Molecular dynamics simulation of molecular network structure and mechanical properties of polymer matrix in PBT propellant

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3,3-Bis(azidomethyl)oxetane (BAMO)/tetrahydrofuran (THF) copolymer (PBT) constitutes the polymer matrix of PBT solid propellant and influences the mechanical properties of the propellant. In this work, the molecular network structure of the PBT propellant matrix was constructed by molecular dynamics method, the influence of different component contents on the mechanical properties was studied, and the structure - mechanical properties relationship at the molecular level was established. The simulation results showed that changes in the content of crosslinker (TMP) and chain extender (DEG) had slight effects on Young's modulus. The tensile strength of the polymer matrix network was positively correlated with the molecular chain length and the number of cross-linking sites formed by TMP. When the isocyanate index R was less than 1, increasing the content of TMP crosslinker led to low conversion rate due to insufficient curing agent, thereby reducing the number of cross-linking sites and the strength of the system. When the isocyanate index R was less than 0.87, the increase of DEG content increased the chain length of the main chain and strengthened the system. Due to the competitive reaction with the curing agent, the difunctional (-OH) chain extender monomer showed stronger reactivity than the trifunctional crosslinker monomer, and the excess chain extender reduced the number of crosslinking sites, destroyed the crosslinking network structure and reduced the strength.