Temperature Dependence of the Heats of Solution of Poly(ethylene glycol) and of Related Compounds

The heats of solution of poly(ethylene glycol) and of related compounds (1,4-dioxane, tetra-hydrofuran, ethylene glycol, diethylene glycol, and several ethyl ethers of ethylene glycol and of diethylene glycol) have been measured as a function of the temperature. The change in the partial molar heat capacity of the solute molecule in the dissolution process, Δ2, is obtained from the temperature coefficient of the heat of solution. The Δ2 for poly(ethylene glycol) is 15 cal/deg per –CH2CH2O– chain unit. This value is in good agreement with those obtained for other low-molecular-weight compounds. The effect of the polar groups (the ethereal oxygen atom and the hydroxyl group) on the iceberg formation around the nonpolar residues has been discussed. From the results obtained, it seems likely that the iceberg formation around the –CH2CH2O– group is somewhat suppressed by the orientation-dependent interactions (hydrogen bond formation) between the ethereal oxygen atom and the water molecule.