Thermally Conductive Polyimide/Boron Nitride Composite Films with Improved Interfacial Compatibility Based on Modified Fillers by Polyimide Brushes

Polyimide-based composite films with high thermal conductivity, good mechanical property and electrical insulating performance are urgently needed in the electronics and microelectronics fields. As one of the key technical challenges to be solved, interfacial compatibility between filler and matrix plays an important role for composite film. Herein, boron nitride was modified by grafting polyimide brushes via a two-step method, and a series of thermally conductive polyimide/boron nitride composite films were prepared. Both characterization and performance results proved that the interfacial interaction and compatibility was greatly enhanced, resulting in a significant reduction in defects and interfacial thermal resistance. The interphase width of transition zone between two phases was also efficiently enlarged due to polyimide brushes grafted on filler surface. As a result, composite films based on polyimide-grafted boron nitride exhibited significantly improved properties compared with those based on pristine filler. Tensile strength can reach up to 80 MPa even if the filler content is as high as 50 wt%. The out-of-plane and in-plane thermal conductivity of composite film increased to 0.841 and 0.850 W·m−1·K−1, respectively. In addition, thermal and dielectric properties of composite films were also enhanced to some extent. The above results indicate that surface modification by chemically grafting polymer brushes is an effective method to improve two-phase interfacial compatibility so as to prepare composite film with enhanced properties.