Synthesis And Characterization Of Bio-based Polyesters With Rigid Skeleton Derived From Furfural

Polyesters have been widely applied to packaging,agriculture,biomedical materials,tissue engineering and other fields,because of their light weight,convenient and easy manufacture.However,the raw materials of the production of thet polyesters primarily rely on petroleum-based materials.Thus,in order to reduce the dependency on fossil fuels,seeking raw materials derived from bio-based polymers have become a research focus in the polymer field.Monomers of bio-based polyesters derived from renewable bio-based polymers,as the significant renewable polymers,have received a lot of attention both in academy and in industry.Up to now,the major commercial bio-based polyesters fall in short in poor heat-resistance,poor barrier properties,and opaqueness because of aliphatic linear structure in polymer main chain,which greatly limits their application.In view of these problems,on the basis of chemical structure designing,I studied the Diels-Alder unsaturated adduct from furanic monomers and maleic anhydride derived from furfural,and prepared different rigid bio-based monomers(diacids and diols).Then,series bio-based polyesters were synthesized via melt polycondensation and ring opening polycondensation.The effect of polyester structure on the properties has been systematically explored.Based on the properties of as-prepared polyesters,cyclic monomers was incorporated into poly(butylene succinate)(PBS)and poly(butylene 2,5-furandicarboxylate)(PBF),and obtain polyesters with excellent comprehensive properties to broaden the application fields.The main contents of this dissertation are as follows:(1)Bio-based oxabicyclic diacids/anhydride with different steric-hindrance were synthesized derived from bio-based furanic small molecules,and the structure of them were verified by 1H NMR.2,5-furandicarboxylic acid(FDCA),as an alternative family to petroleum-based terephthalic acid(PTA),was prepared via K2CO3 promoted C-H carboxylation of furoate in molten sodium formate,and the reaction conditions were optimized.Series bridged-ring-based polyesters from oxabicyclic diacids/anhydride and ethylene glycol(EG),1,3-propanediol(1,3-PDO)and 1,4-butanediol(1,4-BDO)were synthesized via melt polycondensation.The structure,molecular weight,thermal and mechanical property were characterized.The results indicated that polyesters based on monomethyl oxabicyclic diacid(MBDA)and anhydride with dimethyl substituents(d-MBDA)has lower molecular weight than that of polyesters based on oxabicyclic diacid(OBDA).Compared with the polyesters synthesized with the corresponding oxabicyclic anhydride in the literature,the polyesters with higher molecular weight using OBDA in this work were synthesized,leading to better comprehensive performance.PBOB synthesized from OBDA and 1,4-BDO possesses superior thermal stability(Td,5%>33℃),higher Tg(35.7℃),and excellent mechanical property.Series copolyesters(PBOBmFn)were synthesized by first incorporating FDCA into PBOB polyester.The results indicated that the mechanical properties of polyesters were enhanced by incorporating FDCA unit into PBOB.PBOB22F78 exhibit superior comprehensive mechanical properties,with satisfactory tensile strength(34.2± 2.5 MPa)and ductility(εb=467 ± 7%),which were comparable to those of common PBS and polyhydroxyalkanoate(PHB).Cytotoxicity test indicated that PBOB49F51 in RAW264.7 cells and PC 12 cells exhibited less toxic and good security.(2)Based on the Diels-Alder reaction,unsaturated adduct was synthesized derived from bio-based furfural.Then,novel bio-based diacid(TCDA)and anhydride(TCAH)with multicyclic structure were successfully synthesized via serial methyl esterification,oxidation reaction,and acetal reaction.The structures of the novel monomers were characterized by 1H NMR and single crystal X-ray diffraction,revealing a unique W-shaped skeleton of them and high purity.Series of novel bio-based polyesters were synthesized via melt polycondensation of TCDA and α,ω-diols and ring opening polycondensation of TCAH and epoxides.The results indicated that the Tg values of polyesters by melt polycondensation is up to 109℃,and the Tg of polyesters by ring opening polycondensation is up to 174℃.In addition,the multicyclic rigid structure imparts excellent gas barrier properties of these polyesters,comparable to FDCA-based polyesters.The CO2 permeability coefficients of synthesized polyesters(0.129-0.679 barrer)were lower than that of bio-based aliphatic polyester PBS(2.98 barrer)and polylactic acid(PLA,1.09 barrer),which shows a prominent advantage in barrier property.(3)I designed and synthesized different cyclic diols(dicyclic diol(BCDO),tricyclic diol(TCDO)),and multicyclic structure attributes to excellent heat-resistance and gas barrier property of polyesters,comparable to that of petroleum-based materials.The structures of the diols were characterized by 1H NMR and single crystal X-ray diffraction.TCDO exhibit same skeleton with TCDA,and high purity of BCDO and TCDO was obtained.In order to explore the relation between structure and properties of polyesters systematically,four series of bio-based polyesters(PBX,PBeX,PBCX,PTCX)were synthesized based on one-dimensional linear 1,4-BDO,two-dimensional plane 1,2-benzenedimethanol(BeDO)and three-dimensional cyclic diols(BCDO,TCDO)with α,ω-diacids via melt poly condensation.The results revealed that the molecular weight of the four series of polyesters were of the following order:PBX>PBeX>PBCX>PTCX,attributed to the different reaction reactivities of monomers with different dimensionality.The Tgvalues were of the following order:PTCX>PBCX>PBeX>PBX,which was in accordance with the order of the dimensionality,indicating that three-dimensional cyclic monomer impart higher rigidity for polyesters.The Tg of polyester from TCDO and 1.4-succinic acid is up to 88.1℃,superior to that of petroleum-based polyester PET(～80℃).Polyesters in this work are amorphous with the exception of PBX series polyesters,indicating they exhibit excellent transparency.In addition,PBX and PTCX series polyesters could be converted to thermoplastic elastorner by tuning the length of chain of α,ω-diacids.The O2 permeability coefficients of PBeS,PBCG1 and TCDO-based polyesters(0.013-0.180 barrer)were lower than that of common bio-based aliphatic polyesters PBS(1.740 barrer)and PLA(0.370 barrer),which shows a prominent advantage in barrier property.Especially for PTCS with multicyclic structure,the O2 gas barrier property is 4.6-fold than that of petroleum-based polyester PET.(4)Two series of novel bio-based tri-copolyesters(PBTCxSy and PBTCxFy)were synthesized by incorporating multicyclic rigid TCDA into PBS and poly(butylene 2,5-furandicarboxylate)(PBF)via melt polycondensation.The results revealed that the heat-resistance,crystallization behavior,mechanical property,and CO2 gas barrier property of PBS and PBF have been significantly affected by incorporating TCDA unit.For PBTCxSy copolyesters,the Tg values of copolyesters have been remarkably improved by incorporating TCDA.The Tg value is up to 32.4℃ after inserting 67 mol%TCDA unit,which is above room temperature.The crystallization of copolyesters decrease with the increase of TCDA content,and when the TCDA content was 28 mol%or greater,the copolyesters are amorphous,which is also the "ductile-to-brittle" transition.In addition,the CO2 barrier properties of PBTCxSy copolyesters were gradually improved by the increase of TCDA unit.For PBTCxFy copolyesters,the thermal and mechanical properties and barrier properties of them have been improved with the similar variation trend of PBTCxSy copolyesters.Considering the influence of each monomer to the performance of polyesters,a series of novel bio-based quadri-copolyesters(PBTCx(SnFm)y)with comparable properties to petrochemical-based plastics were synthesized in this work.In particular,PBTC15(S10F90)85 exhibited satisfactory Tg(36.7℃)and tensile strength(46.9±9.1 MPa),in addition to superior ductility(εb=830 ± 80%)and CO2 barrier properties(0.029 barrer).The modification of PBS and PBF by the incremental replacement of OBDA with SA or FDCA endow them higher Tg,tensile strength,the elongation at break,and better barrier properties,showing excellent comprehensive properties and have a wide application in packaging and beverage bottle fields.Based on the deficiencies of bio-based polyesters,including poor thermal and mechanical properties and poor barrier properties,and considering resources renewability,this dissertation from molecular structure,bio-based monomers with cyclic rigid framework were synthesized,and series bio-based polyesters with high molecular weight,high barrier property,good transparency,and controllable mechanical properties were synthesized via melt polycondensation using synthesized monomers.This thesis solves the defects of commercial bio-based polyesters in some extent,including brittleness,opacity,and poor barrier properties,and offers important implications on areas like seeking alternatives to petroleum-based polymers and broadening the application fields of polyesters.