Researchers Develop Highly Flexible Polymers Sensitive to Light

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Researchers from Massachusetts Institute of Technology designed a polymer material sensitive to light that can heal itself when damaged.

The research led by Jeremiah Johnson, an associate professor of chemistry at MIT designed a polymer material capable of changing its structure in response to light. This unique property enables the material to alter from a rigid substance to a softer one and heal itself when damaged. The breakthrough material comprises polymers attached to a light-sensitive molecule that aids to change the bonds formed within the material. Such materials are expected to offer wide variety of applications such as coating of cars or satellites that enable quick healing after being damaged. The researchers worked on a previously developed polymer metal-organic cages (polyMOCs) that comprises metal-containing, cage-like structures joined together by flexible polymer linkers. It was created by mixing polymers attached to groups called ligands capable of binding to a metal atom such as palladium. Palladium bonds with four ligand molecules, which in turn creates rigid cage-like clusters with varying ratios of palladium to ligand molecules.

In the current experiment, the researchers aimed to design a material capable of reversibly switching between two different-sized cages. One cage consisted 24 atoms of palladium and 48 ligands and the other with three palladium atoms and six ligand molecules. A light-sensitive molecule called DTE was incorporated into the ligand. Rings are formed in the ligand when DTE is exposed to ultraviolet light. The formation increases the size of the angle at which nitrogen can bond to palladium, which in turn facilitates breaking of the clusters to form larger clusters. When the material was exposed to green light, the ring broke with small bond angles that resulted in reformation of smaller clusters. The process takes about five hours to complete and around seven reversals were achieved with a small percentage of polymers failing to switch back after each reversal, after which the material eventually fell apart. It was observed that the polymers were 10 times softer when the material was in the small-cluster state. The research was published in the journal Nature on July 18, 2018.

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