Phosphorus‐Containing Epoxy Curing Agents via Imine Linkage

Abstract

Two new phenol‐type curing agents, (3) and (4), were synthesized by the condensation of 4 (or 2)‐hydroxybenzaldehyde and 4‐aminophenol, followed by the addition of DOPO to the resulting imine linkage. Two reaction mechanisms, conjugate‐addition and carbocation mechanisms, were proposed. The fact that the ratio of the configuration of the two diastereomers depends on the reaction solvent indicates that the carbocation mechanism is the more reasonable one. (3) and (4) served as curing agents for epoxy resins, and the resulting epoxy thermosets exhibited good flame retardancy, and moderate Tg and thermal stability. The nitrogen‐phosphorus synergistic effect explains the high flame retardancy.magnified image

Syntheses and characterization of two novel 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-based flame retardants for epoxy resin

“…What's more, the T g values of (4)/DDM were slightly higher than that of (4)/DDM with the same phosphorus content, potentially due to that (4)/DDM owned higher cross-linking density than that of the (3)/DDM system for compound (4) possessing one more benzene ring.…”

“…The two novel phosphorus-nitrogen-containing FRs (3) and (4) are obtained by the addition reaction between two imines with DOPO, respectively. Their structures are characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance ( 1 H NMR), carbon ( 13 C) NMR, phosphorous ( 31 P) NMR, and mass spectroscopy (MS).…”

Preparation of phosphorus‐containing phenolic resin and its application in epoxy resin as a curing agent and flame retardant

“…Accordingly, flame‐retardant modification for EP is significant and important for extending the applications . Many methods have been developed to achieve the goal in the previous investigations . So far, there are 2 conventional methods for preparing flame‐retardant EP: physically adding flame retardants into EP (additive type) and chemically combining flame‐retardant elements with EP chains (reactive type) .…”

Flame‐Retarded Epoxy Resins with a Curing Agent of DOPO‐Triazine Based Anhydride

“…As a consequence, a detrimental effect on other properties of the cured epoxy resins emerges. For instance, the glass transition temperature ( T g ) of DGEBA‐based epoxy thermoset bearing flame retardant DOPO group dropped significantly about 14–50 °C in order to meet the V‐0 rating of UL 94 …”