Well-Defined Acetylene-Functionalized Oxanorbornene Polymers and Block Copolymers

Well-defined and high molecular weight acetylene-functionalized poly(oxanorbornenes) were synthesized using ring-opening metathesis polymerization (ROMP) of cobalt-functionalized exo-oxanorbornene monomer 2a. Dicobalt hexacarbonyl, Co2(CO)6, was used as a protecting group for the acetylene moiety. This protecting group was found to be compatible with third-generation Grubbs’ catalyst, offering well-defined homopolymers and block copolymers in high yields (up to 97%). Equally important, it was removed (>99%) by treating the polymers with ceric(IV) ammonium nitrate (CAN), under mild conditions, with no observable unwanted side reactions. This approach yields high fidelity polymers containing the acetylene functionality which is incompatible with Ru-based catalysis. The explosion of click chemistry makes these polymers attractive starting macromolecules for postpolymerization chemistry.