Synthesis and Flame Retardant Behavior of Phosphorous- and Nitrogen-Containing Copolymer and Its Application in Polypropylene

In this study, a 4-(hydroxymethyl)-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane 1-oxide (PEPA)-functionalized acrylate monomer, PEPAA, is designed and utilized for the synthesis of macromolecular flame retardants poly(PEPAA- co -AM) with varying PEPAA/AM ratio through copolymerization with acrylamide (AM). The poly(PEPAA- co -AM) is then incorporated into polypropylene (PP) to prepare PP/poly(PEPAA- co -AM) composites. The flame retardant effect of poly(PEPAA- co -AM) on PP is investigated using cone calorimetric test (CCT), and compared with that of PEPAA homopolymer (P-PEPAA), AM homopolymer (PAM), and blends of P-PEPAA/PAM. The results demonstrate that, in comparison with P-PEPAA, PAM, and blends of P-PEPAA/PAM, the incorporation of poly(PEPAA- co -AM) significantly enhances the flame retardancy of PP. Notably, the best flame retardancy is achieved when the ratio of PEPAA/AM copolymerization in poly(PEPAA- co -AM) is 2/8. The morphology and composition of residual chars from combustion are analyzed using SEM-EDS while the residual graphitization degree is examined through Raman spectroscopy. Additionally, TG-FTIR-MS is utilized to investigate the pyrolysis products in gas phase during thermal decomposition of poly(PEPAA- co -AM). Based on these experimental results, a flame retardant mechanism for poly(PEPAA- co -AM) is proposed. The PP/poly(PEPAA- co -AM) composites not only retain the excellent processing properties of pure PP but also exhibit enhanced mechanical properties.