Thermodynamic characterization of poly (caprolactonediol) by inverse gas chromatography

Abstract

Specific retention volumes, V ⁰ _g , were determined for 21 solute probes on poly (caprolactonediol) (PCLD) in the temperature range 323.15–403.15 K by inverse gas chromatography. The retention diagrams drawn between ln V ⁰ _g versus 1/T are linear for all the solutes since PCLD with ten repeating units in its chain behaving like a non polymeric material under the conditions applied. The stationary phase with melting temperature ~321 K is in the liquid state in the GC column over the temperature range studied and hence found to be suitable to determine infinite dilution partial molar thermodynamic properties of mixing for solutes on PCLD. The V ⁰ _g values have been used to calculate weight fraction activity coefficients Ω^∞ and Flory–Huggins interaction parameters, χ ^∞₁₂ . The average partial molar enthalpy of solution, $\overline{\Updelta H}_{1}^{S} ,$ and partial molar enthalpy of mixing, $\overline{\Updelta H}_{1}^{\infty } ,$ are calculated using V ⁰ _g and Ω^∞ respectively. The average molar enthalpy of vaporization ΔH ^V₁ for solutes have been calculated using $\overline{\Updelta H}_{1}^{\infty }$ and $\overline{\Updelta H}_{1}^{S}$ values and compared with the literature values at 363.15 K which is the average column temperature. The partial molar entropy of mixing, $\overline{\Updelta S}_{1}^{\infty }$calculated at 363.15 K are in good correlation with the average $\overline{\Updelta H}_{1}^{\infty }$values. The total solubility parameter due to Guillet and the Hansen solubility parameters (HSP) are calculated for PCLD using χ ^∞₁₂ values. In the present work the Hansen solubility parameters have been calculated using a new method following the Hansen theory and Huang method with less weight on polar and hydrogen bonding components. The errors in the solubility HSP are lower and the correlation coefficients are better in both the methods compared to unweighted three dimensional model.