Polyimide‐polyurethane/urea block copolymers for highly sensitive humidity sensor with low hysteresis

Abstract

ABSTRACTPolyimide (PI)‐polyurethane‐urea (PU) block copolymers (PI‐PU75/25, PI‐PU50/50, and PI‐PU25/75) were prepared by reaction between anhydride‐terminated poly(amic acid) prepolymers with various number‐average degree of polymerization = 73/49/25) and isocyanate‐terminated urethane‐urea prepolymers with various (11/21/31) to obtain high performance capacitive humidity sensors. Pure PI and PU were also prepared to compare with PI‐PU copolymers. This study examined the effect of PU content on the water absorption %/water vapor transmission rate, thermal and mechanical properties and sensing properties of PI‐PU block copolymers. The thermal stability and mechanical properties of the copolymer decreased markedly with increasing PU content. The sensitivity of sensor increased sharply with increasing PU content from 0 to 25 wt %, and then increased a little. The hysteresis of sensor decreased sharply with increasing PU content up to 50 wt %, and then decreased a little. These results demonstrate the apparent upside of using two copolymers (PI‐PU75/25 and PI‐PU50/50) compared to using pure PI, in terms of sensor performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44973.