Preparation of polyimide-metal complexes with tunable Sol-Gel transition by Introduction of Zn(II)-Coordination

Developing fully rigid-chain polyimides with reversible sol-gel/gel-sol transitions is of great interest for designing high-performance materials. To date, few approaches have been employed to construct polyimide gels other than hydrogen bonding. Here, we report a polyimide-Zn(II) complex with thermo-responsive sol-gel/gel-sol transition behavior by introducing supramolecular coordination interactions. The tunable dynamic sol-gel behaviors of polyimide-Zn(II) complexes were confirmed using rheological methods. Microstructure analysis shows that coordination interactions occur between the benzimidazole molecules and Zn(II) ions. As a result, the apparent viscosity of the polyimide-Zn(II) complex even rises approximately four orders of magnitude higher than that of the PI-neat oligomer solution. Based on the 2D-correlation spectra and X-ray diffraction results, we deduced that the formation of dense chain stacking caused by coordination effects plays an essential part in the reversible sol-gel transition. As a preliminary experiment, this work gives a novel strategy to construct polyimide gels, showing application prospects in the fabrication of porous polyimide membranes, high-performance polyimide fibers, and aerogels, etc.