FUNCTIONALIZATION OF PHOSPHAZENES .1. SYNTHESIS OF PHOSPHAZENE MATERIALS CONTAINING HYDROXYL-GROUPS

In this paper we report the synthesis of 4-hydroxyphenol (hydroquinone)-substituted phosphazene materials, i.e., hexakis(4-hydroxyphenoxy)cyclophosphazene and poly[bis(4-hydroxyphenoxy)phosphazene], by reaction of 4-methoxyphenoxy-substituted cyclo- and polyphosphazenes with an excess of BBr3. An alternative method is based on a Pd-catalyzed hydrogenation under pressure of other phosphazene substrates bearing 4-(benzyloxy)phenoxy substituents. In the case of cyclic phosphazene derivatives, both these reactions take place very smoothly, while a dramatic decrease of the molecular weight is observed for the phosphazene high polymers during the reaction of poly[bis(4-methoxyphenoxy)phosphazene] with boron tribromide and during the hydrogenation process of the poly[bis(4-(benzyloxy)phenoxy)phosphazene]. In the case of poly-[bis(4-methoxyphenoxy)phosphazene], the deblocking reaction of the methoxy group can be modulated to introduce in the phosphazene substrate a predictable amount of OH groups. The successive functionalization of the produced free hydroxyl functions in the phosphazene oligomers and polymers is also discussed by considering the acetylation of these groups as a prototype process for the phosphazene substrates.