유화중합 및 초임계이산화탄소에서의 분산중합에 의한 무기/유기 나노컴포지트의 제조

Abstract

Recently, there has been a lot of work on the elaboration of nanocomposite systems by embedding of inorganic particles into polymeric matrices. These materials represent a new class of polymeric materials which combine the unique physical properties of the inorganic particles with the processability and the flexibility of the organic polymer matrix. Among them, the preparation of core-shell composite particles has received particular attention due to their great potential applications. While various techniques were used to synthesize the core-shell polymer particles, a traditional method has been the emulsion polymerization with inorganic seed particles. Inorganic/organic core-shell nanocomposites were prepared by the emulsion polymerization of methyl methacrylate (MMA) and styrene (St) in the presence of surface-functionalized inorganic nano particles (Al(OH)₃, Mg(OH)₂). Nano-sized inorganic particles were previously functionalized with a silane coupling agent, 3-(trimethoxysilyl) propyl methacrylate (γ-MPS), which was confirmed by FT-IR, BET and XRF analysis. The average size of inorganic seed particles were around 70 nm (Al(OH)₃) and 50nm (Mg(OH)₂). The ratio of the inorganic seed particles to organic monomers, MMA and St, showed a strong influence on the stability of latex as well as the morphology of composites. Al(OH)₃/PMMA core-shell nanocomposites were produced with stable latex emulsion when the weight ratio of Al(OH)₃ to MMA is below 20. With the ratio increased to as high as 30, however, the latexes became less stable with aggregation and the morphology changed to irregular spherical shape. When the polymerization was carried with styrene monomer, spherical and relatively uniform core-shell nanocomposite were produced at 9.1 % of the Al(OH)₃ w/w with respect to St monomer, while irregular larger composites were obtained at higher concentration of the Al(OH)₃. The dispersion polymerization in scCO₂ has been extensively studied since CO₂ was widely recognized as an interesting alternative to conventional organic solvent. The advantages of scCO₂ as a solvent include liquid-like density, low viscosity, high diffusivity, zero surface tension, fast mass-transfer and tunable solvent power. Moreover it is non-toxic, non-flammable, inexpensive, recyclable, and environmentally sound. It also offers advantages of easy separation of products and resolves problems related to solvent removal. In this paper, we report the preparation of silica/PMMA nanocomposites in scCO₂. The method involves the dispersion polymerization of MMA using PDMS-b-PMA as the surfactant in the presence of well dispersed silica nanoparticles which were surface functionalized with the silane coupling agent bearing a polymerizable group. The spherical SiO2/PMMA core-shell nanocomposite particles were successfully produced from the dispersion polymerization in scCO₂. The γ-MPS-functionalized SiO2 were first dispersed in the reaction medium, followed by the polymerization with MMA. The PDMS5k-b-PMA1k stabilizer could sterically stabilize the composite latex particles in scCO₂ to prevent a flocculation during the polymerization. The size of composite particles could be adjusted with varying the stabilizer concentration.