Patent ID: 8389623

Claim:
A nitrile rubber comprising repeating units of at least one α,β-unsaturated nitrile, at least one conjugated diene and optionally one or more further copolymerizable monomers and has an ion index (“II”) according to the general formula (I) in the range from 0 to 60 ppm×mol/g, II = 3 ⁡ [ c ⁢ ⁢ ( Ca 2 + ) 40 ⁢ ⁢ g ⁢ / ⁢ mol + c ⁢ ⁢ ( Mg 2 + ) 24 ⁢ ⁢ g ⁢ / ⁢ mol ] - [ c ⁢ ⁢ ( Na + ) 23 ⁢ ⁢ g ⁢ / ⁢ mol + c ⁢ ⁢ ( K + ) 39 ⁢ ⁢ g ⁢ / ⁢ mol ] ( I ) wherein c(Ca 2+ ), c(Mg 2+ ), c(Na + ) and c(K + ) indicate the concentrations of the calcium, magnesium, sodium and potassium ions in the nitrile rubber in ppm and the concentration of magnesium ions c(Mg 2+ ) is in the range from 50 to 250 ppm and the concentration of calcium ions c(Ca 2+ ) is in the range from 163 to 575 ppm.