Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization techniques are well developed for solution and bulk polymerization systems [1,2]. However, this is not yet the case for the application of RAFT techniques to emulsion polymerization systems.

The RAFT agent 2-phenylprop-2-ylphenyldithioacetate (PPPDTA) has been successfully used in seeded emulsion polymerizations of styrene. The highly water-insoluble PPPDTA was incorporated into the seed latex particles using acetone to facilitate transport. The acetone was then removed and polymerization was initiated using either sodium persulfate or 4,4'-azo-bis(4-cyanopentanoic acid). Unlike previous studies [3,4], the RAFT agent had no adverse effect on latex stability; large amounts of coagulum were not observed. The polymerization reactions were monitored using either dilatometry or calorimetry.

We observed molecular weight control (Mn determined by the concentration of the RAFT agent), reduced molecular weight polydispersity (Mw/Mn ~ 1.3), living character (linear increase of molecular weight with conversion) and an approach to a steady state of polymerization (from which the rate coefficients for radical entry and exit may be calculated [5]). However, a long induction period in comparison to normal emulsion polymerization was also observed. These results will be discussed with respect to possible mechanisms for these effects.

References

1. Rizzardo, E.; Chiefari, J.; Mayadunne, R.; Moad, G.; Thang, S. H. ACS Symp. Ser. 2000, 768, 278.
2. Moad, G.; Chiefari, J.; Chong, Y. K.; Krstina, J.; Mayadunne, R. T. A.; Postma, A.; Rizzardo, E.; Thang, S. H. Polymer International 2000, 49, 993-1001.
3. Monteiro, M. J.; Hodgson, M.; De Brouwer, H. Journal of Polymer Science Part A-Polymer Chemistry 2000, 38, 3864-3874.
4. Uzulina, I.; Kanagasabapathy, S.; Claverie, J. Macromolecular Symposia 2000, 150, 33-38.
5. Gilbert, R. G. Emulsion Polymerization: A Mechanistic Approach; Academic: London, 1995.

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