Oxetane Monomers with Pendant Ferrocenes and Solvent-Free Polymerizations

The synthesis and polymerization of novel ferrocene-based monomers coupled to oxetanes, which are strained four-membered heterocycles with an oxygen atom, is reported for the first time. The ferrocene-oxetane monomers were synthesized in a single step from inexpensive, commercially available products using an ester coupling reaction. One monomer had a single ferrocene coupled pendant to the oxetane ring, and another had two ferrocenes coupled as pendant groups to the oxetane ring. A crystal structure of the monomer with a single pendant ferrocene was obtained and demonstrated that the pendant ferrocene group did not cause additional ring puckering, suggesting that it did not add significant strain to the ring. This monomer was also able to be thermally polymerized without the use of solvent or catalyst because it melted at high temperatures and reacted with a cationic initiator to undergo cationic ring-opening polymerization. The convenient homopolymer synthesis was an improvement and yielded larger molecular weights (Mw = 17,000) in comparison to previous metallopolymer syntheses with polyether backbones. The thermal properties and electrochemical properties of the polymer are discussed. Polymerizations in silicon molds also yielded basic shapes. The monomer with two ferrocenes appended to an oxetane ring did not homopolymerize, presumably due to unfavorable steric interactions.