New Developments in Multidimensional Chromatography of Complex Polymers

Abstract

Summary: Complex polymers are distributed in more than one direction of molecular heterogeneity. In addition to the molar mass distribution, they are frequently distributed with respect to chemical composition, functionality, and molecular heterogeneity. One approach for the analysis of the heterogeneity of complex polymers is their chromatographic separation by combining different separation mechanisms. A typical experimental protocol includes the separation of the sample according to composition to yield fractions that are chemically homogeneous. These fractions are transferred to a size‐selective separation method and analyzed with respect to molar mass. As a result of this two‐dimensional (2D) separation, information on both types of molecular heterogeneity is obtained. So far, 2D chromatography has been applied mostly to polymers that are soluble in organic solvents. There are several problems related to the use of aqueous mobile phases in polymer chromatography. These problems relate to the very polar or ionic character of the polymers and the experimental conditions, including the use of salt‐containing eluents. The present paper addresses the different parameters that influence the chromatographic experiments. For a model polymer system resulting from the grafting of methacrylic acid (MAA) onto poly(ethylene glycol) (PEG), i.e., PEG‐g‐PMAA, it will be shown that different chromatographic techniques including SEC, LC‐CC, and 2D chromatography, as well as coupled LC‐CC/FT‐IR can be used to analyze the molecular complexity of the copolymers.LC‐CC/FT‐IR spectra of a PEG‐g‐PMAA sample as function of the elution volume.imageLC‐CC/FT‐IR spectra of a PEG‐g‐PMAA sample as function of the elution volume.

New Chromatographic and Hyphenated Techniques for Hydrophilic Copolymers

“…This is in agreement with the higher molar mass of Product 2. Obviously, the grafting reaction results in a bimodal graft copolymer distribution where Product 2 is the more advanced reaction product with a higher amount of grafted MAA and a higher molar mass [26] .…”

“…Fig. 6 summarizes the LC-CC chromatograms of the sample set [26] . As one can see, baseline separation of the graft products and non-grafted PEG is obtained.…”

Column selectivity for two‐dimensional liquid chromatography

“…2-D SEC-RP LC separations of water-soluble hydrophilic polymers are less frequent than 2-D separations of polymers soluble in organic solvents, because of problems connected with the very polar or ionic character of the polymers such as PEG-(poly) methacrylate copolymers [115,116]. Partial separation of humic substances using the heart-cut approach in 2-D SEC6RP with a BioSep-S2000 SEC column in the first dimension and Synergi polar RP column in the second dimension is an application example of this approach [117].…”

Structure Determination of Polyacetals by Liquid Chromatography and Hyphenated Techniques

“…[16,17] In the case of the highly crystalline performance (co)polymers like polyacetals or polyamides, HFIP is the solvent of choice in polymer chromatography. [18][19][20] Even the established SEC analysis of copolymers analyzed in HFIP is not straightforward.…”