Inverse microsuspension polymerization

Microsuspension and Inverse-microsuspension. In suspension polymerizations, particle formation occurs through a droplet breakup-coalescence mechanism, with the diameter controlled by the temperature, interfacial tension, agitation intensity and conversion. Suspension polymerizations have typically been characterized by an initiator soluble in the monomer phase and particle diameters in the 50-1000 pm range [40]. Smaller particles (0.2-20 pm) have been produced at higher agitation speeds (lower interfadal tensions) [41] and in such cases a prefix micro has been added to the nomenclature (microsuspension) to reflect both the dominant synthesis conditions (suspension) and the nominal particle size (1 micron). Therefore, microsuspension polymerization has historically referred to a subdomain of suspension polymerization occurring at smaller particle sizes. Based on an analogy to this nomenclature, inverse-microsuspension polymerization has been proposed for similar water-in-oil... 

Figures 11 and 12 show experimental data for copolymerizations of acrylamide with DMAEM at 60 and 50 C. The solid line is the kinetic model for inverse microsuspension polymerization in isoparaffinic solvents stabilized with fatty acid esters of sorbitan. This model was derived for acrylamide homopolymers (66) and has been extended to include copolymerizations with cationic monomers. Good agreement with the data can be observed. The details of the mechanism will be discussed in a subsequent publication (67).

Figure 12. Conversion vs. time data of an inverse microsuspension polymerization of acrylamide and DMAEM at 50 C and 50 wt % total monomer concentration (fjo = 0.875). The phase ratio of water to oil was 0.74 1 y with 10 wt % sorbitan monooleate (based on the organic phase). Polymerization was initiated with 7.373 X 10 mol AIBN. The solid line is the model...

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. 

The free-radical copolymerization of acrylamide with three common cationic comonomers diallyldimethylammonium chloride, dimethyl-aminoethyl methacrylate, and dimethylaminoethyl acrylate, has been investigated. Polymerizations were carried out in solution and inverse microsuspension with azocyanovaleric acid, potassium persulfate, and azobisisobutyronitrile over the temperature range 45 to 60 C. The copolymer reactivity ratios were determined with the error-in-variables method by using residual monomer concentrations measured by high-performance liquid chromatography. This combination of estimation procedure and analytical technique has been found to be superior to any methods previously used for the estimation of reactivity ratios for cationic acrylamide copolymers. A preliminary kinetic investigation of inverse microsuspension copolymerization at high monomer concentrations is also discussed. 

Poly(diallyldimethylammonium chloride) was the first quaternary ammonium polymer approved for potable water clarification by the United States Public Health Service, and has historically been the most widely produced cationic polyelectrolyte. There have been several studies on the kinetics (26-37) and uses of diallyldimethylammonium chloride (DADMAC) (38-45) however, there have been no investigations in inverse microsuspension, the most common industrial method of polymerization. Furthermore, there is considerable disagreement between published reactivity ratios, probably because no satisfactory analytical methods have been described in the literature for residual monomer concentration or copolymer composition. For other commercially important quaternary ammonium polymers, such as dimethylaminoethyl methacrylate and dimethylaminoethyl acrylate, few kinetic data are available (46-51) only Tanaka (37) measured the reactivity ratios. 

Inverse microsuspension is a commercial process for the production of high molecular weight, water-soluble polymers. Monomers are dispersed in a continuous organic phase, usually paraffinic, and sterically stabilized. Polymerization can be initiated with an oil- or water-soluble initiator. 

Figure 13. Experimental monomer composition (o) for an AAM-DMAEM inverse microsuspension copolymerization at 50 C. The reaction conditions are the same as in Figure 12. The dashed line is the predicted compositional drift based on the reactivity ratios measured in solution polymerization. The solid lines are the 95% confidence limits.

W-in-O Water soluble monomer in solution dispersed in a continuous organic phase. Kinetics resemble solution polymerization. Inverse-microsuspension is a subdomain with a higher surfactant concentration, smaller particle size (10 pm) and smaller n (10 ). 

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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