Strain-Induced Ring-Opening Polymerization ofFerrocenylorganocyclotriphosphazenes: A New Synthetic Route to Poly(organophosphazenes)

摘要

Ring-opening polymerization provides an important synthetic route to both organicand inorganic polymers. In most cases, the presence of ring strain within the cycle monomer provides a driving force for the polymerization process. We have utilized the deliberate introduction of ring strain as a means to enhance the polymerization of cyclic phosphazenes. This provides a route for the polymerization of cyclic species that do not normally polymerize or that do so only at relatively high temperatures. This methodology may also be useful for the polymerization of other cyclic inorganic or organic compounds that have so far resisted polymerization. The main synthetic route to poly(organophosphazenes) involves the thermal ring-opening polymerization of hexachlorocyclo-triphosphazene (1) to yield poly(dichlorophosphazene) (2) This macromolecular intermediate than serves as a substrate for chlorine atom replacement by organic nucleophiles to give polymers of general formula 3 (Scheme I, route A). An alternative route to a variety of poly(organophosphazenes) involves the condensation polymerization of N-silylphosphoranimines. In principle, a third route to phosphazene polymers involves the introduction of organic or organometallic side groups at the cyclic trimer level (to give 4) followed by ring-opening polymerization of these species.