Synthesis and Permselectivity of a Soluble Two-Dimensional Macromolecular Sheet by Solid–Solid Interfacial Polycondensation Followed by Chemical Exfoliation

Two-dimensional (2D) network polymers with nano-sized pores are generally insoluble, and therefore, it is difficult to determine their molecular structures and to fabricate their membranes. Soluble 2D network polymer membranes with angstrom-sized pores and thicknesses have not been reported. Herein, novel soluble 2D macromolecular sheets with angstrom-sized pores (24.6 Å) and thickness (3.4 Å) are synthesized by solid–solid interface polycondensation in laminated membranes of two cis–cisoid poly(imino-containing phenylacetylene)s followed by highly selective photocyclic aromatization (SCAT). First, a two-layered laminated polymer membrane that is self-supporting is prepared, and solid–solid interfacial polycondensation is performed. The insoluble three-dimensional (3D) network polymer layer formed is isolated by removing the soluble unreacted polymer layers. Finally, a SCAT reaction is carried out by irradiation of visible light on the insoluble 3D membrane to produce a soluble 2D macromolecular sheet. The precise 2D molecular structure can be displayed, such as the degree of polymerization, thickness, fraction of rings (pores), and pore size, estimated by GPC, AFM, 1H-NMR, IR, and XRD, because the macromolecule is soluble. Composite membranes containing the 2D macromolecular sheet show good oxygen permselectivity exceeding the Robeson upper line, possibly because the angstrom-sized pores and thicknesses produce high oxygen permselectivity without suppressing the permeability.