Rapid Online Analysis of Photopolymerization Kinetics and Molecular Weight Using Diffusion NMR

Abstract

Online, high-throughput molecular weight analysis of polymerizations is rare, with most studies relying on tedious sampling techniques and batchwise postanalysis. The ability to track both monomer conversion and molecular weight evolution in real time could underpin precision polymer development and facilitate study of rapid polymerization reactions. Here, we use a single time-resolved diffusion nuclear magnetic resonance (NMR) experiment to simultaneously study the kinetics and molecular weight evolution during a photopolymerization, with in situ irradiation inside the NMR instrument. As a model system, we used a photoinduced electron transfer reversible addition− fragmentation chain transfer (PET-RAFT) polymerization. The data allow diffusion coefficients and intensities to be calculated every 14 s from which the polymer size and monomer conversion can be extracted. Key to this approach is (1) the use of shuffled gradient amplitudes in the diffusion NMR experiment to access reactions of any rate, (2) the addition of a relaxation agent to increase achievable time resolution and, (3) a sliding correction that accounts for viscosity changes during polymerization. Diffusion NMR offers a uniquely simple, translatable handle for online monitoring of polymerization reactions.

Polymer Grafting to Polydopamine Free Radicals for Universal Surface Functionalization

“…To test this theory, PDA nanoparticles were added to an AIBN-initiated free radical gelation of poly­(ethylene glycol) diacrylate (PEGDA) in DMSO- d 6 at 70 °C. Gelation was conducted in situ during online diffusion NMR analysis, allowing us to track the increasing solution viscosity and gelation kinetics by observing the reduction in the diffusion coefficient ( D ) of an inert small molecule tracer (CHCl 3 ) as the reaction mixture gels. Notably, increased PDA loading yielded a reduced radical gelation rate, similar to that observed for the linear FRP systems (Figure A).…”

Operator-independent high-throughput polymerization screening based on automated inline NMR and online SEC

“…[10] Likewise, in situ methods speed up the process but such methods are limited to a restricted reaction space. [18,19] Moreover, for each series of conditions to be analysed, parallel reactors are still required, limiting the number of experiments possible. Flow reactors, however, are able to integrate real-time data acquisition by placing analytic devices in the stream of synthesis, i.e.…”

Materiomically Designed Polymeric Vehicles for Nucleic Acids: Quo Vadis?

“…90 The same group had earlier demonstrated the utility of autonomous control of polymerization kinetics, aided by in line SEC analysis (Figure 4A), to realize arbitrary degrees of polymerization with high levels of precision. 88 More recently, Fillbrook et al 91 demonstrated that online time-resolved diffusion NMR could measure molecular weight distribution and monomer conversion simultaneously, thereby eliminating the need for a separate SEC analysis step. Further, their approach is particularly effective for solvents in which SEC analysis may be challenging.…”

“…Further, their approach is particularly effective for solvents in which SEC analysis may be challenging. 91 Recently, Knox et al 92 demonstrated multiobjective optimization of RAFT by applying Thompson sampling efficient multiobjective optimization algorithm to resolve the trade-off between dispersity and monomer conversion without any human intervention. This study relied heavily on inline analysis to ensure that their algorithm could be deployed effectively in real-time even if batch processes enable automated synthesis of a large numbers of polymers, bottlenecks will arise from downstream operations such as NMR and SEC analysis, polyplex formation, physical characterization, and sample preparation for biological testing.…”