Seeded emulsion polymerization conversion time curves

Figure 1 gives the conversion-time curves for the seeded emulsion polymerization of styrene in the absence and presence of various low molecular weight additives. Table I summarizes the results given in Figure 1. The rates of polymerization were determined from the straight line portion of the conversion-time curves (below 40% conversion) by least squares analysis of the experimental points. Table I also gives the calculated rates assuming a mere dilution of the monomer in the seed by the additive. It is clear that in every case the rate of polymerization is retarded much more than that due to dilution alone.

Fig. 11. Conversion versus time curves for seeded emulsion polymerizations of styrene with hexadecane present in the monomer phase. T — 333 K.

Typical S-shaped conversion time curves of the emulsion polymerization of MMA, MMA/St or St in the presence of PVC-VAc seed latex (with weight ratio monomer/polymer (M/P) = 2) were obtained. The rate of polymerization of MMA (in interval 2) (Rp = 13.8 g polymer/min) was much higher than that of St (Rp = 2.1 g polymer/min). The comonomer system (MMA/St, 20/30, wt. ratio) revealed an intermediate feature between the two systems (Rp = 5.5 g polymer/min). The same initial rate (Rp = 0.03 g polymer/min) was observed in St and MMA/St runs. In the MMA system, the interval 1 (the low conversion range) was very short (- 5 min). In contrast, the interval 1 is very long in polymerizations of St ( 350 min) and MMA/St ( 250 min). The secondary nucleation of particles was proportional to the SDS concentration. The secondary nucleation was suppressed when the small seed particles with a smaller monomer/polymer ratio were used. In addition, the choice of a less water-soluble monomer is a key factor in performing complete seed polymerization without nucleation of secondary particles. 

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