Molecularly engineered copolyimide film for capacitive humidity sensor

•Various copolyimides were successfully synthesized by simple molecular blending.•Polyimide with fluorine group efficiently reduced hysteresis of humidity sensor.•Humidity sensor performances were improved by controlling hydrophobicity of polyimide. We present a capacitive humidity sensor with molecularly engineered polyimide (PI) sensing layer. Molecularly engineered PIs were successfully prepared by synthesizing polyamic acids (PAAs) through blending of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6-FDA) as monomer, followed by thermal imidization, respectively. The molecularly engineered PIs exhibited high thermal stability as well as controllable water uptake properties. Capacitive performances of the humidity sensor with PIs were efficiently increased via simple molecular blending.