Analysis of hydrophobically modified ethylene oxide urethane rheology modifiers by comprehensive two dimensional liquid chromatography

Abstract

Hydrophobically modified ethylene oxide urethane (HEUR) rheology modifiers are polymers used widely in waterborne coatings and other consumer products. The incorporation of hydrophobic end-groups significantly affects the thickening performance of HEURs. Therefore, understanding the degree of incorporation of hydrophobic end-groups on the polymer chain can help gain important insights on the structure/property relationship for HEUR rheology modifiers.A comprehensive two-dimensional liquid chromatography (2D-LC) method was developed for separating polymeric HEUR rheology modifiers based on the number of hydrophobic end-groups incorporated on the polymer chain. Our 2D-LC method uses a size exclusion chromatography (SEC) separation in the first dimension (1D) using an ultra-high performance Advance Polymer Chromatography (APC) column and a gradient reversed-phase liquid chromatography (RPLC) separation in the second dimension (2D). A low flow rate was used in the first dimension SEC separation to minimize the strong organic eluent transferred to the second dimension LC column. A small inner diameter (ID) LC column was used for the second dimension to reduce the total solvent consumption for routine analysis of process samples. The 1D flow rate, 2D transfer volume and gradient profile were all optimized to avoid polymer breakthrough and to achieve optimal separation of the polymer chains based on end-groups. Three types of polymer chains with 0, 1, and 2 terminal hydrophobes were successfully separated using this method. The total run time was further reduced by implementing flow programing in the first dimension separation. The 2D-LC method was applied to study how the polymerization process recipes affected hydrophobe incorporation and how the hydrophobe incorporation correlated with thickening efficiency. The method was also used to separate HEUR rheology modifier with branched polymer architecture.