Abstract: The invention relates to a process for the hydrogenation of a polymer composed of diene monomer units and nitrile group containing monomer units in which crosslinks formed as a result of the hydrogenation are broken by adding, before, during or after the hydrogenation, a compound that satisfies the formula R1—N(H)—X (I) or (R1)(R2)C═N—Y (II), where R1 is a hydrogen atom, an alkyl or cycloalkyl group with 1-30 carbon atoms, or an aromatic group with 6-30 carbon atoms and R2 is an alkyl or cycloalkyl group with 1-30 carbon atoms, or an aromatic group with 6-30 carbon atoms, X is chosen from the group comprising —R3, —OR4, —SR4, —NR5R6, where R3, R4 and R5 are a hydrogen atom, an alkyl or cycloalkyl group with 1-30 carbon atoms or an aromatic group with 6-30 carbon atoms and R6 is an alkyl or cycloalkyl group with 1-30 carbon atoms or an aromatic group with 6-30 carbon atoms Y is chosen from the group comprising —R7, —OR8, —SR8, —NR9R10 an

Abstract: The invention relates to a process for hydrogenating carbon-carbon double bonds of an unsaturated polymer by adding to the unsaturated polymer (1) a reducing agent selected from the group comprising hydrazines and hydrazine-releasing compounds, (2) an oxidising compound and (3) a catalyst, wherein the catalyst contains an element from group 13 of the Periodic Table of the Elements.