Monomer dispersion

Suspension (co)polymerization is carried out in aqueous solutions of monomers dispersed in the form of 0.1-5 mm diameter droplets by stirring in nonmixed water-organic liquids in the presence of initiators. The organic liquids that are not dissolving monomers and (co)polymers are represented by solvents that either form azeotropic water mixtures (toluene, heptane, cy-... 

We have studied the effect of monomer concentration in the dispersion polymerization of styrene carried out in alcohol-water mixtures as the dispersion media. We used AIBN and poly(acrylic acid) as the initiator and the stabilizer, respectively, and we tried isopropanol, 1-butanol, and 2-butanol as the alcohols [89]. The largest average particle size values were obtained with the highest monomer-dispersion medium volumetric ratios in 1-butanol-water medium having the alcohol-water volumetric ratio of 90 10. The SEM micrographs of these particles are given in Fig. 15. As seen here, a certain size distribution by the formation of small particles, possibly with a secondary nucleation, was observed in the poly-... 

Figure 15 The SEM photographs of the polystyrene particles produced in 90% 1-butanol-10% water medium by the high monomer dispersion medium ratios. Monomer/disper-sion medium volumetric ratio (mL/mL) (a) 2.0/10.0, (b) 2.5/ 10.0. (From Ref. 89. Reproduced with the permission of John Wiley Sons, Inc.)...

In suspension polymerization, the monomer gets dispersed in a liquid, such as water. Mechanical agitation keeps the monomer dispersed. Initiators should be soluble in the monomer. Stabilizers, such as talc or polyvinyl alcohol, prevent polymer chains from adhering to each other and keep the monomer dispersed in the liquid medium. The final polymer appears in a granular form. 

Figure. 3.36. Schematic of the various stages in the formation and the growth of particles from a monomer dispersion during sintering (after Satterfield, 1991).

This is superficially similar to suspension polymerisation. But in this process a monomer dispersed in water, in presence of a surface active agent is polymerised to give a stable polymer latex. 

A stirring rate of about 200 rpm should be adequate to keep the monomer dispersed without the formation of a separate monomer layer. Once polymerization is underway, the rate of agitation may not be important as long as no separate monomer layer forms. Once sodium lauryl sulfate has been added to the water, the nitrogen inlet tube must be raised above the liquid level to reduce foam and bubble formation. 

The dispersed phase of high internal phase emulsions may also be used to prepare polymeric materials in this case, conversion of monomer dispersed droplets to polymer results in latexes or particulates. 

Craft Copolymers with Low Backbone-Polymer Content. The procedure for preparing this kind of graft copolymer is based on the dissolution of the backbone polymer in the monomer, dispersion of this solution in water, and polymerization by means of an organic peroxide. It applies only to soluble backbone polymers, such as most EPR s. As the handling of a too-viscous vinyl chloride/backbone polymer solution is impractical, this procedure is normally used for preparing end products of the type VC/backbone polymer (95-5) or (90-10). 

A quite different approach to chain-growth condensation polymerization is phase-transfer-catalyzed polycondensation of solid monomer dispersed in an... 

Figure 8.1. Schematic illustration of dispersion polymerization reactor, (a) two layers of immiscible liquids - monomer and dispersion fluid (e.g. water), and (b) monomer dispersion achieved by agitation (37).

Micron-size particles can also be prepared by polymerization of monomer dispersion in organic solvents (e.g. alcohol) in which the emerging polymer is not soluble. At the beginning of the process, the reaction mixture is homogenous but during the reaction, stabilized polymer particles precipitate. This method offers uniform particles with a diameter of 2-15 pm (40). 

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-... 

Besides the similarities between mini- and microemulsions, especially with respect to the nucleation process, microemulsions are characterized by very peculiar thermodynamics in this respect, there are many similarities between a macro- and a miniemulsion. Accordingly, we should focus on the reason why monomer dispersions are unstable in macroemulsions, while they are stable in miniemulsions. 

The main reason that the branching which takes place in suspension polymerization does not lead to reactor fouling is primarily due to the fact that each droplet of monomer dispersed in the continuous water phase is like a tiny isolated reactor. The water phase is continuously in contact with the reactor... 

Ultrasound was also used for the dispersion of a surfactant pyrrole, prior to electrooxidation to the conducting polymer [233]. An amphiphilic (pyrrolylalkyl) ammonium monomer dispersion was used to coat the electrode surface with monomer, subsequently electropolymerized to thin films using an aqueous electrolyte for this step. Ultrasound has also been used to assist impregnation of pyrrole monomer into, for example, a conventional polymer matrix prior to polymerization to yield a composite of the conducting and conventional polymers, but is also a pretreatment effect of ultrasound rather than a sonoelectrochemical one [234],... 

Suspension—polymerization of monomers dispersed in an inert phase with monomer-soluble initiator Low dispersion viscosity compared to bulk good heat transfer high polymerization rate and high molecular weight direct application of the latex Smaller reactor capacity than bulk reactor wall fouling wastewater problems Polystyrene, PVC, polypropylene... 

The most commercially successful method of producing processable forms of CEPs has been the aqueous colloidal dispersion route pioneered by Vincent and Armes118 120 (see two recent reviews by Armes121 and Wessling122). Unlike the methods discussed earlier, which all require extensive derivatization of the aniline monomer, dispersions are readily formed from unsubstituted aniline and are readily manufactured in bulk quantities. 

The extent of clustering for any ethylene-l-olefin copolymer can be defined by dividing the run number by the mole percent 1-olefin. This result is called the "monomer dispersity" as shown below ... 

A value of 100 will be obtained for the monomer dispersity whenever the comonomer exists solely as an isolated unit. In Figures 6 and 7, the monomer dispersities of the 1-butene copolymers varied from 60 to 99, the 1-hexene copolymers varied from 85 to 99 and the 1-octene copolymers had monomer dispersities which varied from 96 to 100. This... 

Figure 8 Run Number Versus Density for a Series of Ethylene 1-Butene, Ethylene-l-Hexene and Ethylene-l-Octene Copolymers Possessing Monomer Dispersities of 94-100...

This mechanism excludes the possibility of polymer initiation in monomer droplets because of the relatively small global surface compared to that of micelles or of primary polymec-Q,. particles. However, recently, Ugelstad and Vanderhoff have shown that when monomer dispersion occurs in droplets of very reduced dimensions producing a drastic growth of their surface, the initiation takes place in monomer droplets protected by emulsifiers. 

Virtually all rubber materials, and plastic materials, can be made into an adhesive or sealant compound. This is because many elastomers begin as monomers dispersed in water or solvent and are polymerized in situ. Latex products can remain so, while solid elastomers that are extracted from either water or solvent systems can be solvated with an appropriate organic solvent system. In addition, most solid elastomers exhibit thermal flow characteristics which can make them suitable for hot-melt formulations. And since there are many different rubber polymer families, it stands to reason that there will be many different rubber-based adhesives to identify and describe. Some, however, have... 

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