Intrinsic high-barrier polyimide with low free volume derived from a novel diamine monomer containing rigid planar moiety

An intrinsic high-barrier and thermally stable polyimide (2,7-CPPI) was prepared by the polymerization of pyromellitic dianhydride (PMDA) and novel diamine (2,7-CPDA), which consists of rigid planar carbazole moiety. The resulted 2,7-CPPI exhibits excellent barrier properties, with oxygen transmission rate and water vapor transmission rate low to 0.2 cm3 m−2·day−1 and 0.1 g m−2·day−1, respectively. Wide angle X-ray diffractograms (WAXD), positron annihilation lifetime spectroscopy (PALS) and molecular dynamics simulations reveal that the excellent barrier properties of 2,7-CPPI are mainly ascribed to the crystallinity, high chain rigidity and low free volume, which are resulted from the rigid planar structure and strong hydrogen bonding among molecular chains. Meanwhile, 2,7-CPPI also presents outstanding thermal stability and mechanical properties with a glass transition temperature of 437 °C, 5 wt % loss temperature of 556 °C under N2, coefficient of thermal expansion of 2.89 ppm/K and tensile strength of 143.8 MPa. The polyimide shows attractive potential applications in flexible electronics and high-grade packaging area, especially using as the substrates for top-emitting OLEDs display.