Synthetic organic polymers, unlike single crystals, are usually insoluble and exist as polycrystalline or amorphous products. The ability to synthesize single-crystal porous polymers has been a challenge in the field of polymer science and crystal engineering.
However, in nature, many biomacromolecules achieve single-crystal form through multiple supramolecular interactions. This suggests that reversible supramolecular interactions can be utilized to control the crystallinity of porous polymer materials.
In a recent publication in Nature Synthesis, Prof. Liu Tianfu and Prof. Cao Rong from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences presented a novel strategy for producing single crystals of a porous polymer.
Inspired by the hierarchical structures observed in natural protein crystals and certain nucleic acids, the researchers hypothesized that a combination of 1D covalent chains with tunable dynamic covalent bonds and supramolecular interactions could lead to the direct synthesis of a single-crystal porous polymer with specific cavities, ion channels, and functionalities.
Through a one-pot synthesis, they successfully designed and created a single-crystal porous polymer called PHOF-1, which is based on a hydrogen-bonded organic framework. The structure of PHOF-1 was confirmed using single-crystal X-ray diffraction studies.
The researchers discovered that monomers of 1,4-phenylenebisboronic acid polymerize into a tetramer, forming a nine-membered B4O52- cluster (primary structure). This cluster further extends into 1D covalent chains (secondary structure) that are cross-linked through hydrogen bonds and electrostatic interactions (tertiary structure), ultimately resulting in a hydrogen-bonded organic framework (quaternary structure).
In contrast to insoluble 2D or 3D crosslinked porous polymers, the 1D polymer chains exhibited excellent solubility and solution processability. When dissolved, PHOF-1 maintained its 1D chain structure with a narrow molecular weight distribution and could transition reversibly between single-crystal and amorphous states depending on the rate of solvent evaporation.
Leveraging its solution processibility, the researchers successfully coated PHOF-1 onto a non-woven fabric, creating a functional composite textile capable of capturing NH3 (ammonia).
This innovative design strategy could pave the way for the development of single-crystal porous polymer materials with precise structural information, confined pore spaces, and easy solution processibility.
Source: Chinese Academy of Sciences