Sequence Controlled Ring-opening Copolymerization Of Lactide And Benzylglycolide

In recent years,polyester materials with biocompatibility and biodegradability have attracted more and more attention of polymer scientists.These materials are not only non-toxic and easy to degrade,but also have the advantages of renewable sources,safety and environmental protection in the preparation process.Therefore,they have been widely used in packaging materials,tableware containers,engineering films,clothing materials and biomedical fields.Traditional petroleum based polyolefin materials are often difficult to degrade and will easily cause white pollution.In contrast,biodegrable polyester materials are more in line with the concept of sustainable development of green chemistry.Therefore,it is of great significance to study biodegrable polyester materialsA large number of studies have shown that polymers exhibit a variety of properties due to the different sequence arrangements of monomers.It has been proved to be an effective method to adjust the properties of polymers by controlling the monomer sequence structure in the polymer chains.In the field of polyester synthesis,it has been reported to realize the syntheses of sequence controlled copolymers by regioselective ring opening homopolymerization of asymmetric cyclic ester monomers and by alternating copolymerization of two kinds of asymmetric cyclic ester monomers with a same type..However,the synthesis of AABB type sequence controlled copolymers by alternating ring-opening copolymerization of two different symmetric cyclic ester monomers has not been reported.In this thesis,sequence controlled ring-opening copolymerization of lactide and benzylglycolide was studied as the following three chapters.Chapter 1:Summarizing the research of sequence controlled copolyesters by ring opening polymerization.Chapter 2:Four metal complexes(Triphenol-Zr,BDI-Zn,Salan-Al and TMP-Zn)with high heterotacticity for ring-opening polymerization of racemic lactide(rac-LA)were synthesized and applied to initiate ring-opening polymerization of racemic benzylglycolide(rac-BG).The copolymers were characterized by GPC,NMR,MALDI-TOF,and DSC.The results show that the copolymer(M_n=12000 kg/mol,PDI=1.04)has the highest degree of alternation(95%)when triphenyl zirconium complex was used as initiator.The glass transition temperature(T_g)and thermal decomposition temperature(T_d,5%)of the copolymer are 46.8°C and 292.5°C,respectively.Chapter 3:Based on the second chapter,the ring-opening copolymerization experiments of rac-BG and rac-LA,L-BG and rac-LA,and L-BG and L-LA were carried out by using zinc complex TMP-Zn as an initiator.The results show that when TMP-Zn was used as initiator to catalyze the ring-opening copolymerization of enantiomeric pure BG and racemic LA,the synthesis of block copolymer can be achived well.