INCORPORATING ENERGETIC CHAIN EXTENDERS TO POLYMERIC BINDERS FOR SOLID PROPELLANTS

摘要

Methods were investigated for synthesizing polymeric propellant binders that incorporate rigid and energetic chain extenders using polyurethane linkages. After exploring many methods for synthesizing polyurethanes with hard segment isocyanates, soft segment polyols, and chain extenders, a two-step synthesis process with oven cure at 60-70 degrees C proved to be the most effective. Soft segment oligomers with molecular masses of similar to 1000-1200 were found to produce the optimal reaction conditions. Attenuated total reflectance Fourier transform infrared spectroscopy was used to confirm characteristic polyurethane bonding. Polyurethane polymers with and without chain extenders were then combined with ammonium Perchlorate (20% binder, 80% oxidizer by mass) to form hard strands for testing in a chimney-style strand burner. Strands were tested for burning rate at a range of pressures from 0.5-4.6 MPa, and pressure/burn rate data were fit to a line in log-log space using a multiple regression least squares approach. All tested combinations showed similar burning rates between 0.3 and 1.0 cm/s, increasing with pressure. Typical confidence intervals showed that there was a statistically significant increase in burning rate for a 4,4' -biphenol chain extender, while the most commonly utilized 1,4-butanediol showed the consistently lowest burning rates of any tested additive. These results describe effective methods of introducing chain extenders and further suggest that proper choice of chain extender in a polymeric binder could have an important impact on overall propellant performance.