Solvent modification

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Bean, M. F., Pallante-Morell, S. L., Dulik, D. M., and Fenselau, C. (1990). Protocol for liquid chromatography/mass spectrometry of glutathione conjugates using postcolumn solvent modification. Anal. Chem. 62 121-124. 

The vacuum part of Equation (2.306) has been derived for all but the solvent contribution by Olsen et al. [69,72,73,76], The matrix representation of the solvent modifications to the response equations is found by expanding the last two terms. Generally, the solvent contributions have the following stmcture... 

We obtain the terms for the solvent modifications of the quadratic response functions, denoted wj J, by collecting all terms lor n = 2 in Equation (2.308)... 

The solvent effect on V° can be significant. It derives from the modification of the donor and acceptor transitions densities by the medium, and is in effect regardless of whether or not the molecules interact with each other. V° is therefore the solvent-modified electronic coupling described in Equation (3.139), and as such, can be explicitly dissected into contributions from Coulombic and short-range interactions as well as electron correlation effects. According to the results reported in ref. [47], the solvent modification of Vshort is minor but VCoul is strongly influenced by the medium. In Figure 3.49 we plot results reported in ref. [47] to illustrate that. 

The independence of the limiting characteristic viscosity on the type of solvent means that cpi is independent of the viscosity of the solvent, that is the dimensional characteristic of the internal friction of the macromolecule Cyi is proportional to the viscosity of the solvent and the internal friction is not solely internal. The conclusion that the solvent contributes significantly to the intramolecular viscosity was reported by Schrag (1991), and was dubbed as the solvent modification effect . 

Westall, E. C. and Robinson, A. B. (1970) Solvent modification in Merrifield solid-phase peptide synthesis. J. Org. Chem. 35, 2842-2844. 

The way in which this solvent modification occurs is suggested by the pattern of hyperfine constants for (which is one of the few solvated electron species sufficiently stable to obtain its NMR spectrum). The Knight shift of NMR lines is due to the contact Fermi (isotropic) hyperfine interaction of the excess electron with the magnetic nuclei (X) in the solvent molecules it is the measure of spin density, (0) in the r-type atomic orbitals centered on a given nucleus X ... 

The application of solvent extraction to removal and recovery of templates or SDAs from zeolite channels was initiated by Whitehurst[7] in the 1990s for the extraction of surfactant from mesoporous M41S materials. This method or its improved analogs have become one of the most important techniques to recover surfactants from mesoporous molecular sieves. However, it is still difficult to use this technique to remove and to recover the SDAs from microporous molecular sieves because, first, the size of SDA molecules is similar to that of the channel openings and the molecules are not able to diffuse out from the channels, and, secondly, there are usually strong interactions between the microporous frameworks and the SDA molecules that prevent the SDA molecules from being extracted solely by solvents. Modification of the conventional solvent-extraction technique, such as addition of chemical agents which can adjust the... 

BIA/CAR] Biader Ceipidor, U., Carunchio, V., Pascucci, G., An approach to the study of complex formation by solvent modification. An application to the nickel(ll)-chloride system, Ann. Chim. (Rome), 66, (1976), 727-740. Cited on pages 152, 376. 

Further research is needed in the area of liquid polymer solvent modification by (a) the use of end-caps or different monomers, (b) the addition of surfactants, or (c) expansion of the polymer with CO2. In each of these cases, measurement of solvent physical properties and evaluation of reaction performance are needed. Reaction performance in supported PEG phases with CO2 as the product-bearing phase, especially as a continuous-flow system, should also be investigated. One may anticipate greater ease of handling of the catalyst plus improved mass transfer between phases as a result of a greater surface area. 

It has been common practice in the kinetic theory of dilute solutions to lump the first and third terms together and refer to this combination as it the solvent contribution, and to neglect the fourth and fifth terms. Omitting the fifth term is appropriate for dilute solutions in which polymer-polymer interactions can be Ignored. Neglect of the fourth term, however, may not always be appropriate omission of this term disregards solvent effects, such as the phenomenon of solvent modification that has been observed in recent years [23a, 23b, 23c] This term refers to the tendency for solvent molecules to become preferentially oriented in the neighborhood of the polymer molecules. 

Besides changing the configurational stability of organolithiums, solvent modification can affect the reaction path. Although benzyl chloride reacts with butyllithium in ether to give the Wurtz coupling products, bibenzyl and amylbenzene, tranr-stilbene is also a product (26). Isolation of the chlorobibenzyl was possible. 

Gisser DJ, Ediger MD (1992) Local polymer and solvent dynamics in Aroclor solutions— implications for solvent modification. Macromolecules 25(4) 1284-1293. doi 10.1021/ ma00030a013... 

For instance, by deuterating the solvent one can change the transverse relaxation time of nitroxide radicals by about one order of magnitude, while the longitudinal relaxation is nearly unaffected by such a solvent modification. Such an unwanted interference with other spins may cause difficulties in distance determination. 

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