Synergistic Binary Catalytic Systems For Ring-opening Polymerization And Mechanism Studies Of P-dioxane's Derivatives And NCAs

The use of plastics has brought great convenience to our life,but the random disposal of non degradable plastics has an irreparable impact on the environment.Therefore,the preparation of degradable polymer materials is one of the most effective methods to solve the problems of resource waste and environmental pollution.Among many degradable polymer materials,aliphatic polyester is widely used in biomedicine,agriculture,packaging and other fields because of its good degradability and biocompatibility.At present,the step polycondensation of diols and diacids and the ring-opening polymerization of cyclolactones are the two most commonly used chemical synthesis methods for the preparation of aliphatic polyesters.In contrast,ring opening polymerization has the advantages of good atomic economy(no small molecular by-products),and polymers with high molecular weight and narrow molecular weight distribution can be obtained under mild conditions.Controlled polymerization can even be realized by using appropriate catalytic system.In recent years,organic catalysts and binary synergistic catalytic systems have performed well in ring opening polymerization of cyclolactones,especially organic base/urea and Lewis pairs systems.Therefore,we focus on three important cyclic monomers and use organic base,organic base/urea and Lewis pairs to study the three systems.The main contents include the following aspects:1.We prepared a derivative of p-dioxanone----3-methyl-1,4-dioxo-2-one(MDO).Due to the low ring tension of the six membered ring monomer MDO,it is still a challenge to realize the effective and controllable ring-opening polymerization(ROP)of MDO monomer.We used different organic base/urea as catalysts to achieve ROP of MDO at relatively low temperature.Compared with the previously reported catalysts,1,8-diazabicyclo[5.4.0]dodecyl-7-ene(DBU)/urea showed higher catalytic activity in ROP of MDO and better control of molecular weight and molecular weight distribution;The kinetics of the system was tested;The obtained PMDO was characterized in detail;More importantly,PMDO can be completely depolymerized and recycled into monomer MDO by simple thermal degradation,which establishes a closed cycle process and provides a new strategy for the chemical recovery of degradable polyester.2.The ring-opening polymerization of seven membered ring 1,5-dioxane-2-one(DXO)produced industrially can form degradable polyether esters with completely alternating ether and ester bonds.Although a variety of catalysts have been used for ring opening polymerization of seven membered ring DXO,they are faced with problems such as long polymerization time,high polymerization temperature and uncontrollable polymerization.Therefore,it is a challenge to realize efficient and controllable ring opening polymerization of monomer DXO under mild conditions.Using different organic bases and diethylzinc(Zn Et₂)as Lewis pair catalytic system,we studied the ROP of DXO at room temperature.Compared with the previously reported catalysts,DMAP/Zn Et₂ can achieve complete monomer conversion within 2 h,and can prepare higher molecular weight PDXO with better control of molecular weight and molecular weight distribution;The dynamics of each system was tested;The PDXO samples were characterized in structure and tested in thermodynamics.3.The ring-opening polymerization(ROP)of N-carboxyanhydrides(NCA)can produce a large number of peptides.So far,different initiation/catalyst systems and polymerization conditions have been used to realize the rapid and controllable polymerization of NCAs.However,low nucleophilic initiators(alcohol(-OH)and carboxylic acid(-COOH))will lead to slow polymerization rate and uncontrolled molecular weight and distribution.Therefore,we used catalyst 1,1,3,3-tetramethylguanidine(TMG)to improve the nucleophilicity of initiator to realize the effective and rapid polymerization of benzyl glutamate-n-carboxylic anhydride(blg-nca),and prepared peptides with low distribution;The reason why TMG can significantly improve the initiation and chain growth rate is explained;At the same time,alcohol,carboxylic acid and PEG(PEG-OH,PEG-COOH)were used as initiators to initiate polymerization to form copolypeptides;The catalyst significantly expands the types of initiators,simplifies the ROP of NCA,and expands the potential application of synthetic peptides in many fields.