Relative permittivities, epsilon(r), and refractive indices, n(D), have been measured at (293.15-303.15) K, for the mixtures 1-pentanol + 2,5,8,11,14-pentaoxapentadecane (TEGDME) or TEGDME + octane. These data have been used, together with density measurements available in the literature, to calculate the correlation factors, g(K), according to the Kirkwood-Frohlich equations. The curves of the deviations of epsilon(r) from the ideal behaviour, Delta epsilon(r), of the 1-pentanol + TEGDME system are shifted to high mole fractions of the alcohol, and show a rather large minimum. The shape of the Delta epsilon(r) curves of methanol + TEGDME or + polyethylene glycol dimethyl ether 250 (PEG-250) mixtures is similar. This reveals that polyethers can break the alcohol self-association even at high alkanol concentrations. The higher Delta epsilon(r) values of the methanol solutions are ascribed to large self-association of this alcohol. The Delta epsilon(r) curves of the 1-pentanol + dibutyl ether (DBE) system are nearly symmetrical, and the Delta epsilon(r) values are higher than those of the corresponding TEGDME mixture. This indicates that effects related to the alcohol self-association are much more relevant in the DBE system. These findings are supported by g(K) and molar polarization data. Values of molar refraction of 1-pentanol systems reveal that dispersion forces become more important in the sequence: octane < DBE < TEGDME. Such forces are also more relevant in the 1-pentanol + TEGDME system than in the methanol + TEGDME solution. The comparison of Delta epsilon(r) and g(K) data for TEGDME or DBE + octane mixtures shows than the polyether is a more structured liquid. (C) 2012 Elsevier B.V. All rights reserved.