Polymers critical solution temperatures

Figure 8 Schematic for the transition of lower critical solution temperature polymer. (From Ref. 29.)...

At present, we believe that the jump transitions observed in many of the gels studied here represent first order phase transitions. If this is the case, then the gels studied here are among the first found so far in which a first order phase transition occurs near room temperature in pure aqueous solvent with substantial added salt. Early studies by Tanaka s group with poly(acrylamide) based gels required that hydrophobic solvents such as acetone be added for a discontinuous phase transition to be observed near room temperature [6-10]. The more recently studied gels based on poly(n-isopropylacrylamide) [11, 12] and other lower critical solution temperature polymers show discrete phase transitions in water with no salt [11], but the swelling transitions become continuous when moderate amounts of salt are added [12],... 

The solubility of macromolecules as a rule improves with the rising temperature. Solvent - polymer mixtures usually exhibit the upper consolute temperature or upper critical solution temperature, UCST, with a maximum on the plot of system concentration versus temperature. Above the critical solution temperature, polymer is fully soluble at any concentration. For practical work, the systems with UCST below ambient temperature are welcome. There are, however numerous polymer - solvent systems, in which the solvent quality decreases with increasing temperature. The plot of system concentration versus temperature exhibits a minimum. The phenomenon is called lower consolute temperature or lower critical solution temperature, LCST Polymer is only partially soluble or even insoluble above lower critical solution temperature. This unexpected behavior can be explained by the dominating effect of entropy in case of the stiff polymer chains or by the strong solvent - solvent interactions. The possible adverse effect of rising temperature on polymer solubility must be kept in mind when woiking with low solubility polymers and with multicomponent mobile phases. It may lead to the unforeseen results especially in the polymer HPLC techniques that combine exclusion and interaction retention mechanisms, in coupled methods of polymer HPLC (see section 11.8, Coupled Methods of Polymer HPLC). 

Vlassopoulos, D., Koumoutsakos, A., Anastasiadis, S.H., Hatzikiriakos, S.G., and Englezos, P. (1997) Rheology and phase separation in a model upper critical solution temperature polymer blend. 

Sharma, J. and Clarke, N. (2004) Miscibility determination of a lower critical solution temperature polymer blend by rheology. J. Phys. Chem,... 

BOH Bohossian, T., Charlet, G., and Delmas, G., Solution properties and characterization of polyisoprenes at a lower critical solution temperature, Polymer, 30,1695,1989. 

Supercritical fluids can be used to induce phase separation. Addition of a light SCF to a polymer solvent solution was found to decrease the lower critical solution temperature for phase separation, in some cases by mote than 100°C (1,94). The potential to fractionate polyethylene (95) or accomplish a fractional crystallization (21), both induced by the addition of a supercritical antisolvent, has been proposed. In the latter technique, existence of a pressure eutectic ridge was described, similar to a temperature eutectic trough in a temperature-cooled crystallization. 

Properties. Hydroxypropylcellulose [9004-64-2] (HPC) is a thermoplastic, nonionic cellulose ether that is soluble in water and in many organic solvents. HPC combines organic solvent solubiUty, thermoplasticity, and surface activity with the aqueous thickening and stabilising properties characteristic of other water-soluble ceUulosic polymers described herein. Like the methylceUuloses, HPC exhibits a low critical solution temperature in water. 

Second, Schneider s article reviews recent work (notably by Rowlinson, Kohn and co-workers) on phase relations in binary liquid systems where one of the components is much more volatile than the other (D1, D2, E3, M8, R9). Such systems may have lower critical solution temperatures for these systems, an increase in temperature (and, indirectly, pressure) causes precipitation of the heavy component, thereby providing a possible separation technique, e.g., for the fractionation of polymers. 

The critical point (Ij of the two-phase region encountered at reduced temperatures is called an upper critical solution temperature (UCST), and that of the two-phase region found at elevated temperatures is called, perversely, a lower critical solution temperature (LCST). Figure 2 is drawn assuming that the polymer in solution is monodisperse. However, if the polymer in solution is polydisperse, generally similar, but more vaguely defined, regions of phase separation occur. These are known as "cloud-point" curves. The term "cloud point" results from the visual observation of phase separation - a cloudiness in the mixture. 

The hydrophobic interaction results in the existence of a lower critical solution temperature and in the striking result that raising the temperature reduces the solubility, as can be seen in liquid-liquid phase diagrams (see Figure 5.2a). In general, the solution behaviour of water-soluble polymers... 

Temperature-sensitive polymers, depending on polymer structure and polymer-polymer interactions, generally exhibit two behaviors, lower critical solution temperature (LCST) [31] and upper critical solution temperature (UCST). Phase diagrams for these behaviors are presented in Figure 9. 

Figure 9 Qualitative phase diagram of a polymer solution showing phase separation both on heating (at the lower critical solution temperature) and on cooling (at the upper critical solution temperature). (From Ref. 31.)...

A3 AIBN c Cp DLS DLVO DSC EO GMA HS-DSC KPS LCST Osmotic third virial coefficient 2,2 -Azobis(isobutyronitrile) Polymer concentration Partial heat capacity Dynamic light scattering Derjaguin-Landau-Verwey-Overbeek Differential scanning calorimetry Ethylene oxide Glycidylmethacrylate High-sensitivity differential scanning calorimetry Potassium persulphate Lower critical solution temperature... 

Polymer Adsorption at the Lower Critical Solution Temperature and Its Effect on Colloid Stability... 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

In this study, adsorption behavior of water soluble polymers and their effect on colloid stability have been studied using polystyrene latices plus cellulose derivatives. As the aqueous solution of hydroxy propyl cellulose(HPC) has a lower critical solution temperature(LCST), near 50 °C(6 ), an increased adsorption and strong protection can be expected by treating the latices with HPC at the LCST. 

UOP FCC unit, 11 700-702 UOP/HYDRO MTO process, 18 568 UOP Olex olefin separation process, 17 724 Up-and-Down Method, 25 217 U/Pb decay schemes, 25 393-394 Updraft sintering, 26 565 Upflow anaerobic sludge blanket (UASB) in biological waste treatment, 25 902 Upgraded slag (UGS), 25 12, 33 Upland Cotton, U.S., 8 13 U-Polymer, 20 189 Upper critical solution temperature (UCST), 20 320, 322 Upper explosive limit (UEL), 22 840 Upper flammability limit, 23 115 Upper flammable limit (UFL), 22 840 Upper Freeport (MVB) coal... 

The preparation of monoliths with polyNIPAAm chains grafted to the internal pore surface was discussed previously. The extended solvated polyNIPAAm-chains that are present below the lower critical solution temperature of this particular polymer are more hydrophilic, while the collapsed chains that prevail above the lower critical solution temperature are more hydrophobic. In contrast to isothermal separations in which the surface polarity remains constant throughout the run [ 136], HIC separation of proteins can be achieved at constant salt concentrations (isocratically) while utilizing the hydrophobic-hydrophilic... 

Poly(A-isopropyl acrylamide) (PNIPAAm) is the most extensively studied temperature-sensitive polymer [10-20]. Crosslinked PNIPAAm exhibits drastic swelling transition at its lower critical solution temperature... 

Hydrogels synthesized from polymers and copolymers of N-isopropyl acrylamide (NIPAAm) shrink or swell as the temperature is raised or lowered through their lower critical solution temperature (LCST). 

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