Synthesis Of Poly(ether Ester)s Alternative Multiblock Copolymers Via PROP And Study On Their Properties

Multiblock copolymers(mBCPs)have attracted lots of scientific interests for decades owing to their fascinating microphase-separated morphologies,the associated physical properties,and a growing list of realized and potential applications.The present work is mainly focused on the design and synthesis of well-defined poly(ether ester)alternative multiblock copolymers via polycondensation-coupling ring-opening polymerization(PROP)of cyclic oligomers and dihydroxy-terminated polyethers.Content of the work is summarized as follows:(1)Synthesis,characterization,and kenetics study of poly(ethylene terephthalate)-block-poly(tetramethylene oxide)alternative multiblock copolymers(PET-b-PTMO-b-PET)x.Cyclic oligo(ethylene terephthalate)s(COETs)were synthesized under pseudo-high dilution conditions,and used as monomer to synthesize(PET-b-PTMO-b-PET)x alternative multiblock copolymers via one pot melt polymerization with dihydroxy-terminated PTMO as macroinitiator.The chemical structure of(PET-b-PTMO-b-PET)x was characterized by one-dimensional nuclear magnetic resonance(1H NMR),two-dimensional nuclear magnetic resonance(gCOSY and HSQC),gel permeation chromatography(GPC)and viscometry.The reaction kenetics was revealed that this polymerization has two steps:1)ring-opening polymerization of COETs by PTMO macroinitiator to yield PET-b-PTMO-b-PET triblock.copolymers;2)in situ cascade condensation polymerization of triblock copolymers to form(PET-b-PTMO-b-PET)x,alternative multiblock copolymers.(2)Properties(thermal properties and mechanical properties)and phase separation behavior of(PET-b-PTMO-b-PET)x.The thermal properties of(PET-b-PTMO-b-PET)x were studied by thermal gravimetric analysis(TGA)and differential scanning calorimetry(DSC),respectively.The results indicated that its thermal stability is higher than PTMO homopolymers,and(PET-b-PTMO-b-PET)x multiblock copolymer is double-crystalline.The microphase separation behavior of(PET-b-PTMO-b-PET)x was characterized by small angle X-ray scattering(SAXS)and transmission electron microscopy(TEM).The results showed that molecular weights and content of hard/soft segments,block number of multiblock copolymers play important role in the behavior of phase separation.The mechanical properties of(PET-b-PTMO-b-PET)x were characterized,where the influences of composition of hard/soft segments,molecular weight of soft segment,block number,etc,on the mechanical properties of(PET-b-PTMO-b-PET)x were discussed in detail.(3)Synthesis and characterization of poly(butylene terephthlate)-block-poly(ethylene oxide)alternative multiblock copolymers(PBT-b-PEO-b-PBT)x.(PBT-b-PEO-b-PBT)x with the PEO contents of 52-76 wt%were synthesized by one pot melt polymerization of cyclic oligo(butylene terephthalate)s(COBTs)and dihydroxy-terminated PEO.The chemical structure of(PBT-b-PEO-b-PBT)x was characterized by 1H NMR,gCOSY and GPC.The polymerization kenetics was studied,and the results revealed they follow the PROP mechanism:1)ring-opening polymerization of COBTs by dihydroxy-terminated PEO to yield PBT-b-PEO-b-PBT triblock copolymers;2.in situ cascade condensation polymerization of triblock copolymers to form(PBT-b-PEO-b-PBT)x multiblock copolymers.(4)Properties of(PBT-b-PEO-b-PBT)x-based solid polymer electrolytes(SPEs).The thermal properties of(PBT-b-PEO-b-PBT)x were studied by TGA and DSC,respectively.The results indicate their thermal stability is similar to PBT homopolymers,while DSC measurements reveal the double-crystalline properties of(PBT-b-PEO-b-PBT)x multiblock copolymers.The mechanical properties of(PBT-b-PEO-b-PBT)x were studied and the results showed that Young's modulus decrease with PBT content.The multiblock copolymer-based solid polymer electrolytes(mBCP SPEs),compromised of(PBT-b-PEO-b-PBT)x and lithium bis(trifluoromethane)sulfonimide(LiTFSI),were prepared by solution blending.Crystallization behaviors of(PBT-b-PEO-b-PBT)x mBCP and the corresponding mBCP SPEs were characterized by DSC and wide angle X-ray diffraction(WAXS).The results showed that LiTFSI content significantly affects the crystallization and melting behaviors of the PEO blocks,while they have little effect on PBT segmental crystallization.Microphase separation behavior of(PBT-b-PEO-b-PBT)x mBCP and the corresponding mBCP SPEs were characterized by S AXS and TEM,indicating PBT and PEO domains are apparently segregated.In addition,cyclic voltammetry(CV)was utilized to characterized the electrochemical stability of the mBCP SPEs and reveals that the electrolyte membrane is stable up to 4.4 V.Eletrochemcial impedance spectroscopy(EIS)showed that a maximum ionic conductivity,?8.2 × 10-4 S/cm at 90 ?,was achieved at r([Li+]/[EO])= 0.10 for the mBCP SPEs.And Li | SPE | Li symmetrical cells were assembled to test the lithium dendrite growth resistance of the mBCP SPEs.It was found that the dendrite growth resistance improved a lot for the multiblock copolymers compared with the typical PEO SPE.