Synthesis of Cyclobutyl-Doped Hydroxyl-Terminated Poly(butadiene) Copolymers and Properties Relevant to Propellant Applications

Abstract

Hydroxyl-terminated poly(butadiene) (HTPB) is the preeminent prepolymer employed in binders for solid-rocket motors. While well-known and capable of providing favorable mechanical properties, the synthesis of HTPB is uncontrolled, leading to a lack of uniformity between samples, and, as a pure hydrocarbon, it provides little additional energy to the grain. In this work, we demonstrate the use of ring-opening metathesis polymerization to prepare HTPB that is perfectly telechelic and easily doped with strained cyclobutyl groups via the comonomer δ-pinene, adding additional energy to this otherwise inert polymer through the use of an abundant, domestic source. We report structural, thermochemical, and rheological properties as well, demonstrating the utility of this polymer in applications relevant to solid-rocket motors. Computational investigations into the ring-strains of the monomers are reported, providing insight into their relative reactivity in the copolymerization reaction.