Copolymerization Of2-Methylaziridine With ScCO₂Catalyzed By Salen Metal Complexes

CO2is a kind of abundant and cheap natural resource. Using CO2as raw materials to synthetise polymeric compounds or organics is an effective way to control the environmental pollution and alleviate the pressure of the shortage of resources. The copolymerization of CO2and2-methylaziridine under supercritical conditions provided a kind of aliphatic copolymer containing urethane and amine units, and it showed phase transition phenomena in response to both temperature and pH stimulus. Due to the low reactivity of carbon dioxide, the design of highly active catalysts is very important for the carbon dioxide involved copolymerization.2-Methylaziridine and some different salen metal complexes were synthesized successfully. In the condition of100℃,10MPa,24h, the copolymerization of carbon dioxide and2-methylaziridine catalyzed by these salen metal complexes provided a series of copolymers which molecular weights and urethane contents were different. The experiment results showed that the catalysts were efficient, the urethane contents of the copolymer was increased. When changing the centric metal (Mn, Co, Cu, Zn, Fe) of the salen metal complexes and the structure of the salen ligands, the efficiency of the catalysts was different. When the salen ligand was (R,R)-N,N’-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, the experiment result was best. The LCST value of the poly(urethane-amine)s which catalyzed by (salen)MnCl decreased to38℃, and its weight-average molecular weights was1.35×104.In order to understand the phase transition behaviors of the copolymers, we researched the thermo-responsive and pH-responsive property of the copolymers. The results indicated that the LCST values of the aqueous solution of the copolymers were decrease with the increase of their concentration and pH values of the solution. Therefore the LCST value of the copolymer can be regulated by changing the pH value of the solution in a wide range. In additon, the LCST values of the copolymers were also influenced by their molecular weights and urethane contents. The structures of all copolymers and compounds were characterized by FT-IR,1H NMR, EA. The molecular weights of copolymers were determined by multi-angle laser light scattering (MALLS). The thermal decomposition temperatures of copolymers were characterized by thermogravimetry (TG).