Suspension polymerization inverse

When a water-miscible polymer is to be made via a suspension process, the continuous phase is a water-immiscible fluid, often a hydrocarbon. In such circumstances the adjective inverse is often used to identify the process [118]. The drop phase is often an aqueous monomer solution which contains a water-soluble initiator. Inverse processes that produce very small polymer particles are sometimes referred to as inverse emulsion polymerization but that is often a misnomer because the polymerization mechanism is not always analogous to conventional emulsion polymerization. A more accurate expression is either inverse microsuspension or inverse dispersion polymerization. Here, as with conventional suspension polymerization, the polymerization reaction occurs inside the monomer-containing drops. The drop stabilizers are initially dispersed in the continuous (nonaqueous phase). If particulate solids are used for drop stabilization, the surfaces of the small particles must be rendered hydrophobic. Inverse dispersion polymerization is used to make water-soluble polymers and copolymers from monomers such as acrylic acid, acylamide, and methacrylic acid. These polymers are used in water treatment and as thickening agents for textile applications. Beads of polysaccharides can also be made in inverse suspensions but, in those cases, the polymers are usually preformed before the suspension is created. Physical changes, rather than polymerization reactions, occur in the drops. Conventional stirred reactors are usually used for inverse suspension polymerization and the drop size distribution can be fairly wide. However, Ni et al. [119] found that good control of DSD and PSD could be achieved in the inverse-phase suspension polymerization of acrylamide by using an oscillatory baffled reactor. 

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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...

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). 

Dowding, P.J. Vincent, B. Williams, E. Preparation and swelling properties of poly(NIPAM) Minigel particles prepared by inverse suspension polymerization. J. Colloid Interface Sci. 2000, 221... 

In addition, magnetic latex with hydrophilic polymer can be produced by inverse suspension polymerization using a W/O suspension. Miiller-Schulte et al. reported [118] the preparation of hydrophilic thermally sensitive magnetic polymer particles for an in vivo contactless controlled drug release by using inverse suspension polymerization (Fig. 8). A ferrofluid and initiator ammonium persulphate... 

Moreover, a magnetic molecularly imprinted polymer of 4-divinylpyridine and EGDMA particles was synthesized by inverse suspension polymerization [119]. The reaction was carried out in silicon oil as a dispersion phase, and in the presence of 2,4-dichlorophenoxyacetic acid and MPTS. The advantages of the silicon oil as a continuous phase are a low polarity and immiscibility with the monomer mixture. The prepared particle average size is 20 pm and the magnetic content is very low, at around 1 wt%. 

Liu P, Jiang L, Zhu L, Wang A (2014) Novel covalently cross-linked attapulgite/poly(acrylic acid-co-acrylamide) hybrid hydrogels by inverse suspension polymerization Synthesis optimization and evaluation as adsorbents for toxic heavy metals. Ind Eng Chem Res 53 4277-4285... 

Tubular reactor Inverse suspension polymerization of acrylamide in a batch oscillatory baffled reactor 1 m in length, with a diameter of 5 cm) up to 9 baffles oscillate with a frequency between 1 and 5 Hz 178... 

In the 1990s, Meldal, following the work of Sheppard, developed an improved support which was named PEGA (PEG-polyacrylamide) (125), obtained by inverse suspension polymerization (126) of A/ A -dimethylacrylamide cross-linked with different bis-acrylic-PEG derivatives (Fig. 21, A). 

Besides the normal suspension pol)unerization, the inverse-suspension polymerization is also employed in large-scaled production, which is mainly hmited to the water-soluble monomer, such as the acrylamide and soluble acrylates and the solutions of the monomer and initiator are suspended in an oil phase. 

Inverse suspension polymerization of water-soluble monomers is used to produce superwater-absorbent polymers [127]. 

Wang G, Li M, Chen X. Inverse suspension polymerization of sodium acrylate. J Appl Polym Sci 1997 65 789-794. 

Trijasson, P., Frere, Y., and Gramain, P. (1990) Inverse suspension polymerization of poly(ethylene oxide) methacrylate macromonomers. Macromolecular Rapid Communications, 11,239-243. 

In the vast majority of cases, the suspending medium for suspension polymerization is water, although inverse-suspension polymerizations are also known and used commercially to produce very high molecular weight polymers... 

Kiakamjomwong S, Punchareon P. Influence of reaction parameters on water absorption of neutrahzed poly-(acryhc acid-co-acrylamide) synthesized by inverse suspension polymerization. J Appl Polym Sci 1999 72(10) 1349-66. 

Commercially, suspension polymerization has been hmited to the free-radical addition of water-insoluble liquid monomers. With a volatile monomer such as vinyl chloride, moderate pressures are required to maintain it in the hquid state. It is possible, however, to perform inverse suspension polymerizations with a hydrophilic monomer or an aqueous solution of a water-soluble monomer suspended in a hydrophobic continuous phase. 

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