Molar mass distributions by gradient liquid chromatography: predicting and tailoring selectivity.

Area of Science:

• Polymer Chemistry
• Analytical Chemistry
• Chromatography

Background:

• Interactive liquid chromatography (iLC) is established for polymer characterization beyond molar mass, including chemical composition and tacticity.
• The application of iLC for determining molar mass distributions (MMDs) remains underexplored.
• Traditional size-exclusion chromatography (SEC) has limitations in selectivity for MMD analysis.

Purpose of the Study:

• To explore and develop the application of iLC for the determination of polymer molar mass distributions (MMDs).
• To model and predict the retention behavior of polymers based on molar mass using an expanded reversed-phase liquid chromatography model.
• To compare the selectivity of iLC with size-exclusion chromatography (SEC) for polymer analysis.

Main Methods:

• Developed an expanded reversed-phase liquid chromatography model to describe polymer retention behavior as a function of molar mass.
• Investigated non-linear correlations between molar mass and model parameters.
• Constructed and validated calibration curves (retention time vs. molar mass) using experimental data and matrix-assisted laser desorption ionisation (MALDI) mass spectrometry (MS) of collected fractions.

Main Results:

• The developed model accurately predicts the retention behavior of polystyrene samples across a range of molar masses.
• iLC demonstrated significantly enhanced selectivity compared to SEC, yielding essentially monodisperse fractions in the low-molar mass range.
• Experimentally determined MMDs for narrow-dispersity polystyrene standards were found to be lower than manufacturer values and deviated from MALDI-MS results.

Conclusions:

• Interactive liquid chromatography (iLC) is a viable and highly selective technique for determining polymer molar mass distributions (MMDs).
• The developed model provides accurate predictions of retention behavior, enabling effective MMD determination.
• iLC offers a powerful alternative to SEC for detailed polymer characterization, particularly where high selectivity is required.