Molecular weight distribution suspension polymerization

In suspension polymerization water is used as a diluent and as a heat transfer aid. Suspending agents such as starch and melhylcellulose are used to keep the styrene monomer particles in suspension. The more efficient heat transfer of this process also allows for a narrower molecular weight distribution. 

In the following section on reactor and process types, the preponderance of work on mass/solution polymerization is pointed out with a brief review of the more limited work on suspension and emulsion polymerization. In another broad view of the field (the next section) the distinction between polymerization rate and product distribution is discussed, particularly the preoccupation with molecular weight distribution. 

Tn emulsion polymerization and in some suspension polymerizations, free radicals are generated in a continuous phase and diffuse into a dis-persed-phase particle or droplet where polymerization takes place (5). The molecular weight distributions or, equivalently, the polymer size distributions of these systems depend on the relative rates of radical arrival and termination. Frequently in emulsion polymerization the radicals are terminated so quickly that each particle in the dispersed phase... 

The rate of polymerization was determined from the amount of polymer obtained per unit of time. The productivity of the metallocene catalyst was calculated from the quantity of polymer and the catalyst metal fed into the reactor. The resulting polymers were investigated by gel permeation chromatography (GPC) to determine the molecular weight distribution together with the average molecular weights. The density was measured on pressed films by means of the suspension method in a mixture of water and isopropanol. 13C-NMR-spectroscopy was applied to analyze the composition of copolymers and to evaluate their structure. 

Kinetically, each bead acts as a small independent reactor there is little exchange of material between the beads. Since there is no solvent present at the locus of polymerization, the kinetics are those of bulk polymerization, with the molecular weight distribution (MWD) characteristics similar to those of bulk or solution polymerizations. If water-soluble initiator is used in a suspension polymerization, very little polymerization will occur, since few free radicals will reach the locus of polymerization in the monomer beads. 

Molecular Weight and Molecular Weight Distribution of Polystyrene Obtained with Suspension Polymerization... 

Sample Materials. Vinnol H 60d. Vinnol Y 60, and Vinnol E 6Qg are commercial polyvinylchlorides from Wacker. produced by suspension, bulk, and emulsion polymerization techniques, respectively. All materials have nearly the same molecular weight distribution (MWD) as Solvlc 226 which, (with our SEC calibration) gave M = 74.000, M = 35,000. The samples used in this investigation in the Vinnol 60 series had molecular weights in the range M = 72,000 2000 and... 

A novel method of producing suspension polymers of poly(vinyl acetate) with a closely controlled molecular weight distribution involves the solution polymerization of vinyl acetate in methanol. By varying the ratio of monomer to methanol, a variety of molecular weight distributions may be prepared. The solution polymer is then added with agitation to an aqueous system containing poly(vinyl alcohol). The methanol is then distilled off to give a bead polymer [121]. 

Vinylidene fluoride (b.p. — 84°C) is free-radically polymerized in suspension or emulsion at 10-300 bar and 10-150°C. Suspension-polymerized material contains less branching and consequently a narrower molecular-weight distribution than the emulsion-polymerized material. For this reason, the suspension-polymerized material has higher crystallinity, greater mechanical strength, and better chemical stability. Materials from both polymerization methods contain a considerable proportion of head-to-head linkages. 

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