Faculty Directory
John M. Torkelson

Walter P. Murphy Professor of Chemical and Biological Engineering and Materials Science and Engineering

Contact

2220 Campus Drive
Tech E172
Evanston, IL 60208

847-491-7449Email John Torkelson

Website

Torkelson Research Group


Departments

Chemical and Biological Engineering

Materials Science and Engineering

Education

Ph.D., University of Minnesota

B.S., University of Wisconsin


Research Interests

Sustainable and recyclable/upcyclable polymers and composites, nanoscience and nanotechnology of polymers and soft matter, novel solid-state processing of polymers

Our research motivation is driven by two main desires: (1) to understand at a fundamental level how molecular-scale behavior of polymers relates to macroscale properties; and (2) and to engineer and optimize those polymer properties by tuning molecular-scale responses via dynamic chemistry, nanoscale confinement, chain architecture, and novel solid-state processing, among other methods. For example, our group has recently developed three simple dynamic chemistry approaches that allow for spent thermosets or crosslinked polymers to be recycled by melt-state processing into new crosslinked polymer products with full recovery of crosslink density and associated properties. In one case, we employ exactly the polymers and fillers used in the tire industry but substitute sulfur-based crosslinking with a dynamic alkoxyamine-based crosslinking method; the latter method yields robust crosslinks at elevated-temperature-use conditions but decrosslink at yet higher temperatures like those used in tire molding operations, thus allowing melt-state reprocessing. Two other methods have been developed for polyhydroxyurethane and polythiourethane crosslinked polymers, with these systems also showing promise for monomer recovery from spent polymers.

We are also developing a deeper understanding of how nanoscale confinement of polymers in thin films or in nanocomposites can lead to major changes in properties, including glass transition temperature (which can change by 50 degrees C or more), physical aging, stiffness or modulus, and diffusion, among others. In support of our research efforts, we have developed simple non-destructive characterization tools that allow us to characterize the gradient in behavior from a free surface or substrate/nanofiller. We also doing fundamental research to understand how polymer architecture (e.g., cyclic or ring polymers, stars, hyperbranched polymers, brushes, bottlebrushes, etc.) and copolymer structure can modify the bulk and nanoconfined behaviors of polymers. In turn, we are using that understanding to engineer materials for improved performance. Finally, we also pursuing novel, industrially scalable solid-state processing approaches to design and produce modified polymers, polymer blends, composites, and nanocomposites that cannot be produced by conventional melt-state processing. Our process is the solid-state analog of twin-screw extrusion and allows for much greater work to be done on the polymeric materials during processing. As a result, our solid-state process achieves dispersion levels as well as chemistries that are not attainable with melt-state processing methods.


Significant Recognition

  • McCormick School of Engineering, Teacher of the Year, 2008
  • Associated Student Government Faculty Honor Roll, 2007
  • Polymer Physics Prize (awarded by the Journal of Polymer Science Part B: Polymer Physics), 2004
  • Best Paper Award, Polymer Analysis Division, Society of Plastics Engineers, 2004
  • Charles M.A. Stine Award from the Materials Engineering and Science Division of the American Institute of Chemical Engineering, 2004
  • Fellow, American Physical Society, 1999
  • Associated Student Government Faculty Honor Roll, 1995-96
  • McCormick School Advisor of the Year, 1993-94
  • NSF Presidential Young Investigator Award, 1987-92
  • Ralph A. Teetor Award (Society of Automotive Engineers), 1986
  • Lilly Foundation Teaching Fellowship, 1985-86
  • Tau Beta Pi Outstanding Teaching Award, 1984
  • Technological Institute (now McCormick School) Teacher of the Year, 1984-85

Significant Professional Service

  • Executive Committee of the Division of Polymer Physics of the American Physical Society, 2005-2008
  • Director, Materials Research Center, Northwestern University, 2003-2006
  • Caterpillar Distinguished Lecturer, Dept. of Chemical and Biochemical Engineering, University of Iowa, 2002
  • Chair, Materials Engineering and Science Division, American Institute of Chemical Engineers, 2001-02
  • Associate Dean for Graduate Studies and Research, McCormick School of Engineering, Northwestern University, 1997-2002
  • Bette and Neison Harris Professor of Teaching Excellence, 1995-98

Selected Publications

    L. Li and J.M. Torkelson, "Reprocessable Polymer Networks via Thiourethane Dynamic Chemistry: Recovery of Cross-link Density after Recycling and Proof-of-Principle Solvolysis Leading to Monomer Recovery", Macromolecules 2019, 52, 8207-8216.

    C. Szczepanski and J.M. Torkelson, "Engineering Surface Hydrophilicity via Polymer Chain-End Segregation in Coatings Formed by Photopolymerization", ACS Applied Polymer Materials 2019, 1, 3095-3102.

    X. Chen, L. Li, and J.M. Torkelson, "Recyclable Polymer Networks Containing Hydroxyurethane Dynamic Cross-links: Tuning Morphology, Cross-link Density, and Associated Properties with Chain Extenders", Polymer 2019, 178, 121604.

    T. Wei, K. Jin, and J.M. Torkelson, "Isolating the Effect of Polymer-Grafted Nanoparticle Interactions with Matrix Polymer from Dispersion on Composite Property Enhancement: The Example of Polypropylene/Halloysite Nanocomposites", Polymer 2019, 176, 38-50.

    X. Chen, L. Li, T. Wei, and J.M. Torkelson, "Reprocessable Polymer Networks Designed with Hydroxyurethane Dynamic Cross-links: Effect of Backbone Structure on Network Morphology, Phase Segregation, and Property Recovery", Macromolecular Chemistry and Physics 2019, 22, 1900083.

    S. Hu, X. Chen, and J.M. Torkelson, "Biobased Reprocessable Polyhydroxyurethane Networks: Full Recovery of Crosslinking Density with Three Concurrent Dynamic Chemistries", ACS Sustainable Chemistry & Engineering 2019, 7, 10025-10034.

    X. Chen, L. Li, T. Wei, and J.M. Torkelson, "Reprocessable Polymer Networks Designed with Hydroxyurethane Dynamic Cross-links: Effect of Filler Surface Functionality on Cross-link Density Recovery and Stress Relaxation", ACS Applied Materials & Interfaces 2019, 11, 2398-2407.

    Y. Qiu, L.W. Antony, J.M. Torkelson, J.J. de Pablo, and M.D. Ediger, "Tenfold Increase in the Photostability of an Azobenzene Guest in Vapor-Deposited Glass Mixtures", J. Chem. Phy. 2018, 149, 204503.

    L. Li, S.R. Marrou, and J.M. Torkelson, "Remarkable Glass Transition Breadths up to 120 K Exhibited by Block-Gradient Copolymers and by Gradient Copolymers Plasticized by Oligomer", Polymer 2018, 151, 145-153.

    L. Li, X. Chen, K. Jin, and J.M. Torkelson, "Vitrimers Designed Both to Strongly Suppress Creep and to Recover Original Cross-link Density after Reprocessing: Quantitative Theory and Experiments", Macromolecules 2018, 51, 5537-5546.

    K. Jin, E.K. Leitsch, X. Chen, W.H. Heath, and J.M. Torkelson, "Segmented Thermoplastic Polymers Synthesied by Thiol-Ene Click Chemistry: Examples of Thiol-Norbornene and Thiol-Maleimide Click Reactions", Macromolecules 2019, 51, 3620-3631.

    G. Beniah, W.H.Heath, J. Jeon, and J.M. Torkelson, "Tuning the Properties of Segmented Polyhydroxyurethane via Chain Extender Structure", Journal of Applied Polymer Science 2017, 134, 4492.

    X. Chen, L. Li, K. Jin, and J.M. Torkelson, Reprocessable Polyhydroxyurethane Networks Exhibiting Full Property Recovery and Concurrent Associative and Dissociative Dynamic Chemistry via Transcarbamoylation and Reversity Cyclic Carbonate Aminoloysis", Polymer Chemistry 2017, 8, 6349-6355.

    G. Beniah, W.H. Heath, and J.M. Torkelson, "Functionalization of Hydroxyl Groups in Segmented Polyhydroxyurethane Eliminates Nanophase Separation", Journal of Polymer Chemistry, Part A: Polymer Chemistry 2017, 55, 3347-3351.

    L. Zhang and J.M. Torkelson, "Enhanced Glass Transition Temperature of Low Molecular Weight Poly(methyl methacrylate) by Initiator Fragments Located at Chain Ends", Polymer 2017, 122, 194-199.

    M. Zhang, S. Askar, J.M. Torkelson, and C.L. Brinson, "Stiffness Gradients in Glassy Polymer Model Nanocomposites: Comparisons of Quantitative Characterization by Fluorescence Spectroscopy and Atomic Force Microscopy", Macromolecules 2017, 50, 5447-5458.

    G. Beniah, D.J. Fortman, W.H. Heath, W.R. Dichtel, and J.M. Torkelson, "Non-Isocyanate Polyurethane Thermoplastic Elastomer: Amide-Based Chain Extender Yields Enhanced Nanophase Separation and Properties in Polyhydroxyurethane", Macromolecules 2017, 50, 4425-4434.

    K. Jin and J.M. Torkelson, "Tg-Confinement Effects in Strongly Miscible Blends of Poly(2,6-dimethyl-1,4-phenylene oxide) and Polystyrene: Roles of Bulk Fragility and Chain Segregation", Polymer 2017, 118, 85-96.

    S. Askar, T. Wei, A.W. Tan, and J.M. Torkelson, "Molecular Weight Dependence of the Intrinsic Size Effect on Tg in AAO Template-Supported Polymer Nanorods: A DSC Study", Journal of Chemical Physics 2017, 146, 203323.

    G. Beniah, X. Chen, B. Uno, K. Liu, E.K. Leitsch, J. Jeon, W.H. Heath, K.A. Scheidt, and J.M. Torkelson, "Combined Effects of Carbonate and Soft-Segment Molecular Structures on the Nanophase Separation and Properties of Segmented Polyhydroxyurethane", Macromolecule 2017, 50, 3193-3203.

    K. Jin, L. Li, J.M. Torkelson, "Bulk Physical Aging Behavior of Cross-linked Polystyrene Compared to Its Linear Precursor: Effects of Cross-linking and Aging Temperature", Polymer 2017, 115, 197-203.

    L. Zhang and J.M. Torkelson, "Enhancement of Surface Wettability by Incorporating Polar Initiator Fragments at Chain Ends of Low-Molecular-Weight Polymers", ACS Applied Materials & Interfaces 2017, 9, 12176-12181.

    S. Askar, L. Li, and J.M. Torkelson, "Polystyrene-Grafted Silica Nanoparticles: Investigatin the Molecular Weight Dependence of Glass Transition and Fragility Behavior", Macromolecules 2017, 50, 1589-1598.

    L. Zhang, R. Elupula, S.M. Grayson, and J.M. Torkelson, "Suppression of the Fragility-Confinement Effect via Low Molecular Weight Cyclic or Ring Polymer Topology", Macromolecules 2017, 50, 1147-1154.

    G. Beniah, B.E. Uno, T. Lan, J. Jeon, W.H. Heath, K.A. Scheidt, and J.M. Torkelson, "Tuning Nanophase Separation Behavior in Segmented Polyhydroxyurethane via Judicious Choice of Soft Segment", Polymer 2017, 110, 218-227.

    G. Beniah, K. Liu, W.H. Heath, M.D. Miller, K.A. Scheidt, and J.M. Torkelson, "Novel Thermoplastic Polyhydroxyurethane Elastomers as Effective Damping Materials over Broad Temperature Ranges", European Polymer Journal 2016, 84, 770-783.

    S. Askar and J.M. Torkelson, "Stiffness of Thin, Supported Polystyrene Films: Free-surface, Substrate, and Confinement Effects Characterized by Self-Referencing Fluorescence", Polymer 2016, 99, 417-426.

    K. Jin, L. Li, and J.M. Torkelson, "Recyclable Crosslinked Polymer Networks via One-Step Controlled Radical Polymerization", Advanced Materials 2016, 28, 6746-6750.

    K. Jin and J.M. Torkelson, "Enhanced Tg-Confinement Effect in Cross-Linked Polystyrene Compared to Its Linear Precursor: Roles of Fragility and Chain Architecture:, Macromolecules 2016, 49, 5092-5103.

    E.A. Dhulst, W.H. Heath, and J.M. Torkelson, "Hybrid Thiol-Acrylate-Epoxy Polymer Networks: Comparison of One-Pot Synthesis with Sequential Reactions and Shape Memory Properties", Polymer 2016, 96, 198-204.

    K. Jin, N. Wilmot, W.H. Heath, and J.M. Torkelson, "Phase-Separated Thiol-Epoxy-Acrylate Hybrid Polymer Networks with Controlled Cross-link Density Synthesized by Simultaneous Thiol-Acrylate and Thiol-Epoxy Click Reactions", Macromolecules 2016, 49, 4115-4123.

    E.K. Leitsch, G. Beniah, K. Liu, T. Lan, W.H. Heath, K.A. Scheidt, and J.M. Torkelson, "Nonisocyanate Thermoplastic Polyhydroxyurethane Elastomers via Cyclic Carbonate Aminolysis: Critical Role of Hydroxyl Groups in Controlling Nanophase Separation", ACS Macro Letters 2016, 5, 424-429.

    K.A. Iyer, J. Lechanski, and J.M. Torkelson, "Green Polypropylene/Waste Paper Composites with Superior Modulus and Crystallization Behavior: Optimizing Specific Energy in Solid-State Shear Pulverization for Filler Size Reduction and Dispersion", Composites Part A -- Applied Science and Manufacturing 2016, 83, 47 -55.

    L. Zhang, J.A. Marsiglio, T. Lan, and J.M. Torkelson, "Dramatic Tunability of the Glass Transition Temperature and Fragility of Low Molecular Weight Polystyrene by initiator Fragments Located at Chain Ends", Macromolecules, 2016, 49, 2387-2398.

    L. Chen and J.M. Torkelson, "Tuning the Tg-Confinement Effect in Thin Polymer Films via Minute Levels of Residual Surfactant Which "Cap" the Free Surface", Polymer 2016, 87, 226-235.

    K.A. Iyer, L. Zhang, and J.M. Torkelson, "Direct Use of Natural Antioxidant-Rich Agro-Wastes as Thermal Stabilizer for Polymer: Processing and Recycling", ACS Sustainable Chemistry & Engineering 2016, 4, 881-889.

    T. Lan and J.M. Torkelson, "Fragilitie-Confinement Effects: Apparent Universality as a Function of Scaled Thickness in Films of Freely Depositied, Linear Polymer and Its Absence in Densely Grafted Brushes", Macromolecules 2016, 49, 1331-1343.

    A.W. Tan and J.M. Torkelson, "Poly(methyl methacrylate) Nanotubes in AAO Templates: Designining Nanotube Thickness and Characterizing the Tg-Confinement Effect by DSC", Polymer 2016, 82, 327-336.

    L. Zhang, R. Elupula, S.M. Grayson, and J.M. Torkelson, "Major Impact of Cyclic Chain Topology on the Tg-Confinement Effect of Supported Thin Films of Polystyrene", Macromolecules 2016, 49, 257-268.