Atom transfer radical polymerisation in miniemulsion using anionic surfactants

摘要

Atom transfer radical polymerisation (ATRP) is a controlled/living radical polymerisation (CLRP) technique using transition metal catalysts to generate polymers with low polydispersity and pre-determined molecular weight. Heterogeneous polymerisation systems consist of the monomer suspended in water; miniemulsion polymerisation is a subset of these where the monomer droplets and resulting polymer nanoparticles are approximately 50-500 nm in diameter. The great advantage of miniemulsion polymerisation is the mechanism of particle formation, which is based on monomer droplet nucleation. As such, the diffusion of monomer or other reagents through the aqueous phase is not a requirement. This allows for the integration of hydrophobic solids and liquids into the nanoparticles formed, as well as the use of CLRP techniques, as there is no need for the components to be soluble in the aqueous phase. One of the drawbacks of the ATRP techniques has been that it has been believed to be incompatible with anionic surfactants due to interactions between the anionic moiety of the surfactant and the transition metal catalyst. Anionic surfactants are generally the most common and inexpensive surfactants used in polymer nanoparticle synthesis, and there is thus a desire to make such surfactants compatible with ATRP. In the present work, a method has been developed whereby anionic surfactants, specifically sodium dodecyl sulphate (SDS), can be employed to conduct ATRP in miniemulsion. To this end, a subset of ATRP, AGET (Activators Generated by Electron Transfer) was used to prepare poly(tert-butyl methacrylate) in a miniemulsion system using a variety of surfactants; non-ionic, cationic and anionic. Consistent with previous work, poor results were obtained for the anionic surfactant SDS. The novel method developed entails the addition of a halide salt such as sodium bromide to the SDS-based miniemulsion where the halide salt mitigates the interactions between the transition metal complex and the anionic surfactant, thereby allowing the polymerisation to proceed in a controlled/living manner.