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Densities of binary mixtures of 2,4,6,8-tetramethylcyclotetrasiloxane with benzene, toluene, o-xylene, m-xylene, and p-xylene have been determined at temperatures of (288.15, 298.15, and 308.15) K using an Anton Paar DMA 4500 oscillating u-tube densitometer. Excess molar volumes have been derived from the density data. The experimental data were satisfactorily fitted to the Redlich−Kister equation and the Legendre polynomials. ■ INTRODUCTIONAs one of the most important chemicals, 2,4,6,8-tetramethylcyclotetrasiloxane (D 4 H , CAS RN: 2370-88-9) is widely used in the silicone industry, and its structure is shown in Figure 1. It is a kind of active siloxane containing silicon−hydrogen bond and thus plays an important role in synthesizing hydrogen-containing silicone oil, the cross-linking agents which are essential for addition-type liquid silicone rubbers or silicone resins.The excess properties are used in the design and calculation of the chemical engineering process involving substance separations, heat transfers, mass transfers, and fluid flows. 1 Information about the excess properties of liquid mixtures containing D 4 H and aromatic compounds and their dependence on compositions and temperature is very important fundamental data for their applications in the separation fields. Moreover, excess thermodynamic properties of mixtures are also used to express the deviations of the mixing process from ideality and thus are useful in the study of molecular interactions and arrangements. 2 The excess molar volume (V E ) is one of the important excess properties which can be used in the understanding of molecular interactions between different components of mixtures and also in engineering applications. 3 However, the excess properties involving D 4 H have not been investigated before. Here we report the values of densities and excess molar volumes (V E ) for the binary systems of D 4 H with aromatic hydrocarbon (benzene, toluene, o-xylene, m-xylene, and p-xylene) at T = (288.15, 298.15, and 308.15) K at atmospheric pressure. The V E data were further correlated with the Redlich−Kister equation and the Legendre polynomials.