One-Step Synthesis of Polymer Capsules with Transition Metal

Abstract

Transition metals are widely used as catalysts for organic synthesis because they exhibit a variety of reaction forms and specific selectivity, such as cross-coupling reactions and hydrogenation reactions. In recent years, in order to facilitate the use and recovery of transition metals, many studies have been conducted to support transition metals on carbon fibers, alumina, silica, polymer particles, and so on. In particular, microcapsules containing metal particles are expected to be applied to catalysts, DDS, and sensors.

In order to apply the catalysis material, polymer capsules with transition metal particles such as palladium and gold small particles (capsules with Pd or gold particles) were prepared by one-step suspension (free radical) polymerization. 

In the case of capsules with Pd, ethylene glycol dimethacrylate (EGDM) monomer droplets dissolved tetrakis(triphenylphosphine)palladium(0) (Pd(PPh₃)₄) was polymerized. The color of polymerizing dispersion was changed from orange to black during the polymerization, reduction of Pd(PPh₃)₄ were occurred competitively with the formation of the polymer capsule shell. Gray colored hollow particles were obtained finally. Pd particles couldn't observed in the particles by SEM, however,obtained gray colored capsules acted as a catalyst for the Suzuki-Miyaura cross coupling. 

In the case of capsules with gold particles, suspension polymerization for W/O/W emulsion including chloroauric acid aqueous solution was carried out. During the polymerization, chloroauric acid was reduced by initiator radical as similar with former Pd system, resulting polymer capsule with gold nanoparticles (ca. 100 nm) by one-step suspension polymerization. The encapsulated gold nanoparticles acted as catalysts in the reduction of 4-nitrophenol with high efficiency and reproducibility.

 These results indicate that the polymer capsules containing Pd or Au particles prepared by one-step synthesis, in which the polymer (capsule wall) and metal particles are formed simultaneously, have catalytic ability.