Water soluble polymers homogeneous dispersion

Water Soluble Polymers Produced by Homogeneous Dispersion Polymerization... 

According to the solubility of the core-forming monomer in the reaction media, two different methods—emulsion polymerization and dispersion polymerization— have been exploited to obtain self-assembled nanoparticles by PISA [37, 38]. The dispersion polymerization can be carried out either in water or in organic solvents. The emulsion polymerization starts from a monomer-in-water emulsion, where a water-soluble polymer precursor is chain-extended by polymerizing a water-immiscible monomer, resulting in self-assembled block copolymers. In contrast to the emulsion polymerization, dispersion polymerization is conceptually much simpler and the initial reaction solution is homogeneous. 

Heterogeneous Copolymerization. When copolymer is prepared in a homogeneous solution, kineiic expressions can be used to predict copolymer composition Bulk and dispersion polymerization are somewhat different since the reaction medium is heterogeneous and polymeri/aiion occurs simultaneously in separate loci. In bulk polymerization, for example, the monomer swollen polymer particles support polymerization within the particle core us well as on the particle surface, lit aqueous dispersion or emulsion polymeri/aiion the monomer is actually dispersed in two or three distinct phases a continuous aqueous phase, a monomer droplet phase, and a phase consisting of polymer particles swollen at Ihe surface with monomer. This affect the ultimate polymer composition because llie monomers are partitioned such that the monomer mixture in the aqueous phase is richer in the more water-soluble monomers than the two organic phases. 

In homogeneous free radical polymerization, water is often employed as solvent for water-soluble monomers and polymers with more polar functional substituents such as hydroxyl, amino, oxyethylene, ammonium, and carboxylate groups, along with emulsion, suspension, and dispersion processes. This is also the case for metal-catalyzed living radical polymerization. 

An emulsion polymerization requires the mechanism of polymer particle nudeation to reside outside the monomer droplets. This physical-chemical process involves a series of radical reactions in the continuous phase followed by homogeneous or micellar particle formation. Either of these mechanisms require the initiator to be insoluble in the monomer phase, such as a water soluble initiator and an organically soluble monomer, or vice versa. If, in contrast, the initiator is soluble in the monomer phase, all the components of the reaction are contained in the dispersed phase and the continuous phase serves only to decrease the viscosity and dissipate heat Such polymerizations are categorized as suspensions. The second definition, however, makes no statement as to the magnitude of n and therefore the two criteria are mutually exclusive. 

Emulsion polymerization is the polymerization technique that starts with emulsified monomer in the continuous aqueous phase. Polymer formation takes place in the micelles and is initiated by water-soluble initiators. The monomers are insoluble or sparingly soluble in water. Emulsion polymerization is used very frequently in order to perform encapsulation of inorganic particles with polymers where water-based coatings are required. For the encapsulation of inorganic particles, seeded emulsion polymerization is performed hydrophobic inorganic particles are dispersed with normal surfactants or protective colloids in the aqueous phase. As polymerization on the surface of inorganic particles is always in competition with secondary particle formation, the concentration of the surfactants should be lower than their critical micelle concentration. However, homogeneous nucleation can also occur, which... 

Most emulsion polymers are produced by conventional emulsion polymerisation (202, 204, 215). In this process, monomer droplets are dispersed in a continuous aqueous phase and are kept colloidally stable against coalescence through the use of a surfactant. The surfactant also causes polymer particles to form by homogeneous or micellar nucleation upon initiation. For conventional emulsion polymerisation to be practical, the monomer must be at least slightly water-soluble, to allow the diffusion of monomer from the droplets to the site of polymerisation in the growing polymer particles. 

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