Hydroxyl-terminated polybutadiene

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Hydroxyl-terminated polybutadiene (HTPB) is an oligomer of butadiene terminated at each end with a hydroxyl functional group. It reacts with diisocyanate to form polyurethanes.

HTPB is a translucent liquid with a color similar to wax paper and a viscosity similar to corn syrup. The properties cannot be precisely stated because HTPB is a mixture rather than a pure compound, and it is manufactured to meet customers' specific requirements. An oligomeric unit typically consists of 5–10 butadiene molecules linked together, with each end of the chain terminated with a hydroxyl [OH] group. HTPB is usually cured by an addition reaction with a polyisocyanate compound.

1,3-Butadiene Polymerization.PNG


A solid form is used in model rocketry as a high power fuel known commonly as RBS. It has also found its way into the pyrotechnics industry in mortar tubes for aerial-shell fireworks.

HTPB is used in many solid rocket motors to bind the fuel and oxidizing agent into a solid mass. For example, it is used in all 3/4 stages of the Japanese M-5 rocket satellite launchers and PSLV rocket developed by ISRO for satellite launches. 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).

HTPB is also used as a hybrid rocket fuel.[1] With N2O (nitrous oxide, or "laughing gas") as the oxidizer, it is used to power the SpaceShipTwo hybrid rocket motor developed by SpaceDev.[2]


  1. ^ G. P. Sutton and Oscar Biblar, Rocket Propulsion Elements, (Eighth edition), pp. 595-599, John Wiley and Sons 2010.
  2. ^ "SpaceDev Hybrid Propulsion". SpaceDev. 

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