Synthesis of GAP-PB-GAP triblock copolymer and application as modifier in AP/HTPB composite propellant

A new triblock copolymer polyglycidylazide-block-polybutadiene-block-polygl ycidylazide (GAP-PB-GAP) has been synthesized. The synthesis was done by ca tionic ring opening polymerization of epichlorohydrin (ECH) with HTPB as th e alcohol and boron trifluoride etherate as the catalyst followed by the co nversion of the -CH2Cl group into -CH2N3 group. The presence of the azido g roups in the GAP polymer chain makes it more energetic and the triblock cop olymer can be used as an energetic binder/additive for propellant energy mo dification. Since the triblock copolymer has polybutadiene (PB) as the cent ral block, which is from HTPB itself, it can be used as an additive in HTPB based polymeric formulations to improve their properties. In the present w ork, a part of HTPB, the propellant binder in ammonium perchlorate (AP)/HTP B propellant was removed and replaced with the GAP-PB-GAP copolymer. Burn r ate, mechanical properties, and heat of combustion properties of these prop ellants were measured and compared with the unmodified HTPB/AP propellant. The results show that the burn rate of the HTPB/AP solid propellant could b e enhanced by the addition of the triblock copolymer.