Ring-opening polymerization induced by ringstrain

Ring-opening polymerization is one of the main access routes to heteroatom polymers such as polyphosphazenes or polysiloxanes. Unfortunately, many heteroatom ring systems resist polymerization. We have developed two methods that favor polymerization of hard-to-polymerize systems. Both methods involve the synthesis of rings that are destablized by ring-strain. In the first method, cyclic phosphazenes are prepared that contain a heteroelement such as carbon or sulfur in polace of phosphorus. In the second, the phosphazene ring is bridged by a ferrocenyl or ruthenocenyl unit. The mechanisms of these polymerizations including the use of catalysts, will be discussed.