Phosphonitrilic Compounds. XIII. The Structure and Properties of Poly(difluorophosphazene)

X-Ray diffraction investigation of oriented fibers of high molecular weight poly(difluorophosphazene), (NPF₂)_n, revealed the presence of two molecular conformers. Conformer A, with a chain repeating distance of 6.49 A, was detected at temperatures between +25 and ---36°. Conformer B, observed near ---56°, showed a fiber (c) axis repeat of 4.86 A. An orthorhombic unit cell (space group Cmc2i) was assigned with a = 8.69 å and b = 5.38 å. Structure factor calculations for conformer B indicated a cis, trans-planar chain conformation, with P-N = 1.52 A, P-F = 1.47 A, F-P-F = 95°, N-P-N 119°, and P-N-P 136°. The low-temperature flexibility and high-temperature depolymerization of this polymer were also studied.