Poly lower critical solution temperature

The phase transition temperatures (lower critical solution temperature, LCST) of the pol5miers were obtained from the change in the transmittance of their aqueous solutions (Figure 1). The aqueous solution of the obtained pol5uner was prepared and its transmittance at 500 nm was monitored with increase in the ambient temperature. Both of poly-NIPA and poly-NEA showed a sudden decrease in the transmittance at 37.5 and 69.2 °C, respectively. The result shown in Figure 1 clearly suggests the thermosensitivity of the pol5mers, and the obtained LCST values are close to those reported for poly-NIPA (34.8 °C) [8] and poly-NEA (72 °C) [9]. 

As reported previously [22-23], polyDMAEMA and PolyEAAm have lower critical solution temperatures (LCSTs) at 50° and 80°C, respectively. Interestingly, poly[DMAEMA-co-EAAm (or AAm)] exhibits the LCST between 0° and 50°C, depending on the copolymer composition. 

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... 

An interesting family of polymeric ligands show inverse temperature dependence of solubihty in water, i.e. they can be precipitated from aqueous solutions by increasing the temperature above the so-called cloud point. Typically these ligands contain poly(oxyalkylene) chains, but the phenomenon can be similarly observed with poly(N-isopropyl acrylamide) derivatives (e.g. 132) and methylated cyclodextrins, too. At or above their cloud points these compounds fall off the solution, due to the break-up and loss of the hydration shell which prevents aggregation and precipitation of their molecules. Conversely, upon cooling below this temperature (also called the lower critical solution temperature, LCST) these substances dissolve again. 

Poly(N-isopropylacrylamide) (polyNIPAAM), formed by a free radical polymerization of N-isopropylacrylamide, is a water soluble, temperature sensitive polymer. In aqueous solution, it exhibits a lower critical solution temperature (LCST) in the range of 30-35 C depending on the concentration and the chain length of the polymer. Thus, as the solution temperature is raised above the LCST, the polymer undergoes a reversible phase transition characterized by the separation of a solid phase which redissolves when the solution temperature is lowered below the LCST. Its physicochemical properties have been investigated by several laboratories (1-3). 

Considering the rather complicated processes that take place during dissolution it is not surprising that some systems show peculiar behavior. For example, while solubility generally increases with temperature, there are also polymers that exhibit a negative temperature coefficient of solubility in certain solvents. Thus, poly(ethylene oxide), poly(N-isopropylacrylamide), or poly(methyl vinyl ether) dissolve in water at room temperature but precipitate upon warming. This behavior is found for all polymer-solvent systems showing a lower critical solution temperature (LCST). It can be explained by the temperature-dependent... 

Thus, the PEO segment actually becomes hydrophobic at higher temperatures. This temperature-dependent change converts the amphiphilic block copolymer to a water-insoluble hydrophobic polymer (Topp et al. 1997 Chung et al. 2000). The temperature at which the polymer exhibits this transition is called its lower critical solution temperature (LCST). In addition to PEO, substituted poly(A -isopropyl acrylamide) (PNIPAM Chart 2.1) exhibits temperature sensitivity, where the LCST can be tuned by varying the alkyl fimctionahty. The guest encapsulation combined with the temperature-sensitive precipitation of the polymers has been exploited to sequester and separate guest molecules from aqueous solutions (Fig. 2.4). 

On the other hand, poly(AT-isopropylacrylamide), poly(NIPAM), has a lower critical solution temperature (LOST) at 32 °C in water it is water-soluble below LOST but precipitates above LOST. The thermoresponsive... 

It is widely known that poly(N-isopropylacrylamide), poly(IPAAm), in water has a lower critical solution temperature (LCST) at 32 °C. LCST was originally observed in PEG solutions a long time ago. Rowlinson et al. [40] (1957) explained the lower consolute temperature for PEG in water in terms of negative entropies. The first paper on the LCST of poly(IPAAm) at about 31 °C was presented by Heskins and Guillet in 1968 [41]. They reported that aqueous solution of poly(IPAAm) showed phase separation above this temperature, and ascribed it primarily to an entropy effect on the basis of thermodynamical considerations. 

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],... 

AA AAm Con A DSS DSS-gel LCST MAPTAC MBA MP MP-gel NIPA ONPG PVMA SSPG Tc TMED acrylic acid acrylamide concanavalin A dextran sulfate sodium gel containing Con A/DSS complex lower critical solution temperature [(methacrylamide)propyl]trimethylammonium chloride /V,/V -methylenebis(acrylamide) a-methyl-D-mannopyranoside gel containing Con A/MP complex /V-isopropylacrylamide O-nitrophenyl-P-D-galactopyranoside poly(vinyl methyl ether) stimulus-sensitive polymer gel transition temperature /V,/V,/V, /V -tetramethylethylenediamine... 

Poly(vinyl methyl ether), PVME, is a thermo-sensitive polymer. The aqueous solution has a Lower Critical Solution Temperature (LCST) of 37 °C. Therefore, PVME is soluble in water below its LCST, but insoluble above its LCST. When an aqueous solution of PVME is irradiated with y-rays the solution becomes PVME hydrogel [18, 19]. The gel shows thermo-sensitivity similar to the solution, and swells below 37 °C and shrinks above this temperature. It is important to form a fine porous gel structure to obtain quick response gels. There are two methods for the purpose. One is a method using micro-phase separation by heating. The other is a method using micro-phase separation by blending of polymer solutions. 

Poly(ferrocenylsilanes) with methoxyethoxyethoxy or quaternary ammonium groups on silicon are hydrophilic or soluble in water and display lower critical solution temperature (LSCT) behavior—again, a similarity to polyphosphazenes26 3233 (see Chapter 3). 

Affinity chromatography of streptavidin was performed on a PET chip. The microchannel was first filled with the dual-modified latex beads (as shown in Figure 6.3). The biotinylated beads were surface-modified with a temperature-sensitive polymer, poly(N-isopropylacrylamide (PNIPAAm, 11 kDa). When the temperature was raised above the lower critical solution temperature (LCST) of PNIPAAm, the beads aggregated and adhered to the channel wall, because of a hydrophilic-to-hydrophobic phase transition. Then streptavidin from a sample solution was captured by these adhered biotinylated beads. Thereafter, when the temperature was reduced below the LCST, the beads dissociated and eluted from the channel wall together with the captured streptavidin [203],... 

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... 

Maderek, E. Schulz, V. Wolf, B. A., "Lower Critical Solution Temperatures of Poly(decyl methacrylate) in Hydrocarbons," Eur. Polym. J., 19, 963 (1983). 

Zeman, L. Biros, J. Delmas, G. Patterson, D., "Pressure Effects in Polymer Solution Phase Equilibria. I. The Lower Critical Solution Temperature of Polyisobutylene and Poly-dimethylsiloxane in Lower Alkanes," J. Phys. Chem., 76, 1206 (1972). 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

Poly(amino acid)s (PAAs) have also been used in drug delivery PEO-(l-aspartic acid) block copolymer nano-associates , formed by dialysis from a dimethyl acetamide solution against water, could be loaded with vasopressin. PLA-(L-lysine) block copolymer microcapsules loaded with fluorescently labelled (FITC) dextran showed release profiles dependent on amino acid content. In a nice study, poly(glutamate(OMe)-sarcosine) block copolymer particles were surface-grafted with poly(A-isopropyl acrylamide) (PNIPAAm) to produce a thermally responsive delivery system FITC-dextran release was faster below the lower critical solution temperature (LCST) than above it. PAAs are prepared by ring-opening polymerisation of A-carboxyanhydride amino acid derivatives, as shown in Scheme 1. 

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