PHASE-DIAGRAMS OF QUASI-BINARY POLYMER-SOLUTIONS AND BLENDS

A generalized Flory-Huggins theory is presented for use in fitting and predicting liquid-liquid phase diagrams of quasi-binary polymer solut ions and blends, in which one component may be polydisperse. A tempera ture- and concentration-dependent chi parameter is employed. As has be en demonstrated previously for simple binary systems, the form chosen for chi is sufficient to fit phase diagrams having upper and lower cri tical solution temperatures (UCST and LCST), combination of the two wi th the LCST lying above the UCST, closed loop and hour-glass shapes. I n extending this work to quasi-binary systems, the phase diagrams obta ined are compared with those for binary solutions and blends. It is il lustrated how polymer solutions, in which the polymeric component has the same weight-average molecular weight and even the same polydispers ity index, although having identical spinodals, may exhibit markedly d ifferent cloud-point curves. Comparison is also made with experimental data determined on a model quasi-binary system. Such comparisons may be used to extract the temperature and concentration dependence of chi for the system.