Acrylonitrile-butadiene rubber (NBR) in latex form was selectively hydrogenated by redox system consisting of hydrazine hydrate and hydrogen peroxide, with boric acid as catalyst. Soluble hydrogenated NBR latex was obtained; but the coagulated products were gelled on drying. This problem becomes the major obstacle for the hydrogenation technique to be commercialized. It is important to study the crosslinking reaction in the system and to solve the problem. The cause for the crosslink was investigated in three possibilities: (i) crosslinking caused by the hydrogenation of CN group; (ii) by the oxidation of C=C double bonds and (iii) by radicals in the system. The control of the crosslink was also studied. The oil resistant nitrile group —CN on the polymer chain had no change during drying process. There were no signs of carbonyl group C=O formed by oxidation and amine like groups -NH- formed by the hydrogenation of CN in HNBR gel fraction. The newly formed alkoxyl radicals were detected by ESR spectroscopy analysis in the hydrogenation system after specific reaction time. Crosslinking reaction was controlled to a large extent by using hydroquinone as gel inhibitor.

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