The Research Of Polymerization Initiated By Atmospheric Pressure Plasma

In recent years, the synthesis and application of the high water—absorbing acrylamide polymers have been given more and more attention. They are usually prepared by the solution polymerization method,the microemulsion polymerization method,the inverse emulsion polymerization method,the inverse suspension polymerization method and so on. However, in the preparation process of the polymers, these methods are inevitable to join the initiator,crosslinking agent and the other auxiliary agents, then the polymers contain impurities and the purity is not high, that cause the post-processing difficulty; at the same time, the use of the organic solvents in the polymerization easily causes environmental pollution.The atmospheric pressure plasma-initiated polymerization as a new polymerization method is proposed in this study to solve the defects of the traditional methods. The acrylamide monomer is actived by the atmospheric pressure plasma, and then initiates the polymerization to prapare the super-absorbent acrylamide polymers and the absorbent acrylamide-sodium acrylate copolymers. The effects of the discharge time,the discharge power,the temperature of the polymerization,the concentration of the monomer,the ratio of the monomer,the pH of the polymerization solution and the polymerization time on the conversion,molecular weight and absorption of the polymers have been discussed. The results show that the conversion rate of the polyacrylamide is 70%, the molecular weight of the polyacrylamide is 6.2×10⁶g/mol, the absorption of the polyacrylamide is up to 340g/g under the conditions of the discharge time is 90s, the discharge power is 50W, the temperature of the polymerization is 30℃, the concentration of the monomer is 30%, the polymerization time is 3d; the conversion rate of the acrylamide-sodium acrylate copolymer is 62%, the molecular weight of the acrylamide-sodium acrylate copolymer is 5×10⁶g/mol, the absorption of the acrylamide-sodium acrylate copolymer is up to 560g/g under the conditions of the discharge time is 90s, the discharge power is 50W, the temperature of the polymerization is 30℃, the concentration of the monomer is 30%, the ratio of the monomer is 1:1, the pH of the polymerization solution is 9, the polymerization time is 3d. In this method, the plasma is used as initiated energy and the polymerization needn't external initiator, so the products are pure and the polymerization is pollution-free; at the same time, the atmospheric pressure plasma-initiated polymerization needn't complex vacuum system, so the operating costs reduces greatly.The atmospheric pressure plasma polymerization is generally considered as a free radical mechanism, but some phenomenons in the polymerization process can not be explained by it, such as the generation of the ultra high molecular weight polymers, the high selectivity of the monomer, the strong solvent effect and so on. In order to analyze this unique polymerization mechanism, the study uses the infrared spectra to analyze the structural changes in the groups of the acrylamide monomer treated by the plasma, the nuclear magnetic resonance is used to determine the microstructure change of the active acrylamide.The results show that the C=C in the monomer molecules is fractured and the reactive free radicals are produced when the acrylamide is treated by the plasma; at the same time, the *NH free radical is produced when the H atom transfer from the NH₂ group to the CH₂ group. The chain initiation reaction, the chain growth reaction and the other chemical reaction of the polymerization can be advanved because of the existence of these radical.