Role of reactive surfactants in emulsion polymerization

The reactive surfactant HITENOL BC20 (polyoxyethylene alkylphenyl ether ammonium sulfate) with 20 units of ethylene oxide (EO) was used in emulsion polymerizations of styrene and copolymerization of styrene and n-butyl acrylate. Surfactant characterization shows that surfactant BC20 can not be self-polymerized. The kinetics of emulsion polymerization of styrene using BC20 was found to be similar to the conventional surfactant, in that the reaction rate Rp and number of particles N p increase with increasing surfactant and initiator concentration, and Rp is directly proportional to N p.; The hydrogenation of HITENOL BC20 was carried out (courtesy Air Products & Chemicals, Inc.) for use in experiments to decipher the role of the reactive version in emulsion polymerization. A new method using GPC to determine the chemically-bound surfactant was developed. The results show that about 24 wt% of the H-BC20 was incorporated during the nucleation stages, and after that the bound H-BC20 remained almost constant. In contrast, the amount of bound BC20 started to increase after monomer droplet disappearance. Finally, about 90 wt% of the BC20 was incorporated, of which 52 wt% are on the particle surfaces as determined by conductometric titration, leaving about 38% BC20 buried inside the particles. Results from the control experiments show that particle surface is the main locus for the surfactant incorporation and the total surface area and surface coverage are the decisive factors affecting the extent of the incorporation.; The kinetics of emulsion copolymerization of styrene and n-butyl acrylate using BC20 was investigated, which shows a similar reaction rate profile to the styrene homopolymerization, indicating that the styrene has the most influence on the nucleation mechanism(s) in the copolymerization. A composition drift was observed during the polymerization process where the copolymer is rich in styrene during the initial stages of the polymerization. The latex characterization shows that at the end of the polymerization most of the surfactant was incorporated (93.2%) into the particles.; The latexes with reactive surfactant incorporated on the particle surface show improved stabilities and the resulting films show little surfactant migration, and better water resistance.