Polymer Size–Catalytic Activity Relationships in Solution

The assignment of catalytic activity to specific sizes of polymers in solution is typically obscured by traditional analytical techniques, due to limited detection sensitivity and/or dynamic range. Here, a fluorescence correlation spectroscopy (FCS) method is developed to determine catalytic activity of living polymers of a specific apparent size in solution. Deviation from a single-component FCS data fitting, as assessed by χ2, is also introduced and developed as a “speciation index”—a method to track changes in the relative amount of distinct polymer species with reaction progress. These methods are enabled by incorporating a selectively reactive fluorescent monomer into growing polydicyclopentadiene or polynorbornene during ring-opening metathesis polymerization (ROMP). Compared to polynorbornene, data showed that catalysts in aggregates of polyDCPD had higher activity and retained their activity for longer—outcomes not predictable directly from first principles. The assignment of catalytic activity to polymers of specific sizes, and the determination of how this activity evolves with reaction progress underpin long-term goals in the development and measurement of nanostructures that possess size-dependent catalytic activity.