AbstractRing opening metathesis polymerization (ROMP) is widely used to prepare functional materials with various topological structures. However, it is difficult to prepare polymers with ultra‐high molecular weight (UHMW) directly. We found a new method to prepare UHMW polymers by combining ROMP and acyclic metathesis reaction. First, monomer NB‐2OH was polymerized by ROMP with different feed ratio of NB‐2OH/G3, and obtained well‐defined polymers P(NB‐2OH)n (n = 50, 200, and 463). Then acyclic metathesis reaction was used to synthesize ...