Dispersions, rapid polymerizing

Dispersion of polymeric viscosifiers is often difficult because the initial contact of the untreated polymer with water results in very rapid hydration of the outer layer of particles which creates a sticky, rubbery exterior layer that prevents the interior particles from contacting water. The net effect is formation of what are referred to as nfish eyes" or "gel balls." These hamper efficiency by lowering the viscosity achieved per pound of gelling agent and by creating insoluble particles that can restrict flow both into the formation and back out of it. The normal remedy for this behavior... 

Colloidal stability is usually controlled by the type and amount of the employed surfactant. In miniemulsions, the fusion-fission rate equilibrium during sonication and therefore the size of the droplets directly after primary equilibration depends on the amount of surfactant. For sodium dodecylsulfate (SDS) and styrene at 20% dispersed phase, it spans a range from 180 nm (0.3% SDS relative to styrene) down to 32 nm (50 rel.% SDS) (Fig. 4a). Again, it is anticipated that rapidly polymerized latexes also characterize the parental miniemulsion. As... 

Relationship of Morphology to Mechanical Properties of Rapidly Polymerizing Acrylic Dispersions... 

The mechanical properties of rapidly polymerizing acrylic dispersions, in simulated bioconditions, were directly related to microstructural characteristics. The volume fraction of matrix, the crosslinker volume in the matrix, the particle size distribution of the dispersed phase, and polymeric additives in the matrix or dispersed phase were important microstructural factors. The mechanical properties were most sensitive to volume fraction of crosslinker. Ten percent (vol) of ethylene dimethacrylate produced a significant improvement in flexural strength and impact resistance. Qualitative dynamic impact studies provided some insight into the fracture mechanics of the system. A time scale for the elastic, plastic, and failure phenomena in Izod impact specimens was qualitatively established. The time scale and rate sensitivity of the phenomena were correlated with the fracture surface topography and fracture geometry in impact and flexural samples. 

When a water-soluble monomer dispersed in a continuous oil phase is polymerized with an initiator soluble in the continuous phase, we speak of inverse emulsion polymerization [159]. This system has all the advantages of emulsion polymerizations (rapid polymerization, high degree of polymeriza-... 

In the case of a polymer that is miscible in all proportions with its monomer (e.g., styrene and methyl methacrylate), a very large variation of the range of the dispersed-phase viscosity is observed during the course of polymerization. The initially low viscosity liquid monomer is transformed gradually into an increasingly viscous polymer in monomer solution and, as conversion increases, the dispersed phase acquires the characteristics of a solid particle. Rapid polymerization during the sticky stage minimizes the... 

Most commercial processes use this type of polymerization to produce small uniform capsules in the range of 20-30 micron diameter however, the process can be tuned to produce large microcapsules. The size of these microcapsules and the properties of the wall material/polymer matrix can be altered by using different monomers, utilizing additives, and adjusting reaction conditions. The encapsulation occurs by wall formation around the dispersed core material via the rapid polymerization of monomers at the surface of the droplets or particles. The solution of a multifunctional monomer in the core material is dispersed in an aqueous phase. The polymerization is commenced at the surfaces of the core droplets forming the capsule walls, by adding a reactant to the monomer dispersed in the aqueous phase. 

The specific surface recognition of polymerized liposomes has been demonstrated by a simple model reaction A dispersion of polymerized liposomes of glycolipid 38 was mixed with the lectin Concanavalin A, which caused a rapid agglutination and precipitation of the liposomes. This effect was not observed for polymerized liposomes without sugar headgroups. 

From a practical standpoint, melt intercalation of polymers into such organically modified layered silicates represents an appealing approach to synthesize composite materials consisting of such nanometer thick layers dispersed in polymeric matrix. This is because melt intercalation is rapid and can be readily achieved via melt compounding with traditional polymer processing equipment, while the added shear of such a process can help to break apart the intercalated multi-layer stacks. 

The water solubilities of the functional comonomers are reasonably high since they are usually polar compounds. Therefore, the initiation in the water phase may be too rapid when the initiator or the comonomer concentration is high. In such a case, the particle growth stage cannot be suppressed by the diffusion capture mechanism and the solution or dispersion polymerization of the functional comonomer within water phase may accompany the emulsion copolymerization reaction. This leads to the formation of polymeric products in the form of particle, aggregate, or soluble polymer with different compositions and molecular weights. The yield for the incorporation of functional comonomer into the uniform polymeric particles may be low since some of the functional comonomer may polymerize by an undesired mechanism. 

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