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Origin of dielectric response and conductivity of some alicyclic polyimides



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