Fabrication Of Interconnecting Porous Polymer Materials Templated By High Internal Phase Emulsions And Double Emulsions

High internal phase emulsions (HIPEs) with the internal phase volume fraction higher than74%, are good templates to make interconnecting meso-macro porous monolithic polymeric materials known as polyHIPEs which are attracting much interest as a result of their application in scaffolds for tissue engineering and3D cell culture, supports for catalysts, water purification, etc. Although many factors affecting the size of windows (interconnecting pores) have been reported, the formation mechanism of the open-cell structure has rarely been reported. To prepare stable emulsions, the continuous phase and the water phase must be immisible. Monomers with intermediate hydrophilicity such as methyl methacrylate (MMA) and glycidyl methacrylate (GMA) are difficult to prepare stable HIPEs due to the slight miscibility of the two phases. Until now, there are few reports on the preparation of PMMA PolyHIPEs via MMA HIPE templates, or PGMA polyHIPEs via GMA HIPE templates. PolyHIPEs are usually prepared as monolithic blocks by polymerizing the continuous phase of HIPEs, whose shapes are predetermined by the reaction vessel (or molds). In many applications, large monoliths are not convenient as particles, however, the reported methods used to prepare polyHIPEs particles have some problems. The main work in this thesis is to solve the problems mentioned above in preparing polyHIPEs, which is summarized as follows:1. Study of the formation mechanism of the open-cell structure in polyHIPEs:The effects of unpolymerizable Span80and a polymerizable surfactant12-acryl-oxy-9-octadecenoic acid (AOA) as well as their amount and ratio, the weight fraction of water and the content of cross-linker on the structure of polyHIPEs were investigated. It is found that the phase separation between surfactants and polymer during the polymerization of HIPEs also plays an important role in the formation of open-cell structure of polyHIPEs like volume shrinkage. Using unpolymerizable Span80as the surfactant, P(St-DVB) polyHIPEs with interconnecting porous structure were fabricated. However, when the polymerizable surfactant AOA was used to restrict phase separation, a closed-cell structure of P(St-DVB) polyHIPEs was obtained accompanying with the volume shrinkage of the polyHIPE monoliths. This suggests that the enrichment of unpolymerizable Span80at contact point of water droplets caused by the decreasing compatibility between Span80and polymer during polymerization leads to the formation of open-cell structure of polyHIPEs stabilized by Span80. On the other hand, the copolymerization of the polymerizable AOA with monomers restricts phase separation, so that water droplets were embraced by polymer films, resulting in the formation of closed-cell structure.2. The synthesis of P(MMA-DVB) polyHIPEs:Using long chain compounds as costabilizers, interconnecting porous P(MMA-DVB) polyHIPEs with uniform microstructure were prepared with Span80as the surfactant. The addition of hexadecane was found to be able to decrease the solubility of MMA in water, promoting the stability of MMA HIPEs. The use of hydroxyl terminated polybutadiene (HTPB) was found to increase the viscosity of both oil phase and the prepared MMA HIPEs. Besides, HTPB was found to be able to stabilize inverse emulsions solely, suggesting that HTPB can act as a polymer surfactant in stabilizing MMA HIPEs. The as-prepared P(MMA-DVB) porous monoliths based on HIPEs templates were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and N2sorption analysis, which showed the formation of highly interconnecting pores.3. The synthesis of P(GMA-St-DVB) polyHIPEs:P(GMA-St-DVB) polyHIPEs were prepared using Span80as the surfactant and hexadecane as the costabilizer. The effects of the content of GMA, the weight fraction of water, the content of cross-linker and the addition of porogen on the structure of polyHIPEs were investigated. It was found that the use of50wt%GMA based on monomers led to the formation of closed-cell polyHIPEs, while the content of GMA was decreased to25wt%, open-cell polyHIPEs were obtained, but changing to closed-cell structure again by decreasing the water contents of HIPEs. By increasing the amount of crosslinkers and adding porogen to the oil phase, P(GMA-St-DVB) polyHIPEs with high surface areas (-300m2/g) were prepared. Using P(GMA-St-DVB) polyHIPEs powders as adsorbent in cigarettes, the phenol was reduced by61.3%compared with the blank sample.4. One-step preparation of high internal water phase double emulsions stabilized by a single small-molecular surfactant via catastrophic phase inversion:High internal water phase double emulsions [(W/O HIPE)/W] were prepared via catastrophic phase inversion of water-in-oil high internal phase emulsions (W/O HIPEs) stabilized solely by12-acryloxy-9-octadecenoic acid (AOA) through increasing the content of water phase. It is worth mentioning that this is the first time to use a single small-molecular surfactant to stabilize double emulsions. Using optical microscopy and conductivity monitoring, the effects of the concentrations of surfactant and salts, pH value, oil polarity, addition interval and stirring rate on the formation and the stability of double emulsions as well as the inversion point (IP) have been investigated. Finally, by y-ray initiated polymerization of the as-prepared double emulsions composed of styrene, or n-butyl acrylate, or methyl methacrylate, porous polymer microspheres (also called polyHIPE microspheres) were fabricated with high interconnection which have been confirmed by scanning electron microscopy (SEM).5. The preparation and application of polyHIPEs microspheres:By pouring distilled water into the oil phase containing AOA instead of the above adding dropwise manner, double emulsions formed at a lower content of water via catastrophic phase inversion. The size of W/O droplets was decreased by increasing the stirring rate or lowering the content of AOA. The polymerization of the as-prepared double emulsions by y ray resulted in the formation of interconnected porous microspheres, however, that by chemical initiators to obtain microspheres with closed-cell structure. The as-prepared open-cell polyHIPEs microspheres were applied in the absorption of metallic ions and carriers of catalyst after hydrolysis.