Studies on the thermal properties and flame retardancy of epoxy resins modified with polysiloxane containing organophosphorus and epoxide groups

A novel epoxy resin modifier, phosphorus-containing epoxide siloxane (PES) with pendant epoxide and cyclic phosphorus groups on the side chain of the polysiloxane backbone, was synthesized by the ring-opening reaction of epoxy-siloxane with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). PES was characterized by H-1 NMR and FT-IR measurements, and then it was employed to modify an epoxy resin at various ratios via pre-reaction with 4, 4'-diaminodiphenyl-methane (DDM) as curing agent. In order to compare with the epoxy resins modified with PES, DOPO-containing epoxy resins also cured under the same conditions. The thermal, thermomechanical, and flame-retardant properties of all cured polymers were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), the limited oxygen index (LOI) and cone calorimetry. The results showed that the epoxy resins modified with PES exhibited much better thermal properties and flame retardancy than the DOPO-containing epoxy resins at the same phosphorus content and the neat epoxy resin.