Elucidating the Nucleation Event in the C–C Cross-Coupling Step-Growth Dispersion Polymerization

2022

J. Am. Chem. Soc.

Polymer growth induces physical changes to catalyst microenvironments. Here, these physical changes are quantified in real time and are found to influence microscale chemical catalysis and the polymerization rate. By developing a method to “peer into” optically transparent living-polymer particles, simultaneous imaging of both viscosity changes and chemical activity was achieved for the first time with high spatiotemporal resolution through a combination of fluorescence intensity microscopy and fluorescence lifetime imaging microscopy techniques. Specifically, an increase in microenvironment viscosity led to a corresponding local decrease in the catalytic molecular ruthenium ring-opening metathesis polymerization rate, plausibly by restricting diffusional access to active catalytic centers. Consistent with this diffusional-access model, these viscosity changes were found to be monomer-dependent, showing larger changes in microenvironment viscosity in cross-linked polydicyclopentadiene compared to non-crosslinked polynorbornene. The sensitivity and high spatial resolution of the imaging technique revealed significant variations in microviscosities between different particles and subparticle regions. These revealed spatial heterogeneities would not be observable through alternative ensemble analytical techniques that provide sample-averaged measurements. The observed spatial heterogeneities provide a physical mechanism for variation in catalytic chemical activity on the microscale that may accumulate and lead to nonhomogeneous polymer properties on the bulk scale.

Section: Introductionmentioning

confidence: 99%

Real-Time Polymer Viscosity–Catalytic Activity Relationships on the Microscale

Eivgi

2022

J. Am. Chem. Soc.

“…The potential variations in�and concurrent mechanisms behind�growth of polymer particles in solution are of great interest toward the production of monodispersed polymer materials 48 and control of porous polymers that form by precipitation polymerization. 43 In a solution-phase chemical reaction, the reactants, products, and catalysts exhibit high-speed diffusion and quickly travel long ranges in three dimensions.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Indeed, these molecular ruthenium polymerization catalysts are referred to as “well-defined” due to their set ligand coordination spheres and uniform solution polymerization kinetics when measured by ensemble-averaged analytical techniques. , However, the degree to which growth is truly uniform in solution remains unknown, potentially obscured by ensemble averaging, as are the underlying mechanisms that give rise to variance (Figure a). The potential variations inand concurrent mechanisms behindgrowth of polymer particles in solution are of great interest toward the production of monodispersed polymer materials and control of porous polymers that form by precipitation polymerization…”

Section: Introductionmentioning

confidence: 99%

Growth Kinetics of Single Polymer Particles in Solution via Active-Feedback 3D Tracking

García

et al. 2022

J. Am. Chem. Soc.

The ability to directly observe chemical reactions at the single-molecule and single-particle level has enabled the discovery of behaviors otherwise obscured by ensemble averaging in bulk measurements. However powerful, a common restriction of these studies to date has been the absolute requirement to surface tether or otherwise immobilize the chemical reagent/reaction of interest. This constraint arose from a fundamental limitation of conventional microscopy techniques, which could not track molecules or particles rapidly diffusing in three dimensions, as occurs in solution. However, many chemical processes occur entirely in the solution phase, leaving single-particle/-molecule analysis of this critical area of science beyond the scope of available technology. Here, we report the first kinetics studies of freely diffusing and actively growing single polymer−particles at the singleparticle level freely diffusing in solution. Active-feedback single-particle tracking was used to capture three-dimensional (3D) trajectories and real-time volumetric images of freely diffusing polymer particles (D ≈ 10 −12 m 2 /s) and extract the growth rates of individual particles in the solution phase. The observed growth rates show that the average growth rate is a poor representation of the true underlying variability in polymer−particle growth behavior. These data revealed statistically significant populations of fasterand slower-growing particles at different depths in the sample, showing emergent heterogeneity while particles are still freely diffusing in solution. These results go against the prevailing premise that chemical processes in freely diffusing solution will exhibit uniform kinetics. We anticipate that these studies will launch new directions of solution-phase, nonensemble-averaged measurements of chemical processes.

“…The potential variations in-and concurrent mechanisms behindgrowth of polymers in solution are of great interest towards the production of monodispersed polymers, including of aggregates. 45 In a solution-phase chemical reaction, the reactants, products, and catalysts exhibit highspeed diffusion and quickly travel long ranges in three dimensions. Therefore, an extremely sensitive and rapidly responding method is needed to capture chemical reactions in real time at these high speeds with minimal perturbation, as they occur in synthetically relevant conditions.…”

mentioning

confidence: 99%

“…The impact of such heterogeneous growth at the single-particle level is increased particle size polydispersity, which impacts macroscale polymer properties. 45,53 The characterization of these non-uniform kinetics and the identification of their plausible mechanistic origin may therefore be useful to guide future polymer and catalyst development in the diverse areas of solution-phase polymerization reactions. For example, selection of reaction times, vessel shapes, or initiation rates of catalysts to avoid concentration gradients may provide access to narrower particle-size or molecular weight polydispersity.…”

mentioning

confidence: 99%

Growth Kinetics of Single Polymer Particles in Solution via Active-Feedback 3D Tracking

García

et al. 2021

Preprint

The ability to directly observe chemical reactions at the single-molecule and single-particle level has enabled the discovery of behaviors otherwise obscured by the ensemble averaging in bulk measurements. However powerful, a common restriction of these studies to date has been the absolute requirement to surface tether or otherwise immobilize the chemical reagent/reaction of interest. This constraint arose from a fundamental limitation of conventional microscopy techniques, which could not track molecules or particles rapidly diffusing in three dimensions, as occurs in solution. However, much chemistry occurs in the solution phase, leaving single-particle/-molecule analysis of this critical area of science beyond the scope of available technology. Here we report the first solution-phase studies and measurements of any chemical reaction at single-particle/-molecule level in freely diffusing solution. During chemical reaction, freely diffusing polymer particles (D ~ 10-12 m2/s) yielded single-particle 3D trajectories and real-time volumetric images that were analyzed to extract the growth rates of individual particles. These volumetric images show that the average growth rate is a poor representation of the true underlying variability in polymer-particle growth behavior. These data revealed statistically significant populations of faster- and slower-growing particles at different depths in the sample, showing emergent heterogeneity while particles are still in the solution phase. These results go against the prevailing premise that chemical processes freely diffusing in solution will exhibit uniform kinetics. These new understandings of mechanisms behind polymer growth variations bring about an exciting opportunity to control particle-size and plausibly molecular weight polydispersity by the rational design of conditions to dictate spatial growth gradients. We anticipate that these studies will launch a new field of solution-phase, nonensemble-averaged measurements of chemical reactions.