Showing papers by "DSM published in 1976"

Liquid—liquid phase separation in multicomponent polymer systems XIV. Dilute and concentrated polymer solutions in equilibrium (continued)†

Abstract: The distribution of macromolecules between two liquid phases in solvent/polymer systems depends on molecular weight in a more complicated way than that suggested by classic equations which indicate proportionality between the logarithm of the distribution coefficient and molecular weight or some fractional power thereof The main reason for the discrepancy must be sought in the fact that in such systems equilibria exist between extremely dilute and relatively concentrated polymer solutions If both concentration regimes are included in a single free-enthalpy equation proposed previously, containing no arbitrarily adaptable parameters and smoothly describing the transition between the two states, improved agreement with experiment is obtained, but further developments are needed The molecular-weight dependence of the distribution coefficient appears to provide a sensitive means of discovering the parameters that play an important rǒle in the free enthalpy of mixing

Liquid‐liquid phase separation in multicomponent polymer systems. XIII quasi‐binary phase diagrams with three‐liquid‐phase separation

Abstract: Using the Gibbs free energy of mixing relation of Flory and Huggins with a concentration-dependent interaction parameter one can calculate quasi-binary phase diagrams for solvent-polymer systems. If the polymer has a very asymmetric molecular weight distribution, separation into three-liquid-phases occurs which may result in a cloud-point curve without stable critical point. In the latter case the spinodal does not touch the stable branches of the cloud-point curve and the coexistence curves show marked bends and kinks. These phenomena could be qualitatively verified by experiments on the system cyclohexane-polystyrene. The phase-volume ratio method for the determination of consolute states itself clearly indicates when situations prevail precluding its applicability.