Lignin, obtained through steam explosion from straw, was completely characterized via elemental analysis, gel permeation chromatography, ultraviolet and infrared spectroscopy, and C-13 and H-1 nuclear magnetic resonance spectrometry. Polyurethanes were obtained by treating steam-exploded lignin from straw with 4,4'-methylenebis(phenylisocyanate), 4,4'-methylenebis(phenylisocyanate) -ethandiol, and poly(1,4-butandiol)tolylene-2,4-di-isocyanate terminated. The obtained materials were characterized by using get permeation chromatography, infrared spectroscopy, and scanning electron microscopy. Differential scanning calorimetry analysis showed a T-g at -6 degrees C, assigned to the glass transition of the poly(1,4-butandiol) chains. The presence of ethylene glycol reduced the yields of the polyurethanes. The use of the prepolymer gave the best results in polyurethane formation. Steam-exploded lignin was used as the starting material in the synthesis of polyesters. Lignin was treated with doclecanoyl dichloride. The products were characterized by using gel permeation chromatography, infrared spectroscopy, C-13 and H-1 nuclear magnetic resonance spectrometry, and scanning electron microscopy. (c) 2005 Wiley Periodicals, Inc.