(598b) Water-Induced Crystallization of Poly(trimethyleneglycol)

An unusual and uncommon phase behavior has been observed when small amounts of water are dissolved in poly(trimethlyeneglycol) (i.e. poly(1,3-propane diol).  Poly(trimethylene glycol), (a low molecular weight, transparent colorless liquid with a freezing point of 9 C) freezes upon the addition of water.  The two components do not react; the water elevates the freezing point of the polymer to temperatures as high as 36C.  This phenomena is reversible, as the mixture slowly liquefies when placed in a low humidity environment at 22 C.  Microscopic observations of the crystallization, melting point and DSC measurements, coupled with XRD results, verify that this is a slow crystallization process, rather than a reaction.   This phenomena is not observed when water is added to polyethylene glycol, polypropylene glycol (poly(1,2- propane diol)), or polytetramethylene glycol (polytetrahydrofuran).  To the best of our knowledge, poly(trimethlyeneglycol)and poly(trimethlyeneglycol) dimethylether are the only liquids that exhibit a dramatic increase in freezing point upon the addition of water.  Molecular modeling has been employed to explain why the hydrogen bonding associated with the water causes poly(trimethlyeneglycol) to freeze.