The temperature-concentration phase (T-c) diagrams of the uniform n-alkanes C102H206, C122H246, C162H326, and C198H398 in toluene have been determined for solution concentrations in the range 0.1 to 6% (w/w). The shorter alkanes display a "classical" behavior with the expected, strong dependence of dissolution temperature on solution concentration. The longest alkane displays a very different, "polymeric" type behavior with a concentration independent dissolution temperature (for both extended and folded chain crystals). It is argued that no current theory of polymer dissolution is able to explain this behavior. It is suggested that a locally higher concentration occurs when molecules are partially attached to a crystal either during crystallization or dissolution, and that this increased local concentration accounts for the independence of dissolution temperature on the global concentration. There are some small variations in the dissolution temperature of crystals of the same thickness grown at the same concentration, but at different temperatures. These are ascribed to differences in the stacking of the separate layers.