New copolyesters derived from terephthalic and 2,5-furandicarboxylic acids: A step forward in the development of biobased polyesters

Polymer 54 (2013) 513e519

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New copolyesters derived from terephthalic and 2,5-furandicarboxylic acids: A step forward in the development of biobased polyesters Andreia F. Sousa a, b, *, Marina Matos a, Carmen S.R. Freire a, Armando J.D. Silvestre a, Jorge F.J. Coelho b a b

CICECO and Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal Department of Chemical Engineering, University of Coimbra, Pólo II, Pinhal de Marrocos, 3030-290 Coimbra, Portugal

a r t i c l e i n f o

a b s t r a c t

Article history: Received 20 July 2012 Received in revised form 29 November 2012 Accepted 30 November 2012 Available online 7 December 2012

A straightforward partial substitution of non-renewable poly(ethylene terephthalate) by renewable homologous poly(ethylene furandicarboxylate) was successfully done by random copolymerisation of bis(2-hydroxyethyl) terephthalate and bis(hydroxyethyl)-2,5-furandicarboxylate. Different stoichiometric amounts of these monomers were used and the ensuing copolyesters were characterised in detail by several physical chemistry, thermal and mechanical techniques. All copolyesters have the expected chemical structure incorporating both aromatic and furanic units in different amounts accordingly to the stoichiometric feed-ratio. In particular the copolyester having 20% of furan units (PET-ran-PEF 4/1) have similar properties to those of PET homopolyester, despite some minor differences, being a semicrystalline copolyester with similar glass transition and melting temperatures to those of PET. Also, the mechanical performance of this PET-ran-PEF 4/1 copolyester was in accordance with the PET operating temperature range, tan d and modulus. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: 2,5-Furandicarboxylic acid PET Polyesters

1. Introduction In recent years much has been written about renewable resources and their use in polymer science [1]. The reasons behind this interest are closely related to the announced scarce of petroleum oil in the near future and also because society is genuinely concerned with the environmental problems associated with the increasing fossil CO2 emissions [1]. In this context, several chemicals from vegetable feedstocks have been proposed as monomers for the future polymer chemistry [2,3]. The portfolio of chemicals proposed includes sugars and their derivatives, vegetable oils, organic acids, glycerol, among many others [2,4]. Definitely one of the most promising chemicals, readily available today from polysaccharides and sugars, is 5-hydroxymethylfurfural (HMF) [2]. HMF can be used to synthesise 2,5-furandicarboxylic acid (FDCA), which is structurally analogous to the very important petrochemical terephthalic acid (TPA) [2,4] (Scheme 1). TPA, as it is well known, is used today in the production of one the most important commercial polyester, i.e., poly(ethylene terephthalate) (PET). As mentioned previously the world is changing very rapidly and new green alternatives to this polymer are

* Corresponding author. CICECO and Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal. Tel.: þ351 234 372 571; fax: þ351 234 401 470. E-mail address: [email protected] (A.F. Sousa). 0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymer.2012.11.081

mandatory. In this context, as demonstrated by our research group, FDCA can be used in polycondensation reactions to produce for example the furan homologue of PET, poly(ethylene furandicarboxylate) (PEF) [5e7]. The chemical and thermal characterisation of this polyester confirmed both the success of the polymerisation reaction and the similarity with PET thermal properties (e.g. glass transition, melting and onset of thermal decomposition temperatures around 80, 215 and 300
C, respectively) [7,8]. Additionally, the thermo-mechanical behaviour of PEF was recently studied by DMA [8] indicating a glass transition temperature around 90
C. More importantly, PEF has no longer just an academic interest, since Avantium, announced in 2010 the development of the first PEF bottle [9]. The realm of FDCA can be extended to a more vast number polyesters, besides PEF, like those recently reported by our research group, involving FDCA and three isomers of 1,4:3,6-dianhydrohexitol or 1,3-propanediol [7]. The polycondensation involving FDCA and hydroquinone has also been studied [7,10]. Moreover, the polycondensation using different linear diols (C2eC8) [8] or the random copolymerisations of FDCA with different amounts of ethylene glycol and butanediol [11] have also been reported. Despite the enormous potential of the polyesters based on FDCA, recently a renewed enthusiasm in TPA emerged because of sugar-based p-xylene route to prepare 100% renewable TPA [12]. Indeed, Pepsi announced in 2011 plans for producing the first green PET bottle [13].

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Scheme 1. Chemical structures of TPA (left) and FDCA (right).

However, the replacement of petroleum-based TPA with renewable counterparts, either renewable TPA or FDCA, gives rise to relevant economical issues related with cost-competitiveness. Indeed, in this matter any renewable chemical causes the very same question ‘which is less expensive petroleum-based TPA or renewable-based TPA or is it FDCA?’ Therefore, having in consideration that currently renewable-based chemicals are still expensive one logical approach is to progressively replace PET with its furanic PEF homologue, copolymerising them. This strategy has already been exploited in other fields like for example in the partial substitution of fuel by biofuel where mixtures of both are used. Another example is poly(trimethylene terephthalate), with the trade name Sorona commercialised by the Dupont, using renewable 1,3-propanediol and petrochemical TPA [14]. However, this logic approach has not been reported for PET-co-PEF copolyesters in the last fifty years. Indeed, the literature on these copolyesters, is scanty, consisting only of a communication essentially focussing on their thermo-mechanical analysis [15]. Moreover, considering that the recent developments in the preparation of HMF [2] open the way to the large-scale production of FDCA from C6 carbohydrates, and the fact that the petrochemical TPA is still today one of the most important polymer building blocks, a revival of interest in FDCA and TPA derivatives seems amply justified. In the present work we report the random copolymerisation reactions of bis(hydroxy ethyl) derivatives of TPA and FDCA using different monomeric feed ratios. The ensuing polyesters were characterised in detail, focussing their chemical and mechanical properties. 2. Experimental section 2.1. Materials 2,5-Furandicarboxylic acid (FDCA, 97%), bis(2-hydroxyethyl) terephthalate (BHETP), antimony (III) oxide (Sb2O3, 99%), ethylene glycol (EG, 99.8%), as well as all other reagents and solvents were purchased from SigmaeAldrich Chemicals Co. and used as received. 2.2. Synthesis of bis(hydroxyethyl)-2,5-furandicarboxylate (BHEFDC) Typically BHEFDC was prepared by Fischer esterification of FDCA with an excess of EG, under acidic conditions, as previously reported [7]. FITR (n/cm1): 3368 (OH); 2950, 2884 (C]H); 1715 (C]O); 1575, 1506 (C]C); 1273 (CeO); 1009 (furan ring breathing); 964, 905, 762 (2,5-dibustituted furan). 1H NMR (CD3COCD3, d/ppm): 7.4 (s, H3/H4 furan ring); 4.4 (t, CH2O); 3.9 (t, CH2OH). 13C NMR (CD3COCD3, d/ppm): 158 (C]O); 148 (C2/C5 furan ring); 119 (C3/C4 furan ring); 68 (CH2COOH); 60.5 (CH2OH). ATReFTIR and 1H and 13 C NMR spectra were in accordance with previous results [7]. 2.3. Synthesis of random PET-ran-PEF copolyesters Reactions were carried out in bulk typically using approximately 3e6 g of BHETP monomers and a stoichiometric quantity of

BHEFDC comonomer (nBHETP/nBHEFDC w 4/1, 1/1, 1/4 or 1/9 mol/ mol), and using 1% w/w of Sb2O3 as catalyst. The mixtures were heated progressively from 110
C to 210
C during 5 h, and then kept for 2 h at that maximum temperature under high vacuum (w106 mbar) with constant stirring. The ensuing PET-ran-PEF polymers were dissolved in 1,1,2,2-tetrachloroethane (TCE) with some drops of 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) (w50 mL), and then precipitated, by pouring into an excess of cold methanol (w1 L) to remove the Sb2O3 and the soluble oligomers, filtered, dried under vacuum and weighted. Hereinafter, these polymers are referred as PET-ran-PEF 4/1, PET-ran-PEF 1/1, PET-ran-PEF 1/4 and PET-ran-PEF 1/9. 2.4. Analyses Attenuated total reflectance e Fourier transform infrared (ATRe FTIR) spectra were recorded with a PARAGON 1000 PerkineElmer FTIR spectrometer equipped with a single horizontal Golden Gate ATR cell. 1 H and 13C NMR spectra of the polymers dissolved in deuterated TCE were recorded, at 60
C, using a Bruker AMX 300 spectrometer operating at 300 or 75 MHz, respectively. All chemical shifts are expressed as parts per million downfield from tetramethylsilane used as internal standard. Elemental analyses (C and H) were conducted in triplicate with a LECO TruSpec analyser. Size-exclusion chromatography (SEC) analyses were performed with chromatographer equipped with a PL-EMD 960 light scattering detector, using a set of two PL HFIP columns (300  7.5 mm i.d.) and one PL HFIPgel guard column (50  7.5 mm i.d.), kept at 40
C and previously calibrated with polystyrene standards in the range 4290e96,000 Da. A mixture of CH2Cl2/CHCl3/HFP (70/20/10 in V/V/V%) was used as the mobile phase with a flow rate of 0.7 mL min1. All polymers were dissolved in CH2Cl2/CHCl3/HFP mixture (w9 mg mL1) and filtered through PTFE membrane before injection. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) analysis were performed using a Bruker Daltonik Autoflex III smartbean1 MALDI-TOF-MS mass spectrometer operating in the linear and reflectron positive ion mode. 2,5-Dihydroxybenzoic acid (DHB) was used as matrix in tetrahydrofuran (THF). Samples were dissolved in CH2Cl2/HFP (w5 mg mL1) and mixtures of sample and matrix in 1/1 ratio (V/V) were prepared by dried-droplet approach. An aliquot of the sample (1 mL) was applied on the probe, followed by the matrix solution (1 mL), finally the solvent was allowed to evaporate at room temperature to matrix crystallisation. Differential scanning calorimetry (DSC) thermograms were obtained with a Setaram DSC92 calorimeter using aluminium pans. Scans were conducted under nitrogen with a heating rate of 20
C min1 in the temperature range of 18e300
C. The second heating scans were performed after quenching the melted polymers in liquid nitrogen. Thermogravimetric analyses (TGA) were carried out with a Shimadzu TGA50 analyser equipped with a platinum cell, using platinum pans to encapsulate the samples (w5 mg). Typically, samples were heated at a constant rate of 10
C min1 from room temperature up to 800
C, under a nitrogen flow of 20 mL min1. The thermal decomposition temperatures were taken at the onset of significant (5%) weight loss from the heated sample. X-ray diffraction (XRD) analyses were performed using a Philips X’pert MPD instrument operating with CuKa radiation (l ¼ 1.5405980  A) at 40 kV and 50 mA. Samples were scanned in the 2q range of 3e50
, with a step size of 0.04
, and time per step of 50 s.

A.F. Sousa et al. / Polymer 54 (2013) 513e519

Dynamic mechanical analyses (DMA) of thick samples (10  5  1 mm) were performed with a Tritec 2000 DMA Triton equipment operating in the bending (dual cantilever) mode. Tests were performed at 1 and 10 Hz and the temperature was varied from 90 to 150
C at 2
C min1. 3. Results and discussion

Table 1 Results related to the polytransesterifications carried out in this study. PET-ran-PEF copolyester

Yield (%)a

M wb

Mw/Mnc

4/1 1/1 1/4 1/9

74 92 79 92

14,900 29,400 13,400 47,200

2.4 3.1 2.3 2.9

a

3.1. Synthesis and spectroscopic characterisation of PET-ran-PEF copolyesters PET-ran-PEF copolyesters were prepared in bulk by random polytransesterification reactions using variable proportions of BHETP and BHEFDC monomers (nBHETP/nBHEFDC w 4/1, 1/1, 1/4 or 1/ 9 mol/mol), and the classical antimony (III) oxide catalyst (Scheme 2 and Table 1). Table 1 presents the yield, molecular weight and molecular weight distributions obtained for the different copolyesters studied. The isolation yields of all copolyesters were around 80% (Table 1), quite independent of the stoichiometric ratio of BHETP/ BHEFDC used being an indication of the successful incorporation of both aromatic and furanic units into the copolyesters backbone. The weight-average molecular weight (Mw) of these polyesters varied between 13,000 and 47,000, and the polydispersity index (Mw/Mn) was close to 2 (Table 1). In terms of solubility all copolymers were found to dissolve only in 1,1,1,3,3,3-hexafluoro-2-propanol or mixtures of solvents containing 1,1,1,3,3,3-hexafluoro-2-propanol (e.g. 1,1,2,2-tetrachloroethane/HFP or CH2Cl2/CHCl3/HFP), among the numerous common organic solvents tested (chloroform, dichloromethane, acetone, tetrahydrofuran, etc.). This behaviour was already expected having in consideration that commercial PET, and also PEF, is only soluble in the very same solvents. Hence, this is a very first indication of the similarity between the copolyesters and the homopolyesters counterparts [5]. The ATReFTIR spectra of all the copolyesters synthesised in this work were found to be consistent with the corresponding macromolecular structures. Their spectra (Fig. 1) display a sharp band near 1713 cm1, arising from the C]O stretching vibration, typical of ester groups; and the CeO stretching band appeared around 1264 cm1. No significant absorption in the OH stretching region was detected, confirming that the polymers had reached a plausibly high reaction yield. Additionally, both characteristic bands of furan rings (1577, 1017, 964, 830, 764 cm1) and of benzenic rings (1122, 730 cm1) were detected. The main features of the 1H NMR spectra of furanicearomatic copolyesters (Fig. 2 and Table 2) were found to be in agreement with the FTIR spectral data, displaying both the characteristic resonances attributed to the protons of furan and of benzenic rings at d w7.3 and 8.1 ppm, respectively, thus confirming the incorporation of both these units in the copolyesters.

Scheme 2. Polytransesterification reaction of BHEFC with BHETP.

515

b c

Related to the amount of polymer recovered after precipitation in methanol. Weight-average molecular weight (Mn), determined by SEC in DCM/CHCl3/HFP. Polydispersity index (Mw/Mn) determined by SEC in DCM/CHCl3/HFP.

The relative amount of these units in the copolymers was estimated by the integration ratio of the above mentioned resonances (Table 2). It was found that BHETP was slightly more reactive than BHEFDC, despite their initial stoichiometric feed-ratio (Table 2). For example, PET-ran-PEF was prepared with an initial nBHETP/ nBHEFDC w 1/1 mol mol1, but the monomers actual incorporation in the copolyester was found to be equal to approximately 1.2/1. Two minor resonances at d w 4.0 and 4.5 ppm (CH2CH2OCH2CH2 and CH2OCH2) respectively, associated with etherification sidereactions were also detected [16]. The 13C NMR spectra of PET-ran-PEF copolyesters exhibit the resonances associated with the furan ring (C2, C5 at 146 ppm and C3, C4 at d119 ppm) and the benzenic ring (C20 , C30 , C50 , C60 at d119 ppm and C10, C40 at d133 ppm), with the methylene groups at d63 ppm and the carbonyl ester moieties at d157 and 165 ppm attributed respectively to furanic and benzenic counterparts. The average values of the elemental analyses of all furanice aromatic copolyesters (Table 3) are in close agreement with those calculated theoretically using the stoichiometric feed-ratio. However, a word of caution should be stressed, since these values are affected by the presence of vestigial TCE occluded in the copolyesters as shown in the TGA thermogram (Fig. 4), despite several days of drying (up to 1 week). The chemical structure of the copolyesters was further confirmed by MALDI-ToF-MS spectroscopy both in the linear and reflectron mode. Fig. 3 displays the spectrum of PET-ran-PEF ranging from m/z 500 to 5000. Importantly, two series of main peaks are separated by mass increments exactly equal to the mass of the benzenic and furanic repeating units, i.e., 192 and 182, respectively (see enlarged spectrum of Fig. 2) Additionally, NaTFA addition to samples was tested, but their spectra showed no

Fig. 1. ATReFTIR spectra of PET-ran-PEF 4/1 copolyester.

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Fig. 2. 1H NMR spectrum of PET-ran-PEF 4/1 in TCE d2.

relevant difference compared to those of samples without NaTFA addition. The spectroscopy results clearly suggest the success of the copolymerisations. 3.2. TGA, DSC and XRD analyses The TGA thermograms of copolyesters (Table 4 and Fig. 4) exhibit two major characteristic features, at a maximum degradation temperature (Td) of approximately 400 and 450
C (w60% weight loss), followed by a slower complete volatilisation ending near 600
C. The first two degradation steps are most probably associated with degradation of the furanic and benzenic units of copolyesters, because the corresponding PEF and PET homopolyesters degrade at different temperatures, Td w398 and 440
C, respectively [5,7]. Besides these two steps the progressive incorporation of higher quantities of BHEFDC into the PET-ran-PEF also has an effect in the thermal stability of the resulting copolyesters, lowering their Td, as can be observed in Table 4. All polyesters appeared to be thermally stable up to 260
C (less than 5% weight loss). The pristine PET-ran-PEF copolyesters exhibited a variable degree of crystallinity as indicated by their DSC thermograms

Table 2 Main peaks from the 1H NMR spectra of PET-ran-PEF copolyesters. Assignmenta

d/ppm

Multiplicityb

Table 3 Elemental analysis data of PET-ran-PEF copolyesters.a

Integration

Copolyester

PET-ran-PEF

4.00 4.51 4.73 7.28 8.14 [(AH20 , a b

H30 ,

CH2OCH2 CH2CH2OCH2CH2 CH2CH2 H3, H4 H20 , H30 , H50 , H60 H50 , H60 /2)/AH3, H4]

See Scheme 2. s ¼ singlet, t ¼ triplet.

t t s s s

(Table 4 and Fig. 5). As one could anticipate, the incorporation of both benzenic and furanic units into the polymer backbone in a random fashion has disrupted the typical semi-crystalline character of the pristine homopolymers counterparts [5], especially when equivalent amounts of PET and PEF were introduced (1/1). Indeed, the DSC trace (2nd heating scan) of PET-ran-PEF 1/1 copolyester displays no melting features, showing, instead, a baseline step, corresponding to the glass transition (Tg w 73.4
C). Also, PET-ran-PEF 1/4 copolyester showed a similar behaviour, with its DSC trace displaying a Tg around 75.4
C. However, when only 20% of furanic units were incorporated into the copolyester backbone (PET-ran-PEF 4/1) the ensuing copolyester was semi-crystalline, with its DSC trace (Fig. 5) displaying a melting peak at w220.1
C. After quenching the melted copolyester in liquid nitrogen, the tracing of the ensuing amorphous morphologies displayed a glass transition at w62.4
C (similar to that of PET) and a crystallisation exotherm with a maximum at w125.2
C, followed by the same melting pattern as that of the precipitated precursor. Also, PET-ran-PEF 1/9 first heating trace shows a similar a broad melting peak around w184.0
C. Additionally, using equivalent amounts of oligomeric PET and PEF a block copolyester was prepared (results not shown). As one could anticipate, this block PET-co-PEF copolyester was semicrystalline exhibiting in its second heating trace, after quenching, glass transition, crystallisation and melting features around 79.1,

4/1

1/1

1/4

1/9

1.2 1.4 11.4 1.0 10.7 5.4/1

0.2 0.3 4.3 1.0 2.5 1.2/1

0.4 0.4 4.0 1.7 1.0 1/3.4

0.3 0.3 8.4 3.9 1.0 1/7.8

4/1 1/1 1/4 1/9

C (%)

H (%)

Expb

Calc

Expb

Calc

59.2 56.9 53.4 52.7

60.6 57.8 54.8 53.8

4.2 3.9 3.6 3.5

4.0 3.8 3.5 3.4

a Exp and calc stand for experimental and calculated carbon and hydrogen percentages in the polyesters. b Each value is the average of three experiments with average standard deviation within 0.03e0.3.

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517

Table 4 Decomposition (Td), glass transition (Tg), crystallisation (Tc) and melting (Tm) temperatures of the PET-ran-PEF copolyesters. Copolyester d

PET PET-ran-PEF 4/1 1/1 1/4 1/9 PEFe

Tda

Tgb

Tcc

T mc

450.0

75.1

135.0

255.3

62.4 73.4 75.4 72.7 80.7

125.2 e e e 165.0

220.1 e e 184 213.8

408.2; 403.2; 385.7; 388.8; 398.0

450.9; 632.9 443.3; 592.1 414.4; 558.7 549.6

a Td was determined by TGA at 20
C min1 using the maximum degradation temperature. b Tg was determined by DSC at 20
C min1 (second heating trace) using midpoint approach. c Tc and Tm were determined by DSC at 20
C min1. d PET was synthesised under the same conditions as PET-ran-PEF copolyesters. e See Refs. [5,7] for TGA and DSC results of PEF synthesised under the same conditions as the copolyesters.

Fig. 3. MALDI-ToF-MS spectrum in the linear mode of PET-ran-PEF 4/1 and its enlargement between m/z w1200 and 1800.

125.8 and 255.9
C, respectively. The observation of just one melting peak is in accordance with the fact that the melting temperatures values of either commercial or lab PET and PEF homopolyesters are relatively close (250e265, 255 and 214
C, respectively) [7,17]. The XRD analyses of PET-ran-PEF copolyesters (Fig. 6) corroborated the essential amorphous or semi-crystalline character of these random copolyesters. PET-ran-PEF 1/1 and 1/4 are essentially amorphous, displaying XRD patterns (Fig. 6) with a pronounced amorphous halo around 2q w 20
and broad peaks. However, PET-ran-PEF 4/1 and 1/9 copolyesters preserved some degree of crystallinity, with their XRD patterns showing peaks at 2q w 16
, 22 and 25
. These patterns compared favourably with their homopolyesters counterparts [5,18]. 3.3. DMA analysis The dynamicalemechanical behaviour of PET-ran-PEF copolyesters was studied by DMA analyses (Table 5). The storage modulus (E0 ), loss modulus (E00 ) and tan d of these copolyesters having either a low or a high amount of furanic units (PET-ran-PEF

Fig. 4. TGA and DTGA (dweight dT1) thermogram of PET-ran-PEF 4/1 copolyester.

Fig. 5. DSC thermogram of PET-ran-PEF 4/1 copolyester.

4/1 and 1/9, respectively) were recorded and compared with those of commercial PET (bottle-grade). The E0 traces of copolyesters clearly show, as also observed with a commercial sample of PET, two relaxation transitions dependent on frequency (Fig. 7). Those are one broad step at sub-ambient

Fig. 6. XRD patterns of PET-ran-PEF copolyesters and PEF homopolyester.

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Table 5 Loss modulus (E0 ), storage modulus (E00 ) and tan d of PET-ran-PEF 4/1 and 1/9 copolyesters at b transition and at room temperatures. Tg determined by DSC and DMA (1 Hz) techniques. (E0  109)/Pa

(E00  107)/Pa

Tan d

a

(E00  107)/Pa

Tan d

At T20
C

At Tb PETa PET-ran-PEF 4/1 1/9

(E’  109)/Pa

Tg/
C DMA

2.3

1.1

0.047

2.0

6.6

0.033

98.4

1.0 1.8

5.6 8.8

0.046 0.049

1.0 1.7

4.6 7.0

0.046 0.042

67.5 85.4

DSC

62.4 72.7

Commercial PET sample.

temperatures corresponding to the b transition, usually ascribed to non-cooperative motion of the carbonyl groups and cooperative benzenic ring flips [19]; and another pronounced decrease of modulus at higher temperatures, corresponding to the a transition, i.e., the glass transition. The Tb of PET-ran-PEF 4/1 and 1/9 is equal to approximately 40.9 and 36.3
C, respectively; and Tg of the same copolyesters is equal to approximately 67.5 and 85.4
C (Table 5). The E0 trace of PET (Fig. 7) also displays similar relaxations, although at slightly lower temperature for b transition and at higher temperature for Tg (58.3 and 103.2
C, respectively). This interval corresponds to relatively broader operating temperature ranges for commercial PET compared to copolyesters, which is the temperature range where PET possesses the stiffness to resist deformation and the flexibility not to shatter under strain [20] is broader than the copolyesters. The E0 trace of a PEF homopolyester was previously reported [8], confirming the existence of an a transition around 95
C. However, the sub-ambient behaviour of the homopolymer was not previously reported. More importantly, the E0 values measured at b transition temperature, 20
C and in the region of the glass transition (Table 5) allowed to study the elastic behaviour of the copolyesters in these regions. Typically, the copolyesters incorporating a higher amount of furanic units had a higher E0 (PET-ran-PEF 1/9 > PET-ran-PEF 4/ 1), hence being more stiff. The Tg values obtained by DSC and DMA for both copolyesters are in the same region of values, being the observed differences ascribed to the different determination principles. The storage modulus and tan d traces (see for example Fig. 8) of copolyesters and PET sample obtained in the dual cantilever mode are in accordance with the occurrence of the transitions described above; displaying two peaks.

Fig. 8. Tan d of PET-ran-PEF 4/1 copolyester at 1 and 10 Hz.

4. Conclusions The partially renewable PET-ran-PEF copolyesters reported here showed average molecular weights, thermal and mechanical properties comparable with petrochemical derived materials. The most relevant copolyester corresponds to the PET-ran-PEF 4/1 incorporating 20% of renewable furanic units. This copolyester showed similar properties to commercial PET, displaying glass transition, crystallisation and melting temperatures at 62.4, 125.2 and 220.1
C, respectively; and thermal stability up to 260
C. The operating temperature ranges (40.9 to 67.5
C) determined by DMA were very close to those of PET. Work is in progress to expand the FDCA realm to other furan polymers, including biodegradable furanicealiphatic polyesters. Acknowledgements FCT is gratefully acknowledged for a post-doctorate grant to AFS (SFRH/BPD/73383/2010) and to a fellowship (BI/UI89/5419/2011) to MM. The authors wish to thank to FCT for funding project ‘Development of new polyesters derived from 2,5-furandicarboxylic acid‘ (PTDC/QUI-QUI/101058/2008). They also thank PNRC of FCT for analytical instrumentation support (POCI2010, FEDER, REEQ/515/ CTM/2005 POCI) and for funding CICECO (PEst-C/CTM/LA0011/2011). References

Fig. 7. Loss modulus (E0 ) of PET-ran-PEF 4/1 and 1/9 copolyesters and commercial PET at 1 and 10 Hz.

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