Cyclooctane, thermodynamic properties

Finke, H.L., Scott, D.W., Gross, M.E., Messerly, J.F., Waddington, G. (1956) Cycloheptane, cyclooctane and 1,3,5-cycloheptatriene. Low temperature thermal properties, vapor pressure and derived chemical thermodynamic properties. J. Am. Chem. Soc. 78, 5469-5476. 

Shiohama, Y. Ogawa, H. Mnrakami, S. Fujihara, I. Excess thermodynamic properties of (cis-decalin ortrans-decalin + cyclohexane or methylcyclohexane or cyclooctane) at 298.15 K7. Chem. Thermodyn. 1988, 20,1307-1314 " ... 

We have a dilemma we need a high-quality solvent to insure that the polymer remains in solution when it is formed but we need a solvent whose quality can be easily adjusted to induce the polymer to drop out of solution. How can we resolve it First, we need to know the thermodynamic variables that cause the occurrence of an LCST (chapter 3). The key variable in this instance is the chemical nature of the solvent or, to a first approximation, the critical properties of the solvent. Decreasing the solvent quality shifts the LCST curve to lower temperatures, and it is this variable that we wish to manipulate to force the polymer out of solution. To demonstrate the effect of solvent quality on the location of the LCST curve, consider the difference in LCST behavior for the same polymer, polyisobutylene, in two different solvents, n-pentane and cyclooctane. The LCST curve for the polyisobutylene-rt-pentane system begins at 70°C, while for the polyisobutylene-cyclooctane system it begins at 300°C (Bardin and Patterson, 1969). Cyclooctane, which has a critical temperature near 300°C, is a much better solvent than n-pentane, which has a critical temperature near 200°C, probably because cyclooctane has a greater cohesive energy density that translates into a lower thermal expansion coefficient, or equivalently, a lower free volume. Numerous examples of LCST behavior of polymer-solvent mixtures are available in the literature, demonstrating the effect of solvent quality on the location of the LCST (Freeman and Rowlinson, 1960 Baker et al., 1966 Zeman and Patterson, 1972 Zeman et al., 1972 Allen and Baker, 1965 Saeki et al., 1973, 1974 Cowie and McEwen, 1974). 

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