Thermoplastic elastomeric hydrogenated styrene-butadiene (HSBR) elastomer was prepared by diimide reduction of styrene-butadiene rubber in the latex stage. The products were characterized by infrared, H-1-NMR, C-13-NMR spectroscopy, and differential scanning calorimetry (DSC). The standard free energy change, Delta G(0) at 298 degrees K is -44.7 x 10(4) kJ/mol, indicating that the formation of HSBR is thermodynamically feasible. The value of heat change of the reaction at constant volume, Delta U-T is -41.6 x 10(4) kJ/mol. The effect of different reaction parameters on the level of hydrogenation, calculated from nuclear magnetic resonance spectroscopy, was also investigated. The degree of hydrogenation increases with the increase in reaction time, temperature, the concentration of reactants and catalyst. A maximum of 94% hydrogenation was obtained under the following conditions : time, 4 h; temperature, 45 +/- 2 degrees C; pH, 9.36; cupric sulphate (CuSO4 . 5H(2)O) catalyst concentration, 0.0064 mmol; hydrazine concentration, 0.20 mol; and hydrogen peroxide concentration, 0.26 mol. The diimide reduction of SBR is first-order with respect to olefinic substrate, and the apparent activation energy is 9.5 kJ/mol. The glass transition temperature increases with the increase in saturation level due to development of crystalline segments.