Thermal conductive hybrid polyimide with ultrahigh heat resistance, excellent mechanical properties and low coefficient of thermal expansion

It is a great challenge to fabricate flexible substrate materials with an ultrahigh heat resistance, low coefficient of thermal expansion (CTE) and high thermal conductivity, which is required to process low temperature poly-silicon thin film transistors in active matrix organic light-emitting-diode devices. Despite the development of new monomers is also possible to simultaneously improve the heat resistance and dimensional stability of polyimides, the space for improvement is limited and the cost is greatly increased. Traditional polymer nanocomposites can increase the glass transition temperature (T-g) and reduce the CTE, but they cause a significant drop in mechanical properties. Herein, an amino-functionalized boron nitride nanosheets (BNNS_APS) hybrid polyimide (PI) was prepared by in situ polymerization. The hybrid PI exhibited ultrahigh heat resistance, excellent thermal conductivity, low CTE and good mechanical properties with 1 wt% BNNS_APS doping. The T-g of the hybrid PI was improved up to 473 degrees C and the thermal conductivity was increased by 100% compared with pure PI. The CTE. was less than 7 ppm/K, and the tensile strength and elongation at break increased to 336 MPa and 16.6%, respectively. These results are attributed to the good dispersion of BNNS_APS in the PI matrix and the strong interactions between the BNNS_APS and PI chains. The mechanism was proposed and discussed in detail.