Fabrication, mechanical and electrical properties of polyimide films cured at low-temperature assisted by microwave radiation

Polyimide (PI) films with excellent mechanical and electrical properties were produced at a low temperature assisted by microwave. Depending on the reciprocating movement of dipole molecules excited by microwave, even though under a low temperature, the rotation and conformational changes of functional groups could also be promoted. Thus, reaction between N-H bond and -OH in carboxyl which could realize dehydration and cyclization of polyamic acid proceeded normally. Results revealed that the combination between ambient temperature only at 70°C and microwave power at 2000 W or higher could also produce PI films with imidization degree of 100%. For PI-2000W, compared with traditional PI film (PI-300°C) that generated only at temperature of 300°C, even though on the basis of no any change in molecular structure and addition of filler, the tensile strength, elastic modulus, crystallinity, and apparent density increased by about 21%, 51%, 37%, and 5%, respectively. For electrical properties, conductivity enhanced by one to two orders of magnitude comparing with PI-300°C. Results indicated that while keeping the original molecular structure of PI films unchanged, this work provided a new and effective method to assist the enhancement in mechanical and electrical properties of PI films.