Neutral Polymeric Bonding Agents (NPBA) and Their Use in Smokeless Composite Rocket Propellants Based on HMX‐GAP‐BuNENA

Abstract

Very few efficient bonding agents for use in solid rocket propellants with nitramine filler materials and energetic binder systems are currently available. In this work, we report the synthesis, detailed characterization, and use of neutral polymeric bonding agents (NPBA) in isocyanate‐cured and smokeless composite rocket propellants based on the nitramine octogen (HMX), the energetic binder glycidyl azide polymer (GAP), and the energetic plasticizer N‐butyl‐2‐nitratoethylnitramine (BuNENA). These polymeric bonding agents clearly influenced the viscosity of the uncured propellant mixtures and provided significantly enhanced mechanical properties to the cured propellants, even at low NPBA concentrations (down to 0.001 wt‐% of propellant). A modified NPBA more or less free of hydroxyl functionalities for interactions with isocyanate curing agent provided the same level of mechanical improvement as regular NPBA containing a substantial number of reactive hydroxyl groups. However, some degree of reactivity towards isocyanate is essential for function.

Molecular Dynamics of Neutral Polymer Bonding Agent (NPBA) as Revealed by Solid-State NMR Spectroscopy

“…As shown in Figure 1A, the 1D 13 C spectrum shows characteristic features, including high intensity of CH and CH 2 peaks at 20-45 ppm and downfield resonances of CN and CO groups, respectively, at 122.0 ppm and 175.8 ppm, in good agreement with the structural motif of NPBA. The simple spectral features also suggest that the sample is very unlikely to show large inhomogeneity.…”

“…In addition, the broader shoulder decreases with increasing temperature and nearly disappears at 353 K. As measured by differential scanning calorimeter (DSC), NPBA shows a glass transition temperature, T g , at approximately 329 K. On one hand, the distinct spectra feature between A-B and C-E suggest the faster motion above the T g . On the other hand, the broad line-width of the central peak below T g indicates stronger 13 …”

“…We firstly obtained the 1D 13 C CP/MAS spectrum of NPBA to evaluate the sample homogeneity and assign the resonances of various carbon groups. As shown in Figure 1A, the 1D 13 C spectrum shows characteristic features, including high intensity of CH and CH 2 peaks at 20-45 ppm and downfield resonances of CN and CO groups, respectively, at 122.0 ppm and 175.8 ppm, in good agreement with the structural motif of NPBA.…”

“…The domain structure and mobility of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites with different polyhedral oligomeric silsesquioxane (POSS) contents were investigated by SSNMR techniques including 2D WISE [37] and spin diffusion [45]. In addition, structures and thermal properties of the multiple ordered phases in ethylene-octene and ethylene-butene copolymers have been studied using the measurements of 13 C chemical shift tensors and NMR relaxation times [46].…”

“…It has repetitive aliphatic main chains and branched side chains of varied lengths, showing strong affinity to the polar filters. In addition, the hydroxyl-group rich side chains interact with the binder matrix, promoting the interfacial bonding strength, defined as stretching amplitue of the binding interface between propellants and linear parts [13,14].…”