Polyurethanes can be prepared using polyols obtained from vegetable oils in natura, such as castor oil, or from functionalized vegetable oils, such as hydroxylated soybean oil. These polyurethanes have different valuable properties, determined by their chemical composition and cross-linking density. In this study, soy epoxy polyols with different OH contents were prepared through a one-step reaction using the method of in situ performic acid generation. Polyols with OH functionalities from 1.9 to 3.2 were reacted in bulk with different diisocyanates at a NCO/OH molar ratio of 0.8 and 60°C for 24 h. Mechanical properties of the polyurethanes were determined by dynamic mechanical thermal analysis, hardness (Shore A), and swelling measurements. Polymer networks with glass-transition temperatures (T g ) from -13 to 48°C were obtained. We observed that the higher the OH functionality of the polyols, the higher the T g and cross-linking density of the polyurethane network. The influence of diisocyanate structure (rigid or flexible chain), curing temperature, and curing reaction time on mechanical properties was also investigated.Paper no. J10956 in JAOCS 82, 365-371 (May 2005). KEY WORDS:Hydroxylated soybean oil, mechanical properties, polyurethane, soy epoxy polyol.The use of renewable resources has attracted the attention of many researchers because of their potential to replace petrochemical derivatives (1-3). Soybean oil is an inexpensive, readily available, renewable resource and provides an excellent platform for polymeric materials. Soybean oil is mainly composed of TG molecules derived from unsaturated FA such as oleic acid (22%), linoleic acid (55%), and linolenic acid (7%). Although they possess double bonds, which are the reactive sites for coatings and paints, they need to be functionalized to prepare polymers (4). Polyurethanes (PU) have been prepared from vegetable oils in natura, such as castor oil, or from polyols obtained from vegetable oils, such as corn, sunflower, and soybean oils, and show a number of excellent properties because of the hydrophobic nature of TG (5,6). To use natural oils as raw materials for PU production, multiple hydroxyl functionalities are required. Usually these are obtained by reacting epoxidized oils with low-M.W. mono-or polyfunctional alcohols or acids.Recently, Petrovic et al. (7) reported the effect of the NCO/OH molar ratio on soy-based PU network properties using a methoxylated soy polyol (OH functionality = 3.7) and 4,4′-methylenebis(phenyl isocyanate) (MDI). Glassy polymers were produced when the NCO/OH ratio was between 0.8 and 1.05. Higher cross-linking densities, glass-transition temperatures (T g ), and tensile strengths were observed as the NCO/OH ratio increased. The influence of the diisocyanate structure on the properties of these soy-based PU was also investigated (8).Guo et al. (9) reported the physical and mechanical properties of soy polyol-derived PU prepared by the hydrogenation of hydroformylated soybean oil. When the hydroformylation reaction was rhod...