1 research outputs found
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