Investigating a Catalytic Approach for the Polymerization Reaction of Dichlorophosphinylphosphorimidic Trichloride

Polyphosphazenes are a unique class of macromolecules with an inorganic backbone of phosphorus and nitrogen joined by alternating single and double bonds. Polyphosphazenes have a wide array of actual or potential uses due to the wide variation in side groups possible. Many of which are not found in classic organic polymers. The most common method for synthesizing bulk polydichlorophosphazines, due to the resulting high molecular weight polymer, is via a ring-opening method developed by Allcock and co-workers in 1965.1-3 In 1991 De Jaeger developed a synthesis of polydichlorophosphazene from P-trichloro-N-(dichlorophosphoryl) monophosphazene (Cl3PNP(O)Cl2) (3) that represented an attractive alternative to the Allcock ring-opening polymerization. This synthesis was then further improved upon by Chris Allen, who developed a solvent-free synthesis of polydichlorophosphazine ([PNCl2]n) (2) and phosphorus oxychloride (POCl3) (4) from 3. This work investigated nine catalyst candidates for the melt-phase condensation polymerization of 3 to 2 and 4. Complex 3 was synthesized using the Allen method and purified. Nine catalysts chosen from four main classes of chemicals were then investigated. Five of these catalysts were eliminated due to inactivity, and the remaining four, cyclopentadienyl iron carbonyl dimer, (h5-C5H5)2Fe2(CO)4, tris(pentafluorophenyl)borane, trimethylaluminum, and titanium tetrachloride, were investigated further.