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Brantley Group Publishes in Polymer Chemistry

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The Brantley Group published their work “Ion Specific Fluorescence Modulation of Polyvinyl Alcohol-Boronate Matrices” in Polymer Chemistry. Brian Jacobs, graduate student in the Brantley Lab, is the primary author. 

Borylated polymers are emerging as valuable chemosensors that can report analyte binding through an array of responses. Fluorescent materials are particularly valuable in this regard, as modulation of their photophysical properties can facilitate rapid substrate detection and quantitation.

“In this manuscript, we report the condensation of aryl boronic acids onto polyvinyl alcohol (PVA) to afford fluorescent polymers, a phenomenon that has been widely overlooked,” Jacobs said. “ Importantly, selective modulation of the photophysical properties was observed in the presence of borophilic anions (e.g. fluoride, hydroxide, and cyanide).”

Density functional theory (DFT) calculations, performed by collaborator Jacob Townsend in the Vogiatzis Research Group, suggested that a combination of covalent and non-covalent interactions were crucial for anion binding. Time-dependent DFT computations were also performed to explain the appearance of a distinct peak in the polymer’s absorbace profile.

“Lastly, films of these PVA-aryl boronates were employed in ion extraction studies, highlighting a useful secondary function these materials possess,” Jacobs said. “Given the ease with which these polymers can be accessed, they could serve as general platforms for developing ion selective membranes or detectors.”

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Kent & Zhao’s Most Read Article

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Shape Changing Brush Polymers Are Receiving Attention. 

Molecular bottlebrushes are complex polymers composed of polymeric side chains densely grafted on a relatively long backbone polymer. These types of polymers are found in our body and show important biological functions, e.g., joint lubrication by lubricin.

In an effort to develop smart polymers mimicking the function of the von Willebrand Factor, a protein important in the blood clotting cascade, Ethan W. Kent, a doctoral graduate student in Bin Zhao’s research laboratory, recently designed and synthesized dually responsive shape-changing star molecular bottlebrushes.

At acidic pH values and lower temperatures, the molecules take on a three-arm star shape with a span size of ~ 180 nm. When the pH is increased to basic or temperature is raised, the molecules undergo dramatic shape changes from stars to spheres with an average dimension of ~ 80 nm. 

“It is really cool to see these molecules change their shapes spontaneously,” Kent said. These brush polymers have potential in drug delivery, molecular actuators, and sensors. Ethan is currently applying his responsive brush polymers in sensors.

This work has been published in Macromolecules, an ACS journal in polymer science. The paper has been on the list of Most Read Articles in Macromolecules for nearly two months. “It is really exciting to see our paper garner a lot of attention” Kent said.        

UT-ORNL: Small Nanoparticles Have Surprisingly Big Effects on Polymer Nanocomposites

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Alexei SokolovPolymer nanocomposites mix particles billionths of a meter (nanometers, nm) in diameter with polymers, which are long molecular chains. Often used to make injection-molded products, they are common in automobiles, fire retardants, packaging materials, drug-delivery systems, medical devices, coatings, adhesives, sensors, membranes and consumer goods.

When a team of scientists, including UT’s Alexei Sokolov, tried to verify that shrinking the nanoparticle size would adversely affect the mechanical properties of polymer nanocomposites, they got a big surprise. They found an unexpectedly large effect of small nanoparticles.

The findings were reported recently in the journal ACS Nano.

In addition to Sokolov, the team included scientists from Oak Ridge National Laboratory, and the University of Illinois at Urbana-Champaign. Sokolov is a UT-ORNL Governor’s Chair based in the Department of Chemistry.

Blending nanoparticles and polymers enables dramatic improvements in the properties of polymer materials. Nanoparticle size, spatial organization and interactions with polymer chains are critical in determining behavior of composites. Understanding these effects will allow for the improved design of new composite polymers, as scientists can tune mechanical, chemical, electrical, optical and thermal properties.

Small nanoparticles stick to segments of polymer chain about the same size as the nanoparticles themselves. These interactions produce a polymer nanocomposite that is easier to process because nanoparticles move fast, quickly making the material less viscous. At right, many segments of a polymer chain stick to a larger nanoparticle, making it difficult for that nanoparticle to move. Its slower movement results in a viscous material that is more difficult to process. Source: ORNL

Until recently, scientists believed an optimal nanoparticle size must exist. Decreasing the size would be good only to a point, as the smallest particles tend to plasticize at low loadings and aggregate at high loadings, both of which harm macroscopic properties of polymer nanocomposites.

“We see a shift in paradigm where going to really small nanoparticles enables accessing totally new properties,” Sokolov said. That increased access to new properties happens because small particles move faster than large ones and interact with fewer polymer segments on the same chain. Many more polymer segments stick to a large nanoparticle, making dissociation of a chain from that nanoparticle difficult.

“Now we realize that we can tune the mobility of the particles—how fast they can move, by changing particle size, and how strongly they will interact with the polymer, by changing their surface,” Sokolov said. “We can tune properties of composite materials over a much larger range than we could ever achieve with larger nanoparticles.”

Continue reading on the Oak Ridge National Laboratory website.

Professor Dadmun Named ACS Fellow

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Mark DadmunDr. Mark Dadmun, Professor of Chemistry, was named 2015 American Chemical Society (ACS) Fellow. Dadmun received his B.S. in Chemical Engineering from the University of Massachusetts and a Ph.D. from the University of Massachusetts working with Prof. M. Muthukumar in Polymer Science and Engineering.  He subsequently was awarded a National Research Council Post-doctoral Fellowship, which was completed at the National Institute of Standards and Technology working with Dr. Charles Han.  Prof. Dadmun then joined the faculty of the Chemistry Department at the University of Tennessee, where he is now a Full Professor.  His current appointments include Joint Faculty at Oak Ridge National Laboratory in the Chemical Science Division and Founding Director of the Soft Materials Research in Tennessee (SMART) Center.

The fellows program began in 2009 as a way to recognize and honor ACS members for outstanding achievements in and contributions to science, the profession, and ACS*. “Through their work, Mark Dadmun and the entire class of 2015 ACS Fellows are using the transforming power of chemistry to improve health, protect the planet, and feed the world’s population.  Through their service in the community they are making science accessible to all, supporting students and teachers, and giving back through countless acts of public outreach,” said ACS President Diane Grob Schmidt.

Click to view the complete list of 2015 ACS Fellows published on C&EN.

*From ACS web site.