Phosphazenes fluorophosphazenes

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). 

Hexachlorocyclotriphosphazene (3.19) is prepared on an industrial scale by the interaction of phosphorus pentachloride with ammonium chloride in an organic solvent such as chlorobenzene. This compound, after careful purification and protection from moisture, is heated in the molten state at temperatures between 210 and 250 °C to induce polymerization.15-18 The mechanism of this reaction is discussed in a later section. Here it is sufficient to note that the process can also be applied, with minor variations, to cyclic phosphazo-phosphazenes (3.22a, 3.23), to cyclic fluorophosphazenes (3.24,3.25), and to cyclic carbo- (3.26), thio- (3.27), and thionyl (3.28) -phosphazenes. 

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