Development And Application Of Metal Catalytic Systems For The Polyester Materials

The traditional petroleum-derived plastics are difficult to degrade,which has caused long-term environmental pollution problems,the development of degradable materials can reduce the dependence on traditional plastics,and the polyester material is a relatively mature biodegradable material and has been applied in many fields.Polylactide is a kind of polyester material that has been successfully commercialized,it is produced by ring-opening polymerization of lactide in the process of industrialization,and has become an ideal degradable material due to green source and excellent performance.CO2-based polycarbonate obtained by the copolymerization of epoxide and carbon dioxide has also received extensive attention in the field of environment-friendly materials,the copolymerization of epoxide and cyclic anhydride is an effective way to prepare polyesters with diverse structures.Over years of research and development,the theories and methods of synthesizing these materials have become completed.However,the development and application of catalytic system,one of its core research directions,still has very high research value,through the development of catalytic system,it is expected to reduce the cost of existing process technology,develop new synthetic methods,and finally obtain block polymers with new structure and properties.In this contribution,we have carried out a series of new attempts in the development and application of new catalytic initiation mechanisms and efficient catalytic systems.Considering the requirement for high activity and selectivity of the catalytic system for the copolymerization of epoxide and carbon dioxide,based on the structural design of the catalyst,we designed a novel trinuclear Salen-Co catalyst system,and this catalytic system applies the intramolecular conjugation properties of trinuclear SalenCo complex,the electrophilicity of the metal center is improved by the synergism of the intramolecular metal center,and which improve the catalytic performance of the trinuclear complex,this improvement makes the catalytic system show higher catalytic activity and selectivity,and it can efficiently catalyze the copolymerization of propylene oxide and carbon dioxide in the absence of a nucleophilic cocatalyst.With the absence of cocatalyst,this catalyst can efficiently catalyze copolymerization,and a small amount of water in the system can significantly improve the catalytic activity,even in the presence of approximately 100 catalyst equivalents of water,copolymerization can still maintain activity to produce polymers,and it can catalyze the ternary copolymerization of propylene oxide,carbon dioxide and lactide in one pot to obtain copolymers.Using the effect of this structure on the catalytic performance of the central metal,the catalytic performance of trinuclear Salen-Al complex in the copolymerization of epoxide and cyclic anhydride was studied.In this Salen-Al catalytic system,the special structure of the complex also plays an envisaged role,highly efficient catalytic copolymerization can be achieved in the absence of nucleophilic cocatalysts through intramolecular synergy of complex,the alkoxy initiation mechanism in the copolymerization process is clarified due to the absence of the cocatalyst,under the guidance of this mechanism,the direct initiation of epoxide and cyclic anhydride copolymerization by hydroxyl compounds can be realized.Using this mechanism,triblock or tetrablock copolymers can be easily synthesized,it can provide a new option for the synthesis of multiblock copolymers.In the industrialization of polylactide,the catalytic system for ring-opening polymerization of lactide is required to be inexpensive,stable and low toxic.Based on the ring-opening polymerization mechanism of lactide,which has been widely studied,the catalytic system needs to have a metal-alkoxy structure as the initiator group,however,this kind of structure is sensitive to impurities such as water and oxygen,which increases the difficulty of practical application of a large number of catalytic systems,In order to solve the problems in this practical engineering application,we applied the epoxide in-situ initiation strategy to introduce inexpensive,stable and lowtoxic metal salts into the catalytic system for ring-opening polymerization of lactide.Commercialized metal salts can be used to catalyze bulk polymerization with high activity under the in-situ initiation of epoxide to obtain polylactide materials with high molecular weight.In the bulk polymerization of lactide(LA),FeCl3 showed remarkable activity.Under 0.02%loading,FeCl3 can catalyze LA polymerization with 98%monomer conversion to produce polylactide(PLA)with an Mn value of 142 kg mol-1.In general,the residual lactic acid in LA is difcult to remove and affects the molecular weight of PLA.However,using the strategy of in situ initiation of epoxides,even with the loading of 5%lactic acid,FeCl3 can still catalyze polymerization to produce PLA,while in the presence of 500 ppm lactic acid,FeCl3 can catalyze polymerization to produce the PLA with an Mn value of 80.8 kg mol-1.This strategy was also suitable to the commercial catalyst Sn(Oct)2 for LA polymerization.In the presence of epoxides,Sn(Oct)2 can catalyze the polymerization even with 200 ppm loading of lactic acid,with 0.03%Sn(Oct)2,as high as 99%of LA was converted,and the polymer showed a molar mass of 125 kgmol-1.The application of this research result is expected to reduce the requirements for the purity of lactide in engineering applications,thereby simplifying the purification process of lactide and reducing production costs.Through the research of this contribution,we hope to provide new strategies and ways for the development and application of the catalytic system for the synthesis of degradable polyester materials and the utilization of carbon dioxide and lay a foundation for further engineering applications.