Structure–Property Relationship of Polyimides Based on Pyromellitic Dianhydride and Short-Chain Aliphatic Diamines for Dielectric Material Applications Aaron F. Baldwin, 1 Rui Ma, 1 Chenchen Wang, 2 Rampi Ramprasad, 2 Gregory A. Sotzing 1,3 1 The Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 2 Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 3 Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269 Correspondence to: G. A. Sotzing (E - mail: sotzing@mail.ims.uconn.edu) ABSTRACT: Most polyolefins that are used for dielectric materials exhibit a low dielectric constant and operating temperatures up to 70  C. Polyimides offer a means to a higher dielectric constant material by the introduction of a polar group in the polymer backbone and are thermally stable at temperatures exceeding 250  C. A common dianhydride, pyromellitic dianhydride (PMDA), is reacted with various short-chain diamines to produce polymers with high imide density. Homopolymers and copolymers synthesized had dielectric constants ranging from 3.96 to 6.57. These materials exhibit a dielectric constant twice that of biaxially oriented polypropylene and therefore a twofold increase in capacitance as well as maintaining low dissipation factors that are acceptable for this application. The experimental dielectric constants of these materials are also compared to density functional theory calculations and exhibit a close relationship. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000–000, 2013 KEYWORDS: dielectric properties; polyimides; structure-property relations Received 10 January 2013; accepted 26 February 2013; published online DOI: 10.1002/app.39240 INTRODUCTION There is a current push by the industrial complex to move away from traditional pneumatic, hydraulic, and mechanical devices to electrochemical ones which are controlled electri- cally. 1 Thus, there is a need for a high-energy storage system to operate these new devices. The best solution to this problem is the incorporation of high-energy density capacitor banks in which the electrical energy can be stored over long charging times and released as needed through short pulses. 2 For this system to operate efficiently and to reduce the size of the over- all capacitor bank, an insulating material is needed that pos- sesses a large dielectric constant while still maintaining a low dielectric loss. The two benchmark polymer dielectric materi- als, biaxially oriented polypropylene (BOPP) and polyvinyli- dene fluoride (PVDF), have dielectric constants of 2.2 and 10, respectively. 3–6 Polyimides are attractive materials for this application as they have a more polar backbone and thus a higher dielectric con- stant than polyolefins. The fact that make polyimides even more desirable is that they are thermally stable at temperatures exceeding 250  C, twice the operating temperature of most com- mon dielectric materials, making them able to withstand the heat generation that these capacitor banks will give rise to and there is less need for cooling the entire capacitor bank. 7 Most common polymers used as dielectric materials exhibit severe decrease in dielectric strength around 70  C. 8 Interestingly, a search of recent literature yields little work being done in this field. Instead, polyimides are being researched as a possible replacement of silicon dioxide in applications such as the insulating material in semiconductors, printed microelec- tronics, and so forth. 9–13 Most studies of polyimides in elec- tronic applications have looked at ways to reduce the dielectric constant of the material. The reduction of the dielectric con- stant has been controlled by lowering the polarizability of the polymer through modification of the backbone with the incor- poration of bulky, space-filling groups, the replacement of hydrogen with fluorine atoms, or a combination of both. The introduction of space-filling groups, such as aromatics, increases the free volume and thus decreasing the dipolar and atomic polarizability, whereas fluorine replacement will reduce the total polarizability through the heightening of the hydrophobicity of the polymer. 14–22 V C 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.39240 1