Associative thickener polymers

Figure 1.4 Network structure formed by an aqueous surfactant solution mixed with an associative thickening polymer hydroxyethylcellulose (HEC) with cetyl (16-carbon alkyl) side branches. (Reprinted from Clarke 1993, by courtesy of Marcel Dekker, Inc.)...

Aqueous concentrate of an associative thickening polymer, and use of a nonionic surfactant for reducing the viscosity of the concentrate... 

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. 

HydrophobicaHy Modified, Ethoxylated Urethane. HEUR associative thickeners are in effect poly(oxyethylene) polymers that contain terminal hydrophobe units (66). They can be synthesized via esterification with monoacids, tosylation reactions, or direct reaction with monoisocyanates. There are problems associated with aH of the methods of synthesis. The general commercial procedure for their synthesis is by a step-growth addition of... 

Resin Solubilizers. In general, water-soluble resins ate amine salts of acidic polymers. Water-soluble coatings formulated with AMP-95 and DMAMP-80 exhibit superior performance (15,16) (see Water-SOLUBLE polymers). AMP-95, used in conjunction with associative thickeners (17) or hydroxy-ethylceUulose, provides for the most efficient utilization of such thickeners. It also is the neutralizer of choice for use with hair spray resins. 

The level of technical service support provided for a given product generally tracks in large part where the suppHer considers thek product to be located within the spectmm of commodity to specialty chemicals. Technical service support levels for pure chemicals usually provided in large quantities for specific synthetic or processing needs, eg, ammonia (qv), sulfuric acid (see SuLFURic ACID AND SULFURTRIOXIDe), formaldehyde (qv), oxygen (qv), and so forth, are considerably less than for more complex materials or blends of materials provided for multistep downstream processes. Examples of the latter are many polymers, colorants, flocculants, impact modifiers, associative thickeners, etc. For the former materials, providing specifications of purity and physical properties often comprises the full extent of technical service requked or expected by customers. These materials are termed undifferentiated chemicals (9),... 

HEUR associative thickeners are in effect poly(oxyethylene) polymers that contain terminal hydrophobe units. They can be synthesized via esterification with monoacids. tosylation reactions, or direct reaction with monoisocyanates. 

Wenz G, Weickenmeier M, Huff J. Association thickener by host-guest interaction of P-cyclodextrin polymers and guest polymers. In Glass JE, ed. Associative Polymers in Aqueous Media. Symposium Series 765, American Chemical Society, Washington, DC, 2000 Chapter 16 271-283. 

Primary polymer structure may account for some of the viscosity loss behaviour, but VI improvers which function as associative thickeners are a major confounding factor. When the physically associated multi-polymer structures enter a shear field, they can dissociate into their separate molecular species. These smaller individual polymers are low enough in molecular weight that they degrade either slowly or not at all. When the molecules leave the shear field, they associate again so that there is little or no permanent loss of viscosity. However, when in the shear field, the contribution to viscosity is from the smaller, distorted individual molecules. The net result is a system which exhibits a high temporary viscosity loss relative to its low permanent viscosity loss. 

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