Low critical solution temperature LCST

In Fig. 3.3a and b, it was possible to observe the maximum value of ttc at the different temperatures that the monolayer can reach. At higher temperatures, rrc increases, PVP exhibits a low critical solution temperature (LCST) in water [45]. The PVP in 0.55 M aqueous Na2S04 exhibits a lower LCST at 301 K. For soluble amphiphilic monolayers, such as those of PVP, when the temperature is changed the loss of monolayer material must be considered due to the solubilization in the subphase. 

Yang, Xie, and Wu reported the syntheses of 2-ferrocenylethyl methacrylate, acrylate, methacrylamide, and acrylamide.231 Scheme 2.44 shows the preparation of the water-soluble polymer 167 by the copolymerization of 2-ferrocenylacrylamide with isopropylacrylamide. Depending on the ratio of organometallic-to-organic units the copolymer possessed low critical solution temperatures (LCST) of 26-29°C. Comparatively the pure organic poly(lV-iso-propylacrylamide) possessed an LCST of 32°C. 

If the temperature rises above another incompatibihty area may appear. Such an area has been observed in some polymer-solvent systems, which are characterized by a low critical solution temperature, LCST, T2c- In Figure 6.1, LCST is higher n UCST. The negative dependence of polymer-plasticizer compatibility on temperature suggests the theoretical probability that LCST also occurs in polymer-plasticizer systems such as PVC with either dii-sodecyl adipate, dibutyl phthalate, or tributyl phosphate. 

The organometallic copolymer of ferrocenylethylacrylamide and isopropy-lacrylamide was prepared and was foimd to be soluble in water due to the minimal incorporation of the organometallic monomer. These polymers exhibited low critical solution temperatures (LCSTs) ranging from 26-29°C when compared to the LCST of 32°C for poly(A -isopropylacrylamide)." ... 

Thermoresponsive hydrogels can swell or desweU in response to changes in temperature, thus undergoing a volume change at low critical solution temperature (LCST) in water. Above the LCST, the hydrogels are hydrophobic and expel water below the LCST, they are hydrophilic and absorb water [160, 161]. Due... 

The surfaces of liposomes have been coated [17] with thermosensitive pol5uners such as poly(A -isopropylacrylamide) [poly(NIPAM)] by taking advantage of the phase transition of polymers. The molecular structure of a hydrophobically modified poly(NIPAM), which has been studied in the preparation of temperature-sensitive Uposomes [17], is depicted in Fig. 7. Poly(NlPAM) exhibits a low critical solution temperature (LCST) around 32°C, and the LCST can be altered toward the body temperature by co-pol5unerization [56], The pol5uner is in an expanded form at low temperature, but above the critical temperature it is in a contracted form. The interactions of SUVs and hydrophobically modified poly(NIPAM) were studied by fluorescence spectroscopy [88]. More recently, sonicated DPPC and egg PC Uposomes coated with a copolymer of NIPAM and octadecylacrylate in a molar ratio of 100 1 were prepared [17,89], It was shown that above the LCST of the copolymer, the release of calcein and carboxyfluorescein from... 

It is clear from the low Q data in the top half of Figure 10.1, that the pronounced gel peak (corresponding to an interlayer spacing of approximately 75 A) observed at T = +5°C has completely disappeared at -5°C. The gel has collapsed, just as we observed with respect to increases in temperature in Chapter 1. In a manner of speaking, we could say that the results given in Chapter 1 show that the gel has an upper critical solution temperature (UCST), so the results in Figure 10.1 show that the gel also has a lower critical solution temperature (LCST). We labeled the former... 

LLE strongly depends on the temperature and the molecular weight. Typically, two LLE areas are observed, one at low tanperatures (UCST = upper critical solution temperature) and one at high temperatures (LCST = lower critical solution temperature). LCST is typically observed at temperatures between the boiling point and the critical temperature of the solvent. 

One of the main features of nonionic water-soluble cellulose derivatives is that they exhibit, like some other polyethers, an inverse solubility-temperature behavior, i.e. there is phase separation on heating above the so-called lower critical solution temperature (LCST). The temperature at which a polymer-rich phase separates is normally referred to as the cloud point (CP). For ideal solutions, this temperature corresponds to the theta-temperature. Actually, for some derivatives, the cloud point may be preceded, if the concentration is not too low, by a sol-gel transformation with an increase in viscosity and possibly formation of liquid crystals (see Sect. 3.5). As it will be seen later, this reversible thermotropic behavior may be detrimental to the performance of the derivatives or can be advantageneously utilized to develop applications. 

There are several different methods to separate PNIPAM-supported catalysts from the reaction mixtures. Both liquid-solid separations and liquid-liquid separations can be used. The most frequently used liquid-solid separation method takes advantage of the varying solubility of polymers in different solvents. For example, PNIP AM can be precipitated from THF into hexanes. PNI-PAM copolymers also exhibit lower critical solution temperature (LCST) behavior. Specifically, PNIPAM and its copolymers can be prepared such that these polymers are soluble in water at low temperature but precipitate when heated up. This property may be used as either a purification method or a separation tech-nique.[l 1] A thermomorphic system is a liquid-liquid biphasic system developed in our group. It uses various solvent mixtures with temperature-dependent miscibility to effect separation of catalysts from substrates and products, as shown in Figure 2. 

The lower critical solution temperature (LCST) phase behavior exhibited by the nanocrystals is often found for low molecular weight solutes in supercritical fluids (25,26) and also for polymers dissolved in SCFs, and results from compressibility differences between the polymer and the solvent (15). As the temperature increases or the pressure decreases, the solvent prefers to leave the solute to increase its volume and entropy. The same mechanism that governs phase separation in supercritical fluids also drives flocculation of two surfaces with steric stabilizers, as has been shown with theory (22) and simulation (23). 

Addition of an anti-solvent to a polymer solution causes the polymer solution to split into a polymer-rich phase and a solvent-rich phase. When a non-solvent is added the overall density of the original solvent becomes lower, which decreases the Lower Critical Solution Temperature (LCST) of the solution. A liquid-liquid phase-split thus occurs without raising the temperature. A low-molecular weight anti-solvent like CO2, propane or ethane can effectively decrease the LCST of the polymer solution (6) and thus induce a liquid-liquid phase-split. It is due to this effect that Gas Anti-Solvent precipitation of polymers has focused on the production of polymer particles with a specific size, structure or shape such as micro tubes (7) or micro balloons (8). Phase separation phenomena in PPE solutions during the formation of polymer membranes by the addition of a conventional anti-solvent have been described by (9). 

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