Tailoring Polymers, One Electron at a Time

Significance 

Recently, studies involving the use of external stimuli to control polymerizations have attracted considerable interest among researchers. Amongst the various available external stimuli such as mechanical force, chemical reagents and applied voltages, light has become ever more popular. It has enabled the effective manipulation of various reactions like in atom transfer radical polymerization where photo-active molecules are utilized to control the initiation, propagation and termination stages of polymerization.

Despite providing impressive polymerization control, unfortunately, these methods have been incapable of directing the resultant polymer’s microstructure. To address this limitation, Jordan M. Kaiser, W. Curtis Anderson, and Professor Brian K. Long at the University of Tennessee (Department of Chemistry) have recently discovered that visible light may be used in conjunction with a redox-active olefin polymerization catalyst and a photoreductant to control the microstructure of polyethylene; one of the world’s most widely produced and utilized polymers. Their work was recently published in the research journal, Polymer Chemistry (DOI: 10.1016/j.ccr.2018.06.007).

Their research team employed visible light as an external stimulus that could alter the electronic nature of the polymerization catalyst and thereby modulate polyethylene branching density and microstructure during the polymerization. This was accomplished via the use of an iridium-based photoreductant and a redox-active nickel α-diimine olefin polymerization catalyst. They supported their findings through quantitative 13C NMR spectroscopy, gel permeation chromatography (GPC) and 1H NMR spectroscopy, which were used to quantify the changes in the branching densities of the polymers.

This study is the first report to successfully demonstrate the use of visible light as an external stimulus for polyolefin microstructure modulation. Long and Kaiser believe that this work further confirms the vast potential of employing redox-active olefin polymerization catalysts coupled with external stimuli to predictably alter catalytic reactivity. The authors are optimistic that this study will help advance future polymerization research efforts, and that it may one-day be extended to other polymeric materials, resulting in the ability to tailor polymers with desired properties for various applications.

 

Tailoring Polymers, One Electron at a Time - Advances in Engineering

About the author

Brian K. Long Brian studied chemistry as an undergraduate at North Georgia College & State University where he conducted research with Professor Dan Thompson. He was selected as an NSF-REU student at Furman University and worked with Professors John Wheeler and Noel A. P. Kane-Maguire. After completing his B.S. degree in 2003, Brian attended the University of Texas at Austin for his doctoral studies working under Professor C. Grant Willson, and was co-advised by Christopher W. Bielawski. His research involved the synthesis and application of traditional and nontraditional resist chemistries as well as nonlinear optical materials. After receiving his Ph.D. in 2009, Brian began his postdoctoral studies at Cornell University under the supervision of Professor Geoffrey W. Coates. While at Cornell, he focused on the design, synthesis and application of olefin polymerization catalysts.

Brian has since returned to the southeast and is currently an assistant professor of chemistry at the University of Tennessee (UTK). During his time at UTK, Brian has been the recipient of the Ffrancon Williams Endowed Faculty Award, an Army Research Office Young Investigator Award, and a Department of Energy Early Career Award.

About the author

Jordan M. Kaiser Jordan was born and raised in Hanover Park, Illinois. He earned his BS in Chemical Physics in 2014 from Lewis University and conducted undergraduate research under the guidance of Dr. Jason Keleher on the performance of nanoparticles for chemical mechanical planarization. Currently in the Long group at The University of Tennessee-Knoxville (UTK), Jordan works on multiple projects that span the development of transition metal catalysts, redox chemistry, and photochemical influences for olefin polymerizations. In 2018, he was selected for the Excellence in Polymer Graduate Research Symposium at the 2018 Spring ACS National meeting in New Orleans, and was awarded the East Tennessee ACS Graduate fellowship.

Jordan is an active member in UTK’s Graduate Student Society having held positions such as President, Secretary, Social Chair, and he is currently serving as a Graduate Student Senate Representative. In his free time, he enjoys volunteering at a local elementary school, anything outdoors, watching sports, and playing on the UTK club volleyball team.

Reference

Kaiser, J., Anderson, W., & Long, B. (2018). Photochemical regulation of a redox-active olefin polymerization catalyst: controlling polyethylene microstructure with visible lightPolymer Chemistry9(13), 1567-1570.

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