Study On The Synthesis And Properties Of Polyhexanediol 2,5-furandicarboxylates

The depletion of fossil resources alongside environmental pollution have raised the concerns on the development of sustainable energy and chemical compounds.In this paper,a biomass-based platform chemical,5-hydroxymethylfurfural（HMF）was used as the raw material to prepare 2,5-furandicarboxylic acid（FDCA）under the oxidation of potassium ferrate.And the effect of the stabilizer for potassium ferrate on the oxidation of HMF to FDCA was evaluated.Then,the prepared FDCA was used as the monomer for the synthesis of polyhexanediol 2,5-furandicarboxylate（PHF）by direct esterification method.Firstly,the reaction system of potassium ferrate/NaOH/K₂HPO₄ was constructed,and the effect of NaOH and dipotassium phosphate dosage on the oxidation transformation of HMF to FDCA was studied.The results showed that the highest FDCA yield of 82.4%was obtained at the temperature of 25°C in 15 min when the reaction solution volume was 10 mL,the concentration of HMF,potassium ferrate,dipotassium phosphate and sodium hydroxide was 0.1mol/L,1.5 mol/L,1.6 mol/L and 0.4 mol/L,respectively.Furthermore,it was found that the addition of Fe（OH）₃ will improve the oxidation of HMF to FDCA,the FDCA yield increased to91.7%when 1 mmol/L Fe（OH）₃ was added.FTIR results of the obtained oxidation product revealed that the infrared absorption peaks of furan ring,terminal hydroxyl group and carboxyl group of FDCA can be observed obviously.The ¹H NMR and ¹³C NMR results further indicated that the characteristic peaks of proton on the furan ring and carboxyl group,the characteristic absorption peaks of carbon atoms on the furan ring,tert carbon and carboxyl can be found,which indicated that the obtained oxidation product is FDCA.Secondly,the prepared FDCA and the sell 1,6-hexanediol（1,6-HDO）were used as the monomer to synthetise polyhexanediol 2,5-furandicarboxylate（PHF）with a direct esterification method.The results showed that a highest intrinsic viscosity of 0.803 dL/g can be obtained when the FDCA/1,6-HDO mole ratio was 1:3,the esterification temperature was 180°C,the butyl titanate dosage was 0.003 mmol,the esterification time was 60 min,the polycondensation temperature was 250°C,the polycondensation time was 60 min,and the antioxidant dosage was 0.005 mmol,the limiting reduced viscosity of the obtained polyester was 0.225 dL/g,and the molecular weight was about 12,000.The differential scanning calorimetry（DSC）results indicated that the Tg,Tc,and Tm of the obtained polyester was 29°C,48°C,and 145°C,respectively.The thermogravimetry（TG）results showed that the thermal decomposition temperature of the obtained polyester was between 385°C and 415°C.Compared with petroleum based polyester products,poly（ethylene terephthalate）（PET）,the obtained polyester has lower Tg,Tc and Tm.The glass transition temperature and cold crystallization temperature are close to room temperature,while the thermal decomposition temperature is only slightly lower than PET.Tensile tests showed that the tensile modulus of the obtained polyester was between 447⁴79 MPa,the tensile strength was between 34.2³6.5 MPa and elongation at break was 215²20%.The tensile modulus and strength is obviously lower than that of PET,while the elongation at break is obviously higher than that of PET.Furthermore,the FTIR results revealed that the polyester products had infrared absorption peaks of furan ring,six element carbon chain and carboxyl group,with a weak hydroxyl infrared absorption peaks.The ¹H NMR results indicated that the characteristic peaks of the furan ring,hydrogen on hydroxyl carbon and two kinds of methylene on 1,6-HDO exited in the obtained polyester,and the peak area ratio is 1:2:2:2.The ¹³C NMR results further displayed that the obtained products had the characteristic absorption peaks of quaternary carbon,tertiary carbon on furan cyclic,the carboxyl carbon,1,6 diol hydroxyl carbon and two kinds of methylene carbon,and the peak area ratio is 1:1:1:1:1:1.All these results revealed that the obtained polyester products were PHF.