Thallium in the Synthesis of Phosphazene Derivatives: Donor- Substituted Polyphosphazenes.

The current interest in poly(organophosphazenes)[-N=P(R sub 2)-] sub x may be attributed to the synthetic versatility afforded by the precursor [polydichlorophosphazene, (NPCl sub 2) sub x],and the excellent mechanical and chemical stability properties of this class of polymers. The nature of the substituents which may be attached to the polyphosphazene backbone is ultimately limited by the properties of the reactive intermediates which are required to effect the appropriate functionalization. In the present study we have employed thallium salts to carry out substitution reactions on hexachlorocyclotriphosphazene [(NPCl sub 2) sub 3]and polydichlorophosphazene [(NPCl sub 2) sub x]. The thallium aryloxides were found to be similar in reactivity to their alkali metal counterparts. However, the thallium aryloxides, are easier to prepare and they give rise to well-defined, stable solids which serve as convenient reaction intermediates for organophosphazene synthesis. The chief drawback to the new procedure is the toxicity and expense of thallium compounds. Organothallium salts have been used to prepare a range of phenoxy-substituted cyclotriphosphazenes and polyphosphazenes. Two new donor-substituted polyphosphazenes (R = OC sub 6 H sub 4 - 4 -SMe and R = OC sub 6 H sub 4 -4- NMe sub 2), undergo iodine doping, and the latter polymer is the most highly conducting polyphosphazene yet to be reported (>10 sup (-4)S/cm).