Synthesis Of CO₂-based Polycarbonate Block Terpolymers And Study On Their Stereocomplexation

The copolymerization reaction of epoxy alkanes and carbon dioxide developed forty years.Through the reasonable design of catalyst,many problems of the reaction are being solved one by one.But the synthesis of block copolymer still exist problems such as difficult to purification.Therefore preparation of the diblock and multiblock of unimodal distribution has been the research hotspot and difficulty in this field.Furthermore,the stereocomplex of block copolymers has not been researched.This thesis focuses on the synthesis of stereoregular CO₂-based polycarbonate block terpolymers from the immortal stepwise asymmetric copolymerization of CO₂ and different meso-epoxides in the presence of enol chain transfer,mediated by robust catalyst systems consisting of biphenol-linker bimetallic Co?III?complex in conjunction with an ionic cocatalyst,PPNX?PPN=bis?triphenylphosphine?iminium,X=2,4-dinitrophenoxide?.Various polycarbonate block terpolymers were obtained in perfectly unimodal distribution and narrow polydispersity.The structures were characterized by GPC,DSC and NMR.They all possess only one broad glass transition temperature between the T_g of their constituents,which could be adjusted by altering the composition of different polycarbonate segments.Various stereocomplexed block polymers were formed by mixing isotactic and block and parent polycarbonates with different configurations.In the process,a general rule is showed,each segment maintains its own character to form stereocomplex without any effect on other segments.Block polymers transformed from amorphous to crystalline with the formation of stereocomplex.When crystalline stereocomplexed of one segment in block polymer was formed,the T_g of block polymer increased because crystalline segment restrains movement of amorphous segment.In this thesis,the T_g of?R?-PCBC-b-PCPC increased from 70 ^oC to 73 ^oC after formed stereocomplex with?S?-PCPC.