Isotope and pressure dependence of liquid-liquid equilibria in polymer solutions. 5. Measurements of solute and solvent isotope effects in polystyrene-acetone and polystyrene-methylcyclopentane. 6. A continuous polydisperse thermodynamic interpretation of demixing measurements in polystyrene-acetone and polystyrene-methylcyclopentane solutions

(Liquid + liquid) equilibria of (polystyrene + nitroethane). Molecular weight, pressure, and isotope effects

“…Reproducibility was checked by making some preliminary test measurements on two wellstudied systems (PS + methylcyclopentane and PS + acetone). Results were in excellent agreement (8) with those obtained by Luszczyk et al (1) A schematic diagram of the phase equilibria apparatus is shown in figure 1. Light from a He-Ne LASER (L) passes across the solution contained in the cell (C), which is immersed in a high precision oil (or water) bath (BT).…”

“…It is based on a similar apparatus conceived and built by Szydlowski et al (14) which was recently used in the study of several polymer + solvent systems. (1,(14)(15)(16) However, the present apparatus has some improvements, namely in the pressure generating system and in the control and data acquisition features.…”

“…In order to avoid long thermal relaxation times, which are much longer than pressure relaxation ones, isothermal operation is preferable. (1,(14)(15)(16) Cloud-points ( p, T, w ps ) are detected when light from a He-Ne LASER passes across the solution and there is a sudden increase in scattered light accompanied by a sudden decrease in transmitted light exiting the cell. Scattered light intensity is captured at low angle (2 < 2θ/ deg < 4) in the outer part of a bifurcated optical cable, while transmitted light is captured in the inner portion of this cable.…”

“…Furthermore, systems involving polymers often show "unusual" liquid-liquid phase behaviour, like demixing both upon cooling (upper critical solution temperature, UCST) and heating (lower critical solution temperature, LCST), even in those cases where specific strong interactions are absent. (1,2) Therefore, most polymer systems exhibit both UCST and LCST behaviour. Sometimes both low and high pressure immiscibility (upper critical solution pressure, UCSP, and lower critical solution pressure, LCSP, respectively) can also be found, (2)(3)(4) while more complicated phase diagrams like those exhibiting "hourglass", bimodal shapes, and islands of miscibility inside a two-phase region have also been experimentally proven.…”

“…Sometimes both low and high pressure immiscibility (upper critical solution pressure, UCSP, and lower critical solution pressure, LCSP, respectively) can also be found, (2)(3)(4) while more complicated phase diagrams like those exhibiting "hourglass", bimodal shapes, and islands of miscibility inside a two-phase region have also been experimentally proven. (1,(5)(6)(7) For all these reasons, polymer solution thermodynamics has become an important research topic during the last decades. The work reported in this paper is part of a more global research program that includes the experimental determination and the theoretical interpretation (6,8,9) of polymer + solvent liquid-liquid phase diagrams, namely the effect of concentration, pressure, polymer molecular weight, polydispersity, and tacticity, as well as the isotope substitution effect on polymer and/or solvent.…”