EMULSION POLYMERIZATION OF STYRENE USING AN ALKALI-SOLUBLE RANDOM COPOLYMER AS POLYMERIC EMULSIFIER

An alkali-soluble random copolymer (ASR), poly(styrene/alpha-methylsty rene/ acrylic acid), was used as a polymeric emulsifier in the emulsio n polymerization of styrene. The calorimetric technique was applied to study the kinetics of emulsion polymerization of styrene using ASR an d a conventional ionic emulsifier, sodium dodecyl benzenesulfonate (SD BS). ASR could form aggregates like micelles, and the solubilization a bility of the aggregates was dependent on the neutralization degree of ASR. The rate of polymerization in the ASR system was lower than that in the SDBS system. This result can be explained by the creation of a hairy ASR layer around the particle surface, which decreases the diff usion rate of free radicals through this region. Although a decrease i n particle size was observed, the rate of polymerization decreased wit h increasing ASR concentration. The higher the concentration of ASR is , the thicker and denser ASR layer may be, and the more difficult it w ould therefore be for radicals to reach the particle through this laye r of ASR. The rate of polymerization decreased with increasing the neu tralization degree of ASR. The aggregates with high. neutralization of ASR are less efficient in solubilizing the monomer and capturing init iator radicals than that of the lower neutralization degree, which lea ds to decrease in rate of polymerization. (C) 1998 John Wiley & Sons, Inc.