Synthesis, structure-property relationships of polyphosphoramides with high char residues

A series of polyphosphoramides with high char residues were successfully synthesized using solution polycondensation and well characterized. The thermal properties and flammability were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and microscale combustion calorimeter (MCC). The evolved gases during decomposition were also analyzed using Fourier transform infrared coupled with the thermogravimetric analyzer (TG-IR) technique. The char residues of the polyphosphoramides were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and Raman spectroscopy. The results showed that polyphosphoramides with sufficient molecular weights could be obtained, having high glass transition temperatures (T(g)s), high thermal stabilities, as well as lower flammability depending on the diamines incorporated. The char residues showed much difference among each other. Interestingly, one sample containing an ether group in the backbone exhibited a honeycomb-like char morphology, associated with a high degree of graphitization.