Zinc-based Catalysts And Their Catalytic Properties For The Ring-opening Polymerization Of Lactones

Aliphatic polyester materials represented by polycaprolactone are a class of very important biodegradable resin materials.They have good mechanical properties,hydrolysis and biocompatibility,and are considered to be a promising replacement of petrochemicals.Great progress has been made in the fields of synthesis,manufacturing and processing.And due to their degradable properties,aliphatic polyester materials are also a research hotspot in the biomedical field.With the continuous development of bio-energy and chemical products,there will be more process and industrial enterprises of cyclic ester compounds in the future.The key to convert these cyclic esters into synthetic resin materials is how to obtain a highly efficient catalyst that can regulate the ring-opening polymerization process.Metal complexes have been focused for the ring-opening polymerization of cyclic esters due to the diversities of metal species and coordination forms.Metal zinc is nontoxic to humans,so the resulting polyesters produced by zinc complexes have good environmental compatibility and potential medical value.In recent years,more and more researchers have begun to study the synthesis of different ligands for zinc complexes to obtain higher activity and controllable molecular weights for the ring-opening polymerization of cyclic esters.This thesis is divided into the following three parts:The first part introduces the current overview of aliphatic polyesters and the main catalytic systems of the ring-opening polymerization of lactones.The metal catalytic system is developed to classify the ring-opening polymerization of lactone monomers by zinc complexes.In the second part,two types of zinc catalysts were synthesized,containing a 2,6-bisamino-phenol or a 2,6-bisimino-phenol ligands.The structures of ligands and their zinc complexes were characterized by FT-IR,1H NMR,13C NMR and elemental analysis.These two types of zinc catalysts exhibit distinct catalytic activities in the ring-opening polymerization of lactones.The experimental results showed that the reduced zinc complexes 5-8 containing 2,6-bisamino-phenol ligands have high activity for the ring-opening polymerization of ?-caprolactone and 8-valerolactone.And zinc complex 8 containing a large sterically hindered substituents has the weakest activity.However,zinc complexes 1-4 bearing 2,6-bisimino-phenol ligands were substantially inactive in the ring-opening polymerization of lactones.In the third part,zinc complex 5 was used to study the ring-opening copolymerization of ?-caprolactone and ?-valerolactone on the basis of homopolymerization.The composition of the copolymers obtained by varying feed ratio of two monomers was investigated.Block or random copolymers were prepared by different feed mode(one-batch or sequential).The molecular weights,molecular weight distribution,structure and thermal properties of copolymers were characterized by GPC,1H NMR,13C NMR,and DSC.It was found that the copolymers obtained by premixing the two monomers are random copolymers.In the random copolymers system,the thermal properties of the obtained copolymerized product vary with the addition of the components.When the ratio of ?-caprolactone to ?-valerolactone is 1:1,the obtained copolymer has the lowest melting point.The polymerization carried by sequential addition of different monomers resulted in block copolymers,DSC analysis showed that block copolymers have better thermal properties than random copolymers with similar composition.