Post-modification of polyoxanorbornene via sequential "click" reactions for the preparation of flame retardant polymers

Ring -opening metathesis polymerization (ROMP) is a widely applicable method for synthesizing different macromolecular structures due to the diversity of functional groups, and the ROMP system has been widely studied in the literature for the preparation of flame retardant polyoxanorbonene (PONB) derivatives. This work aims to synthesize alpha-bromo ester functional PONB followed by grafting phosphorus groups by orthogonally sequential "click" reactions onto those PONBs. Thus, phosphorus groups incorporated covalently to the side chain and main chains of PONB by nucleophilic thio-bromo and radical thiol-ene "click" reactions, respectively. The effect of phosphorus content in the synthesized polymers on the thermal stability and decomposition properties was investigated by thermogravimetric analysis (TGA). The TGA tests revealed that char yield increases when phosphorus content increases, illustrating an efficient flame retardancy effect. The heat release peak value of polymers was decreased with increasing phosphorus groups from 67.60 W/g to 47.24 and 43.40 W/ g by microscale combustion calorimeter (MCC) measurement, respectively. Additionally, vertical and horizontal burning tests were conducted to determine whether phosphorus -containing PONBs have flame-retardant or selfextinguishing properties. According to the burning tests of polymer solutions -impregnated filter papers, it was noted that phosphorous -containing polymers showed slow ignition and self -extinguishing behavior.