Low critical solubility temperature

Polymers in Poor Solvents or at Low Critical Solubility Temperature... 

PROPERTIES OF SPECIAL INTEREST Exhibition of low critical solubility temperature in water at 32°C provides for interesting applications in separation science. 

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. 

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. 

A/-ISOpropyl Acrylamid6. Homopolymers from A(-isopropyl acrylamide (NlPAAm) are well known and have been of great interest because of their low critical solution temperature (LOST) behavior in water-solution. The polymer is soluble at low temperatures in water and precipitates above the LOST upon heating. Those kinds of polymers are potentially useful in the pharmaceutical or medical area. The homo- and copolymerization with water-soluble comonomers such as 2-hydroxyethyl methacrylate and characterization of the corresponding polymers of NlPAAm are described in some papers. In the case of copolymerization with hydrophobic comonomers, the use of an organic solvent is necessary, otherwise the polymerization has to be carried out in emulsion. But the different solubilities of the monomers in water often make the copol3unerization of water-soluble and water-insoluble monomers by classical emulsion polymerization difficult. Because of the above discussed property of cyclodextrin derivatives, these problems can be avoided if the copolymerization reactions are performed in the presence of cyclodextrin derivatives. 

For most polymers soluble in organic (nonpolar) solvents, the solubility increases upon heating. For water-soluble polymers, the situation is more delicate the solubility may either increase or decrease as a function of temperature. The solubility limit is often called upper (or lower) critical solubility temperature (UCST or LOST, respectively). For many water-soluble polymers, the LOST is relatively low (from 27-28 C for poly(N-isopropylacry-lamide) (PNIPAM) to about 100 °C for poly(ethylene oxide) (PEO)) and can be reached at normal atmospheric pressure such polymers are often referred to as thermosensitive. In terms of Flory theory of polymer solutions, the UCST or the LCST can be associated with the 6 temperature. Below UCST (above LCST), the polymer solution undergoes macroscopic phase separation into homogenous polymer-rich phase (precipitate) and dilute... 

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)." ... 

The polymer has lower-limit critical solubility temperature (LCST) in water, and dissolves in water at low temperatures. It does not dissolve >32°C. 

Most hydrophobic substances have low solubilities in water, and in the case of liquids, water is also sparingly soluble in the pure substance. Some substances such as butanols and chlorophenols display relatively high mutual solubilities. As temperature increases, these mutual solubilities increase until a point of total miscibility is reached at a critical solution temperature. Above this temperature, no mutual solubilities exist. A simple plot of solubility versus temperature thus ends at this critical point. At low temperatures near freezing, the phase diagram also become complex. Example of such systems have been reported for sec-butyl alcohol (2-butanol) by Ochi et al. (1996) and for chlorophenols by Jaoui et al. (1999). 

Supercritical fluids show unique physicochemical properties, such as density, diffusivity, solubility, and viscosity all can be easily controlled by changing temperature and pressure. Thus, these fluids are attractive as a useful solvent for chemical reactions and the following purification. Particularly, supercritical C02(scC02) has the advantages of relatively low critical temperature and pressure (critical temperature (71.) = 304.2 K, critical pressure (Pc) = 7.28 MPa), non-flammability, and inexpensiveness. 

The melting behavior for TPP in the presence of compressed pentane (Figure 1) is characterized by an interrupted three-phase, SLG equilibrium line which terminates at a LCEP. This behavior is characteristic of a gas and a solid with low mutual solubility, and is expected when the triple-point temperature of the solid is much greater than the critical temperature of the gas (3). At temperatures just above the LCEP temperature, TPP does not melt in the presence of compressed pentane, and gas-solid equilibrium is observed at pressures up to two hundred atmospheres (Figure 3). 

Poly(N-isopropylacrylamide) (PNIPAM) is the most studied thermosensitive polymer in aqueous media. It is soluble in water at low temperatures but becomes insoluble when the temperature is increased above a certain temperature ( 32 °C) (lower critical solution temperature), which is related to the coil-to-globule transition [64, 65]. In the case of a polymer network, a volume change occurs reversibly within a narrow temperature range. The properties of such microgels can be varied to a great extent by the introduction... 

Carbon dioxide can be used as a reaction solvent when pressurized (supercritical carbon dioxide, SCCO2). Carbon dioxide is nontoxic, inexpensive, abundant, and easily recycled. These properties have made it attractive as an extraction solvent. The low critical temperature of CO2 (Ti ) 31.1 °C ensures that SCCO2 is a safe solvent for many applications. " There are solubility issues that suggest SCCO2 is a rather polar solvent. For example, many systems with hydrocarbon chains are... 

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