It has always been evident that one can have a metal or a plastic, but not both, in one. However, a Chinese research team has recently described a polymer with a metallic backbone that is thermally stable, conductive and has intriguing optoelectronic capabilities in the journal Angewandte Chemie.
Image Credit: Angewandte Chemie
It is challenging to provide polymers with properties of a metal, such as strong thermal and electrical conductivity, due to the differing electronic structures of metal and nonmetal atoms. The benefits of both types of materials could be combined by polymers with metal backbones, which could also pave the way for the development of new functional materials.
The weak connections between the metal atoms that prevent a polymer backbone from stabilizing to the same degree as nonmetal atoms in traditional polymers are the source of the issue. A stable polymer with a nickel atom-based backbone has recently been created by a team led by Guowei Wang and Huisheng Peng.
Calixarene, a chalice-shaped molecule with four binding sites, was employed by the team from East China University of Science and Technology (Shanghai, China) and Fudan University as the “scaffold” for the metal polymer.
They bound four poly(aminopyridine) chains to the calixarenes, bundling and parallelizing the four chains. The chains can be constructed progressively from individual building blocks or by connecting multiple larger building blocks.
The team is able to construct chains of equal length by employing an iterative synthetic approach in which protective groups and end caps are bound and then eliminated. The metalation is then completed, and nickel can be bound by the nitrogen atoms in the chain molecules.
The nickel atoms are linked together in a single line because their distance from one another perfectly matches the distance of metal-metal connections.
X-Ray structural investigation revealed that the four poly(aminopyridine) chains stabilize the nickel chain by forming a helix around it. Thus, the team was able to produce polymers with a nickel backbone and precisely defined length.
They created variants with 3 to 21 nickel atoms. Interestingly, the Ni-Ni bonds are made stronger as the chain length grows since the distance between nickel atoms reduces.
The new materials can be processed in a solution and have properties like thermal stability and electrical conductivity. They show robust length-dependent light absorption with small band gaps, which is encouraging for semiconductors and optoelectronic devices. Other transition metals, including copper and cobalt, might be added to the new synthetic approach.
Journal Reference:
Zeng, K., et al. (2023) Metal-Backboned Polymers with Well-Defined Lengths. Angewandte Chemie International Edition. doi:10.1002/anie.202216060.