Synthesis, Thermochemistry, and Cure Behavior of Oligocyclobutane-Containing Prepolymers Relevant to Propellant Applications

Abstract

While hydroxy-terminated polybutadiene (HTPB) has been traditionally employed as a binder prepolymer for solid rocket booster applications, the hydrocarbon main chain is energetically inert and contributes little to the overall energy content of the formulation. Here, (1,n′-divinyl)oligocyclobutane (DVOCB), a structural isomer of polybutadiene containing 1,3-enchained cyclobutanes in the polymer backbone, is investigated as a prepolymer candidate. The synthetic modularity of DVOCB is also demonstrated through postsynthetic dihydroxylation to generate hydroxy-terminated oligocyclobutane (HTOC), the direct structural isomer of HTPB. Because the main chain of these cyclobutyl-containing prepolymer candidates is composed of strained four-membered rings as repeat units, the use of these molecules in binder applications was targeted to increase the energy density of the formulations. The measurement of the energetic content of both oligomers by constant volume (bomb) calorimetry indicated that DVOCB and HTOC are 16−18% more energetic than their linear congeners. Further, their ability to participate as synthetic analogues of HTPB was demonstrated through thermal, rheological, and curing studies to generate polyurethanes or polythioethers.