This lecture covers the phase separations of polymers in solution, discussing concepts such as C-C bond length, micelles, block-copolymer domain size, and the miscibility of polymers. It delves into the driving forces behind phase separation, including changes in entropy and enthalpy. The Flory Huggins theory is introduced, along with the conditions for phase separation to occur. The lecture also explores phase diagrams for polymer solutions and the occurrence of phase separation under different conditions.