The Buna-N rubber is a carbon chain unsaturated polar rubber which has an alkene reactivity similar to SBR and the like in terms of unsaturation, but the NBR becomes a highly polar rubber due to the strong polar unit of ACN.

Butadiene is mainly trans-1,4-polymerized in the molecular chain. Butadiene and acrylonitrile are randomly copolymerized, and NBR is a non-crystalline rubber. The polarity of NBR is derived from the acrylonitrile unit, and ACN is a strongly polar compound because nitrile-CN is a particularly electronegative group.