Effect of functional groups of magnolol-based cyclic phosphonate on structure and properties of flame retardant epoxy resin

Abstract Functional group of a flame retardant may change performance and reaction mechanism of polymers to some extent. In this paper, magnolol-based cyclic phosphonates with double bond (DPDO) and epoxy group (EDPDO) were synthesized, and used in epoxy resin (EP). The EP/DPDO have better flame retardancy than that of EP/EDPDO in the UL-94 and LOI tests, while the pHRR of the latter decreases more that of the former in cone calorimetry test. Moreover, EP/EDPDO has higher glass transition temperature. Both DPDO and EDPDO do not deteriorate the mechanical properties and transparence of EP greatly. It is shown that the mechanism of the two is different. The DPDO is free in the resin, while the EDPDO is fixed in the framework of EP, therefore DPDO works in the gas and condensed phase, and EDPDO remains in the condensed phase. This work provides a simple solution to regulate the structure and performance of EP materials.