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

Hydoxyl-terminated polybutadiene (HTPB), an important polymeric fuel binder for composite propellants, has been utilised to anchor tungsten hexachlori de, a well-known metathesis catalyst. This anchored catalyst polymerises va rious monomers like phenylacetylene (PA) and norbornene (NBE) to give tribl ock copolymers via metathesis polymerisation. The triblock copolymers thus obtained are of the type polyA-block-polybutadiene-block-polyA and have bee n characterised by spectroscopic, thermal and gel permeation chromatographi c techniques. As block copolymers have the characteristics of the individual polymers, th ey can be used as substitutes or additives in analogous polymeric formulati ons to improve the matrix properties. These triblock copolymers obtained fr om HTPB were employed as additives to a solid propellant mixture based on H TPB with ammonium perchlorate (oxidiser), dioctyl adipate (plasticiser) and toluene diisocyanate (curing agent). Burning rate studies of these propell ant mixtures were conducted under various pressures to evaluate the individ ual ballistic nature. It was found that NBE-based additive imparts higher b urning rate than the HTPB-based propellant. The effect of copper chromite a s a burning rate modifier in this new formulation was also evaluated. The m echanical 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 bur ning rate studies of the propellants based on these polymers. (C) 1999 Else vier Science B.V. All rights reserved.