Inverse suspension

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. 

An inverse suspension polymerization involves an organic solvent as the continuous phase with droplets of a water-soluble monomer (e.g., acrylamide), either neat or dissolved in water. Microsuspension polymerizations are suspension polymerizations in which the size of monomer droplets is about 1 pm. 

Fig. 15 Optical images of DNA-based materials for environmental purpose, a DNA-alginic acid hybrid matrix coagulated by Ca2+, in fiber, film, and gel form, b DNA-immobilized porous glass beads prepared by UV-irradiation. c DNA-polyacrylamide hydrogel beads synthesized by inverse suspension polymerization...

Nevertheless, for inverse miniemulsions the surfactant is used in a very efficient way, at least as compared to inverse micro emulsions [47,48] or inverse suspensions [49] which are used for subsequent polymerization processes. Again, the surface coverage of the inverse miniemulsion droplets with surfactant is incomplete and empty inverse micelles are absent. Again this is important for the interpretation of the reaction mechanism. 

Commercially, suspension polymerizations have been limited to the free radical polymerization of water-insoluble liquid monomers to prepare a number of granular polymers, including polystyrene, poly(vinyl acetate), poly(methyl methacrylate), polytetrafluoroethylene, extrusion and injection-molding grades of poly(vinyl chloride), poly(styrene-co-acrylonitrile) (SAN), and extrusion-grade poly(vinylidene chloride-covinyl chloride). It is possible, however, to perform inverse suspension polymerizations, where water-soluble monomer (e.g., acrylamide) is dispersed in a continuous hydrophobic organic solvent. 

Zhu and coworkers have reported the synthesis of functionalized poly(vinyl alcohol) resins for use as scavengers [13]. This was achieved via inverse suspension polymerization along side epichlorohydrin as a cross-linker. These resins were found to have excellent swelling characteristics in DMF, CH3OH, dioxane, THF, CH2C12 and H20. These were then functionalized with glutaric aldehyde to provide a polymer-supported aldehyde (Scheme 8.8). 

Synthesis of gel particles in the pm-range (micro-gels) (Pelton 2000) using different techniques, e.g., thermo-sensitive micro-gels based on NIPAAm by inverse suspension polymerization (Bajpai et al. 2007) or inverse emulsion polymerization (Hirotsu et al. 1987). 

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. 

Over the past decade there has been extensive interest in the kinetics and colloidal behavior of water-in-oil polymerizations. However, these efforts have focused on the elucidation of a general set of phenomena to describe water-in-oil processes, without distinguishing inverse-emulsion and inverse-suspension sub-domains. A confounding factor is certainly the inconsistent nomenclature inverse-suspensions (Ila) are within the inverse-macroemulsion polymerization domain (II), and are often described as inverse-emulsions, where the prefix macro has been omitted for brevity. However, inverse-emulsion (lib) is itself a... 

Isopar-M SMO AIBN 1 1 6 30-50 47 Baade and Reichert [49] Inverse micelles not detected. Polymerization in monomer droplets. Kinetic latex stability. Solution-like kinetics, with interfacial reactions Inverse- Suspension... 

Heterophase processes should be primarily distinguished based on their emulsion structure (oil-in-water or water-in-oil) and type of stability (kinetic or thermodynamic). This identifies four mutually independent polymerization regimes, each with unique colloidal and chemical behavior. L Macroemulsion, II. Inverse-Macroemulsion, HI. Microemulsion, IV. Inverse-Microemulsion. The macroemulsion and inverse-macroemulsion domains can be further subdivided into Suspension (la), Emulsion (lb), Inverse-suspension (Ha) and Inverse-emulsion (lib) subdomains based on a transition at the critical micelle concentration. 

Inverse-suspension, inverse-emulsion and inverse-microemulsion polymerizations should be developed independently as has been the precedent for oil-inwater polymerizations. This includes explicitly considering the unique chemistry of various emulsifiers, organic phases, monomers and initiators. Furthermore, the chemical and colloidal models for each of the three water-in-oil polymerizations will be specific to a given type of organic phase and a restricted family of emulsifiers. 

Investigations of water-in-oil polymerizations employing new monomers or emulsifiers for which kinetic or colloidal characterization is incomplete, require careful nomenclature designation. Under such circumstances a general description such as Water-in-Oil Polymerization or Heterophase Polymerization is recommended until the physical and chemical nature of the polymerizations can be identified. The designations inverse-suspension, inverse-emulsion and inverse-microemulsion should be reserved for processes for which a relatively advanced level of understanding exists. 

Ionized gels were acrylic acid-sodium acrylate copolymers. The samples were provided by Norsolor Company. The gels were obtained through an inverse suspension process. In this technique, the aqueous phase, containing an hydrophilic monomer, was dispersed in an organic phase, such as an alicyclic or aliphatic hydrocarbon. 

The inverse suspension was obtained by mixing the organic solution of a nonionic surfactant with the aqueous solution of partially neutralized acrylic acid salt. The temperature was then raised, and the polymerization reaction was carried out for several hours. The samples were then dried and ready for swelling kinetics experiments. They were transferred into an excess of solvent, and the time at which they looked homogeneous was f = 0 for the kinetics experiments. 

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