Radical monomer concentration inside particle

The rate coefficient for desorption of monomeric radicals may be written as a function of the diffusivity of monomer both in the water phase and inside the particle, the aqueous monomer concentration, the monomer concentration in the particle, and the swollen radius ... 

M] in Equation 12.44 has been replaced by [Mp] in Equation 12.45. This makes sense, since the monomer concentration that feeds the radicals in emulsion polymerization (at the appropriate reaction site) is indeed the monomer concentration in the polymer (latex) particles. Since [R] in Equation 12.44 represents total radical concentration, it has been replaced by the product (N n), which represents the total number of radicals present at the reaction site (the main locus of polymerization, which is inside the monomer-swollen polymer particles). is the total number of particles (usually per lit of water) and n represents the average number of radicals per particle. N, Avogadro s number, appears in the equation simply for unit conversion. Needless to say. Equation 12.45 is completely analogous to Equation 12.44. 

Desorption results in a decrease in the concentration of growing radicals inside the particles, and causes the rate of polymerization to decrease. It is strongly connected to the probability of chain transfer to monomer as smaller radicals cross the interface faster than larger radicals. For monomers with higher chain-transfer rates to monomer (such as ethylene, vinyl acetate, or vinyl chloride), radical exit represents the major process of reducing n to values much less than 0.5. However, for styrene also, the correct kinetic description requires the consideration of radical desorption. Exit is not only literally, but also mechanistically, the opposite of entry the radical must reach the particle surface and must then overcome the barrier for desorption exerted by the interface. 

To investigate the effect of high-pressure CO2 on the polymerization reaction as well as to determine the amount of monomer inside the polymer particles, electron beam experiments have been performed [19]. Pulsed electron beam polymerization involves the generation of radicals in the aqueous phase, this being activated by an electron beam. These radicals initiate the polymerization of the residual monomer inside the latex particles. Based on the molecular weight of the newly formed polymer chains, the local monomer concentration in the polymer particles can be calculated. The growth time of a polymer chain is directly... 

In summary of this part, the average number of radicals per compartment is the centerpiece of heterophase polymerization kinetics. Its value depends mainly on the rate with which active, propagating centers appear inside the particles either by decomposition of monomer-soluble initiators or by entry from the continuous phase. Furthermore, particle size and overall concentration of compartments influence h in such a way that it increases with both increasing D and decreasing N. If the viscosity inside the particles is so high that termination by radical recombination is hindered, h increases as an expression of the gel effect in compartmentalized polymerization systems. 

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