Hybrid electric cars, the electro propulsion of ships, and militant electromagnetic railguns are all examples of new electrochemical devices that are being introduced to the contemporary industry. High energy density storage systems are needed to function these devices, demanding the advancement of high energy density capacitors that are capable of storing large amounts of energy over long periods of time. This project aims to discover the cause of dielectric breakdown, which, if discovered, would lend suggestions of how to increase the energy density of a capacitor to make it better able to power an electrochemical device. Polymers represent an intriguing class of dielectric materials for use in capacitors because of their easier processing techniques, and increased mechanical integrity, compared to their inorganic counterparts. Further, the Navy would like materials that undergo ‘graceful’ failure. ULTEM 1000 polyetherimide was chosen to study because of its high glass transition temperature, making it stable at the high temperatures associated with these capacitors. ULTEM 1000 derivatives were synthesized through step-polymerization combining 4,4-Bisphenol A Dianhydride, m-Phenylenediamine, and differing end cap molecules that incorporate a specific free volume defect at the ends of the polymer chains. The cause of dielectric breakdown is not currently understood, but it is known that free volume defects decrease dielectric constant suggesting that these modifications will also affect dielectric breakdown. t-Butylaniline, Tri-t-butylaniline, and 1-aminoadamantane were chosen as end caps because of their bulky substituents allowing for free volume variation in the polymer film. Polymer molecular weight was controlled using these endcap reagents, and higher molecular weights resulted in fewer endcaps and hence lower free volume. Polymers were synthesized with molecular weights of ca. 40kDa as determined by gel permeation chromatography and nuclear magnetic resonance spectroscopy. Pure polymer samples are then subjected to dielectric testing during which their Weibull DC breakdown are compared to commercial ULTEM 1000 produced by SABIC company.

Toward an understanding of dielectric breakdown through incorporating defects into polyetherimides

2019 Spring National Meeting

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