Hydrogenation of nitrile-butadiene rubber latex via utilization of diimide was investigated by examining hydrogenation efficiency and hydrogenation degree. It has been found that the hydrogenation efficiency, which is defined as the ratio of the amount of hydrogen peroxide consumed for the hydrogenation to the total amount of hydrogen peroxide reacted, varies with both the type of catalyst and degree of hydrogenation. The use of boric acid, as a promoter, can bring the hydrogenation efficiency to a level of nearly 100% when the degree of hydrogenation is below 60%. The hydrogenation efficiency, when copper ion, silver ion or ferrous ion is used as a catalyst, is lower than the hydrogenation efficiency in the presence of boric acid. Hydrogenation efficiency decreases very quickly with an increase in the degree of hydrogenation irrespective of the catalysts employed. It is postulated that the decrease of hydrogenation efficiency in the range of low hydrogenation degree results from side reactions at the interphase of the latex particles, which are modulated by the catalyst and the addition rate of hydrogen peroxide; whereas, the decrease in the hydrogenation efficiency in the range of high hydrogenation degree is caused by side reactions within the polymer phase. Using radical scavengers, in this process, did not show any evidence in helping to suppress the degree of gel formation. (C) 2004 Elsevier B.V. All rights reserved.