Hydrophobically modified water-soluble

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

A class of systems extensively investigated by means of PFG-NMR are colloids. They are usually hydrophobically modified water-soluble polymers, that is, polymers with a water-soluble skeleton bearing one or more hydrophobic units, which allow the self-assembling of the polymer in water solution and the interaction with surfactants.77... 

Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles. 

Akay G and Wakeman RJ. Electric field enhanced crossflow microfiltration of hydrophobically modified water soluble polymers. J Membr Sci 1997 131 229-236. 

In a novel process, FIPI was also applied to the emulsiflcation of polymer melts in water, thus providing an alternative method to emulsion polymerization for the production of latexes. " " In fact, some thermoplastic melts (such as polyethylene) cannot be obtained through the emulsion polymerization route hence, the present technique is an example of PI providing a novel product form. To achieve the emulsiflcation of thermoplastics, it is necessary to operate near or above 100°C and at elevated pressures, which necessitates the use of polymer processing equipment fitted with a MFCS mixer at the outlet. It was found that molecular surfactants could not be used to obtain the initial (water-in-polymer melt) emulsion. Instead, hydrophobically modified water-soluble polymers were used as the surface active material. After the phase inversion in the MFCS mixer, the resulting emulsion was diluted to the level required. This also freezes the molten latexes. The important attributes of FIPI emulsification include a low level of surfactant use, low temperature processing, production of submicrometer particles with a narrow size distribution, and production of novel products. 

A historical perspective on the development of hydrophobe-modified, water-soluble polymers is presented. The various synthetic procedures used to obtain different associative thickeners are discussed in terms of the complexities in ionogenic monomer polymerizations. This discussion serves two purposes. The first is to present the peculiarities in anionic and cationic polymer synthesis in contiguity with previous work on water-soluble polymers that related only to their use. The second purpose is to draw parallels between the discontinuities in the classical chain-growth polymerization of nonionic with ionogenic monomers and those that should be expected to occur with hydrophobe-modified monomers, but for which there are insufficient data in associative thickener technology to define properly. 

Historical Development of Hydrophobe-Modified Water-Soluble Polymers... 

Will a significant market development occur with the RAM thickeners or hydrophobe-modified, water-soluble polymers not discussed in this text (e.g., in petroleum recovery processes) Adsorption and divalent ion sensitivity are key parameters in this area, and the properties are not properly... 

Applications in which dynamic uniaxial elongational viscosities (DUEVs) have been important to the performance of water-borne formulations are discussed. The achievement of high viscosities at low shear rates with minimum mechanical degradation of the water-soluble polymer and with minimum viscoelastic effects in applications that involved converging flows are discussed. These two factors serve as driving forces for the acceptance of hydrophobically modified water-soluble polymers. Complexities arising from the combined contribution of shear and elongational deformations in applications and in their measurement are discussed in the final section. 

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. 

Polymer-surfactant interactions are the basis for the rheological behavior of MHAPs. Other surfactant-polymer systems have previously been investigated. One example is the interaction of surfactants with polymers such as poly(ethylene oxide), which results in greater solution viscosities than with the polymer alone (e.g., ref. 25 and references therein). The interaction of surfactants or latexes with hydrophobically modified water-soluble polymers has also been shown to produce unique rheology (2, 5, 26, 27). In these systems, the latex particles or the surfactant micelles serve as reversible cross-link points with a hydrophobic region of a polymer molecule in dynamic association with a latex particle or surfactant micelle (27). 

Associative ASTs. Nonionic and anionic associative thickeners are presently considered state of the art in many important industrial applications. The anionic associative thickeners are a subclass of hydrophobically modified, water-soluble polymers (HWSPs), and are predominantly represented by hydrophobically modified ASTs (HASEs and HASNEs), the chemical architectures of which were previously described. Because these polymers are very similar to conventional ASTs in molecular weight and carboxyl content, thickening is by a dual mechanism hydrodynamically (a function of molecular weight, anionic content, cross-link density, and other... 

X HE RELATIVE COST OF MANUFACTURING hydrophobically modified, water-soluble polymers is the primary determinant in their market acceptance. The lowest-cost associative thickeners used in coating formulations are hydrophobically modified, alkali-swellable emulsions (HASE). The extensive history leading to the development of this technology is reviewed in the preceding chapter their utilization and limitations are discussed in Chapters 27 and 28. 

Conventional polymers at a given molecular weight increase in viscosity monotonically until a critical concentration, c (discussed in Chapter 10) is reached. Above this concentration, the viscosity increases as a power fimc-tion. The same phenomenon is observed with low molecular weight, hydrophobe-modified, water-soluble polymers, but the distinctive increase in... 

These viscosity effects of the addition of surfactant to a solution of a hydrophobically modified water-soluble polymer are general, although the effect will be modified by other interactions such as electrostatic ones. As exemplified in Figure 20.11, addition of an oppositely charged surfactant to a solution of a hydrophobically... 

A hydrophobically modified water-soluble polymer (HM-polymer) can be viewed as a modified surfactant. It forms micelles, or hydrophobic microdomains, on its own at very low concentrations (intramolecularly, at infinite dilution) and these micelles can solubilize hydrophobic molecules. Furthermore, an HM-polymer and a surfactant in general have a strong tendency to form mixed micelles in a similar way as two surfactants. Two stoichiometries are important for HM-polymer-surfactant systems, i.e. the alkyl chain stoichiometry and the charge stoichiometry. 

Figure 20.13. The viscosity of a solution of a hydrophobically modified water-soluble polymer and a surfactant compared to the concentration of micelles (determined by fluorescence quenching). The viscosity (filled circles) has a maximum when the micelle concentration starts to increase. The system illustrated is that of hydroxyethyl cellulose (1 wt%) and sodium dodecyl sulfate (SDS). (S. Nilsson, Ph. D. Thesis, Lund University, Sweden, 1999)...

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