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]. 

Uses. There are about forty to fifty organic peroxides commercially available in more than seventy formulations designed for specific applications which include (1) initiators for vinyl monomer polymerizations, and copolymerizations of monomers such as vinyl chloride, ethylene, styrene, vinyl acetate, acrylics, fluoroolefins and buta-dienestyrene (2) curing agents for thermoset polyesters, styrenated alkyds and oils, silicone rubbers and poly allyl diglycol carbonates ... 

Recently waterborne coatings based on fluoroolefin-vinyl ether terpolymers have been reported, in which a macromonomer with a hydrophilic side chain was copolymerized with fluoroolefin [2.36], [2.36a]. 

A fluorinated monomer susceptible to copolymerizing or terpolymerizing vinylidene fluoride is needed to undergo free-radical attack to render peroxide curable elastomeric co- or terpolymers of VDF [35]. So, this monomer must be functionalized or halogenated to ensure a free-radical crosslinking. The monomers mainly used are bromine-containing fluoroolefins such as [42,43] ... 

The copolymerization of fluoroolefin and vinyl ester has also been studied, one example is CTFE and vinyl pyvalate, which afford a random copolymer, as expected from these monomer reactivities shown in Fig. 5. The copolymer is featured by ultra thin film formation by casting and the resultant film shows a relatively high oxygen permeability. One practical application of thie ultra thin film supported by a porous sheet is an oxygen enricher for medical use, supplying the air with 40 wt% oxygen concentration (7). 

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