A new thermally conductive polyimide composite film has been developed. It is based on a dispersion of different particle sizes of boron nitride (BN) in a polyimide (PI) precursor, polyamic acid (PAA). Subsequently, thermal imidization of PAA at 350 °C produced the corresponding polyimide composites. 3-Mercaptopropionic acid was used as the surfactant to modify the BN surface for the dispersion of BN in the polymer. The PI/BN composites showed different thermal conductivities at different proportion of BN particle sizes and contents. The thermal conductivity of the PI/BN composite was up to 1.2 W/m-k, for a mixture containing 30 wt % of micro and nanosized BN fillers in the polyimide matrix. The PI/BN composites had excellent thermal properties. Their glass transition temperatures were above 360 °C, and thermal decomposition temperatures were over 536 °C.
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