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A preliminary study on polyhydrazides incorporating furan moieties
European Polymer Journal 38 (2002) 667–673 www.elsevier.com/locate/europolj
A preliminary study on polyhydrazides incorporating furan moieties Aljia Afli a, Souhir Gharbi a, Rachid El Gharbi a, Yves Le Bigot b, Alessandro Gandini c,* a b
Laboratoire de Synth ese et Physicochimie Organique, Facult e des Sciences, Universit e de Sfax, 3038 Sfax, Tunisia Laboratoire de Catalyse, Chimie Fine et Polym eres, ENSCT, 118 route de Narbonne, 31077 Toulouse Cedex, France c Mat eriaux Polym eres, Ecole Francßaise de Papeterie et des Industries Graphiques (INPG), BP65, 38402 Saint Martin d’H eres, France Received 30 May 2001; accepted 26 July 2001
Abstract Solution and interfacial polycondensation of difuranic dihydrazides with aromatic or aliphatic dicarboxylic acid dichlorides led to the corresponding polyhydrazides which were characterized in terms of structure and average chain length. Their conversion to the corresponding polyoxadiazoles was also examined. Model compounds were prepared to facilitate the synthesis and the characterization of the polymers. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polycondensation; Polyhydrazides; Furans; Oxadiazoles
1. Introduction The synthesis of polymers bearing furan moieties constitutes an interesting way to exploit the vegetable biomass, as shown by the rich literature dealing with a large variety of structures and properties [1]. Most studies on furanic polymers based on polycondensation reactions have been carried out using 2,5-furandicarboxylic acid (or its derivatives) as the basic monomer [1]. Recently however, we reported the synthesis of several polyesters [2–4] and polyamides [5–7] obtained from new difuranic monomers and various diols or diamines. The pursuit of this investigation based on the use of this novel difuranic structure led us to examine the possibility of preparing furanic polyhydrazides. To the best of our knowledge, this family of furanic polymers has been the subject of only one short report which described the reaction of 2,5-furandicarboxylic acid dichloride with terephthalic dihydrazide or the 2,5-furan * Corresponding author. Tel.: +33-4-76826947; fax: +33-476826933. E-mail address: [email protected] (A. Gandini).
homologue in amidic solvents [8]. These polycondensations yielded low molecular weight products which were not characterized in any detail. The lack of more thorough studies on this topic prompted us to undertake a systematic approach to the synthesis and properties of this type of material and to their conversion to polyoxadiazoles. The presence of both furan and 1,3,4-oxadiazole heterocycles in the final macromolecules could give rise to thermally stable materials with potential applications in electronic devices. We report here some preliminary results on (i) the application of polycondensation techniques requiring mild conditions for the preparation of polyhydrazides based on difuranic dihydrazides and aliphatic, aromatic or furanic dicarboxylic acid dichlorides and (ii) their cyclodehydration to the corresponding polyoxadiazoles which might display interesting properties as materials for electronic applications.
2. Experimental The syntheses of model compounds and polymers called upon the use of furoyl chloride (FC), furyl
0014-3057/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 1 ) 0 0 2 3 7 - 3
668
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
hydrazide (FH), hydrazine hydrate (HMH), ethyl 2furoate (EF), terephthaloyl chloride (TC), adipoyl chloride (AC), various aldehydes and ketones and triethyl benzyl ammonium chloride (TEBAC). All these reagents were high purity commercial products and were therefore employed as received. All solvents were purified by standard techniques prior to their use.
groups, viz. (i) in N-methyl pyrrolidone (NMP) at 0 °C for 6 h (the products were precipitated with an excess of water); (ii) in CH2 Cl2 /H2 O/OH at room temperature for 3 h (the products precipitated out of the organic phase and were separated by filtration).
2.1. Preparation of furanic monomers
The polycondensations of the difuranic dihydrazides 1–9 with AC or TC were conducted following two alternative techniques, namely: (i) Frazer and Wallenberger’s method [9] was adopted without modifications for solution polycondensations. This procedure involved the polycondensation under nitrogen of dihydrazides with dicarboxylic acid dichlorides in NMP at 0 °C for 12 h. (ii) Interfacial polycondensations were carried out at room temperature using a 0.2 M NaOH aqueous solution containing TEBAC coupled with a methylene chloride organic phase. Equal molar amounts of the complementary monomers were introduced in each phase to give a 0.2 M concentration of the dicarboxylic acid dichloride in CH2 Cl2 and a 0.1 M concentration of the difuranic dihyrazide in the aqueous phase. The resulting biphasic reaction mixture was then stirred at 700 rpm for 3 h at room temperature before being poured into an excess of water in order to precipitate the poly-
A wide range of difuranic dihydrazides were prepared in good yields from the corresponding diesters, obtained in turn by the condensation of EF with the corresponding aldehyde or ketone as reported in detail elsewhere [3], following the procedure described previously by Frazer and Wallenberger [9] applied to the reaction of the difuranic diester with HMH, as shown in Scheme 1. All these novel dihydrazides were purified by recrystallization from water and their structure confirmed by elemental analysis and FTIR, 1 H- and 13 CNMR spectroscopy. 2.2. Synthesis of model oligomers The dimeric and trimeric model compounds 10–12 (see below) were prepared by two different procedures, using the appropriate stoichiometry between functional
2.3. Synthesis of polyhydrazides
Scheme 1. Synthesis of difuranic dihydrazides.
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
hydrazide. The ensuing white powder was isolated by filtration, washed with acetone and vacuum dried at 90 °C to constant weight.
669
ucts. As an example, Fig. 1 shows the 1 H-NMR and FTIR spectra related to 12. 3.2. Polymers
2.4. Cyclodehydration reaction Model compound 12 and polymer 1 þ TC were dehydrated with an excess of thionyl chloride under reflux for 30 min to yield the corresponding 1,3,4-oxadiazole and furan–oxadiazole polymer in 94–97% yields. 2.5. Structural and size characterization The structures of all products were assessed by FTIR, H- and 13 C-NMR spectroscopy. Inherent viscosities were determined at 25 °C from DMSO or H2 SO4 solutions with polymer concentrations of 1.5 or 5 g l1 , respectively. 1
3. Results and discussion 3.1. Model compounds The three model compounds 10–12 were prepared in order to gain a preliminary insight into the feasibility and optimization of the corresponding polycondensations. These compounds were the result of the stoichiometric condensation of FH with FC, AC or TC, respectively, as shown in Scheme 2. The yields of each product obtained with homogeneous reactions were 97–98%. Interfacial condensations led to yields which depended mostly on the OH concentration in the aqueous phase. The best results were obtained when this concentration was equivalent to that of the NH2 groups of FH. The various spectra of 10–12 confirmed their expected structures, without evidence of spurious prod-
The overall polycondensation process related to difuranic dihydrazides 1–9 and TC or AC, leading to the corresponding polyhydrazides, is shown in Scheme 3. Table 1 gives the conditions and results related to the two techniques of polycondensation used in this study to prepare some of the relevant materials. The yields express the percentage of polymer precipitated in water. The progress of the reaction was followed by the evolution of the inherent viscosity and the changes in the 1 H-NMR spectra of samples withdrawn at regular intervals from the reaction media. The higher molecular weight obtained by interfacial polycondensation, as suggested by the fact that polymers became insoluble in DMSO and had to be characterized by dissolving them in sulphuric acid, coupled with high yields, were also encountered with other monomer combinations and suggested that this synthetic procedure was better suited to the synthesis of our novel polyhydrazides. The FTIR, 1 H- and 13 C-NMR spectra of all these polymers confirmed their regular linear structure, devoid of detectable anomalies. Fig. 2 shows the 1 H-NMR spectra of dihydrazide 1 and its corresponding furanic– aromatic polymer 1 þ TC as examples of satisfactory structural features. 3.3. Oxadiazoles Aromatic polyhydrazides are known to undergo cyclodehydration either by heating in vacuo at 100–200 °C, or in solution using an appropriate dehydrating
Scheme 2. Synthesis of model compounds (10, m.p. 231 °C; 11, m.p. 210 °C; 12, m.p. 304 °C).
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A. Afli et al. / European Polymer Journal 38 (2002) 667–673
Fig. 1. 1 H-NMR (in DMSO d6 ) and FTIR (KBr pellet) spectra of 12.
Scheme 3. Synthesis of furanic-aromatic or -aliphatic polyhydrazides.
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
671
Table 1 Yields and inherent viscosities (ml g1 , 1.5 g l1 in DMSO at 25 °C) of polyhydrazides Polymer
1 þ AC
1 þ TC
2 þ AC
2 þ TC
8 þ AC
8 þ TC
Solution
Yield (%) ginh
81 38
98 56
89 39
96 21
95 50
93 35
Interfacial
Yield (%) ginh
71 53
75 17a
85 11a
65 17a
95 12a
98 19a
a
Measured at 5 g l1 in 98% H2 SO4 at 25 °C.
Fig. 2. 1 H-NMR spectra (in DMSO d6 ) of dihydrazide 1 and polyhydrazide 1 þ TC.
agent [10]. In order to assess the feasibility of this chemical modification on our polymers, we tested it first on model compound 12 and then applied it to polymer 1 þ TC (Scheme 4). The presence of 1,3,4-oxadiazole rings between the furanic and aromatic moieties was established by spec-
troscopic analyses. Thus, the FTIR spectra of cyclo12 (Fig. 3) and cyclo(1 þ TC) showed the presence of the characteristic peaks of the 1,3,4-oxadiazole ring at 1620 and 970 cm1 and the absence of the original peaks at 3300 and 1670 cm1 arising from the OCNHNHCO functions. These features suggested that the cyclodehydration
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A. Afli et al. / European Polymer Journal 38 (2002) 667–673
Scheme 4. Synthesis of 1,3,4-oxadiazoles.
Fig. 3. 1 H-NMR (in DMSO d6 ) and FTIR (KBr pellet) spectra of cyclo12.
reaction had gone to completion, as confirmed by the fact that the 1 H-NMR spectrum of cyclo12 (Fig. 3) showed no residual resonance in the region of 9–10 ppm, indicating the absence of hydrazide NH protons.
4. Conclusion Polyhydrazides with reasonably high molecular weights, bearing furanic and aromatic or aliphatic
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
moieties in their backbone, can be obtained in good yields by reacting the appropriate combinations of furanic dihydrazides and diacid dichlorides. These materials undergo cyclodehydration to give the corresponding polyoxadiazoles. Work is in progress to optimize these syntheses, extend the range of structures and assess the properties of all ensuing materials. References [1] Gandini A, Belgacem MN. Progr Polym Sci 1997;22:1203. [2] Khrouf A, Boufi S, El Gharbi R, Gandini A. Polym Int 1999;48:649.
673
[3] Khrouf A, Abid M, Boufi S, El Gharbi R, Gandini A. Macromol Chem Phys 1998;199:2755. [4] Gharbi S, Andreolety JP, Gandini A. Eur Polym J 2000;36:463. [5] Gharbi S, Gandini A. Acta Polym 1999;50:293. [6] Abid M, El Gharbi R, Gandini A. Polymer 2000;41: 3555. [7] Gharbi S, Afli A, El Gharbi R, Gandini A. Polym Int 2001;50:509. [8] Heertjes PM, Kok GJ. Delft Progr Rep 1974;A1:59. [9] Frazer AH, Wallenberger FT. J Polym Sci 1964;A2: 1137,1147. [10] Sato M, Yokoyama M. J Polym Sci Polym Chem 1980; 18:2751.
A preliminary study on polyhydrazides incorporating furan moieties Aljia Afli a, Souhir Gharbi a, Rachid El Gharbi a, Yves Le Bigot b, Alessandro Gandini c,* a b
Laboratoire de Synth ese et Physicochimie Organique, Facult e des Sciences, Universit e de Sfax, 3038 Sfax, Tunisia Laboratoire de Catalyse, Chimie Fine et Polym eres, ENSCT, 118 route de Narbonne, 31077 Toulouse Cedex, France c Mat eriaux Polym eres, Ecole Francßaise de Papeterie et des Industries Graphiques (INPG), BP65, 38402 Saint Martin d’H eres, France Received 30 May 2001; accepted 26 July 2001
Abstract Solution and interfacial polycondensation of difuranic dihydrazides with aromatic or aliphatic dicarboxylic acid dichlorides led to the corresponding polyhydrazides which were characterized in terms of structure and average chain length. Their conversion to the corresponding polyoxadiazoles was also examined. Model compounds were prepared to facilitate the synthesis and the characterization of the polymers. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polycondensation; Polyhydrazides; Furans; Oxadiazoles
1. Introduction The synthesis of polymers bearing furan moieties constitutes an interesting way to exploit the vegetable biomass, as shown by the rich literature dealing with a large variety of structures and properties [1]. Most studies on furanic polymers based on polycondensation reactions have been carried out using 2,5-furandicarboxylic acid (or its derivatives) as the basic monomer [1]. Recently however, we reported the synthesis of several polyesters [2–4] and polyamides [5–7] obtained from new difuranic monomers and various diols or diamines. The pursuit of this investigation based on the use of this novel difuranic structure led us to examine the possibility of preparing furanic polyhydrazides. To the best of our knowledge, this family of furanic polymers has been the subject of only one short report which described the reaction of 2,5-furandicarboxylic acid dichloride with terephthalic dihydrazide or the 2,5-furan * Corresponding author. Tel.: +33-4-76826947; fax: +33-476826933. E-mail address: [email protected] (A. Gandini).
homologue in amidic solvents [8]. These polycondensations yielded low molecular weight products which were not characterized in any detail. The lack of more thorough studies on this topic prompted us to undertake a systematic approach to the synthesis and properties of this type of material and to their conversion to polyoxadiazoles. The presence of both furan and 1,3,4-oxadiazole heterocycles in the final macromolecules could give rise to thermally stable materials with potential applications in electronic devices. We report here some preliminary results on (i) the application of polycondensation techniques requiring mild conditions for the preparation of polyhydrazides based on difuranic dihydrazides and aliphatic, aromatic or furanic dicarboxylic acid dichlorides and (ii) their cyclodehydration to the corresponding polyoxadiazoles which might display interesting properties as materials for electronic applications.
2. Experimental The syntheses of model compounds and polymers called upon the use of furoyl chloride (FC), furyl
0014-3057/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 1 ) 0 0 2 3 7 - 3
668
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
hydrazide (FH), hydrazine hydrate (HMH), ethyl 2furoate (EF), terephthaloyl chloride (TC), adipoyl chloride (AC), various aldehydes and ketones and triethyl benzyl ammonium chloride (TEBAC). All these reagents were high purity commercial products and were therefore employed as received. All solvents were purified by standard techniques prior to their use.
groups, viz. (i) in N-methyl pyrrolidone (NMP) at 0 °C for 6 h (the products were precipitated with an excess of water); (ii) in CH2 Cl2 /H2 O/OH at room temperature for 3 h (the products precipitated out of the organic phase and were separated by filtration).
2.1. Preparation of furanic monomers
The polycondensations of the difuranic dihydrazides 1–9 with AC or TC were conducted following two alternative techniques, namely: (i) Frazer and Wallenberger’s method [9] was adopted without modifications for solution polycondensations. This procedure involved the polycondensation under nitrogen of dihydrazides with dicarboxylic acid dichlorides in NMP at 0 °C for 12 h. (ii) Interfacial polycondensations were carried out at room temperature using a 0.2 M NaOH aqueous solution containing TEBAC coupled with a methylene chloride organic phase. Equal molar amounts of the complementary monomers were introduced in each phase to give a 0.2 M concentration of the dicarboxylic acid dichloride in CH2 Cl2 and a 0.1 M concentration of the difuranic dihyrazide in the aqueous phase. The resulting biphasic reaction mixture was then stirred at 700 rpm for 3 h at room temperature before being poured into an excess of water in order to precipitate the poly-
A wide range of difuranic dihydrazides were prepared in good yields from the corresponding diesters, obtained in turn by the condensation of EF with the corresponding aldehyde or ketone as reported in detail elsewhere [3], following the procedure described previously by Frazer and Wallenberger [9] applied to the reaction of the difuranic diester with HMH, as shown in Scheme 1. All these novel dihydrazides were purified by recrystallization from water and their structure confirmed by elemental analysis and FTIR, 1 H- and 13 CNMR spectroscopy. 2.2. Synthesis of model oligomers The dimeric and trimeric model compounds 10–12 (see below) were prepared by two different procedures, using the appropriate stoichiometry between functional
2.3. Synthesis of polyhydrazides
Scheme 1. Synthesis of difuranic dihydrazides.
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
hydrazide. The ensuing white powder was isolated by filtration, washed with acetone and vacuum dried at 90 °C to constant weight.
669
ucts. As an example, Fig. 1 shows the 1 H-NMR and FTIR spectra related to 12. 3.2. Polymers
2.4. Cyclodehydration reaction Model compound 12 and polymer 1 þ TC were dehydrated with an excess of thionyl chloride under reflux for 30 min to yield the corresponding 1,3,4-oxadiazole and furan–oxadiazole polymer in 94–97% yields. 2.5. Structural and size characterization The structures of all products were assessed by FTIR, H- and 13 C-NMR spectroscopy. Inherent viscosities were determined at 25 °C from DMSO or H2 SO4 solutions with polymer concentrations of 1.5 or 5 g l1 , respectively. 1
3. Results and discussion 3.1. Model compounds The three model compounds 10–12 were prepared in order to gain a preliminary insight into the feasibility and optimization of the corresponding polycondensations. These compounds were the result of the stoichiometric condensation of FH with FC, AC or TC, respectively, as shown in Scheme 2. The yields of each product obtained with homogeneous reactions were 97–98%. Interfacial condensations led to yields which depended mostly on the OH concentration in the aqueous phase. The best results were obtained when this concentration was equivalent to that of the NH2 groups of FH. The various spectra of 10–12 confirmed their expected structures, without evidence of spurious prod-
The overall polycondensation process related to difuranic dihydrazides 1–9 and TC or AC, leading to the corresponding polyhydrazides, is shown in Scheme 3. Table 1 gives the conditions and results related to the two techniques of polycondensation used in this study to prepare some of the relevant materials. The yields express the percentage of polymer precipitated in water. The progress of the reaction was followed by the evolution of the inherent viscosity and the changes in the 1 H-NMR spectra of samples withdrawn at regular intervals from the reaction media. The higher molecular weight obtained by interfacial polycondensation, as suggested by the fact that polymers became insoluble in DMSO and had to be characterized by dissolving them in sulphuric acid, coupled with high yields, were also encountered with other monomer combinations and suggested that this synthetic procedure was better suited to the synthesis of our novel polyhydrazides. The FTIR, 1 H- and 13 C-NMR spectra of all these polymers confirmed their regular linear structure, devoid of detectable anomalies. Fig. 2 shows the 1 H-NMR spectra of dihydrazide 1 and its corresponding furanic– aromatic polymer 1 þ TC as examples of satisfactory structural features. 3.3. Oxadiazoles Aromatic polyhydrazides are known to undergo cyclodehydration either by heating in vacuo at 100–200 °C, or in solution using an appropriate dehydrating
Scheme 2. Synthesis of model compounds (10, m.p. 231 °C; 11, m.p. 210 °C; 12, m.p. 304 °C).
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A. Afli et al. / European Polymer Journal 38 (2002) 667–673
Fig. 1. 1 H-NMR (in DMSO d6 ) and FTIR (KBr pellet) spectra of 12.
Scheme 3. Synthesis of furanic-aromatic or -aliphatic polyhydrazides.
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
671
Table 1 Yields and inherent viscosities (ml g1 , 1.5 g l1 in DMSO at 25 °C) of polyhydrazides Polymer
1 þ AC
1 þ TC
2 þ AC
2 þ TC
8 þ AC
8 þ TC
Solution
Yield (%) ginh
81 38
98 56
89 39
96 21
95 50
93 35
Interfacial
Yield (%) ginh
71 53
75 17a
85 11a
65 17a
95 12a
98 19a
a
Measured at 5 g l1 in 98% H2 SO4 at 25 °C.
Fig. 2. 1 H-NMR spectra (in DMSO d6 ) of dihydrazide 1 and polyhydrazide 1 þ TC.
agent [10]. In order to assess the feasibility of this chemical modification on our polymers, we tested it first on model compound 12 and then applied it to polymer 1 þ TC (Scheme 4). The presence of 1,3,4-oxadiazole rings between the furanic and aromatic moieties was established by spec-
troscopic analyses. Thus, the FTIR spectra of cyclo12 (Fig. 3) and cyclo(1 þ TC) showed the presence of the characteristic peaks of the 1,3,4-oxadiazole ring at 1620 and 970 cm1 and the absence of the original peaks at 3300 and 1670 cm1 arising from the OCNHNHCO functions. These features suggested that the cyclodehydration
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A. Afli et al. / European Polymer Journal 38 (2002) 667–673
Scheme 4. Synthesis of 1,3,4-oxadiazoles.
Fig. 3. 1 H-NMR (in DMSO d6 ) and FTIR (KBr pellet) spectra of cyclo12.
reaction had gone to completion, as confirmed by the fact that the 1 H-NMR spectrum of cyclo12 (Fig. 3) showed no residual resonance in the region of 9–10 ppm, indicating the absence of hydrazide NH protons.
4. Conclusion Polyhydrazides with reasonably high molecular weights, bearing furanic and aromatic or aliphatic
A. Afli et al. / European Polymer Journal 38 (2002) 667–673
moieties in their backbone, can be obtained in good yields by reacting the appropriate combinations of furanic dihydrazides and diacid dichlorides. These materials undergo cyclodehydration to give the corresponding polyoxadiazoles. Work is in progress to optimize these syntheses, extend the range of structures and assess the properties of all ensuing materials. References [1] Gandini A, Belgacem MN. Progr Polym Sci 1997;22:1203. [2] Khrouf A, Boufi S, El Gharbi R, Gandini A. Polym Int 1999;48:649.
673
[3] Khrouf A, Abid M, Boufi S, El Gharbi R, Gandini A. Macromol Chem Phys 1998;199:2755. [4] Gharbi S, Andreolety JP, Gandini A. Eur Polym J 2000;36:463. [5] Gharbi S, Gandini A. Acta Polym 1999;50:293. [6] Abid M, El Gharbi R, Gandini A. Polymer 2000;41: 3555. [7] Gharbi S, Afli A, El Gharbi R, Gandini A. Polym Int 2001;50:509. [8] Heertjes PM, Kok GJ. Delft Progr Rep 1974;A1:59. [9] Frazer AH, Wallenberger FT. J Polym Sci 1964;A2: 1137,1147. [10] Sato M, Yokoyama M. J Polym Sci Polym Chem 1980; 18:2751.