HTPB-based adhesive network is usually used in cured solid propellants, in which the crucial issue involved in the storage and use is aging problem. The quantum chemistry calculation was used to analyze the relationship between homolytic bond dissociation energy of two HTPB-TDI binder models and bond decomposition caused by aging. The computational results were proved to be reliable and suitable for comparative analysis. The BDE values of C-O bonds connected with CH₂ group were calculated to be minima, suggesting that they are the weakest bonds resulting in decomposition during thermal aging. The main degradation product is CO₂. In the binder formed by the reaction of allylic primary hydroxyl of HTPB and TDI, the α-C-H is the weakest X-H (X=C, N) bond, suggesting that it is vulnerable to free radical attack accompanying the hydrogen transfer. The possible mechanism of aging for the easy-cleavage C-O bonds was proposed. The calculated activation energies of C-O bonds cleavage are approximately equal to the corresponding BDE values, indicating that the formation of radicals accompanies a barrier-free release of CO₂ during thermal aging. The half-life time of such aging process was described by an exponential decay function of temperature. The aging of HTPB-TDI binder accelerates with increasing temperature. The radical recombination reactions of decomposed amino radicals and alkyl radicals are supported by thermodynamic data calculated. Molecular dynamic simulations were used to analyze the variation in the network structures and effect on mechanical properteis of HTPB-TDI binder models before and after aging. It is found that the density of the system decreases with release and diffusion of CO₂, and the corresponding tensile modulus and shear modulus increase with aging.

Key words: HTPB-based binder, ond dissociation energy, echanical properties