Insight Into Solventless Production of Hydrophobically Modified Ethoxylated Urethanes (HEURs): The Role of Moisture Concentration, Reaction Temperature, and Mixing Efficiency

In this work, we report for the first time on the influence of the quality of reactants and reaction conditions on the production of hydrophobically modified ethoxylated urethanes (HEURs) and selected prepolymers without the use of solvents. We show that the polyol water concentration is detrimental to the progress of the main urethane forming reaction, confirming the necessity of carefully drying the reactants below 1000 ppm to suppress the consumption of diisocyanate toward urea during HEUR synthesis. Increasing the mixing speed (≈30 to 750 rpm), reaction temperature (80–110 °C), and catalyst concentration (0.035–2.1 wt % bismuth carboxylate) can significantly increase the rate of molecular weight buildup, but their effect decreases with time as the bulk viscosity increases and mixing limitations eventually take over, leading to the Weissenberg effect and chain growth termination. Consequently, for the selected formulation, the maximum product molecular weight attained lies in the range of ≈20 000–22 000 g/mol, irrespective of the specific process conditions applied

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

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