Living Polymerization of Monomers Containing endo-Tricyclo[4.2.2.02,5]deca-3,9-diene Using Second Generation Grubbs and Hoveyda-Grubbs Catalysts: Approach to Synthesis of Well-Defined Star Polymers

Living ROMP of monomers containing endo-tricyclo[4.2.2.0(2,5)]deca-3,9-diene (TD) moieties was successfully performed using thermally stable second generation Grubbs and Hoveyda-Grubbs catalysts. Even slow-initiating catalysts enabled the living polymerization to give polymers with a narrow polydispersity index and controlled molecular weight because, the unique structure of the TD monomers resulted in much faster initiation and slower propagation than conventional norbornene monomers. Kinetic analyses confirmed that the ratio of initiation/propagation rate (k(i)/k(p)) of the TD monomers was 10 to 200 times larger than that of norbornene derivatives. To demonstrate the living nature of the ROMP, block copolymers were successfully prepared using second generation Hoveyda-Grubbs catalyst for the first time. In addition, three-arm star polymers were prepared by core-first approach using Hoveyda-Grubbs type three-arm initiator, owing to the living ROMP of TD monomers with this stable catalyst. Also, star diblock copolymer was prepared with precise molecular weight and narrow PDI of 1.03. Since these star polymers contained bulky second or third generation dendrons, these dendronized three-arm star polymers were visualized under atomic force microscopy (AFM) to confirm the star-shape topology.