Solution-grown crystal of poly[bis(4-ethylphenoxy)phosphazene

Abstract

The lattice parameters of polyorganophosphazenes are considered to involve significantly important information for understanding molecular chain packings in both their crystalline and mesomorphic states [1]. Since Kojima and Magill [2] first reported on the lattice constants of poly[bis(2,2,2-trifluoroethoxy)phosphazene] from its well-defined solutiongrown crystal, several works along these lines have already been published [3-7], calling attention to structural similarities between phosphazene polymers and organic flexible polymers. To substantiate various qualities of these inorganic polymers in terms of material characterization, further approaches on solution-grown crystals of other crystallizable polyphosphazenes will be necessary. In this study we investigated the structural features of solution-grown crystals of poly[bis(4ethylphenoxy)phosphazene] [PB(4-Et)PP] and examined the lattice constants using a transmission electron microscope. The thermotropic transition behaviour of the polymer was previously reported by Tanaka et al. [8] by solid-state 31p-nuclear magnetic resonance spectroscopy. Well-purified hexachlorocyclotriphosphazene was polymerized in 1,2,4-trichlorobenzene with sulphamic acid to polydichlorophosphazene [9]; the polymer was then reacted with sodium 4-ethylphenoxide in a toluene-di(ethyleneglycol dimethyl ether) mixture at 115 °C for 48 h [10], yielding the PB(4-Et)PP polymer. The purified polymer indicated the following results of elemental analysis (theoretical values): C 66.84% (66.90%), H 6.33% (6.30%) and N 4.91% (4.88%). The residual chlorine content was <0.01%. Infrared spectroscopy for the polymer showed very strong absorption at 1321 cm -1, assigned to the asymmetric stretching vibration mode of P N bonds. The weight average molecular weight and molecular weight distribution index of the polymer were characterized as Mw = 4.65 x 105 and Mw/M n --4.49, respectively, by a gel-permeation chromatography method. Solution-grown crystals of PB(4-Et)PP were made by dissolving the polymer in N,N-dimethylformamide at 140 °C just below the boiling point of this solvent. The final solution concentration was designed to be 0.005wt% by adding n-propyl alcohol into the solution at 90 °C and the solution was then slowly cooled to room temperature. In this case n-propyl alcohol played the role of a poor