The planar sheet structure is compared to linear polymer strands, not to a 3 dimensional cube polymer.
The strength advantage would be more like layers of carbon fiber cloth compared to loose fiberglass fibers. Even with the same resin the sheets have a significant advantage structurally.
>The new material is a two-dimensional polymer that self-assembles into sheets, unlike all other polymers, which form one-dimensional, spaghetti-like chains. Until now, scientists had believed it was impossible to induce polymers to form 2D sheets.
The existing thermoplastic polymers use 1D chains.
The thermosetting polymers are initially synthesized as 1D chains, but after they are made into their intended form, the curing reaction cross-links all the 1D chains into a 3D network.
Because of its 3D structure, a cured thermosetting polymer can no longer be dissolved or melted. At high temperatures it will decompose or burn, instead of melting.
However, the thermosetting polymers, unlike covalent crystals like diamond, boron or silicon, have a 3D structure with big holes in it, so they are permeable to gases and other substances with small molecules.
The 2D polymer discussed in the parent article has a 2D structure similar to graphite sheets, i.e. a dense 2D lattice, without holes or pores.
This dense structure allows applications that cannot be done with traditional polymer coatings. This coating should be inpermeable like a glass, without being fragile.
The fact that it is light, as mentioned in the title, is pretty much irrelevant, because this is a material that is suitable only for coatings on objects made of other materials, not for the bulk material of an object.
The article also said that one of biggest challenges with making 2D polymer was keeping it 2D without it going 3D. But there was no explanation why that would be worse.
Normally the molecules can only assemble in a chain. They can make solids in three dimensions by being long and making a big tangled mess. It's like extruding dough into spaghetti, then stirring it around to make a big tangled ball. Instead, they found a way to roll the dough out into an arbitrarily large flat lasagna-like noodle. Then they stacked them and found they stick to each other well and could make a much stronger material than the spaghetti ball. The only real limit being the amount of dough and a space to roll it out on.
All crystals are by definition self-assembled 3D lattices.
However, single crystals are inconvenient as materials, because growing a crystal (i.e. self-assembling it) is a slow process.
Moreover, growing a single crystal so that it will have some useful form is difficult for a few forms and impossible for most forms.
Therefore the normal way to make something from a single crystal is by growing a large crystal and then removing much of it, leaving only the desired form.
Because of this disadvantages, making anything out of a self-assembled 3D lattice, a.k.a. crystal, is restricted to a few applications where the properties of a single crystal are essential, i.e. various electronic or optical devices.
In most cases, the most convenient materials are either thermoplastic materials, i.e. metals, glasses or thermoplastic polymers, or materials that are produced in a soft plastic state and after forming they can be transformed into a hard state by some treatment, i.e. ceramics, cements or thermosetting polymers.
A disordered 3D lattice is an amorphous material, e.g. a glass (unlike a crystal, which is obtained by very slow cooling, to allow time for the self-assembling of the ordered lattice, a glass is obtained by very fast cooling, which does not allow time for ordered self-assembling) or a thermosetting polymer.
The strength advantage would be more like layers of carbon fiber cloth compared to loose fiberglass fibers. Even with the same resin the sheets have a significant advantage structurally.