Poly(alkylene 2,5-furandicarboxylate)s (PEF and PBF) by ring opening polymerization

Article abstract of DOI:10.1016/j.polymer.2016.02.003

The preparation of cyclic ethylene and butylene 2,5-furandicarboxylate oligoesters and their conversion to furan-based polyesters poly(ethylene furanoate) (PEF) and poly(butylene furanoate) (PBF) by ring-opening polymerization (ROP) are described. The cyclic oligoesters were obtained in high yields by both high dilution condensation and thermal cyclodepolymerization methods, and they consisted of mixtures of small size species. Cyclic dimer, trimer and tetramer oligoesters were isolated by semipreparative chromatography and found to be crystalline compounds melting within the 140-200°C range. ROP catalyzed by Sn(Oct)₂ of both mixtures and individual species afforded PEF and PBF with weight-average molecular weights between 50,000 and 60,000 g mol^-1. Polymerization rate was found to be higher for butylene than for ethylene cyclic oligofuranoates, and also to increase slightly as cycle size decreased. The thermal properties of PEF and PBF prepared by ROP were in full agreement with those reported for these polyesters obtained by melt polycondensation.

Full text of DOI:10.1016/j.polymer.2016.02.003

Accepted Manuscript
Poly(alkylene 2,5-furandicarboxylate)s (PEF and PBF) by Ring Opening
Polymerization
Juan Carlos Morales-Huerta, Antxon Martínez de Ilarduya, Sebastián Muñoz-Guerra
PII:
S0032-3861(16)30083-0
10.1016/j.polymer.2016.02.003
JPOL 18435
DOI:
Reference:
To appear in: Polymer
Received Date: 19 November 2015
Revised Date: 31 January 2016
Accepted Date: 1 February 2016
Please cite this article as: Morales-Huerta JC, Martínez de Ilarduya A, Muñoz-Guerra S, Poly(alkylene
2,5-furandicarboxylate)s (PEF and PBF) by Ring Opening Polymerization, Polymer (2016), doi: 10.1016/
j.polymer.2016.02.003.
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FDCA
HDC
PC
COOH
HOOC
O
O
C
O
C
O
O
CDP
m
O
polyfuranoates
cyclic oligofuranoates
ROP

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Poly(alkylene 2,5-furandicarboxylate)s (PEF and PBF)
by Ring Opening Polymerization
Juan Carlos Morales-Huerta, Antxon Martínez de Ilarduya
and Sebastián Muñoz-Guerra*
Department d’Enginyeria Química, Universitat Politècnica de Catalunya, ETSEIB,
Diagonal 647,8028 Barcelona, Spain
Abstract: The preparation of cyclic ethylene and butylene 2,5-furandicarboxylate oligoesters
and their conversion to furan-based polyesters poly(ethylene furanoate) (PEF) and
poly(butylene furanoate) (PBF) by ring-opening polymerization (ROP) are described. The cyclic
oligoesters were obtained in high yields by both high dilution condensation and thermal
cyclodepolymerization methods, and they consisted of mixtures of small size species. Cyclic
dimer, trimer and tetramer oligoesters were isolated by semipreparative chromatography and
found to be crystalline compounds melting within the 140-200 ºC range. ROP catalyzed by
Sn(Oct)2 of both mixtures and individual species afforded PEF and PBF with weight-average
molecular weights between 50,000 and 60,000 g·mol-1. Polymerization rate was found to be
higher for butylene than for ethylene cyclic oligofuranoates, and also to increase slightly as
cycle size decreased. The thermal properties of PEF and PBF prepared by ROP were in full
agreement with those reported for these polyesters obtained by melt polycondensation.
Keywords: polyfuranoates, ring opening polymerization, bio-based aromatic polyesters
Introduction
2,5-Furandicarboxylic acid (FDCA) is a sugar-based compound that has
attained high notoriety in these last years due to its great potential as a renewable
platform for the synthesis of a wide variety of chemicals,1-3 and in particular of polymers
produced by polycondensation.4-5 The outstanding relevance of FDCA to the
development of new bio-based polyesters has been updated in an excellent review
published recently by Sousa et al.6 The chemical structure, thermal stability and
aromatic nature of FDCA are features that make this diacid specially suitable for
replacing terephthalic acid in the preparation of the important engineering
thermoplastics poly(ethylene terephthalate) (PET) and poly(butylene terephthalate)
(PBT) (Scheme 1). In fact, most of efforts made up to date on the development of
FDCA as monomer have been addressed to the synthesis of poly(ethylene 2,5-

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furandicarboxylate) (PEF) and poly(butylene 2,5-furandicarboxylate) (PBF)
homopolyesters7-9 and copolyesters,10-14 and Avantium in Netherlands started in 2010
the industrial production of PEF on multi-ton scale for fibers and packaging. The
aliphatic-furanic polyesters based on FDCA have been shown to have enhanced
11,15-17
thermo-mechanical
polyesters.
and biodegradable18-19 properties over existing terephthalate
Both PEF and PBF are usually synthesized from either pristine FDCA7-9 or its
dimethyl ester,15 by polycondensation in the melt through a two-steps process.
Organometallic catalysts, temperatures well above the Tm of the resulting
polyfuranoate, and periods of time of hours to days are required to attain high reaction
extents. The main processing difficult arises from the high melt viscosity achieved by
the reaction mixture that severely hampers mass transfer and makes therefore difficult
to remove the volatile condensation products.20 Post-polycondensation in the solid
state is performed as a third-step in order to increase further the molecular weight.14,15
The severe conditions applied in the polycondensation usually imply some
discoloration and eventual generation of minor amounts of secondary products.
Ring opening polymerization (ROP) is a well-stablished technique that has been
extensively used for the polymerization of a wide variety of cyclic compounds and in
particular of cyclic oligoesters.21 The relatively soft reaction conditions applied in this
method makes feasible to synthesize high molecular weight polymers in good yields
without perceivable chemical alteration of the product. Specific advantages of ROP are
a high polymerization rate, the absence of reaction coproducts, and the low viscosity
retained by the reaction until high conversions are attained. Consequently the
formation of secondary by-products is almost insignificant, the remaining monomer can
be easily removed, and discoloration is minimized. Both PET22-24 and PBT22,25,26 have
been successfully synthesized by ROP of cyclic oligo(alkylene terephthalate)s applying
temperatures between 200 ºC and 300 ºC and times of minutes. The oligoesters
required for these syntheses were furnished either by condensation of terephthaloyl

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dichloride with diols in highly diluted solution (HDC, high dilution condensation) or by
thermal depolymerization in solution of the corresponding polyester (CD,
cyclodepolymerization) methods. The CD method is particularly interesting with regards
to the potential recycling of the polyester.27
In the present paper we wish to report on the preparation of high molecular
weight PEF and PBF by ROP of the corresponding cyclic oligo(alkylene 2,5-
furandicarboxylate)s. Both the HDC and CD methods have been here applied for the
synthesis of these cyclic oligoesters, and the influence of cycle size on polymerization
rate has been investigated. The synthetic pathway followed in this work is depicted in
Scheme 2. The characteristics of the resulting PEF and PBF are compared with those
reported for the same polyesters obtained by polycondensation. A paper reporting the
preparation of PBF by ROP came out just in these last days. In such work
polymerization was accomplished using a mixture of cyclic butylene furanoates
prepared by HDC to obtain a PBF with moderate molecular weight.28
EXPERIMENTAL SECTION
Materials. 2,5-Furan dicarboxylic acid (FDCA, >99% purity) was a donation of Drs. K
Wilsens and B. Noordover (Technische Universiteit, of Eindhoven, NL). Other
reagents as 1,4-butanediol (BD, 99%), ethylene glycol (EG, 99%) and thionyl chloride
(SOCl2, 99%), as well as catalysts dibutyltin(IV) oxide (DBTO, 98%), di-
azabicyclo[2.2.2] octane (DABCO, 99%) and tin(II) ethylhexanoate (Sn(Oct)2, 99%),
were purchased from Sigma-Aldrich Co. Antioxidants Irganox 1010 and Irgafos 126
used for polycondensation reactions were gifts from BASF. Solvents used for
reaction, isolation and purification were of high-purity grade and used as received
except dichloromethane (DCM), tetrahydrofurane (THF) and dichlorobenzene (DCB)
that were dried on 3Å-molecular sieves. DABCO catalyst was purified by sublimation.

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1
Measurements. H and 13C NMR spectra were recorded on a Bruker AMX-300
spectrometer at 25 °C, operating at 300.1 and 75.5 MHz, respectively. Compounds
were dissolved in deuterated chloroform (CDCl3) or a mixture of trifluoroacetic acid
(TFA) and CDCl3, and spectra were internally referenced to tetramethylsilane (TMS).
1
About 10 and 50 mg of sample in 1 mL of solvent were used for H and 13C NMR,
1
respectively. Sixty-four scans were recorded for H and between 1,000 and 10,000
scans for 13C NMR. Molecular weight analysis was performed by GPC on a Waters
equipment provided with RI and UV detectors. 100 µL of 0.1% (w/v) sample solution
was injected and chromatographed with a flow of 0.5 mL·min-1. HR5E and HR2 Waters
linear Styragel columns (7.8 mm x 300 mm, pore size 103–104 Å) packed with
crosslinked polystyrene and protected with a precolumn were used. Molar mass
average and distributions were calculated against PMMA standards. High-performance
liquid chromatography (HPLC) analysis was performed at 25 °C in a Waters
apparatus equipped with a UV detector of Applied Biosystems, operating at 254 nm
wavelength, and a Scharlau Science column (Si60, 5µm; 250 x 4.6 mm). Cyclic
oligomers (1 mg) were dissolved in CHCl3 (1 mL) and eluted with hexane/1,4-dioxane
70/30 (v/v) at a flow rate of 1.0 mL·min-1. Semipreparative HPLC was performed
using a Scharlau Science column (Si60, 100 µm x 19 mm) with the cyclic oligomers
sample (35 mg) dissolved in CHCl3 (3 mL) and eluted with a mixture of hexane/1,4-
dioxane 70/30 (v/v) with a flow rate of 17 mL·min-1. Individual fractions were collected
with an UV-monitored Waters Fraction Collector III.
Matrix-assisted laser desorption/ionization time of flight (MALDI-ToF) mass
spectra were recorded in a 4700 Proteomics Analyser instrument of Applied
Biosystems (Proteomics Platform of Barcelona Science Park, University of
Barcelona). Spectra acquisition was performed in the MS reflector positive-ion mode.
About 0.1 mg of sample was dissolved in 50 µL of DCM and 2 µL of this solution were
mixed with an equal volume of DCM solution of anthracene (10 mg·mL-1), and the

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mixture left to evaporate to dryness onto the stainless steel plate of the analyser. The
residue was then covered with 2 µL of a solution of 2,5-dihydroxibenzoic acid in
acetonitrile/H2O (1/1) containing 0.1% TFA, and the mixture was left to dry prior to
exposition to the laser beam.
Thermogravimetric analysis (TGA) of cyclic oligomers and polymers was
performed on a Mettler-Toledo TGA/DSC 1 Star System under a nitrogen flow of 20
mL·min-1 at a heating rate of 10 °C·min -1 and within a temperature range of 30-700
°C. The non-destructive thermal behaviour was exami ned by differential scanning
calorimetry (DSC) within the 30-200 ºC range using a Perking-Elmer Pyris apparatus.
Thermograms were obtained from 4-6 mg samples at heating and cooling rates of 10
°C·min -1 under a nitrogen flow of 20 mL·min-1. Indium and zinc were used as
standards for temperature and enthalpy calibration, respectively. The glass transition
temperature (Tg) was taken as the inflection point of the heating traces recorded at 20
°C·min -1 from melt-quenched samples, and the melting temperature (Tm) was taken
as the maximum of the endothermic peak appearing on the heating traces recorded
from samples crystallized from the melt. X-rays diffraction was made in the
Synchrotron ALBA facility (Barcelona) using powder samples which were irradiated
with a bean energy corresponding to 0.1 nm wavelength.
Synthesis of cyclic oligomers by pseudo-high dilution cyclization (HDC). 2,5-
Furandicarbonyl dichloride (FDCA-Cl2) was prepared according to the method
reported by Gomes et al.7 with minor modifications. In brief, 6.4 mmol (1 g) of FDCA
was made to react with 2 mL of SOCl2 in the presence of 10 µL of dimethyl
formamide (DMF) for 8 hours under reflux. After removing the excess of SOCl2 the
residual product was purified by high vacuum sublimation. FDCA-Cl2 was obtained as
1
a white powder in 90% yield and m.p. = 79 °C. H NMR (
δ
ppm, CDCl3, 300 MHz):
7.60 (s, 2H). 13C NMR (
δ ppm, CDCl3, 75.5 MHz): 155.9, 149.4, 123.3. These NMR
spectra are accessible in the SI file (Figure SI-1).

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Cyclic oligomers c(BF)n and c(EF)n were synthesized by applying the method
reported by Brunelle et al.22 for the synthesis of oligo(alkylene phthalates).Error!
Bookmark not defined. A three-necked round bottom flask was charged with 25 mL
of DCM and cooled to 0°C, and then 12.5 mmol (1.40 g) of DABCO were added
under stirring. 5 mmol (0.96 g) of FDCA-Cl2 in 10 mL of DCM and 5 mmol (0.46 g) of
BD or 10 mL of EG (0.31 g) in 10 mL of THF were drop-wise added simultaneously
for 40 min using two addition funnels in order to maintain the reagents equimolarity in
the reaction mixture. The reaction was finished by adding 1 mL of water followed by 5
mL of 1M HCl, and after stirring for 5 min, it was diluted with DCM and filtered. The
filtrate was washed with 0.1M HCl, dried on MgSO4, and evaporated to dryness to
render a mixture of linear and cyclic oligomers. Linear oligomers were removed by
chromatography through a short column of silica gel using a cold mixture of
DCM/diethyl ether 90/10 (v/v) as eluent. The cyclic oligomeric mixture was
fractionated into individual size species by preparative HPLC using a mixture of
1
hexane/dioxane 60/40 (v/v). c(BF)n: H NMR (
δ
ppm, CDCl3, 300 MHz): 7.23, 7.24,
7.25 (3s, 2H), 4.40 (m, 4H), 1.92, 1.99 (2m, 4H), 13C NMR (
δ
ppm, CDCl3, 75.5 MHz):
1
158.1, 157.9, 146.7, 146.5, 118.7, 118.6, 118.5, 65.0, 64.8, 25.4. c(EF)n: H NMR
(
δ
ppm, CDCl3, 300 MHz): 7.37, 7.23, 7.21 (3s,4H), 4.68, 4.67, 4.65 (3s, 4H). 13C
NMR ( ppm, CDCl3, 75.5 MHz): 157.6, 157.5, 146.5, 119.3, 119.1, 62.8.
δ
Synthesis of cyclic oligomers by cyclodepolymerization (CD). c(BF)n and c(EF)n
were also prepared by cyclodepolymerization of PBF and PEF polyesters previously
synthesized by melt polycondensation as it will be described below. The procedure
recently reported by us29 for the preparation of cyclic oligo(hexamethylene
terephthalate)s was followed. 0.8 g of PBF or PEF (previously dried overnight in a
vacuum oven at 60 °C), 20 mL of dried DCB and 3% mo l of DBTO were introduced
into a 50 mL round-bottom flask fitted with a magnetic stirrer and a condenser. The
mixture was stirred for 7 days under reflux and then it was cooled at room

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temperature, filtered, and the solvent evaporated under vacuum at 50 °C. In order
to remove the linear oligomers the solid residue was chromatographed on a short
column of silica gel using a mixture of DCM and diethyl ether 90/10 (v/v) as eluent.
1
c(BF)n: Yield: 60%. H NMR (δ, CDCl3, 300 MHz): 7.23, 7.21, 7.20 (3s, 2H), 4.41
(m, 4H), 1.98, 1.92 (2m, 4H). 13C NMR (δ ppm, CDCl3, 75.5 MHz): 158.1, 158.0,
1
146.7, 146.5, 118.8, 118.6, 118.5, 65.0, 64.9, 64.8. c(EF)n: H NMR (δ ppm, CDCl3,
300 MHz): 7.35, 7.23, 7.21, (3s, 2H), 4.68, 4.67, 4.65 (3s, 4H). 13C NMR (δ ppm,
1
CDCl3, 75.5 MHz): 157.6, 157.5, 146.5, 119.3, 62.8. The H NMR spectra of the
c(BF)n and c(EF)n mixtures are accessible in the SI file (Figure SI-2).
Synthesis of PBF and PEF by polycondensation in the melt. Dimethyl 2,5-
furandicarboxylate (FDCA-Me2) was synthetized following the method reported by
Gubbels et al.30 based on the Fischer esterification of FDCA with MeOH. A round
bottom flask was charged with 25.6 mmol (4 g) of FDCA, 1.38 mol (55.3 g) of
MeOH, and 1mL of 12M HCl. The mixture left to react for 18 h under reflux and the
reaction was then stopped by adding 0.5M methanol solution of KOH. The solution
was then evaporated to dryness and the residue extracted with CHCl3. The extract
was then washed with water (200 mL), dried on MgSO4 and evaporated to render a
solid that was crystallized from CHCl3 upon adding hexane and cooling. Yield: 75%.
1
m.p.: 112 °C; H NMR (
δ
ppm, CDCl3, 300 MHz): 3.94 (s, 6H), 7.23 (s, 2H). 13C
NMR (δ ppm, CDCl3, 300 MHz): 52.4, 118.5, 146.9, 158.4. These NMR spectra are
accessible in the SI file (Figure SI-3).
The synthesis of PBF and PEF polyesters used for cyclodepolymerization
was carried out by polycondensation in the melt following the usual two-steps
method repeatedly described in literature.31 In the first step (transesterification),
10.9 mmol (2.0 g) of FDCA-Me2 was made to react with 23 mmol (2.15 g) of BD or
EG (1.42 g) in the presence of 5 µL of Sn(Oct)2 as catalyst and Irganox 1010 and
Irgafos 126 (0.1% relative of the total amount of the monomer) as antioxidants at

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180 and 225 ºC for PBF and PEF, respectively, in a three necked flask provided
with mechanical stirring and under a nitrogen atmosphere for 4 h. The
1
transesterification process was followed by H NMR spectroscopy and when the
FDCA-Me2 conversion exceeded 95%, the second step of polycondensation was
initiated by increasing the temperature up to 220 and 250 ºC for PBF and PEF,
respectively, and reducing the pressure to 0.5-1 mbar. The reaction was left to
proceed under such conditions for 4 h. Analysis of the obtained polyesters were
performed without previous treatment. PBF: Yield: 85%. m.p.: 168.2 °C. 1H NMR (
ppm, CDCl3/TFA, 300 MHz): 7.34 (s,2H), 4.49 (bm, 4H), 1.97 (bm, 4H) .13C NMR (
δ
δ
ppm, CDCl3/TFA, 75.5 MHz): 161.1, 147.1, 120.5, 67.2, 25.3. PEF: Yield: 80%.
1
m.p.: 210 °C. H NMR (
δ
ppm, CDCl3/TFA, 300 MHz): 7.30 (s, 2H), 4.71 (s, 4H).13C
1
NMR (
δ
ppm, CDCl3/TFA, 75.5 MHz): 159.3, 146.4, 120.2, 63.8. H NMR and 13C
NMR spectra of PBF and PEF as well as a brief account of their main
characteristics are included in the SI file (Figures SI-4 and Table SI-1).
Synthesis of PBF and PEF by ROP of c(BF)n and c(EF)n. 2.37 mmol (0.5 g) of
c(BF)n or 2.7 mmol (0.5 g) of c(EF)n coming from HDC along with 0.5% mol of
Sn(Oct)2 were dissolved in 5 mL of DCM in a vial and dried under vacuum at room
temperature for 24 h. Subsequently, the mixture was made to react for 2h into a
three-necked round-bottom flask provided with mechanical stirring at 220 and 250
°C for PBF and PEF, respectively. Samples at differ ent times were taken off to
1
follow the evolution in the molecular weight. PBF: H NMR (
δ
ppm, CDCl3/TFA, 300
MHz): 7.30 (s, 2H), 4.46 (m, 4H), 1.93 (m, 4H). 13C NMR (δ ppm, CDCl3/TFA, 75.5
1
MHz): 160.3, 146.7, 120.0, 66.6, 25.0. PEF: H NMR (δ ppm, CDCl3/TFA, 300 MHz):
7.29 (s, 2H), 4.70 (s, 4H).13C NMR (
120.1, 63.7.
δ ppm, CDCl3/TFA, 75.5 MHz): 159.1, 146.3,
For the synthesis of PBF from individual c(BF)m species the polymerization
reactions were carried out in the DSC. 5 mg of c(BF)2, c(BF)3 or c(BF)4 and 0.5 %-mol

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of Sn(Oct)2 were dissolved in 1 mL of DCM in a vial and dried under vacuum at room
temperature for 24 h. Aliquot amounts of the mixture were then placed in aluminium
pans heated at 220 ºC for periods of time going from 5 min up to 2 h. At scheduled
1
1
times the capsules were opened and the sample analysed by H NMR and GPC. H
NMR (sample obtained from c(BF)2) (
4.48 (m, 4H), 1.95 (m, 4H). 13C NMR (
120.5, 67.2, 25.3.
δ
δ
ppm, CDCl3/TFA, 300 MHz): 7.32 (s, 2H),
ppm, CDCl3/TFA, 75.5 MHz): 161.1, 147.1,
RESULTS AND DISCUSSION
Synthesis and characterization of cyclic oligo(alkylene 2,5-furandicarboxylate)s.
The synthesis of the cyclic oligo(alkylene 2,5-furandicarboxylate)s, abbreviated c(AF)n
with A being ethylene or butylene, was carried out by two well-known cyclization
methods, namely pseudo-high dilution (HDC) and cyclodepolymerization (CDP).
Results obtained by both methods are compared in Table 1.
The HDC method was developed by Brunelle et al.32 for the synthesis of a
variety of macrocycles containing carbonate or carboxylate functions. The method
consists of mixing carefully highly diluted solutions of the diacyl dichloride and the
appropriate diol in the presence of catalytic amounts of DABCO and one equivalent of
trimethylamine. The application of this method to the preparation of c(AF)n required
previously the preparation of the 2,5-furandicarbonyl dichloride (FDCA-Cl2), which was
successfully achieved by reaction of commercial 2,5-furandicarboxylic acid with SOCl2.
The cyclization reaction was conducted in DCM at 0 ºC and using reagents
concentrations of around 5 mM. The crude reaction product was obtained in ~80%
yield, and by 1H NMR, it was shown to contain mostly cyclic oligomers accompanied by
a small amount of linear species (Figure SI-5). The linear species could be efficiently
removed by flash chromatography and the purified product, which was obtained in
around 65% yield, consisted of a mixture of cyclic oligomers of varying small size
1
whose H NMR spectra did not present detectable signals arising from hydroxyl or

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carboxylic end groups (Figure 1). As it is shown in Figure 2, the analysis of the purified
(AF)m mixtures by HPLC chromatography combined with MALDI-ToF spectrometry
revealed that they mainly contained dimer, trimer and tetramer cycles together with
minor amounts of pentamer and others cycles of larger sizes. Cyclic dimer and trimer
together accounted for about 90% of the content of both c(BF)n and c(EF)n mixtures but
the ratio of these two species in the two mixtures was almost reversed. The c(BF)n
mixture was fractionated by semipreparative HPLC with a yield higher than 80% to
render homogeneous fractions of c(BF)2, c(BF)3 and c(BF)4 species whose cycle size
and purity could be ascertained by MALDI-Tof analysis (Figure 3). The 1H NMR spectra
of these fractions showed specific signals according to cycle size so that a clear
distinction between dimer and higher size cycles is feasible by comparing to each
other. These spectra are shown in Figure SI-6 of the SI file. The heating DSC traces of
these fractions together with those registered for the c(BF)n and c(EF)n mixtures are
compared in Figure 4a. Prominent endothermal peaks arising from melting and
appearing at temperatures increasing with cycle size were recorded from the three
homogeneous c(BF)n fractions. On the other hand, the DSC trace registered from the
c(BF)n mixture displayed a broad peak centered at ~147 ºC and covering the range of
temperatures observed for the three isolated fraction peaks. The DSC trace of the
c(EF)n mixture displayed a peak of similar features to that of c(BF)n but displaced about
40 ºC higher, which is a result according to the Tm values of their respective derived
polymers PBF (~170 ºC) and PEF (~210 ºC). The crystallinity present in both individual
and mixed samples was corroborated by powder X-ray diffraction at wide angles which
provided patterns containing peaks characteristic of crystalline material that
disappeared upon heating at temperatures above melting. (Figure SI-7). The thermal
stability of the c(BF)n and c(EF)n mixtures was examined by TGA under inert
atmosphere and the traces registered from the two mixtures are compared in Figure
4b. The two samples started to lose weight at temperatures near to 300 ºC with the
weight fall happening at ~380 ºC and ~390 ºC for c(EF)n and c(BF)n, respectively.

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The preparation of c(AF)n by CDP was then explored given the relevance that
this method has to the potential chemical recycling of PAF polyesters. We have
recently made use of this method with success for the synthesis of cyclic
oligo(hexamethylene terephthalate)s.29 In this case the previously synthesized PBF
and PEF polyesters were dissolved in DCB and subjected to heating at 180 ºC in the
presence of DBTO. Results were no very far from those obtained by the HDC method
so that cyclic oligomeric mixtures comprising essentially dimer, trimer and tetramer
were obtained in approximate 60% yields for both c(EF)n and c(BF)n (Figure 5).
However significant differences in cycle size composition were observed between the
two methods with a more equilibrated proportion being obtained by the HDC method.
Such differences are particularly noticeable for c(BF)n where the c(BF)2/c(BF)3 ratio
changed approximately from 2 to 1 according to cyclization was induced either by
condensation or depolymerization (Table 1). Since CDP took place at high
temperatures and long times, it is probably that transesterification reactions involving
interconversion of cycles of different sizes happened along with cycle formation. On the
contrary, the low temperatures and short times applied for HDC are unfavorable
conditions for the occurrence of interconversion reactions so cycle sizes initially
generated in the condensation reaction would be preserved. The different compositions
observed for the (AF)m mixtures could therefore respond to which kind of driven factor,
thermodynamic or kinetics, is operating in the process.
Synthesis of poly(alkylene 2,5-furandicarboxylate)s by ROP. The synthesis of
poly(butylene 2,5-furandicarboxylate) (PBF) and poly(ethylene 2,5-furandicarboxylate)
(PEF) was accomplished by ROP of c(BF)n and c(EF)n mixtures respectively, by
applying the usual melt procedure catalyzed by Sn(Oct)2. As it is shown in Figure 6, the
chemical constitution and purity of the resulting polyesters was ascertained by 1H NMR.
It is worthy to note that no signals arising from diethylene glycol units were detected in
the PEF spectrum despite that etherification involving hydroxyl end groups is a

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1
secondary reaction difficult to avoid in melt polycondensation (compare with the H
NMR spectra recorded from PEF obtained by polycondensation which is shown in
Figure SI-4). In order to investigate the influence of cycle size on the ROP of c(AF)n,
the homogeneous fractions c(BF)2, c(BF)3 and c(BF)4 were polymerized under identical
conditions to those used for the c(BF)n mixture, and polymer growing was compared for
the four systems. The study was also extended to the polymerization of the c(EF)n
mixture in order to compare results for different alkylene units. Polymer growing was
estimated by following the evolution of the molecular weight of the forming polyester
with time by GPC analysis of the reaction mass. The changes observed in both weight-
and number-average molecular weights along reaction time for polymerizations carried
out at different temperatures are shown in Figure 7. The inspection of these plots leads
to conclude the following: a) c(BF)n polymerized initially faster than c(EF)n but after two
hours of reaction similar molecular weights were reached in the two systems. In fact,
an asymptotic profile was observed in the first case whereas a tendentiously linear
trend was displayed by the second one. b) The molecular weight increasing rate was
found to be higher for smaller cycle sizes although such differences are mild and tend
to disappear at high conversions. c) The profiles obtained for the c(BF)n mixture were
comparable to those of the individual fractions revealing that polymerization proceeded
in this case at an approximate average rate. d) As expected, the polymerization rate
increased with temperature with variations being larger for c(BF)n than for c(EF)n;
furthermore polymerization of c(EF)n required higher temperatures than c(BF)n to attain
similar molecular weights.
The thermal properties of the PBF and PEF polyfuranoates samples obtained
after reaction for two hours at 240 ºC were then evaluated. The DSC and TGA traces
registered from them are depicted in Figure 8 and their most characteristic parameters
are collected in Table 2. Ranges of data reported by different authors for these
polyesters prepared by melt polycondensation are also included for comparison. As it
can be seen, the polyfuranoates obtained by ROP display molecular weights perfectly

ACCEPTED MANUSCRIPT
comparable to those obtained by polycondensation or even higher. The same can be
said about the decomposition, glass transition and melting temperatures.
A brief comment on the paper recently published on PBF28 obtained by ROP
should be made. In such work, PBF was synthesized from a mixture of cyclic (butylene
2,5-furandicarboxylate)s enriched in trimers and tetramers and with an average cycle
size significantly larger than that of the mixtures used in the present work. The
polymerization was there conducted in a DSC pan with the oligomeric sample mixed
with tetrakis(2-ethylhexyl) titanate catalyst and heating at 270 ºC for 15 min. The PBF
thus obtained showed a number-average molecular weight about 6,000 g·mol-1 and
values of Tg and Tm of 35 ºC and 169 ºC, respectively. In the light of our results (Figure
8) may be inferred that the relative low molecular weight obtained for PBF in that work
is very likely due to the short polymerization time applied and also to the relative larger
cycle sizes used for feeding. The low transition temperatures that are observed for the
synthesized sample is nothing more than a consequence of its low molecular weight;
the strong dependence of thermal parameters on molecular weight in PAF’s is a well-
known fact.
Conclusion
In the present work, PBF and PEF were successfully synthesized by ring
opening polymerization catalyzed by Sn(Oct)2. The cyclic oligoesters used for
feeding could be prepared in high yields by both high-dilution and thermal
cyclodepolymerization methods as mixtures containing substantially from dimer to
tetramer species. The cyclic oligo(butylene 2,5-furandicarboxylate) mixture could be
fractionated by semi-preparative HPLC to provide homogeneous dimer, trimer and
tetramer fractions. Polymerization of mixtures and individual fractions under the
same conditions revealed that polymerization rate was favored by smaller cycle
sizes. It was also found that the oligo(ethylene 2,5-furandicarboxylate) cycles were
more reluctant to polymerize than the butylene ones and they required higher

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reaction temperature to reach similar conversions. In all cases, polyfuranoates of
high molecular weight, exempted of detectable chain defects, and displaying
thermal parameters in perfect agreement with those reported in the literature for the
same polymers prepared by polycondensation were obtained in good yields. The
results reported in this papers demonstrate the potential of the ring opening
polymerization method as a suitable option for the synthesis of poly(alkylene
furanoate)s.
Acknowledgements
Financial support for this research was given by MINECO with grant MAT-
2012-38044-CO3-03. J. Carlos Morales thanks to CONACYT (Mexico) for the Ph.D.
grant awarded. Authors are indebted to Ana Gamarra Montes for her assistance
with XRD experiment and data processing.
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Table 1. Cyclic (Alkylene 2,5-furandicarboxylate) Oligomers: Compared Synthesis Results.
Methoda
c(AF)n
Precursors
Yield (%)b
Composition (n:2/3/4)c
Crude Flashed
Mixture
Fractionated
HDC
c(BF)n
c(EF)n
FDCA-Cl2 + BD
FDCA-Cl2 + EG
80
78
67
64
62/30/8
20/74/6
50/22/9
n.d.
CD
c(BF)n
c(EF)n
PBF
PEF
74
72
60
60
41/49/10
24/58/18
33/35/9
n.d.
aHDC: High Dilution Cyclization carried out in DCM at 0 ºC in the presence of DABCO/TEA; CD: Cyclodepolymerization
reaction carried out in DCB at 180 ºC catalysed by DBTO.
bYields for the crude oligomeric mixture and after removal of the linear species (flashed).
cComposition in c(BF)2, c(BF)3 and c(BF)4 before and after fractionation. n.d: not determined.
Table 2. Compared Properties of Poly(alkylene 2,5-furandicarboxylate)s
Obtained by ROP and Melt Polycondensation.
a
b
c
c
Method PAF Monomer
Mw
Ða
To
Tg
Tm
(g·mol-1)
(ºC)
(ºC) (ºC)
ROP
PBF
c(BF)n
58,000
2.3
273
41
168
c(BF)2
c(BF)3
c(BF)4
65,000
59,900
57,000
1.9
2.0
2.1
nd
nd
nd
40
42
41
171
169
168
PEF
c(EF)n
55,000
1.4
337
80
215
PCd
PBF
FDCA
PEF
65,000-
2.8-
310-400
30- 168-
FDCA
FDCA-
47,000-
80,000e
2.4-
n.d
300-390
n.d
80-
200-
239
aWeight-average molecular weight and dispersity measured by GPC.
bOnset degradation temperature corresponding to 10% of mass loss measured by TGA.
cGlass transition and melting temperatures measured by DSC.
dPBF and PEF obtained by polycondensation in the melt from FDCA or FDCA-Me2 and BD or EG; data
expressed as ranges of values reported in references 7-15.
eAfter SSP (solid-state postpolycondensation).

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O
O
C
C
PET
PBT
O
O
O
O
C
O
O
C
O
PEF
PBF
O
O
O
C
C
C
O
C
O
O
O
O
O
Scheme 1. Aliphatic-aromatic polyesters from terephthalic acid and 2,5-furandicarboxylic acid.
SOCl2
DMF
MeOH
HCl
COOH
HOOC
O
FDCA
COOMe
MeOOC
COCl
ClOC
O
O
FDCA-Me2
FDCA-Cl2
OH
m
OH
HO
m=1 or 2
DABCO
HO
m
m=1 or 2
O
m
O
m
DBTO
DCB, 180 ºC
O
C
O
C
O
O
C
O
C
O
O
n
O
m=1, PEF; m=2, PBF
m=2 c(BF)n; m=1 c(EF)n
Sn(Oct)2 220-250 ºC
Scheme 2. Synthesis of PEF and PBF by ROP of cyclic oligo(alkylene 2,5-furandicarboxylate)s
prepared either by condensation in solution or by cyclodepolymerization.

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TMS
a
c
O
O
C
O
C n
O
O
b
c(BF)n
a
c
b
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
(ppm)
TMS
a
O
b
O
C
O
C
O
O
b
a
n
c(EF)n
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
(ppm)
1
Figure 1. H NMR spectra of cyclic oligomers c(BF)n (top) and c(EF)n (bottom) mixtures
prepared by HDC with indication of peak assignments.

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100
c(BF)2
c(BF)2
90
80
70
60
50
40
30
20
10
0
210
c
(BF)3
c
(BF)4
CHCl3
5
0
10
15
20
25
30
35
40
45
400
600
800
1000
1200
1400
mass (m·z-1)
time (min)
100
c(EF)3
c(EF)3
80
60
40
20
0
182
c
(EF)2
c
(BF)4
CHCl3
5
0
10
15
20
25
30
35
40
45
400
600
800
1000
1200
1400
mass(m·z-1)
time (min)
Figure 2. HPLC chromatograms (left) and MALDI-TOF (right) spectra of cyclic oligomers c(BF)n
(top) and c(EF)n (bottom) mixtures obtained by HDC.

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c(BF)2
c(BF)3
c(BF)4
0
5
10 15 20 25 30 35 40 45
time (min)
c
(BF)
2 c(BF)3
653.1
443.5
c(BF)4
863.8
400 600 800 1000 1200 1400 1600 1800 2000
mass (m·z-1)
Figure 3. HPLC chromatograms (top) and MALDI-TOF spectra (bottom) of individual cyclic
oligo(butylene 2,5-furandicarboxylate)s obtained by HDC.

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146 °C
c
(BF)2
(BF)3
(BF)4
148 °C
153 °C
c
c
147 °C
c(BF)n
188 °C
c(EF)n
80 90 100 110 120 130 140 150 160 170 180 190 200
Temperature (°C)
0.0
100
80
60
40
20
0
-0.1
-0.2
c
(BF)n
c(EF)n
100
150
200
250
300
350
400
450
Temperature (°C)
Figure 4. Top: DSC of individual cyclic oligo(butylene 2,5-furandicarboxylate)s and c(BF)n and
c(EF)n mixtures. Bottom: TGA traces of c(BF)n and c(EF)n mixtures and their derivative curves.

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c
(BF)3
c
(BF)2
c
(BF)4
CHCl3
5
0
10
15
20
25
30
35
40
45
time (min)
c
(EF)3
c
(EF)2
c
(EF)4
CHCl3
0
5
10
15
20
25
30
35
40
45
time (min)
Figure 5. HPLC of c(BF)n (top) and c(EF)n (bottom) prepared by CD.

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a
a
c
O
O
C
O
C
O
O
b
n
PBF
TMS
b
c
*
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
(ppm)
TMS
a
O
O
C
O
C
O
O
b
n
PEF
*
b
a
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
(ppm)
Figure 6. 1H NMR spectra of PBF and PEF obtained via ROP. (*) Chlororform.

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70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
Mn
(BF)2
(BF)3
(BF)4
Mw
(BF)2
(BF)3
(BF)4
Mn
(BF)2
(BF)3
Mw
(BF)2
(BF)3
(BF)4
c
c
c
c
c
c
c
c
c
c(BF)4
c
c
200
210
220
Temperature (°C)
230
240
0
20
40
60
time (min)
80
100
120
70
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
Mn
Mw
260 °C
250 °C
240 °C
240 °C
220 °C
200 °C
240 °C
220 °C
200 °C
260 °C
250 °C
240 °C
Mw
Mn
0
20
40
60
time (min)
80
100
120
0
20
40
60
80
100
120
time (min)
Figure 7. Evolution of molecular weight in the ROP of cyclic oligo(alkylene 2,5-furandicarboxylate)s as a function of temperature and time. Top: Compared
individual cyclic oligo(butylene 2,5-furandicarboxylate)s. Bottom: Compared c(BF)n and c(EF)n mixtures for different temperatures.

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170 °C
165 °C
PBF
PEF
215 °C
214 °C
40 60 80 100 120 140 160 180 200 220
Temperature (°C)
100
0,0
80
60
40
20
0
-0,1
-0,2
-0,3
-0,4
PBF
PEF
100
200
300
400
500
600
Temperature (°C)
Figure 8. Top: First heating, cooling and second heating DSC traces of PBF and PEF. Bottom:
TGA traces registered under inert atmosphere of PBF and PEF.
26

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Highlights
1. Cyclic oligoesters of BF and EF were prepared in high yields by both high-dilution
and thermal cyclodepolymerization methods. ´
2. PBF and PEF were successfully synthesized by ring opening polymerization
catalyzed by tin octanoate.
3. The results demonstrate the potential of the ring opening polymerization method as
a suitable option for the synthesis of poly(alkylene furanoate)s.