An Alternative Synthetic Strategy for Butyl‐Ferrocene‐Grafted Hydroxyl‐Terminated Polybutadiene (Butacene) as a Combustion Rate Modifier

ABSTRACT Ferrocene‐based burn rate catalysts (BRCs) have attracted much attention for use in solid propellant (SP) because of their excellent microscopic homogeneities in distribution, good compatibility with organic binder and enhancing the ignitability of the SP. Though the Butacene (butyl‐ferrocene grafted hydroxyl‐terminated polybutadiene), the most popular BRC, is commercially available, the reported synthetic routes of Butacene are tedious, inconsistent, misleading and often not reproducible. This article presents an alternative, readily executable, industrially scalable and reproducible synthetic method for the preparation of Butacene and the resulting samples were characterized by various techniques, including spectroscopic, molecular weight, viscosity and thermal, etc. This work also first time demonstrates that the percentage of iron content in Butacene, which is a crucial factor to be effective as BRC, can be readily altered by varying monomer to initiator ratio. All the physical characteristic measurements showed that the resulting Butacene has the required physical properties to be used as BRC in the propellant formulation. Further, the solid composite propellant prepared using the synthesized Butacene displayed significantly higher burn rate and lower pressure index in comparison to pristine HTPB. A 50% enhancement in the burn rate with low pressure index (0.27) was observed in the case of SP, which was made using only 30% of synthesized Butacene along with 70% pristine HTPB. Further, the synthesized Butacene were cured to prepare polyurethanes (PUs) which showed similar thermal profile, glass transition temperature (T g ) and excellent mechanical properties like pristine HTPB.