Controlled functionalization of poly(4-methyl-1-pentene) films for high energy storage applications

A new family of poly(4-methyl-1-pentene) ionomer [PMP-(NH₃)_xA-y] (x = 1, 2, 3 and A = Cl^-, SO₄^2-, PO₄^3-, y = NH₃ content) modified (NH₃⁺)_xA^x- ionic groups has been synthesized. The ionomers were synthesised using either a traditional Ziegler-Natta or a metallocene catalyst for the copolymerisation of 4-methyl-1-pentene and bis(trimethylsilyl)amino-1-hexene. A systematic study was conducted on the effect of the subsequent work-up procedures that can prevent undesirable side reactions during the synthesis of the [PMP-(NH₃)_xA-y] ionomers. The resulting PMP-based copolymers were carefully monitored by a combination of nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), mechanical properties, dielectric properties, and electric displacement-electric field (D-E) hysteresis loop measurements. Our results reveal that the [PMP-(NH₃)_xA-y] ionomer films show a significantly enhanced dielectric constant (∼5) and higher breakdown field (∼612 MV m^-1) as compared with pure PMP films. Additionally, these PMP-based films show good frequency and temperature stabilities (up to 160 °C). A reliable energy storage capacity above 7 J cm^-3 can be obtained, and is twice the energy storage capacity of state-of-the-art biaxially oriented polypropylene films, which can be attractive for technological applications for energy storage devices.