Barrier and thermal properties of polyimide derived from a diamine monomer containing a rigid planar moiety

An aromatic polyimide (3,6-CPI) was prepared by the polymerization of pyromellitic dianhydride and diamine (3,6-CDA) containing a rigid planar carbazole moiety. The synthesized polyimide shows outstanding barrier properties with oxygen permeation rate and water vapor permeation rate low at 7.9 cm3 m−2 day−1 and 9.8 g m−2 day−1, respectively. Wide angle X-ray diffraction, positron annihilation lifetime spectroscopy and molecular dynamics simulations reveal that the excellent barrier properties of 3,6-CPI are mainly due to the crystallinity and low free volume of the polymer, which result from the rigid planar backbone structure and strong interchain hydrogen bonding. In addition, the polyimide exhibits excellent thermal stability and favorable mechanical properties with a 5 wt% weight-loss temperature of 559 °C in nitrogen, a glass transition temperature (Tg) of 397 °C and a tensile strength of 115.4 MPa. The as-synthesized polyimide shows potential packaging applications in the field of flexible electronics and displays, flexible and thin film photovoltaics, and light-emitting diodes. © 2017 Society of Chemical Industry