A widely-used type of synthetic rubber produced by the polymerization of butadiene with acrylonitrile, invented in the mid-1930s in Germany and available in the United States just prior to the outbreak of World War II. Different grades of Buna N contain differing amounts of acrylonitrile (the amount can vary from 15:40%), greater amounts of acrylonitrile imparting greater resistance to oils. Buna N rubber is resistant to aliphatic hydrocarbons, alcohols, water, and other substances, but not to aromatic hydrocarbons or esters. Buna N (and other synthetic rubbers such as neoprene) have more stable properties than natural rubbers. Buna N is widely used in the manufacture of printing press rollers, such as those for inking, dampening, and impression, as well as blankets used in offset lithography and plates used in flexography. Buna N is also known as Perbunan and NBR. Buna S, a synthetic rubber developed at the same time as Buna N, is produced by polymerizing butadiene with styrene and is widely used for tires and other such uses.