Analysis of partly bio-derived nonionic polyethylene glycol-based rheology modifiers by comprehensive two-dimensional liquid chromatography

Abstract

Rheology modifiers (RMs) are polymeric molecules providing rheological control of formulations, which are important in product application, shelf-life, and aesthetic perception. Bio-derived polyethylene glycol (PEG)-based RMs thicken formulations through nonionic-associative thickening where at least two hydrophobic end groups from a RM molecule interact with other hydrophobic groups of other RM molecules or ingredients in the formulation to form an associative network. We report a comprehensive two-dimensional liquid chromatography (2D-LC) separation of partly bio-derived PEG-based RMs in size exclusion chromatography (SEC) × reversed-phase liquid chromatography (RPLC) mode for the separation of RM components based on both molecular weight distribution and end group hydrophobe distribution. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is first performed to gain understanding of the molecular weight, number of distributions, and approximate sample complexity, which helps with the SEC column selection. A thorough solubility screening is then conducted to identify the compatible SEC mobile phases and the gradient range for the RPLC column. Then, both SEC and RPLC methods are developed for the successful comprehensive SEC × RPLC separation of polymers with 0, 1, 2, 3, and 4 terminal hydrophobes. Finally, high resolution mass spectrometry mass profiler is used to further explain the minor secondary interaction mechanism of the SEC separation and confirm the MALDI results.

Keywords: ELSD Mass profiler; Rheology modifier; Two-dimensional liquid chromatography.