University of Illinois Urbana-Champaign

Tunable viscoelasticity, morphology, and charge transport of dynamic covalent polymers

Jang, Seongon

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Description

Title
Tunable viscoelasticity, morphology, and charge transport of dynamic covalent polymers
Author(s)
Jang, Seongon
Issue Date
2025-08-13
Director of Research (if dissertation) or Advisor (if thesis)
Evans, Christopher M
Doctoral Committee Chair(s)
Evans, Christopher M
Committee Member(s)
  • Schroeder, Charles M
  • Zhou, Yuecheng
  • Kuenstler, Alexa
Department of Study
Materials Science & Engineerng
Discipline
Materials Science & Engr
Degree Granting Institution
University of Illinois Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • Dynamic covalent bonds
  • Vitrimers
  • Dynamic conjugated polymers
  • Viscoelasticity
  • Morphology
  • Charge transport
Abstract
Dynamic covalent bonds are reversible chemical linkages, enabling materials to undergo bond rearrangements in response to external stimuli. This dynamic behavior has led to the emergence of vitrimers that retain network integrity while exhibiting flow at elevated temperatures via associative bond exchange. Vitrimers show great potential as reprocessable and recyclable solid polymer electrolytes with tunable mechanical and transport properties, offering a safer and more stable alternative to conventional liquid electrolytes. Compared to crosslinked systems, the role of dynamic covalent bond exchange in rigid, linear conjugated polymers remains relatively underexplored, despite its potential to enhance morphology and charge transport. In a first project, the influence of crosslinking density and salt concentration on viscoelasticity, salt coordination, and ionic conductivity in vinylogous urethane (VU) vitrimers was systematically studied. Salt-containing vitrimers showed faster relaxation behavior compared to salt-free vitrimers due to the catalytic effects of Li ions. Higher crosslinking density with shorter linkers led to slower relaxation, which was attributed to restricted chain mobility. Ion conductivity was strongly coupled to segmental dynamics. Li ions preferentially interact with ethylene oxide (EO) chains rather than VU sites, particularly in longer-linker systems that offer enhanced ion solvation. Salt-containing vitrimers could be reprocessed and recycled using hot-pressing without significant degradation, unlike salt-free systems. In a second project, polymer networks with tunable ratios of neutral and ionic dynamic crosslinks were synthesized, and their composition was quantitatively characterized by 11B solid-state NMR. Shear rheology demonstrated that networks containing only neutral crosslinks exhibited a single damping peak associated with the glass transition Tg. On the other hand, the incorporation of ionic crosslinks introduced an additional damping mode with distinct exchange kinetics along with the appearance of a fourth damping process, indicating more complex relaxation behavior. In a third project, the influence of various salts on the viscoelasticity, morphology, and ionic conductivity of imine vitrimer electrolytes was systematically studied. Salt incorporation enhanced stress relaxation, with smaller cations, whereas smaller anions resulted in slower relaxation behavior due to the reduced fraction of free cations. Activation energy Ea varied with ion size, due to the combined contributions of chain diffusion, bond exchange kinetics, and salt dissociation. Wide-angle X-ray scattering (WAXS) patterns revealed that anions primarily governed the morphology of vitrimers. Larger anions, such as TFSI, reduced crystallinity due to their plasticizing effects. Ionic charge transport increased with larger anions due to greater ion dissociation. Imine-based vitrimers were fully recyclable, maintaining mechanical and conductive properties after degradation and repolymerization. Mixed salt vitrimers showed tunable modulus and conductivity values, intermediate between those of single salt vitrimers. In a fourth project, dynamic imine-based conjugated polymers (DQT-DP) exhibited significant improvements in crystallinity and electrical conductivity through solid-state processing and acid-doping compared to non-dynamic counterparts (DQT-NP). Hot-pressing of DQT-DP below its melting temperature Tm promoted imine bond exchanges, increasing melting enthalpy and enhancing pi-pi stacking. The electronic conductivity of DQT-DP also increased due to morphological improvement. Acid doping using p-toluene sulfonic acid (PTSA) further improved backbone planarity and crystallinity via proton-catalyzed exchanges, leading to higher conductivity. In contrast, non-dynamic DQT-NP showed minimal changes in morphology or conductivity after hot-pressing and acid doping. Results from DFT simulations supported the experimental results, showing increased backbone planarity upon imine protonation.
Graduation Semester
2025-12
Type of Resource
Thesis
Handle URL
https://hdl.handle.net/2142/132613
Copyright and License Information
Copyright 2025 Seongon Jang

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Graduate Theses and Dissertations at Illinois