Induced nematic phase in a polymer/liquid crystal mixtureWe present new experimental measurements of the molecular weight ͑MW͒ distributions in coexisting liquid phases for three polymer/solvent systems. We studied samples at the critical compositions and at four temperatures in the two-phase regions. For polystyrene in methylcyclohexane ͑with an upper critical solution point͒, we observed the expected fractionation between phases, with a higher average MW in the lower, polymer-rich phase. For poly͑ethylene oxide͒ in 2, 6-lutidineϩwater ͑with a lower critical solution point͒, the total polymer mass is nearly equal in the two phases, but the polymers of higher average MW equilibrate into the upper, 2,6-lutidine-rich phase. For poly͑ethylene oxide͒ in isobutyric acidϩwater ͑with an upper critical solution point͒, most of the total polymer mass is in the upper, isobutyric acid-rich phase, but the polymers of higher average MW equilibrate into the lower, water-rich phase; moreover, the fractionation in this case is quite dramatic, with almost a factor of 2 difference in average MW between the phases and a significant decrease in polydispersity for the lower phase. Our results support prior experimental results on this phenomenon that find that a basic Flory-Huggins ͑FH͒ theory is inadequate. More recent theoretical considerations suggest that the difference between FH theory and experiments is due to non-mean field effects, but this theory awaits direct comparison to experiments.