Synthesis of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide derivative grafted polyethylene films for improving the flame retardant and anti‐dripping properties

Two novel flame retardant and anti‐dripping PE films were successfully synthesized in three steps. PE‐g‐GMA film was first prepared by simultaneous electron beam irradiation to graft glycidyl methacrylate (GMA) onto PE film. 4,4′‐[1,4‐phenyl‐bis(9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐yl)dimethyneimino)]diphenol (DOPO‐t) and 4,4′‐[1,3‐phenyl‐bis (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐yl)dimethyneimino)]diphenol (DOPO‐m) were then fabricated via a one‐pot method. Finally, two DOPO derivative functionalized PE films were obtained through the ring opening reactions of PE‐g‐GMA film with DOPO‐t and DOPO‐m, respectively. Combustion properties, flame retardancy, thermal performance, and thermal shrinkage of these films were evaluated. Compared with pure PE film, the burning rate of anti‐dripping DOPO‐t/DOPO‐m functionalized PE films was reduced by 13.2% and 50.0%, and the limiting oxygen index value climbed to 18.5 and 19.5, respectively. The residual chars from DOPO‐t/DOPO‐m functionalized PE films at 700°C were increased, and the shrinkage ratio decreased remarkably, which could effectively prevent the spread of fire. We also discussed the effect of structural difference between DOPO‐t and DOPO‐m on the above properties and the flame retardant mechanism of two DOPO derivative functionalized PE films preliminarily. This work provides a method for introducing DOPO derivatives into PE molecules to improve their flame retardancy and anti‐dripping properties. We have synthesized two DOPO derivative functionalized PE films by simultaneous electron beam irradiation‐induced grafting and ring opening reaction. Compared with the pure PE film, the modified films show improved flame retardancy and anti‐dripping performance with more residual chars and lower thermal shrinkage. By contrast, DOPO‐m is superior to DOPO‐t in improving the above properties, and we further discuss the effect of the structural difference between DOPO‐t and DOPO‐m on the above properties and the flame retardant mechanism of two DOPO derivative functionalized PE films preliminarily.