Patent ID: 8664340

Claim:
A nitrile rubber comprising repeating units of at least one α,β-unsaturated nitrile and at least one conjugated diene and having an ion index (“II”) according to the general formula (I) in the range from 7 to 26 ppm×mol/g, ion ⁢ ⁢ index = 3 ⁢ ⁢ c ⁡ ( Ca 2 + ) 40 ⁢ ⁢ g ⁢ / ⁢ mol - [ c ⁢ ⁢ ( Na + ) 23 ⁢ ⁢ g ⁢ / ⁢ mol + c ⁢ ⁢ ( K + ) 39 ⁢ ⁢ g ⁢ / ⁢ mol ] ( I ) where c(Ca 2+ ), c(Na + ) and c(K + ) indicate the concentrations of the calcium, sodium and potassium ions in the nitrile rubber in ppm and wherein the concentration of calcium ions, c(Ca 2+ ), is from 325 to 620 ppm, the concentration of sodium ions, c(Na + ), is from 105 to 575 ppm, and the concentration of potassium ions, c(K + ), is from 8 to 17 ppm.