Origin of dielectric response and conductivity of some alicyclic polyimides

Abstract

High‐performance alicyclic‐containing polyimides for advanced applications, derived from 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic acid anhydride or bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐ tetracarboxylic dianhydride and two flexible aromatic diamines, were synthesized by a classical two‐step polycondensation reaction. The dielectric spectra behavior over wide frequency and temperature ranges of 1 Hz‐1 MHz and –150°C÷+250°C, respectively, was investigated according to chemical and micro‐structural aspects. The dielectric constants have low values and are dependent on dianhydride flexibility and diamine links, in relation with the charge–transfer complex (CTC) and free volume, and, consequently, with packing of the polymer chains and polarizable groups per volume units. All polyimide films develop two relaxation processes, i.e., γ and β relaxation, involving different enthalpy and entropy contributions induced by their chemical structures. Frequency–temperature‐dependent conductivity showed that conductivity increased with frequency and also that energy bandgap representation could be suitable for explaining the temperature influence on AC‐conductivity. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Influence of two structural phases of Fe3O4and γ-Fe2O3on the properties of polyimide/iron oxide composites

“…According to the literature, the low remanence‐to‐saturation ratio of magnetization of all poly(DOCDA‐ODA)/Fe 3 O 4 composite films at different concentrations (5, 10 and 20 wt%), at 250 °C and 300 °C, respectively, suggest soft magnetic properties of the composite . The S values for system II (characterized by a 5–20 wt% filler inclusion, Table ) are similar to those, 0.19 − 0.34, reported in the literature for magnetite and cobalt ferrite nanoparticles functionalized with acrylic acid monomers . The present and the literature results are lower than the standard value of S = M r / M s , corresponding to completely blocked non‐interacting nanoparticles, ascribed to slow magnetization dynamics.…”

Evaluation of proton conductivity of sulfonated polyimide/dihydroxy naphthalene charge-transfer complex hybrid membranes

“…These CT complexes provide typical characteristics to polymer films such as the brown color derived from CT complex . However, all PIs and SPIs can be used as electronic insulators and PEMs, indicating that electronic conductivity deriving from intramolecular CT complex formation can be ignored . In this study, we introduced the CT complex in the SPI films positively by using stronger CT interaction than intramolecular CT interaction between SPIs, allowing the CT complex formation between SPI and DHN to dominantly occur instead of intramolecular CT interaction between SPIs .…”

“…22 However, all PIs and SPIs can be used as electronic insulators and PEMs, indicating that electronic conductivity deriving from intramolecular CT complex formation can be ignored. 23 In this study, we introduced the CT complex in the SPI films positively by using stronger CT interaction than intramolecular CT interaction between SPIs, allowing the CT complex formation between SPI and DHN to dominantly occur instead of intramolecular CT interaction between SPIs. 18 This strong CT interaction between NDI in SPI and DHN might work as an electronic conductive unit, although the typical CT complex electronic conductors did not show the alternatively oriented geometry formed between SPI and DHN.…”

Electrical properties of polyimide composite films containing TiO2 nanotubes

“…The dependence of conductivity of many amorphous materials, such as polyimides, on frequency can be written using the following equation : where σ DC is the DC‐conductivity, A is the pre‐exponential factor and n is the fractional exponent ranging from 0 to 1. The fractional exponent n was calculated from the frequency dependent conductivity , and the values from 0.63 to 1.07 were obtained for the temperature range of 0‐280°C (Fig. b).…”