Heterogeneous polymerization process

Heterogeneous polymerization processes (emulsion, miniemulsion, non-aqueous dispersion) offer another possibility for reducing the rate of termination through what are known as compartmcntalization effects. In emulsion polymerization, it is believed that the mechanism for chain stoppage within the particles is not radical-radical termination but transfer to monomer (Section 5.2.1.5). These possibilities have provided impetus for the development ofliving heterogeneous polymerization (Sections 9.3.6.6, 9.4.3.2, 9.5.3.6). 

The various homogeneous and heterogeneous polymerization processes used, generally yield mixtures of polymers having different stereoregularity, which can be fractionated by solvent extraction. 

The various latexes were characterized with respect to particle size and size distribution, surface charge and functional group density, and electrophoretic mobility behavior. As observed by transmission electron microscopy all latexes were found highly monodisperse with a uniformity ratio between 1.001 and 1.010, a property due to the short duration of the nucleation period involved in the various radical-initiated heterogeneous polymerization processes. The surface charge density was determined by a colorimetric titration method reported elsewhere [13]. 

Heterophase polymerization systems can be defined as two-phase systems in which the resulting polymer and/or starting monomer are in the form of a fine dispersion in an immiscible liquid medium defined as the polymerization medium , continuous phase , or outer phase . Even if oil-in-water (o/w) systems are greatly preferred on an industrial scale, water-in-oil (w/o) systems may also be envisaged for specific purposes. Heterogeneous polymerization processes can be classified as suspension, dispersion, precipitation, emulsion, or miniemulsion techniques according to interdependent criteria which are the initial state of the polymerization mixture, the kinetics of polymerization, the mechanism of particle formation and the size and shape of the final polymer particles (Fig. 4.2) [18]. 

Chemical Reaction Kinetics in Polymer Systems TABLE 6-7 Comparison Heterogeneous Polymerization Processes... 

In general, we can distinguish homogeneous and heterogeneous polymerization processes. Homogeneous processes take place within the substance in question (with the monomer or the formed polymer acting as reaction medium) or in a solvent. Heterogeneous processes include precipitation, slurry phase, suspension, emulsion, or gas-phase polymerizations. 

In addition to emulsion, dispersion, and suspension polymerization, there are other industrial heterogeneous polymerization processes (Table 2). Of particular importance are slurry and gas-phase processes for polyolefin production, which are also included in Section 4.32.13. 

Heterogeneous polymerization processes (emulsion, miniemulsion, nonaqueous dispersion) offer another possibility for reducing the rate of termination through what are known as compartmentalization effects. In emulsion polymerization, it is... 

Figure 3 Slurry-phase heterogeneous polymerization process.

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