Two Worlds, One Material

Polymers with a metal backbone

Until now, it has been clear: you can have a metal or a plastic, but
not both in one. However, things don’t have to stay that way. In the
journal Angewandte Chemie, a Chinese research team has now
reported a polymer with a metallic backbone that is conductive,
thermally stable, and has interesting optoelectronic properties.

Two Worlds, One Material - Polymers with a metal backbone

© Wiley-VCH, re-use with credit to ‘Angewandte Chemie’ and a link to the original article.

Because of the different electronic structures of metal and nonmetal
atoms, it is difficult to confer the properties of metals, such as high
thermal and electrical conductivity, upon polymers. Polymers with a
metal backbone could combine the advantages of both types of material
and open routes to materials with novel functionality. The problem lies
in the weak bonds between the metal atoms, which cannot stabilize a
polymer backbone to the same extent as the nonmetal atoms of
conventional polymers. A team led by Guowei Wang and Huisheng Peng has
now successfully synthesized a stable polymer with a backbone made of
nickel atoms.

The team at Fudan University and East China University of Science and
Technology (Shanghai, China) used a chalice-shaped molecule
(calixarene) with four binding sites as the “scaffold” for the metal
polymer. They attached four poly(aminopyridine) chains to the
calixarenes, which bundles the four chains and aligns them in parallel.
Synthesis of the chains can be carried out stepwise from individual
building blocks or several larger blocks can be linked together. By
using an iterative synthetic procedure in which protective groups and
end caps are bound and then removed, the team is able to produce chains
of equal length. They then carry out the metalation. The nitrogen atoms
of the chain molecules can bind nickel. Their distance from each other
exactly matches the distance of metal-metal bonds, causing the nickel
atoms to link together in a single line. The four poly(aminopyridine)
chains wrap around the nickel chain in a helix, as shown by X-ray
structure analysis, and stabilize it. The team was thus able to
synthesize polymers with a nickel backbone and precisely controlled
length. They produced versions with three to 21 nickel atoms.
Interestingly, the distance between nickel atoms decreases as the chain
length increases, strengthening the Ni-Ni bonds.

The new materials may conduct electricity, are thermally stable, and
can be processed in solution. They demonstrate strong length-dependent
light absorption with narrow band gaps, which is promising for
optoelectronic devices and semiconductors. The new synthetic strategy
could also be expanded to other transition metals such as copper and

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About the Author

Dr. Huisheng Peng is
a Chair Professor at the Department of Macromolecular Science at Fudan
University. His research centers on smart polymer fiber materials and
devices. He is recognized as a pioneer of fiber electronics.

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