Sustainable associative thickeners based on hydrophobically modified ethoxylated poly(hydroxy-urethane)s end-capped by long alkyl chains

Hydrophobically modified ethoxylated urethanes (HEURs) are associative polymers applied as thickening additives in various waterborne systems, such as emulsions, coatings and printing inks. Their conventional synthesis, based on diisocyanates, poses environmental and health threats during both manufacture and application. Hence, in this paper we present an approach for the next generation of sustainable and CO2-rich polyurethane rheological modifiers - isocyanate-free HEURs (IFHEURs) obtained through poly(hydroxy-urethane) route. The hydrophilic core of the IFHEURs was prepared by step-growth polyaddition between diamine and poly(ethylene glycol) bis(cyclic carbonate) - synthesized using CO2 as a green source of the carbonate bonds. Such obtained prepolymer with terminal carbonate groups was subsequently modified with hydrophobic amines using reactive extrusion method, which enabled efficient homogenisation of the viscous reaction systems and reaching high end-capping functionality after only 2 h. In contrast to previously reported studies, the synthetic procedure was both solvent- and catalyst-free and allowed to incorporate up to 11 wt% of CO2 into the backbone of the final products. The structural analysis of the obtained IFHEURs using NMR and FT-IR spectroscopy and MALDI-ToF mass spectrometry confirmed obtaining the desired telechelic architecture resembling standard HEUR materials. The associative behavior of the IFHEURs in aqueous solutions was addressed in a rheological study, which revealed typical thickening mechanisms exhibited by rheological additives.