Polymer microcapsules prepared in inverse emulsion by 60Co γ-ray induced interfacial polymerization

Inverse emulsion was usually applied to polymerization of hydrophilic monomers, such as acrylamide, acrylic acid, salt of acrylic acid, and N-isopropylacrylamide. However, there have been few reports of one-step synthesis hydrophobic polymer hollow spheres or microcapsules in inverse emulsion system via an interfacial polymerization approach under mild reaction conditions. The motivation of this work is to explore the formation mechanism of polymer microcapsules via γ-ray irradiation in W/O inverse emulsion system. Utilizing the strong reducing radical (OH, hydrated electron) and oxidant radical (eaq-, hydroxyl radical) produced in aqueous phase by 60Co γ-ray irradiation, two interfacial redox initiation systems were proposed and applied to the preparation of polymer microcapsules. In this work, BPO (benzoyl peroxide)-eaq- and DMA (N, N-dimethyl aniline)-OH were used to control the polymerization position at the water-oil interface. High viscosity of external oil phase, high inner phase emulsion and polymeric surfactant were employed to depress the homogeneous nuclei and enhance stability of the inverse emulsion during polymerization. A typical inverse emulsion of water : Span80: kerosene : styrene = 20ml : 2.0g :10ml/4ml (including 0.050g BPO) was irradiated to 20 kGy by 60Co γ-rays at a dose rate of 65 Gy/min. Finally, polystyrene microcapsules were synthesized successfully with an average diameter of 400 nm and shell thickness of 50 nm. The productivity of micro-capsules decreased with the increasing of styrene content due to the homogeneous nuclei. When cyclohexane was used as the oil phase, porous polymer materials can be successfully obtained. Because of the multiplicity in choosing oil-soluble monomers and substances being dissolved in the aqueous phase, this approach revealed interests in encapsulation of bioactive materials or drugs. (authors)