Lower critical solubility temperature

A poly(propylenamine) dendrimer (11, Fig. 6.37) functionalised with poly-(N-isopropylacrylamide) (PIPAAm) (see Section 4.1.2) was used as dendritic host for anionic cobalt(II)-phthalocyanine complexes (a, b) as guests, which are held together by supramolecular (electrostatic and hydrophobic) interactions [57]. These dendritic complexes were investigated as catalysts in the above-mentioned oxidation of thiols, where they show a remarkable temperature dependence the reaction rate suddenly increases above 34°C. One attempted explanation assumes that the dendritic arms undergo phase separation and contraction above the Lower Critical Solubility Temperature (LCST). At this temperature the phthalocyanine complex site is more readily accessible for substrates and the reaction rate is therefore higher. 

Charlet, G. Ducasse, R. Delmas, G., "Thermodynamic Properties of Polyolefin Solutions at High Temperature 2. Lower Critical Solubility Temperatures for Polybutene-1, Polypen-tene-1 and Poly(4-methylpentene-1) in Hydrocarbon Solvents and Determination of the Polymer-Solvent Interaction Parameter," Polymer, 22, 1190 (1981). 

PES is miscible with DGEBA or DPEDC at room temperature, and PES-DGEBA blends have a lower critical solubility temperature (LCST) behavior (Figure 2). But because of CE reactions at temperatures greater than 100 °C, the comparison between CE and DGEBA is not possible. 

Miscibility of the blend components has an obvious effect on morphology (for more detailed discussions see Chapter 8). During processing, the hydrostatic and shear stresses can change the lower critical solubility temperature (LCST) by at least 60°C. This may result in formation (inside the processing unit) of a miscible blend. The blend emerging from the extruder may phase separates by the spinodal decomposition mechanism into a co-continuous structure, whose degree of dispersion can be controlled example PET/PC blends. 

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... 

ALL Allcock, H.R. and Dudley, G.K., Lower critical solubility temperature study of alkyl ether based polyphosphazenes, Macro/wo/ecM/es, 29, 1313,1996. 

Roth et al. [42] used steady-state fluorescence measurements to study the emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The total fluorescent dye content in the samples was <0.02 mol%. As shown in Figure 25.15a, before phase separation the fluorescence intensity of the spectra decreased slowly with increasing temperature. However, after phase separation (see Figure 25.15b) a sharp increase in fluorescence intensity was observed, which was attributed to the removal of fluorescence quenching of the dye by the local presence of the more polar PVME component in the misdble state. These results showed clearly that the PS/PVME blend displays a lower critical solubility temperature (LCST) type of phase diagram. 

LCST Lower critical solubility temperature molecules... 

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