About

Gregory McKenna is a Research Professor in the Department of Chemical and Biomolecular Engineering at NC State University. His research focuses on small molecular interactions with glassy polymers, torsion and normal force measurements, nanorheology and nanomechanics, melt and solution rheometry, and residual stresses in composite materials. He has made significant contributions to the understanding of polymer behavior and material properties through his experimental and theoretical work. Throughout his career, McKenna has received numerous honors and awards, including fellowships in the Society of Rheology, the American Institute of Chemical Engineers, and the American Association for the Advancement of Science. He has also been recognized with prestigious awards such as the Bingham Medal of the Society of Rheology, the George Stafford Whitby Award for Distinguished Teaching and Research, and the U.S. Department of Commerce Silver Medal. His educational background includes a PhD in Materials Science and Engineering from the University of Utah, an MS in Composite Materials from MIT, and a BS in Engineering Mechanics from the U.S. Air Force Academy. McKenna's work has advanced the understanding of polymer and composite material behavior, contributing to both academic research and practical applications in materials science.

Research topics

• Chemistry
• Materials science
• Organic chemistry
• Polymer chemistry
• Physics
• Thermodynamics
• Structural engineering
• Quantum mechanics
• Statistical physics
• Geotechnical engineering
• Geology
• Mathematics
• Engineering
• Statistics
• Environmental science

Selected publications

• Ring polymer physics and rheology: Challenges and opportunities

  Journal of Rheology · 2025-12-31 · 5 citations

  article

  Understanding the structure and dynamics of ring or cyclic polymers is a long-standing challenge in polymer science, with important implications for emerging biological phenomena such as chromosome territories. This Perspective article provides a comprehensive overview of the current state of ring polymer physics and rheology, highlighting emerging challenges and opportunities for future research. Key scientific questions are considered regarding the properties of synthetic and biological ring polymer systems using theory, simulations, and experiments. This article was inspired by stimulating discussions at a CECAM Flagship workshop on Ring Polymer Dynamics in Prato, Italy, in June 2023. Several of the concepts and results discussed here are also presented in the Journal of Rheology virtual issue on ring polymers (https://pubs.aip.org/jor/collection/1392/Ring-Polymers). Broadly, this article aims to spark conceptual advances in polymer physics and rheology by exploring new phenomena and open scientific questions that are unique to ring polymer systems.

  PublisherDOI

• Di-Tyrosine Cross-Linking of Elastin-Like Polypeptides through Ruthenium Photoreaction To Form Scaffolds: Fine Tuning Mechanical Properties and Improving Cytocompatibility

  Biomacromolecules · 2025-02-19 · 3 citations

  article

  Ensuring that the mechanical properties of tissue engineering scaffolds align with those of the target tissues is crucial for their successful integration and functional performance. Tyrosine-tyrosine cross-links are found in nature in numerous proteins including resilin that exhibit enhanced toughness and energy storage capacity. Herein, we investigated the potential of tuning the mechanical properties of scaffolds made from elastin-like polypeptides (ELPs) containing tyrosine residues. Ruthenium-based photoreaction was used to form tyrosine cross-links. To enhance the cytocompatibility of the ELP scaffold, a continuous mode of washing was developed to remove residual ruthenium from the scaffolds. The continuous mode of washing was significantly superior in removing ruthenium and did so in a significantly shorter time as compared to batch washing and the conventional semibatch washing (also called dialysis washing). The range of storage moduli of the fabricated scaffolds spanned tens of Pa to hundreds of kPa. Human fibroblast cells were found to grow in the scaffolds and proliferate. Overall, this work offers a rationale for further developing tyrosine cross-linked ELPs for a broad range of tissue engineering applications.

  PublisherDOI

• SOME COMMENTS ON THE NATURE OF GLASSES: OR A BRIEF HISTORY OF TIME AND TEMPERATURE IN GLASS-FORMING LIQUIDS

  Rubber Chemistry and Technology · 2024-10-01 · 2 citations

  article1st authorCorresponding

  ABSTRACT I undertake a brief presentation of the early history of the development of our modern understanding of glass-forming liquids that provides a look at how the scientific and technological communities were viewing the state of the art and how the knowledge in the field developed. I discuss aspects of our understanding from how the Vogel–Fulcher–Tammann (VFT) equation became known to questions about the development of the concept of the “ideal” glass transition. The framework for this history leads us to ask whether some of the cautions that the pioneering researchers provided should have been taken more seriously by the community. I discuss, in particular, the view presented by Tammann and Hesse [ Z. Anorg. Allg. Chem . 156 , 245 (1926)] cautioning that the apparent singularity of the viscosity at a finite temperature was not physical and how the, now famous, VFT equation is accurate for interpolation rather than for extrapolation. The other point is the strong sense by much of the glass community that the so-called Kauzmann paradox [ Chem. Rev . 43 , 219 (1948)] is fundamental to glass-formation despite the comment by Kauzmann himself that the extrapolation of the entropy to negative values is “operationally meaningless.” I build on these ideas through a presentation of my own data and that of others that addresses the Tammann and Hesse comment through experiments that show that there is not a viscosity (or relaxation time) divergence near to the Kauzmann or VFT temperatures, and I show that the equilibrium entropy of a polymer that cannot crystallize shows no evidence of an ideal glass transition that is often invoked as a means of avoiding the Kauzmann paradox. In addition to providing some sense of the history of time (or a brief history of time and temperature in glass-forming liquids, with apologies to Stephen Hawking) and viscosity, I think that the data presented lead to the conclusion that much of our understanding of the problem of glass-formation is based on misleading interpretations of the original works as well as being inconsistent with the newer data that have been published over that past 25 yr or so. On an optimistic note, there are newer models that do not rely on the VFT divergence or the Kauzmann paradox to account for glass-formation in supercooled or equilibrium liquids. In addition, the experimental situation clearly leads to the possibility of deeper investigations into the “deep glassy state” through “finessing” the geological timescale issue of creating equilibrium glasses. Such investigations are ultimately important to understanding behavior of glassy materials, especially polymers, that are used deep in the glassy state, but still close enough to the glass temperature that models able to reliably predict their behavior require better representations of glass-formation to engineer their performance.

  PublisherDOI

• Issue Information ‐ Cover Description

  Journal of Polymer Science · 2024-03-01

  paratextOpen access

  The cover image by Simon van Hurne depicts the formation of a dynamic covalent boronate-TetraAzaADamantane bond, which could be integrated in a covalent adaptable network.As a result of the on-going dynamic bond exchange reactions within this network, the material could undergo stress relaxation.At the same time, the more robust triple bonding motif allowed for stronger materials compared to their conventional boronate ester-based counterparts.

  PublisherOA PDFDOI

• On the glass transition temperature of TNT

  Thermochimica Acta · 2024-03-28 · 1 citations

  articleSenior authorCorresponding
  PublisherDOI

• Investigation of the structure, filler interaction and degradation of disulfide elastomers made by Reversible Radical Recombination Polymerization (R3P)

  European Polymer Journal · 2023-03-25 · 2 citations

  articleOpen access
  PublisherOA PDFDOI

• Searching for the ideal glass transition: Going to yotta seconds and beyond

  Journal of Non-Crystalline Solids · 2023-02-09 · 12 citations

  articleSenior authorCorresponding
  PublisherDOI

• Polymer Macrocycles: A novel topology to control dynamics of rubbery materials

  2023-02-24

  reportOpen accessSenior author

  We have successfully made synthetic polymer rings that are larger than previously reported having entanglement numbers as high as $Z_w$≈300 if the rings entangled as do linear chains. The synthesis was carried out using reversible radical recombination polymerization (R3P) of dithiols which produces a polymer with a very small persistence length. The reported results show surprising dilute solution behaviors due to the fact that polymeric rings expand more than their linear counterparts for polymer chains having a large number of persistence lengths, as developed in this study. The results strongly argue for a systematic investigation of the dilute solution properties of rings having different persistence lengths in different quality solvents, where the theta-condition should lead to results that are independent of the persistence length. For the rheological investigations related to chain entanglements, the polyDODT rings could be diluted so that the rheological data covered from less than one entanglement spacing relative to the linear counterpart to a value of $Z_w$=300. Importantly, because we were able to dilute extremely high entanglement number polyDODT rings to a similar entanglement number as those reported for polystyrene rings that were highly purified using LCCC, we demonstrated that the dynamics of the polyDODT rings virtually overlaps with the dynamics of the polystyrene rings which is very strong evidence that these high molecular weight polyDODT rings are of high purity. Our results demonstrate that the onset of entanglement in rings, as evidenced by the appearance of a rubbery plateau $G_N^0$ and by the onset of a strong power-law dependence of the viscosity on molecular weight (η~$M_w^{5.8}$) or entanglement number (η~$Z_w^{5.8}$), occurs at much higher molecular weights or polymer concentrations than is the case for linear chains. These results should serve as a benchmark for future investigations of the behavior of entangled, circular macromolecules.

  PublisherDOI

• Correction to “Substrate Effects on Glass Transition and Free Surface Viscoelasticity of Ultrathin Polystyrene Films”

  Macromolecules · 2023-06-29

  articleSenior author

  ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "Substrate Effects on Glass Transition and Free Surface Viscoelasticity of Ultrathin Polystyrene Films"Heedong YoonHeedong YoonMore by Heedong Yoon and Gregory B. McKenna*Gregory B. McKennaMore by Gregory B. McKennahttps://orcid.org/0000-0002-5676-9930Cite this: Macromolecules 2023, 56, 13, 5225–5227Publication Date (Web):June 29, 2023Publication History Received17 May 2023Published online29 June 2023Published inissue 11 July 2023https://pubs.acs.org/doi/10.1021/acs.macromol.3c00970https://doi.org/10.1021/acs.macromol.3c00970correctionACS PublicationsCopyright © 2023 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views439Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (1 MB) Get e-Alertsclose Get e-Alerts

  PublisherDOI

• Polymer Macrocycles: A novel topology to control dynamics of rubbery materials (Final Report)

  2023-02-24

  reportOpen access1st authorCorresponding

  We have successfully made synthetic polymer rings that are larger than previously reported having entanglement numbers as high as Z_w≈300 if the rings entangled as do linear chains. The synthesis was carried out using reversible radical recombination polymerization (R3P) of dithiols which produces a polymer with a very small persistence length. The reported results show surprising dilute solution behaviors due to the fact that polymeric rings expand more than their linear counterparts for polymer chains having a large number of persistence lengths, as developed in this study. The results strongly argue for a systematic investigation of the dilute solution properties of rings having different persistence lengths in different quality solvents, where the theta-condition should lead to results that are independent of the persistence length. For the rheological investigations related to chain entanglements, the polyDODT rings could be diluted so that the rheological data covered from less than one entanglement spacing relative to the linear counterpart to a value of Z_w=300. Importantly, because we were able to dilute extremely high entanglement number polyDODT rings to a similar entanglement number as those reported for polystyrene rings that were highly purified using LCCC, we demonstrated that the dynamics of the polyDODT rings virtually overlaps with the dynamics of the polystyrene rings which is very strong evidence that these high molecular weight polyDODT rings are of high purity. Our results demonstrate that the onset of entanglement in rings, as evidenced by the appearance of a rubbery plateau G_N⁰ and by the onset of a strong power-law dependence of the viscosity on molecular weight (η~M_w^5.8) or entanglement number (η~Z_w^5.8), occurs at much higher molecular weights or polymer concentrations than is the case for linear chains. These results should serve as a benchmark for future investigations of the behavior of entangled, circular macromolecules.

  PublisherOA PDFDOI

Recent grants

• The Nanomechanical and Viscoelastic Responses of Ultrathin Polymer Films

  NSF · $809k · 2016–2024

• GOALI/Collaborative Research: Processing and Stability of Amorphous Dispersions for Advanced Pharmaceutical Applications

  NSF · $254k · 2017–2020

• Collaborative Research: EAGER Proposal on Non-Homogeneous Flow Fields in Nonlinear Rheology: A Challenge to Current Paradigms?

  NSF · $127k · 2009–2012

• UNS: Collaborative Research: Testing the paradigms of the colloidal glass: Novel concentration jump experiments and large scale computer modeling

  NSF · $175k · 2015–2018

• Collaborative Research: A Nanoparticle Embedment Method to Determine Surface and Interface Properties of Viscoelastic Liquids and Solids

  NSF · $120k · 2006–2009

Frequent coauthors

• Sindee L. Simon

  North Carolina State University

  63 shared

• Paul A. O’Connell

  27 shared

• Xiaoguang Peng

  Texas Tech University

  24 shared

• Dejie Kong

  Texas Tech University

  21 shared

• Sourya Banik

  Texas Tech University

  20 shared

• Yung P. Koh

  North Carolina State University

  18 shared

• Charles M. Schroeder

  Nathan Kline Institute for Psychiatric Research

  17 shared

• Heedong Yoon

  Drexel University

  16 shared

Labs

• McKenna GroupPI

  Not provided

Awards & honors

• Polymer Engineering and Science publishes (Virtual) Special…
• Fellowship in the Society of Rheology (SOR) 2020
• Fellowship in the American Institute of Chemical Engineers (…
• Fellow, American Association for the Advancement of Science…
• North American Thermal Analysis Society Fellow 2017