Hydrophobically modified acrylamide

Regardless of the application, the placement (i.e., terminal or internal, isolated or in block sequences) of the hydrophobe-modified monomer in the macromolecular chain is important to the performance of the polymer. The difficulties encountered in determining the sequence structure of hydrophobe-modified acrylamide (water-insoluble) monomers in acrylamide copolymers are discussed in Chapter 20. In this respect, the bicontinuous nature of microemulsions may prove an advantageous method of synthesis. The surfactants used in such a process, however, are significantly more interfacially active than the surfactants used in most application formulations and may detract from the performance of RAM copolymers. The most recent patent (20) in the RAM area discusses the synthesis of RAM copolymers by a microemulsion process, but complexities due to surfactant differences in formulations are not addressed. 

Conceptual Model. The behavior of the hydrophobically modified acrylamide copolymers of this work has led us to propose the model illustrated in Figure 10. The hydrophobic groups on the N-alkylacrylam-ide-acrylamide copolymers exhibit concentration-dependent association. In region 1, low hydrophobe concentration on the copolymer, low copolymer concentration, or both conditions are insufficient to bring about significant association. In region 2, hydrophobic association increases, but associations... 

Middleton, J. C., D. F. Cummins and C. L. McCormick, Rheological Properties of Hydrophobically Modified Acrylamide-Based Polyelectrolytes, in Water-Soluble Polymers Synthesis, Solution Properties and Applications, Shalaby, S. W., McCormick, C. L., Butler, G. B., Eds., ACS Symposium Series No. 467, American Chemical Society, Washington, t)C, 1991, pp. 338-348. 

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 modified acrylamide polymer that is hydrophobically associating has remarkably improved the properties of salt resistance and temperature resistance, compared with high-molecular-weight polyacrylamide [1351]. 

The subject of surfactant-modified, water-soluble polymers, briefly discussed in Water-Soluble Polymers, is addressed in the last three sections (Chapters 16-28) of this book. These associative thickeners are covered in detail, ranging from the maleic acid copolymers of variable compositions introduced in various commercial markets in the early 1960s to the most recent entries (that is, in the open literature), hydrophobe-modified poly (acrylamide). Chapter 23 is complementary to the spectroscopic studies in Chapters 13-15 it explores new approaches to understanding associations in aqueous media. The three hydrophobe-modified polymers that have gained commercial acceptance in the 1980s, (hydroxyethyl)cellulose, eth-oxylate urethanes, and alkali-swellable emulsions, are discussed in detail. In particular, hydrophobe-modified (hydroxyethyl)cellulose, which is... 

Effing JJ, Kwak JCT. 1995. Photoswitchable phase separation in hydrophobically modified poly(acrylamide)/surfactant systems. Angew Chem Int Ed Engl 34(1) 88 90. 

Effing JJ, McLennan IJ, Kwak JCT. 1994. Associative phase separation observed in a hydrophobically modified poly(acrylamide)/sodium dodecyl sulfate system. J Phys Chem 98(10) 2499 2502. 

Howley C, Marangoni DG, Kwak JCT. 1997. Association and phase behavior of hydrophobically modified photoresponsive poly(acrylamide)s in the presence of ionic surfactant. Coll Polym Sci 275(8) 760 768. 

Voorn and coworkers demonstrated the inverse Pickering miniemulsion polymerization of aqueous acrylamide and 2-hydroxyethyl methacrylate in cyclohexane using hydrophobically modified Montmorillonite platelets (cloisite 20A) as solids stabilizer [110]. 

The behavior of polymers is also affected by their chemical identities. For instance, if the polymer is actually a copolymer, or if it is cross-linked or hydrophobically modified, variations from typical solution behavior occur. These examples are addressed in this chapter when they become relevant. Simple linear polymers include poly[(meth)acrylic acid], poly(acrylamide), poly(ethylene oxide), polymers and random copolymers of poly(ethylene oxide) and (propylene oxide), poly(vinyl alcohol), and poly(vinylpyrroli-done). Such polymers primarily influence solution viscosity through random chain entanglement. However, all of these polymers possess functional sites, which allows them to bind interpolymerically and aids in chain entanglement. These functional sites also allow all of these polymers to dissolve in highly polar aqueous mediums under the right conditions. We will focus on these polymers initially. 

There is a class of hydrophobically modified water-soluble polymers known as associative thickeners (AT polymers) that are used in cotmnercial applications for rheology control (11-22). AT polymers and their model polymers include copolymers of acrylamide or (meth)acrylic acid with associative comonomers containing an oligomeric ethylene oxide (EO) chain as a spacer between a polymerizable moiety and terminal hydrophobe (11-16,23), Associative comonomer units in such copolymers play a role as stickers in aqueous solutions. The content of associative comonomers in AT copolymers is usually veiy low (< 2 mol %) because AT polymers are... 

Carboxymethylcellulose, polyethylene glycol Combination of a cellulose ether with clay Amide-modified carboxyl-containing polysaccharide Sodium aluminate and magnesium oxide Thermally stable hydroxyethylcellulose 30% ammonium or sodium thiosulfate and 20% hydroxyethylcellulose (HEC) Acrylic acid copolymer and oxyalkylene with hydrophobic group Copolymers acrylamide-acrylate and vinyl sulfonate-vinylamide Cationic polygalactomannans and anionic xanthan gum Copolymer from vinyl urethanes and acrylic acid or alkyl acrylates 2-Nitroalkyl ether-modified starch Polymer of glucuronic acid... 

In 1996, Gauglitz and coworkers coated surfaces with various amino-and carboxy-substituted polymers [198], The polymers tested were branched poly-(ethyleneimine), a,co-amino-functionalized PEG, chitosan, poly(acrylamide-co-acrylic acid) and an amino-modified dextran. The amino-substituted polymers were immobilized on glass by first immobilizing an aminosilane, followed by succinic anhydride/A-hydroxysuccinimide linker chemistry. Poly(acrylamide-co-acrylic acid) was directly coupled to an aminosilanized surface. When probed with 1 mg mL 1 ovalbumin solution, nonspecific adsorption was lowest for the dextran derivative. Notably, nonspecific adsorption increased in most cases when a hydrophobic hapten (atrazine) was coupled to the polymer-modified surface. 

Photochemical grafting of monomers/molecules onto substrates continues to show interest in terms of improving property requirements. Dyes have been effectively photografted onto polypropylene and nylon 6 films using 1,2-diphenyl-2,2-dimethoxyethanone while methacrylic acid and acrylamide have been successfully photografted onto polypropylene sheets using benzophenone as a sensitiser in order to modify the surface of the polymer from a hydrophobic to a hydrophilic one. A styrene-2,2,6,6-tetramethyl-4-piperidinyl... 

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