Iranian Scientific Association of Energetic Materials

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Binders in composite propellants have a crucial role to affect the physical and thermochemical properties. So it is necessary to choose the binder ingredient appropriately. The suitable binders have a high solid loading, good mechanical and process ability properties. Polycaprolactone due to the polar groups in their structures are able to mix with other nitrate esters. At this point of view, they are suitable binders. In the other hand, polyglycidyl nitrate with ONO2 groups is a high energetic polymer however, it has not suitable mechanical properties. Consequently, it is possible to use the good mechanical properties of polycaprolactone and energetic properties of polyglycidyl nitrate by the synthesis of the PCL-PGN-PCL three-block copolymer. In this research, the PCL-PGN-PCL three-block copolymer was synthesized for the first time. First, polyglycidyl nitrate as a monomer was synthesized using epichlorohydrin (60% total yield of the reaction). Then, polyglycidyl nitrate was synthesized by using this monomer (70% yield). Finally, the new PCL-PGN-PCL three-block copolymer was synthesized by ring opening polymerization of caprolactone as monomer and poly glycidyl nitrate (PGN) as a macro initiator in the presence of dibutyl tin laurate as a catalyst. The differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were performed to investigate the thermal characteristics of this copolymer. The Tg was -45.2 °C. In addition, there was one pick in the GPC chromatogram that improved the formation of PCL-PGN-PCL three-block copolymer. The PCL-PGN-PCL three-block copolymer was characterized by 1HNMR, 13CNMR and IR spectroscopy methods. In the last part, the synthesis process of the PCL-PGN-PCL three-block copolymer was optimized. The 115° C and 19 hours and 0.01 g of catalyst for 1g initiator considered as the optimized condition. Toluene was chosen as a solvent and the monomer was added gradually into the reaction media. The yield of reaction in this condition was 81%. Also, the optimization of molar ratios of monomer to initiator in 20:1, 10:1 and 5:1 was done and the molar ratio of 5:1 showed the best molecular dispersity.

Keywords: PCL-PGN-PCL three-block copolymer, poly glycidyl nitrate, poly caprolactone

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