Density rho, viscosity eta and refractive index n(D) have been experimentally measured for four binary mixtures of poly(propylene glycol) of average molecular weight 425 + toluene/o-xylene/m-xylene/p-xylene over the temperature range T = (293.15-333.15) K with temperature step 5 K and at atmospheric pressure. From the experimental data excess molar volumes V-E, deviations in refractive index Delta n(D), viscosity deviations Delta eta and excess Gibbs free energy of activation of viscous flow Delta G(*E) were calculated and fitted with Redlich-Kister polynomial in order to analyze non-ideal behavior of the studied mixtures. From Delta G(*) values excess entropy AS(*E) and excess enthalpy of activation of viscous flow Delta H-*E were also calculated. It was shown that specific weak, but numerous, attractive interactions and entropic effect, due to difference in size of the pure component molecules, are responsible for volumetric and viscosity behaviour of the studied systems. The viscosities of the studied systems were predicted with the UNIFAC-VISCO and ASOG-VISCO models and correlated with the McAllister equation. (C) 2018 Elsevier Ltd.