Effects of polydispersity on liquid–liquid equilibrium of polymeric fluids

The effects of polymer polydispersity on the liquid–liquid equilibrium (LLE) of polymer solutions were investigated for the simple case of polydisperse polymer solutions: mixtures composed of a solvent and two monodisperse polymers of different molecular weights. Various quasi-binary cloud point curves including the upper critical solution temperature (UCST), lower critical solution temperature (LCST), both UCST and LCST, and closed loop miscibility were determined from thermal optical analysis (TOA). To describe the phase equilibrium of polydisperse polymer solutions, we extended the chain length contribution term in the modified double lattice chain length dependent model (extended MDL-CL). Phase equilibrium calculations were conducted for several ternary systems including hypothetical hourglass type LLE. The extended MDL-CL model appropriately described the effect of polymer polydispersity on the LLE of polymer solutions and the calculated results were in satisfactory agreement with the experimental data.