Enhancing thermal dimensional stability of polyimide composite films through in-situ constructing highly interfacial grafting degree to constrain early chain relaxation

Flexible polyimide composite films (PIFs) with superior thermal properties are critical for ever-accelerable developed flexible display technology. Herein, we proposed thermal dimensional stability of PIFs can be improved with assistance of constraining early relaxation of macromolecular chains. The constrained structure was successfully architected through mechano-mixing fluorinated multi-walled carbon nanotube (F-MWCNT) into benzimidazole-contained PI (PABZ-PI). Through constraining early chain relaxation behaviors via utilizing advantage of high interfacial grafting degree between N–H of benzimidazole in PI and C–F in F-MWCNT, experimental results manifested the half-peak widths of Tan δ curves of composite films (PABZ-PI/F-MWCNT) were noticeable narrowed 34%–51%, thus making their coefficient of thermal expansion (CTE) significantly decreasing. Compared with benzimidazole-contained PI without introducing nanofillers, only adding 2 wt% F-MWCNT (PABZ-PI/F-MWCNT-2), the initiating relaxation temperature of PABZ-PI/F-MWCNT-2 improved 49%, and the CTE value noticeably reduced 64%. In addition, the glass-transition temperature (T g ) of composite films was high up to 422 °C–426 °C. Besides, tensile strength increased, water absorption decreased and electrical insulations of composite films were well maintained.