The new 2D polymer, named 2DPA-1, is stronger than steel and as light as plastic; it self-assembles into sheets, unlike all other polymers, which form spaghetti-like 1D chains.
2DPA-1 is a 2D polymer that self-assembles into sheets and could be used as a lightweight, durable coating for car parts or cell phones, or as a building material for bridges or other structures. Image credit: Christine Daniloff, MIT.
Polymers, which include all plastics, consist of chains of building blocks called monomers. These chains grow by adding new molecules onto their ends.
Once formed, polymers can be shaped into 3D objects, such as water bottles, using injection molding.
Polymer scientists have long hypothesized that if polymers could be induced to grow into a 2D sheet, they should form extremely strong, lightweight materials.
However, many decades of work in this field led to the conclusion that it was impossible to create such sheets.
However, MIT Professor Michael Strano and and his colleagues came up with a new polymerization process that allows them to generate a 2D sheet called a polyaramide.
For the monomer building blocks, they use a compound called melamine, which contains a ring of carbon and nitrogen atoms.
Under the right conditions, these monomers can grow in two dimensions, forming disks.
These disks stack on top of each other, held together by hydrogen bonds between the layers, which make the structure very stable and strong.
“Instead of making a spaghetti-like molecule, we can make a sheet-like molecular plane, where we get molecules to hook themselves together in two dimensions,” Professor Strano said.
“This mechanism happens spontaneously in solution, and after we synthesize the material, we can easily spin-coat thin films that are extraordinarily strong.”
Because the material self-assembles in solution, it can be made in large quantities by simply increasing the quantity of the starting materials.
The researchers showed that they could coat surfaces with films of the material, which they call 2DPA-1.
“With this advance, we have planar molecules that are going to be much easier to fashion into a very strong, but extremely thin material,” Professor Strano said.
The scientists found that the elastic modulus of 2DPA-1 — a measure of how much force it takes to deform a material — is between four and six times greater than that of bulletproof glass.
They also found that its yield strength, or how much force it takes to break the material, is twice that of steel, even though the material has only about one-sixth the density of steel.
Another key feature of 2DPA-1 is that it is impermeable to gases. While other polymers are made from coiled chains with gaps that allow gases to seep through, the new material is made from monomers that lock together like LEGOs, and molecules cannot get between them.
“This could allow us to create ultrathin coatings that can completely prevent water or gases from getting through,” Professor Strano said.
“This kind of barrier coating could be used to protect metal in cars and other vehicles, or steel structures.”
The study is published in the journal Nature.
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Y. Zeng et al. 2022. Irreversible synthesis of an ultrastrong two-dimensional polymeric material. Nature 602, 91-95; doi: 10.1038/s41586-021-04296-3
