Preparation of Thermally Conductive and Flame Retardant Epoxy Composites from Polyethylenimine–Boron Nitride Skeleton and Phosphate Ester Hyperbranched Flame Retardant

In the electronics field, the demand for polymer-based interface materials with high thermal conductivity is increasing. In this study, a three-dimensional thermally conductive framework was fabricated using a bidirectional freezing technique, incorporating hexagonal boron nitride (h-BN) as the primary filler and polyethylenimine (PEI) as the binder. Moreover, a phosphate ester hyperbranched flame retardant (DTFR) was synthesized. It was miscible with the epoxy (EP) prepolymer, allowing the flame retardant to be immersed into the three-dimensional thermal conductivity skeleton along with the EP prepolymer. The thermal conductivity of EP composites was increased to 1.35 W m^–1 K^–1 by introducing only 12.5 vol % of h-BN, exhibiting an increase of 744% compared to that of control EP. In addition, the peak of heat release rate and total heat release of EP composites containing 4% DTFR was significantly reduced by 41.5 and 34.9%, respectively, and the limiting oxygen index was improved from 23.7 to 31.5% compared with that of control EP. This work was believed to provide an interesting and promising strategy for preparing EP composites with good thermal conductivity, homogeneous fire safety, low dielectric constant, and low dielectric loss.