Emulsion styrene butadiene rubber (ESBR) is widely used in tire manufacturing due to its excellent physical properties and environmentally friendly water-based synthesis process. However, its free-radical mechanism leads to side reactions such as coupling and disproportionation, which terminate chain growth and complicate molecular weight distribution (MWD) control. The resulting broad MWD increases energy loss and negatively affects mechanical and viscoelastic properties.
In this study, we report the first successful synthesis of SBR via ab initio reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization using poly(acrylic acid-b-styrene) with a trithiocarbonate end group as a reactive surfactant. By employing RAFT polymerization, we successfully synthesized ESBR with a narrow MWD. The polymerization was confirmed using FT-IR and NMR spectroscopy, while particle size was analyzed using dynamic light scattering (DLS).
Furthermore, we fabricated a SBR, natural rubber (NR), and aramid chip composite using RAFT ESBR as a dispersant for the aramid chip. The acrylic acid (AA) block at the polymer chain end facilitates hydrogen bonding with the aramid surface, while the butadiene units in the SBR segment participate in the vulcanization reaction with the base rubber. This molecular design improves both the dispersion of aramid chip within the rubber matrix and the mechanical properties of the resulting composite.