Synthesis of Linear and Cyclic Poly(allenamer)s by Powerful Cyclic–Alkyl–Amino–Carbene (CAAC) Ruthenium Catalysts and Facile Post‐modification

Cyclic polymers are very attractive due to their unique properties; however, so far, they have simple and less reactive backbone structures due to synthetic limitations, restricting their further post‐modification. Notably, allenes present a potentially useful platform in polymer chemistry due to their well‐established toolbox in organic chemistry. Nevertheless, the biggest challenge remains in synthesizing poly(allenamer)s with high allene contents or polymerization efficiency, as well as synthesizing different types of cyclic poly(allenamer)s. Herein, we synthesized linear and cyclic poly(allenamer)s via ring‐opening metathesis polymerization (ROMP) and ring‐expansion metathesis polymerization (REMP), employing highly efficient cyclic–alkyl–amino–carbene (CAAC) ruthenium catalysts. Mechanistic studies suggested CAAC ligands enhanced stability of propagating Ru vinylidene, enabling various linear and cyclic poly(allenamer)s with turnover number up to 1360 and molecular weight reaching 549 kDa. Their cyclic architecture was thoroughly characterized by multiangle light scattering size‐exclusion chromatography (MALS SEC) with viscometer. Moreover, controlled ROMP of a highly reactive α‐substituted cyclic allene was achieved using third‐generation Grubbs' catalyst. Finally, we demonstrated highly efficient and selective post‐modifications on poly(allenamer)s with primary and secondary alcohols. This broadens the scope of cyclic polymers with improved efficiency and structural control, affording a practical platform for diverse macromolecules.