Synthesis, Characterization And Application In Propellant Of PBA Energetic Thermoplastic Elastomers

With the development of the modern weapons, the higher requirement has been proposed. High energy, insensitive and low signature have become the development trend of the solid propellants. According to the energetic binder requirements of solid propellants, poly（3,3’-bisazidomethyl oxetane-3-azidomethyl-3’-methyl oxetane） energetic thermoplastic elastomer（PBA） was designed and prepared in this paper. And the interaction between PBA and the conventional ingredients applied in solid propellant was investigated for the application of PBA in the field of solid propellants.（1） The energetic prepolymer poly（3-azidomethyl-3’-methyl oxetane）（PAMMO） was synthesized by the indirect synthesis method. The kinetic of the azido reaction, the chemical structure and the property of PAMMO were investigated in this paper. The FT-IR、¹H NMR、¹³C NMR、¹⁵N NMR results showed the successful synthesis of PAMMO. And the relative molecular weight of PAMMO was undercontrol, the molecular weight distribution was narrow, the glass transition temperature（Tg） was-44.5℃, DTG peak temperature was 266.1℃, H50 was higher than 120 cm,the friction sensitivity was 0%;（2） PBA was prepared according to the polyurethane pynthesis process by linking PAMMO and poly（3,3’-bisazidomethyl oxetane）（PBAMO） with different diisocyanate, different content of the hard segment and different mass ratio of PBAMO and PAMMO. The reaction condition and the proprmance of PBA were investigated to select better PBA for the application in propellant. The results showed that TDI based PBA had the best overall perormance with the maximum stress 5.24 MPa, the breaking elongation 390%, η0 94.41Pa·s. The heats of formation were calculated by group additivity method and heats of combustion method. The calculated results showed that TDI based PBA had higher heats of formation. TG/DSC-IR was employed to investigate the thermal decomposition process and kinetics of PBA. The results showed that the thermal decomposition of PBA including two stages which were corresponding to the thermal decomposition of azido group and the left polymer chain. The thermal decomposition activation energy was nearly 169.37kJ·mol-1, and the mechanism function can be described as G（α） =-ln（1- α）. Kinetic compensation effect was employed to verify the mechanism function, and the results showed that, when α<0.7, G（α） =-ln（1- α） was suitable to simulate the thermal decomposition of PBA;（3）The PBA/RDX（HMX, AP, Al） samples were shaped by rolling method. The results of the vacuum stability test showed that PBA was compatible with these ingredients used in solid propellants. The mechanical property results showed that the maximum stress and breaking elongation of the composite samples were decreased with adding the solid fillers. The solid fillers could destroy the integrity of the PBA matrix. DMA tests showed that the interaction between the solid fillers and PBA resulted in Tg of PBA increasing. The rheological property studies showed that the solid fillers could increase the viscosity of the composite samples. The thermal decomposition of the composites samples showed that RDX, HMX and PBA promoted the decomposition for each other, and AP promoted the decomposition of PBA. With the addation of Bu-NENA or GAPA, Tg of PBA composite samples became lower, which could improve the processing performance and mechanical property at low temperature for PBA based propellant;（4）The minimum free energy method was empolyed to calculate the energy parameters for PBA/Bu-NENA and PBA/GAPA based propellants. The calculated stanrd standard theoretical specific impulse was 275.46 s and 275.19 s for 15PBA/5Bu-NENA/20RDX/38.5AP/18Al/3.5others and 15PBA/5GAPA/28HMX/30.5 AP/18Al/3.5others respectively. For PBA/Bu-NENA based propellant, the density was 1.767g·cm^-3, the explosion heat was 5263.03kJ·kg^-1, the impact sensitivity H50 was 47.5cm, the friction sensitivity was 48%, the breaking elongation at-40℃ was 4%, and the maximum stress at 50℃ was 0.77 MPa. For PBA/GAPA based propellant, the density was 1.774g·cm^-3, the explosion heat was 5184.77kJ·kg^-1, the impact sensitivity H50 was 62.5cm, the friction sensitivity was 40%, the breaking elongation at-40℃ was 2%, and the maximum stress at 50℃ was 0.72 MPa. The aging test results showed that PBA was stabe in the aging period either in PBA/Bu-NENA based propelant or PBA/GAPA based propellant. But, the mechanical property decreased with aging for PBA/Bu-NENA peopellant due to the volatilization of Bu-NENA. PBA/GAPA based propellant kept the mechanical property well under the aging period.