Bridged phosphorylated diamines: Synthesis, thermal stability and flame retarding properties in epoxy resins

The synthesis of different phosphorylated m-phenylenediamines is described. In this context a new synthetic pathway to 10-chloro-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-Cl) is reported. The reactivities of DOPO-Cl and 10-chloro-9,10-dihydro-9-oxa-10-phosphaphenanthrene (DOP-Cl) towards amines have been compared. Decomposition properties of the pure compounds have been determined by thermogravimetric analysis (TGA) and indicate a relationship between the chemical environment around the phosphorus atom and the thermostability of the corresponding compound. All substances were incorporated into the epoxy novolac resin system DEN438/DICY/Fenuron. Thermal as well as flame retarding properties of the cured epoxy resins have been investigated by differential scanning analysis (DSC) and UL-94 test. The changes of the glass transition temperature (Tg) and the decomposition temperature of the cured epoxy resins are small compared to the pure epoxy resin. The synthesized 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide (DOPS), diphenylphosphine sulfide (Ph2PO) and 5,5-dimethyl-1,3,2-dioxaphosphinane 2-sulfide (DDPS) derivatives exhibit a pronounced flame retardant effect in DEN438/DICY/Fenuron.