Dielectric behavior of gamma-cyclodextrin polymer and carboxymethyl gamma-cyclodextrin polymer cross-linked both by epichlorohydrin

The γ-cyclodextrin polymer (γ-CDP) and carboxymethyl-γ-cyclodextrin polymer (CM-γ-CDP) cross-linked both by epichlorohydrin were investigated via dielectric spectroscopy over the frequency range 0.1–100 kHz and the temperature ranges 122.0–472.4 K and 123.6–460.3 K, respectively. The γ-CDP reveals a thermally reversible transformation of some normal hydrogen bonds to flip-flop type at Ttrans = 199.1 K, whereas the CM-γ-CDP doesn’t show any transformation of hydrogen bonds. Both systems present in the lnσ vs 1/T plot two linear parts following the Arrhenius equation. In the case of γ-CDP, the first linear part during cooling (a) has activation energy Eα = 0.41 eV and during heating (b) has Eα = 0.42 eV in the range 259.7–310.0 K. The second linear part (c) in the range 316.5–357.1 K has Eα = 0.36 eV. The corresponding values of CM-γ-CDP are Eα = 0.32 eV (a), Eα = 0.33 eV (b) in the range 242.1–295.1 K and Eα = 0.91 eV (c) in the range 307–366.1 K. The linear parts (a) and (b) of both polymers are related to the accumulation of protons in the grain-boundary regions as it is depicted in the Cole-Cole plots. The linear part (c) is related to the proton migration from the grain-boundary region to the electrodes and the dehydration process taking place. The ac-conductivity of CM-γ-CDP is considerably higher than that of γ-CDP as the partial hydrogen replacement of some hydroxyl groups by carboxymethyl moiety, renders numerous protons more flexible to move along the hydrogen-bonded network, contributing to the conductivity. Both systems after the dehydration process, presented a newly-formed hydrogen bonded network due to the reorientation of hydrogen bonded chains at T > 397.0 K for γ-CDP and T > 420.9 K for CM-γ-CDP.