Application of azide-containing molecules as modifiers of HTPB: Synthesis and evaluation of properties

Hydroxyl-terminated polybutadiene (HTPB) has been widely modified and copolymerized with azide substances to be applicable as an elastomer binder in a composite solid propellant (CSP). This research presents a systematic evaluation of the HTPB chemical modification performed with two types of azide-containing molecules such as ethylene glycol bis-(azidoacetate) (EGBAA) and octyl-1-azide. The chemical modification of HTPB was carried out through the bulk reaction between the HTPB double bonds and azide pendant groups. The synthesis was performed by measuring gas evolution in a pressure-vacuum stability device. Through size exclusion chromatography and Fourier-transform infrared spectroscopy, the molar mass and the formation of carbon-nitrogen bonds were evaluated, respectively. Elemental analysis detected nitrogen in the modified HTPB. Differential scanning calorimetry revealed changes in the glass transition temperature (Tg). The final products were dependent on the type of azide molecules. Thermogravimetric analysis showed that HTPB modified with EGBAA presented higher thermal stability. Solid and viscous elastomers were achieved with modification by EGBAA and octyl azide, respectively. Both are potentially suitable for use as binders in CSP.