ZURICH, SWITZERLAND (March 9, 12 p.m. ET) — Swiss scientists have produced regularly ordered planar polymers for the first time. On the nanometer scale, the materials look like a sort of “molecular carpet.”
The research group was led by ETH Zürich (Swiss Federal Institute of Technology) scientists Dieter Schlüter and Junji Sakamoto. The Swiss Federal Laboratories for Materials Science and Technology (Empa) collaborated in the work.
The team had first to create monomer molecules constrained to join together purely two-dimensionally instead of linearly or even three-dimensionally. Two-dimensional polymers must have three or more covalent bonds between the regularly repeating monomer units. The scientists had to find out which mode of chemical bonding and which environment was most conducive to producing the “molecular carpet.”
The researchers decided to do the synthesis via a single polymer crystal – that is, a crystal with a flawlessly homogeneous laminar lattice. Research student Patrick Kissel generated photochemically sensitive monomers, for which polymerization in hexagonally configured layers is energetically optimal. Polymerization is triggered through irradiation by light with a wavelength of 470 nanometers. To separate the individual layers from one another the researchers boiled the crystal in a suitable solvent. Each layer was then a two-dimensional polymer.
Rolf Erni says: “It's really tricky to not destroy the 2D polymers when confirming their structure by transmission electron microscopy (TEM). This was a really tough nut to crack.”
Sakamoto says that one possible application of the 2D polymers is highly selective filtration of mixtures of very small molecules.
The work is reported in the peer-reviewed journal Nature Chemistry.