Onflow liquid chromatography at critical conditions coupled to 1H and 2H nuclear magnetic resonance as powerful tools for the separation of poly(methylmethacrylate) according to isotopic composition

• Separation of PMMA based on differences in H and D isotope composition was developed.
• Liquid chromatography at critical conditions separated PMMA regarding H/D isotopes.
• Critical conditions were developed for both H-PMMA and D-PMMA.
• Onflow NMR detection was used with both H and D observation.
• H and D NMR detection clearly identified H-PMMA and D-PMMA in blends.

The present work addresses a major challenge in polymer chromatography by developing a method to separate and analyze polymers with identical molar masses, chemical structures and tacticities that is solely based on differences in isotope composition. For the first time, liquid chromatography at critical conditions (LCCC) was used to separate PMMA regarding the H and D isotopes. At critical conditions of H-PMMA, D-PMMA eluted in the adsorption mode and vice versa. By online onflow LCCC-NMR, both PMMA species were clearly identified. Different from other detectors, NMR can distinguish between H and D. Onflow LCCC-H/NMR and LCCC-D/NMR measurements were carried out and the H/D-blend components were detected. 1H and 13C NMR provided the tacticity of protonated PMMA. Double resonance 13C{H} and triple resonance 13C{H,D} provided the tacticity of the deuterated samples. Samples with similar tacticities were used to ensure that separation occurs solely regarding the isotope labeling.