How does increasing the acrylonitrile content change nitrile rubber?

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In the production of nitrile rubber (NBR), which is a copolymer of acrylonitrile and butadiene, the proportion of acrylonitrile typically ranges from 15 to 50 percent. Increasing the acrylonitrile content significantly alters the material's physical properties:

Improved Performance: The rubber exhibits higher strength, increased resistance to swelling when exposed to hydrocarbon oils, and lower permeability to gases.1
Reduced Low-Temperature Flexibility: The material becomes less flexible at lower temperatures. This occurs because polyacrylonitrile has a higher glass transition temperature, meaning the molecules lock into a rigid, glassy state at higher temperatures than they would with a lower acrylonitrile concentration.1

These characteristics make high-acrylonitrile variants particularly suitable for demanding applications like automotive seals and gaskets that require superior resistance to hot oils.1