Polyesters bearing furan moieties

Polyesters bearing furan moietiesIV. Solution and interfacial polycondensation of 2,2 '-

bis(5-chloroformyl-2-furyl)propane with various diols andbisphenols

Souhir Gharbia, Jean-Pierre Andreoletyb, Alessandro Gandinib,*aLaboratoire de SyntheÁse et Physicochimie Organique, FaculteÂ des Sciences de Sfax, 3038 Sfax, Tunisia

bEcole Franc° aise de Papeterie et des Industries Graphiques (INPG), BP65, 38402 Saint Martin d'HeÁres, France

Received 11 January 1999; received in revised form 18 March 1999; accepted 29 March 1999

Abstract

Polyesters based on a difuranic diacid chloride and various aliphatic diols or bisphenols were prepared bysolution and interfacial polycondensation. The latter procedure gave, after optimization, materials with much higher

molecular weights. These polymers were characterized in terms of both structure and thermal properties. # 2000Elsevier Science Ltd. All rights reserved.

1. Introduction

Polyesters bearing furan units in their backbone

have attracted only sporadic attention in the last few

decades. A recent review on furan-based polymers [1]

gives the state-of-the-art on this particular topic.

Essentially, after the work by Moore's group [1,2]

about twenty years ago, which covered a wide range of

structures, but often with little e�ort devoted to optim-

ization, the only other speci®c studies dealt with di�er-

ent synthetic approaches. Thus, [1,3], an unsaturated

furanic ester-alcohol was polymerized by transesteri®-

cation to give a crystalline photosensitive polyester.

More recently [4±6], the joint research between our

laboratories has produced a study on the use of novel

difuranic diesters, which were condensed with various

aliphatic diols through high-temperature polycondensa-

tion reactions. A thorough kinetic investigation was

conducted on these systems [6]. The ensuing polyesters

have regular structures and reasonably high molecular

weights [5], and are presently being characterised in

terms of their physical properties. The other furanic

polyesters reported in recent years [7] are based on the

use of 2,5-furandicarboxylic acid chloride with sugar-

derived diols and on a similar combination, but with

difuranic acidic monomers [8].

The pursuit of this collaboration has led us to exam-

ine the possibility of preparing furanic polyesters by

condensation routes, permitting the use of mild con-

ditions which could extend the realm of diols to be

coupled with our new difuranic monomers. In fact,

these structures can be obtained in good yields through

a general synthetic pathway which involves the con-

densation of a 2-furoate (a derivative of furfural) with

a wide variety of aldehydes and ketones [4,5], and rep-

resent therefore an interesting new addition to the

domain of monomers from renewable resources [1].

Therefore, solution as well as interfacial polyesteri®ca-

tion procedures were tested in order to verify this

European Polymer Journal 36 (2000) 463±472

0014-3057/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PII: S0014-3057(99 )00103-2

* Corresponding author. Fax: +33-4-7682-6933.

working hypothesis, and the present paper describesthe outcome of a preliminary set of experiments.

2. Experimental

2,2 '-bis(5-chloroformyl-2-furyl) propane 1 was pre-pared by treating the corresponding acid with SOCl2in the presence of a small aliquot of DMF. The acid

had in turn been obtained by saponi®cation of itsdiethyl ester [4,5] and subsequent acidi®cation. Thepuri®cation of 1 involved a double vacuum distillation

(bp 1708C/0.07 Torr) followed by two recrystallizationsfrom n-hexane: mp 468C. Its Fourier transform infra

red (FTIR) and 1H-NMR spectra con®rmed the

expected structure, namely FTIR (cmÿ1, KBr pellet):

3150 (1CH Fu), 2985 (CH3), 1740 (C1O), 1035(furan ring breathing mode), 980 and 815 (Fu); 300

MHz 1H-NMR �d from TMS in CDCl3): 1.68 (s, 6H,

CH3), 6.32 (d, 2H, H3Fu), 7.35 (d, 2H, H4Fu).

All diols and bis-phenols were commercial products.

They were puri®ed as follows: ethylene glycol 2a and1,4-butanediol 2b were vacuum distilled in the presence

of CaH2; 1,6-hexanediol 2c, 1,4-bis(hydroxymethyl)-

benzene 2d and 2,2 '-bis(hydroxyphenyl)propane(bisphenol A) 2e were thrice recrystallized from dry

toluene; 2,5-bis(hydromethyl)furan (a kind gift from

QO chemicals) 2f was vacuum sublimed at 708C/0.07

Fig. 1. 300 MHz 1H-NMR spectrum of polyester 1+2a in CDCl3.

S. Gharbi et al. / European Polymer Journal 36 (2000) 463±472464

Torr. High-purity hydroquinone 2g, methylhydroqui-

none 2h, phenylhydroquinone 2i and 2,7-bis(hydroxy)naphthalene 2j, were used as received.

The various solvents and Lewis bases employed in thisstudy were thoroughly puri®ed by standard techniques.

Four commercial phase-transfer agents, viz. triethylben-zylammonium chloride (TEBAC), tetrabutylammonium

bromide (TBAB), tetrabutylammonium bisulfate(TBAS) and hexadecyltrimethylammonium bromide

(HTAB) were used without further puri®cation.Solution polycondensations were carried out under

nitrogen with magnetic stirring using a wide variety ofconditions as discussed below, but with the common

principle of catalyzing the reaction through the intro-duction of a proton trap. Polymers were recovered by

precipitation into an excess of ethanol, ®ltration andvacuum drying at 608C to constant weight. The term

`yield' will be used in this work to express the amountof material obtained following these operations. The

oligomers soluble in ethanol were not isolated.Interfacial polymerizations were carried out at room

temperature using a 0.2 M NaOH aqueous solution/methylene chloride system stirred mechanically at 700

rpm. The bisphenol was dissolved in the basic aqueous

solution and the phase-transfer agent added to it, justbefore mixing it with the methylene chloride solution

containing the diacid chloride. Equal molar amountsof the complementary monomers were introduced ineach phase to give 0.2 M concentration for the acid

chloride in CH2Cl2 and a 0.1 M concentration of thebisphenol in the aqueous phase. At the end of the reac-tion, the resulting emulsion was poured into an excess

of ethanol, and the polyesters thus precipitated wereisolated as described above for the solution exper-iments.

Polymers were characterised by FTIR and 1H-NMRspectroscopy, inherent viscosity (measured in chloro-form at 258C with a polymer concentration of 3 g lÿ1),vapor- pressure osmometry (VPO), SEC (THF, ultra-

styragel, polystyrene calibration) and thermal analyses(DSC and TGA).

3. Results and discussion

The general polycondensation reaction scheme re-lated to this investigation is:

Fig. 2. FTIR spectrum (KBr pellet) of polyester 1+2d.

S. Gharbi et al. / European Polymer Journal 36 (2000) 463±472 465

In the reactions conducted in solution a proton trapinsured the removal of HCl, whereas in the case of

interfacial procedures, the presence of NaOH in theaqueous phase produced the corresponding neutraliz-ation.

3.1. Solution polymerization

Ethylene glycol 2a was selected for a thorough study

aimed at optimizing the polyester yield and molecularweight. Various solvents were tested ranging in po-larity and nucleophilic or electrophilic character fromtoluene to DMF and methylene chloride. No major

trend was observed within this large domain of mediasince yields varied only by a few percent and inherentviscosities �Z� ¯uctuated randomly between 0.16 and

0.22 dl gÿ1. The monomer concentration was changedbetween 0.5 and 2.2 M and this produced a consider-able increase in polymer yield, whereas Z remained

essentially constant. With a 1 M solution of 2a, themolar concentration of 1 was varied from the stoichio-metric value up to a molar excess of 10%. A maximumin both yields and Z was obtained with a 5% excess,

suggesting that a small amount of COCl moieties had,in fact, been hydrolyzed (the corresponding carboxylicacid function is inactive in these systems). All the

above preliminary runs were conducted in the presenceof 3 mol lÿ1 of pyridine. Triethylamine was also tested,but gave less encouraging results in terms of polymer

molecular weight. The role of the reaction temperaturewas also inspected: between 0 and 608C, no major

change was detected, but the most adequate tempera-

ture was around 258C. All reactions reached an asymp-

totic stillness, characterized by limiting values of both

polymer yield and inherent viscosity, which required

about 24 h.

The best conditions related to the system 1+2a can

be summarized as follows. The solution of acid chlor-

ide must be added dropwise for about 30 min to the

stirred diol solution kept at 08C. The best solvent was

found to be chloroform. After the addition of the acid

chloride, the polymerizing solution was allowed to

reach room temperature. The glycol concentration was

close to 1 M, with 5% excess of 1. Approximately

50% molar excess of pyridine was used with respect to

the HCl generated in the polycondensation. The reac-

tion time required to attain the asymptotic conditions

was 24 h. With these conditions, yields were reproduci-

bly close to 70% and Z reached 0.22 dl g-1. The Mn

value for this polymer, determined by VPO, was 2600,

whereas SEC gave a value of 4800 (Ip = 2.3). This dis-

crepancy must be attributed to low-molecular weight

impurities for VPO and the speci®c polymer structure

(radically di�erent from that of polystyrene) for SEC:

it seems likely that the actual value of Mn should lie

between those two limits.

The FTIR and 1H-NMR spectra of this polyester

con®rmed its expected structure and were indeed essen-

tially the same as those reported in our previous study

[4,5]. The major FTIR features included the ester

peaks at 1721 and 1294 cmÿ1, the vibrations arising

from the heterocycle at 3100, 1517, 1024, 950 and 760


cmÿ1 and the aliphatic CH2 and C±O modes at 2965and 1136 cmÿ1, respectively. Fig. 1 shows the basic res-

onances arising from the structure of the repeat units,but also the presence of the two methylene groupsattached to a terminal OH groups (two small peaks at3.9 and 4.4 ppm [4,5]). If the other end group in these

polyester chains was a COOH function, arising fromthe hydrolysis of the corresponding COCl moiety, theratio of the areas related to the di�erent methylene res-

onances, indicated a DPn of about 14, viz., an Mn ofabout 2500, in fair agreement with the value obtainedby VPO.

The application of the optimized operating mode to1+2b and 1+2c gave the same yields of the corre-sponding aliphatic polyesters, with inherent viscosities

attaining 0.25 dl gÿ1. The use of bisphenol 2e was lesssuccessful, since we only obtained 30% of an ethanol-

insoluble polymer with Z � 0:16 dl gÿ1 (Mn = 3000 byVPO and 4400 by SEC, Ip = 2.5), probably becausethis technique of polyesteri®cation was not suited tothe speci®c system (see below). The spectra of all these

products were consistent with their respective struc-tures.When we switched to the benzylic diol 2d, we found

that most of the parameters which had given the bestresults with the aliphatic counterparts were also suit-able, except that reactions were slower although they

gave higher yields and Z values if they were carried outfor 4 days (asymptotic results). Since 2d was insolublein chloroform, these reactions were in fact conducted

Fig. 3. 300 MHz 1H-NMR spectrum of polyester 1+2d in CDCl3.


in a 50/50 v/v mixture of CHCl3/pyridine and gave a90% yield of a polymer with Z � 0:48 dl gÿ1 (Mn =6000 by VPO and 8400 by SEC, Ip = 2.3). Figs. 2 and

3 report, respectively, the FTIR and the 1H-NMRspectra of this novel polyester. The corresponding ex-periments with 2f, carried out in the same conditions,gave the totally furanic polyester in 70% yield and Z �0:30 dl gÿ1 (Mn = 3400 by VPO and 6400 by SEC, Ip= 2.1). The spectroscopic characterization of this newpolymer also agreed with the expected structure.

3.2. Interfacial polycondensation

It is well known that phenols are particularly well

suited for interfacial polycondensations [9] because oftheir acidic character, which favours the formation ofthe corresponding phenoxy ions. The only mention of

a synthesis of this type, involving furanic monomers,dealt essentially with the use of the various isomers offurandicarboxylic acid chloride with bisphenols [10]:

the polyesters obtained had very low-molecularweights, as suggested by their modest intrinsic viscos-ities.

We chose the system 1+2e to carry out a detailedsearch for optimal synthetic conditions. The par-

ameters scanned were: the nature of the organic

medium; the role of the monomer concentration inboth phases; the e�ect of the pH of the aqueous

phase; the nature and the concentration of thephase-transfer agent and the reaction temperature.

The best results were obtained by using a 0.1 M

concentration of 2e in a 0.2 M NaOH solution(lower concentrations gave poor results and higher

concentrations produced the partial hydrolysis of thepolyester), a 0.2 M concentration of 1 in methylene

chloride (in toluene the polymer precipitated during

the synthesis), 0.12 mmol of TBAB in a total volumeof 75 ml (50 ml of aqueous solution + 25 ml of

CH2Cl2 solution), for reactions carried out at room

temperature for 3 h. The ensuing furanic-aromaticpolyester was obtained in excellent yields (95±98%)

and had high inherent viscosity (1.1±1.15 dl gÿ1, corre-sponding to a VPO-based Mn at the limit of detection

of the osmometer and a SEC-based Mn of 30.000, Ip= 2.3). Typical FTIR and 1H-NMR spectra of thispolymer are given in Figs. 4 and 5, respectively, and

Fig. 4. FTIR spectrum (KBr pellet) of polyester 1+2e.


show that all the features are consistent with a regular

structure.The use of 2g resulted in an insoluble polymer

which precipitated early in the reaction. Its FTIR spec-

trum was qualitatively identical to that shown in Fig.4, in tune with the fact that these two polyesters bear

all the same chemical moieties, albeit in di�erent pro-portions. The disruption of chain symmetry by the use

of the corresponding methyl-substituted hydroquinone2h produced a soluble polyester in near-quantitative

yields with Z � 0:92 dl gÿ1. With the phenyl-substi-tuted homologue 2i, both yields (around 75%) and in-

herent viscosities (about 0.6 dl gÿ1) were lower,

probably because of the steric hindrance associatedwith this monomer.

The replacement of 2e by 2j in reactions conductedin the same conditions, gave the corresponding fura-

nic±naphthalenic polyester in a 90% yield with Z �0:58 dl gÿ1 (Mn = 10.000 by VPO and 14.000 by SEC,Ip = 2.4), whose structure was veri®ed spectroscopi-

cally. The lower viscosity, with respect to the phenolichomologue, stems most probably from the fact that 2jwas not puri®ed.

3.3. Thermal characterization of the polyesters

The DSC thermograms of the various polymers pre-

pared in this study indicated a predominantly amor-phous character with clear-cut glass transitions, asshown in the typical tracing of Fig. 6. Table 1 reports

Fig. 5. 300 MHz 1H-NMR spectrum of polyester 1+2e in CDCl3.


the values of Tg as a function of the structure of the

polyester. The trends are quite straightforward in that

the increase in chain sti�ness is accompanied by a cor-

responding increase in Tg, particularly when going

from furanic-aliphatic to furanic-aromatic structures.

The TGA analysis of these polymers showed a good

thermal stability with an onset of degradation (Table

1) consistently higher than 3008C, except for the polye-

sters 1+2d and 1+2f whose somewhat higher fragility

must be attributed to the methylene groups attached to

Table 1

Average molecular weights (obtained by SEC), glass transition temperature and onset of thermal decomposition of the various

furanic polyesters synthesized in this work

� Polymers obtained in solution.�� Polymers obtained by interfacial polycondensation.


Fig. 6. DSC tracing of polyester 1+2e.

Fig. 7. TGA tracings of polyesters 1+2d and 1+2e.


the benzene and furan rings, respectively. This is con-

®rmed by the actual shape of the thermograms, asshown in Fig. 7, in which the benzylic structure 1+2d

shows two distinct degradation steps, compared with asingle feature (and at a higher temperature) for the

phenolic counterpart 1+2e.

4. Conclusion

With respect to the transesteri®cation technique

adopted in our previous study, furanic polyestersobtained by polycondensation in solution had similarmolecular weights, whereas phase transfer proceduresallowed us to conduct the synthesis of furanic-aromatic

polyesters with considerably higher chain lengths. Thelatter technique proved particularly interesting alsobecause it provided a means of obtaining these new

structures in near-quantitative yields.

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Fig. 7 (continued)


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Polyesters bearing furan moieties