Co-polymer sequence determination by SEC coupled to Pyrolysis GC

Wouter Knol developed a method to determine the sequence of co-polymers using SEC coupled to Pyrolysis GC.

Polymers are complex mixtures of molecules featuring distributions molar mass, chemical composition, end-groups, etc. One of these distributions is the sequence distribution, which describes the order or monomers in the polymer backbone. The sequence is notoriously hard to study as it requires the monitoring of subunits in the polymer backbone.

Figure 1. Schematic representation of random, block and alternating co-polymers. Reproduced with permission from [1].

This is typically done using 13C-NMR which is insensitive (a measurement typically requires ±50 mg of sample) and yields complex spectra. Pyrolysis-GC is a less investigated alternative method to determine the copolymer sequence. Although py-GC its less accurate it can be calibrated with a sample with a known sequence. The main advantage of py-GC is its sensitivity, only requiring a few micrograms of sample for an analysis. This allows sequence to be combined with LC separations.

CAST member Wouter Knol introduced Py-GC coupled to size-exclusion chromatography (SEC) to monitor the sequence of polymers as a function of molar mass. This information was previously not practically obtainable. The developed method thus offers more in-depth information on polymer structures aiding in the development of the materials of the future.

Figure 2. Fitted modified-Pearson-VII distributions on both the UV (A) and RID (B) signal of sample 5 the normalized original signal (blue) is indicated on the left-side vertical axis. The reconstructed signal consisting of the two modified-Pearson fits (MP1 and MP2), is overlaid in orange. The weight fraction styrene determined by py-GC is indicated by the dots (right-side vertical axis). Reproduced with permission from [1].

The technique was used to determine the sequence heterogeneity across the molar mass distribution. In the study, pyrolysis GC-MS analysis of dimeric units was found to allow co-polymers to be sequenced. A sophisticated calibration approach was established utilising the superior sensitivity and resolution of Pyrolysis GC over 13C-NMR to obtain accurate quantitative sequence information on styrene-methyl methacrylate co-polymers. 

The work was part of the research line by Prof. Ron Peters who is professor by special appointment in Bioterials Analysis at the Van ‘t Hoff Institute for Molecular Sciences at the University of Amsterdam.

The work was published open access in Journal of Chromatography A and can be downloaded here.

References

[1] Co-Polymer sequence determination over the molar mass distribution by size-exclusion chromatography combined with pyrolysis – gas chromatography, W.C. Knol, T. Gruendling, P.J. Schoenmakers, B.W.J. Pirok, R.A.H. Peters, Chromatogr. A, 2022, 1670, 462973, DOI: 10.1016/j.chroma.2022.462973

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