We synthesized a series of chalcone-based polyphosphonates and polyurethanes as self-extinguishing flameretardant polymers and characterized them via FTIR, 1 H, 13 C, 31 P NMR, HRMS, gel permeation chromatography, and inductively coupled plasma−optical emission spectrometry. The thermal stability of the synthesized polymer series was tested by thermogravimetric and evolved gas analysis under both N 2 and air atmospheres as well as microscale combustion calorimetry analysis. After thermal treatment, residue analysis was carried out using scanning electron microscopy with energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy, and decomposition mechanisms are proposed.