Acrylamide inverse emulsions

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 extent of conversion during an acrylamide polymerization is most easily followed by determining the disappearance of the monomer. High performance liquid chromatography (hplc) is often found best for this purpose. An hplc method in which poly(acrylamide) inverse emulsions can be used directly has been developed (238). In the case of copolymers, hplc protocols that allow the simultaneous determination of all the unreacted monomers can be used to evaluate compositional drift as a function of conversion. 

Manufacturing processes have been improved by use of on-line computer control and statistical process control leading to more uniform final products. Production methods now include inverse (water-in-oil) suspension polymerization, inverse emulsion polymerization, and continuous aqueous solution polymerization on moving belts. Conventional azo, peroxy, redox, and gamma-ray initiators are used in batch and continuous processes. Recent patents describe processes for preparing transparent and stable microlatexes by inverse microemulsion polymerization. New methods have also been described for reducing residual acrylamide monomer in finished products. 

Fig. 10. Amide end-capped poly(hexafluoropropy-lene oxide) used for the inverse emulsion polymerization of acrylamide in C02 [123]...

In the conventional emulsion polymerization, a hydrophobic monomer is emulsified in water and polymerization initiated with a water-soluble initiator. Emulson polymerization can also be carried out as an inverse emulsion polymerization [Poehlein, 1986]. Here, an aqueous solution of a hydrophilic monomer is emulsified in a nonpolar organic solvent such as xylene or paraffin and polymerization initiated with an oil-soluble initiator. The two types of emulsion polymerizations are referred to as oil-in-water (o/w) and water-in-oil (w/o) emulsions, respectively. Inverse emulsion polymerization is used in various commerical polymerizations and copolymerizations of acrylamide as well as other water-soluble monomers. The end use of the reverse latices often involves their addition to water at the point of application. The polymer dissolves readily in water, and the aqueous solution is used in applications such as secondary oil recovery and flocculation (clarification of wastewater, metal recovery). 

These superabsorbents are synthesized via free radical polymerization of acrylic acid or its salts in presence of a crosslinker (crosslinking copolymerization). Initiators are commonly used, water-soluble compounds (e.g., peroxodi-sulfates, redox systems). As crosslinking comonomers bis-methacrylates or N,hT-methylenebis-(acrylamide) are mostly applied. The copolymerization can be carried out in aqueous solution (see Example 5-11 or as dispersion of aqueous drops in a hydrocarbon (inverse emulsion polymerization, see Sect. 2.2.4.2). 

Adamsky, F. A. Beckman, E. J. Inverse Emulsion Polymerization of Acrylamide in Supercritical Carbon Dioxide. Macromolecules 1994, 27, 312. 

Hernandez-Barajas J, Hunkeler DJ (1997) Inverse-emulsion copolymerization of acrylamide and quaternary ammonium cationic monomers with block copolymeric surfactants copolymer composition control using batch and semi-batch techniques. Polymer 38(2) 449—458... 

Glukhikh V, Graillat C, Pichot C (1987) Inverse emulsion polymerization of acrylamide. II. Synthesis and characterization of copolymers with methacrylic acid. J Polym Sci Polym Chem Ed 25(4) 1127-1161... 

The concentrated emulsion polymerization was also applied to an aqueous solution of acrylamide dispersed in decane. Compared to the conventional inverse emulsion polymerization [20], a much smaller amount of organic solvent is employed to produce polymer latexes. 

Villarroya, S., Thurecht, K.J., and Howdle, S.M. 2008. HRP-mediated inverse emulsion polymerisation of acrylamide in supercritical carbon dioxide. Green Chemistry, 10 863-67. 

Inverse Emulsion Polymerization of Acrylamide in Near-Critical and Supercritical Continuous Phases... 

Emulsion polymerization typically refers to the polymerization of a nonaqueous material in water. The polymerization of a water-soluble material in a nonaqueous continuum has been called inverse emulsion polymerization. The inverse emulsion polymerization technique is used to synthesize a wide range of polymers for a variety of applications such as wall paper adhesive, waste water fiocculant, additives for oil recovery fluids, and retention aids. The emulsion polymerization technique involves water-soluble polymer, usually in aqueous solution, emulsified in continuous oil phase using water in oil emulsifier. The inverse emulsion is polymerized using an oil- or water-soluble initiator. The product is a colloidal dispersion of sub-microscopic particles with particle size ranging from 0.05 to 0.3 pm. The typical water-soluble monomers used are sodium p-vinyl benzene sulfonate, sodium vinyl sulfonate, 2-sulfo ethyl acrylate, acrylic acid, and acrylamide. The preferred emulsifiers are Sorbitan monostearate and the oil phase is xylene. The proposed kinetics involve initiation in polymer swollen micelles, which results in the production of high molecular weight colloidal dispersion of water-swollen polymer particles in oil. 

The effect of branching on the performance of 75% DADMAC/25% acrylamide copolymers in dewatering 100% waste-activated sludge was also investigated. A series of copolymers was prepared by an inverse emulsion method adding up to 0.5 mol % TAMAC (based on DADMAC... 

Howdle et al. was the first to report on the enzymatic emulsion polymerization of water-soluble acrylamide monomers in a w/c microemulsion [75]. Acrylamide is one of the few monomers that show limited solubility in supercritical C02, and hence was particularly suited to inverse emulsion polymerization [61]. In this report, Howdle et al. showed that the yields and molecular weights obtained via polymerization in C02 are comparable to those generated in a conventional polymerization in an alkane/water medium. Indeed, polymer molecular weights up to 900 kDa were observed when a surfactant was not used and molecular weights around 300 kDa when a perfhiropolyether was used. The generally accepted mechanism for this reaction is shown in Figure 13.5. 

Inverse emulsion polymerization of acrylamide in supercritical carbon dioxide. Macromolecules, 27 (1),... 

Villarroya, S., Thurecht, K.J., and Howdle, S.M. (2008) HRP-mediated inverse emulsion polymerisation of acrylamide in supercritical carbon dioxide. Green Chem., 10 (8), 863-867. Schomberg, D.S., Salzman, M., and Stephan, D. (1993) Enzyme Handbook vol. 7, Springer-Verlag, Berlin Heidelberg, pp. 1-6. 

Inverse Emulsion Polymerization. Water-soluble monomers can be polymerized by emulsifying water solutions of these monomers in an organic continuous phase. This process, called inverse emulsion polymerization, yields a product comprised of a colloidal suspension of droplets of aqueous polymer solution. The original study of an inverse system by Vanderhoff et al. (20) involved the monomer sodium p-vinyIbenzene sulfonate, an organic phase of xylene. Span 60 as the emulsifier, and either benzoyl peroxide or potassium persulfate initiator. Later work by Kurenkov et al. (21) involved acrylamide in a toluene continuous phase, potassium persulfate, and Sentaraid-5 (emulsifier). DiStefano (22) examined three monomers acrylamide, dimethylaminoethyacrylate... 

Using this categorization we can also identify some existing nomenclature Hunkeler and Hamielec s inverse-microsuspension refers to two system 1) potassium persulfate/acrylamide-water/organic/low HLB stabilizer [32] which is an inverse-suspension by the proposed scheme, and 2) AIBN/acrylami-de-water/organic/low HLB stabilizer [29] which is an inverse-emulsion. 

The mechanical stability of polymers was related to the polymer s conformation in some of the earlier drag-reduction studies. Above a critical stress, degradation was faster the more contracted and entangled the polymer s conformation (5-7). In petroleum applications the mechanical instability of synthetic relative to carbohydrate polymers was well-recognized. The relative stability problems (possibly related to DUEVs (8)) encountered in the use of high molecular weight hydrolyzed poly(acrylamide) (HPAM) led to the development of an inverse-emulsion polymerization technique (9). (Current research directions using this technique are discussed in Chapter 9.)... 

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