Synthesis and Characterization of Hyperbranched Polyazomethine Ablators for Space Exploration Applications

A novel series of ablative composites containing a hyperbranched polyazomethine synthesized inside a carbon fiber preform (HyPAZA) were prepared, which have similar density to phenolic impregnated carbon ablators (∼0.3 g/cc). A novel method of synthesizing strong hyperbranched polyazomethine thermosets has been developed, enabling polyazomethines to be studied in ablators for the first time. Several formulations of HyPAZA perform better than the phenolic impregnated carbon ablator in terms of polymer char yield, composite mechanical strength, CO2 laser ablation tests at heat fluxes of 550 and 1100 W/cm2, and small-scale arcjet testing at a heat flux of 400 W/cm2. Char yields of hyperbranched polyazomethines were as high as 79% at 1000°C by thermogravimetric analysis. This is one of the highest char yields ever reported for a fully organic polymer. Some HyPAZA composites are over 10 times stronger than the carbon fiber preform, as determined by compression tests. Specimens were also tested in an arcjet ...