Elucidating and Mitigating Photo-Induced Catalyst Poisoning in Ring-Opening Metathesis Polymerization to Enable the Precision Synthesis and Assembly of Azopolymers

Abstract Ring-opening metathesis polymerization (ROMP) offers a robust route to functional polymers, yet the controlled polymerization of bulky azobenzene-functionalized norbornenes frequently suffers from an unexplained loss of livingness. Using in situ NMR kinetics, we identify ambient photoisomerization as the root cause of this catalyst deactivation. We demonstrate that trace photogenerated Z-isomers act as potent stoichiometric inhibitors that irreversibly cleave the active Ru═C bond via competitive chelation. Intriguingly, increasing the steric bulk of the monomeric spacers and terminal tails counterintuitively accelerates the polymerization rate. This added steric hindrance acts as a “kinetic shield” that effectively restricts the competitive chelation of Z-isomers. By simply executing the polymerizations in the dark, the living character of the Grubbs catalyst is completely preserved. This protocol enables the quantitative synthesis of high-molecular-weight azopolymers (DP ≈ 1000) and precisely defined ABC triblock architectures, with chain lengths strictly dictated by initial stoichiometry. Leveraging this rescued catalytic livingness, we employed the ring-opening metathesis polymerization–polymerization-induced self-assembly (ROMP–PISA) strategy to synthesize liquid crystalline nanoparticles. Driven by the high solvophobicity of the PISA process, these assemblies initially form well-defined primary globules. By subsequently modulating the thermodynamic environment—either via evaporation-induced solvent plasticization on substrates or direct solvent shifting in the bulk solution—these confined azobenzene blocks are granted the mobility to reorganize. This triggers a programmed morphological evolution from the initial globular precursors into extended anisotropic worms and stacked-disc superstructures, reflecting the inherent self-assembling propensity of the rigid mesogens. Ultimately, resolving this photo-induced catalyst poisoning provides a reliable synthetic foundation for the precision engineering and programmable hierarchical assembly of complex photodynamic nanomaterials.