Schmidt, Anneliese
(2024)
Design of High-Capacitance Polymers: Side Chain Length and Polarity Effects on Permittivity.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
This is the latest version of this item.
Abstract
Dielectric polymers (DPs) are attracting attention for applications in energy storage devices and potential as greener materials. This work serves to expand and explore a variation of side chain (SC) DPs, which addresses one major challenge, inherently low permittivity. This design of SCDPs combines a long aliphatic backbone, having low permittivity and loss, with conjugated SCs, having high permittivity and loss, and is expected to demonstrate these characteristics. Cast films, subjected to a dipole-aligning external field, achieved high permittivities. Effective dipole orientation, facilitated by backbone flexibility and SC conjugation for electron mobility, increased the induced dipole.
A series of polymers with an alkyl backbone and variable length phenylene ethynylene (PhE) SCs were prepared. Diolefin macromonomers, containing a halogenated phenyl, were polymerized via ADMET. Sonogashira coupling of PhE units gave SCs that were 1, 2, and 3 units long, and post-polymerization coupling gave polymers termed: poly-dimer, with two phenyls; poly-trimer, with three phenyls; poly-tetramer, with four phenyls. PhE units were of 2 types: a 2,5-alkoxy functionalized phenyl, for improved solubility, and a 4-nitrile functionalized phenyl, to enhance polarity.
The effects of conjugation length, polarity, and poling the polymers’ permittivities were studied. Sample films, prepared by solution deposition between brass electrodes, were characterized by broadband dielectric spectroscopy at 20 °C and 1 kHz. The type of solvent used showed little effect, whereas the amount of solvent present changed the materials’ response significantly. All unpoled polymers exhibited high permittivities: backbone and poly-tetramer ~4.3; poly-dimer ~4.6; poly-trimer ~4.9. Poling at a 15-volt potential increased their permittivities: backbone ~4.9; poly-dimer ~12.4; poly-trimer ~7.1; poly-tetramer ~5.9. This increase over the unpoled samples demonstrated their potential as high-performance DPs. After poling, the backbone’s small increase, Δε'=0.6, was expected. Surprisingly, as the SC length increased, the Δε' decreased, showing a maximum of: poly-dimer Δε'=7.8; poly-trimer Δε'=2.2; poly-tetramer Δε'=1.6. Alignment of increasingly longer SCs was expected to yield incrementally higher permittivities. One explanation, since permittivities were highly dependent on mobility, longer SCs may remain partially hindered to rotation, despite plasticization. The correlation between SC length and poled permittivity indicates hinderance may increase with SC length and prevent maximum alignment.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
8 May 2024 |
| Date Type: |
Publication |
| Defense Date: |
8 December 2023 |
| Approval Date: |
8 May 2024 |
| Submission Date: |
5 January 2024 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
211 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
dielectric polymers
broadband dielectric spectroscopy |
| Date Deposited: |
08 May 2024 17:42 |
| Last Modified: |
08 May 2024 17:42 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/45925 |
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Design of High-Capacitance Polymers: Side Chain Length and Polarity Effects on Permittivity. (deposited 08 May 2024 17:42)
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