Synthesis of charring agent and its derivatives of dipentaerythritol polycyclicphosphonates flame retardants

Charring agent (dipentaerythritol (DPER) biphosphite) was synthesized and characterized by Fourier transform infrared (FTIR), hydrogen nuclear magnetic resonance, and elemental analysis. Then, three halogen-free intumescent flame retardants, DPER biphosphite trimethyl phosphate (DTMP), DPER biphosphite triethyl phosphate (DTEP), and DPER biphosphite dimethyl methyl phosphonate (DDMMP) were prepared and highly thermally stable polymers were obtained. FTIR demonstrated that new peaks of P–C and P=O were formed in the three FRs in comparison with that of DPER biphosphite. Thermogravimetric analysis indicated that DPER biphosphite could have a profound effect on increasing char yield and P–C bonds confer a higher thermal stability to the polymers. The results of UL-94 burn test showed that the polymers prepared had good flame retardance.