Synthesis Of Salen Complexes And The Studies Of Their Catalytic Properties In Copolymerization Of Carbon Dioxide And Propylene Oxide

Carbon dioxide is one of the main gases causing the greenhouse effect and is considered a safe, non-toxic and abundant Cl resource. The cycloaddition reaction from carbon dioxide and epoxides to prepare aliphatic polycarbonate has attracted extensive attention. The polycarbonate has wide application prospect due to its biodegradability and the carbon dioxide fixation.In this paper, a series of Salen ligands were synthesized, and characterized by FT-IR, MS,'H-NMR and EA. The structure of Salen complexes from Salen ligands and Fe, Co, Mn, Al were characterized using FT-IR, EA,'H-NMR and UV-Vis. It is first reported the crystal structure of salen Fe?Cl complex. The crystal structure shows that this kind of complexes was the hexa-coordinate. Their configuration was octahedral structure.With tetrabutylammonium bromide as cocatalyst, this paper investigated catalytic properties of SalenFe, SalenCo, SalenMn, SalenAl in copolymerization of carbon dioxide and propylene oxide. Among them, the catalysate of SalenFe, SalenMn were cyclic carbonates, while the catalysate of SalenCo, SalenAl were polycarbonates and the SalenCo complexes exhibited higher catalytic activity. The influence factors were studied in detail, such as reaction temperature, pressure, time and the Molar Ratios of PO/catalyst. When reaction temperature was under 50?, the yield of polymers increases with the increase of polymerization temperature; When the temperature above 50?, the yield began to decrease; When the temperature reached 80?, the product were mainly cyclic carbonates. With the increase of CO2 pressure, polymer production increases; When CO2 pressure was more than 3 MPa, the polymer production began to decline. The increase of time is beneficial to the increase of propylene oxide conversion rate, the yield was almost not increased with prolonging the time to 15 h later. When the catalyst concentration increased, catalytic activity increases, the yield of polymers firstly increased and then decreases.; When the amount of catalyst increased to a certain extent, but go against polymerization, easy to generate cyclic carbonates. Under the optimal conditions, the polycarbonte selectivity was up to nearly 100%, the head-to-tail structrue in the polycarbonte reached 81%, the number average molecular weight was 1.82 × 104 g/mol and the initial decomposition temperature of PPC was 181.7?.