ABSTRACT: Polyurethanes can be prepared using polyols ob- tained 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, deter- mined 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 prop- erties of the polyurethanes were determined by dynamic mechan- ical thermal analysis, hardness (Shore A), and swelling measure- ments. 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-link- ing density of the polyurethane network. The influence of diiso- cyanate structure (rigid or flexible chain), curing temperature, and curing reaction time on mechanical properties was also investi- gated. 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 petro- chemical derivatives (1–3). Soybean oil is an inexpensive, readily available, renewable resource and provides an excel- lent 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 reac- tive sites for coatings and paints, they need to be functional- ized 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, sun- flower, and soybean oils, and show a number of excellent prop- erties because of the hydrophobic nature of TG (5,6). To use natural oils as raw materials for PU production, multiple hy- droxyl functionalities are required. Usually these are obtained by reacting epoxidized oils with low-M.W. mono- or polyfunc- tional 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 tempera- tures (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 proper- ties of soy polyol-derived PU prepared by the hydrogenation of hydroformylated soybean oil. When the hydroformylation reaction was rhodium catalyzed, an OH functionality of 4.1 was obtained, yielding a rigid PU after reaction with MDI. On the other hand, a cobalt-catalyzed hydroformylated polyol pre- sented an OH functionality of approximately 2.7, resulting in a polymer with poorer mechanical properties. Javni et al. (10) also prepared a series of PU from halo- genated, hydrogenated, methoxylated, epoxidized soybean oil with an average OH functionality of 3.8. PU based on nonhalo- genated soy polyols showed higher thermal stability but lower T g and mechanical properties. Our group has studied different methods of functionalizing vegetable oils to obtain new raw materials for the preparation of biorenewable materials (11,12). In this study, we prepared formiated epoxy soy polyols in a one-step synthesis and inves- tigated their influence on the mechanical properties of PU net- works. Soy polyols having OH functionalities from 1.9 to 3.2 were reacted with different diisocyanates at a constant NCO/OH molar ratio. The effect of the diisocyanate structure and the PU curing conditions (time and temperature) also were investigated. EXPERIMENTAL PROCEDURES Materials. 2,4-Toluene diisocyanate (TDI) was purified by dis- tillation under reduced pressure. MDI and 1,6-hexamethylene diisocyanate (HDI) were used as received but were degassed. All diisocyanates were supplied by Bayer AG (Leverkusen, Germany). The NCO index was determined according to ASTM D5155-96 (13). Toluene (Merck, Darmstadt, Germany) was dried under sodium and distilled before use under a nitro- gen atmosphere. Soy polyol synthesis. Fifty grams (0.26 mol of double bonds) of degummed soybean oil (MM = 868 g/mol and 4.5 Copyright © 2005 by AOCS Press 365 JAOCS, Vol. 82, no. 5 (2005) *To whom correspondence should be addressed at Instituto de Química– UFRGS, CP 15003, 91501-970, Porto Alegre, RS, Brazil. E-mail: petzhold@iq.ufrgs.br Polyurethane Networks from Formiated Soy Polyols: Synthesis and Mechanical Characterization Luciane L. Monteavaro, Eduardo O. da Silva, Ana Paula O. Costa, Dimitrios Samios, Annelise E. Gerbase, and Cesar L. Petzhold* Instituto de Química, Universidade Federal do Rio Grande do Sul, 91501-970, Porto Alegre, Brazil