Hydroxyl-terminated polybutadiene

Hydroxyl-terminated polybutadiene (HTPB) is a polymer of butadiene terminated at each end with a hydroxyl functional group. It reacts with diisocyanate to form polyurethane, a stable and easily stored synthetic material.

HTPB is a translucent liquid with a very similar color to wax paper, it is highly viscous. The properties cannot be precisely stated, because HTPB is manufactured in various grades to meet specific requirements. HTPB is thus a generic name for a class of compounds. It consists of many butadiene molecules linked together into a polymer forming polybutadiene. Both ends of the chain are terminated with a hydroxide ion [OH-], thus giving it the name Hydroxyl-Terminated Polybutadiene. It is used in model rocketry as a high power fuel known commonly as RBS. It has also found its way into the pyrotechnics industry with a use as mortar tubes for aerial-shell fireworks. It is insoluble in water making it a good sealant. Although it is used in rocket fuel it does not ignite easily – it requires temperatures in excess of 773K to combust. The curing agent for it is usually a polyisocyanate compound.

Uses

HTPB is used in many solid rocket motors to bind the fuel and oxidizing agent into a solid mass. It is also used as a hybrid rocket fuel. Together with N₂O (nitrous oxide, or "laughing gas") as the oxidizer, it is used to power the SpaceShipOne hybrid rocket motor developed by SpaceDev. It also powers all 3/4 stages of the Japanese M-5 rocket satellite launchers. JAXA describe the fuel as "HTPB/AP/Al=12/68/20" which means, proportioned by mass, HTPB 12% (binder and fuel), Ammonium perchlorate 68% (oxidizer), and Aluminium powder, 20% (fuel).

External links

• Technical Literature, from Sartomer, a manufacturer of HTPB
• US Patent 5159123 description of synthesis and other details.