Photo: DTU

The polymer revolution has just begun

Wednesday 25 Jan 17
by Morten Andersen


Copolymers (such as plastic) are formed by polymerization of two or more different monomeric compounds. Unlike a homopolymer, which is formed by polymerization of one monomer.
There are a very large number of theoretical possibilities for the formation of copolymers. Many have special properties, and have therefore had a great impact on society. Examples include butadiene-styrene copolymers (SB rubber, 'synthetic rubber'), isobutylene-isoprene copolymers (butyl rubber), vinylidene chloride-vinyl chloride copolymers (e.g. household film) and acrylonitrile-vinyl acetate copolymers (Orlon-fibres for clothing).

Source: Gyldendals Den Store Danske

Foto: DTU
Frank S. Bates has had a long-standing collaboration with DTU Nanotech. His lecture at DTU in September 2016 flowed out of this.

H.C. Ørsted lectures

Twice a year, DTU invites prominent foreign researchers to lecture on their work, research findings, and the prospects within their field of research at the so-called Ørsted Lectures. The lectures are open to all.

Watch or revisit some of the previous lectures and find out about upcoming lectures.

Rapid recovery following a heart attack. Chewing gum that can be easily removed from the pavement. Strong materials with soft surfaces. Meet one of the world's leading experts in polymers—materials with amazing properties.

As a chemical and materials engineer Frank Bates is always looking for practical solutions to societal problems, but another part of him desires to investigate the fundamental behaviour of matter. In polymers he found the perfect field for combining both approaches.

Polymers have already revolutionized our society, but according to Frank S. Bates, Professor at the University of Minnesota, USA, there is a lot more to come.

“Just to take an example, my group is currently involved in collaboration with cardiologists. Our joint research suggests that patients recovering from heart attacks do much better when treated with certain polymers.”

According to the studies, the polymers act as surfactants that promote cell recovery in the heart.

“In fact we do not fully understand the mechanism involved. Research on this is still ongoing. However, my point here is to show why polymers are so fascinating. It seems that a substance, which is sold in bulk quantities all over the world, with slight modifications can become a high value chemical.”

Materials with magical properties

Frank Bates’ name is mainly associated with the study of complex polymers. Different polymers can be joined within the same molecule. This is known as a co-polymer. The result can be a molecule with different chemical and/or different thermodynamic properties depending on which side it is approached from. For instance, it could be hydrophilic at one side and hydrophobic at the other; or it could be stiff and mechanically strong at one side, and soft at the other.

While co-polymers promise a range of applications where materials seem to have “magic” properties, Frank Bates sees an even greater challenge facing polymer science:

“We cannot ignore the fact that polymer materials pile up to form giant islands floating around in our oceans. We have to develop sustainable polymers.”

Replace oil with lactic acid

From a chemist’s point of view this shouldn’t be too hard, he emphasizes:

“Rather than depending on hydrocarbon feedstocks as we do today, it is absolutely possible to extract our monomers from sugars, cellulose and other renewable resources. Further, it is possible to have these monomers joined in polymers for a given period of time – performing their job – after which they will degrade back into monomers, which will then degrade further into carbon dioxide and water. However, the big problem is that the hydrocarbon based polymers are just so cheap.”

Two hydrocarbon based polymers, polyethylene (PE), and polypropylene (PP), jointly account for 2/3 of the world’s polymer consumption, which totals 400 billion USD annually in value.

“For instance, lactic acid which can be derived from renewable feedstock is shown to be very promising as a bio-polymer resource. It is currently too costly, but we shouldn’t let that discourage us.”

Perhaps the biggest difference between hydrocarbon and biological feedstocks is that the latter contain oxygen.

“The presence of oxygen changes the thermodynamics significantly. Therefore, you can’t expect the same synthesis pathways to be efficient. However, I strongly believe that other pathways can be found where oxygen is not just less problematic, but directly helpful. The production of PE and PP has been optimized over more than 80 years, while research in bio-polymers has only taken place during the last decade. Thus we have every reason to expect costs to drop as more efficient processes are found. In my view this is imperative. You can’t force people to buy more expensive products only because they are better for the environment.”

Chewing gum led to new knowledge

Frank Bates is directly engaged in this quest through his work with the Center for Sustainable Polymers at the University of Minnesota. Other discoveries from his group may take part as well.

"Polymers continue to provide new features that amaze us!"
Professor Frank S. Bates, University of Minnesota

“What we do is fundamental research. But I always tell my students that practical applications should be kept in mind. Actually, this goes both ways. New theory leads to new applications, but we also see that applications inspire new theory.”

A recent example is a joint industry project with Wrigley Chewing Gum.

“We wanted to see if we could create chewing gum which would not stick to sideways and similar surfaces after use, and would thus be much easier to remove.”

A consumer product has not yet been marketed, as the company lacks a clear incentive. It is not evident that consumers will prefer a more environmentally benign product. Still, from a scientific point of view the project was highly successful yielding four patents – and new insight.

More specifically, Frank Bates and his colleagues have found so called quasi-crystals in the polymers. These are self-organized supramolecular aggregates that exhibit both solid-like, crystalline properties and liquid-like amorphous properties.

“We were astonished by the X-ray pattern which we saw from our diblock copolymer melt. Evidently, we had found new insight regarding symmetry breaking, which is a fundamental feature in various types of materials science. This is a key part not only of polymer science but also e.g. in metal melts and alloys.”

Illustration: PantherMedia

Bates' research group can build polymers with different properties in the same molecule. For example, a substance can be water-repellent and absorbent at the same time.

Experiments were carried out in Denmark

The interview with Dynamo takes place just before Frank Bates addresses a large audience at DTU in his H.C. Ørsted lecture focused mainly at exactly these fundamental perspectives. The invitation was based on a longstanding Danish-American connection.

“Kristoffer Almdal (today Professor at DTU Nanotech, Editor’s remark) was my first Postdocs. We literally built my lab together. After Kristoffer returned to Denmark, we kept up our collaboration. For a number of years he facilitated neutron beam time for my group at the former Danish research facility DR3 at DTU’s Risø campus.”

To an outsider it may seem surprising that a US scientist would travel as far as Denmark to obtain time at an experimental facility.

“Well, neutron beam time is a truly limited resource. You need either a nuclear plant or a dedicated spallation source. Neither solution is within reach of a normal university setting due to both safety and economic concerns. In the USA we have just two facilities. They are both operated as national laboratories, meaning that researchers and industry all across the country compete for time.”

The DR3 reactor was closed down in 2000. Since, Frank Bates has taken his experiments to the two US facilities and sometimes to facilities in Europe.

“When it comes to neutron scattering, Europe is more advanced than the US. The facility at Grenoble, France, is in my view the best in the world, while also German and Swiss facilities rank highly. Further, the European Spallation Source (ESS) in Sweden will become the leading source in the world once it opens. I understand that Denmark is a co-owner of ESS, and look forward to cash in on my Danish connections once again!”

Copolymers as drug delivery systems

Why is neutron scattering so crucial in polymer science?

“When you examine crystals and other hard structures often X-ray will be highly useful, but for soft materials like polymers, neutrons are, for certain purposes, even better. A strong method is to label molecules in the polymers through substitution of deuterium for hydrogen. Subsequently, you will be able to follow how the atoms and molecules will organize in both time and space. This is a unique tool.”

Besides polymers, the same is true for medicine and a range of other biological fields.

“Just to take an example, drug delivery is a topic which includes both polymer and biological insight. Co-polymers have a strong potential as drug delivery vehicles. My training as a chemical engineer hardly qualifies me for medical research, but in recent years I have been so involved, I almost feel I am in that field!”

Still, future applications in more traditional engineering fields are also possible.

“An interesting feature in co-polymers is that you can pattern surfaces including silicon wafers with exquisite nanoscale resolution. These materials are being developed to permit manufacturing of computer chips and memory devices with unparalleled spatial resolution in an effort to sustain the ever increasing appetite for computational speed and storage capacity. “

Inspired by the wings of butterflies

Regarding the quasi-crystals one interesting perspective is in photonics. It is well known that light can be manipulated in materials by use of so called photonic band gaps. These gaps need to be manufactured very accurately at tiny length scales ranging from 100 nano-metres to 1 micron. This is an immense challenge to traditional manufacturing techniques. The ability of co-polymers to self-assembly with built-in quasi-crystals could be a solution.”

A related research field is micro-structuring of surfaces to provide certain properties. A topic included in Kristoffer Almdal’s current research.

“For instance, scientist at DTU Nanotech and others have shown that micro-structuring can alter the apparent colour of a material. This is a principle known from the wings of butterflies. In other words, applying the right structure can replace dye. Now we are back at the sustainability angle!”

“This yet again confirms another observation in polymer science made by Bates. So many times during my carrier have I heard the phrase “now we know everything there is to know” about a given subject. I have to admit that I have even used it myself on some occasions. But every time have we been proven wrong. Polymers continue to provide new features that amaze us!”


Foto: DTU

Frank S. Bates is a Professor in Materials Science in the Department of Chemical Engineering and Materials Science at the University of Minnesota in USA. He heads the Bates Research Group, which does research into the thermodynamic and dynamic properties of polymer materials.

He completed chemical engineering and materials science studies at the Massachusetts Institute of Technology (MIT) in 1979. He was also awarded a PhD from MIT in 1982.

Frank Bates is particularly known for his studies of copolymers, whereby different polymers are combined to obtain new properties. Frank Bates is a member of the US National Academy of Engineering, and the American Academy of Arts and Sciences.