Preparation Of Shape-controllable Fluoropolymer Materials Via Normal And Inverse Phase Miniemulsion Template Method

The fluoropolymers with the porous structure or the hollow microsphere have many excellent features,such as high specific surface area,light weight and strong adsorption capacity.These porous materials or hollow microspheres can be used in oil–water separation,tissue engineering,supports for catalysts,gas storage and separation,among others.The fluorinated materials exhibit high UV resistance,high weather resistance,anti-corrosion,aging resistance,hydrophobic and lipophobic properties owing to the presence of fluorine atoms.At present,various methodologies have been developed to prepare porous polymeric materials,for example,molding or casting techniques,physical or chemical gas foaming methodologies,phase separation of block-polymers,and high internal phase emulsion?HIPE?.Among them,HIPE template methodology by which porous polymers can be fabricated with controllable morphologies,well-defined porosities and high specific surface areas,is one of the most effective and facile strategies to create macroporous polymer materials.In this paper,a series of stable emulsion including water-in-CO₂?W/C?emulsion,multiple emulsion and water-in-oil emulsion?W/O?were obtained by adding a suitable co-emulsifier.Supercritical carbon dioxide?sc-CO₂?was selected because of its good compatibility with fluoromonomers and also it is non-toxic and environmentally-friendly solvent.Then a porous structure,hollow microsphere structure and fluorine-containing porous monolith with smaller diameter of pores??1?m?were obtained after polymerization.The main research content can be summarized as the following parts:?1?An amphiphilic polymer,poly?ethylene glycol?methyl ether-b-poly?trifluoroethyl methacrylate?(mPEG₄₅-b-P?TFEMA?_n)were prepared by reversible addition fragmentation chain transfer polymerization?RAFT?to stabilize W/C emulsion,in which TFEMA was used as the segment of CO₂-philic,and mPEG₄₅ as the hydrophilic segment.Firstly,RAFT agent S-1-Dodecyl-S?-??,??-dimethyl-???-acetic acid?trithiocarbonate?DDMAT?and macro-chain transfer agent(mPEG₄₅-DDMAT)was synthesized.Then the block polymer mPEG₄₅-b-P?TFEMA?_n with different lengths of fluoro-segment was prepared with different raw ratios.It was verified that the chemical structures of both the RAFT agent and the macromolecular chain transfer agent were correct.In addition,the block polymer mPEG₄₅-b-P?TFEMA?_n was used as an emulsifier because it possessed the characteristics of emulsifier.?2?The choice of a suitable surfactant is key to the formation of stable water-in-CO₂?W/C?or CO₂-in-water?C/W?emulsion.It is even more critical in stabilization of the emulsion containing carbon dioxide?CO₂?.In this section,a stable W/C emulsion was successfully prepared by using the fluorine-containing amphiphilic block polymer mPEG₄₅-b-P?TFEMA?_n as an emulsifier which was obtained from RAFT,as discussed previously.In case of W/C emulsion,CO₂ and TFEMA were acted as the continuous phase and water as the internal phase.It has been found that in the length of the block polymer mPEG₄₅-b-P?TFEMA?_n,fluorine-containing chain end had a significant effect on the morphology of the polymer and the type of emulsion formed.The morphology of the polymer was observed by scanning electron microscopy which confirmed the type of emulsion formed.With the fluorine-containing end segment,the morphology of the polymer changed from a small hollow sphere in the large hollow sphere to a hollow spherical to a porous structure.Correspondingly,it was be concluded that the type of emulsion could went through the process from water-in-CO₂-in-water-in-CO₂?W/C/W/C?emulsion to water-in-CO₂-in-water?W/C/W?emulsion to water-in-CO₂?W/C?emulsion.Also,suitable co-surfactants were identified in this study.Investigations were also attempted to check the effect of the amount of surfactant,cross-linker and water/CO₂ ratio on the type of emulsion formed as well as the morphology of the resultant polymer.?3?A single type of W/C emulsion was not formed as expected via using sc-CO₂ as a medium.On the contrary,various types of emulsions were formed.After a suitable co-emulsifier was selected to assist stabilizing the emulsion,the pore diameter of the fluorinated emulsion was further reduced and the resulting porous material having a good morphology compare to the porous monolith made by W/C emulsion.At present,it is very difficult to have a small pore size?<5?m?with a high internal phase emulsion or a high viscosity emulsion.In this part,fluoroporous foams with a pore diameter of about 1?m have been obtained via addition of suitable co-emulsifiers.