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 (T(g)s, 139-175 degrees C from DSC, 138-155 degrees C from TMA and 159-193 degrees C from DMA), high thermal stability with T-d,T-5 (wt) (%) over 300 degrees 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. (c) 2007 Wiley Periodicals