Significant Improvement in the Flame Retardancy and Thermal Conductivity of the Epoxy Resin via Constructing a Branched Flame Retardant Based on SI-ATRP Initiated by Dopamine-Modified Boron Nitride

The rapid development of integrated circuits and micro-devices has brought serious thermal failure and huge fire hazards to polymer composites due to the inefficient heat dissipation. Here, in order to simultaneously achieve the excellent thermal conductivity (TC) and flame retardancy (FR) of composites, we proposed a strategy of grafting a flame retardant on the surface of an exfoliated boron nitride nanosheet (BNNS). Briefly, the atom transfer radical polymerization (ATRP) reaction was initiated on the surface of the BNNS with predeposited polydopamine to obtain poly(glycidyl methacrylate) (PGMA) chain with high graft density, and then the flame-retardant molecule 6H-dibenz(C,E)(1,2)oxaphosphorin-6-oxide (DOPO) was further decorated to form a flame-retardant functionalized BNNS with branched structure. Due to the improvement of interfacial compatibility, the BNNS exhibits uniform dispersion and robust interfacial interaction with the epoxy resin (EP), which will further promote the formation of heat conduction paths and the reduction of interfacial thermal resistance (Rb). In particular, the EP composite containing 30 wt % BNNS-DOPO exhibits a TC of 1.25 W/m·K, exceeding that of the composite loaded with serious aggregated BNNS by 32%. Simultaneously, the EP composite with only 20 wt % BNNS-DOPO presents a superior FR with an obvious decrease in the values of peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) compared to EP, corresponding to a reduction of 47.6, 44.7, 46.5, and 50%, respectively. The enhanced FR is mainly ascribed to the catalytic carbonization of DOPO, and the continuous and compact protective layer formed by the char combined with the BNNS effectively prevents the exchange of heat, oxygen, and volatile gases. Therefore, this surface modification strategy of the BNNS provides a new idea for exploring thermally conductive and flame-retardant composites.