Thermal Degradation Behavior of Thermally‐Oxidized Hydroxyl‐Terminated Polybutadiene (HTPB): An Assessment of Thermal Stability

Abstract Thermal analysis was performed on different thermally oxidized hydroxyl‐terminated polybutadiene (HTPB) samples, varying in molecular weights, polydispersities, and viscosities. The HTPB sample was subjected to thermal ageing at 65 °C for 10 weeks and periodically withdrawn for thermal analysis. During thermal ageing, HTPB undergoes chain rearrangements that may include scission and subsequent crosslinking, leading to a higher average molecular weight and viscosity. Differential scanning calorimeter (DSC) and thermogravimetric analyses were performed on thermally oxidized HTPB samples under inert heating conditions to investigate their degradation behavior. The DSC results revealed no significant correlations between the glass transition ( T g ) and the samples' molecular weight, viscosity, and polydispersity. In TGA, all HTPB samples showed a two‐step thermal decomposition process characterized by two distinct mass loss stages. Notably, the first stage exhibited a lower total mass loss and a considerably lower peak rate of mass loss than the second stage. The thermal stability of HTPB is significantly compromised by thermal‐oxidative degradation, leading to a pronounced decrease in the initial degradation temperature ( T IDT ) values, from 372 °C (pristine or 0 week) to 228 °C (10 weeks). Furthermore, we measured the energy of activation ( E a ) and the pre‐exponential factor ( A ) from TGA data using the Coats–Redfern integral equation. Notably, we observed a slight but systematic increase in both E a and A as the molecular weight of the aged samples increased.