Synthesis of styrene–butadiene copolymer nanoparticles via semi-batch differential microemulsion polymerization

Abstract

Styrene–butadiene rubber (SBR) nanoparticles were prepared in a semi-batch differential microemulsion polymerization (DMP) system using sodium oleate as the emulsifier. The size of the SBR nanoparticles could be easily tailored by controlling the monomer addition speed, the reaction temperature, the composition of the monomer feed stream and the amount of a surfactant introduced to the process. The smallest particle size, which is about 8nm, was achieved at 70°C with a very low surfactant concentration (25mM) as well as a reasonable conversion (72%). Moreover, the effects of n-dodecyl mercaptan (n-DDM), which was used as the chain transfer agent, on the particle size and the reaction conversion were investigated. Larger spherical particles and higher reaction conversions were observed at a higher n-DDM concentration. n-DDM can well regulate the SBR molecular weight of a polymer and a higher n-DDM concentration resulted in a smaller molecular weight. The DMP is found to be a very effective approach that requires a minimum amount of surfactant to prepare fine-tuned polymeric nanoparticles.