Exploring the telechelic block copolymers of polybutadiene and ϵ-caprolactone for composite propellant application

Abstract

In this study, synthesis of three hydroxyl-terminated block copolymers of varying molecular weight by ring opening polymerization of ԑ-caprolactone using hydroxyl-terminated poly butadiene as the initiator and stannous octoate as the catalyst was attempted. These block copolymers were specifically synthesized for its application in solid rocket propellants as an energetic binder. The desired chemical links between blocks were noticed in 1H nuclear magnetic resonance (NMR) and 13C NMR spectra, followed by confirmation in 1H/13C heteronuclear single quantum coherence and Fourier transform infrared spectra. To specify these block copolymers, various properties such as hydroxyl value (OH value), number average molecular weight (M¯n), specific gravity (ρ), rheological properties, glass transition temperature (Tg), thermal decomposition, and miscibility with nitrate ester plasticizers were determined. Additionally, the mechanical properties of the samples were evaluated using isocyanates as curators at NCO/OH equivalence ratio of 0.8 and 1.0. Finally, the best combination was selected based on physicochemical properties and miscibility with nitrate esters for further evaluation in composite propellant. We also theoretically studied the ballistic parameters of composite propellants by the NASA CEC-71 program to observe the gain of density impulse as the plasticizer to polymer ratio was increased.