Effect of temperature and composition on the density, refractive index, and excess quantities of binary mixtures of 2,4,6,8-tetramethyl-2,4,6,8-tetraethenylcyclotetrasiloxane with aromatic hydrocarbons

https://doi.org/10.1016/j.jct.2012.08.010Get rights and content

Abstract

Density and refractive index were determined for the binary mixtures containing 2,4,6,8-tetramethyl-2,4,6,8-tetraethenylcyclotetrasiloxane (D4Vi) and aromatic hydrocarbons (ethylbenzene, o-xylene, m-xylene, and p-xylene) at five temperatures (288.15, 298.15, 308.15, 318.15, and 328.15) K and atmospheric pressure by a DMA4500&RXA170 combined system. The density and refractive index correlations for these systems were tested by an empirical second order polynomial and by the Lorentz–Lorenz equation. Excess molar volumes were calculated and correlated by the Redlich–Kister equation and the Legendre polynomials. The values of the volume expansivity (coefficient of thermal expansion) of pure chemicals and four binary solutions were estimated from temperature dependence of densities. Values of partial excess volumes at infinite dilution for these four binary systems at different temperatures were calculated either from the adjustable parameters of Redlich–Kister smoothing equation or the Legendre polynomials. The deviations in refractive index were calculated and correlated by the Redlich–Kister polynomial expansions. The molar refractions were calculated from the Lorentz–Lorenz equation. The deviations in molar refractions were calculated and correlated by the Redlich–Kister polynomial expansions. Factors affected these excess quantities were discussed. The results obtained indicate that the excess molar volumes, the deviations in refractive index and the deviations in molar reactions at each temperature are negative. The system {D4Vi(1)+o-xylene(2)} exhibits the maximum negative deviations from ideality among these four systems, which is the result of multiple factors such as the partial interstitial accommodation effect, the steric hindrance, the size of molecule and the instantaneous dipole-induced dipole interactions.

Highlights

► Values of ρ and nD of binary mixtures at different temperatures were measured. ► Volume expansivity of pure components and four mixtures were calculated. ► Excess quantities were correlated well with the Legendre polynomials and R–K equation. ► All the excess quantities were negative in the whole composition range. ► Binary mixtures of D4Vi and o-xylene exhibited the maximum deviations in excess quantities.

Introduction

In recent years, with the gradual depletion of oil resources and their fast rising prices, some synthetic rubbers initiated from oil or natural gas resources will gradually be replaced by silicone rubbers since the latter does not depend on the oil or natural gas resources at all. On the other hand, since the structural parameters of the Si–O bond, such as its length and angle, are quite different from that of C–C, Cdouble bondC or triple bond, therefore, compared with other synthetic polymers, silicone based polymers possess incomparable physical and chemical properties such as excellent resistance to oxygen, ozone, and ultraviolet light. Among all the industrialized silicone intermediates, 2,4,6,8-tetramethyl-2,4,6,8-tetraethenylcyclotetrasiloxane (D4Vi, CAS RN: 2554-06-5) is currently one of the most important intermediates and its annual consumption is ranked in the second place in silicone industry. The molecule structure of D4Vi is presented in figure 1. The most significant application of D4Vi is that they can be used produce the matrix for various silicone oils, rubbers or silicone resins, which is achieved through copolymerization with octamethylcyclotetracyclosiloxane (D4) or other monomers conducted in bulk or in the solution. The presence of vinyl groups as substituents along the siloxane polymer chain is crucial to the vulcanization of silicone elastomers, whether the elastomer is peroxide cured or whether the elastomer is cured through the Pt-catalyzed hydrosilylation reaction between a siliconhydride crosslinker and the vinyl groups.

Cyclosiloxanes form a series of non polar compounds and they can dissolve completely in aromatic hydrocarbons, therefore, some special silicone polymers are prepared by means of solution polymerization and these solvents are selected as the reaction media. Among these solvents, ethylbenzene and xylene isomers are preferred due to their low toxicity relative to benzene or toluene. These four solvents are also of great importance in the petrochemical industry, because they are the main basis for the manufacture of many organic compounds.

It is known that the mixing of different compounds gives rise to properties such as volume, enthalpy and entropy of mixing, which reflect the extent of the deviations from non-ideality. The excess properties are necessary for the design and calculation of the chemical engineering process involving substance separation, heat transfer, mass transfer and fluid flow [1]. The information about the excess properties of liquid mixtures containing D4Vi and aromatic compounds, and their dependence on composition and temperature are very important fundamental data for their applications in the separation fields. To date, many studies have been focused on binary or ternary systems consisted of Ionic Liquids (ILs) or H-bond containing chemicals such as alcohols with non-polar or polar solvents [2], [3], [4], [5], [6], [7]. With these studies, some important factors responsible for the positive or negative deviations from ideality for binary polar–polar or non-polar–polar systems have been discussed. However, a survey of the literature shows that very few reports have ever been made on the excess quantities for binary solutions of cylcosiloxanes with aromatic hydrocarbons.

To conduct research on excess quantities of binary mixtures of cyclosiloxane with aromatic hydrocarbons and to investigate the interactions that take place between solute–solute, solute–solvent, and solvent–solvent for binary non-polar systems, here we measured the densities and the refraction index for the binary systems of D4Vi with aromatic hydrocarbon (ethylbenezne, o-xylene, m-xylene, and p-xylene) at T = (288.15, 298.15, 308.15, 318.15, and 328.15) K and atmospheric pressure. The volume expansivity (α), excess molar volume (VmE), molar refraction (Rm), the deviations in refractive index (ΔnD) and the deviations in molar refraction (ΔRm) for these four binary systems were calculated and further correlated with the Redlich–Kister equation and the Legendre polynomials.

Section snippets

Chemicals and materials

The material, 2,4,6,8-tetramethyl-2,4,6,8-tetraethenylcyclotetrasiloxane (D4Vi), was obtained from commercial sources and purified by a vacuum distillation method. Ethylbenzene, o-xylene, m-xylene, and p-xylene were provided by Alfa Aesar. All chemicals above were dried with molecular sieves of 4 · 10−10 m and filtrated through a filter (0.45 μm). The purities of these chemicals were confirmed by a gas–liquid chromatography (table 1). Before use, all chemicals were degassed in an ultrasonic bath.

Volume expansivity of pure components

The temperature dependence of experimental densities for the four binary systems studied is presented in table 3 and graphically shown in figure 2. One can observe that the density decreases as both temperature and D4Vi composition in the systems increase.

The volume expansivity (coefficient of thermal expansion), α, defined by equation (1), can be calculated from the density–temperature dependence,α=1VVTP=-1ρρTP.

If an elemental transformation is performed on the right-hand term in equation

Conclusions

The new physico-chemical properties of the important monomer 2,4,6,8-tetramethyl-2,4,6,8-tetraethenylcyclotetrasiloxane were developed as densities and refractive index of the pure compound, and of mixtures with ethylbenzene, o-xylene, m-xylene, and p-xylene. The negative deviations in mole fraction or in volume fraction over the whole range were observed for excess molar volumes, the deviations in refractive index as well as the deviations in molar refractions in these four systems. From the

Acknowledgements

This work was supported by Zhejiang Provincial Technologies R&D Program of China (Grant No. 2011C21026), the Scientific and Technological Innovation Project (20100331T17) sponsored by Hangzhou Science and Technology Bureau of China and Zhejiang Provincial Natural Science Foundation of China (Grant No. Y4090016).

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