Polyacrylamide dispersions

II. Polyacrylamide (Dispersed Phase)-Polystyrene (Continuous Phase) Composite (Table 7). 

Prepolymers of this type can also act as inisurfs for dispersion polymerizations in organic solvents by using prepolymers soluble in the particualr solvent. This can be determined by appropriate choice of the monomer in the polymerizations forming the prepolymer. So for instance the vinyl acetate prepolymer can be used to obtain stable polyacrylamide dispersions with a solid content of upto 50% by polymerization in methanol [47]. Another application of this type of polymeric azoinitiator mentioned very briefly is the preparation of graft and block copolymers [55,5Q. The chemical composition of the blocks as well as the polymerization technique employed can be matched over a wide range to obtain polymers with desired properties. 

Polyacrylamide dispersant, latex paints Nonoxynol-1 Nonoxynol-3 Nonoxynol-13 Nonoxynol-30 Nonoxynol-40 Nonoxynol-50... 

Sodium laureth sulfate dispersant, plasters Polyacrylamide dispersant, plastics... 

In the polyacrylamide dispersion polymerization process, multivalent salts are used for the purpose of insolubilizing and depositing the polymer and are formulated to produce a poor solvent for the particular polyacrylamide being synthesized. At the onset of polymerization reaction, the formed polymer is soluble in the polymerization medium. As the reaction progresses, the polymer phase separates forming particles (0.1-10 pm) that are kept from agglomeration by the use of polymeric stabilizers. A mechanistic hypothesis of the formation of polyacrylamide dispersions was reported by Selvarajan [43]. 

POWDERS,HANDLING - DISPERSION OF POWDERS IN LIQUIDS] (Vol 19) -polyacrylamides in [ACRYLAMIDE POLYMERS] (Voll)... 

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. 

The most commonly used combination of chemicals to produce a polyacrylamide gel is acrylamide, bis acrylamide, buffer, ammonium persulfate, and tetramethylenediarnine (TEMED). TEMED and ammonium persulfate are catalysts to the polymerization reaction. The TEMED causes the persulfate to produce free radicals, causing polymerization. Because this is a free-radical driven reaction, the mixture of reagents must be degassed before it is used. The mixture polymerizes quickly after TEMED addition, so it should be poured into the gel-casting apparatus as quickly as possible. Once the gel is poured into a prepared form, a comb can be appHed to the top portion of the gel before polymerization occurs. This comb sets small indentations permanently into the top portion of the gel which can be used to load samples. If the comb is used, samples are then typically mixed with a heavier solution, such as glycerol, before the sample is appHed to the gel, to prevent the sample from dispersing into the reservoir buffer. 

Dispersants andfloeculants. These are important for the control of slimes that sometimes interfere with the selectivity and increase reagent consumption. For example, soda ash, lime sodium silicate, and lignin sulfonates are used as dispersants, and starch and polyacrylamide are used as flocculants. 

Suspension polymerization of water-insoluble monomers (e.g., styrene and divinylbenzene) involves the formation of an oil droplet suspension of the monomer in water with direct conversions of individual monomer droplets into the corresponding polymer beads. Preparation of beaded polymers from water-soluble monomers (e.g., acrylamide) is similar, except that an aqueous solution of monomers is dispersed in oil to form a water-in-oil (w/o) droplet suspension. Subsequent polymerization of the monomer droplets produces the corresponding swollen hydrophilic polyacrylamide beads. These processes are often referred to as inverse suspension polymerization. 

Beaded acrylamide resins (28) are generally produced by w/o inverse-suspension polymerization. This involves the dispersion of an aqueous solution of the monomer and an initiator (e.g., ammonium peroxodisulfates) with a droplet stabilizer such as carboxymethylcellulose or cellulose acetate butyrate in an immiscible liquid (the oil phase), such as 1,2-dichloroethane, toluene, or a liquid paraffin. A polymerization catalyst, usually tetramethylethylenediamine, may also be added to the monomer mixture. The polymerization of beaded acrylamide resin is carried out at relatively low temperatures (20-50°C), and the polymerization is complete within a relatively short period (1-5 hr). The polymerization of most acrylamides proceeds at a substantially faster rate than that of styrene in o/w suspension polymerization. The problem with droplet coagulation during the synthesis of beaded polyacrylamide by w/o suspension polymerization is usually less critical than that with a styrene-based resin. 

Polyacrylamides are nonionic polymers, usually with much higher molecular weights (MW from 100,000 up to 12 or 15 M). They often are copolymerized with polyacrylates. Depending on the MW ratios employed, they may act as colloidal dispersants, sludge conditioners, or flocculants. Nonionics such as polyacrylamides (and isobutylenes) are particularly useful at dispersing uncharged particles. 

By performing in situ the polymerization of acrylamide in water/AOT/toluene microemulsions, clear and stable inverse latexes of water-swollen polyacrylamide particles stabilized by AOT and dispersed in toluene have been found [192-194], It was shown that the final dispersions consist of two species of particles in equilibrium, surfactant-coated polymer particles (size about 400 A) with narrow size distribution and small AOT micelles (size about 30 A). 

Partially hydrolyzed polyacrylamides, carboxymethylcellulose, polysaccharides, and acrylamido methylpropane sulfonate have been screened to investigate the performance of aluminum citrate as a chelate-type crosslinker. An overview of the performance of 18 different polymers has been presented in the literature [1646]. The performance of the colloidal dispersion gels depends strongly on the type and the quality of the polymer used. The gels were mixed with the polymers at two polymer concentrations, at three polymer-to-aluminum ratios, and in different concentrations of potassium chloride. The gels were quantitatively tested 1,7, 14, and 28 days after preparation. 

Flocculation was correlated with both adsorption density and estimated surface coverage for the nonionic and 33% hydrolyzed polyacrylamides. Maximum settling rate was obtained with the nonionic flocculent at 0.1 and with the hydrolyzed sample at 0.2 surface coverage. Supernatant clarity showed a maximum at a surface coverage of Na-kaolinite by the hydrolyzed polyacrylamide of 0.1. At higher surface coverages (such as 0.5) considered in the past to be optimum for flocculation, complete dispersion was obtained with both the nonionic and the anionic polymer. 

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