Characterization of Polymer Molecular Weight Distribution by NMR Diffusometry: Experimental Criteria and Findings

Area of Science:

• Polymer Science
• Analytical Chemistry
• Physical Chemistry

Background:

• NMR diffusometry is valuable for polymer molecular weight (M) and molecular weight distribution (MWD) determination.
• Generic detection, chemical selectivity, and quantitation are key advantages of NMR diffusometry.
• Understanding measurement conditions is crucial for accurate MWD characterization.

Purpose of the Study:

• To investigate the impact of diffusion measurement conditions on polymer MWD determination.
• To establish the critical dilute concentration (C*dilute) as a boundary for negligible polymer chain interactions.
• To validate the theoretical link between C*dilute, molecular weight, polydispersity, and chain conformation.

Main Methods:

• Utilizing NMR diffusometry to measure polymer diffusion.
• Defining and applying the critical dilute concentration (C*dilute).
• Quantitative analysis of MWD under varying concentration conditions.

Main Results:

• Solid evidence validates the theory linking C*dilute to polymer properties (M, polydispersity, conformation).
• Violating the sufficiently dilute condition significantly impacts M/MWD characterization.
• Disparities in literature data can be rationalized by considering these findings.

Conclusions:

• Provides essential guidance for accurate M/MWD characterization using NMR diffusion.
• Offers new insights into chain conformation-diffusion interplay, particularly for globular structures like proteins.
• Presents a novel approach for characterizing polymer architecture and molecular weight.