Progress of Polymerization

A variety of behaviors are observed for the polymerization rate versus conversion depending on the relative rates of initiation, propagation, and termination, which are in turn dependent on the monomer and reaction conditions (Fig. 4-2). Irrespective of the particular behavior observed, three intervals (I, II, III) can be discerned in all emulsion polymerizations based on the particle number N (the concentration of polymer particles in units of number of 

Polymerization proceeds in the polymer particles as the monomer concentration in the particles is maintained at the equilibrium (saturation) level by diffusion of monomer from solution, which in turn is maintained at the saturation level by dissolution of monomer 

The particle number remains the same in interval III as in interval II, but the monomer concentration decreases with time, since monomer droplets are no longer present. The decrease in 4 m is slower with the more water-soluble monomers as the monomer in solution acts as a reservoir. The presence of a gel effect continues in interval IE. The quantitative interplay of a decreasing monomer concentration with the gel effect determines the exact behavior observed in this interval (GF or H). Polymerization continues at a steadily decreasing rate as the monomer concentration in the polymer particles decreases. Final conversions of essentially 100% are usually achieved. The final polymer particles, spherical in shape, usually have diameters of 50-300 nm, which places them intermediate in size between the initial micelles and monomer droplets. 

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The currently accepted mechanism of the alkali metal-mediated Wurtz-type condensation of dichlorosilanes is essentially that outlined in COMC II (1995) (chapter Organopolysilanes, p 98) which derived from studies by Gautier and Worsfold,42 and the groups of Matyjaszewski43 and Jones,22,44,45 a modified polymerization scheme of which is included here. The mechanism was deduced from careful observations on the progress of polymerizations in different solvents (such as those which better stabilize anions and those which do not), at different temperatures,44 with additives, and with different alkali metal reductants. Silyl anions, silyl anion radicals,42 and silyl radicals28,46,47 are believed to be involved, as shown in Scheme 3. 

Seeded polymerization is defined as polymerization of post-added monomer in the presence of particles. A conventional example of seeded polymerization is the polymerization of styrene (St) and acryronitrile (AN) in the dispersion of polybutadiene (PB) particles. In this polymerization, a portion of St and AN penetrates into the PB particle and the other portion stays in the aqueous phase. The former graft-polymerize with PB or polymerize by themselves in PB particle. The progress of polymerization in the particle leads to phase inversion to form a salami structured particle in which PB islands are dispersed in a poly(St-co-AN) sea. St and AN in aqueous phase may polymerize to form independent particles. 

Figure 6a. t C H) NMR spectra showing the progress of polymerization of 4.5M butadiene-,sC, with 6.2M n-BueLi in cyclopentane at 26°C. Aliphatic portion only. Times of reaction are given at the right side. 

Figure 5.3 Schematic diagram of the progress of polymerization of a polysilane, showing defect-controlled chain growth and termination. Reprinted with permission from reference 20. Copyright 2003 American Chemical Society.

The structure of aluminate in aqueous solution is gradually decomposed and the moiety of the network structure of aluminate, aluminum tetrahydroxide, and the hydrates occur as the predominant chemical species in the aqueous solution. The structure of chemical species in aqueous solution changes from fourfold coordination structure to sixfold coordination structure with H20 molecules. At this time, polymerization begins to proceed. Hexaaquaaluminum cation serves as a core to form the network structure of Al(OH)3 by the progress of polymerization. Finally, Al(OH)3 precipitates and crystallizes. 

Figure 29.2. Progress of polymerization of a-Arb and P-Arb responding to the addition of H202.

A kinetic model developed for imseeded emulsion polymerization based on the knowledge and conclusions obtained above could explain the progress of polymerization inside both the monomer droplets and the latex particles in the seeded emulsion polymerization of St initiated by AIBN at 50 °C. 

Fig. 2 Variatl on of surface tension of aqueous phase of reaction mixture with progress of polymerization.

Effect of emulsifier concentration upon the number of polymer particles and the progress of polymerization ... 

Figs.7 and 8 respectively show the effect of Initial initiator concentration on the number of polymer particles and the progress of polymerization at fixed Initial emulsifier and monomer concentrations. It can be concluded that the number of polymer particles Is Independent of Initial Initiator concentration, as shown In Fig.7. Fig.9 shows log-log plots of polymerization raterp(g/ cc-HaO sec)versus Initiator concentration, rp Is calculated from the slope of the linear portion of the monomer conversion versus time plot shown In Fig.8. The order of reaction with respect to the Initiator concentration Is found to be approximately 0.5 from... 

In Fig.16 is shown, as an example, the variation of value of n with the progress of polymerization, calculated with the use of Egs.Q.0), (6) cuid (7), the observed values of Nip shown in Fig.4, emd rp,obtcdned from graphical differentiation of monomer conversion versus time curve in Fig.5. In this case, it is assumed that kp 3300 7/mole sec( ). 

The progress of polymerization of Matrimid 5292 can be monitored by Py-GC/MS [19]. The levels of methylphenol, 4-succinimido-4 -aminodiphenylmethane, and 2-(2-propenyl)-4-methylphenol are increased in the pyrolysate as the degree of curing increases. At the same time, the level of 3,3 -diallyl bisphenol A decreases with increasing cure. 

Figure 13-4 Progression of polymeric backbones from polyacetylene to carbyne.

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