Influence of prepolymer molecular weight on the rheology and kinetics of HEUR-thickened Latex Suspensions

Hydrophobically Modified Ethoxylated Urethanes (HEURs) were synthesized by a step growth polymerization of polyethylene glycol (PEG, M n = 4000, 6000, 8000) with isophorone diisocyanate (IPDI). The thickeners were produced with different sizes of the hydrophilic section by changing the molar ratios of reactants. The hydrophobic ends, 1-tetradecanol (C14), was constant for all prepared samples. The structure, molecular weight and polymer dispersity index (PDI) of HEUR were characterized by 1 H NMR, IR and GPC respectively. The rheological behavior of the HEUR-thickened latex (Latex/HEUR) was determined by oscillatory and flow experiments. Dramatic increases in viscosity of Latex/HEUR are obtained. Under flow conditions the Latex/HEUR fits the Cross model, showing two regions, a Newtonian and a shear thinning one. Broad thixotropy are observed in hysteresis tests and three interval thixotropy test (3ITT) with decreasing molecular weight of the prepolymer, which was analyzed using a second-order kinetic equation. The results of atomic force microscopy (AFM) and the flow-levelling performance tests for Latex/HEUR films show smoother surface and better levelling with the increase of the hydrophilic component size.