Synthesis, Optimization, and Investigation of the Characteristics of the Triblock Copolymer Polypropylene Glycol-Poly Glycidyl Azide-Polypropylene Glycol

Due to the important role of the binder of compound engines, many studies have been done to improve their mechanical and thermal characteristics. Glycidyl azide polymer is used as an energetic binder in compound engines. The aim of this research is to improve the thermal properties and glass transition temperature of this energetic binder by copolymerizing it. So, the energetic triblock the copolymer of polypropylene glycol- glycidyl azide polymer- polypropylene glycol (PPG-GAP-PPG) (Mn = 1800 g/mol) was synthesized. For this purpose glycidyl azide polymer (GAP) (Mn = 1006 g/mol) was synthesized by poly epichlorohydrin The GAP was used as the initiator. The GAP triblock copolymer was synthesized by ring-opening polymerization of polypropylene oxide in the presence of boron trifluoride etherate (BF3·OEt2) as the catalyst. The synthesized triblock copolymer was characterized by Fourier-transform infrared (FT-IR) and nuclear magnetic resonance spectroscopy. The glass transition temperature (Tg) of the triblock copolymer was characterized by differential scanning calorimetry (DSC). The DSC result showed that the glass transition temperature (Tg) of the triblock copolymer (Tg = −63 °C) is lower than the neat low molecular weight GAP (Tg = −53 °C). The thermal stability of GAP and PPG-GAP-PPG triblock copolymer was investigated using differential thermogravimetric analysis (DTG). The result indicated that the triblock copolymer is more stable than the GAP. To optimize the synthesis conditions of the triblock copolymer PPG-GAP-PPG synthesis condition, the effect of temperature and catalyst on molecular weight, and copolymerization efficiency were investigated. The best mood for the synthesis of the triblock copolymer was the yield (86%) at 10-15 ºC, and 1% by weight of the catalyst.The DSC result showed that the glass transition temperature of the copolymer (Tg = -63° C) was lower than that of low molecular weight glycidyl azide (Tg = -53 ° C). In order to optimize the synthesis conditions of PPG-GAP-PPG triblock copolymer, the influence of temperature and catalyst variables on molecular weight and copolymerization efficiency was investigated. The highest yield (86%) was obtained at 10-15 ° C and 1% of catalyst.