Oligoradicals

As the micelles grow by absorption of more monomer and formation of polymer, they become relatively large particles that absorb soap from micelles that have not been inoculated or stung by oligoradicals. Thus, in stage II, when about 20% of the monomer has been converted to polymer, the micelles disappear and are replaced by large, but fewer, monomer-polymer particles. 

In the case of template processes, this mechanism must be completed by terms accounting for interaction between template, monomer, and polymer. This subject is discussed in more detail in Chapter 8. Intermolecular forces lead to absorption of the monomer on the template or, if interaction between monomer and template is too weak, oligoradicals form complexes with the template. Taking into account these differences in interaction, this case of template polymerization can be divided into two types. In Type I, monomer is preadsorbed by, or complexed with, template macromolecules. Initiation, propagation and perhaps mostly termination take place on the template. The mechanism can be represented by the scheme given in Figure 2.7. 

Termination can be realized both by macroradicals on the template (template-template termination) or by recombination of radicals on the template with macroradicals or oligoradicals not connected with the template (cross-termination). For some systems, it is difficult to decide whether they are type I or type II. The intermediate systems can also exist. 

In all of these considerations concerning the rate of radical capture and its effect on the rate of particle formation we have been hampered by the lack of a mathematical solution for the concentration of oligoradicals in the aqueous phase, Cs. 

Equation 16 tends to underestimate the number of particles except during the earliest few seconds of reaction, but serves as an extremely useful predictor for assessing the effect of experimental variables on the number of primary particles formed as a function of time. In Figure 3 are shown some calculations for styrene polymerization in which results from this approximative equation (curves A) are compared to those for the full numerical solution (curves C) at two values for jcr (30). It can be seen that when the oligoradical solubility is reduced (jcr = 10- 5), the rate of nucleation and final number of particles are greatly increased. This is, of course, in the absence of change in any other variable. 

F than that for a more fully swollen particle, because of less likelihood for termination of the adsorbed oligoradical. 

Burdett et al. [9,10] reported calculations by means of the moments method on the nets (3, 9, 4, 8 and 5, 7 ). Hoffmann, Eisenstein and Balaban (11] discussed a hypothetical strain-free oligoradical with 8-membered rings whose carbon atoms have sp2 -hybridization. 

Polymeric species Living oligoradicals in The propagating radicals The polymer is at A chain-length-dependent... 

If the oligoradical reaches its critical chain length for water solubility, it will precipitate to form primary particles ... 

The kinetics of inverse emulsion polymerization can be classified more or less arbitrarily into two subclasses according to the solubility of the initiator. Note that the solubility in water of oil-soluble initiators was found to be oihanced (up to a factor of 3) by the presence of monomo [23,28,29], making possible initiation by radical pairs formed in the aqueous dispersed phase. On the other hand, homogeneous nucleation mechanisms generating oligoradicals in the continuous phase can also be operative in inverse emulsions due to the maiginal solubility of acrylamide in organic media (1.6 wt% in isoparaffinic solvents and 2 wt% in toluene) [3]. 

How does a radical or an oligoradical enter a particle or a micelle ... 

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