ABSTRACT Biaxial-oriented polypropylene (BOPP) thin films are currently used as dielectrics in state-of-the-art capacitors that show many advantages, such as low energy loss and high breakdown strength, but a limited energy density (<2 J/cm3). This paper reviews some of our experimental results in functionalization of polypropylene with the objective to increase its electric energy density and maintain all desirable properties. A family of PP copolymers with various moieties, such as OH, O-Si(CH3)3, long chain branching, and cross-linking structure, have been systematically synthesized and studied to examine their dielectric properties (i.e. dielectric constant, dielectric loss, breakdown strength, polarization under various temperatures and electric fields). Evidently, a high molecular weight poly(propylene-co-hexen-6-ol) copolymer (PP-OH) containing 4.2 mol% of polar OH groups shows a dielectric constant (ε) of about 4.6 (more than 2 times of BOPP)—which is independent on a wide range of temperatures and frequencies—and high breakdown strength > 600 MV/m. The PP-OH dielectric demonstrates a linear reversible charge storage behavior with high releasing energy density > 7 J/cm3 (2 - 3 times of BOPP) after an applied electric field at E = 600 MV/m, without showing any significant increase of energy loss and remnant polarization at zero electric field. On the other hand, a cross-linked polypropylene (x-PP) exhibits an ε ~ 3, which is independent of a wide range of temperatures and frequencies, slim polarization loops, high breakdown strength (E = 650 MV/m), narrow breakdown distribution, and reliable energy storage capacity > 5 J/cm3 (double that of state-of-the-art BOPP capacitors), without showing any increase in energy loss.
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T. C. Mike Chung, "Functionalization of Polypropylene with High Dielectric Properties: Applications in Electric Energy Storage," Green and Sustainable Chemistry, Vol. 2 No. 2, 2012, pp. 29-37. doi: 10.4236/gsc.2012.22006.
 M. Winter and R. J. Brodd, “What Are Batteries, Fuel Cells, and Supercapacitors?” Chemical Reviews, Vol. 104, No. 10, 2004, pp. 4245-4270. doi:10.1021/cr020730k
 W. J. Sarjeant, “Advanced Power Sources for Space Missions, NAS-NRC (EEB) Committee on Advanced Spaced Based High Power Technologies,” National Academy Press, Washington DC, 1989.
 W. J. Sarjeant, J. Zirnheld and F. W. MacDougall, “Capacitors,” IEEE Transactions on Plasma Science, Vol. 26, No. 5, 1998, pp. 1368-1392. doi:10.1109/27.736020
 M. Villegas, J. F. Fernandez, C. Moure and P. Duran, “Preparation, Microstructural Development and Dielectric Properties of Pb(Mg1/3Nb2/3)O3-Pb(TixZr1?x)O3 Multilayer Ceramic Capacitors,” Journal of Materials Science, Vol. 29, No. 19, 1994, pp. 4999-5004.
 G. R. Love, “Energy Storage in Ceramic Dielectrics,” Journal of the American Ceramic Society, Vol. 73, No. 2, 1990, pp. 323-328.
 C. W. Reed and S. W. Cichanowski, “The Fundamentals of Aging in HV Polymer-Film Capacitors,” IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 1, No. 5, 1994, pp. 904-922. doi:10.1109/94.326658
 W. J. Sarjeant, F. W. MacDougall and D. W. Larson, “Energy Storage in Polymer Laminate Structures-Ageing and Diagnostic Approaches for Life Validation,” IEEE Electrical Insulation Magazine, Vol. 13, No. 1, 1997, pp. 20-24. doi:10.1109/57.567394
 J. H. Tortai, N. Bonifaci, A. Denat and C. Trassy, “Diagnostic of the Self-Healing of Metallized Polypropylene Film by Modeling of the Broadening Emission Lines of Aluminum Emitted by Plasma Discharge” Journal of Applied Physics, Vol. 97, No. 5, 2005, Article ID: 53304.
 M. Rabuffi and G. Picci, “Status Quo and Future Prospects for Metallized Polypropylene Energy Storage Capacitors,” IEEE Transactions on Plasma Science, Vol. 30, No. 5, 2002, pp. 1939-1942.
 G. Picci and M. Rabuffi, “Pulse Handling Capability of Energy Storage Metallized Film Capacitors,” IEEE Transactions on Plasma Science, Vol. 28, No. 5, 2000, pp. 1603-1606. doi:10.1109/27.901241
 J. A. Langston, J. Y. Dong and T. C. Chung, “One-Pot Process of Preparing Long Chain Branched Polypropylene (LCBPP) Using C2-Symmetric Metallocene Complex and A ‘T’ Reagent,” Macromolecules, Vol. 38, No. 14, 2005, pp. 5849-5853. doi:10.1021/ma0506841
 J. A. Langston, R. H. Colby, T. Shimizu, T. Suzuki, M. Aoki and T. C. Chung, “Synthesis and Characterization of Long Chain Branched Isotactic Polypropy-lene (LCBPP) via Metallocene Catalyst and T-Reagent,” Macromolecules, Vol. 40, No. 8, 2007, pp. 2712-2720.
 T. C. Chung and A. Petchsuk, “Ferroelectric Polymers with Giant Electrostriction; Based on Semicrystalline Ter-polymers Containing Vinylidene Difluroride, Trifluroethylene and Third Monomer,” US Patent No. 6,355,749, 2002.
 Z. C. Zhang and T. C. Chung, “Fluoro-Terpolymer Based Capacitors Having High Energy Density, Low Energy Loss, and High Pulsed Charge-Discharge Cycles,” Macromolecules, Vol. 40, No. 4, 2007, pp. 783-785.
 Z. C. Zhang and T. C. Chung, “The Structure-Property Relationship of PVDF-Based Polymers with Energy Storage and Loss under Applied Electric Fields,” Macromolecules, Vol. 40, No. 26, 2007, pp. 9391-9397.
 T. C. Chung and A. Petchsuk, “Synthesis and Properties of Ferroelectric Fluoro-Terpolymers with Curie Transition at Ambient Temperature,” Macromolecules, Vol. 35, No. 20, 2002, pp. 7678-7684. doi:10.1021/ma020504c
 Z. Wang, Z. C. Zhang and T. C. Chung, “High Dielectric VDF/TrFE/CTFE Terpolymers Pre-pared by Hydrogenation of VDF/CTFE Copolymers; Synthesis and Characterization,” Macromolecules, Vol. 39, No. 13, 2006, pp. 4268-4271. doi:10.1021/ma060738m
 T. C. Chung, “Functionalization of Polyolefins,” Academic Press, London, 2002.
 T. C. Chung, “Synthesis of Functional Polyolefin Copolymers with Graft and Block Structures,” Progress in Polymer Science, Vol. 27, No. 1, 2002, pp. 39-85.
 X. Yuan, Y. Mat-suyama and T. C. Chung, “Synthesis of Functionalized Isotactic Polypropylene Dielectrics for Electric Storage Application,” Macromolecules, Vol. 43, No. 9, 2010, pp. 4011-4015. doi:10.1021/ma100209d
 W. Lin, Z. Shao, J. Y. Dong and T. C. Chung, “Cross- Linked Polypropylene Prepared by PP Copolymers Containing Flexible Styrene Groups,” Macromo-lecules, Vol. 42, No. 11, 2009, pp. 3750-3754.
 X. Yuan and T. C. Chung, “Cross-Linking Effect on Dielectric Properties of Polypropy-lene Thin Films and Applications in Electric Energy Storage,” Applied Physics Letters, Vol. 98, No. 6, 2011, Article ID 62901.
 J. Artbauer, “Electric Strength of Polymers,” Journal of Physics D: Applied Physics, Vol. 29, No. 2, 1996, p. 446.
 C. C. Xu, J. Ho and S. A. Boggs, “Automatic Breakdown Voltage Measurement of Polymer Films,” IEEE Electrical Insulation Magazine, Vol. 24, No. 6, 2008, pp. 30-34.