Determination of Molecular Weight in Emulsion Polymerization

We have already observed that emulsion polymerization has three phases (i.e., water, polymer particle, and micelles). In each of these, the following radical polymerization reactions occur  

Most of the polymer is present in polymer particles and, in view of this, we must analyze the polymer formation therein if we want to determine the average chain length and the polydispersity index. We have already noted that initiator radicals are absorbed on the surface of polymer particles, initiating the formation of polymer radicals. These polymer radicals grow and terminate according to Eq. (7.6.1) or get desorbed. For the analysis presented in this section, we assume that dead polymer chains do not get desorbed, even though polymer radicals (i.e., P ) 

FIGURE 7.9 Formation of branched polymer in the emulsion polymerization of vinyl acetate and vinyl chloride. 

In writing Eq. (7.6.2), expressions for termination and initiation have not been included. Within a given particle, these reactions are small due to a sufficiently slow rate of polymerization and, therefore, have neghgible influence on the molecular weight distribution. 

We can similarly make a mole balance equation within polymer particles for polymer radicals P,. and derive the following reaction, assuming that the steady-state approximation is valid  

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