Composite propellants are considered as major sources of chemical energy for rocket propellants. In the preparation of composite propellant energetic formulations, the propellant binder plays a vital role. Various energetic polymeric binders were developed during last five decades to satisfy safety, high energy and processing conditions. In this review, we discuss the various synthetic routes for of preparation of high energetic polymeric binders, including glycidyl azide polymers (GAP)s, GAP co-polymers, oxetane polymers, oxirane polymers, azido polyesters, N, N′-bonded epoxy binders, aliphatic vinyl azide polymers and poly(allyl azide) (PAAz).

https://www.tandfonline.com/doi/pdf/10.1163/156855506777351045

Synthesis of azido polymers as potential energetic propellant binders

Cross-linked co-polymers containing glycidyl azide polymer (GAP) and hydroxyl-terminated poly(butadiene) (HTPB) segments have been obtained by chemical reactions. The reactions involves two steps. In the first step the GAP macroinitiator (GAPMI) is synthesized by the condensation reaction of GAP-diol with 4,4'-azobis(4-cyanopentanoic acid) (ACPA) in the presence of N-methyl-2-chloropyridinium iodide (MCPI). The GAPMI obtained is used for the cross-linking or grafting reactions with HTPB at an elevated temperature in the second step. The cross-linked co-polymers are isolated from the crude reaction mixture by fractional precipitation technique using chloroform as solvent and methanol as non-solvent. The co-polymers have been well characterized by using IR, 1H-NMR and 13C-NMR spectral analysis, and the molecular weights of the co-polymers have been determined by gel permeation-chromatography (GPC) and vapour pressure osmometry (VPO). The co-polymer exhibited two glass transition temperatures for HTPB-GAP co...

https://www.tandfonline.com/doi/pdf/10.1163/1568555053603215

Synthesis and characterization of HTPB-GAP cross-linked co-polymers

Hydroxyl terminated polybutadiene (HTPB) as a telechelic liquid polymer has been widely used in propellants and explosives and many modified-HTPBs have been reported in the literature. As a binder or additive in propellants and explosives, the chemical modification of HTPB for improving certain properties of propellants has been summarized in detail in this article. According to the application drawbacks of HTPB, modified-HTPB can be classified differently. Furthermore, there are polymers that have been modified on their energetic properties, such as GAP-PB-GAP, BAMO-PB-BAMO, AMMOPB-AMMO, Nitro-HTPB, HTPB-DNB and NHTPB. Pre-polymers modified on their combustion properties include Butacene®, FPDS-g-HTPB, Fc-HTPB, BiFc-g-HTPB, HTPB→[Fe(CO)3]x, PPA-HTPB-PPA and PNBE-HTPB-PNBE. HTPBs are also modified in curing systems containing, for example ETPB, PTPB, PrTPB, AzTPB, and PUPB, and other modification results are reviewed. Additionally, this overview is expected to provide an outlook for further studies in these fields.

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Hydroxyl Terminated Polybutadiene: Chemical Modification and Application of these Modifiers in Propellants and Explosives

Synthesis and Characterization of Low Molecular Weight Azido Polymers as High Energetic Plasticizers

Nanometer metal oxides were highly desirable to increase the burning rate of composite solid propellant because of their high catalytic activities. However, poor dispersibility limits their wide applications. In this work, the dispersibility of CuO was enhanced significantly by attachment to the mesoporous silica SBA-15. CuO/SBA-15 composites were prepared by using impregnation method with as-prepared SBA-15 as support, and the occluded template (P123) in SBA-15 promoted the dispersion of CuO on SBA-15. X-ray diffraction (XRD) revealed that no CuO crystalline visible in the composite and N2 adsorption-desorption showed a great amount of CuO dispersion on SBA-15. As the catalyst of propellant, CuO/SBA-15 composite not only enhanced the burning rate of propellant but also decreased the pressure exponent. With the addition of 1 wt% CuO/SBA-15 in the propellant, the burning rate of AP-based propellant increased 9.5%, and pressure exponent decreased 17.3%.

Preparation of CuO Modified SBA-15 and Applications as Catalyst in AP/HTPB Solid State Propellants

Hydoxyl-terminated polybutadiene (HTPB), an important polymeric fuel binder for composite propellants, has been utilised to anchor tungsten hexachloride, a well-known metathesis catalyst. This anchored catalyst polymerises various monomers like phenylacetylene (PA) and norbornene (NBE) to give triblock copolymers via metathesis polymerisation. The triblock copolymers thus obtained are of the type polyA-block-polybutadiene-block-polyA and have been characterised by spectroscopic, thermal and gel permeation chromatographic techniques. As block copolymers have the characteristics of the individual polymers, they can be used as substitutes or additives in analogous polymeric formulations to improve the matrix properties. These triblock copolymers obtained from HTPB were employed as additives to a solid propellant mixture based on HTPB with ammonium perchlorate (oxidiser), dioctyl adipate (plasticiser) and toluene diisocyanate (curing agent). Burning rate studies of these propellant mixtures were conducted under various pressures to evaluate the individual ballistic nature. It was found that NBE-based additive imparts higher burning rate than the HTPB-based propellant. The effect of copper chromite as a burning rate modifier in this new formulation was also evaluated. The mechanical properties of the propellants were measured and compared to show the effect of triblock in the binder network. This paper mainly focuses on the synthesis and characterisation of the above triblock copolymers and burning rate studies of the propellants based on these polymers.

G. Sundararajan

Papers

Synthesis of triblock copolymers (polyA-polybutadiene-polyA) and applications as additives in composite propellants