Phosphazenes commercial elastomers

Applications. Among the P—O- and P—N-substituted polymers, the fluoroalkoxy- and aryloxy-substituted polymers have so far shown the greatest commercial promise (14—16). Both poly[bis(2,2,2-trifluoroethoxy)phosphazene] [27290-40-0] and poly(diphenoxyphosphazene) [28212-48-8] are microcrystalline, thermoplastic polymers. However, when the substituent symmetry is dismpted with a randomly placed second substituent of different length, the polymers become amorphous and serve as good elastomers. Following initial development of the fluorophosphazene elastomers by the Firestone Tire and Rubber Co., both the fluoroalkoxy (EYPEL-F) and aryloxy (EYPEL-A) elastomers were manufactured by the Ethyl Corp. in the United States from the mid-1980s until 1993 (see ELASTOLffiRS,SYNTHETic-PHOSPHAZENEs). 

In the case of poly(alkoxyphosphazenes) (IV) or poly(aryloxyphos-phazenes) (V) a dramatic change in properties can arise by employing combinations of substituents. Polymers such as (NP CHjCF ) and (NP CgH,).) are semicrystalline thermoplastics (Table I). With the introduction of two or more substituents of sufficiently different size, elastomers are obtained (Figure 4). Another requirement for elastomeric behavior is that the substituents be randomly distributed along the P-N backbone. This principle was first demonstrated by Rose (9), and subsequent work in several industrial laboratories has led to the development of phosphazene elastomers of commercial interest. A phosphazene fluoroelastomer and a phosphazene elastomer with mixed aryloxy side chains are showing promise for military and commercial applications. These elastomers are the subject of another paper in this symposium (10). 

Other Applications. Thus far the phosphazene fluoroelastomers (PNF) and aryloxyphosphazene elastomers (APN) have moved to the commercial stage. In addition to elastomers, phosphazenes are being investigated as fluids, resins and plastics. Other areas which hold promise include fire resistant paints (55), fiber blends and additives, agrichemicals and herbicides, drug release agents and electrically conducting polymers (6). 

Two commercial phosphazene elastomers were developed and marketed in the mid-1980s, namely, poly(fluoroalkoxyphosphazene) elastomer (ASTM International designation FZ) and poly(aryloxyphosphazene) elastomer (ASTM International designation PZ) [109]. The structure of the fluorinated product is as follows [110] ... 

Phosphazene elastomers were very successful throughout the 1980s, being used mainly in military and aerospace industry. However, because of their high cost and relatively small volume market, they are not available commercially other than on special orders. 

This paper has reviewed the most recent developments of phosphazene elastomers and touched briefly in some phosphazenes of related Interest. At the time of this writing. Firestone was the supplier of the PNF and APN elastomers. Ethyl Corporation recently licensed the phosphazene technology from Firestone (49). and thus the continued availability of these elastomers Is assured for further commercial development. 

This is illustrated in Scheme I. Occasionally, as when bulky diethylamino units are introduced first, this technique permits the synthesis of polymers in which each phosphorus bears only one bulky unit and one less hindered substituent (non-geminal structure) [22] rather than structures that contain both geminal and non-geminal side group arrangements. Sequential or simultaneous co-substitution reactions are used for the preparation and manufacture of commercial high performance phosphazene elastomers of the type shown in structure 10 [15-17]. 

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