Molecular weight cloud point

Appearance color water number average molecular weight cloud point polyethylene glycol ash iron unsaturation acidity or basicity refractive index iodine number viscosity surface tension, 0.01% aqueous... 

Tempera.ture Effect. Near the boiling point of water, the solubiUty—temperature relationship undergoes an abmpt inversion. Over a narrow temperature range, solutions become cloudy and the polymer precipitates the polymer caimot dissolve in water above this precipitation temperature. In Figure 4, this limit or cloud point is shown as a function of polymer concentration for poly(ethylene oxide) of 2 x 10 molecular weight. 

Solubility. PPO polyols with a molecular weight below 700 are water soluble. The triol is slightly more water soluble than the diol. The solubihty in water decreases with increasing temperature. This inverse solubiUty causes a cloud point which is important in characteri2ing copolymers of propylene oxide and ethylene oxide. 

Miscible blends of high molecular weight polymers often exhibit LOST behavior (3) blends that are miscible only because of relatively low molecular weights may show UCST behavior (11). The cloud-point temperatures associated with Hquid—Hquid phase separation can often be adequately determined by simple visual observations (39) nevertheless, instmmented light transmission or scattering measurements frequendy are used (49). The cloud point observed maybe a sensitive function of the rate of temperature change used, owing to the kinetics of the phase-separation process (39). 

A melamine laminating resin used to saturate the print and overlay papers of a typical decorative laminate might contain two moles of formaldehyde for each mole of melamine. In order to inhibit crystallization of methylo1 melamines, the reaction is continued until about one-fourth of the reaction product has been converted to low molecular weight polymer. A simple deterrnination of free formaldehyde may be used to foUow the first stage of the reaction, and the build-up of polymer in the reaction mixture may be followed by cloud-point dilution or viscosity tests. 

The association of the graft copolymers in water at room temperature was studied by DLS [180]. The hydrodynamic radius of the various copolymers in dilute aqueous solutions at 20 °C, well below the cloud point, was determined for solutions ranging in concentration from 1 to 10 gL1. Similar measurements were also conducted for solutions of an unmodified PVCL of similar molecular weight (Fig. 24a). The hydrodynamic radius of PVCL is of the same order of magnitude in aqueous solution and in tetrahydofuran, a good sol-... 

According to this concept, it is expected that polymer molecules, especially high molecular weight polymers, give an increased adsorption at a temperature close to the cloud point, and particles with the thick(or dense) adsorption layer of polymer formed out of a poor solvent would show strong protection against flocculation. 

General Comments. The (P, T) cloud curve for the PIB of > -2 xlO dissolved in 2-methylbutane agreed,within experimental error, with other values reported in the literature (6,2.) The slope of the curve differed from other results but this could have been caused by the molecular weight distribution exhibited by the sample used in this study. The cloud point curve for an infinite molecular weight polymer, i.e. 0 conditions, was established from our measurements and from literature data and is shown plotted in Figure 2. It can be seen that 0 increase as a function of applied pressure with a slope (dT/dP)c of 0.56. 

The properties of solutions of macromolecular substances depend on the solvent, the temperature, and the molecular weight of the chain molecules. Hence, the (average) molecular weight of polymers can be determined by measuring the solution properties such as the viscosity of dilute solutions. However, prior to this, some details have to be known about the solubility of the polymer to be analyzed. When the solubility of a polymer has to be determined, it is important to realize that macromolecules often show behavioral extremes they may be either infinitely soluble in a solvent, completely insoluble, or only swellable to a well-defined extent. Saturated solutions in contact with a nonswollen solid phase, as is normally observed with low-molecular-weight compounds, do not occur in the case of polymeric materials. The suitability of a solvent for a specific polymer, therefore, cannot be quantified in terms of a classic saturated solution. It is much better expressed in terms of the amount of a precipitant that must be added to the polymer solution to initiate precipitation (cloud point). A more exact measure for the quality of a solvent is the second virial coefficient of the osmotic pressure determined for the corresponding solution, or the viscosity numbers in different solvents. 

The cloud point curves of the epoxy monomer/PEI blend and BPACY monomer/PEI blend exhibited an upper critical solution temperature (UCST) behavior, whereas partially cured epoxy/PEI blend and BPACY/PEI blend showed bimodal UCST curves with two critical compositions, ft is attributed to the fact that, at lower conversion, thermoset resin has a bimodal distribution of molecular weight in which unreacted thermoset monomer and partially reacted thermoset dimer or trimer exist simultaneously. The rubber/epoxy systems that shows bimodal UCST behavior have been reported in previous papers [40,46]. Figure 3.7 shows the cloud point curve of epoxy/PEI system. With the increase in conversion (molecular weight) of epoxy resin, the bimodal UCST curve shifts to higher temperature region. 

One of the important quality control parameters is the cloud point — the temperature at which a solution of the polymer changes to a suspension or vice versa (see Figure 1.3). An examination of Plutonic product literature shows the effects of both EO/PO ratio and molecular weight. Since we recognize that these effects also impact solubility, we chose to look elsewhere for an answer controlling all these factors in the field might be problematic. 

Sjoberg, A., G. Karlstrom, and F. Tjerneld. 1989. Effects on the cloud point of aqueous polyethylene glycol) solutions upon addition of low molecular weight saccharid ftacromolecules22 4512-4516. 

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