A component to control the viscosity of phase change material formulations is made by reacting selected nucleophiles, including fatty acid/alcohol reactants with an isocyanate, is disclosed. The addition of the isocyanate and the different nucleophiles will create a viscosity modifying component of low viscosity that can be formulated with higher molecular weight polyamide resins to achieve increased toughness in phase change solid imaging materials and carrier compositions used to make phase change ink jet inks.