Hydrophobe incorporation determination

Because the level of hydrophobic monomer in the feed is usually low (<1 mol %), no analysis has been successful in measuring hydrophobe incorporation into the polymer. To date, hydrophobe incorporation has been inferred on the basis of a comparison of hydrophobe-containing polymer solution properties to those of corresponding polymers with no hydrophobe. The subject of this chapter is to present recent results obtained with a technique developed to quantitatively determine the incorporation of hydrophobic monomer into a water-soluble polymer. 

For studies of hydrophobe incorporation as a function of conversion of monomer to polymer, aliquots were removed from the reaction polymerization mixture at various times, weighed, and slowly poured into methanol that contained 1000 ppm of hydroquinone. The precipitated polymer was isolated as described and then weighed to determine percent conversion. 

Determination of Hydrophobe Incorporation. A quantitative UV spectrophotometric technique was developed for the determination of the incorporation of hydrophobic monomer into a water-soluble polymer. The technique was based on UV spectroscopic detection of hydrophobic monomers containing phenyl groups. The placement of the phenyl groups into... 

The incorporation of hydrophobic monomer into the polymers was determined by a comparison of the absorptivity of the hydrophobe unit in the polymer to the corresponding model. With the assumption that the absorptivity of the hydrophobe in the polymer ik the same as that of the model, the ratio of polymer absorptivity to model gives the weight fraction of hydrophobe (jch) in the polymer (equation 3). Converting Xh to mole fraction and dividing by the feed content in mole percent of hydrophobic monomer (My) results in the hydrophobe incorporation. The expressions for incorporation into RAM and HRAM polymers are given by equations 4 and 5, respectively. 

Hydrophobe Incorporation. With N-4-ethylphenylacrylamide as the hydrophobic monomer, it was possible to determine incorporation into... 

C4RAM at all concentrations of N-butylphenylacrylamide hydrophobe was not soluble in ethanolic solvent therefore, only the hydrolyzed polymers (C4HRAM) were evaluated in 2% ethanol. As shown by the data in Table III, all of the hydrolyzed polymer systems of C4HRAM and one polymer (l-CgHRAM) that contained 1-acrylamido-l-phenylhexane were determined to have >90% hydrophobe incorporation. 

Despite their utility, hydrophobically associating water soluble polymers are difficult to synthesis and characterize. This chapter reviews the synthetic routes developed to overcome problems associated with mixing oil-soluble and water-soluble reagents/monomers. It also describes methods for determining the amount of hydrophobe incorporated via NMR, UV, and degradation/GC. 

G. M. Omann and M. Glaser, Biosynthetic incorporation of fluorescent carbazolylun-decanoic acid into membrane phospholipids of LM cells and determination of quenching constants and partition coefficients of hydrophobic quenchers, Biochemistry 23, 4962-4969 (1984). 

As explained above in Section n, incorporation of chiral amino acids in the linker arms between the template and the hgating hydroxamate groups not only allows one to determine the directionality of the hehcal twist, but also permits one to modify the chelator properties such as buUciness, hydrophobicity and receptor selectivity. 

Heretofore, ionic liquids incorporating the 1,3-dialkylimidazolium cation have been preferred as they interact weakly with the anions and are more thermally stable than the quaternary ammonium cations. Recently, the physical properties of 1,2,3,4-tetraalkylimidazolium- and 1,3-dialkylimidazolium-containing ionic liquids in combination with various hydrophobic and hydrophilic anions have been systematically investigated (36,41). The melting point, thermal stability, density, viscosity, and other physical properties have been correlated with alkyl chain length of the imidazolium cation and the nature of the anion. The anion mainly determines water miscibility and has the most dramatic effect on the properties. An increase in the alkyl chain length of the cations from butyl to octyl, for example, increases the hydrophobicity and viscosity of the ionic liquid, whereas densities and surface tension values decrease, as expected. 

Classical QSAR will continue to play its part in the optimization and selection of drug candidates. A fundamental difficulty with classical (property-based) QSAR is an over-reliance on the relevance of hydrophobicity, electrostatic and simple bulk steric effects as determinants of relative potency. We know that conformation is crucially important, but this is ignored in the classical approaches. The need for a structure-based QSAR method which also incorporates conformational flexibility might be met by development of a neural network (Livingstone and Salt, 1992 So and Richards, 1992) or machine learning program (King et al., 1992). 

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