Hydrophobic resins

On further heating the methylolmelamines condense and a point is reached where hydrophobic resin separates out on cooling. The resinification is strongly dependent on the pH and is at a minimum at about pH 10.0-10.5. An increase or decrease of pH from this value will result in a considerable increase in resinification rates. 

Surface active agents are important components of foam formulations. They decrease the surface tension of the system and facilitate the dispersion of water in the hydrophobic resin. In addition they can aid nucleation, stabilise the foam and control cell structure. A wide range of such agents, both ionic and non-ionic, has been used at various times but the success of the one-shot process has been due in no small measure to the development of the water-soluble polyether siloxanes. These are either block or graft copolymers of a polydimethylsiloxane with a polyalkylene oxide (the latter usually an ethylene oxide-propylene oxide copolymer). Since these materials are susceptible to hydrolysis they should be used within a few days of mixing with water. 

Instead of using organic solvents, hydrophobic resin, AmberliteTM XAD, has been used to control the substrate concentration [19]. When XAD is added to the reaction mixture, substrate and products are adsorbed to the hydrophobic resin, XAD, since... 

The carbon dioxide concentration in the film can also be controlled by other physical and chemical parameters, for instance the type of catalyst (influencing the reaction rate constants) or the use of more hydrophobic resin (influencing the water concentration). 

Y )- Benzyl morpholine is a potent appetite suppressant drug. The synthesis of 2-(/ )-benzyl-morpholine began with the reduction of the unsaturated bromocinnamaldehyde to the corresponding saturated (X)-bromo-alcohol by baker s yeast, with a very low ee of 63%. However, an efficient transformation can be achieved by controlling the substrate concentration with the addition of hydrophobic resin Amberlite XAD-1180 [26]. With a resin-to-substrate ratio of one and an initial substrate concentration of 5 gL, the saturated (X)-bromo-alcohol was recovered at nearly quantitative yield and 98.6% ee. 

To avoid this, we have employed hydrophobic resins for concentration and isolation of the products from aqueous media [49]. Organics are retained on the resin and subsequently can be desorbed with solvents such as ethanol, which is useful for green chemistry as it is readily recyclable, renewable and biodegradable. Nonextractive processes offer convenience, can be conducted with high throughput and afford low waste owing to ready disposal of the spent water, recyclability of the resin and the solvent used for desorption. 

For the solid-phase synthesis of glycopeptides, both polystyrene and PEG-based resins have been successfully used. Experiments that compare the rates of reactions on various resins have revealed that the rate of reaction completely depends on the nature of the reaction itself 45 Some reactions perform better on hydrophobic resins, while others are better on hydrophilic resins. 

M. Imazato, H. Hommura, G. Sudo, K. Katori, and K. Tanaka. The amount of hydrophobic resin binder in the microdiffusion layer for DMFC. Journal of Fuel Cell Science and Technology 1 (2004) 66-68. 

Recall from Chapter 23.2.4 that humic substances are isolated from seawater by adsorption on a hydrophobic resin followed by elution using solvents of varying pH. The desorbed compounds are fractionated into two classes, humic acids fulvic acids based on their solubility behavior. A model structure for a humic acid is illustrated in Figure 23.10a in which fragments of biomolecules, such as sugars, oligosaccharides. 

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). 

Cameron, T. I., Liten, A. D., Lawrence, J., Farenmark, J., and Turpen, T. H. (1998). Recovery of two recombinant human lysozomal enzymes from plant tissue by expanded bed adsorption with hydrophobic resins. Int. Conf. Expanded Bed Adsorption, 2nd, Napa Valley, CA, 1998, Abstr., p. 10.2. 

Ammonium sulfate is frequently used as lyotropic salt to promote hydrophobic interaction. It is also known that in the presence of this salt, antibodies tend to precipitate (see Section IV.D.i) and share their water content with the solid phase with consequent association. This is a dual mechanism where each phenomenon contributes for the adsorption of the antibody on an hydrophobic resin and has been frequently used for purification of antibodies from different sources.106-109... 

Humic substances are a broad class of organic compounds operationaUy defined by their solubility at different pHs and retention on hydrophobic resins (Aiken, 1988 Thurman, 1985). There are three operational sub-categories of humic substances humic acids, which are soluble at a higher pH but become insoluble at a pH < 2 (isolated using XAD-8 resin) fulvic acids, which are hydrophilic acids soluble under aU pH conditions (isolated using XAD-4 resin), and humin, which is insoluble at any pH (Ishiwatari, 1992). For a review of humic substances in aquatic systems, see Hessen and Tranvik (1998), Benner (2002), and Chapter 3 by Aluwihare and Meador, this volume. 

In order to seal cracks in wet conditions hydrophobic systems are used in conjunction with a hydrophilic polyurethane resin system. These are rapid foaming and setting resins which stop the flow of water when injected into cracks in concrete in the presence of moving water, providing an effective system of crack sealing in wet conditions. As soon as the hydrophilic resin stops the flow of water, the hydrophobic resin can be reinjected to produce a permanent seal. 

Humic and flilvic acids are traditionally extracted from soils and sediment samples as the sodium salts by using sodium hydroxide solution. The material that remains contains the insoluble humin fraction (Figure 3). The alkaline supernatant is acidified to pH 2 with HCl. The humic acid precipitates and the fulvic acid remains in solution with other small molecules such as simple sugars and amino acids. These molecules can be separated by passing the solution through a hydrophobic resin, such as the methacrylate cross-linked polymer, XAD-8. The fulvic acids will sorb to the resin while the more hydrophilic molecules pass through the column. The fulvic acid can be removed with dilute base. 

Aqueous samples are treated similarly beginning with the acidification step. The entire sample is then put through the hydrophobic resin, and the fulvic acids are eluted at pH 7. The humic acids are removed with 0.1 M NaOH (2). After extraction, purification of the samples can be accomplished by freeze-drying and dialysis. The use of strong acids and bases has been criticized for several reasons. They can promote degradation, decarboxylation, oxidation, and condensation reactions. Strong acids and bases can also dissolve siliceous materials and lyse cells, resulting in contamination of the sample. Other extractants have been proposed, such as sodium pyrophosphate or sodium fluoride however, the classical procedure offers the most complete dissolution of humic material from solid samples and is still most often used (72). 

Properties White, free-flowing, amorphous powder or aqueous solution. D 1.23-1.29, bulk d 151b/ft3, hygroscopic. Soluble in water and organic solvents compatible with wide range of hydrophilic and hydrophobic resins. 

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