Nitrile rubber, often called Buna-N, is the most commonly used elastomer for O-rings and other sealing devices. Nitrile is a copolymer of butadiene and acrylonitrile (ACN). The name Buna-N is derived from butadiene and natrium (the Latin name for sodium, the catalyst used in polymerizing butadiene). The “N” stands for acrylonitrile.
The butadiene segment imparts elasticity and low temperature flexibility. It also contains the unsaturated double bond that is the site for crosslinking, or vulcanization. This unsaturated double bond is also the main attack site for heat, chemicals, and oxidation.