Thermal properties and flame retardancy of novel epoxy based on phosphorus-modified Schiff-base

Through addition reaction of Schiff-base terephthalylidene-bis-( p -aminophenol) ( DP-1 ) and diethyl phosphite (DEP), a novel phosphorus-modified epoxy, 4,4'-diglycidyl-(terephthalylidene-bis-( p -aminophenol))diphosphonate ether ( EP-2 ), was obtained. An modification reaction between EP-2 and DP-1 resulted in an epoxy compound, EP-3 , possessing both phosphonate groups and CN imine groups. The structure of EP-2 was characterized by Fourier transform infrared (FTIR), elemental analysis (EA), 1 H, 13 C, and 31 P NMR analyses. The thermal properties of phosphorus-modified epoxies cured with 4,4'-diaminodiphenylmethane (MDA) and 4,4'-diaminodiphenyl ether (DDE) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The activation energies of dynamic thermal degradation ( E d ) were calculated using Kissinger and Ozawa's methods. The thermal degradation mechanism was characterized using thermogravimetric analysis/infrared spectrometry (TG-IR). In addition, the flame retardancy of phosphorus-modified epoxy thermosets was evaluated using limiting oxygen index (LOI) and UL-94 vertical test methods. Via an ingenious design, phosphonate groups were successfully introduced into the backbone of the epoxies; the flame retardancy of phosphorus-modified epoxy thermosets was distinctly improved. Due to incorporation of CN imine group, the phosphorus-modified epoxy thermosets exhibited high thermal stabilities; the values of glass-transition temperatures ( T g s) were about 201–210°C, the values of E d were about 220–490 kJ/mol and char yields at 700°C were 49–53% in nitrogen and 45–50% in air. These results showed an improvement in the thermal properties of phosphorus-modified epoxy by the incorporation of CN imine groups. Copyright © 2010 John Wiley & Sons, Ltd.