Epoxy-Functionalized Polysiloxane and DOPO Synergistically Enhance Flame Retardancy of Epoxy Resin Composites

A series of intrinsic flame-retardant epoxy resins were prepared by adding dual epoxy-functionalized polysiloxane (PDMS-GE) and DOPO to the epoxy resin (EP) of the DGEBA/DDM (60/20) system for curing reaction. The results showed that PDMS-GE and DOPO had excellent synergistic flame retardancy on EP, which was conducive to the formation of large-sized SiO2 particles and the formation of stable and dense char when the material burns. In this work, the LOI of the composite DGEBA/DDM/PDMS-GE/DOPO (60/20/5/5) reached 37.3, which was better than that of the material with only PDMS-GE or DOPO added and was 11.4 higher than that of neat EP. Compared with neat EP, the PHRR and THR of the CCT test were also reduced by 51.0 and 48.0%, respectively, and its UL-94 test reached the V-0 level. At the same time, the material also showed good hydrophobicity, and its water contact angle reached 102.63°. Based on the good dielectric properties and molecular chain flexibility of the PDMS structure, the dielectric constant of the prepared composite material at 14.2 GHz was reduced to 2.63, and the impact strength was also improved by about 33% relative to neat EP.