Novel organophosphorus flame retardants and their synergistic application in novolac epoxy resin

The novel oligomeric organophosphorus compounds oligo[DOPAc-2-TAEI] (oDOPI), oligo[DOPAc-1-DMPAc-1-TAEI] (oDOMPI) and oligo(DMPAc-2-TAEI) (oDMPI) were prepared in a one-pot process. At first, a Phospha-Michael-addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and/or dimethylphosphite (DMP) to tris(acryloyloxy)ethyl isocyanurate (TAEI) was carried out using a ratio that approximately one third of the acrylate groups remained, which were subsequently polymerized. The novel FR's as well as two commercially available flame retardants (FR's), a phosphazene (PZ) and a phosphorus-containing oligomeric compound with aromatic OH-groups, were incorporated into the epoxy novolac resin system DEN438/DICY/Fenuron, with and without the synergists melamine polyphosphate (MPP) and boehmite (AlO(OH)). The influence on glass transition temperature (T-g) was determined by differential scanning calorimetry (DSC) and the minimum phosphorus contents needed to pass the vertical burning test UL-94 with a V-O classification was identified. The synergistic approach, especially the addition of MPP, led to a highly increased performance with the amount of needed organophosphorus FR being reduced significantly without any drop of T-g. Most promising systems were investigated by TGA and cone calorimetry and the residue after the cone measurements was observed by scanning electron microscopy (SEM). These investigations indicate that the superior flame-retardant properties are evoked by formation of dense char combined with gas-phase action of the organophosphorus compounds. (C) 2018 Elsevier Ltd. All rights reserved.