Ceiling Temperature Influence on The Synthesis of MT-4 and Aging Behavior of Polyurethane Polymer

The stability of the bonding agent in the polymeric binder system has a significant impact on the long-term aging performance of composite solid rocket propellants (CSRPs). This work investigates the influence of synthesis temperature on the structure and performance of a novel MT-4 bonding agent (Poly(isopropyl amine N-(2-methyl-1-aziridinyl) phosphine oxide adipate)-co-(isopropyl amine tartrate)), synthesized at different temperatures (50–90 °C). The produced MT-4 analogues were incorporated into hydroxyl-terminated polybutadiene (HTPB)-based propellant formulations at a fixed concentration of 0.3 wt%. The bonding agents were characterized by FTIR, aziridine content, and viscosity measurements. Mechanical properties were evaluated before and after accelerated aging (55 days at 65 °C, equivalent to approximately five years of natural aging). The results indicate that synthesis temperature strongly affects the MT-4 structure and propellant performance. The MT-4 synthesized at 60 °C produced the best mechanical balance, with a tensile strength of 7.04 kg/cm² and an elongation of 53.3%, due to improved interfacial bonding and reduced dewetting. In contrast, MT-4 synthesized at 90 °C showed thermal instability near its ceiling temperature, leading to depolymerization and a color change, resulting in poor aged properties (elongation 18.6% and modulus 57.7 kg/cm²). These results demonstrate that MT-4 can improve mechanical and aging behavior; however, synthesis conditions must be carefully controlled to avoid depolymerization