Mutual solubility and lower critical solution temperature for water plus glycol ether systems

Mutual solubility and the lower critical solution temperature (LCST) are reported for a number of water + ethylene glycol ether and water + propylene glycol ether systems near atmospheric pressure. For the systems studied, the LCST is in the range of - 10 degrees C to 48 degrees C. Glycol ethers are unusual organic solvents in that they have both hydrophobic and hydrophilic functionality and can hydrogen bond with water. Because of this, their interactions with water are complex and difficult to predict. The presence of an LCST is characteristic of hydrogen-bonding mixtures, and the value of the LCST reflects the relative magnitude of hydrophobic/hydrophilic interactions in solution. A higher LCST value is indicative of a glycol ether with greater hydrophilic character. For water + ethylene glycol ether mixtures, the glycol ether becomes increasingly hydrophilic (LCST increases) as the number of oxyalkylene repeating units increases. The opposite effect is seen for water + propylene glycol ether mixtures. In this case, the glycol ether becomes more hydrophobic (LCST decreases) as the number of oxyalkylene repeating units increases. The results clearly demonstrate that water + glycol ether interactions are strong functions of both chemical structure and temperature.