| Abstrakt: |
The normal (p = 101.325 kPa) boiling-temperature behavior of a homologous series, TB, as a function of the number of repeat units, N, is fit by a hyperbolic function whose limiting value asymptotically approaches TB(∞) = (1217 ± 246) K for series related to polyethylene and approximately TB(∞) = 915 K for those related to polytetrafluoroethylene. Normal boiling temperatures have been fit to the function TB = TB(∞)[1−1/(aBN +bB)] where aB and bB are constants characteristic of the series investigated. Similar behavior is observed for the critical temperature, TC. As the number of repeat units, N, approaches infinity, TB and TC are found to converge. This provides an indirect method of determining TC(∞). Combined with a few other experimentally determined critical temperatures, the TC of an entire series can be predicted. Consistent with the convergence of TB and TC, the limiting critical pressure, PC(∞), is found to approach 1 atm as N approaches infinity. The vaporization enthalpy and entropy at the boiling temperature, ΔlgHm(TB) and ΔlgSm(TB), used initially to suggest hyperbolic behavior of TB, show complex behavior with increasing N. This behavior is discussed in terms of a simple mathematical model proposed previously. |
