Abstract: Solvent-free, hydrophobically modified urethane (HEURs) compositions produced by reactive extrusion, methods of producing the same, and coating compositions containing the same are described. Such HEURs can be used as solvent-free or low-solvent rheology modifiers in coatings formulations. The HEURs compositions herein are formed by reactive extrusion of a polyether polyol and an isocyanate functional material in the presence of a metal catalyst, and an hydrophobic, end-capping modifier without the need for organic solvents, co-solvents, and/or surfactants. In certain aspects, compositions and methods herein do not require the costly stripping of organic solvent to provide useable product, allow for a 100% active solids HEUR that can be added directly to the grind stage of making a paint composition, and are free of VOC-contributing solvents or co-solvent.