Polyacrylamide forms

Flow Properties. In water, high molecular weight polyacrylamide forms viscous homogeneous solutions. 

During polymerization, acrylamide and bisacrylamide monomers couple together across their double bonds. Linear chains of polyacrylamide form with bisacrylamide molecules cross-linking adjacent chains. The pendant carboxamide groups (-CO-NH2) from the acrylamide monomer are subject to hydrolysis to carboxyls ( COO ) as gels age.42 Only freshly made gels should be used in most IEF work. 

Furthermore, soluble collagen grafted with polyacrylamide formed fibrils on heating to 37 °C at neutral pH, but unlike the native collagen, these fibrils did not redissolve on cooling to 2°C (8). These results indicate that the redispersion property of soluble collagen is impaired, probably by attachment of the polyacrylamide side chains to the collagen molecule. 

Polyacrylamide forms water-based gels at concentrations around 4%w/v, which exhibit pseudoplastic behavior. A PAAm ophthalmic gel containing pilocarpine was compared with other gel vehicles the ocular bioavailability for the PAAm gel was three times greater than that of the aqueous control solution. The kinetics of ibuprofen release for crosslinked PAAm gels was studied. A kinetic model was proposed for swelling induced loading of insulin into crosslinked PAAm gels. ... 

Crystalline polyacrylamide forms with metal alkyls in hydrocarbon solvents by anionic mechanism [271]. The product is insoluble in water and in dimethylformamide. 

Many creative methods for modifying polyacrylamides formed by inverse emulsion polymerization for enhanced activity in target applications are found in the patent literature. Flesher reported the synthesis of a cross-linked, water swellable polymer, useful for flocculation in high shear dewatering devices, by adding a small amount of a divinylic cross-linking agent [10]. 

Polyacrylamides and partially hydrolyzed polyacrylamides form gels in the presence of Cr(III) and other trivalent cations. 2- 4>95 In one process, polyacrylamide at a concentration of a few thousand ppm is mixed with sodium dichromate at a concentration of a few hundred ppm and a reducing agent, such as sodium bisulfite, sodium thiosulfate, or thiourea. Cr(Vl) in the dichromate is reduced to Cr([II), which subsequently reacts with the polymer to form crosslinks and a 3D gel structure. The chemical process is summarized by... 

A sample of polyacrylamide forms solutions in water that can be fitted by a Huggins equation plot over the range of 1.0 < iir< 1.5 with a slope of 0.700 (g/dl) and an intercept of 1.35 dl/g. If the data from the Huggins equation at relative viscosities of 1.0 and 1.5 are used to fit the Martin equation, specific viscosity can be predicted at a concentration of 5.0 g/dl ... 

Directions for preparing a potentiometric biosensor for penicillin are provided in this experiment. The enzyme penicillinase is immobilized in a polyacrylamide polymer formed on the surface of a glass pH electrode. The electrode shows a linear response to penicillin G over a concentration range of 10 M to 10 M. 

There are several forms of electrophoresis. In slab gel electrophoresis the conducting buffer is retained within a porous gel of agarose or polyacrylamide. Slabs are formed by pouring the gel between two glass plates separated by spacers. Typical thicknesses are 0.25-1 mm. Gel electrophoresis is an important technique in biochemistry, in which it is frequently used for DNA sequencing. Although it is a powerful tool for the qualitative analysis of complex mixtures, it is less useful for quantitative work. 

The yields of this reaction are typically 40—80%. C-nmr studies (41) indicate that the reaction is a second-order process between polyacrylamide and dim ethyl am in om eth an ol, which is one of the equiUbrium products formed in the reaction between formaldehyde and dimethylamine [124-40-3] C2H2N. The Mannich reaction is reversible. Extensive dialysis of Mannich polyacrylamides removes all of the dimethyl aminomethyl substituents (42). 

Methylol Formation. Polyacrylamide reacts with formaldehyde to form an /V-methylo1 derivative. The reaction is conducted at pH 7—8.8 to avoid cross-linking, which will occur at lower pH. The copolymer can also be prepared by copolymerizing acrylamide with commercially available A/-methylolacrylamide [924-42-5] C4H2NO2. These derivatives are useful in several mining appHcations (49,50). They are also useful as chemical grouts. 

Transamidation. Polyacrylamide reacts with primary amines such as hydrazine [302-01-2], N2H4, (54) and hydroxjlamine [7803-49-8]. NH O, (55—57) to form substituted amides with loss of ammonia. 

Hoffman Degradation. Polyacrylamide reacts with alkaline sodium hypochlorite [7681-52-9], NaOCl, or calcium hypochlorite [7778-54-3], Ca(OCl)2, to form a polymer with primary amine groups (58). Optimum conditions for the reaction include a slight molar excess of sodium hypochlorite, a large excess of sodium hydroxide, and low temperature (59). Cross-linking sometimes occurs if the polymer concentration is high. High temperatures can result in chain scission. 

Reaction with Chlorine. Polyacrylamide reacts with chlorine under acid conditions to form reasonably stable A/-chloroamides. The polymers are water soluble and can provide good wet strength and wet web strength in paper (60). 

Polyacrylamides are manufactured by free-radical polymerization of acrylamide to form chains of the stmcture shown, where n can range from several up to 400,000. 

Microemulsion Polymerization. Polyacrylamide microemulsions are low viscosity, non settling, clear, thermodynamically stable water-in-od emulsions with particle sizes less than about 100 nm (98—100). They were developed to try to overcome the inherent settling problems of the larger particle size, conventional inverse emulsion polyacrylamides. To achieve the smaller microemulsion particle size, increased surfactant levels are required, making this system more expensive than inverse emulsions. Acrylamide microemulsions form spontaneously when the correct combinations and types of oils, surfactants, and aqueous monomer solutions are combined. Consequendy, no homogenization is required. Polymerization of acrylamide microemulsions is conducted similarly to conventional acrylamide inverse emulsions. To date, polyacrylamide microemulsions have not been commercialized, although work has continued in an effort to exploit the unique features of this technology (100). 

The principal monomer is acrylamide [79-06-17, where R = H and R = NH2, made by the hydrolysis of acrylonitrile. The homopolymer [9003-05-8] of acrylamide, which in theory has no electrical charge, has some use as a flocculant however, the majority of acrylamide-based flocculants are copolymers with acryHc monomers containing charged functional groups, such as those shown in Figure 1, or polymers containing functional groups formed by modification of acrylamide homopolymers or copolymers (Fig. 2). The chemistry of polyacrylamides has been reviewed by several authors (18—20) (see... 

Fig. 2. Functional groups on modified polyacrylamides (a) formed by reaction with dimethylamine and formaldehyde (Mannich reaction) (b), quatemized Mannich amine (c), carboxylate formed by acid or base-cataly2ed hydrolysis or copolymerization with sodium acrylate and (d), hydroxamate formed by...

If either dry powders or inverse emulsions are not properly mixed with water, large lumps of polymer form that do not dissolve. This not only wastes material, but can also cause downstream problems. This is especially tme for paper where visible defects may be formed. Specialized equipment for dissolving both dry polymers and inverse emulsions on a continuous basis is available (22,23). Some care must be taken with regard to water quaUty when dissolving polyacrylamides. Anionic polymers can degrade rapidly in the presence of ferrous ion sometimes present in well water (24). Some cationic polymers can lose charge by hydrolysis at high pH (25). 

Poly(ethylene oxide)s [25372-68-3] are made by condensation of ethylene oxide with a basic catalyst. In order to achieve a very high molecular weight, water and other compounds that can act as chain terminators must be rigorously excluded. Polymers up to a molecular weight of 8 million are available commercially in the form of dry powders (27). These must be dissolved carefliUy using similar techniques to those used for dry polyacrylamides. Poly(ethylene oxide)s precipitate from water solutions just below the boiling point (see Polyethers, ethylene oxide polymers). 

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

Low molecular weight (1000—5000) polyacrylates and copolymers of acryflc acid and AMPS are used as dispersants for weighted water-base muds (64). These materials, 40—50% of which is the active polymer, are usually provided in a Hquid form. They are particularly useful where high temperatures are encountered or in muds, which derive most of their viscosity from fine drill soHds, and polymers such as xanthan gum and polyacrylamide. Another high temperature polymer, a sulfonated styrene maleic—anhydride copolymer, is provided in powdered form (65,66). AH of these materials are used in relatively low (ca 0.2—0.7 kg/m (0.5—2 lb /bbl)) concentrations in the mud. 

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