this invention relates to a process for minimizing or reducing the amount of residual free hydrazine in polymer latices . the process is particularly useful in the manufacture of hydrogenated nitrile rubber which is resistant to oxidative degradation at high temperatures , as well as resistant to corrosive environments such as acid environments . nitrile rubbers are useful in the manufacture of fan belts , seals , gaskets , and hoses in increasingly small and hot - running car engines .