Polybutadiene acrylonitrile

Polybutadiene acrylonitrile (PBAN) copolymer, also noted as polybutadiene—acrylic acid—acrylonitrile terpolymer is a copolymer compound used most frequently as a rocket propellant fuel mixed with ammonium perchlorate oxidizer. It was the binder formulation widely used on the 1960s–1970s big boosters (e.g., Titan III and Space Shuttle SRBs).

Source: Wikipedia — Polybutadiene acrylonitrile (CC BY-SA 4.0)