Absolute characterization of polymers with light scattering and UHP-SEC

Absolute Characterization of Polymers with UHP-SEC and Light Scattering

Significance of the Topic

UHP-SEC accelerates polymer separations dramatically, reducing analysis times to under 90 seconds and cutting solvent and sample consumption. When combined with multi-angle light scattering (MALS), it provides absolute molar mass and size measurements, overcoming limitations of conventional SEC calibration for branched, co- and rod-like polymers.

Objectives and Study Overview

This study evaluates the integration of UHP-SEC with online MALS (and embedded DLS and refractometry) to demonstrate throughput gains, identify calibration pitfalls, and validate the absence of shear degradation by comparing UHP-SEC-MALS to standard SEC-MALS.

Methodology and Instrumentation

Analyses were performed on an Acquity UPLC system with APC SEC columns (125 and 450 Å pores), a microDAWN MALS detector, microOptilab RI detector, and ASTRA software. Typical conditions included 4–20 µL injections at 0.5–1.0 mL/min. Measurements combined scattering intensity, concentration signals and angular dependence to determine molar mass (M), radius of gyration (Rg) and hydrodynamic radius (Rh) directly.

Main Results and Discussion

• Calibration Pitfalls: Column-only calibration misrepresents narrow standards and fails under non-ideal polymer-column interactions, leading to incorrect molar mass ranges.
• Absolute Determination: SEC-MALS revealed true narrow distributions of a 30 kDa polystyrene standard, despite calibration suggesting broad spans.
• High-Pressure Validation: UHP-SEC-MALS and SEC-MALS analyses of a 1.5 MDa polystyrene sample yielded identical weight-average molar mass and rms radii, confirming no shear-induced degradation.
• Conformational Sensitivity: Elongated epoxy resins elute earlier and exhibit lower molar mass at a given volume compared to linear polymers; UHP-SEC-MALS quantifies these differences precisely.
• Copolymer Analysis: Triple detection (MALS, UV, dRI) enables absolute copolymer composition and molar mass determination without narrow reference standards.

Benefits and Practical Applications

• High throughput with sub-90-second runs.
• Reduced solvent and sample usage.
• Direct, calibration-free measurement of molar mass and size.
• Reliable analysis of branched, rigid or heterogeneous polymers.
• Enhanced QC methods by eliminating calibration drift and non-ideal interactions.

Future Trends and Opportunities

Advances in column chemistries, faster light scattering detectors and integration of viscometry or advanced DLS modules will expand size ranges, improve shear testing, and facilitate real-time process monitoring. Development of new surface modifications will further reduce non-ideal interactions.

Conclusion

UHP-SEC coupled with online MALS provides rapid, absolute characterization of polymers across diverse architectures without reliance on calibration standards. It delivers accurate molar mass and size measurements under ultra-high pressures, making it essential for research, quality control and industrial applications.

References

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3. Rowland SM, Striegel AM. Analytical Chemistry 84(11):4812–4820 (2012).