Online Coupling of Two-Dimensional Liquid Chromatography and NMR for the Analysis of Complex Polymers

Abstract

For the first time, comprehensive two-dimensional liquid chromatography (2D-LC) of complex polymers is coupled online to 1H NMR. 2D-LC is used to separate mixtures of poly(ethylene oxide)s with regard to chemical composition and molar mass. The present samples contain polymers with different end groups and chain distributions. In the first LC dimension, liquid chromatography at critical conditions (LCCC) is used for the selective separation according to the end groups. Fractions that are then uniform regarding their end groups are automatically transferred into the second LC dimension which separates the fractions regarding their chain length distributions using liquid adsorption chromatography. The eluate from 2D-LC is directly introduced into the 1H NMR for on-flow analysis. The online coupling of one- and two-dimensional chromatography with 1H NMR detection is demonstrated. The NMR is coupled to both individual separations as well as to the entire two-dimensional separation. As a result of this multidimensional analysis quantitative information is obtained on the types and topology of end groups and the chain length distributions within each functionality fraction.

Multiple‐Injection Method in High‐Temperature Two‐Dimensional Liquid Chromatography (2D HT‐LC)

“…Yet, an enormous potential of this technique becomes obvious when considering the hyphenation of 2D HT‐LC (or HT‐LC) systems with post separation characterization. A direct benefit lies in the on‐line hyphenation, e.g., with NMR in on‐flow mode, where solvent signal suppression by special pulse sequences is required. But in the same sense an improved amount of analyte is helpful for off‐line characterization by for example DSC, where the now standard DSC instrumentation and methods may then be used instead of HyperDSC and thus quantitative data can be obtained.…”

Liquid chromatography of synthetic polymers under critical conditions of enthalpic interactions 4: Sample recovery

“…Two‐component eluents are employed in most LC CC studies. The control of a single‐component eluent strength by means of temperature adjustment is rather difficult . Beaudoin et al have demonstrated that the recovery of polystyrene from bare silica gel depended on the thermodynamic quality of the critical eluent .…”

“…This approach was proposed by Skvortsov and Gorbunov and it has been used by numerous authors. . In any case, the sample recovery should be carefully checked before the LC CC method is employed for molecular characterization of complex polymers and complex polymer systems.…”

HPLC‐1H‐NMR Characterization of Polystyrene‐block‐Polyisoprene Copolymers: LCCC‐1H‐NMR Using a Single Mobile Phase

“…By using LCCC‐NMR, blends of PI having different microstructures were separated and analyzed by the authors . Most recently comprehensive two‐dimensional liquid chromatography was coupled on‐line with 1 H‐NMR for the analysis of poly(ethylene oxide)s having different endgroups and chain length distributions …”

“…[28] Most recently comprehensive two-dimensional liquid chromatography was coupled on-line with 1 H-NMR for the analysis of poly(ethylene oxide)s having different endgroups and chain length distributions. [29] In the present study PS-b-PI copolymers will be analyzed by the on-line hyphenation of liquid chromatography at critical conditions with 1 H-NMR. The block copolymers were synthesized by sequential living anionic polymerization.…”