Flame-retardant epoxy resins from o-cresol novolac epoxy cured with a phosphorus-containing aralkyl novolac

Abstract

A novel phosphorus-containing aralkyl novolac (Ar-DOPO-N) was prepared from the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) first with terephthaldicarboxaldehyde and subsequently with phenol. The chemical structures of the synthesized compounds were characterized with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. Ar-DOPO-N blended with phenol formaldehyde novolac was used as a curing agent for o-cresol formaldehyde novolac epoxy, resulting in cured epoxy resins with various phosphorus contents. The epoxy resins exhibited high glass-transition temperatures (159-177°C), good thermal stability (>320°C), and retardation on thermal degradation rates. High char yields and high limited oxygen indices (26-32.5) were observed, indicating the resins' good flame retardance. Using a melamine-modified phenol formaldehyde novolac to replace phenol formaldehyde novolac in the curing composition further enhanced the cured epoxy resins' glass-transition temperatures (160-186°C) and limited oxygen index values (28-33.5).