Hydrophobic association structural parameters

The solubility parameter of water is 17 or 23, depending on the association structure of water used in the calculation. None of the values listed in Table II are within two units of either value and by the general rules of the solubility concept, none of the polymers in Table II should be water soluble. Homopolymers of monomers c, e, or f in Figure 3 are not water soluble. The solubility values listed for the W-SPs studied do not correlate with the equilibrium pressures observed. A general correlation is noted if the values of the most hydrophobic segments (i.e., the oxypropyl, oxybutyl and acetate) are compared with PMVE. The... 

Based on the earlier work of Meyer and Overton, who showed that the narcotic effect of anesthetics was related to their oil/water partition coefficients, Hansch and his co-workers have demonstrated unequivocally the importance of hydrophobic parameters such as log P (where P is, usually, the octanol/water partition coefficient) in QSAR analysis.28 The so-called classical QSAR approach, pioneered by Hansch, involves stepwise multiple regression analysis (MRA) in the generation of activity correlations with structural descriptors, such as physicochemical parameters (log P, molar refractivity, etc.) or substituent constants such as ir, a, and Es (where these represent hydrophobic, electronic, and steric effects, respectively). The Hansch approach has been very successful in accurately predicting effects in many biological systems, some of which have been subsequently rationalized by inspection of the three-dimensional structures of receptor proteins.28 The use of log P (and its associated substituent parameter, tr) is very important in toxicity,29-32 as well as in other forms of bioactivity, because of the role of hydrophobicity in molecular transport across cell membranes and other biological barriers. 

Hydrophobic associations in random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate and some methacrylamides and methacrylates substituted with bulky hydrophobes are described with a focus on preferential intrapolymer self-association which leads to the formation of single-macromolecular assemblies (i.e., unimolecular micelles). Structural parameters that critically determine the type of the macromolecular association (i.e., intra- vs. interpolymer associations) are discussed, which include the type of hydrophobes, their content in a polymer, sequence distribution of electrolyte and hydrophobic monomer units, and the type of spacer bonding. Functionalization of single-macromolecular assemblies with some photoactive chromophores is also presented. 

Hydrophobically associating polymers are water soluble polymers containing a small amount of hydrophobic functionality. The conformation of the polymer in solution is influenced by a variety of structural parameters. Polymer architecture, such as random or blocky arrangement of the hydrophobic groups will have a significant influence on polymer conformation and interactions in solution. The presence of hydrophobic functionality can result in inter- or intramolecular association or some combination of both. The relative amounts of these types of association will affect the conformation of the molecules in solution and in turn the properties of the solution. While many chemically different systems, such as hydrophobically modified cellulose [19], urethanes [15], and others [11] have been described in the literature, we will focus on only a few critical structures. To illustrate the relationships between structure and the observed solution phenomena, three types of hydrophobically associating polymers will be discussed as shown in Fig. 3.1. These are ... 

Hydrophobically associating water soluble polymers can be prepared either by copolymerization of a hydrophilic and a hydrophobic monomer or by modification of a precursor water-soluble polymer. A typical example of materials prepared by the first method is the hydrophobic derivatives of polyacrylamide (PAM) [10-15]. The copolymerization occurs in the presence of a surfactant in order to increase the solubility of the hydrophobic component in the water and the resulting polymers exhibit a rather block structure the hydrophobic groups have a rather block distribution on the PAM chain [10, 13-15]. The size of the hydrophobic blocks can be controlled by the quantity of the surfactant added (see also the contribution of Prof. McCormick group in this book). Unfortunately this copolymerization technique does not allow the simultaneous control of all the molecular parameters (i.e. polymer molecular weight, degree of modification and alkyl group distribution). 

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