Ring Opening Metathesis Polymerization of Cyclooctadiene and Cyclooctene with Dihydrofuran: Influence of Ru Fischer Carbene

Vinyl ethers are commonly used to deactivate Grubbs catalysts and terminate ring opening metathesis polymerization (ROMP) by forming Fischer carbene species with attenuated metathesis reactivity. However, we recently demonstrated that a cyclic enol ether, 2,3-dihydrofuran (DHF), can in fact be homopolymerized or copolymerized with norbornene derivatives. 1,5-Cyclooctadiene (COD) and cyclooctene (COE) consist of an important class of ROMP monomers, and we describe here a study of their copolymerization with DHF. Addition of DHF greatly suppressed the ROMP activity of COD and COE and resulted in significant alkene isomerization of COD. Chloranil was found to be an effective additive to prevent undesired isomerization and promote copolymerization. As a result, high molecular weight COD/COE and DHF copolymers were synthesized. Hydrolysis of the enol ether main chain linkages yields polyalkenamers with alcohol and aldehyde end groups. This study encourages further exploration of the in situ formed Ru Fischer carbene species in ROMP to access degradable polymers.