The effect of the reactive surfactant HITE-NOL BC20 (polyoxyethylene alkylphenyl ether ammonium sulfate; 20 U of ethylene oxide (EO)) on the emulsion polymerization of styrene was studied via reaction calorimetry (Mettler RC1; 708C). For polymerizations carried out above the cmc of BC20, the reaction kinetics and evolution of the number of particles (N p ) resembled those reported using the conventional surfactant sodium lauryl sulfate, indicating that nucleation proceeded by a combination of micellar and homogenous nucleation (Interval I and Stage 2). The reaction rate (R p ) not only increased with increasing initiator (K 2 S 2 O 8 ) and surfactant concentrations, as expected, but the increase in rate in Stage 2 was dependent on the initiator concentration and independent of the surfactant concentration. This is consistent with the proposed nucleation mechanisms. The molecular weight increased with increasing surfactant concentration and decreasing initiator concentration as would also be expected for a conventional surfactant. The dependencies of R p and N p on the BC20 and initiator concentrations, however, were lower than the classical Smith-Ewart values (0.21-0.25 ) although R p was found to be directly proportional to N p . Chain transfer to the reactive surfactant is considered a likely source of divergence.

Micrometer-sized particles were formed by controlled aggregation of carboxylated polystyrene colloidal spheres having a mean diameter of about 200 nm with a commercial cationic coagulant. To identify the parameters governing the size and structure of the aggregates, the aggregate size distribution was studied over a period of time with dynamic light scattering. The effect of the particle concentration, pH, and ionic strength on the aggregation behavior was investigated. The coagulant concentration used for present studies was 5 parts per hundred on the basis of the polystyrene particles and the particle concentrations used were 10-15%. The particle size distribution for the latex suspensions was also investigated with a 10% aluminum sulfate [Al 2 (SO4) 3 Á14H 2 O] solution as a model coagulant. With the commercial coagulant, aggregation was found to be slower at lower pH than at neutral pH. At pH 6, the particles started to aggregate within minutes and form aggregates of about 1000 nm. We expected that lowering the pH would reduce interparticle repulsive forces and enhance the collision efficiency. However, at a lower pH of 2, the aggregation process slowed down. Increasing the ionic strength at neutral pH led to a broader aggregate size distribution, and the population of larger aggregates increased. The suspensions with the model coagulant showed similar behavior.

The reactive surfactant HITENOL BC20 (polyoxyethylene alkylphenyl ether ammonium sulfate containing 20 units of ethylene oxide) was used in emulsion polymerizations of styrene with potassium persulfate as initiator. A new method to determine the amount of chemically bound surfactant was developed using GPC combined with UV detection as shown in the figure. Comparing this GPC method with the serum replacement/FTIR method reveals it to be a relatively simple and more effective means of characterization.

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