Polybutadiene acrylonitrile
Polybutadiene acrylonitrile (PBAN) copolymer, also noted as polybutadiene — acrylic acid — acrylonitrile terpolymer.
This was the binder formulation widely used on the 1960-70's big boosters (e.g., Titan III and Space Shuttle SRBs). It is also sometimes used by amateurs due to simplicity, very low cost, and lower toxicity than the more common hydroxyl-terminated polybutadiene (HTPB). HTPB uses isocyanates for curing, which have a relatively quick curing time; however, they are also generally toxic. PBAN based propellants also have a slightly higher performance than HTPB based propellants.[1]
PBAN is normally cured with the addition of an epoxy resin, taking several days at elevated temperatures to cure.
PBAN was to be used in future NASA missions, most notably the Constellation program, later canceled, as this copolymer was to be used in the first stage of the Ares I rocket in five segments.