Polymer choosing hydrophobic polymers

A critical factor in the success of a particular separation in an ABS may be the choice of polymer. The polymer not only affects the distribution of the solute between the phases but also has a considerable effect on the physical characteristics of the phases. It may be possible to fine-tune the polymer-rich phase by choosing from a variety of commercially available polymers whose hydrophobicity increases as PEG < Pluronic [block PEG/ polypropylene glycol (PPG) copolymers] < PPG < polytetramethylene glycol (Fig. 3 [36—40]). PPG-2000 is essentially water insoluble (and thus can be utilized neat) but is included for comparison with the ABS systems. The Pluronic polymer used, L64, has a very narrow range of usefulness [41], At low polymer and salt concentrations it forms a monophasic system. If the concentration of polymer and salt is too high, the polymer tends to foam out of solution. 

As well as the more common oil in water suspension methods, it is also possible to make stable water in oil suspensions by choosing alternative surfactants with much lower hydrophilic/lipophilic balance values, combined with solvents such as hydrocarbons as the dispersing phase. These can be used to make beaded polymers from water-soluble monomers such as acrylamide. Although little work has been done to date with imprinting in aqueous conditions (using hydrophobic interactions... 

These results demonstrate that with this model system it is not possible to determine the precise number of LMA monomers in a micelle or in a hydrophobic region of the polymer molecule rather, by choosing an appropriate level of mercaptoethanol and keeping it constant throughout all experiments, the change in the average PLMA MW as polymerization conditions are changed is determined. For this work, 0.072 M mercaptoethanol was always used. Because the model system yields relative results, a series of experiments were often run without propanamide to reduce the experimental complexity. 

The variety of structures encountered in microemulsions offers great versatility for choosing the locus of polymerization. Besides polymerization in globular microemulsions, several studies have dealt with polymerization of monomers in the other phases of microemulsions. One of the main goals underlying these studies was to use the microstructure of microemulsions as a template to produce solid polymers with similar characteristics. For example, incorporation of large amount of hydrophobic monomers in the continuous phase of W/O microemulsions should yield solid polymers with a Swiss cheese-like structure capable of encapsulating the disperse phase (water). This would allow the inclusion of materials (metallic colloidal particles as catalysts, photochromic compounds, etc.) in the disperse phase that would otherwise be insoluble in the polymer. 

Owing to the well-defined stereochemistry, the diversities in choosing hydropbobic/hydrophilic amino acids, and specific secondary structures, polypeptides have been intensively investigated as a biomaterial.Contrary to the random hydrophobically driven self-assembly of the most synthetic polymer, the secondary structures of the polypeptides such as a-helix, /3-sheet, and random coil significantly affect the gelation behavior. 

Biomaterials. Adsorbed polymers find many apphcations as surface modifiers in biomedical apphcations. By choosing a combination of hydrophobic and hydrophilic copolsrmers, surfaces can be modified to make them biocompatible (65) (see Biomolecules at Interfaces). In the area of tissue engineering (qv), adsorbed layers with specihc amino acid sequences can be used to promote cell adhesion and proliferation. The recent developments in the design of biochips to analyze specihc DNA molecules also take advantage of this technology. Polymer adsorption on patterned surfaces can be used to mimic pattern recognition. This effect can be used to develop sensors and molecular-scale separation processes (66). 

This novel sequential photoinduced graft polymerization was tested by Bowman et al. [MA 99] on hydrophobic porous polypropylene (PP) membrane in the presence of acrylic acid. Experimental results showed that the grafting density and the graft polymer chain length could be controlled by choosing the suitable reaction conditions in both steps. In addition, the method substantially eliminates the formation of imdesired homopolymer... 

The second application of luminescence spectroscopy in polymer science has been as a tool to study polymer systems themselves. Here a fluorescent or phosphorescent dye is introduced into a polymer environment as a molecular sensor of the environment. One chooses the dye with a knowledge of its spectroscopy in the hopes that changes in its emission spectrum, or, in a pulsed experiment, its emission decay profile, will convey detailed molecular level information about the polymer system itself. These are the experiments which mimic applications of luminescent sensor techniques in biology, where these dyes provide information about hydrophobicity in proteins, local polarity at water-membrane interfaces, distances in antibody-antigen interactions, and a wide variety of other issues concerning system morphology and dynamics. 

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