Thermal Properties and Flame Retardancy of Epoxy Resins Modified with Polysiloxane Containing Epoxy Groups and Redistributed Poly(2,6-dimethyl-l,4-phenylene) Chains

To improve the thermal property and flame retardancy of epoxy resins, a novel modifier was synthesized through the reaction between the redistributed product of poly(2,6-dimethyl-1 ,4-phenylene oxide) (REPPO) and the polysiloxane having pendant epoxy groups. Gel permeation chromatography (GPC) was used to confirm the redistribution reaction and identify the average molecular weight of the redistributed products. FTIR and 1H NMR measurements were employed to characterize the structures of the products. This REPPO-containing polysiloxane (PSREPPO) was used to modify a bisphenol A epoxy resin at different contents where 4,4 -diaminod iphenylmethane (DDM) acting as the curing agent. The cured samples were examined by scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and limited oxygen-index (LOI) methods. The SEM results showed that the use of PSREPPO has improved the phase compatibility and increased toughness of the samples. The DSC results showed that the modifier could improve the Tgs of the epoxy resins. An epoxy/PSREPPO ratio of 100/40 gives an increase of 26.53°C in its T9 value compared to the unmodified epoxy resin. The TGA resultsshowed that the Td50% of the samples increased also with the increase of PSREPPO content; although it decreased when the content of PSREPPO exceeded above a certain value . Char yield at 700°C and LOI values increased with the increase of the content of PSREPPO. In conclusion , the PSREPPO-modified samples improved the thermal properties and flame retardancy of the epoxy resins.