Ambient Temperature Synthesis of Poly(dichlorophosphazene) with Molecular Weight Control

摘要

We wish to report a new method for the synthesis of poly-(dichlorpphosphazene), which is an essential intermediate for the preparation of most organophosphazene high polymers. The new method allows the synthesis of poly(dichlorophosphazene) at room temperature, in the bulk state or in solution, provides an opportunity for control over the polymer molecular weight and structure, and allows access to polyphosphazenes with narrow polydispersities. Macromolecular substitution reactions carried out on poly-(dichlorophosphazene) produce a wide range of inorganic-organic polymers (Scheme 1). These polymers comprise a large class of macromolecules with a variety of well-established and useful properties, which are determined largely by the side groups linked to the polymer backbone. Thus, polyphosphazenes which are hydrophobic or hydrophilic, amorphous or microcrystalline, or which possess liquid crystalline, photo-chromic, nonlinear optical, or useful biomedical properties have been prepared. However, the currently available ring-opening polymerization and condensation routes to poly(dichlorophos-phazene) all involve the use of elevated temperatures, and the molten state ring-opening polymerization route provides little or no control over the molecular weight. Given the substantial number of polymers accessible by the macromolecular substitution route, the development of improved methods for the synthesis of poly(dichlorophosphazene) is extremely important from both academic and industrial viewpoints. Furthermore, a predictable control of the molecular weight of poly(dichlo-rophosphazene) is a key requirement for the further development of this field. We report here a controllable, reliable, and simple synthetic pathway to poly(dichlorophosphazene) via the PCl_5-initiated polymerization of trichloro(trimethylsilyl)phos-phoranimine (Cl_3P=NSiMe_3, 3).