Molecular weight solvent effect

We immerse a weighed sample of a crosslinked polymer in a suitable solvent and allow it to swell for up to 24 hours. We calculate the molecular weight of effective chains from Eq. 5.7. 

Deficiency of cross-linker molecules (off-balancing of stoichoimetry) was found to increase the relaxation exponent value [7, 65, 66]. The gel becomes more lossy , and stress relaxation is accelerated. Adding of a non-reacting low molecular weight solvent also increases the relaxation exponent [58, 65], even in physical gels [67]. Both effects have been attributed to screening [44, 65],... 

The measurements from linear chains revealed two unexpected results. First, the p-parameter was found to be 16-23% lower than predicted by theory both in 6-solvents and in good solvents190 192,204-209. In other words, the hydrodynamic radius is larger than theoretically expected. Second, the p-parameter decreases for lower molecular weights the effect is more pronounced for the polymers in a 6-solvent than in a good solvent. 

Continuous homogeneous catalysis is achieved by membrane filtration, which separates the polymeric catalyst from low molecular weight solvent and products. Hydrogenation of 1-pentene with the soluble pofymer-attached Wilkinson catalyst affords n-pentane in quantitative yield A variety of other catalysts have been attached to functionalized polystyrenes Besides linear polystyrenes, poly(ethylene glycol)s, polyvinylpyrrolidinones and poly(vinyl chloride)s have been used for the liquid-phase catalysis. Instead of membrane filtration for separating the polymer-bound catalyst, selective precipitation has been found to be very effective. In all... 

The solubilities of nonpolar nonacidic gases in water are usually small compared to those in nonaqueous solvents this behavior is usually attributed to the hydrophobic effect [3]. However, the solubility of the same gases in nonpolar solvents is much higher. The solubilities of gases in high molecular weight solvents, such as liquid (or molten)... 

The presence of strongly bonded regions, presumably composed of low-mobility molecules, obviously will inhibit hydrodynamic flow just as polymer dissolved in low-molecular-weight solvent does. Furthermore this effect will amplify as temperature declines. Thus it is not surprising that viscosity should experimentally diverge at Ts. 

It is difficult to describe all possible fields of application of analytical isotachophoresis. To predict feasablllty for Isotachophoresis as an analytical method, the ratio of molecular weight to effective charge can be used. Generally this ratio should not exceed 3000. Needless to say the compound must have a sufficient solubility in the solvent chosen. A brief survey of applications will be given and further information can be found in the references [3,5,6]. ... 

The gas properties have no effect on liquid holdup at low pressure and low gas rates, when the liquid flow is affected only by gravity forces. At high gas velocity the holdup decreases because of shear at the gas-liquid interface. Several correlations have been proposed to account for the effects of liquid and gas properties on holdup, but these correlations are complex and quite different in form [20], which makes comparisons difficult. Furthermore, most of the data are from studies at ambient conditions using water or low-molecular-weight solvents. More data are needed from reactors operating at industrial conditions. 

As shown recently [52,55], SAKS together with contrast variation is the method of choice for a detailed study of this problem. The electron densities of low-molecular-weight solvents as e.g. methyl methacrylate (MMA) are much smaller than that of soHd PMMA. It should thus be possible to detect even a small layer at the surface of the particles in which the solvent is enriched. Therefore the wall-repulsion effect should lead to a thin shell near the surface of the particles in which the polymer concentration is depleted. 

The manifestation of the excluded-volume effects in a polymer coil (swelling) depends on the quality of a particular low-molecular-weight solvent (solvent strength) for a given polymer and on the chain length. The effective monomer-monomer exduded-volume parameter depends on the balance of repulsion arising due to geometrical exduded volume... 

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