1 research outputs found
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