Unveiling the early-stage condensed-phase decomposition of tetrazole-grafted HTPB as energetic binder-experimental and quantum mechanistic revelations

The emergence of azole-grafted hydroxyl-terminated polybutadiene (HTPB), specifically tetrazole-grafted HTPB (Tetz-HTPB), has sparked considerable interest recently owing to its remarkable energetic properties, synthetic capabilities, and physicochemical characteristics as an energetic binder (EB) for solid rocket propellant (SRP) compositions. The current study focusses on an extensive examination of the thermal properties of this new binder under slow pyrolysis condition using TGA-DTG and c-DTA analyses. To comprehend the complex bond-breaking mechanisms of polymer-based materials, the initial stage decomposition of Tetz-HTPB in the condensed phase was analysed by integrating experimental and theoretical methods. The experimental study clarifies that, unlike HTPB, the initial stage breakdown of Tetz-HTPB occurs at 190 °C with the release of N₂ and HCN as primary gaseous products, while thermal crosslinking of this polymer does not commence at this stage and instead starts at 290 °C. Such peculiar experimental outcome, later supported by quantum mechanics computations, offers valuable insights into the mechanism of bond-breaking at this stage. Further kinetic analysis showed that Tetz-HTPB has somewhat shorter shelf life than HTPB and Nitro-HTPB due to its low reaction constant value, 4.4E-07 min⁻¹ at 50 °C, even at closed pierced lid conditions. Moreover, the current research explores multiple aspects of the thermal properties of Tetz-HTPB, including the initial stage decomposition mechanism, shelf-life behaviour for long-term storage, etc. with an emphasis on its potential use as an EB in cutting-edge propellant research and development.