Liquid chromatography of polymers under limiting conditions of adsorption: III. Role of experimental variables

Abstract

LC of polymers under limiting conditions of adsorption (LC LCA) is a novel method based on different mobility of (pore excluded) macromolecules compared to (pore permeating) solvent molecules. Polymer sample is injected in a solvent preventing its adsorption within the column. Eluent promotes sample adsorption. Under these conditions, macromolecules cannot leave its initial solvent and elute from the column independently of their molar mass. In contrast, a less interactive simultaneously injected polymer leaves its initial solvent zone and is eluted in the size exclusion mode. As a result, chemically different polymer species can be discriminated. The effect of selected experimental conditions was studied on the LC LCA behavior of poly(methyl methacrylate)s eluted from bare silica gel columns. The parameters were packing pore diameter, injected sample volume and concentration, as well as column temperature. The size independent elution was only little affected by the above parameters and LC LCA produced well-focused peaks. The LC LCA mechanism was operative even at a very large sample of both volume and concentration. This makes LC LCA a robust and user-friendly method, likely suitable also for characterization of minor components of polymer mixtures.

Separation of Parent Homopolymers from Diblock Copolymers by Liquid Chromatography under Limiting Conditions Desorption, 1 ‐ Principle of the Method

“…The THF suppressed adsorption of PS and PMMA within the bare silica gel 39–42, 48. It acted as a ‘desorli’ for both polymers and permitted their elution from the column in the SEC mode.…”

“…The barrier volume was 1 000 µL for the (300 × 8) mm column packed with Kromasil 60 and 300 µL for a column packed with Kromasil C‐18. The volume of the barrier was chosen so that its dilution during the column passage would not reduce the concentration of elution preventing liquid under about 50% of its initial level 42. Time intervals between barriers depended on the size of column used.…”

“…So far, six different LC LC procedures have been tested. Three retention mechanisms were applied, namely adsorption,39–42 enthalpic partition,43 and phase separation (precipitation),44–46 each of them with two experimental arrangements: i) the eluent created a continuous barrier and the sample was injected in an interaction‐preventing solvent,42–44 and ii) a narrow local barrier was formed with the sample solvent itself39 or it was injected immediately before sample solution 40, 41, 43, 45, 46…”

“…It has been shown36, 39–46 that under optimized LC LC conditions, macromolecules elute independently of their molar mass. No upper limit of molar mass was observed 42. A further important advantage of the LC LC methods lies in their experimental simplicity, which also includes isocratic elution mode.…”

“…Generally, the LC LC procedures are rather robust as to eluent composition variations. A further benefit of LC LC is the peak focusing 41–43, 45. As a result, the LC LC columns may accept large sample volumes, easily over 10% (ten percent!)…”