Construction of phosphonitrile derivative-hybridized EPDM dense crosslinked networks for enhanced mechanics and ablation resistance

With the development of aerospace technology, the thermal insulation layer between the engine casing and the propellant needs to have excellent mechanical and ablative resistance properties to meet higher environmental requirements. Herein, two novel reactive phosphonitrile derivatives containing P and N heteroatoms, namely, hexa(2-allylphenoxy) cyclotriphosphonitrile (HAPPCP) and hexa(3-ethynylphenylamino) cyclotriphosphonitrile (HEACP), were designed and synthesized to crosslink with EPDM for modulating its chain structure on a molecular scale, forming P- and N-atom hybridized EPDM dense crosslinked networks, which collectively improve the mechanical and ablative resistance. Results showed that HEACP was more effective for boosting the overall performance, accompanied by improvements of 64.6% and 89.2% in tensile strength and breaking elongation, respectively, and reductions of 52.6% and 33.1% in the linear ablation rate and mass ablation rate, respectively. The ablation-condensed phase, microscopic carbon crystal structure, and the gas-phase thermal barrier mechanism were investigated to elucidate the ablative resistance mechanism.