Novel flame retardant thermosets from nitrogen-containing and phosphorus-containing epoxy resins cured with dicyandiamide



A novel phosphorus-containing epoxy resin (EPN-D) was prepared by addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and epoxy phenol- formaldehyde novolac resin (EPN). The reaction was monitored by epoxide equivalent weight (EEW) titration, and its structure was confirmed by FTIR and NMR spectra. Halogen-free epoxy resins containing EPN-D resin and a nitrogen-containing epoxy resin (XT resin) were cured with dicyandiamide (DICY) to give new halogen-free epoxy thermosets. Thermal properties of these thermosets were studied by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), thermal mechanical analyzer (TMA) and thermal-gravimetric analysis (TGA). They exhibited very high glass transition temperatures (Tgs, 139–175°C from DSC, 138–155°C from TMA and 159–193°C from DMA), high thermal stability with Td,5 wt % over 300°C when the weight ratio of XT/EPN-D is ≥1. The flame-retardancy of these thermosets was evaluated by limiting oxygen index (LOI) and UL-94 vertical test. The thermosets containing isocyanurate and DOPO moieties showed high LOI (32.7–43.7) and could achieve UL-94 V-0/V-1 grade. Isocyanurate and DOPO moieties had an obvious synergistic effect on the improvement of the flame retardancy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007