Synthesis of Open-Chain Poly(difluorophosphazene) and Its Reactions with Alkoxides, Aryloxides, and Amines

The first synthesis of a soluble form of high molecular weight poly(difluorophosphazene), (NPF²)_n, has been carried out, and the reactions of this polymer with amines, alkoxides, or aryloxides have been examined. Poly(difluorophosphazene) reacted smoothly with sodium trifluoroethoxide to yield high molecular weight [NP(OCH₂CF₃)₂]_n. However, reactions with amines, such as methylamine, n-butylamine, dimethylamine, or aniline, resulted in some chain cleavage and in the formation of nongeminal, partly substituted products of the general formula [NPF(NHR)]_n. The limited chain cleavage was ascribed partly to hydrogen fluoride attack on the polymer backbone and also to subsequent hydrolysis of residual P-F bonds. Comparisons with the chemistry of poly(dichlorophosphazene), (NPCl₂)_n, indicate fundamental differences between the substitution chemistry of the fluoro- and chlorophosphazene systems, and explanations for these differences are suggested. From a synthetic viewpoint, the unusual reactivity of (NPF₂)_n provides reaction routes to stable new poly(organophosphazenes), such as [NP(NHC₄H₉)(OCH₂CF₃)]_n, that are not accessible through (NPC1₂)_n.