In situ phase separation of novel phosphorus-containing polyester in epoxy resins towards simultaneously improved thermal conductivity and fire safety

•A novel phosphorus-containing polyester (PBHPI) was synthesized and used for RIPS.•Phase-separated structures were in situ formed via RIPS between EP and PBHPI.•BNNSs were localized at the interface to construct thermally conductive networks.•The resultant composites concurrently showed fire safety and thermal conductivity.