One-Step versus Two-Step Synthesis of Hydrophobically Modified Ethoxylated Urethanes: Benefits and Limitations

Abstract

Associative thickeners, such as hydrophobically modified ethoxylated urethanes (HEURs), are an important class of rheological modifiers allowing precise control and optimization of the rheology of waterborne coatings. In this work, we present a novel, comprehensive investigation of one-step and two-step HEUR synthesis processes, highlighting their impact on the final HEUR properties. In the conventional one-step process (current industrial practice), there are inherent limitations in producing high molecular weight polymers due to the complex competition between end-capping and polymerization. We show that the two-step method allows for much higher molecular weight polymers than the one-step method while using less amounts of toxic diisocyanates. Additionally, using the two-step method, the polymerization can be simply and efficiently controlled by the addition timepoint of the end-capping agent, which can be tailored to provide HEURs with a wide range of molecular weight and polydispersity index. However, the efficient end-capping of high molecular weight polymers remains a challenge when using conventional mixing equipment in batch reactors due to mass transfer and mixing limitations associated with the significant increase in the bulk viscosity of the reaction mixture. To overcome these limitations, alternative and more efficient mixing technologies, such as reactive extruders, should be considered for the efficient end-capping of high molecular weight polymers.

Tailoring Waterborne Coating Rheology with Hydrophobically Modified Ethoxylated Urethanes (HEURs): Molecular Architecture Insights Supported by CG-MD Simulations

“…In all experiments, the reaction temperature was 85 °C, the reaction time was 60 min, and the catalyst concentration was set to 0.01% based on the total mass of the reactive mixture. Based on the findings of our previous work, 41 for the one-step HEUR synthesis, we utilized an HMDI/PEG ratio of 1.5 and octanol/PEG ratio of 1. At this reaction stoichiometry, our one-step synthesis maximizes HEUR molecular weight by effectively tripling the molecular weight of the utilized PEG, ensuring complete end-capping.…”

Hydrophobically modified ethoxylated urethane polymers: terminal sticker group influences on thickening and dispersing

“…For ethoxylated urethane polymer synthesis, moisture removing is crucial as water also reacts with isocyanate and will in uence the structure of resultant polymers. To eliminate moisture in uence and batch variation, paralleled static bulk polymerization [12] was utilized here. The hydroxyl containing reactants (TSP/MPEG2000, PEG8000) were dried at 130℃ for 2 hours under vacuum, till moisture content < 0.05wt% (Karl-Fisher method).…”