The motion of single molecular ruthenium catalysts during and after single turnover events of ring-opening metathesis polymerization is imaged through single-molecule superresolution tracking with positional accuracy of ±32 nm. This tracking is achieved through real-time incorporation of spectrally tagged monomer units into active polymer chains ends during living polymerization; thus, by design, only active-catalyst motion is detected and imaged, without convolution by inactive catalysts. The catalysts show diverse individualistic diffusive behaviors with respect to time that persist for up to 20 s. Catalysts occupy three mobility populations: quasi-stationary (23%), intermediate (53%, 65 nm), and large (24%, 145 nm) step sizes. Differences in catalyst mobility populations also exist between individual aggregates (<i>p</i> &lt; 0.001). Such differential motion indicates widely different local catalyst microenvironments during catalytic turnover. Molecular weight measurement characterizes that these aggregates are composed of relatively uniform oligomers, indicating that differences in local polymer entanglement rather than chain length polydispersity cause these catalyst mobility differences on the microscale. These mobility differences, observable uniquely through single-catalyst-tracking microscopy, likely impact individual catalyst turnover rate and selectivity and plausibly give rise to property distributions observable in bulk polymers, leading to a revised understanding of “uniform” chemical processes.

Superresolved motions of single molecular catalysts during polymerization

ACS Spring 2022

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