Solution properties hydrophobically associating polymers

X HE RHEOLOGICAL PROPERTIES OF WATER-BASED FLUIDS can be controlled with hydrophobically associating polymers. Hydrophobically associating polymers are synthetically derived, water-soluble polymers that contain a small number of oil-soluble or hydrophobic groups. When these polymers are dissolved in aqueous solution, the hydrophobic groups aggregate to minimize their exposure to water, in a fashion analogous to that of surfactants... 

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 ... 

Zhang, Y. X., Da, A. H., Butler, G. B., and Hogen-Esch, T. E.1992. A fluorine-containing hydrophobically associating polymer. I. Synthesis and solution properties of copolymers of acrylamide and fluorine-containing acrylates or methacrylates. J. Polym. Sci., Part A Polym. Chem. 30 1383-1391. 

As mentioned in Sect. 2.2.3, the biodistribution of HPMA copolymers depends on many factors. Molecular weight influences the uptake in the isolated tissue of yolk sac [266] as well as the elimination in vivo [124, 125,267,268]. Nonspecific increase in the rate of polymer uptake can be achieved by incorporation of positively charged or hydrophobic comonomers into the HPMA copolymer structure, such as methacryloyloxyethyltrimethylammonium chloride [22], N-methacryloyltyrosinamide [21], or N-[2-(4-hydroxyphenyl)ethyl]acrylamide [267]. The incorporation of hydrophobic moieties may influence the solution properties of the HPMA copolymer conjugates [132,134,269]. The interaction with the cellular surface may depend on the association number and the stability of the micelles. 

The rheological properties of all HMHEC polymers are profoundly affected by the hydrophobe molar substitution (MS) and the hydrophobe chain length. For any given hydrophobic moiety, there is a threshold hydrophobe MS below which there are no significant associative interactions. The most common phenomenological evidence for associative behavior is a dramatic increase in the solution viscosity of HMHEC polymers as a function of hydrophobe MS. The solution viscosity of HMHEC polymers continues to increase as a function of hydrophobe MS until the maximum limit of solubility is reached, as which point the HMHEC polymer becomes insoluble in water.33... 

The properties of poly(methacrylic acid) show that considerable association of the o-methyl groups occurs in aqueous solutions of this polymer (Ji). This association is often referred to as a hydrophobic Interaction. Some properties of other polymers, such as the polycondensate between L-lysine and 1,3-benzenedisulfonyl chloride ( ), are also attributed to hydrophobic interactions between parts of the polymer chains. 

Hydrophobically modified water-soluble polymers (HMWSPs) exhibit enhanced solution viscosity and unique rheological properties. These properties can be explained in terms of intermolecular associations via hydrophobes. This chapter describes the synthesis and solution properties of HMWSPs, Particularly discussed are the solution properties of hydrophobically modified hydroxyethytjcellulose (HMHEC) in aqueous and surfactant systems, HMHECs interact with surfactants and thus modify solution viscosities. The structure and the concentration of the surfactant dictate the solution behavior of HMHEC. The unique solution properties of HMHEC can be exploited to meet industrial demands for specific formulations or applications. 

A few years ago, Landoll (2-4) reported that grafting a small amount of long-chain alkyl hydrophobes onto a nonionic water-soluble polymer leads to associative thickening behavior (i.e., enhanced viscosity, surface activity, and unusual rheological properties). This chapter deals with the general methods of preparation and solution properties of hydrophobically modified nonionic WSPs. Particularly described are the solution properties of hydrophobically modified (hydroxyethyl)cellulose (HMHEC) in aqueous and surfactant systems. 

X HE USE OF HYDROPHOBIC INTERACTIONS to produce associative thickeners has increased markedly over the past 10 years in such diverse areas as surface coatings and enhanced oil recovery. The desired thickening properties are produced by relatively low molecular weight polymers that are reversibly cross-linked by pendant hydrophobic moieties to give a three-dimensional network. To maintain solubility, the number of hydrophobes per soluble molecule is low, and the chain length is typical of that used in surfactants (i.e., Cs-Cie). In solution, the hydrophobes appear to associate in an analogous fashion to micellization, in that, in the absence of surfactants. 

The nature of hydrophobic interactions and their effects on the structure and properties of water have been extensively studied, particularly for small molecules (i 3). In contrast, the introduction of hydrophobic associations into synthetic water-soluble polymers to control solution rheology has received rather limited and recent study (4-7). To better understand the relationships between polymer structure and solution properties, we have synthesized and characterized a series of copolymers of acrylamide and N-substituted alkylacrylamides and terpolymers containing anionically charged carboxyl groups. Solution properties of these systems have been obtained in both the dilute and semidilute concentration regime, to probe the influence of intra- and intermolecular interactions. In addition, the influence of the shear field and solvent quality on the associations was studied. 

Hydrophobic associations can dominate polymer conformation in solution and solution rheological properties. Intrinsic viscosity and Huggins interaction coefficients provided information on the conformation and intramolecular aggregation behavior of these polymers in dilute solution. The presence of hydrophobic associations caused a decrease in the intrinsic viscosity and an increase in the Huggins constant. These effects could be counterbalanced by increasing the ionic charge on the polymer through hydrolysis or by copolymerization with sodium acrylate. 

Hydrophobically modified, ethoxylated urethanes (HEURs) are the thickeners of choice in exterior coatings and in corrosion-resistant, high-gloss industrial latex finishes. This chapter presents an overview of our research efforts and discusses approaches to the synthesis of HEUR polymers with different molecular architectures, geometrical influences on solution properties, and viable mechanisms by which this class of associative thickener effects desirable coatings rheology and applied film properties. 

Finally, we have considered polymer solutions in good solvents only. For industrial applications, one tends to use more and more water as a solvent. Water soluble polymers have specific properties due to the character of the interactions between monomers in water. Most water soluble polymers, for example, carry ionic charges (they are polyelectrolytes) if the polymers contain hydrophobic groups, they have interesting associating properties. The surface behavior of polyelectrolytes and associating polymers is the subject of intense experimental and theoretical studies [44]. 

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