We describe the initial studies of the complex aqueous phase behavior of poly(trimethylene ether) glycol (PO3G), a renewably sourced polyether glycol. Cloud point measurement revealed that a low molecular weight PO3G exhibits both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) in water in the temperature range between 30 degrees C and 80 degrees C. At low concentrations of PO3G, the polymer solutions exhibit LCST-type phase behavior. In the intermediate concentration ranges, PO3G and water are immiscible. However, at higher concentrations of PO3G, the solutions show UCST-type phase behavior. In addition, both the LCSTs and UCSTs can be easily tuned over a wide range by varying the amount of alcohol co-solvents. These findings have potential applications in the design of personal care applications and in the development of thermosensitive smart materials. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012