Hirschfelder et al. proposed the first model for LCST systems in 1937, postulating that the unusual behavior was due to strong directional interactions, such as hydrogen bonding, between unlike molecules. In this explanation, at low temperature, molecules of two liquids A and B form energeticallyfavorable interactions with one another, producing low-temperature mixing. However, at high temperatures, the system can gain more entropy by phase separating. This is plausible if extended oligomeric structures can form in the mixture that are not present in one or both of the phase separated liquids. Despite the importance of the LCST phenomenon, rigorous studies, with direct experimental evidence for this hypothesis, are lacking.