| Carbon dioxide is an abundant and cheap C1feedstock, the introduction ofcarbon dioxide into polymers through chemical fixation is an effective way from theviewpoints of both resource utilization and environmental protection. Thecopolymerization of CO2with2-methylaziridine will produce poly(urethane-amine)sconsisting of both urethane and amine units in the polymer chain. Aqueous solutionof the copolymer shows an excellent dual stimuli-responsive behavior to bothtemperature and pH value. The aqueous solution of the copolymer shows a phasetransition behavior owing to the hydrophobic nature of the urethane linkages and thehydrophilic nature of the amine linkages. Thus the lower critical solutiontemperature (LCST) of the aqueous solution of the copolymer could be adjusted byvarifying the urethane content in the compolymers.The copolymerization of CO2with2-methylaziridine would provide acopolymer with a low yield and a less urethane content if a proper catalyst is notprovided. Thus, an efficient catalyst is highly desired. In this thesis, a class ofcatalysts is investigated by the combination of imidazolium-based ionic liquids andLewis acidic salts, such as MnCl2, FeCl3, etc. Results indicated that the catalyticactivity was largely varied with different combinations of Lewis acidic salts, ionicliquids and their molar ratios. The combination of BmimHSO4with MnCl2wasfound to show a good catalytic activity with the highest polymer yield obtained. Theoptimal polymerization conditions were found with the reaction temperature of80oC,10.5MPa of CO2pressure and1.0mol%of catalyst for12h reaction time,under which poly(urethane-amine) was obtained in71.9%yield with48.6%urethane content.The thermo-/pH-responsive measurement suggested that the LCST of thecopolymer decreased with the increase in the concentration of its aqueous solution.The LCST varied in a broad range of78-20oC when the pH value adjusted from9.5to12.6. |
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