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Synthesis and characterization of some aliphatic–aromatic poly(Schiff base)s
European Polymer Journal 37 (2001) 2213±2216
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Synthesis and characterization of some aliphatic±aromatic poly(Schi base)s Otilia Catanescu a, Mircea Grigoras a, Georgiana Colotin a, Alina Dobreanu a, Nicolae Hurduc b, Cristofor I. Simionescu b,* a
b
``P. Poni'' Institute of Macromolecular Chemistry, 41A Gr. Ghica Voda Alley, 6600-Iasi, Romania Faculty of Chemical Engineering, Department of Macromolecules, ``Gh. Asachi'' Technical University, 71D Mangeron Boulevard, 6600-Iasi, Romania Received 28 December 2000; received in revised form 20 April 2001; accepted 30 April 2001
Abstract Polymers with azomethine structure containing 1,5-naphthyl or 1,4-phenyl moieties were synthesised through polycondensation of some dialdehydes with diamines. Both monomers and polymers were characterised by IR and 1 HNMR techniques. Thermogravimetric analyses were made for all the synthesised polymers in order to study their thermal behaviour. Ó 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction Several research teams made studies on poly(azomethine)s during the time. Interest for this type of materials is due to their good properties: thermal, conducting [1± 3], ®bre forming [4,5], liquid crystalline [6,7] and nonlinear optical [8,9] properties that are the result of their chemical structure. The high thermal stability of fully aromatic poly(Schi base)s is given by the great number of aromatic rings, the extent of the electronic conjugation over the entire molecule leading to polymers with high conducting properties. In order to lower the transition temperatures and to improve their solubility, several methods are used: the introduction of alkyl or alkoxy groups in the ortho-position of the aromatic ring [8], use of a mixture of solvents in polycondensation or the inclusion of aliphatic ¯exible spacers between main chain aromatic rings. This paper presents the synthesis and characterisation of some aliphatic±aromatic poly(Schi base)s obtained by polycondensation reactions of two aromatic
*
Corresponding author. Fax: +40-3221-1299. E-mail address: [email protected] (C.I. Simionescu).
diamines (1,4-phenylenediamine (PD) and 1,5-naphthalenediamine (ND)) with some aliphatic±aromatic dialdehydes.
2. Experimental 2.1. Materials Aldrich supplied 1,4-phenylenediamine (PD), 1,5naphthalenediamine (ND) and the catalyst (p-toluenesulfonic acid), while the dialdehydes were synthesised according to the literature data [10]. The monomers were puri®ed by recrystallization. The solvents (toluene and N ,N-dimethylformamide (DMF)) were supplied by Chimopar (Romania) and Fluka, respectively, and were used as received. 2.2. Monomer synthesis Dialdehydes were obtained according to the reactions presented in Scheme 1. 4,40 -Diformyl-a,--diphenoxyalkane and 4,40 -diformyl0 2,2 -dimethoxy-a,--diphenoxybutane were prepared as follows: 0.2 mol p-hydroxybenzaldehyde dissolved in 25 ml of DMF was added into a 250 ml three-necked ¯ask
0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 1 ) 0 0 1 1 9 - 7
2214
O. Catanescu et al. / European Polymer Journal 37 (2001) 2213±2216
2.4. Characterisation All monomers and polymers were characterised by IR (KBr pellet) and 1 H-NMR spectroscopy. IR spectra were recorded on a Specord M80 spectrometer, while 1 H-NMR spectra were obtained on a JNM-C 60HL (60 MHz) at room temperature, in CDCl3 . Also, a thermogravimetric study was performed for all polymers in order to investigate their thermal stability. The thermograms were recorded in air atmosphere on a MOM Budapest derivatograph, at a heating rate of 12.5°C/ min. Melting points were determined on an optical microscope (Boetius).
Scheme 1. Synthesis of the aliphatic±aromatic dialdehydes.
equipped with a condenser and magnetic stir bar. Then, 0.25 mol anhydrous sodium carbonate and 0.1 mol of corresponding a,--dibromoalkane dissolved in 25 ml DMF were also added to the reaction ¯ask. The mixture was heated for 4 h at 150°C under continuous stirring. After cooling, the product was poured into 2 l of cold water (approx. 5°C), then ®ltered. The precipitate was washed once with KOH and three times with water, dried and ®nally recrystallised from ethanol. Yields and some properties of the synthesised dialdehydes are listed in Table 1. 2.3. Polymer synthesis (general method) An equimolecular mixture of 5 mmol PD or ND and 5 mmol dialdehyde dissolved in 20 ml DMF were added into a 250 ml three-necked ¯ask equipped with a condenser, a collector tube and a magnetic stir bar. Then 2 ml toluene (in order to remove water as an azeotrop) and p-toluenesulfonic acid as catalyst were added. The reaction mixture was stirred 6 h at re¯ux under argon atmosphere. The product was precipitated in water, ®ltered o, then dried.
2.4.1. IR (KBr pellets), cm 1 2.4.1.1. Monomers. All monomers have similar spectra, although some dierences appear in the case of monomer M3 compared with monomers M1 and M2 . They all present characteristic signals for terminal aldehyde group at 1690±1700 cm 1 . Weak absorption peaks appear within the 3500±3300 and 3000±2000 cm 1 , respectively, region assigned to m C±H of naphthalene and phenylene rings, while strong absorption peaks appear within the 1700±1000 cm 1 domain attributed to m C±C and b C±H vibrations, respectively. Somewhat weaker signals, attributed to c C±H and ring vibrations, appear within the 850±400 cm 1 domain. Fig. 1 presents one characteristic IR spectrum of the monomers (e.g., M2 spectrum). 2.4.1.2. Polymers. There are visible and signi®cant changes in the spectra of the polymers in comparison with the spectra of the monomers. Some of the signals are disappeared, while others are much smaller in the amplitude. Also, the signal at 1610±1630 cm 1 and the obviously diminished signal at 1700 cm 1 clearly indicates the ±CH@N± link formed during the polymerisation process. The compared signals from the spectra of polymers, attributed to ±CHO and ±CH@N± groups, indicate a low degree of polymerisation (we assumed DP 6±11). Fig. 1 also presents the IR spectrum of the polymer P1 .
Table 1 Some properties of the monomers Yield (%)
Ma
Tm b (°C)
Elemental analysis Calculated
M1 M2 M3 a b
68 50 69
M ± molecular weight. Tm ± melting temperature.
270 298 358
100±102 93±95 155±158
Found
C (%)
H (%)
C (%)
H (%)
71.11 72.48 67.03
5.18 6.04 6.14
70.69 71.15 66.91
5.55 6.16 5.98
O. Catanescu et al. / European Polymer Journal 37 (2001) 2213±2216
2215
Scheme 2. Reaction scheme for polymer synthesis.
Fig. 1. IR spectra of monomer M2 (1) and polymer P1 (2).
2.4.2. 1 H-NMR (CDCl3 , TMS as internal standard, room temperature), d, ppm Due to the poor solubility of the polymers in common organic solvents, their 1 H-NMR spectra could not be properly recorded. There were obtained only broad signals situated somewhat in the same positions as in the monomers' spectra. The 1 H-NMR spectra corroborated with the IR spectra of the polymers suggested that the synthesis of polymers followed the reaction presented in Scheme 2 (Table 2). 2.5. Results and discussion The general reaction scheme for the synthesis of polymers and the structure of the poly(azomethine)s is given in Scheme 2. Because none of the polymers is soluble in common organic solvents, their molecular weights could not be obtained. We did not perform viscosimetric measure-
ments because the solubilization of poly(azomethine)s in sulphuric acid leads to the modi®cation of their structure (scission of azomethine linkage). This is clearly indicated by the IR spectra recorded for 1,3,4-oxadiazole containing polyazomethine before and after viscosity measurements (polymers prepared by Saegusa et al. [11]). The thermal stability of the polymers was investigated, the weight loss (%) thermograms being presented in Fig. 2. Data presented in Table 3 suggest that these polymers have good thermal stability (the starting weight loss temperatures for all polymers are situated within the 370±400°C domain), their behaviour being similar over the whole degradation process. This means that the small dierence between spacers (only two methylene groups) and the presence of the ±OCH3 group in the ortho position of polymer P5 have little in¯uence on their thermal stability. Analysing Fig. 2 one may say that the degradation process has only one stage, the polymers suering a main weight loss within 360±450°C domain. Based on their similar structures, one may assume that, due to the high temperature, the ±N@CH± linkage is the ®rst that is breaking, in all cases.
Table 2 The positions of the proton signals in the 1 H-NMR spectra of the monomers Monomer
d (ppm)
M1 M2 M3
9.7 (s, 1H, ±CHO), 6.75±7.75 (m, 8H, aromatic protons), 4.3 (t, 4H, ±O±CH2 ±) 9.4 (s, 1H, ±CHO), 6.70±7.9 (m, 8H, aromatic protons), 4.15 (t, 4H, ±O±CH2 ±), 2.1 (m, 4H, ±CH2 ±) 9.65 (s, 1H, ±CHO), 6.8±7.5 (m, 8H, aromatic protons), 4.2 (t, 4H, ±O±CH2 ±), 3.9 (s, 6H, ±O±CH3 ), 2.15 (m, 4H, ±CH2 ±)
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O. Catanescu et al. / European Polymer Journal 37 (2001) 2213±2216
In comparison with polyamide±azomethine ethers prepared by Li and Chang [10], no liquid crystalline properties were observed. This must be due to the length of the spacers that was too short compared with the rigid segment of the chain backbone. Also, the more pronounced rigidity of the polymers (the main reason for the absence of the liquid crystalline properties) in comparison with those synthesised by Li and Chang (with n 4) derives from the fact that our polymers are simply poly(azomethine)s and not polyamide±azomethine ethers, the amide group introducing some degree of ¯exibility within the chain.
References Fig. 2. Weight loss (%) vs. temperature for the synthesised polymers; (1) P1 , (2) P2 , (3) P3 , (4) P4 , (5) P5 .
Table 3 Some thermogravimetric characteristics of the synthesised polymers Symbol
Ts a
T1 (10% weight loss), °C
T2 (50% weight loss), °C
T3 (90% weight loss), °C
P1 P2 P3 P4 P5
369 390 384 400 393
425 433 413 425 415
647 660 650 660 620
853 865 815 875 840
a Ts ± starting weight loss temperature for the degradation process.
[1] Yang CJ, Jenekhe SA. Macromolecules 1995;28:1130. [2] Morgan PW, Kwolek SL, Pletcher TC. Macromolecules 1987;20:729. [3] Destri S, Porzio W, Dubitsky Y. Synth Met 1995;75:25. [4] Yang HH. Aromatic high-strength ®bers. New York: Wiley-Interscience; 1989. p. 641. [5] Morgan PW, Pletcher TC, Kwolek SL. Polym Prepr 1983;24:470. [6] Cerrada P, Oriol L, Pinol M, Serrano JL, Alonso PJ, Puertolas JA, Iribarren I, Munoz Guerra S. Macromolecules 1999;32:3565. [7] Ogiri S, Ikeda M, Kanazawa A, Shiono T, Ikeda T. Polymer 1999;40:2145. [8] Thomas O, Inganas O, Andersson MR. Macromolecules 1998;31:2676. [9] Weaver MS, Bradley DDC. Synth Met 1996;81:61. [10] Li C-H, Chang T-C. J Polym Sci Part A: Polym Chem 1990;28(13):3625. [11] Saegusa Y, Sekiba K, Nakamura S. J Polym Sci Part A: Polym Chem 1990;28(13):3647.
www.elsevier.com/locate/europolj
Synthesis and characterization of some aliphatic±aromatic poly(Schi base)s Otilia Catanescu a, Mircea Grigoras a, Georgiana Colotin a, Alina Dobreanu a, Nicolae Hurduc b, Cristofor I. Simionescu b,* a
b
``P. Poni'' Institute of Macromolecular Chemistry, 41A Gr. Ghica Voda Alley, 6600-Iasi, Romania Faculty of Chemical Engineering, Department of Macromolecules, ``Gh. Asachi'' Technical University, 71D Mangeron Boulevard, 6600-Iasi, Romania Received 28 December 2000; received in revised form 20 April 2001; accepted 30 April 2001
Abstract Polymers with azomethine structure containing 1,5-naphthyl or 1,4-phenyl moieties were synthesised through polycondensation of some dialdehydes with diamines. Both monomers and polymers were characterised by IR and 1 HNMR techniques. Thermogravimetric analyses were made for all the synthesised polymers in order to study their thermal behaviour. Ó 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction Several research teams made studies on poly(azomethine)s during the time. Interest for this type of materials is due to their good properties: thermal, conducting [1± 3], ®bre forming [4,5], liquid crystalline [6,7] and nonlinear optical [8,9] properties that are the result of their chemical structure. The high thermal stability of fully aromatic poly(Schi base)s is given by the great number of aromatic rings, the extent of the electronic conjugation over the entire molecule leading to polymers with high conducting properties. In order to lower the transition temperatures and to improve their solubility, several methods are used: the introduction of alkyl or alkoxy groups in the ortho-position of the aromatic ring [8], use of a mixture of solvents in polycondensation or the inclusion of aliphatic ¯exible spacers between main chain aromatic rings. This paper presents the synthesis and characterisation of some aliphatic±aromatic poly(Schi base)s obtained by polycondensation reactions of two aromatic
*
Corresponding author. Fax: +40-3221-1299. E-mail address: [email protected] (C.I. Simionescu).
diamines (1,4-phenylenediamine (PD) and 1,5-naphthalenediamine (ND)) with some aliphatic±aromatic dialdehydes.
2. Experimental 2.1. Materials Aldrich supplied 1,4-phenylenediamine (PD), 1,5naphthalenediamine (ND) and the catalyst (p-toluenesulfonic acid), while the dialdehydes were synthesised according to the literature data [10]. The monomers were puri®ed by recrystallization. The solvents (toluene and N ,N-dimethylformamide (DMF)) were supplied by Chimopar (Romania) and Fluka, respectively, and were used as received. 2.2. Monomer synthesis Dialdehydes were obtained according to the reactions presented in Scheme 1. 4,40 -Diformyl-a,--diphenoxyalkane and 4,40 -diformyl0 2,2 -dimethoxy-a,--diphenoxybutane were prepared as follows: 0.2 mol p-hydroxybenzaldehyde dissolved in 25 ml of DMF was added into a 250 ml three-necked ¯ask
0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 1 ) 0 0 1 1 9 - 7
2214
O. Catanescu et al. / European Polymer Journal 37 (2001) 2213±2216
2.4. Characterisation All monomers and polymers were characterised by IR (KBr pellet) and 1 H-NMR spectroscopy. IR spectra were recorded on a Specord M80 spectrometer, while 1 H-NMR spectra were obtained on a JNM-C 60HL (60 MHz) at room temperature, in CDCl3 . Also, a thermogravimetric study was performed for all polymers in order to investigate their thermal stability. The thermograms were recorded in air atmosphere on a MOM Budapest derivatograph, at a heating rate of 12.5°C/ min. Melting points were determined on an optical microscope (Boetius).
Scheme 1. Synthesis of the aliphatic±aromatic dialdehydes.
equipped with a condenser and magnetic stir bar. Then, 0.25 mol anhydrous sodium carbonate and 0.1 mol of corresponding a,--dibromoalkane dissolved in 25 ml DMF were also added to the reaction ¯ask. The mixture was heated for 4 h at 150°C under continuous stirring. After cooling, the product was poured into 2 l of cold water (approx. 5°C), then ®ltered. The precipitate was washed once with KOH and three times with water, dried and ®nally recrystallised from ethanol. Yields and some properties of the synthesised dialdehydes are listed in Table 1. 2.3. Polymer synthesis (general method) An equimolecular mixture of 5 mmol PD or ND and 5 mmol dialdehyde dissolved in 20 ml DMF were added into a 250 ml three-necked ¯ask equipped with a condenser, a collector tube and a magnetic stir bar. Then 2 ml toluene (in order to remove water as an azeotrop) and p-toluenesulfonic acid as catalyst were added. The reaction mixture was stirred 6 h at re¯ux under argon atmosphere. The product was precipitated in water, ®ltered o, then dried.
2.4.1. IR (KBr pellets), cm 1 2.4.1.1. Monomers. All monomers have similar spectra, although some dierences appear in the case of monomer M3 compared with monomers M1 and M2 . They all present characteristic signals for terminal aldehyde group at 1690±1700 cm 1 . Weak absorption peaks appear within the 3500±3300 and 3000±2000 cm 1 , respectively, region assigned to m C±H of naphthalene and phenylene rings, while strong absorption peaks appear within the 1700±1000 cm 1 domain attributed to m C±C and b C±H vibrations, respectively. Somewhat weaker signals, attributed to c C±H and ring vibrations, appear within the 850±400 cm 1 domain. Fig. 1 presents one characteristic IR spectrum of the monomers (e.g., M2 spectrum). 2.4.1.2. Polymers. There are visible and signi®cant changes in the spectra of the polymers in comparison with the spectra of the monomers. Some of the signals are disappeared, while others are much smaller in the amplitude. Also, the signal at 1610±1630 cm 1 and the obviously diminished signal at 1700 cm 1 clearly indicates the ±CH@N± link formed during the polymerisation process. The compared signals from the spectra of polymers, attributed to ±CHO and ±CH@N± groups, indicate a low degree of polymerisation (we assumed DP 6±11). Fig. 1 also presents the IR spectrum of the polymer P1 .
Table 1 Some properties of the monomers Yield (%)
Ma
Tm b (°C)
Elemental analysis Calculated
M1 M2 M3 a b
68 50 69
M ± molecular weight. Tm ± melting temperature.
270 298 358
100±102 93±95 155±158
Found
C (%)
H (%)
C (%)
H (%)
71.11 72.48 67.03
5.18 6.04 6.14
70.69 71.15 66.91
5.55 6.16 5.98
O. Catanescu et al. / European Polymer Journal 37 (2001) 2213±2216
2215
Scheme 2. Reaction scheme for polymer synthesis.
Fig. 1. IR spectra of monomer M2 (1) and polymer P1 (2).
2.4.2. 1 H-NMR (CDCl3 , TMS as internal standard, room temperature), d, ppm Due to the poor solubility of the polymers in common organic solvents, their 1 H-NMR spectra could not be properly recorded. There were obtained only broad signals situated somewhat in the same positions as in the monomers' spectra. The 1 H-NMR spectra corroborated with the IR spectra of the polymers suggested that the synthesis of polymers followed the reaction presented in Scheme 2 (Table 2). 2.5. Results and discussion The general reaction scheme for the synthesis of polymers and the structure of the poly(azomethine)s is given in Scheme 2. Because none of the polymers is soluble in common organic solvents, their molecular weights could not be obtained. We did not perform viscosimetric measure-
ments because the solubilization of poly(azomethine)s in sulphuric acid leads to the modi®cation of their structure (scission of azomethine linkage). This is clearly indicated by the IR spectra recorded for 1,3,4-oxadiazole containing polyazomethine before and after viscosity measurements (polymers prepared by Saegusa et al. [11]). The thermal stability of the polymers was investigated, the weight loss (%) thermograms being presented in Fig. 2. Data presented in Table 3 suggest that these polymers have good thermal stability (the starting weight loss temperatures for all polymers are situated within the 370±400°C domain), their behaviour being similar over the whole degradation process. This means that the small dierence between spacers (only two methylene groups) and the presence of the ±OCH3 group in the ortho position of polymer P5 have little in¯uence on their thermal stability. Analysing Fig. 2 one may say that the degradation process has only one stage, the polymers suering a main weight loss within 360±450°C domain. Based on their similar structures, one may assume that, due to the high temperature, the ±N@CH± linkage is the ®rst that is breaking, in all cases.
Table 2 The positions of the proton signals in the 1 H-NMR spectra of the monomers Monomer
d (ppm)
M1 M2 M3
9.7 (s, 1H, ±CHO), 6.75±7.75 (m, 8H, aromatic protons), 4.3 (t, 4H, ±O±CH2 ±) 9.4 (s, 1H, ±CHO), 6.70±7.9 (m, 8H, aromatic protons), 4.15 (t, 4H, ±O±CH2 ±), 2.1 (m, 4H, ±CH2 ±) 9.65 (s, 1H, ±CHO), 6.8±7.5 (m, 8H, aromatic protons), 4.2 (t, 4H, ±O±CH2 ±), 3.9 (s, 6H, ±O±CH3 ), 2.15 (m, 4H, ±CH2 ±)
2216
O. Catanescu et al. / European Polymer Journal 37 (2001) 2213±2216
In comparison with polyamide±azomethine ethers prepared by Li and Chang [10], no liquid crystalline properties were observed. This must be due to the length of the spacers that was too short compared with the rigid segment of the chain backbone. Also, the more pronounced rigidity of the polymers (the main reason for the absence of the liquid crystalline properties) in comparison with those synthesised by Li and Chang (with n 4) derives from the fact that our polymers are simply poly(azomethine)s and not polyamide±azomethine ethers, the amide group introducing some degree of ¯exibility within the chain.
References Fig. 2. Weight loss (%) vs. temperature for the synthesised polymers; (1) P1 , (2) P2 , (3) P3 , (4) P4 , (5) P5 .
Table 3 Some thermogravimetric characteristics of the synthesised polymers Symbol
Ts a
T1 (10% weight loss), °C
T2 (50% weight loss), °C
T3 (90% weight loss), °C
P1 P2 P3 P4 P5
369 390 384 400 393
425 433 413 425 415
647 660 650 660 620
853 865 815 875 840
a Ts ± starting weight loss temperature for the degradation process.
[1] Yang CJ, Jenekhe SA. Macromolecules 1995;28:1130. [2] Morgan PW, Kwolek SL, Pletcher TC. Macromolecules 1987;20:729. [3] Destri S, Porzio W, Dubitsky Y. Synth Met 1995;75:25. [4] Yang HH. Aromatic high-strength ®bers. New York: Wiley-Interscience; 1989. p. 641. [5] Morgan PW, Pletcher TC, Kwolek SL. Polym Prepr 1983;24:470. [6] Cerrada P, Oriol L, Pinol M, Serrano JL, Alonso PJ, Puertolas JA, Iribarren I, Munoz Guerra S. Macromolecules 1999;32:3565. [7] Ogiri S, Ikeda M, Kanazawa A, Shiono T, Ikeda T. Polymer 1999;40:2145. [8] Thomas O, Inganas O, Andersson MR. Macromolecules 1998;31:2676. [9] Weaver MS, Bradley DDC. Synth Met 1996;81:61. [10] Li C-H, Chang T-C. J Polym Sci Part A: Polym Chem 1990;28(13):3625. [11] Saegusa Y, Sekiba K, Nakamura S. J Polym Sci Part A: Polym Chem 1990;28(13):3647.