A series of furan-aromatic polyesters synthesized via direct esterification method based on renewable resources

A Series of Furan-Aromatic Polyesters Synthesized via Direct

Esterification Method Based on Renewable Resources

Min Jiang, Qian Liu, Qiang Zhang, Chong Ye, Guangyuan Zhou

Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,

No.5625, Ren Min Street, Changchun, 130022 Jilin, China

Correspondence to: G. Zhou (E-mail: [email protected])

Received 9 September 2011; accepted 15 November 2011; published online 7 December 2011

DOI: 10.1002/pola.25859

ABSTRACT: A series of furan-aromatic polyesters were suc-

cessfully synthesized via direct esterification method starting

from 2,5-furandicarboxylic acid, ethylene glycol, 1,3-propane-

diol, 1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol and

characterized by Fourier transform infrared spectroscopy

(FTIR), nuclear magnetic resonance spectroscopy (1H NMR),

X-ray diffraction (XRD), differential scanning calorimeter

(DSC), thermogravimetric analysis (TGA), dynamic mechani-

cal analysis (DMA), tensile tests, and so on. The preliminary

evidence clearly showed that direct esterification method

was rewarding and worthy to synthesize these furan-aro-

matic polyesters. The densities of furan-aromatic polyesters

were ranging from 1.19 to 1.38 kg/m3. The FTIR and 1H NMR

confirmed their expected structures in detail. The results of

XRD showed that these furan-aromatic polyesters were crys-

talline polyesters. The results of DSC, TGA, DMA, and tensile

tests showed that they behaved as thermoplastic polyester,

had satisfactory thermal and mechanical properties, and their

thermal stabilities were quite similar to that of corresponding

benzene-aromatic polyesters. The results of contact angle mea-

surement showed that they were hydrophilic. The properties

above showed that furan-aromatic polyesters based on renew-

able resources could be a viable alternative to their successful

petrochemical benzene-aromatic counterpart. Furthermore, they

could be used as biopolymer materials according their satisfac-

tory thermal and mechanical properties and hydrophilicity in the

future. VC 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym

Chem 50: 1026–1036, 2012

KEYWORDS: direct esterification method; esterification; furan-ar-

omatic polyesters; 2,5-furandicarboxylic acid; polycondensa-

tion; polyesters; renewable resources

INTRODUCTION Renewable feedstocks are becoming impor-tant suppliers of large industries including the fuels andchemicals industries. Renewable polymers and plastics arebeing developed to replace petrochemical plastics in a widearray of applications from textiles and resins to rigid flexiblefoams. It is likely that in the near future many platformchemicals and polymer materials will be manufactured start-ing from nonfood crops and biomass.1–3

Recently, the interest is quite obvious in the development ofthe preparation of nonpetroleum-derived furan-aromaticpolymeric materials such as polyamides, polyurethanes, poly-esters, and so on.4–7 2,5-Furandicarboxylic acid (FDCA) is amember of the furan family and has a large potential asmonomer to synthesize polyester, polyurethane, and polyam-ide. On the one hand, FDCA can be formed from C6 sugarsand polysaccharides based on C5 glycosidic units.8–10 It is abiomass-derived product.11,12 On the other hand, Benzene-aromatic polyesters, such as poly(ethylene terephthalate)(PET), poly(trimethylene terephthalate), and poly(butyleneterephthalate) (PBT) are excellent thermoplastic polymersand have been widely investigated for decades.13,14 However,

one of their materials-terephthalic acid is petrochemicalsand depends on oil resources. Seeking a counterpart of ter-ephthalic acid from renewable resources has become adeveloping trend as oil prices get higher; oil is not renew-able and oil will eventually run. The structure of FDCA issimilar to terephthalic acid, and FDCA has been consideredas replacement for terephthalic acid. Moreover, some techni-cal barriers on the development of effective and selectivepreparation of 5-hydroxymethylfurfural facilitates the wayfor synthesizing FDCA15,16 lately. Actually, the polyestersbearing furan rings have been reported for decades. Shonoet al.17 studied the synthesis of polyesters containing thefuran ring from dimethyl ester based on FDCA. Mooreet al.18 developed polyesters derived from FDCA and 2,5-bis(hydroxymethyl) furan or 1,6-hexanediol some 30 years ago.Lately, Gandini et al.19 reported the synthesis and someproperties of poly (ethylene terephthalate) based on FDCAand ethylene glycol via transesterification and polycondensa-tion method. What we focus on is the possible polymeriza-tion of FDCA with different diol, the effective way to preparefuran-aromatic polyesters, and the structure and properties

VC 2011 Wiley Periodicals, Inc.

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of furan-aromatic polyester. The purpose of this researchwork is to demonstrate straightforward preparation using tra-ditional catalyst and normal method, and structure and prop-erties of a series of furan-aromatic polyesters based on FDCA,ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexane-diol, and 1,8-octanediol, and the comparisons with corre-sponding benzene-aromatic polyesters were also studied.

EXPERIMENTAL

MaterialsFDCA (pure grade >99.5%) was obtained from Satachem. Eth-ylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol,and 1,8-Octanediol were purchased from China National Medi-cines. 1,1,2,2-Tetrachloroethane and phenol were purchasedfrom Beijing Chemical Works. Tetrabutyl titanate (99%) wasbrought from Tianjin No1 Chemical Reagent Factory.

Synthesis of Furan-Aromatic PolyestersPoly(ethylene 2,5-furandicarboxylate) (PEF), poly(trimethy-lene 2,5-furandicarboxylate) (PTF), poly(butylene 2,5-furan-dicarboxylate) (PBF), poly(hexylene 2,5-furandicarboxylate)(PHF), and poly(octylene 2,5-furandicarboxylate) (POF) weresynthesized via direct esterification method.

The esterification reaction was performed as follows: dioland FDCA and tetrabutyl titanate were put into a 50-mLthree-neck round-bottomed flask. Before the esterificationperiod, the three-neck round-bottomed flask was replacedby nitrogen at least three times to make sure that therewas no residual oxygen inside the flask. The reactionwas protected by nitrogen. The stirrer was turned on ata stirring speed of 120 rmp. The temperature in thereactor was set at 210–235 �C. The esterification reac-tion was finished when water as its byproduct wasdischarged.

When the pressure in the reactor decreased gradually to70 Pa and the temperature was set to 235–245 �C withinseveral hours, the condensation reaction began with the stir-ring rate of 160 rpm. The temperature and pressure in thereactor were kept stable.

The final polymers were purified by being dissolved ino-chlorophenol and being precipitated in methanol for threetimes, and being dried in vacuum oven at 120 �C for 72 h.

The synthesis conditions of PEF, PTF, PBF, PHF and POFwere displayed in detail in Table 1.

TABLE 1 The Synthesis Conditions of PEF, PTF, PBF, PHF, and POF

Sample Diol FDCA:Diol (mol:mol) Etep (�C) Tp (min) Ptep (�C) Pt (min)

PEF Ethylene glycol 1.0:1.6 210 70 240 480

PTF 1,3-Propanediol 1.0:1.6 230 40 240 240

PBF 1,4-Butanediol 1.0:2.0 230 90 245 120

PHF 1,6-Hexanediol 1.0:1.2 235 60 235 180

POF 1,8-Octanediol 1.0:1.2 220 70 240 300

Etep, esterification temperature; Tp, time of arriving at clear point; Ptep, polycondensation temperature; Pt, polycondensation time.

FIGURE 1 The structures of PEF, PTF, PBF, PHF, and POF.

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FDCAFTIR (v/cm�1): 3121 (¼¼CH); 1700 (C¼¼O); 1572, 1510(C¼¼C); 1278 (CAO); 963, 851, 782 (¼¼CH); 1H NMR (DMSO-d6, d/ppm): 7.30, (s 2H, H3, H4, furan ring); 13.62, (s 2H,ACOOH). 13C NMR (DMSO-d6, d/ppm): 159.12, (C¼¼O);145.24, (C2, C5, furan ring); 118.53, (C3, C4, furan ring).

PEFFTIR (Fig. 2; v/cm�1): 3121 (¼¼CH); 2974, 2913 (CAH); 1734(C¼¼O); 1576, 1508 (C¼¼C); 1266 (CAO); 967, 834, 764 (¼¼CH);1H NMR (Fig. 3; CF3COOD, d/ppm): 7.19, (s 2H, H3, H4, furanring); 4.61, (t 4H, ACH2ACH2A). 13C NMR (Fig. 4; C3F6DOD andCF3COOD, d/ppm): 158.88, (C¼¼O); 145.56, (C2, C5, furan ring);120.28, (C3, C4, furan ring); 62.52 (ACH2ACH2A).

PTFFTIR (Fig. 2; v/cm�1): 3120, (¼¼CH); 2968, 2783, (CAH); 1717,(C¼¼O); 1583, 1508 (C¼¼C); 1271 (CAO); 966, 824, 763 (¼¼CH).1H NMR (Fig. 3; CF3COOD, d/ppm): 7.11, (s 2H, H3 H4 furanring); 4.39, (t 4H, ACH2ACH2ACH2A); 2.09, (q 2H,ACH2ACH2ACH2A). 13C NMR (Fig. 4; C3F6DOD, d/ppm): 159.12,(C¼¼O); 145.54, (C2, C5, furan ring); 118.56, (C3, C4, furan ring);61.79 (ACH2ACH2ACH2A); 26.02, (ACH2ACH2ACH2A).

PBFFTIR (Fig. 2; v/cm�1): 3120, (¼¼CH); 2963, 2791, (CAH);1715, (C¼¼O); 1577, 1508 (C¼¼C); 1269 (CAO); 966, 823,763 (¼¼CH). 1H NMR (Fig. 3; CF3COOD, d/ppm): PBF 7.17, (s2H, H3, H4, furan ring); 4.35, (t, 4H, ACH2ACH2ACH2

ACH2A); 1.82, (q, 4H, ACH2ACH2ACH2ACH2A).13C NMR(Fig. 4; C3F6DOD, d/ppm): 159.27, (C¼¼O); 145.56, (C2, C5,furan ring); 118.36, (C3, C4, furan ring); 65.01 (ACH2ACH2

ACH2ACH2A); 23.37, (ACH2ACH2ACH2ACH2A).

PHFFTIR (Fig. 2; v/cm�1): 3119, (¼¼CH); 2940, 2859, (CAH);1722, (C¼¼O); 1576, 1509 (C¼¼C); 1270 (CAO); 981, 818,768 (¼¼CH). 1H NMR (Fig. 3; CF3COOD, d/ppm): 7.09, (s 2H,

H3, H4, furan ring), 4.23, (t 4H, ACH2ACH2ACH2ACH2

ACH2ACH2A), 1.63, (m 4H, ACH2ACH2ACH2ACH2ACH2

ACH2A); 1.31, (m 4H, ACH2ACH2ACH2ACH2ACH2 ACH2A).13C NMR (Fig. 4; C3F6DOD, d/ppm): 159.48, (C¼¼O); 145.66,(C2, C5, furan ring); 118.26, (C3, C4, furan ring); 65.78(ACH2ACH2ACH2ACH2ACH2ACH2A); 26.66, (ACH2ACH2

ACH2ACH2ACH2ACH2A); 23.77, (ACH2ACH2ACH2ACH2

ACH2ACH2A).

POFFTIR (Fig. 2; v/cm�1): 3120, (¼¼CH); 2936, 2858, (CAH);1734, (C¼¼O); 1576, 1509 (C¼¼C); 1273 (CAO); 968, 820,768 (¼¼CH). 1H NMR (Fig. 3; CF3COOD, d/ppm): 7.12, (s 2H,H3 H4 furan ring), 4.24, (t 4H, ACH2ACH2ACH2ACH2

ACH2ACH2ACH2ACH2A); 1.61, (m 4H, ACH2ACH2ACH2

ACH2ACH2ACH2ACH2ACH2A); 1.23, (m 8H, ACH2ACH2

ACH2ACH2ACH2ACH2ACH2ACH2A). 13C NMR (Fig. 4;C3F6DOD, d/ppm): 159.69, (C¼¼O); 145.83, (C2, C5, furanring); 119.36, (C3, C4, furan ring); 66.20 (ACH2ACH2ACH2

ACH2ACH2ACH2ACH2ACH2A); 27.55, (ACH2ACH2ACH2ACH2

ACH2ACH2ACH2ACH2A); 26.88, (ACH2ACH2ACH2ACH2ACH2

ACH2ACH2ACH2A); 24.15, (ACH2ACH2ACH2ACH2ACH2ACH2

ACH2ACH2A).

CharacterizationFourier Transform Infrared Spectroscopy (FTIR)Infrared spectra data of furan-aromatic polyesters wereobtained from FTIR spectrometer (Bruker Vertex 70 FTIR)with a diamond ATR accessory. The spectra were recordedin the range of 4000–600 cm�1.

Nuclear Magnetic Resonance Spectroscopy (NMR)The 1H NMR and 13C NMR measurement was carried out ona Varian Mercury Plus 400-MHz NMR spectrometer operat-ing at 399.95 MHz for 1H and 100.58 MHz for 13C at roomtemperature. Each of furan-aromatic polyester was dissolvedwith CF3COOD or C3F6OD2 with tetramethylsilane (TMS) asthe internal reference.

Specific ViscosityThe specific viscosities (gsp) of furan-aromatic polyesterswere measured at a concentration of 0.5 g/dL in 1,1,2,2-tet-rachloroethane/phenol (1:1 w/w) under 25 �C by using anUbbelohde viscometer by the standard method.

gsp/C expresses reduced viscosity and its unit is dL/g. C isthe concentration of 0.5 g/dL furan-aromatic polyesters in1,1,2,2-tetrachloroethane/phenol (1:1 w/w) under 25 �C.

Molecular Weights and DistributionWeight-average molecular weight (Mw), number-averagemolecular weight (Mn), and their distribution (PDI) wereobtained by gel permeation chromatography using a liner HFIPcolumn and a Waters 515 HPLC with OPTILAB DSP interferomet-ric refractometer (Wyatt Technology) as detector. The eluent washexafluoroisopropanol at a flow rate of 1.0 mL/min at 40 �C.Monodispersed polymethyl methacrylate standard was used.

DensityThe densities of furan-aromatic polyesters were calculatedby formula.

FIGURE 2 Typical ATR-FTIR spectrums of PEF, PTF, PBF, PHF,

and POF.


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q ¼ m=ðV1 � V2Þ;

where q is the density (kg/m3), m is the quality of the sam-ple (kg), V1 is the volume of water in cylinder (m3), and V2is the volume of water in cylinder which solid sampleimmerged in (m3).

Thermal AnalysisThe differential scanning calorimeter (DSC) analyses wereperformed with A Mettler Toledo, DSC 1 DSC, calibrated withzinc standards. The samples were got after quenching the

melted in liquid nitrogen. Sample of 6 6 0.1 mg was used inthe test. The samples were sealed in aluminum pans andheated to 20 �C above the melting point a heating rate of10 �C /min in nitrogen.

Thermogravimetric AnalysisThe thermal stability was determined by thermogravimetricanalysis (TGA) using Mettler Toledo, TGA/DSC 1 series appara-tus. The thermal analyzer was temperature calibrated by usingthe Curie point of nickel as a reference. Samples (6 6 0.5 mg)

FIGURE 3 Typical 1H NMR spectrums of PEF, PTF, PBF, PHF, and POF in CF3COOD.



were heated from 30 to 600 �C at a heating rate of 10 �C/minin nitrogen.

X-Ray Diffraction TestsThe X-ray diffraction (XRD) patterns of furan-aromatic poly-esters were carried out on PW1700s X-ray diffractmeter,using Cu Ka radiation.

Dynamic Mechanical AnalysisDynamic mechanical properties of samples were analyzedusing a dynamic mechanical analysis (DMA; Q800, TA Instru-

ments). Rectangular specimens, 40 mm in length, 5 mm inwidth, and 1.6 mm in thickness were prepared. The meas-urements were taken in tension mode at a frequency of 1 Hzand strain of 0.1%. The temperature ranged from -10 to180 �C at a scanning rate of 2 �C/min. The storage modulus(E0), loss modulus (E00), and loss factor (tan d) of the sampleswere measured as a function of temperature.

Tensile TestsThe tensile tests were performed using a INSTRON-1121 testerwith a strain rate of 2 mm/min at room temperature. Three

FIGURE 4 Typical 13C NMR spectrums of PEF, PTF, PBF, PHF, and POF in C3F6DOD.


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dumbbell-Shaped specimens (15 � 3.23 � 3.20 mm3) wereemployed in each testing to determine average of tensile modu-lus (E), tensile strength (rm) and elongation at break (eb).

The samples for tensile test and DMA were directly injec-tion-molded into standard test specimens by using DSMXplore injection molding machine (Netherlands).

Contact Angle MeasurementContact angle were measured with a DSA100 (KRUSS) con-tact angle goniometer with 12 lL of water at room tempera-ture and the results reported were the mean values of threereplicates.

RESULTS AND DISCUSSION

Synthesis and Structure CharacterizationA series of furan-aromatic polyesters, which comprised ofpoly (ethylene 2,5-furandicarboxylate) (PEF), poly(trimethy-lene 2,5-furandicarboxylate) (PTF), poly(butylene 2,5-furan-dicarboxylate) (PBF), poly(hexylene 2,5-furandicarboxylate)(PHF), and poly(octylene 2, 5-furandicarboxylate) (POF),were prepared via direct esterification method, which hasbecome the main process of benzene-aromatic polyestesrand the preferred technology route. The synthesis route wasshowed in Scheme 1. What we focused on was to reveal po-lymerization conditions of these series of furan-aromatic pol-yesters. Here, tetrabutyl titanate acted as catalyst not onlyfor the esterification reaction but also for polycondensationreaction. As showed in Scheme 1 and Table 1, it was foundthat this synthesis method needed no hundredfold excess ofdiol (diol:FDCA = 2.0:1.0), no solution, one catalyst, mildreaction condition, and less reaction time for the wholepreparation progress. Importantly, this method was fit forthe reaction of FDCA with various of aliphatic diols, had onlyone step, and did not need to synthesize middle monomer,such as 2,5-furandicarbonyl chloride, dimethyl furan-2,5-dicarboxylate, and so on. It proved that our method wasmost rewarding and worthwhile compared with other meth-ods including polytransesterification of FDCA diester diol,transesterification of the FDCA dimethyl ester with an excessof EG followed by the polytransesterification of ensuingproduct and solution polycondensation between the FDCAdichloride and EG.

Figure 1 displayed the typical structures of PEF, PTF, PBF,PHF, and POF. The final products were purified and provedto be expected structures by FTIR, 1H NMR, and 13C NMR.

The ATR-FTIR spectra data of these furan-aromatic polyest-ers were reported in Table 2. The typical and characteristicbands peaks of furan rings for furan-aromatic polyesters,such as the C¼¼C peak appeared around 1570 and 1510 cm�1,furan ring breathing peak appeared around 1020 cm�1, andbending motions peak associated with furan ring appearedaround 970, 830, and 770 cm�1, were present compared withFDCA, as given in Table 2 and showed in Fig. 2. In addition,the C¼¼O of ester carbonyl group peak (1715–1734 cm�1), theCAO of ester carbonyl group peak (1266–1273 cm�1)and CAH of ACH2 group peak (2936–2974 cm�1 and 2858–2913 cm�1) were also present (Table 2 and Fig. 2).

The data of 1H NMR and 13C NMR spectra (Figs. 3 and 4) forfuran-aromatic polyesters were list in Tables 3 and 4. As canbe seen, the spectra of PEF, PTF, PBF, PHF, and POF weresimilar in terms of the resonance peaks associated the furanring (H3/H4 around 7.10 ppm; C¼¼O, C2/C5 and C3/C4around 159.20, 145.50, and 119.30 ppm) and the methylenemoieties directly attached to the ester group (ACH2 around4.40 ppm; ACH2 around 62.50 ppm). The only differenceappeared in the middle CH2 groups in the furan-aromaticpolyesters. The chemical shifts of H portion in 1H NMR andC atom in 13C NMR spectra related to furan ring were verysimilar when furan-aromatic polyesters were compared withFDCA. For PEF, the chemical shift of C3/C4 carbons of thefuran ring (120.28 ppm) was confirmed by using CF3COODas deuterated reagent because the C3/C4 carbons peak over-lapped with the C3F6DOD peak (Fig. 4). Furthermore, the rel-ative integration ratio were reasonable both in 1H NMR and13C NMR spectra (Figs. 3 and 4). For PEF, the resonance ofthe H3 and H4 furan protons at 7.19 ppm to that of esterCH2 at 4.61 ppm was the expected 1:2 integration ratio. ForPTF, the resonance of the H3 and H4 furan protons at7.11 ppm to that of OCH2 at 4.39 ppm was the expected 1:2integration ratio. The resonance of the CH2 next to the OCH2 at2.09 ppm to that of OCH2 at 4.38 ppm was the expected 1:2integration ratio. For PBF, the resonance of the H3 and H4furan protons at 7.17 ppm to that of OCH2 at 4.35 ppm wasthe expected 1:2 integration ratio. The resonance of two CH2

next to the OCH2 at 1.82 ppm to that of OCH2 at 4.35 ppm

SCHEME 1 The synthesis route of furan-aromatic polyesters via direct esterification method.



was the expected 1:1 integration ratio. For PHF, the reso-nance of the H3 and H4 furan protons at 7.09 ppm to that ofOCH2 at 4.23 ppm was the expected 1:2 integration ratio.The resonance of two CH2 next to the OCH2 at 1.63 ppm tothat of OCH2 at 4.23 ppm was the expected 1:1 integrationratio. The resonance of two CH2 being at distance of theOCH2 at 1.31 ppm to that of OCH2 at 4.23 ppm was theexpected 1:1 integration ratio. For POF, the resonance ofthe H3 and H4 furan protons at 7.12 ppm to that of OCH2 at4.24 ppm was the expected 1:2 integration ratio. The reso-nance of two CH2 next to the OCH2 at 1.61 ppm to that ofOCH2 at 4.24 ppm was the expected 1:1 integration ratio.The resonance of four CH2 being at distance of the OCH2 at1.23 ppm to that of OCH2 at 4.24 ppm was the expected 2:1integration ratio. The relative integration ratio of C atompeak in 13C NMR spectra was also fit to the ratio of differentcarbon number for each of furan-aromatic polyesters (Fig.4). In all furan-aromatic polyesters, the spectra were foundto be consistent with the expected structure in terms of bothchemical shifts and relative integrations. No significant Hportion and C atom peak of ACH2 attached to the end AOHgroup in 1H NMR and in 13C NMR spectra were detected forall furan-aromatic polyesters, which suggested that the poly-mers had reached a high molecular weight and confirmedthe GPC data.

These series of furan-aromatic polyesters looked darkbrown, flaxen, and translucent depending on their structureand crystallinity. The gsp/C, Mw, Mn, PDI, and densities of PEF,PTF, PBF, PHF, and POF based on optimized synthesis conditionswere listed in Table 5. Their densities were ranged from 1.19 to1.38 kg/m3 (Table 5). It was also found that these furan-aromatic polyesters were dissolved only in trifluoroacetic acid,1,1,2,2-tetrachloroethane/phenol, o-cresol/trichloromethane,o-chlorophenol besides phenyl, ethyl alcohol, n-butane, tolu-ene, acetone, and butylene oxide.

Crystallinity PropertiesThe presence of crystallinity on furan-aromatic polyesterswas also corroborated by XRD (Fig. 4). PEF X-ray diffracto-gram, respectively, displayed four sharp signals at 2y ¼16.22�, 17.99�, 23.59�, and 26.81�. PTF, PBF, PHF, and POFshowed three signals, respectively, at 2y ¼ 16.95�, 23.49�,25.25�, at 2y ¼ 18.19�, 22.45�, 25.04�, at 2y ¼ 13.00�,16.74�, 24.31�, and at 2y ¼ 12.39�, 16.33�, 23.48�. The sharppeaks of PEF, PHF, and POF suggested their high degree ofmacromolecular order. PEF, PTF, PBF, PHF, and POF werecrystalline polyesters.

Thermal PropertiesThe amorphous morphologies of above furan-aromatic poly-esters and benzene-aromatic polyesters were got after

TABLE 2 ATR-FTIR Data of Furan-Aromatic Polyesters

Assignment

Frequency (cm�1)

PEF PTF PBF PHF POF FDCAa

¼¼CH (FR) 3,121 3,120 3,120 3,119 3,120 3,121

CAH (CH2) 2,974, 2,913 2,968, 2,906 2,963, 2,898 2,940, 2,859 2,936, 2,858 –

C¼¼O (ester) 1,734 1,717 1,715 1,722 1,734 1,700

C¼¼C (FR) 1,576, 1,508 1,583, 1,508 1,577, 1,508 1,576, 1,509 1,576, 1,509 1,572, 1,519

CAO (ester) 1,266 1,271 1,269 1,270 1,273 1,278

FR breathing 1,014 1,019 1,021 1,020 1,015 1,032

Bending motions (FR) 967, 834, 764 966, 824, 763 968, 823, 765 981, 818, 768 968, 820, 768 963, 851, 782

a The FTIR data of FDCA was obtained from DSBS integrated spectral database system.

TABLE 3 1H NMR (CF3COOD, d/ppm) Data of Furan-Aromatic Polyesters

Assignment

1H NMR

PEF PTF PBF PHF POF FDCA

H3, H4 (FR) 7.19(s) 7.11(s) 7.17(s) 7.09(s) 7.12(s) 7.30

ACH2A (CH2)nACH2A 4.61(t) 4.39(t) 4.35(t) 4.23 (t) 4.24 (t) –

n ¼ 0 n ¼ 1 n ¼ 2 n ¼ 4 n ¼ 6

ACH2A (CH2)nACH2A – 2.09 (q) 1.82 (q) – – –

n ¼ 1 n ¼ 2

ACH2ACH2A (CH2)qACH2ACH2A – – – 1.63(m) 1.61(m) –

q ¼ 2 q ¼ 4

ACH2ACH2A (CH2)qACH2ACH2A – – – 1.31(m) 1.23(m) –

q ¼ 2 q ¼ 2


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quenching the melted in liquid nitrogen. Figure 5 displayedthe DSC traces of amorphous morphologies of PEF, PTF, PBF,PHF, and POF, and the glass transition temperature (Tg) andmelting point (Tm) were listed in Table 3. As we can see,every polyester had one Tg (21.8–89.9 �C) and Tg decreasedwith the increasing of the methylene number of aliphaticdiols. Tm shifted a much down as the methylene numberincreased but there was no Tm for PTF. The reason was thatthe higher content of the methylene number of aliphaticdiols, the higher facility was found for furan-aromatic polyes-ter chain. There was obvious crystallization exotherm peakat 95.0 �C for PBF. The Tg and Tm values of PEF versus PET,PBF versus PBT, PHF versus PHT, and POF versus POT dif-fered litter.

Figure 6 showed the thermal gravimetrical traces of PEF,PTF, PBF, PHF, and PEOF, and an index of Td was tenta-tively applied to evaluate their thermal stabilities. The Tdvalues were between 373.1–389.3 �C compared with382.2–407.3 �C of corresponding benzene-aromatic poly-esters (Table 3). They all exhibited a thermo weight-loss pro-cess in nitrogen and the value of Tdm were between 389.0–407.4 �C (Table 3), which was similar to 399.3–440.0 �Cfor benzene-aromatic polyesters. Residue at 500 �C: PEF >

PTF > PBF > PHF > POF. It could be seen that the thermalstabilities of above furan-aromatic polyesters were quite sim-ilar to that of corresponding benzene-aromatic polyesters.

Dynamitic Mechanical PropertiesFigure 7 plotted the changes of E0 , E00, and tan d as increas-ing temperature. It was seen that the three parameters forall samples showed the similar alteration.

The measured E0 assesses the elastic property of the mate-rial. Figure 7(a) showed that the E0 , which represents themodulus in bending of specimen, kept constant at low

TABLE 4 13C NMR (C3F6DOD, d/ppm) Data of Furan-Aromatic Polyesters

Assignment

13C NMR

PEF PTF PBF PHF POF FDCA

C (C¼¼O) 158.88 159.12 159.27 159.48 159.69 159.12

C2, C5 (FR) 145.56 145.54 145.56 145.66 145.83 147.24

C3, C4 (FR) 120.28a 118.56 118.36 118.26 119.36 118.53

ACH2A (CH2)nACH2A 62.52 61.79 65.01 65.78 66.20 –

n ¼ 1 n ¼ 2 n ¼ 4 n ¼ 6

ACH2A (CH2)nACH2A – – 23.37 – – –

n ¼ 2

ACH2ACH2A (CH2)qACH2ACH2A – – – 26.66 27.55 –

q ¼ 2 q ¼ 4

ACH2ACH2A (CH2)qACH2ACH2A – – – 23.77 – –

q ¼ 2

ACH2ACH2ACH2ACH2ACH2ACH2 ACH2ACH2A – – – – 26.88 –

ACH2ACH2ACH2ACH2ACH2ACH2ACH2ACH2A – – – – 24.15 –

a 120.28 ppm was confirmed by using CF3COOD as deuterated reagent.

TABLE 5 The gsp/C, Mw, Mn, PDI and Densities of PEF, PTF,

PBF, PHF, and POF

Sample gsp/C (dL/g) Mn (�104) Mw (�104) PDI q (kg/m3)

PEF 1.20 10.53 25.20 2.39 1.36

PTF 1.21 6.02 8.98 1.49 1.38

PBF 1.41 1.78 4.23 2.38 1.29

PHF 1.04 3.21 6.67 2.08 1.27

POF 0.69 2.07 4.75 2.29 1.19

TABLE 6 The Results of DSC and TGA of Furan-Aromatic

Polyesters

Sample

DSC TGA

Tg (�C) Tm (�C) Td (�C) Tdm (�C)

PEF 89.9 210.4 389.3 407.4

PET 79.020 246.020 407.321,22 440.021,22

PTF 57.9 no 375.3 396.4

PTT 4520 229.020 382.223 399.323

PBF 30.5 172.2 373.1 392.2

PBT 48.521,26 227.121,26 384.024,25 407.024,25

PHF 28.1 148.2 374.8 389.0

PHT 36.1 150.7 386.1 400.0

POF 21.8 148.6 375.1 390.7

POT 17.4 132.8 385.5 403.6

Tg, the glass-transition temperature; Tm, melting point; Td, thermal

decomposed temperature; Tdm, temperature at the maximum degrada-

tion rate; PET, polyethylene terephthalate; PTT, polytrimethylene tereph-

thalate; PBT, polybutylene terephthalate; PHT, polyhexylene

terephthalate; POT, polyoctylene terephthalate (PHT and POT were syn-

thesized via direct esterification method in our laboratory).



temperature range. When the temperature increasing, the E0

dropped rapidly and then reached a plateau. The distinctinflexibility of furan aromatic polyesters at room tempera-ture: PEF > PTF > PBF > PHF > POF.

E00 gives the quantity of energy lost or absorbed by the ma-terial after withdrawal of load, signifying the viscousproperty of the viscoelastic material. As showed in Figure7(b), the E00 first increased in response to the increasingtemperature, and then dropped rapidly when the tempera-ture exceeded Tg due to the change in intramolecular fric-tion. The peak of E00 curve for furan-aromatic polyestersshifted to lower temperature with the increasing of themethylene number of aliphatic diols. Furthermore, the E00

value corresponding to the peak tended to reduce withthe increasing of the methylene number of aliphatic diols,indicative of the more prominent viscous characteristic,because E00 evaluated the viscous property of the visco-elastic material. The possible reason was concluded thatthe increasing of methylene number of aliphatic diolsweakened the flexibility of the furan-aromatic polyesterchains, which caused the reduction of the motion resist-ance of the chain segments.

In this article, the glass transition temperature of furan-aromatic polyester was defined as the temperature wherethe loss factor reached a maximum. It was obviouslyobserved that the higher content of methylene number ofaliphatic diols, the lower Tg was found for fruan-aromaticpolyesters as showed in Figure 7(c). The maximum tan dvalue of each sample was located around Tg at which thechain segments began to move and the stronger intramo-lecular friction should be overcome. When the temperatureexceeded Tg, the tan d value dropped due to the relativelyeasier movement of the chain segments at higher tempera-ture. The Tgs got by DMA were similar to those got by DSCfor furan-aromatic polyesters.

Tensile PropertiesThe stress–strain curves (Fig. 8) indicated that these furan-aromatic polyesters behaved as thermoplastic polyesters andexhibited satisfactory mechanical properties. They showedbetter tensile modulus ranging from 340 to 2070 MPa, ten-sile strength from 19.8 to 68.2 MPa, and lower elongation atbreak from 4.2 to 210% (Table 7). Thereinto, ensile modulusdecreased with the increasing of the methylene number ofaliphatic diols for furan-aromatic polyester.

Hydrophilicity PropertiesTo investigate the hydrophilicity of PEF, PTF, PBF, PHF,and POF, the water contact angels were measured. The

FIGURE 5 X-ray diffractograms of PEF, PTF, PBF, PHF, and

POF.

FIGURE 6 DSC traces of furan-aromatic polyesters at a scan-

ning rate of 10 �C/min.

FIGURE 7 TGA traces of furan-aromatic polyesters at a scan-

ning rate of 10 �C /min.


POLYMER SCIENCE


samples were melted slightly over their melting point (Tm)completely and then were directly injection-molded intostandard test specimens (20 � 15 � 2 mm3) just overtheir glass transition temperature (Tg). As show in Table8, the contact angles of furan-aromatic polyesters wereabout 67�–86� and lower than 90�, which suggested theywere hydrophilic.

CONCLUSIONS

A series of furan-aromatic polyesters, including PEF, PTF,PBF, PHF, and POF, were successfully synthesized via directesterification method starting from FDCA, ethylene glycol,1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 1,8-octa-nediol. The preliminary evidence here clearly showed that itwas readily possible to synthesize these furan-aromatic poly-esters via direct esterification method by use of renewableresources (not only FDCA but also diols, which can be pre-pared via biological fermentation). The densities of furan-aromatic polyesters were ranging from 1.19 to 1.38 kg/m3.Furan-aromatic polyesters were crystalline polyesters. TheirTg and Tm were at 21.8–89.9 �C and at 148.2–210.4 �C. Theirthermal stabilities were quite similar to that of correspond-ing benzene-aromatic polyesters. Tensile strength, tensilemodulus, and elongation at break ranged from 340 to 2070MPa, from 19.8–68.2 MPa, and from 4.2 to 210%, respec-tively. The viscoelastic properties of furan-aromatic polyest-ers were analyze by DMA. It was found that both loss modu-lus E00 and tan d corresponding to the peak tended toweaken with the increasing of the methylene number of ali-phatic diols for furan-aromatic polyesters. The contact anglesof furan-aromatic polyesters were about 67–86� and lower

FIGURE 8 Changes in storage modulus E’ (a), loss modulus E’’

(b) and loss factor tan d (c) for furan-aromatic polyesters.

TABLE 7 Mechanical Properties (Tensile Modulus, E, Tensile

strength, rm, and Elongation at break, eb) of Furan-Aromatic

Polyesters

No. Polyester E (MPa) rm (MPa) eb (%)

1 PEF 2,070 66.7 4.2

2 PTF 1,550 68.2 46

3 PBF 1,110 19.8 2.8

4 PHF 493 35.5 210

5 POF 340 20.3 15

FIGURE 9 Stress–strain curves of furan-aromatic polyesters. 1-

PEF, 2-PTF, 3-PBF, 4-PHF, and 5-POF.



than 90�, which suggested that they were hydrophilic. Theproperties of furan-aromatic polyesters based on renewableresources will endow them to be a viable alternative to theirsuccessful petrochemical benzene-aromatic counterpart and tobe used as biopolymer materials in the future. Details on biode-gradability and biocompatibility will be assessed and reportedlater. Further copolymers are also under way to study.

The authors thanks the National Nature Science Foundation ofChina (Project No: 51103152) for financial support.

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TABLE 8 Water Contact Angle of Furan-Aromatic Polyesters

Sample PEF PTF PBF PHF POF

Contact angle (�) 67.03 86.38 83.68 80.41 86.16


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Documents

A series of furan-aromatic polyesters synthesized via direct esterification method based on renewable resources