On-line fractionated size exclusion chromatography–nuclear magnetic resonance of polymers with 1H and 2H nuclear magnetic resonance detection

A new approach for on-line SEC–NMR is introduced. The method combines time slicing, fractionation with adjusted loop collection and automatic stop-flow NMR analysis. It will be called on-line fractionated SEC–NMR. This technique allows the precise determination of molar mass distributions for any polymer which can be detected by NMR. It is a significant improvement of sensitivity and accuracy compared to onflow SEC–NMR and exhibits a much easier experimental setup than off-line SEC–NMR fractionation. The new method was applied to protonated and deuterated block copolymers by using 1H NMR and for the first time also 2H NMR detection. In this case block copolymers can be correctly characterized according to their block length distributions. As the consequence very precise molar mass parameters Mn and Mw can be determined. The results of the on-line fractionated SEC–NMR are in very good agreement with the multi detector analysis. The new technique also proposes a method for separating the true copolymer and low molar mass fractions in the mixture, whose structures are confirmed by HPLC–FTIR and 2D chromatography.

► A new on-line fractionated SEC–NMR method is introduced.
► Time slicing and loop collection is combined with stop-flow and NMR detection.
► Higher NMR sensitivity and better quantification of SEC fractions is obtained.
► Correct determination of the molar mass distribution is achieved.
► Results in very good agreement with multi detector analysis.