A Star Shape Branched Hydrophilic Polyurethane Dispersant Containing Carboxyl and Amino Anchoring Groups for Inducing Strong Thixotropy in Aqueous Titanium Dioxide Pastes

ABSTRACT A star‐shape branched hydrophilic polyurethane dispersant containing carboxyl and amino anchoring groups for inducing strong thixotropy in aqueous titanium dioxide pigment pastes was developed in this work. Water soluble linear and branched polyurethanes containing different anchoring groups including carboxyl and amino groups were synthesized and well characterized. Different polyurethanes were used as dispersants in titanium dioxide and carbon black pastes. The viscosity test, particle size analysis, rheological behavior, and storage stability tests indicated that the dispersing performance of the branched polyurethane dispersant was significantly better than their linear analogues. The branched dispersant containing both carboxyl and amino groups (BCA) exhibited the optimal performance. The titanium dioxide paste prepared using BCA as the dispersant with a pigment mass fraction of 50 wt.% exhibited a viscosity as low as 177.5 mPa s, an average particle size of 366.0 nm, and outstanding storage stability. Furthermore, the TiO 2 pigment paste dispersed with BCA delivers a power‐law index of 0.19, showing favorable shear‐thinning performance. It is presumed that the synergistic anchoring effect of carboxyl and amino groups strengthens the binding between dispersant and pigment surface. The star‐shape branched structure may contribute to the formation of a thicker adsorption layer on pigment surfaces, and loose reversible ion‐pair interactions together with hydrogen‐bonding among amino and carboxyl moieties are hypothesized to endow the TiO 2 pastes with distinctive thixotropic properties.