Synthesis of triblock copolymers (polyA-polybutadiene-polyA) and applications as additives in composite propellants

TLDR: In this article, the authors used triblock copolymers obtained from HTPB as additive to a solid propellant mixture based on HTPB with ammonium perchlorate (oxidiser), dioctyl adipate (plasticiser), and toluene diisocyanate (curing agent).

Abstract: Hydoxyl-terminated polybutadiene (HTPB), an important polymeric fuel binder for composite propellants, has been utilised to anchor tungsten hexachloride, a well-known metathesis catalyst. This anchored catalyst polymerises various monomers like phenylacetylene (PA) and norbornene (NBE) to give triblock copolymers via metathesis polymerisation. The triblock copolymers thus obtained are of the type polyA-block-polybutadiene-block-polyA and have been characterised by spectroscopic, thermal and gel permeation chromatographic techniques. As block copolymers have the characteristics of the individual polymers, they can be used as substitutes or additives in analogous polymeric formulations to improve the matrix properties. These triblock copolymers obtained from HTPB were employed as additives to a solid propellant mixture based on HTPB with ammonium perchlorate (oxidiser), dioctyl adipate (plasticiser) and toluene diisocyanate (curing agent). Burning rate studies of these propellant mixtures were conducted under various pressures to evaluate the individual ballistic nature. It was found that NBE-based additive imparts higher burning rate than the HTPB-based propellant. The effect of copper chromite as a burning rate modifier in this new formulation was also evaluated. The mechanical properties of the propellants were measured and compared to show the effect of triblock in the binder network. This paper mainly focuses on the synthesis and characterisation of the above triblock copolymers and burning rate studies of the propellants based on these polymers.