High-performance copolyimide fibers containing quinazolinone moiety: Preparation, structure and properties

Copolyimide (co-PI) fibers with superior mechanical properties and high thermal stability were developed via a two-step polymerization/imidization process based on a new design of introducing an aromatic heterocyclic diamine monomer, 2-(4-aminophenyl)-6-amino-4(3H)-quinazolinone (AAQ) into rigid homopolyimide backbones of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (p-PDA). Effects of the incorporated AAQ moieties on the micro-structure and properties of the prepared fibers were investigated. Fourier transform infrared (FTIR) results indicated that hydrogen bonding is formed between the AAQ and cyclic imide units that effectively strengthens the intermolecular interactions. This has been considered to be the key factor responsible for the significantly enhanced mechanical properties of the co-PI fibers. Two-dimensional wide angle X-ray diffraction (2D WAXD) spectra showed that the co-PI fibers are highly oriented with well-ordered 2D structures along both the fiber and transverse directions. The co-PI fibers reached the optimum tensile strength and modulus of 2.8 GPa and 115 GPa, respectively, at the AAQ/p-PDA molar ratio of 5/5. The fiber also exhibited high thermal stability, with a 5%-weight-loss temperature of 599 °C under N2 and 564 °C in air.