Syntheses of Two Dopo-Based Reactive Additives as Flame Retardants and Co-Curing Agents for Epoxy Resins

GRAPHICAL ABSTRACT

Abstract

Two novel phosphorus-nitrogen-containing flame retardants, 1,1′,2,2′-tetra-hydroxyl-4′′, 4′′′-biphenylene-bis[amino-((10′′′′-O-10′′′′-H-9′′′′-oxa-10′′′′λ⁵-phosphaphenanthrene-10′′′′-yl))-methyl]}-bisphenol (3) and 1,1′,2,2′-tetra-hydroxyl-{4′′,4′′′-phenylene-bis[amino-((10′′′′- O-10′′′′- H-9′′′′- oxa-10′′′′λ⁵-phosphaphenanthrene-10′′′′-yl))-methyl]}-bis-phenol (4) were synthesized by two steps: 1,1′,2,2′-tetra-hydroxyl-{4′′,4′′′- bi-phenylene-bis[amino-methyl]}-bis-phenol, imine (1), was synthesized through condensation reaction between 3,4-dihydroxybenzaldehyde and 4,4′-diaminobiphenyl; and, 1,1′,2,2′-tetra-hydroxyl-{4′′,4′′′- phenylene-bis[amino-methyl]}-bis-phenol, imine (2) was synthesized by the reaction of 3,4-dihydroxybenzaldehyde and 1,4-phenylenediamine; then, addition reactions between 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide and the two imines, the (3) and (4) were obtained, respectively. (1)–(4) were characterized by FTIR, NMR, and MS. (3) and (4) reacted with epoxy resins as co-curing agents with 4,4′-diaminodiphenylmethane. Compared with control samples, (3) or (4) co-cured epoxy thermosets with phosphorus content of 1.0 wt% possessed good flame retardant properties with LOI value reaching more than 36.0, higher char yields. The glass translation temperature (T_g) of thermosets containing (3) or (4) were characterized with suitable changes by DSC test.

Keywords:

• Flame retardant
• epoxy resin
• thermal stability
• phosphorus