IBM invents tough polymers

IBM Research has announced new thermosetting polymers, claimed variously to be resistant to cracking, strong, self-healing, and completely recyclable.

IBM polymer with carbon nanotubes

It was designed by combining high-performance computing and synthetic polymer chemistry.

“Two related classes of materials have been discovered which possess a very distinctive range of properties that include high stiffness, solvent resistance, the ability to heal themselves once a crack is introduced, and can be used as a resin for filled composite materials to further bolster its strength,” said the firm.

According to IBM’s paper in Science – ‘Recyclable, strong thermosets and organogels via paraformaldehyde condensation with diamines

One class has been dubbed ‘hemiaminal dynamic covalent networks’ (HDCNs), formed by a reaction between paraformaldehyde and 4,4ʹ-oxydianiline (ODA).

After heating to drive off trapped solvent and re-arrange covalent bonds, these form stronger, but more brittle poly(hexahydrotriazine)s (PHTs) – the other new class of polymer.

Both are thermosetting polymers. HDCNs are flexible, and PHTs have high Young’s moduli (up to ~14Gpascal (similar to bone), or 20GPa after reinforcement with carbon nanotubes).

This compares with 2-4GPa for nylon and 17GPa for glass-reinforced polyester.

Unlike most thermosetting plastics, both HDCNs and PHTs can be digested for recycling – using strong acid (PH<2) to recover bisaniline monomers.

However, both are resistant to weak acid, and any alkaline.

If poly(ethylene glycol) diamine monomers are used to form HDCNs, the result is elastic gels which incorporate the production solvent.

If these gels are cut, and touched back together, chemical bonds reformed to make a single object again within seconds – due to hydrogen-bonding in the hemiaminal polymer network.

These could be seen as adhesives or for mixing with other polymers to induce self-healing properties.

“We’re now able to predict how molecules will respond to chemical reactions and build new polymer structures with significant guidance from computation that facilitates accelerated materials discovery,” said IBM scientist James Hedrick. “This is unique to IBM and allows us to address the complex needs of advanced materials for applications in transportation, microelectronic or advanced manufacturing.”

Common plastics are: polyesters (cloths and drink bottles), polyacrylics (paints), polyethylene (milk containers), polyolefins (food packaging), polystyrene (phased out from food packaging), structural polymers (epoxies, polyamides and polyimides) (cars and planes).

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