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

Authors: 
Enick, R., University of Pittsburgh
Koronaios, P., University of Pittsburgh
Morganstein, B., University of Pittsburgh
Velankar, S., University of Pittsburgh
Keith, J. A., University of Pittsburgh

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.