Catalyst Inefficiencies: Supported Ring-Opening Metathesis Polymerization Catalyst Yields Its Ensemble Rate from a Small Number of Molecular Active Sites

A supported ruthenium metathesis catalyst misleadingly appears efficient on the basis of ensemble rate data. Nonaveraged single-particle microscopy studies described herein reveal a significant interparticle and intraparticle reactivity heterogeneity and a potential of increasing catalytic efficiency. These SEM, EDS, and optical microscopy studies of ring-opening metathesis polymerization establish a mechanism for this spatial distribution in which most of the molecular ruthenium centers are catalytically inactive. Further, the morphology of the growing polynorbornene arises from its synthesis at individual catalytically active regions. These results suggest an expanded role for single-particle microscopy in detecting spatial reactivity heterogeneity and mechanisms of polymer morphology formation, even in such “large” systems of ∼10¹⁵ immobilized molecular complexes, and in employing this detected heterogeneity to identify and implement specific methods for improving catalysts