EMULSION POLYMERIZATION OF STYRENE STABILIZED BY MIXED ANIONIC AND NONIONIC SURFACTANTS

The mixed SDS/NP-40 (anionic/nonionic) surfactants were used to examin e the generality of Smith-Ewart theory which was originally proposed f or emulsion polymerization systems containing anionic surfactants. Our results are consistent with Smith-Ewart theory only when the wt% of N P-40 in the surfactant mixture ([NP-40]) is less than 30%. However, th e reaction system deviates from Smith-Ewart theory dramatically when [ NP-40] is greater than 50%. The steric stabilization effect provided b y pure NP-40 is not strong enough to prohibit the interactive particle s from flocculating with one another. On the other hand, the mixed sur factant system can greatly improve the latex stability via the synerge tic effects provided by both the electrostatic and steric stabilizatio n mechanisms and, thereby, retard the limited flocculation process. Th e mixed surfactant system SDS/NP-40 (20/80) is the best, because it re sults in the best reproducibility of the experiment and the greatest p olymerization rate. (C) 1997 Elsevier Science Ltd.