Home Article

Light-triggered programmable network polymers show great potential

2020-04-05

Two plastic “springs” are being tested for their tension. One of them snaps when it is stretched to 1.5 times its original length while the other remains intact even when it is stretched to twice its original length. They are made of the same material, but they are different from each other inthat the second spring has been “light-triggered”.

Recently, the research team led by Prof. XIE Tao from the College of Chemical and Biological Engineering developed a topology isomerizable network (TIN), which can be programmed into many topological states with distinctive and spatially definable mechanical properties via a photo-latent catalyst. Their research findings are published in the March 27 issue of Science Advances.

Network topological isomerization via transesterification. UV, ultraviolet

Isomerization of small molecules is a basic concept in organic chemistry. For covalent polymers, the more bond connections in a single macromolecule there are, the more opportunities there will be. Non–cross-linked polymers with identical compositions can exist in various forms, ranging from linear to blocky, grafted, star-shaped, or even bottle-brushed architectures. This richness in macromolecular topology plays an essential role in polymer science, as it renders it possible to design materials with markedly different properties using the same set of monomer(s). Such topological control is, more often than not, achieved at the polymerization stage, and alterationsto topology are not permitted afterward. The same limitation also applies to covalent polymer networks, although the impact of network topology on physical properties is also well recognized.  

Dynamic covalent bonds, on the other hand, open up various avenues for the design of cross-linked polymer networks. Via reversible covalent bond breaking/reforming,recyclable/reconfigurable/self-healable network polymers can be fabricated. For these purposes, it is vital that the network topology should remain statistically identical throughout the bond exchange process.  

Against this background, researchers developed the novel TIN, at the core of which is the network topological heterogeneity. This stands in stark contrast with typical dynamic covalent polymer networks whose topology is non-programmable. A suite of factors, including the solid-state isomerization, the light-triggering mechanism, and the multiple topological states, further allow spatiotemporal topological patterning. Hence, a single network polymer can be programmed into an infinite number of polymers. A wide variety of materials with similar characteristics can be designed by exploring the rich library of dynamic covalent chemistry.  

Thanks to this proper network design, isomerization among many topologies (e.g., block, gradient, and random) can be achieved. Alternative designs may also include dynamic network mainframe, extending beyond the permanent mainframe for the current system. The wide design space allows access to different programmable materials to meet various demands. The conceptual device applications represent the tip of an iceberg, as the practical benefit has yet to be fully explored in many other technological areas such as artificial muscle, flexible electronics, and three-dimensional printing.