Organic Acid-base Pair Catalytic Epoxy/Acid Anhydride Alternating Copolymerization To Prepare Degradable Polyester

Polyesters are one of the most attractive polymeric materials.owing to their different carbon chain framework and great physical properties.They are produced at a magnitude of hundreds of million tons every year in the worldwide and and have been extensively studied and applied in fibers,soft drink bottles,food packagings and biomedical devices etc Step-growth polymerization of diacids or diesters with diols is the most frequently used to synthesize polyesters due to the large amounts of available monomers and tailored resultant polyester structures and properties both in academia and industry.However,this method has several drawbacks,including the nessary of high temperature and long reaction temperature and vacuum condition to remove byproducts and the difficulty in controlling molecular weight and polymer structure due to side-reaction.Meanwhile the ratio of monomers must be strictly controlled,and the polymerization process is cumbersome and energy consumption is high.In contrast to step-growth polymerization,the ring-opening alternating copolymerization(ROAP)of epoxides and cycle anhydrides to synthesize polyesters is more controllable and engery-saving.This method obtain polyester compounds with rich structuresthrough adjusting the structure of epoxides and cyclic anhydrides which provides more possibilities for synthesizing polyester materials with different properties.Moreover the reaction is atom-economic and have good chemoselectivity and can realize"living/controlled"polymerization.This paper focuses on the alternating copolymerization of epoxides and cyclic anhydrides catalyzed by organocatalysts,and discusses the effects of the catalytic system on the ROAP of epoxide and cyclicanhydride.The contents are as follows:1.The ROAP of epoxides and and cyclic anhydrides were carried out with alcohols as initiators using cyclic trimeric phosphazene base(CTPB)/urea binary catalyst system.The study found that the use of CTPB/urea binary catalyst system can obtained polyesters with well-defined alternating structures without forming polyether homopolymers even if the polymerization time was extended.The well-defined alternating structures of polymers were characterized with ¹H NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy(MALDI-TOF MS)using different alcohols as initiators.The molecular weights of polymer linearly increased while remaining a relative low dispersities with the increasing feed molar ratio(from 2.5 k Da to 6.4 k Da).These results indicated a good control of ROAP over the molecular weights This binary catalyst system can catalyzed the ROAP of different epoxides(propylene oxide(PO),epichlorohydrin(ECH))and PA and obtained different polyesters(P(PA-alt-PO)and P(PA-alt-ECH))with well-defined alternating structures.2.organic bases(DMAP,DBU,TDB,t-Bu P₁)and protic acids(MSA,DPP)were uesd to catalyzed the ROAP of epoxides and cyclic anhydrides The study found that the acid-base pair catalyst can realize the ROAPof PA/CHO and have high catalytic activity.By comparing the catalytic activity of different the acid-base pairs,it is found that DMAP/DPP is the optimal catalyst,TOF=574 h^-1.P(PA-alt-PO)was prepared with well-defined alternating structure using DMAP/DPP,but the transesterification side reaction was occurred when the reaction time was extended.