Synthesis Of Poly （Vinyl Acetate） Hydrocarbon-based CO₂-philic Polymers And Their Applications

With the development of industry, plenty of fossil fuel and organic solvent are widely used, which lead to the pollution of air, soil and water greatly. It is one of effective ways to decrease the environment pollution by developing green chemistry. Supercritical carbon dioxide (sc-CO2) or condense carbon dioxide (L-CO2) is known as green solvent, which is non-toxic, non-flammable, non-pollution, natural and stable. CO2has been widely used in polymeric foams, small organic molecules extraction et al. However, SC-CO2or L-CO2has so weak solvent power that most of polar materials are difficult to dissolve in it, and this unfavorable factor can be overvcome with the help of CO2-philic polymer. Fluorinated or silicone-based polymers show good solubility, and have been widely used to prepare CO2-in-water (C/W) or water-in-CO2(W/C) emulsion or microemulsion, or as stabilizers in dispersion polymerization. However, the high cost of these materials may prohibit their use on an industrial scale, and fluoropolymers tend to have poor environmental degradability, and this could negate the environmental advantages associated with the use of CO2. The lack of inexpensive CO2-soluble polymers and surfactants is a significant barrier to the future implementation of this solvent technology. By comparing the cloud point pressures of plenty of hydrocarbon-based polymers, oligo(vinyl acetate)(OVAc) exhibited anomalously high solubility in CO2, and can be used as latent CO2-philic materials to be widely used in industrial scale. PVAc-based materials have been used in emulsion preparation and dispersion polymerization. Till present, the knowledge about the nature of OVAc-based homopolymers, or copolymers as well as applications still need further study. The main contents of the thesis are listed as follows:Firstly, a novel bifunctional xanthate bis[2-(2-(O-ethyl dithiocarbonate) propionate ethoxy)-4,4’-dicarbonyl-2,2’-bipyridine](X-bpy-X) was synthesized to control vinyl acetate (VAc) polymerization as a RAFT/MADIX agent, and then the bpy moiety was introduced into the OVAc chain successfully. A series of oligo (vinyl acetate)-bipyridine-oligo(vinyl acetate)(OVAc-bpy) with PDI of1.5and molecular weight range of1000-3500were obtained. The phase behaviour of OVAc-bpy in supercritical carbon dioxide (SC-CO2) was determined by cloud point method. Compared with OVAc homopolymers with similar degree of polymerization (DP), OVAc-bpy has lower solubility due to the existence of bpy moieties. The lowest cloud point pressure was achieved in SC-CO2at Mn,GPC=1900. OVAc-bpy was used as ligand to extract the metal ions by using SC-CO2as solvent. The extraction rate can be as high as98%(for Ni2+) and reasonably good for other metal ions (Cu2+and Co2+) without using any additive.Secondly, a new difunctional RAFT agent, including the structure of xanthate group and2-bromopropionyl group was synthesized. The xanthate group can be used as chain transfer agent (CTA) to control the polymerization of VAc, and the2-bromopropionyl group can be as initiator by ATRP to initiate the polymerization of2-(dimethylamino) ethyl methacrylate (DMAEMA). A new amphiphilic cation surfactant OVAc-b-PDMAEMA was obtained, which can emulsify CO2/H2O system, and get high internal phase emulsion (the dispersion phase volume fraction occupying more than80%v/v of the emulsion volume). The emulsion can keep stable more than12h. The hydrophilic ability of the surfactant can be greatly affected by many factors including ionic strength, pH of solution, the ratio of hydrophilic/CO2-philic chain length and so on, which also affect the emulsifying capacity of surfactants. When polymerizing of the continuous phase of C/W (40%w/v, AM solution) emulsion, the PAM-based highly porous emulsion-tempalted materials was obtained with tunable size and interconnected pores size, and the average size was in10-25μm.Thirdly, if using sodium p-styrenesulfonate (SSNa) as the second monomer, PVAc-Br as the macromolecular-initiator, a new amphiphilic anion surfanctant PVAc-b-PSSNa was prepared. PVAc-b-PSSNa not only can emulsify AM solution (40%, w/v), but can emulsify30%(w/v)2-acrylamide-2-methylpropanesulfonic sodium (AMPS) solution completely whose ionic strength gets to1.16mol/L, and keep stable for2.5h. The corresponding monolisthic materials can be obtained by polymerizing the emulsion.