Transforming Cyclic Allenes into Precision Macromolecular Building Blocks

Abstract Ring-opening allene metathesis polymerization (ROAlMP) provides direct access to polyallenamers containing reactive allene functionality within the polymer backbone, yet achieving controlled polymerization has remained a major challenge. Here, we report an additive-assisted ROAlMP strategy in which triphenylphosphine (PPh3) or 3,5-dichloropyridine (3,5-Cl2Py) modulates catalyst speciation to enable controlled polymerization behavior, affording polyallenamers with predictable molecular weight (Mn up to 70 kDa) and moderate dispersities (Đ < 1.4). This enhanced control enables the synthesis of di- and triblock copolymers spanning three distinct classes of metathesis-active monomers, including cyclic alkenes, diynes, and cyclic allenes, while also providing access to self-assembled nanostructured materials containing allene-rich domains. We further demonstrate that these domains can be selectively stabilized through backbone [2 + 2] photocrosslinking, a capability inherently encoded within the polymer backbone and achieved without additional monomer functionalization. Finally, to illustrate the unique chemical opportunities afforded by backbone allenes, the resulting polyallenamers were subjected to iodonium-induced annulation, generating naphthalene-containing polymer backbones with pronounced changes in their photophysical behavior. Collectively, these results establish additive-controlled ROAlMP as a versatile platform for precision polyallenamer synthesis and highlight the unique materials opportunities enabled by allene-containing polymer backbones.