Phosphonitrile fluoroelastomers

The advent of the rubbers based on perfluoro(methyl vinyl ether) considered in the last section and the phosphonitrilic fluoroelastomers discussed in the next would seem to place any commercial future for these materials in serious doubt. 

The totally inorganic polyphosphonitrilic chloride has long been known to exhibit rubbery properties (Stokes, 1895). It is prepared by the reaction of phosphorus pentachloride with ammonium chloride by the following reaction  

The rubbery linear polymer is rapidly degraded by moisture and has been little more than a laboratory curiosity. 

In order to improve hydrolytic stability chlorine groups have been replaced by such moieties as alkoxy, aryloxy and amine groups. Most of the early modifications were cross-linked and thus intractable and difficult to characterize. For this reason little progress was made until Allcock and Kugel (1965) disclosed methods of termination at low conversions to give a material that remained soluble. 

The first fluorophosphonitrilic polymers were produced three years later (Rose, 1968) by the addition of sodium trifluoroethoxide and heptafluorobutoxide to the solid polyphosphonitrilic chloride, poly(dichlorophosphazene)  

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With mixtures of alkoxy substituents having longer alkyl chains, crystallization can be avoided to produce an amorphous rubber. The product is referred to as phosphonitrilic fluoroelastomer, a semiorganic rubber. The rubber can be cross-linked with free-radical initiators or by radiation. A... 

D. F. Lohr and J. A. Beckman, "PNF Phosphonitrilic Fluoroelastomer Properties and Applications, a publication by Firestone. 

Phosphonitrilic fluoroelastomers have a phosphonitrilic backbone with trifluoroethoxy and heptafluorobutoxy side groups. The rubbers are useful in the temperature range from -100 F to 300 F, are solvent-resistant and nonflammable. 

Poly((2-trifluoroethoxy)( 1 -difluoro-2,3,4-hexafluoropentoxy) phosphazene) Phosphonitrilic fluoroelastomers... 

Rose, S.H. Synthesis of phosphonitrilic fluoroelastomers. Journal of Polymer Science Part B-Polymer Letters 6(12PB), 837 (1968). doi 10.1002/pol.l968.110061203... 

There also exists a number of speciality rubbers whose applications are either very limited or well established. These include the chlorinated polyethylenes, the epichlorhydrin rubbers, the fluorosilicones, the ethylene-vinyl acetate rubbers, the polysulphides, the nitroso rubbers and the phosphonitrile fluoroelastomers. Changes in the uses of these materials are likely to have very little impact on the usage of general purpose and major special purpose rubbers. They have also been the subject of a recent review. ... 

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