View source for Hydroxyl-terminated polybutadiene

{{Short description|Chemical compound}}
'''Hydroxyl-terminated polybutadiene''' ('''HTPB''') is an [[oligomer]] of [[butadiene]] terminated at each end with a [[hydroxyl]] [[functional group]]. It reacts with [[isocyanates]] to form [[polyurethane]] polymers.

HTPB is a translucent liquid with a color similar to wax paper and a viscosity similar to corn syrup. The properties vary because HTPB is a [[mixture]] rather than a pure [[chemical compound|compound]], and it is manufactured to meet customers' specific requirements. A typical HTPB is R-45HTLO.<ref>http://www.crayvalley.com/docs/TDS/poly-bd-r-45htlo.pdf {{Webarchive|url=https://web.archive.org/web/20160216042503/http://www.crayvalley.com/docs/TDS/poly-bd-r-45htlo.pdf |date=2016-02-16 }} {{Bare URL PDF|date=March 2022}}</ref>  This product consists of oligomeric units typically containing 40–50 butadiene molecules bonded together, with each end of the chain terminated with a hydroxyl [OH] group: 
[[File:1,3-Butadiene Polymerization.svg|center|600x600px]]
R-45HTLO has a [[Functionality (chemistry)|functionality]] of 2.4-2.6, which means that there is (approximately) one additional hydroxyl group located along the chain for every two oligomeric units.  This provides side-to-side linkage for a stronger cured product.  HTPB is usually cured by an [[addition reaction]] with di- or poly-[[isocyanate]] compounds.

==Uses==

===Materials production===
Polyurethanes prepared from HTPB can be engineered for specific physical properties; polyurethanes may be highly elastic or tough and rigid. Some products include: rigid foam insulation panels; durable elastomeric wheels and tires (used for [[Steel roller coaster|roller coaster]]s, [[escalator]]s, [[Skateboard#Wheels|skateboards]], etc.); automotive suspension [[Bushing (isolator)|bushings]]; electrical potting compounds; high-performance [[adhesive]]s; surface coatings and surface sealants; [[synthetic fibers]] (e.g., [[Spandex]]); [[carpet]] underlay; hard-plastic parts (e.g., for electronic instruments).

===Rocket propellant===
{{anchor |HTPB solid rocket propellant}}
An important application of HTPB is in [[solid rocket propellant]]. It binds the [[oxidizing agent]], fuel and other ingredients into a solid but elastic mass in most composite propellant systems. The cured polyurethane acts as a fuel in such mixtures. For example, HTPB is used in all 3/4 stages of the Japanese [[M-5 rocket|M-5]] launch vehicles and in 1/3 stages of the Indian [[PSLV]] launch vehicle. [[JAXA]] describes the propellant as "HTPB/AP/Al=12/68/20", which means, proportioned by mass, HTPB plus curative 12% (binder and fuel), [[ammonium perchlorate]] 68% (oxidizer), and [[aluminum]] powder 20% (fuel).

Similar propellants, often referred to as APCP ([[ammonium perchlorate composite propellant]]) are used in larger model rockets.  A typical APCP propellant mixture produces 2–3 times the [[specific impulse]] of the [[black powder]] propellant used in most smaller rocket motors.

HTPB is also used as a [[hybrid rocket]] fuel.<ref>{{Cite book |last=Sutton |first=George Paul |title=Rocket propulsion elements |last2=Biblarz |first2=Oscar |date=2010 |publisher=Wiley |isbn=978-0-470-08024-5 |edition=8th |location=Hoboken, N.J |pages=595–599}}</ref> With N<sub>2</sub>O ([[nitrous oxide]], or "laughing gas") as the oxidizer, it is used to power the [[SpaceShipTwo]] hybrid rocket motor developed by [[SpaceDev]].<ref>{{cite web |url=http://www.spacedev.com/hybrid_detail.php?id=1 |title=SpaceDev Hybrid Propulsion |publisher=SpaceDev |access-date=2008-07-24 |archive-url=https://web.archive.org/web/20071105030248/http://www.spacedev.com/hybrid_detail.php?id=1 |archive-date=2007-11-05 |url-status=dead }}</ref> The land speed record attempt [[Bloodhound LSR]]  was intended to use HTPB with a [[high-test peroxide]] oxidizer, but that plan was altered in 2017.

==See also==
*[[Polybutadiene acrylonitrile]]
== References ==
{{reflist}}

==External links==
{{Commons category}}
*[https://web.archive.org/web/20120325152256/http://www.wikipatents.com/US-Patent-5159123/synthesis-of-hydroxyl-terminated-polybutadienes-using-glycol-ether/Page-3 US Patent 5159123] description of synthesis and other details.

[[Category:Polyols]]
[[Category:Organic polymers]]
[[Category:Rocket fuels]]