The effects of different positions of the pyridine functional groups on the dielectric relaxation of the heterocyclic polyurethane-urea elastomers

Abstract

The relationship between the position of the pyridine functional groups and the dielectric relaxation properties of the polyurethane-urea elastomers was investigated by means of dielectric relaxation spectroscopy in a broad temperature and frequency range. Pyridine-based polyurethane-urea were obtained from poly(tetramethylene ether) glycol, 1,6-hexamethylene diisocyanate and 2,6-diaminopyridine or 2,3-diaminopyridine as chain extenders, by a two steps pre-polymer method. The dielectric and relaxation properties of linear and cross-linked samples were studied by broadband dielectric relaxation spectroscopy. The changes in the position of the amino group on the pyridine ring, from position 3 to position 6 toward the nitrogen atom, have been found to strongly influence the dielectric relaxation behavior of the synthesized samples. Within the frequency range of 100–106Hz, all polyurethane-urea films develop three relaxation processes (γ, β and α relaxation) that take place successively as temperature inscreases. Spectra were obtained using the Havriliak—Negami function and revealed the existence of one conductivity process and at least two relaxation processes. The parameters of the conductivity and relaxation processes were calculated and discussed according to the differing functional group position. The intensity of the relaxation process is reduced for the polyurethane urea using 2,3-diaminopyridine as a chain extender. The different structural designs significantly influence the values of dielectric constants and those of dielectric loss.