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New class of industrial polymers

News International-French

19 May 2014

Scientists from IBM Research have discovered a new class of polymer materials that can potentially transform manufacturing and fabrication in the fields of transportation, aerospace, and microelectronics.

Through the approach of combining high performance computing with synthetic polymer chemistry, these new materials are the first to demonstrate resistance to cracking, strength higher than bone, the ability to reform to their original shape (self-heal), all while being completely recyclable back to their starting material. Also, these materials can be transformed into new polymer structures to further bolster their strength by 50% - making them ultra strong and lightweight. This research was published in the peer-reviewed journal, Science, with collaborators including UC Berkeley, Eindhoven University of Technology and King Abdulaziz City for Science and Technology (KACST.), Saudi Arabia.

However, today’s polymer materials are limited in some ways. In transportation and aerospace, structural components or composites are exposed to many environmental factors (de-icing of planes, exposure to fuels, cleaning products, etc.) and exhibit poor environmental stress crack resistance (i.e., catastrophic failure upon exposure to a solvent). Also, these polymers are difficult to recycle because they cannot be remolded or reworked once cured or thermally decomposed by heating to high temperatures. As a result, these end up in the landfill together with toxins such as plasticizers, fillers, and color additives which are not biodegradable.

IBM’s discovery of a new family of materials with a range of tunable and desirable properties provides an opportunity for exploratory research and applications development to academia, materials manufacturers and end users of high performance materials. Two new 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 to be used as a resin for filled composite materials to further bolster their strength.

Also, the ability to selectively recycle a structural component would have significant impact in the semiconductor industry, advanced manufacturing or advanced composites for transportation, as one would be able to rework high-value but defective manufactured parts or chips instead of throwing them away. This could bolster fabrication yields, save money and significantly decrease microelectronic waste.

IBM scientists used a novel ‘computational chemistry’ hybrid approach to accelerate the materials discovery process that couples lab experimentation with the use of high-performance computing to model new polymer forming reactions. The unconventional method is a departure from traditional techniques and led to the identification of several previously undiscovered classes of polymers in what was believed to be an established area of materials science researched extensively since the 1950s.

Ideally, scientists could insert a list of requirements into a computer to design a material that meets those exact conditions. Unfortunately, the reality now is that materials are still primarily discovered only by experimenting in the lab based on the scientist’s knowledge, experience and educated guesses. IBM Research’s computational chemistry efforts can take out a lot of this guesswork and accelerate a whole new range of potential applications from developing a disease-specific drugs or cheap, light, tough and completely recyclable panels on a car.

How it works
These polymers, formed from the same inexpensive starting material through a condensation reaction, these molecules join together and lose small molecules as by-products such as water or alcohol and were created in an operationally simple procedure and are tunable.

At high temperatures (250°C) the polymer becomes strong due to a rearrangement of covalent bonds and loss of the solvent that is trapped in the polymer (now stronger than bone and fiberboard), but as a consequence is more brittle.
This polymer remain intact when it is exposed to basic water, but selectively decomposes when exposed to very acidic water. This means that under the right conditions, this polymer can be reverted back to its starting materials, which enables it for reuse for other polymers. The material can also be manufactured to have even higher strength if carbon nanotubes or other reinforcing fillers are mixed into the polymer and are heated to high temperatures. This process enables polymers to have properties similar to metals, which is why these “composite blends” are used for manufacturing in airplane and cars. An advantage to using polymers in this case over metals is that they are more lightweight, which in the transportation industry translates to savings in fuel costs.

At low temperatures, another type of polymer can be formed into elastic gels that are still stronger than most polymers, but still maintains its flexibility because of solvent that is trapped within the network, stretching like a rubber band.
Probably the most unexpected and remarkable characteristic of these gels is that if they are severed and the pieces are placed back in proximity so they physically touch, the chemical bonds are reformed between the pieces making it a single unit again within seconds. This type of polymer is called a "self healing" polymer because of its ability to do this and is made possible here due to hydrogen-bonding interactions in the hemiaminal polymer network. One could envision using these types of materials as adhesives or mixing in with other polymers to induce self-healing properties in the polymer mixture. Furthermore, these polymers are reversible constructs which means that can be recycled in neutral water, and that they might find use in applications that require reversible assemblies, such as drug cargo delivery.

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