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A series of covalently cross-linked poly(ionic liquid) networks were prepared using thiol-ene "click" photopolymerization. In these networks, imidazolium groups are placed in the backbone and pendant to the main chain, creating a "hybrid"-type network architecture. The pendant imidazolium groups were incorporated into the networks from monofunctional "ene" monomers that contained either a terminal alkyl group at the imidazolium N-3 position of variable length (R = C1, C4, C8, C12, C16, or C20) or a variable alkyl tether spacer (n = 6 or 10) between the newly formed sulfide and the imidazolium ring. Thermal characterization of these networks indicated a general decrease in Tg as the length of the terminal alkyl chain length increased from C1 to C8, followed by an abrupt increase in Tg up to C20 due to increased van der Waals interactions between longer chains. X-ray scattering data confirmed the presence of chain-extended crystallites within the network cavities for the C16 and C20 systems, leading to the observed increase in Tg and the appearance of a melting transition for both systems. Ionic conductivities of the PIL networks were determined from dielectric relaxation spectroscopy (10-6 to 10-7 S/cm at 30 °C, 30% RH), and a direct correlation with polymer Tg was found.
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This contribution was identified by Dr. Timothy Long (Virginia Tech) as the Best Presentation in the “Ionic Liquids in Polymer Science & Engineering: From Molecular Design to Energy & Beyond” session of the 2018 ACS Fall National Meeting in Boston. This work was supported by a Research in Undergraduate Institutions (RUI) award from the National Science Foundation, Division of Materials Research, Polymers Program (DMR-1708632). Thermal and mechanical analyses were conducted in the Polymer and Materials Science Laboratory (PMCL) at Murray State University. DMA support was provided by the Department of Chemistry at Murray State University as a result of support from the National Science Foundation (Major Research Instrumentation) under DMR-1427778. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.
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- Period 5