Synthesis And Properties Of 2,5-Furandicarboxylic Acid And Its Bio-based Aromatic Polyesters

Biobased polymers could reduce the consumption of crude oiland GHG emissionCO₂.As we know,the current popular bio-based polymers,such as polylactic acid?PLA?,poly?butylene succinate??PBS?,polyhydroxyalkanoates?PHAs?are all featured by aliphatic or long soft chain,which leads to the relatively lower thermal and mechanical properties when compared with the engineering plastics like poly?ethylene terephthalate??PET?and polycarbonate?PC?.The primary reason corresponding to the weak properties might be the lack of aromatic or rigid units in the molecular architectures.Therefore,developing the bio-based platform chemicals with unique structures and preparing polymers with better properties is always the challenge facing us.2,5-furandicarboxylic acid?FDCA?,which can be derived from polysaccharides or sugars,is a promising bio-based platform chemical for the synthesis of rigid polymers.Considering its great potential in establishing the green chemistry industry,it has been selected as one of the top 12 potential platform chemicals by US Department of Energy and the wide utilization of FDCA might be a start to the bio-based polymers with satisfied properties.Fromfuran and furancarboxylic acid,the high purity 2,5-FDCA was prepared in our lab..Based on which,the bio-based polyester poly?ethylene 2,5-furandicarboxylate??PEF?and its copolyesters modified by 1,4-cyclohexanedimethylene?CHDM?with different configuration weresynthesized.After the chemical structures confirmation,their proeprties were investigaged in detail.The main achievements are:1.A novel efficient synthetic route for the preparation of 2,5-FDCA,firstly,the 2,5-diacetylfuran?2,5-DAF?was synthesized from furan and acetic anhydride through a two-step Friedel–Crafts reaction catalyzed by the common acid systems.Then the classical Iodoform Reaction was taken to convert 2,5-DAF into 2,5-FDCA.The purity of the resulted 2,5-FDCA was as high as 99.6%and the quality yield relative to furan was high up to 82.3%.During the reaction,the by-products,acetic acid and iodoform,were easy to be recycled and no other unmanageable or toxic wastes were detected.These all indicate that the method described here has great potential to be industrially scaled up and the widely application of 2,5-FDCA is expectable.2.Poly?ethylene 2,5-furandicarboxylate-co-ethylene terephthalate??PEFT?is synthesized via direct polycondensation method with 2,5-FDCA and terephthalic acid.The intrinsic viscosity of PEFT ranges from 0.65 to 0.98 dL/g.The PEFT copolyesters have a single T_g between 69.5-84.1 ^oC and the T_m deceased from 249.6^oC to 213.0 ^oC.Then we synthesized the dimethyl furan-2,5-dicarboxylate?DMFD?with 2,5-FDCA and methyl alcohol.It was noted that the PEF synthesis of DMFD and EG showed the glass transition temperature of 87.6 ^oC,the weak melting point at212.9 ^oC and the 5%weight loss temperature at about 381 ^oC,and the barrier to CO₂and O₂ of PEF was increased 13.1 and 5.8 times,respectively,when compared with those of PET.3.A series of poly?ethylene-cyclohexanedimethylene 2,5-furandicarboxylate?s?PECFs?with different compositions were synthesized from 2,5-FDCA,1,4-cyclohexanedimethylene?CHDM?and EG.The intrinsic viscosity of PECFs could reach up to 0.77-0.92 dL/g agreed with the M_w from 46900 to 76500 g/ml and had narrow polydispersity between 1.48 and 1.64.The crystallization ability,tensile modulus and strength of PECFs were decreased with the increasing content of CHDM at first?0-59%?,and with the introduction of more CHDM?76-100%?units,they were increased accordingly.The CHDM units introduced into PEF molecular chain could efficiently improve the flexibility of PEF and gained excellent mechanical properties.PECF-76 has well crystallization?T_m=225.4 ^oC and?H_m=27.2J/g?,mechanical Properties?1760 MPa and 63 MPa?and O₂ and CO₂ barrier properties,to be a novel polyester synthesis firstly application in packaging field such as plastics beer bottles.4.PECFs with different contents of trans-or cis-CHDM isomers,were synthesized to investigate the influence of CHDM configuration on its properties.The intrinsic viscosity of obtained PECFs were in the range of 0.68-0.87 dL/g and M_w were varied from 49600 to 87000 g/mol with the molar-mass dispersity of 1.7-1.9.The T_m,?H_m,T_g of PECFs were also increased with the increasing content of trans-CHDM from PECF-trans 10 to PECF-trans 98,such as from 82.5 ^oC to 89.2 ^oC for T_g,from 189.1^oC to 252.3 ^oC for T_m and from 4.5 J/g to 36.7 J/g for?H_m.The tensile modulus and strength increased from 1700 MPa and 52 MPa for PECF-trans 10 to 1900 MPa and80 MPa for PECF-trans 98.5.The bio-based polyester demonstrating great potential to be used as engineering plastic,poly?1,4-cyclohexanedimethylene furandicarboxylate??PCF?was synthesized from 2,5-FDCA and CHDM with different steric conformation.The intrinsic viscosity of resulted polyesters could reach up to 0.72-0.80 dL/g and M_w was determined to be varied from 38000 to 44700 g/mol with a polydispersity index of 1.69-1.88.As the increasement of trans-CHDM from PCF-trans 10 to PCF-trans 98,the T_g increased from 71 ^oC to 87 ^oC,T_m increased from 219 ^oC to 291 ^oC and?H_m increased from42.8 J/g to 82.3 J/g.The synthesized PCFs demonstrated very high crystallinity and crystallization rate as well as good thermal stability,indicated by the high melting enthalpy,short t_1/2 of about only 7 seconds.Based on above results,it could conclude that the bio-based PCFs showed great potential to be used as the engineering plastic and it was the first time that the FDCA-based polyesters demonstrating extremely high crystalline and satisfied mechanical properties was reported.6.In order to obtain the amorphous PEF copolyesters with higher T_g,better transparencyandgoodbarrierproperties,itwasmodifiedby2,2,4,4-tetramethyl-1,3-cyclobutanediol?CBDO?via copolymerization and a series of copolyesterspoly?ethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol2,5-furandicarboxylate?s?PETFs?were prepared.The intrinsic viscosity of PETF-4,PETF-10,PETF-15 and PETF-23,where the number of 4,10,15,23 stands for the mole fraction of CBDO in the copolyesters,were between 0.71-0.79d L/g and their M_w were varied from 38100 to 41800 g/mol with the polydispersity index of 2.1-2.3.When the CBDO content was up to 10%,PETF-10 was the completely amorphous copolyesters with high T_g of 91.0 ^oC,high transmittance at 90.1%by cutoff at 700 nm,tensile modulus of 3100MPa and the tensile strength of 97 MPa.The CO₂ and O₂barrier properties of PETF-10 were 6.8 fold and 4.6 fold than that of PET.