Swelling solvents effect

Together with this solvent effect, another effect, called phase soaking, occurs in the retention gap technique if a large volume of solvent vapour has saturated the carrier gas, the properties of the stationary phase can be altered by swelling (thicker apparent film), a change in the viscosity or changed polarity. The consequence is that the column shows an increased retention power, which can be used to better retain the most volatile components. 

A study of the reaction kinetics of the reaction of butyl isocyanate with wood has been performed (West and Banks, 1986 West and Banks, 1987). Reactions were performed without catalyst and using pyridine, triethylamine, 1,4-diazobicyclo [2,2,2-octane] or di-butyl-tin-diacetate as catalyst. The data showed that no catalyst was effective without the presence of a swelling solvent. Kinetic profiles were obtained, which were deconvo-luted to yield two component reaction curves. It was considered that these two curves represented reaction with lignin and the holocellulose component of the cell wall. 

Intraparticle diffusion limits rates in triphase catalysis whenever the reaction is fast enough to prevent attaiment of an equilibrium distribution of reactant throughout the gel catalyst. Numerous experimental parameters affect intraparticle diffusion. If mass transfer is not rate-limiting, particle size effects on observed rates can be attributed entirely to intraparticle diffusion. Polymer % cross-linking (% CL), % ring substitution (% RS), swelling solvent, and the size of reactant molecule all can affect both intrinsic reactivity and intraparticle diffusion. Typical particle size effects on the... 

The activity of polymer-supported crown ethers depends on solvent. As shown in Fig. 11, rates for Br-I exchange reactions with catalysts 34 and 41 increased with a change in solvent from toluene to chlorobenzene. Since the reaction with catalyst 34 is limited substantially by intrinsic reactivity (Fig. 10), the rate increase must be due to an increase in intrinsic reactivity. The reaction with catalyst 41 is limited by both intrinsic reactivity and intraparticle diffusion (Fig. 10), and the rate increase from toluene to chlorobenzene corresponds with increases in both parameters. Solvent effects on rates with polymer-supported phase transfer catalysts differ from those with soluble phase transfer catalysts60. With the soluble catalysts rates increase (for a limited number of reactions) with decreased polarity of solvent60), while with the polymeric catalysts rates increase with increased polarity of solvent74). Solvents swell polymer-supported catalysts and influence the microenvironment of active sites as well as intraparticle diffusion. The microenvironment, especially hydration... 

Perhaps, unsurprisingly, the effects of polymer matrix on the reaction rate are probably at least as complex as solvent effects in solution-phase reactions, and broad generalizations about the characteristics of any given support in a series of different reactions are inappropriate. Reaction rates on supports depend on solvent swelling, selective adsorption, hydrogen bonding, hydrophobicity, and polarity. No single polymer support is best for all reactions. 

Suspension of PVC in a swelling solvent such as chlorobenzene may remove the lower molecular weight fraction which would be expected to contain the greatest number of reactive or thermally sensitive chain ends. The limited contribution of this fractionation effect was confirmed by swelling PVC in chlorobenzene, adding methanol, and isolating the polymer under the conditions used in the grafting reaction. 

A simple expression governs the solubility of a liquid solute in a solvent, provided the solvent is practically insoluble in the liquid solute and that, again, only dispersion forces are operative between them. The first condition yields for the activity of the solute in its practically neat liquid phase, as well as in the saturated solution in equilibrium with it, to a2 1 and In a2 0. This dispenses effectively with the first term on the right hand side of Eq. (2.10). For a given liquid solute, the solubility parameter of the solvent dictates the solubility and constitutes entirely the solvent effect on it. This fact has found much application in the determination of the solubilities of certain liquid polymers in various solvents, the mole fraction x2 and volume V2 then pertain to the monomer of the solute. If, however, the solvent is also soluble in the liquid solute, as is the case when a solvent is capable of swelling a polymer, then the mutual solubility is given by ... 

Typical spectra obtained for the probed attached at the network junction are shown in Figs. 2 and 3 The probe in THF possesses the highest ratio for CT/LE. An increased intensity for the LE was measured for the swollen sample. This effect can be explained by different polarity /mobility of the probe One can assume that covalent bonded probes possess another probe mobility than free dissolved probe molecules. Furthermore, the covalent bonded probe molecule that shows a higher polarity in comparison to the siloxane chains is located at the network junction. The attached probe molecule is surrounded mainly by siloxane chains of the network. Addition of polar swelling solvents leads to an increase of the CT-emission and the ratio CT/LE is mainly influenced by the composition of polymer and swelling agent (compare spectra for dried and swollen N1 samples in Fig. 2). Therefore, the covalently bonded probe shows another fluorescence behavior in comparison to the free dissolved probes that can be surrounded also by solvent molecules. 

Polymer surfaces that are subjected to different environmental conditions are frequently met by the practitioner. The understanding of swelling and solvent effects is key to the selection of materials in many applications, where polymers are used in contact with liquid media. Using AFM liquid cells, the underlying effects can be directly investigated. 

Lillie, M.A. and Gosline, J.M. The effects of swellings solvents on the glass transition in elastin and other proteins. The Glassy State in Foods, J.M.V. Blanshard and P.J. Lillford, eds., Nottinghan University Press, Loughborough, UK, pp. 281-301. 1993, Chapter 17. 

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