Hydroxyl-terminated polybutadiene (HTPB) is a common ingredient in rocket propellants, but its thermochemical properties (composition, density, and heat of formation) are not well defined. A survey of the literature and thermochemical databases indicated wide ranges for these properties, especially heat of formation. Six group additive schemes were used to estimate the heat of formation of HTPB and analyze the effects of hydroxyl functionalization and curing reactions. Good agreement is observed between the methods for HTPB isomer units, but cumulative differences result in significant disparities for larger, practical polymers. Increased hydroxyl functionality and the curing reaction are predicted to yield nonnegligible decreases in the heat of formation. The heat of formation of propellant-grade, isophorone-diisocayante-cured HTPB R-45M () was computed as or . Chemical equilibrium analyses were completed for solid propellants composed of ammonium perchlorate and HTPB, and for hybrid rocket engines based on HTPB burning with liquid oxygen or nitrous oxide, where the heat of formation of HTPB was varied within a reasonable range. The chemical equilibrium analysis computations indicated that combustion gas properties and theoretical propellant performance can vary up to 5% within practical operating conditions for the range of HTPB heats of formation implemented.
 , “Micro-Structural Effect on Hydroxy Terminated Poly Butadiene (HTPB) Prepolymer and HTPB Based Composite Propellant,” Journal of Molecular Nanotechnology and Nanomedicine, Vol. 1, No. 1, 2017, pp. 1–7.
 Technical Data Sheet: Poly bd® R-45M, Cray Valley USA, 2010.
 , Rocket Propulsion Elements, 8th ed., Wiley, New York, 2010.
 , “Calculation of the Energetic Characteristics of TN in Composite Solid Propellants,” Air Force Systems Command AD-A164 310, FTD-ID(RS)T-0961-85, Baltimore, MD, 1986.
 , “High-Performance Propellants Based on Hydrazinium Nitroformate,” Journal of Propulsion and Power, Vol. 11, No. 4, 1995, pp. 856–869. https://doi.org/10.2514/3.23911
 , “Guidelines to Higher Energy Gun Propellants,” 27th International Annual Conference of ICT, Fraunhofer Inst. for Chemical Technology, 1996.
 , “Some Rules for the Design of High Solid Loading Compsite Solid Propellants and Explosives,” 27th International Annual Conference of ICT, Fraunhofer Inst. for Chemical Technology, 1996.
 , “A Kinetic Model for the Premixed Combustion of a Fine AP/HTPB Composite Propellant,” 36th AIAA Aerospace Sciences Meeting, AIAA Paper 1998-0447, 1998. https://doi.org/10.2514/6.1998-447
 , “Recent Developments and Challenges in the Ignition and Combustion of Solid Propellants,” International Journal of Energetic Materials and Chemical Propulsion, Vol. 4, No. 1, 1997, pp. 515–548. https://doi.org/10.1615/IntJEnergeticMaterialsChemProp.v4.i1-6.510
 , “Sandwich Propellant Combustion: Modeling and Experimental Comparison,” Proceedings of the Combustion Institute, Vol. 29, No. 2, 2002, pp. 2963–2973. https://doi.org/10.1016/S1540-7489(02)80362-5
 , “Design of a Lab-Scale Hydrogen Peroxide/Hydroxyl Terminated Polybutadiene Hybrid Rocket Motor,” 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, AIAA Paper 2003-4744, 2003. https://doi.org/10.2514/6.2003-4744
 , “Thrust Modulation in a Nitrous-Oxide/Hydroxyl-Terminated Polybutadiene Hybrid Rocket Motor,” 42nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA Paper 2006-4503, 2006. https://doi.org/10.2514/6.2006-4503
 , “Hybrid Rocket Fuel Regression Rate Data and Modeling,” 42nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA Paper 2006-4504, 2006. https://doi.org/10.2514/6.2006-4504
 , “Review of Solid-Fuel Regression Rate Behavior in Classical and Nonclassical Hybrid Rocket Motors,” Fundamentals of Hybrid Rocket Combustion and Propulsion, edited byKuo K. K. and Chiaverini M. J., AIAA, Reston, VA, 2007, Chap. 2. https://doi.org/10.2514/4.866876
 , “Solid-Fuel Pyrolysis Phenomena and Regression Rate, Part 1: Mechanisms,” Fundamentals of Hybrid Rocket Combustion and Propulsion, edited by Kuo K. K. and Chiaverini M. J., AIAA, Reston, VA, 2007, Chap. 3. https://doi.org/10.2514/4.866876
 , “Metals, Energetic Additives, and Special Binders Used in Solid Fuels for Hybrid Rockets,” Fundamentals of Hybrid Rocket Combustion and Propulsion, edited byKuo K. K. and Chiaverini M. J., AIAA, Reston, VA, 2007, Chap. 10. https://doi.org/10.2514/4.866876
 , “Emerging Trends in Advanced High Energy Materials,” Combustion, Explosion, and Shock Waves, Vol. 43, No. 1, 2007, pp. 62–72. https://doi.org/10.1007/s10573-007-0010-9
 , “Correlation of Hybrid Rocket Propellant Regression Measurements with Enthalpy-Balance Model Predictions,” Journal of Spacecraft and Rockets, Vol. 45, No. 5, 2008, pp. 1010–1020. https://doi.org/10.2514/1.33804
 , “Advances in High Energy Materials,” Defence Science Journal, Vol. 60, No. 2, 2010, pp. 137–151. https://doi.org/10.14429/dsj.60.327
 , “Regression Rate Study of PVC/HTPB Hybrid Rocket Fuels,” International Journal of Mechanical and Industrial Engineering, Vol. 1, No. 1, 2011, pp. 64–67. https://doi.org/10.47893/IJMIE.2011.1015
 , “Solid Propellants and Their Combustion Characteristics,” Applications of Turbulent and Multiphase Combustion, Wiley, New York, 2012, Chap. 1. https://doi.org/10.1002/9781118127575
 , Energetic Polymers: Binders and Plasticizers for Enhancing Performance, Wiley–VCH, New York, 2012.
 , “High-Energy Metal Fuels for Rocket Propulsion: Characterization and Performance,” Chinese Journal of Explosives and Propellants, Vol. 36, No. 6, 2013, pp. 1–14.
 , “Performance of Dicyclopentadiene/H2O2-Based Hybrid Rocket Motors with Metal Hydride Additives,” Journal of Propulsion and Power, Vol. 29, No. 5, 2013, pp. 1122–1129. https://doi.org/10.2514/1.B34867
 , “Metal Nanopowders: Production, Characterization, and Energetic Applications,” Metal Nanopowder: Production, Characterization, and Energetic Applications, edited by Gromov A. A. and Teipel U., 1st ed., Wiley-VCH, New York, 2014, Chap. 12.
 , “Evaluation of Fuel Additives for Hybrid Rockets and SFRJ Systems,” 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA Paper 2014-3647, 2014. https://doi.org/10.2514/6.2014-3647
 , “Effect of Varying Design Options on the Transient Behavior of a Hybrid Rocket Motor,” Journal of Aerospace Technology and Management, Vol. 6, No. 1, 2014, pp. 69–82. https://doi.org/10.5028/jatm.v6i1.268
 , “Thermochemistry of Combustion,” Propellants and Explosives: Thermochemical Aspects of Combustion, 3rd ed., Wiley–VCH, New York, 2015, Chap. 2. https://doi.org/10.1002/9783527693481
 , “Energetics of Propellants and Explosives,” Propellants and Explosives: Thermochemical Aspects of Combustion, 3rd ed., Wiley–VCH, New York, 2015, Chap. 4. https://doi.org/10.1002/9783527693481
 , “Investigation of Selected Ingredients of Composite Propellants Using DTA, SEM and Calorimetric Techniques,” Central European Journal of Energetic Materials, Vol. 12, No. 2, 2015, pp. 323–330.
 , “Hybrid Rocket Combustion and Applications to Space Exploration Missions,” Ph.D. Dissertation, Stanford Univ., Stanford, CA, 2015.
 , “Hybrid Rocket Motors Regression Rate Prediction through CFD Simulations,” 6th European Conference for Aeronautics and Space Sciences, EUCASS Paper 2015-074, 2015. https://doi.org/10.13009/EUCASS2017-614
 , “Rocket Solid Propellant Alternative Based on Ammonium Dinitramide,” National Institute for Aerospace Research (INCAS) Bulletin, Vol. 9, No. 1, 2017, pp. 17–24. https://doi.org/10.13111/2066-8201.2017.9.1.2
 , “Theoretical Studies on the Propulsive Performance and Explosive Performance of Strained Polycyclic Cage Compounds,” New Journal of Chemistry, Vol. 41, No. 3, 2017, pp. 920–930. https://doi.org/10.1039/C6NJ02444K
 , “New Directions in the Area of Modern Energetic Polymers: An Overview,” Combustion, Explosion, and Shockwaves, Vol. 53, No. 4, 2017, pp. 371–387. https://doi.org/10.1134/S0010508217040013
 , “Innovative Solid Rocket Propellant Formulations for Space Propulsion,” Energetic Materials Research, Applications, and New Technologies, edited by Goncalves R. F. B., Rocco J. A. F. F. and Iha K., ICI Global, Hershey, PA, 2018, Chap. 1. https://doi.org/10.4018/978-1-5225-2903-3
 , “Organic Fillers for Solid Rocket Fuel,” M.S. Thesis, KTH Royal Inst. of Technology, Stockholm, 2018.
 , “An Overview on Properties, Thermal Decomposition, and Combustion Behavior of ADN and AND Based Solid Propellants,” Defence Technology, Vol. 14, No. 6, 2018, pp. 661–673. https://doi.org/10.1016/j.dt.2018.03.009
 , “Combustion and Thermochemistry,” Rocket Propulsion, 1st ed., Cambridge Univ. Press, Cambridge, England, U.K., 2019, Chap. 5. https://doi.org/10.1017/9781108381376
 , “Theoretical Performance Analysis of Hybrid Rocket Propellants Aiming at the Design of a Test Bench and a Propulsive System,” 8th European Conference for Aeronautics and Space Sciences, EUCASS Paper 2019-488, 2019. https://doi.org/10.13009/EUCASS2019-488
 , “Thermodynamic Data,” Chemical Rockets: Performance Prediction and Internal Ballistics Design, Springer, New York, 2020, Chap. 6. https://doi.org/10.1007/978-3-030-26965-4_6
 , “Theoretical Computations of Equilibrium Compositions, Thermodynamic Properties, and Performance Characteristics of Propellant Systems,” Naval Weapons Center ADA-069832, China Lake, CA, 1979.
 , “Additivity Rules for the Estimation of Molecular Properties. Thermodynamic Properties,” Journal of Chemical Physics, Vol. 29, No. 3, 1958, pp. 546–572. https://doi.org/10.1063/1.1744539
 , “Additivity Rules for the Estimation of Thermochemical Properties,” Chemical Reviews, Vol. 69, No. 3, 1969, pp. 279–324. https://doi.org/10.1021/cr60259a002
 , “Revised Group Additivity Parameters for the Enthalpies of Formation of Oxygen-Containing Organic Compounds,” Journal of Physical Chemistry, Vol. 77 No. 13, 1973, pp. 1687–1691. https://doi.org/10.1021/j100632a019
 , Thermochemical Kinetics: Methods for the Estimation of Thermochemical Data and Rate Parameters, 2nd ed., Wiley, New York, 1976.
 , “Revised Group Additivity Values for Enthalpies of Formation (at 298 K) of Carbon-Hydrogen and Carbon-Hydrogen-Oxygen Compounds,” Journal of Physical and Chemical Reference Data, Vol. 25, No. 6, 1996, pp. 1411–1481. https://doi.org/10.1063/1.555988
 , “Estimation of the Thermodynamic Properties of Hydrocarbons at 298.15,” Journal of Physical and Chemical Reference Data, Vol. 17, No. 4, 1988, pp. 1637–1678. https://doi.org/10.1063/1.555814
 , “Estimation of the Thermodynamic Properties of C-H-N-O-S-Halogen Compounds at 298.15,” Journal of Physical and Chemical Reference Data, Vol. 22, No. 4, 1993, pp. 805–1159. https://doi.org/10.1063/1.555927
 , “Prediction of Enthalpy of Formation in the Solid State (at 298.15 K) Using Second-Order Group Contributions. Part 1. Carbon-Hydrogen and Carbon-Hydrogen-Oxygen Compounds,” Journal of Physical and Chemical Reference Data, Vol. 35, No. 3, 2006, pp. 1443–1457. https://doi.org/10.1063/1.2203111
 , “Prediction of Enthalpy of Formation in the Solid State (at 298.15 K) Using Second-Order Group Contributions. Part 2. Carbon-Hydrogen, Carbon-Hydrogen-Oxygen, and Carbon-Hydrogen-Nitrogen-Oxygen Compounds,” Journal of Physical and Chemical Reference Data, Vol. 36, No. 1, 2007, pp. 19–58. https://doi.org/10.1063/1.2435401
 , “Group Additivity Values for Estimating the Enthalpy of Formation of Organic Compounds: An Update and Reappraisal. 1. C, H, and, O,” Journal of Physical Chemistry A, Vol. 115, No. 38, 2011, pp. 10,576–10,586. https://doi.org/10.1021/jp202721k
 , “Group Additivity Values for Estimating the Enthalpy of Formation of Organic Compounds: An Update and Reappraisal. 2. C, H, N, O, S, and Halogens,” Journal of Physical Chemistry A, Vol. 116, No. 26, 2012, pp. 7196–7209. https://doi.org/10.1021/jp303780m
 , “Estimation of the Free Enthalpy (Gibbs Free Energy) of Formation of Organic Compounds from Group Contributions,” Chemical Engineering Science, Vol. 1, No. 2, 1951, pp. 66–80. https://doi.org/10.1016/0009-2509(51)85002-4
 , “Thermochemical Properties,” Properties of Polymers: Their Correlation with Chemical Structure, their Numerical Estimation and Prediction from Additive Group Contributions, 4th ed., Elsevier, New York, 2008, Chap. 20.
 NIST Standard Reference Database 25, NIST Structures and Properties Database and Estimation Program, 2018, https://webbook.nist.gov/chemistry/grp-add/ga-app/.
 , “Estimation of Heats of Formation of Organic Compounds by Additivity Methods,” Chemical Reviews, Vol. 93, No. 7, 1993, pp. 2419–2438. https://doi.org/10.1021/cr00023a005
 , “Critical Evaluation of Thermochemical Properties of C1–C4 Species: Updated Group-Contributions to Estimate Thermochemical Properties,” Journal of Physical and Chemical Reference Data, Vol. 44, No. 1, 2015, Paper 013101. https://doi.org/10.1063/1.4902535
 , “Prediction of Heat and Free Energies of Organic Compounds,” Industrial and Engineering Chemistry, Vol. 41, No. 5, 1949, pp. 1070–1076. https://doi.org/10.1021/ie50473a041
 , “The Vibration Frequencies and Thermodynamic Functions of Long Chain Hydrocarbons,” Journal of Chemical Physics, Vol. 8, No. 9, 1940, pp. 711–720. https://doi.org/10.1063/1.1750742
 , Toepassingen van De Thermodynamika Chemische Processen, Waltman, Delft, The Netherlands, 1945.
 , “Analytical and Experimental Comparisons of HTPB and ABS Hybrid Rocket Fuels,” 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA Paper 2011-5909, 2011. https://doi.org/10.2514/6.2011-5909
 , “Comparing Hydroxyl Terminated Polybutadiene and Acrylonitrile Butadiene Styrene as Hybrid Rocket Fuels,” Journal of Propulsion and Power, Vol. 29, No. 3, 2013, pp. 582–592. https://doi.org/10.2514/1.B34382
 , “NMR Analysis of Hydroxyl-Terminated Polybutadiene End Groups and Reactivity Differences with Monoisocyanates,” Journal of Polymer Science Part A: Polymer Chemistry, Vol. 56, No. 23, 2018, pp. 2665–2671. https://doi.org/10.1002/pola.29250
 , “Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications. Part I: Analysis,” NASA Reference Publication 1311, 1994.
 , “Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications. Part II: Users Manual and Program Description,” NASA Reference Publication 1311, 1996.
 , “Hybrid Propellant Rockets,” Rocket Propulsion Elements, 8th ed., Wiley, New York, 2010, Chap. 16.
 , “Hydrogen Peroxide, Hydroxyl Ammonium Nitrate, and Other Storable Oxidizers,” Fundamentals of Hybrid Rocket Combustion and Propulsion, edited by Kuo K. K. and Chiaverini M. J., 2007, Chap. 11. https://doi.org/10.2514/4.866876
 NIST Chemistry WebBook, NIST Standard Reference Database Number 69, 2020. https://doi.org/10.18434/T4D303