The Synthesis Of Metal-Organic Frameworks And Their Catalytic Application In The Ring-Opening Polymerization Of L-Lactide

Metal-organic frameworks(MOFs)represent a new type of organic-inorganic hybrid materials developed quickly in recent years,which are composed of inorganic metal units and organic ligands.MOFs have high surface area,porosity,diverse topological structure and have broad application prospects in gas adsorption,drug transport,molecular sieve and other fields.In recent years,the application of MOFs in the field of catalysis has been developed quickly,the metal center and unsaturated coordination ligand can provide acid-basic active sites which could catalyze many types of organic reaction.Poly(lactic acid)has attracted many researchers due to their biodegradability,biocompatibility and bioabsorbability.The ring-opening polymerization of lactide monomer is the most common method for the synthesis of PLA with high molecular weight.Many homogeneous organometallic compounds and lewis acid systems can efficiently initiate the ring-opening polymerization of lactide but impurities remaining in the poly(lactic acid)may affect their quality and adversely affect their applications.In order to study the application of MOFs in the ring-opening polymerization of L-Lactide,we mainly discuss the synthesis of MOFs and their catalytic activities as heterogeneous catalysts in the ring-opening polymerization of LLactide.The main contents are as follows:ZIF-8,Zn/Co-ZIF and ZIF-67 with different metal center were synthesized by room temperature method firstly,their structure was characterized and analyzed by powder X-ray diffraction,scanning electron microscope and so on,then use them catalyze the ring-opening polymerization of L-Lactide.Under the same polymerization conditions,ZIF-67 shows the highest catalytic activity.Compared to 2-methylimidazolate(linker)as a catalyst under the same reaction condition,the poly(lactic acid)obtained with ZIF-67 has highly isotactic structure.In addition,the matrix assisted laser desorption ionization-time of flight(MALDI-TOF)mass spectrum indicates that the poly(lactic acid)obtained with ZIF-67 is almost linear structure.ZIF-67 can be reused for three times without significantly loss of catalytic activity.Secondly,in order to explore the differences in the catalytic activity of MOFs synthesized by different method,we synthesis ZIF-67 by solvothermal method and spray-drying method respectively.Their structure was characterized and analyzed by powder X-ray diffraction,scanning electron microscope and so on.Under the same polymerization conditions,the catalytic activity of ZIF-67 synthesized by spray-drying method is significantly higher than ZIF-67 synthesized by solvothermal method,the poly(lactic acid)product has highly isotactic structure.In addition,in the presence of L-lactic acid,the ZIF-67 synthesized by spray-drying method still has high catalytic activity but the structure of ZIF-67 was destroyed,the polymerization becomes to a homogeneous system.At last,ZIF-L-Zn and ZIF-L-Co were synthesized by room temperature method.Their structure was characterized and analyzed by powder X-ray diffraction,scanning electron microscope and so on.Under the same polymerization conditions,the catalytic activity of ZIF-L-Co is slight higher than ZIF-L-Zn and the poly(lactic acid)has highly isotactic structure.ZIF-L-Co can be reused for four times without significantly loss of catalytic activity.