Controlled radical polymerization of styrene in miniemulsion mediated by PEO-based trithiocarbonate macromolecular RAFT agents

Abstract

Poly(ethylene oxide) (PEO) based macroRAFT agents with various chemical structures have been used as both stabilizer and control agent for the polymerization of styrene in miniemulsion conditions. Trithiocarbonate (PEO-DTTC (Z = thiododecyl), PEO-PTTC (Z = thiopropyl)) functional groups were attached to a commercial monomethyl ether PEO (M_n = 2000 g mol⁻¹). PEO-DTTC and PEO-PTTC allowed the formation of stable miniemulsions of styrene in water. Our previous results (A. M. Dos Santos, T. Le Bris, C. Graillat, F. D'Agosto, M. Lansalot, Macromolecules, 2009, 42, 946) showed that PEO-based dithiobenzoate (PEO-DB) led to controlled polymerization but also to broad molar mass distribution (PDI = 1.9) and multipopulated polymer chains. The switch from PEO-DB to PEO-DTTC greatly improved the molar mass distribution (PDI = 1.6). This was ascribed to the ability of PEO-DTTC to be localized at the water/monomer droplets interface. An increase in PEO-DTTC concentration improved the control of the polymerization. However, the concomitant formation of micelles favored secondary nucleation. This was attenuated by the use of PEO-PTTC, less prone to form micelles in water which greatly improved both the quality of control (PDI = 1.3) and the particle size distribution and showed that the particles were constituted of well-defined PEO-b-PS polymer chains. These results could be attributed to a more efficient anchoring of PEO-PTTC at the monomer droplet or particle/water interface showing the crucial role of the macroRAFT structure in these systems.