- Email: [email protected]
Facile synthesis of new optically active poly(amide–imide)s derived from N,N′-(pyromellitoyl)-bis-l -leucine diacid chloride and aromatic diamines under microwave irradiation
European Polymer Journal 37 (2001) 2435±2442
www.elsevier.com/locate/europolj
Facile synthesis of new optically active poly(amide±imide)s derived from N ,N 0-(pyromellitoyl)-bis-L -leucine diacid chloride and aromatic diamines under microwave irradiation Shadpour E. Mallakpour *, Abdol-Reza Hajipour *, Sakineh Habibi Organic Polymer Chemistry Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, I.R. Iran Received 3 January 2001; received in revised form 13 June 2001; accepted 14 June 2001
Abstract Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) was reacted with L -leucine (2) in a mixture of acetic acid and pyridine (3:2) and the resulting imide-acid [N ,N 0 -(pyromellitoyl)-bis-L -leucine diacid] (4) was obtained in high yield. The compound (4) was converted to the N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) by reaction with thionyl chloride. A new facile and rapid polycondensation reaction of this diacid chloride (5) with several aromatic diamines such as 4,40 -diaminodiphenylsulfone (4,40 -sulfonyldianiline) (6a), 4,40 -diaminodiphenyl methane (6b), p-phenylenediamine (6c), m-phenylenediamine (6d), 2,4-diaminotoluene (6e) and benzidine (6f) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol. The polymerization reactions proceeded rapidly and are completed within 12 min, producing a series of optically active poly(amide±imide)s with good yield and moderate inherent viscosity of 0.28±0.46 dl/g. All of the above polymers were fully characterized by IR, elemental analyses and speci®c rotation. Some structural characterization and physical properties of these optically active poly(amide±imide)s are reported. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Pyromellitic dianhydride; Optically active polymers; Microwave-assisted rapid polycondensation; Poly(amide±imide)s; Microwave oven; Inherent viscosity
1. Introduction Recently there has been growing interest in the application of microwave irradiation in chemical reactions. The reactions are very fast and are completed within a short period of time [1±3]. Recently we have used microwave irradiation for the synthesis of organic compounds as well as macromolecules [4±11]. The synthesis and application of optically active polymers have been paid more attention recently. Polymers with chiral structures are biologically very important [12]. Recently, we have synthesized optically active polymers by dierent methods [13±16] such as modi®-
cation of polybutadiene with an optically active substituted urazole group [13] Diels±Alder-ene reactions [14,15] and reaction of an optically active monomer with several diamines via solution polymerization [16]. This paper reports a rapid and highly ecient method for the synthesis of new optically active poly(amide± imide)s (PAI)s from the polycondensation reaction of N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride with aromatic diamines under microwave irradiation.
2. Experimental 2.1. Materials
*
Corresponding authors. Tel.: +98-311-891-3168; fax: +98311-891-2350. E-mail address: [email protected] (S.E. Mallakpour).
Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) (from Merck Chemical Co.) was
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 5 1 - 3
2436
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
puri®ed by recrystallization from acetic anhydride follow by sublimation, 4,40 -diaminodiphenylsulfone (6a) and 4,40 -diaminodiphenylmethane (6b) were puri®ed by recrystallization from water and water/ethanol respectively. 1,4-phenylenediamine (6c) and 1,3-phenylenediamine (6d) and 2,4-diaminotoluene (6e) were puri®ed by sublimation. The other chemicals (from Fluka Chemical Co., Aldrich Chemical Co. and Riedel±deHaen AG) were used as obtained without further puri®cation. 2.2. Apparatus The apparatus used for the polycondensation was a Samsung domestic microwave oven (2450 MHz, 900 W) without any modi®cation, but all of the polymerization reactions were carried out in a hood with strong ventilation. 2.3. Measurements IR spectra were recorded on Shimadzu 435 IR spectrophotometer. Spectra of solids were carried out using KBr pellets. Vibrational transition frequencies are reported in wave number (cm 1 ). Band intensities are assigned as weak (w), medium (m), shoulder (sh), strong (s) and broad (br). Inherent viscosities were measured by a standard procedure using a Cannon Fenske Routine Viscometer (Germany). Speci®c rotations were measured by a Perkin±Elmer-241 Polarimeter (Germany). Thermal gravimetric analysis (TGA) data for polymers were taken on a Mettler TGA-50 in nitrogen atmosphere at a rate of 10°C/min. Elemental analyses were performed by Tarbiet Moderres University, Tehran, I.R. Iran.
3. Monomer synthesis 3.1. N,N 0 -(pyromellitoyl)-bis-L -leucine diacid (4) Into a 25 ml round-bottomed ¯ask 1.00 g (4:58 10 3 mol) of pyromellitic dianhydride (benzene-1,2,4,5tetracarboxylic dianhydride) (1), 1.200 g (9:170 10 3 mol) of L -leucine (2), 10 ml of mixture of acetic acid and pyridine (3:2) and a stirring bar were placed. The mixture was stirred and re¯uxed for 15 h. The solvents were removed under reduced pressure and 5 ml of cold concentrated HCl was added. A white precipitate was formed, ®ltered o, washed with water and dried, to give 1.78 g (87.7%) of compound (4). Recrystallization from N-N-dimethylformamide (DMF)-water mixture gave white crystals m.p. 292±294°C, a25 D 0:2° (0.050 g in 10 ml DMF); IR (KBr): 3650±3000 (m, br), 2980 (m), 2940 (m), 2900 (m), 1780 (m), 1760 (s), 1710 (s, br), 1470
(m), 1460 (w), 1385 (s), 1370 (m), 1275 (m), 1240 (m), 1200 (m), 1160 (m), 1120 (m), 1090 (m), 1060 (m), 960 (w), 820 (m), 870 (w), 830 (m), 810 (m, sh), 740 (m), 680 (w), 630 (m), 570 (w), cm 1 . Elemental analysis: calculated for C22 H24 N2 O8 , C (59.45%), H (5.44%), N (6.30%); found, C (59.48%), H (5.46%), N (6.38%).
3.2. N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) Into a 25 ml round-bottomed ¯ask were placed 0.50 g (1:120 10 3 mol) of compound (4) and 4 ml (an excess amount) of thionyl chloride. The mixture was re¯uxed overnight. Unreacted thionyl chloride was removed under reduced pressure and the residue was washed with n-hexane, to leave 0.520 g (96.0%) of white crystals. m:p: 166±168°C a25 D 1:2° (0.100 g in 10 ml DMF); IR (KBr): 3550 (w), 3100 (w), 2950 (m), 2910 (m), 2900 (m), 2850 (m), 1850 (s), 1775 (s), 1720 (s, br), 1465 (m), 1460 (m), 1440 (m), 1380 (s), 1360 (s), 1270 (w), 1250 (w), 1230 (m), 1170 (m), 1150 (m), 1130 (m), 1120 (w), 1090 (m), 1040 (m), 990 (m), 950 (m, sh), 940 (m), 920 (m), 870 (m), 840 (m), 820 (m), 760 (m), 740 (m), 720 (m), 660 (w), 620 (w), 600 (m), 560 (m), 500 (w), cm 1 . Elemental analysis: calculated for C22 H22 N2 O6 Cl2 , C (54.90%), H (4.61%), N (5.82%); found, C (55.12%), H (4.67%), N (5.97%).
4. Polymerization: synthesis of polymer (7a) The PAIs were prepared by the following procedure (using polymer (7a) as an example). Into a porcelain dish was placed 0.10 g (2:078 10 4 mol) of diacid chloride (5) and 0.059 g (2:078 10 4 mol) of diamine (6a). After the reagents were completely ground 0.20 ml of o-cresol as a solvent was added, and the mixture was ground for 10 min., then the reaction mixture was irradiated in the microwave oven for 12 min. The resulting homogeneous glassy polymer ®lm was isolated by adding methanol and triturating, followed by ®ltration. Powdered polymer was dried at 80°C for 15 h under vacuum to leave 0.139 g (89.7%) of pale-yellow solid (7a); IR (KBr): 3450 (m, br), 3200 (m, sh), 3100 (m), 3050 (m), 2950 (m), 1780 (m), 1720 (s, br), 1650 (m), 1590 (s), 1530 (s, br), 1500 (m), 1475 (m), 1470 (m), 1410 (m), 1380 (s), 1360 (s), 1320 (s), 1250 (m), 1190 (m), 1150 (s), 1100 (s), 1080 (m), 1030 (w), 1000 (w), 950 (w), 840 (m), 780 (w), 730 (m), 680 (w), 620 (m), 570 (m) cm 1 . The other PAIs (7b±f) were prepared in a procedure similar to that mentioned above.
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
2437
4.1. Polymer (7b) IR (KBr): 3400 (m, br), 3200 (m), 3100 (m), 3050 (m), 2950 (m), 2900 (m), 2850 (m), 1770 (m), 1720 (s, br), 1680 (m), 1660 (m), 1635 (w), 1600 (m), 1510 (s), 1460 (w), 1450 (w), 1430 (w), 1410 (m), 1380 (s), 1350 (s), 1320 (m), 1250 (m), 1150 (w), 1100 (w), 1080 (m), 1020 (w), 980 (w), 920 (w), 840 (w), 820 (m), 760 (w), 720 (m), 690 (w), 620 (w), 560 (w) cm 1 . 4.2. Polymer (7c) IR (KBr): 3350 (m, br), 3100 (m), 3050 (m), 2950 (m), 2900 (m), 2850 (m), 1770 (m), 1720 (s, br), 1680 (s, sh), 1630 (m), 1610 (m), 1540 (m), 1510 (s), 1470 (m), 1450 (m), 1400 (m), 1380 (s), 1350 (s), 1300 (m), 1240 (m), 1150 (m), 1110 (w), 1080 (m), 980 (w), 940 (w), 920 (m), 860 (m), 820 (m), 720 (m), 620 (w), 560 (w), 510 (w) cm 1 . 4.3. Polymer (7d) IR (KBr): 3300 (m, br), 3100 (m), 2950 (m), 2900 (m), 2850 (m), 1775 (m), 1720 (s, br), 1610 (s), 1530 (s), 1480 (m), 1470 (m, sh), 1440 (m), 1420 (m), 1380 (s), 1350 (s), 1250 (m), 1210 (m), 1170 (m), 1150 (m), 1110 (m), 1080 (m), 910 (m), 860 (m), 840 (m), 820 (m), 780 (m), 720 (m), 680 (m), 620 (w), 560 (m) cm 1 . 4.4. Polymer (7e) IR (KBr): 3300 (m, br), 3100 (m), 2950 (m), 2900 (m), 2850 (m), 1775 (m), 1720 (s, br), 1600 (m), 1520 (s), 1500 (s), 1470 (m), 1450 (m), 1380 (s), 1350 (s), 1250 (m), 1210 (m), 1150 (m), 1110 (m), 1080 (m), 980 (w), 940 (w), 920 (m), 860 (m), 840 (w), 820 (m), 720 (m), 620 (w), 560 (m) cm 1 . 4.5. Polymer (7f ) IR (KBr): 3300 (m, br), 3050 (m), 2950 (m), 2850 (m), 1775 (m), 1720 (s, br), 1600 (m), 1500 (s), 1460 (m), 1380 (s), 1350 (s), 1320 (m), 1270 (m), 1240 (m), 1150 (m), 1080 (m), 1000 (w), 920 (m), 820 (m), 720 (m), 620 (w), 560 (w), 510 (w) cm 1 .
5. Results and discussion 5.1. Monomer synthesis N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) was prepared by the three-step procedure as shown in Scheme 1. The asymmetric diacid compound (4) was synthesized by the condensation reaction of dianhydride
Scheme 1. Synthesis of N ,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5).
(1) with two moles of L -leucine (2) in a mixture of acetic acid and pyridine (3:2). The intermediate amic-acid (3) was not isolated and dehydration was performed under re¯uxing conditions. The resulting symmetric diacid (4) was converted to its diacid chloride derivative (5) by
2438
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
reaction with thionyl chloride. Washing with n-hexane puri®ed the monomer (5). Chemical structure and purity of the optically active monomers (4) and (5) were proved using elemental analysis IR. The IR spectrum of compound (4) showed a broad and strong peak at 3500±3000 cm 1 which was assigned to the COOH groups and two absorption bands at 1760 and 1710 cm 1 which are characteristic peaks for imide rings. Disappearance of strong acidic hydroxyl peak in IR spectrum of compound (5) con®rmed a complete conversion of diacid (4) to diacid chloride (5). On the other hand, because of the electron withdrawing character of the Cl group, the two carbonyl peaks of diacid chloride in comparison with its starting diacid, was shifted to higher frequency. 5.2. Polymer synthesis PAIs (7a±f) were synthesized by microwave-assisted polycondensation reactions of an equimolar mixture of monomer (5) with six dierent aromatic diamines (6a±f) as shown in Scheme 2. Recently we have used microwave irradiation technique and synthesized novel poly(amide±imide)s as well as poly(ester±imide)s [8±11]. Microwave-assisted polycondensation proceeds rapidly compared to conventional solution polycondensation and is almost completed within a short period of time. This method should become more and more important due to its high-eciency utilization of heat energy. In this work the microwave-assisted polycondensation reactions were performed in a porcelain dish in the presence of small amount of a polar organic medium such as
Table 1 Some physical properties of PAIs (7a±f) Diamine
6a 6b 6c 6d 6e 6f a b
Polymer Polymer code
Yield (%)
ginh (dl/g)a
b a25 D
7a 7b 7c 7d 7e 7f
89.7 81.8 87.6 80.7 89.3 87.0
0.46 0.39 0.30 0.34 0.28 0.29
1.0 0.6 0.4 0.4 0.4 0.2
Measured at a concentration of 0.5 g/dl in DMF at 25°C. Measured at a concentration of 0.10 g/dl in DMF at 25°C.
o-cresol that acts as a primary microwave absorber. The reaction mixture was irradiated for 12 min. The resulting PAIs (7a±f) were obtained in good yield. The reaction yields and some physical data are listed in Table 1. 5.3. Polymer characterization The structures of these polymers were con®rmed as PAIs by means of elemental analysis and IR spectroscopy. Elemental analysis values of the resulting polymers are listed in Table 2. The IR spectra of all polymers exhibited characteristic absorptions for the imide ring at 1720 and 1780 cm 1 due to the symmetrical and asymmetrical carbonyl stretching vibration. Bands of amide groups appeared around 3450 cm 1 (N±H) and an overlapped peak (shoulder like) around 1680 cm 1 (C@O). All of them exhibited strong absorbance at 1360±1380 cm 1 and
Scheme 2. Preparation of PAIs (7a±7f).
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
2439
Table 2 Elemental analysis of PAIs (7a±f) Polymer
Formula
7a
(C34 H32 N4 O8 S)n (657)n
7b
(C35 H34 N4 O6 )n (606)n
7c
(C28 H28 N4 O6 )n (516)n
7d
(C28 H28 N4 O6 )n (516)n
7e
(C29 H30 N4 O6 )n (530)n
7f
(C34 H32 N4 O6 )n (592)n
Elemental analysis (%) Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb
Moisture intake (%)a
C
H
N
62.18 60.00 62.28 69.28 67.42 69.24 65.09 63.00 64.71 65.09 63.39 64.25 65.63 66.92 68.12 68.89 63.73 65.32
4.91 5.09 4.89 5.65 5.76 5.60 5.47 5.64 5.48 5.47 5.64 5.57 5.70 5.67 5.57 5.45 5.75 5.60
8.54 8.36 8.68 9.24 8.91 9.15 10.85 9.92 10.19 10.85 10.20 10.32 10.56 9.10 9.30 9.46 10.04 10.29
3.8 2.7 2.7 1.2 1.8 2.5
a Moisture intake % W W0W0 100, W weight of polymer sample after standing at room temperature and W0 weight of polymer sample after drying in vacuum at 100°C for 10 h. b Corrected value for C and N found value 100 moisture intake=100, and corrected value for H found value 100 moisture intake=100.
Fig. 1. IR (KBr) spectrum of PAIs (7d).
2440
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
730 cm 1 , that show the presence of the imide heterocycle in these polymers. The polymer (7a) showed characteristic absorptions at 1320 and 1100 cm 1 due to the sulfone moiety (SO2 stretching). Fig. 1 shows a typical IR spectrum PAIs (7d). All polymers are soluble in aprotic polar solvents such as N,N-dimethylacetamide (DMAc), DMF, NMP, dimethylsulfoxide (DMSO) and protic solvents such as sulfuric acid and are insoluble in organic solvents such as tetrahydrofuran (THF), chloroform, acetone and benzene. 5.4. Thermal properties The thermal decomposition temperature of three PAIs (7a), (7b) and (7d) were evaluated by means of thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) under nitrogen atmosphere at a rate of heating of 10°C/min respectively. Table 3 summarizes the thermal properties of three PAIs (7a), (7b) and (7d). The PAIs (7a), (7b) and (7d) exhibited good resistance to thermal decomposition up to 300°C in nitrogen with minimum decomposition, but above this temperature the decomposition is faster. The temperature of 5% weight loss for all these polymers ranged from 218°C to 365°C and the temperature of 10% weight loss for these polymers ranged from 370°C to 412°C. The residual
Table 3 Thermal properties of PAIs (7a), (7b) and (7d) Polymer
Decomposition temperature (°C) T5 a
Decomposition temperature °C T10 b
Char yield (%)c
7a 7b 7d
365 270 218
412 380 370
36.95 39.82 24.27
a
Temperature at which 5% weight loss was recorded by TGA at heating rate of 10°C/min in N2 . b Temperature at which 10% weight loss was recorded by TGA at heating rate of 10°C/min in N2 . c Percentage weight of material left undecomposed after TGA analysis at maximum temperature 600°C in N2 .
weight for these polymers at 600°C ranged from 24.27% to 39.82% (Figs. 2±4).
6. Summary and conclusions The present work has shown that N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) is an interesting monomer which contains both a pyromellitimide group as well as chiral L -leucine groups. Thus, a series of new optically active PAIs having inherent viscosities of 0.28± 0.46 dl/g were synthesized by microwave assisted polycondensation reaction of the optically active monomer
Fig. 2. TGA and DTG curves of PAIs (7a) under nitrogen atmosphere.
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
2441
Fig. 3. TGA and DTG curves of PAIs (7b) under nitrogen atmosphere.
Fig. 4. TGA and DTG curves of PAIs (7d) under nitrogen atmosphere.
(5) with six dierent aromatic diamine (6a±f). These aromatic PAIs are optically active and are soluble in various organic solvents and have good thermal stability. The resulting novel polymers have potential to be
used in a column chromatography technique for the separation of enantiomeric mixtures. Furthermore, the above results demonstrate that microwave heating is an ecient method (shorter reaction time and high
2442
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
eciency of energy) for the polycondensation reactions. We are currently using this method for the synthesis of novel polymers and modi®cation of polymers. Acknowledgements We wish to express our gratitude to the Research Aairs Division Isfahan University of Technology (IUT), Isfahan, for ®nancial support. We thank Amine Pharmaceutical center, Isfahan, I.R, Iran for recording optical rotations. References [1] Gedye R, Smith F, Westaway HA, Baldisera L, Laberge L, Rousell J. Tetrahedron Lett 1986;27:279. [2] Abramovich RA. Org Prep Proceed Int 1991;23:683. [3] Caddick S. Tetrahedron 1995;51:10403. [4] Hajipour AR, Mallakpour SE, Afrousheh A. Tetrahedron 1999;55:2311.
[5] Hajipour AR, Mallakpour SE, Imanzadeh G. J Chem Res 1999:228. [6] Hajipour AR, Mallakpour SE, Khoee S. Synlett 2000;5:740. [7] Mallakpour SE, Hajipour AR, Khoee S. J Polym Sci Polym Chem Ed 2000;38:1154. [8] Mallakpour SE, Hajipour AR, Khoee S. J Appl Polym Sci 2000;77:3003. [9] Mallakpour SE, Hajipour AR, Faghihi K. Polym Int 2000;49:1383. [10] Mallakpour SE, Hajipour AR, Zamanlou MR. J Polym Sci Polym Chem Ed 2001;39:177. [11] Mallakpour SE, Hajipour AR, Faghihi K. Eur Polym J 2001;37:119. [12] Okamoto Y, Nakano T. Chem Rev 1994;94:349. [13] Mallakpour SE, Hajipour AR, Khoee S, Sheikholeslami B. Polym Int 1998;47:193. [14] Mallakpour SE, Hajipour AR, Mahdavian AR, Khoee S. J Polym Sci Polym Chem Ed 1999;37:1211. [15] Mallakpour SE, Hajipour AR, Mahdavian AR, Ra®emanzelat F. Polym Int 1999;48:109. [16] Mallakpour SE, Hajipour AR, Khoee S. Polym Int 1999;48:1133.
www.elsevier.com/locate/europolj
Facile synthesis of new optically active poly(amide±imide)s derived from N ,N 0-(pyromellitoyl)-bis-L -leucine diacid chloride and aromatic diamines under microwave irradiation Shadpour E. Mallakpour *, Abdol-Reza Hajipour *, Sakineh Habibi Organic Polymer Chemistry Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, I.R. Iran Received 3 January 2001; received in revised form 13 June 2001; accepted 14 June 2001
Abstract Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) was reacted with L -leucine (2) in a mixture of acetic acid and pyridine (3:2) and the resulting imide-acid [N ,N 0 -(pyromellitoyl)-bis-L -leucine diacid] (4) was obtained in high yield. The compound (4) was converted to the N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) by reaction with thionyl chloride. A new facile and rapid polycondensation reaction of this diacid chloride (5) with several aromatic diamines such as 4,40 -diaminodiphenylsulfone (4,40 -sulfonyldianiline) (6a), 4,40 -diaminodiphenyl methane (6b), p-phenylenediamine (6c), m-phenylenediamine (6d), 2,4-diaminotoluene (6e) and benzidine (6f) was developed by using a domestic microwave oven in the presence of a small amount of a polar organic medium such as o-cresol. The polymerization reactions proceeded rapidly and are completed within 12 min, producing a series of optically active poly(amide±imide)s with good yield and moderate inherent viscosity of 0.28±0.46 dl/g. All of the above polymers were fully characterized by IR, elemental analyses and speci®c rotation. Some structural characterization and physical properties of these optically active poly(amide±imide)s are reported. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Pyromellitic dianhydride; Optically active polymers; Microwave-assisted rapid polycondensation; Poly(amide±imide)s; Microwave oven; Inherent viscosity
1. Introduction Recently there has been growing interest in the application of microwave irradiation in chemical reactions. The reactions are very fast and are completed within a short period of time [1±3]. Recently we have used microwave irradiation for the synthesis of organic compounds as well as macromolecules [4±11]. The synthesis and application of optically active polymers have been paid more attention recently. Polymers with chiral structures are biologically very important [12]. Recently, we have synthesized optically active polymers by dierent methods [13±16] such as modi®-
cation of polybutadiene with an optically active substituted urazole group [13] Diels±Alder-ene reactions [14,15] and reaction of an optically active monomer with several diamines via solution polymerization [16]. This paper reports a rapid and highly ecient method for the synthesis of new optically active poly(amide± imide)s (PAI)s from the polycondensation reaction of N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride with aromatic diamines under microwave irradiation.
2. Experimental 2.1. Materials
*
Corresponding authors. Tel.: +98-311-891-3168; fax: +98311-891-2350. E-mail address: [email protected] (S.E. Mallakpour).
Pyromellitic dianhydride (benzene-1,2,4,5-tetracarboxylic dianhydride) (1) (from Merck Chemical Co.) was
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 5 1 - 3
2436
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
puri®ed by recrystallization from acetic anhydride follow by sublimation, 4,40 -diaminodiphenylsulfone (6a) and 4,40 -diaminodiphenylmethane (6b) were puri®ed by recrystallization from water and water/ethanol respectively. 1,4-phenylenediamine (6c) and 1,3-phenylenediamine (6d) and 2,4-diaminotoluene (6e) were puri®ed by sublimation. The other chemicals (from Fluka Chemical Co., Aldrich Chemical Co. and Riedel±deHaen AG) were used as obtained without further puri®cation. 2.2. Apparatus The apparatus used for the polycondensation was a Samsung domestic microwave oven (2450 MHz, 900 W) without any modi®cation, but all of the polymerization reactions were carried out in a hood with strong ventilation. 2.3. Measurements IR spectra were recorded on Shimadzu 435 IR spectrophotometer. Spectra of solids were carried out using KBr pellets. Vibrational transition frequencies are reported in wave number (cm 1 ). Band intensities are assigned as weak (w), medium (m), shoulder (sh), strong (s) and broad (br). Inherent viscosities were measured by a standard procedure using a Cannon Fenske Routine Viscometer (Germany). Speci®c rotations were measured by a Perkin±Elmer-241 Polarimeter (Germany). Thermal gravimetric analysis (TGA) data for polymers were taken on a Mettler TGA-50 in nitrogen atmosphere at a rate of 10°C/min. Elemental analyses were performed by Tarbiet Moderres University, Tehran, I.R. Iran.
3. Monomer synthesis 3.1. N,N 0 -(pyromellitoyl)-bis-L -leucine diacid (4) Into a 25 ml round-bottomed ¯ask 1.00 g (4:58 10 3 mol) of pyromellitic dianhydride (benzene-1,2,4,5tetracarboxylic dianhydride) (1), 1.200 g (9:170 10 3 mol) of L -leucine (2), 10 ml of mixture of acetic acid and pyridine (3:2) and a stirring bar were placed. The mixture was stirred and re¯uxed for 15 h. The solvents were removed under reduced pressure and 5 ml of cold concentrated HCl was added. A white precipitate was formed, ®ltered o, washed with water and dried, to give 1.78 g (87.7%) of compound (4). Recrystallization from N-N-dimethylformamide (DMF)-water mixture gave white crystals m.p. 292±294°C, a25 D 0:2° (0.050 g in 10 ml DMF); IR (KBr): 3650±3000 (m, br), 2980 (m), 2940 (m), 2900 (m), 1780 (m), 1760 (s), 1710 (s, br), 1470
(m), 1460 (w), 1385 (s), 1370 (m), 1275 (m), 1240 (m), 1200 (m), 1160 (m), 1120 (m), 1090 (m), 1060 (m), 960 (w), 820 (m), 870 (w), 830 (m), 810 (m, sh), 740 (m), 680 (w), 630 (m), 570 (w), cm 1 . Elemental analysis: calculated for C22 H24 N2 O8 , C (59.45%), H (5.44%), N (6.30%); found, C (59.48%), H (5.46%), N (6.38%).
3.2. N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) Into a 25 ml round-bottomed ¯ask were placed 0.50 g (1:120 10 3 mol) of compound (4) and 4 ml (an excess amount) of thionyl chloride. The mixture was re¯uxed overnight. Unreacted thionyl chloride was removed under reduced pressure and the residue was washed with n-hexane, to leave 0.520 g (96.0%) of white crystals. m:p: 166±168°C a25 D 1:2° (0.100 g in 10 ml DMF); IR (KBr): 3550 (w), 3100 (w), 2950 (m), 2910 (m), 2900 (m), 2850 (m), 1850 (s), 1775 (s), 1720 (s, br), 1465 (m), 1460 (m), 1440 (m), 1380 (s), 1360 (s), 1270 (w), 1250 (w), 1230 (m), 1170 (m), 1150 (m), 1130 (m), 1120 (w), 1090 (m), 1040 (m), 990 (m), 950 (m, sh), 940 (m), 920 (m), 870 (m), 840 (m), 820 (m), 760 (m), 740 (m), 720 (m), 660 (w), 620 (w), 600 (m), 560 (m), 500 (w), cm 1 . Elemental analysis: calculated for C22 H22 N2 O6 Cl2 , C (54.90%), H (4.61%), N (5.82%); found, C (55.12%), H (4.67%), N (5.97%).
4. Polymerization: synthesis of polymer (7a) The PAIs were prepared by the following procedure (using polymer (7a) as an example). Into a porcelain dish was placed 0.10 g (2:078 10 4 mol) of diacid chloride (5) and 0.059 g (2:078 10 4 mol) of diamine (6a). After the reagents were completely ground 0.20 ml of o-cresol as a solvent was added, and the mixture was ground for 10 min., then the reaction mixture was irradiated in the microwave oven for 12 min. The resulting homogeneous glassy polymer ®lm was isolated by adding methanol and triturating, followed by ®ltration. Powdered polymer was dried at 80°C for 15 h under vacuum to leave 0.139 g (89.7%) of pale-yellow solid (7a); IR (KBr): 3450 (m, br), 3200 (m, sh), 3100 (m), 3050 (m), 2950 (m), 1780 (m), 1720 (s, br), 1650 (m), 1590 (s), 1530 (s, br), 1500 (m), 1475 (m), 1470 (m), 1410 (m), 1380 (s), 1360 (s), 1320 (s), 1250 (m), 1190 (m), 1150 (s), 1100 (s), 1080 (m), 1030 (w), 1000 (w), 950 (w), 840 (m), 780 (w), 730 (m), 680 (w), 620 (m), 570 (m) cm 1 . The other PAIs (7b±f) were prepared in a procedure similar to that mentioned above.
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
2437
4.1. Polymer (7b) IR (KBr): 3400 (m, br), 3200 (m), 3100 (m), 3050 (m), 2950 (m), 2900 (m), 2850 (m), 1770 (m), 1720 (s, br), 1680 (m), 1660 (m), 1635 (w), 1600 (m), 1510 (s), 1460 (w), 1450 (w), 1430 (w), 1410 (m), 1380 (s), 1350 (s), 1320 (m), 1250 (m), 1150 (w), 1100 (w), 1080 (m), 1020 (w), 980 (w), 920 (w), 840 (w), 820 (m), 760 (w), 720 (m), 690 (w), 620 (w), 560 (w) cm 1 . 4.2. Polymer (7c) IR (KBr): 3350 (m, br), 3100 (m), 3050 (m), 2950 (m), 2900 (m), 2850 (m), 1770 (m), 1720 (s, br), 1680 (s, sh), 1630 (m), 1610 (m), 1540 (m), 1510 (s), 1470 (m), 1450 (m), 1400 (m), 1380 (s), 1350 (s), 1300 (m), 1240 (m), 1150 (m), 1110 (w), 1080 (m), 980 (w), 940 (w), 920 (m), 860 (m), 820 (m), 720 (m), 620 (w), 560 (w), 510 (w) cm 1 . 4.3. Polymer (7d) IR (KBr): 3300 (m, br), 3100 (m), 2950 (m), 2900 (m), 2850 (m), 1775 (m), 1720 (s, br), 1610 (s), 1530 (s), 1480 (m), 1470 (m, sh), 1440 (m), 1420 (m), 1380 (s), 1350 (s), 1250 (m), 1210 (m), 1170 (m), 1150 (m), 1110 (m), 1080 (m), 910 (m), 860 (m), 840 (m), 820 (m), 780 (m), 720 (m), 680 (m), 620 (w), 560 (m) cm 1 . 4.4. Polymer (7e) IR (KBr): 3300 (m, br), 3100 (m), 2950 (m), 2900 (m), 2850 (m), 1775 (m), 1720 (s, br), 1600 (m), 1520 (s), 1500 (s), 1470 (m), 1450 (m), 1380 (s), 1350 (s), 1250 (m), 1210 (m), 1150 (m), 1110 (m), 1080 (m), 980 (w), 940 (w), 920 (m), 860 (m), 840 (w), 820 (m), 720 (m), 620 (w), 560 (m) cm 1 . 4.5. Polymer (7f ) IR (KBr): 3300 (m, br), 3050 (m), 2950 (m), 2850 (m), 1775 (m), 1720 (s, br), 1600 (m), 1500 (s), 1460 (m), 1380 (s), 1350 (s), 1320 (m), 1270 (m), 1240 (m), 1150 (m), 1080 (m), 1000 (w), 920 (m), 820 (m), 720 (m), 620 (w), 560 (w), 510 (w) cm 1 .
5. Results and discussion 5.1. Monomer synthesis N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) was prepared by the three-step procedure as shown in Scheme 1. The asymmetric diacid compound (4) was synthesized by the condensation reaction of dianhydride
Scheme 1. Synthesis of N ,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5).
(1) with two moles of L -leucine (2) in a mixture of acetic acid and pyridine (3:2). The intermediate amic-acid (3) was not isolated and dehydration was performed under re¯uxing conditions. The resulting symmetric diacid (4) was converted to its diacid chloride derivative (5) by
2438
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
reaction with thionyl chloride. Washing with n-hexane puri®ed the monomer (5). Chemical structure and purity of the optically active monomers (4) and (5) were proved using elemental analysis IR. The IR spectrum of compound (4) showed a broad and strong peak at 3500±3000 cm 1 which was assigned to the COOH groups and two absorption bands at 1760 and 1710 cm 1 which are characteristic peaks for imide rings. Disappearance of strong acidic hydroxyl peak in IR spectrum of compound (5) con®rmed a complete conversion of diacid (4) to diacid chloride (5). On the other hand, because of the electron withdrawing character of the Cl group, the two carbonyl peaks of diacid chloride in comparison with its starting diacid, was shifted to higher frequency. 5.2. Polymer synthesis PAIs (7a±f) were synthesized by microwave-assisted polycondensation reactions of an equimolar mixture of monomer (5) with six dierent aromatic diamines (6a±f) as shown in Scheme 2. Recently we have used microwave irradiation technique and synthesized novel poly(amide±imide)s as well as poly(ester±imide)s [8±11]. Microwave-assisted polycondensation proceeds rapidly compared to conventional solution polycondensation and is almost completed within a short period of time. This method should become more and more important due to its high-eciency utilization of heat energy. In this work the microwave-assisted polycondensation reactions were performed in a porcelain dish in the presence of small amount of a polar organic medium such as
Table 1 Some physical properties of PAIs (7a±f) Diamine
6a 6b 6c 6d 6e 6f a b
Polymer Polymer code
Yield (%)
ginh (dl/g)a
b a25 D
7a 7b 7c 7d 7e 7f
89.7 81.8 87.6 80.7 89.3 87.0
0.46 0.39 0.30 0.34 0.28 0.29
1.0 0.6 0.4 0.4 0.4 0.2
Measured at a concentration of 0.5 g/dl in DMF at 25°C. Measured at a concentration of 0.10 g/dl in DMF at 25°C.
o-cresol that acts as a primary microwave absorber. The reaction mixture was irradiated for 12 min. The resulting PAIs (7a±f) were obtained in good yield. The reaction yields and some physical data are listed in Table 1. 5.3. Polymer characterization The structures of these polymers were con®rmed as PAIs by means of elemental analysis and IR spectroscopy. Elemental analysis values of the resulting polymers are listed in Table 2. The IR spectra of all polymers exhibited characteristic absorptions for the imide ring at 1720 and 1780 cm 1 due to the symmetrical and asymmetrical carbonyl stretching vibration. Bands of amide groups appeared around 3450 cm 1 (N±H) and an overlapped peak (shoulder like) around 1680 cm 1 (C@O). All of them exhibited strong absorbance at 1360±1380 cm 1 and
Scheme 2. Preparation of PAIs (7a±7f).
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
2439
Table 2 Elemental analysis of PAIs (7a±f) Polymer
Formula
7a
(C34 H32 N4 O8 S)n (657)n
7b
(C35 H34 N4 O6 )n (606)n
7c
(C28 H28 N4 O6 )n (516)n
7d
(C28 H28 N4 O6 )n (516)n
7e
(C29 H30 N4 O6 )n (530)n
7f
(C34 H32 N4 O6 )n (592)n
Elemental analysis (%) Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb Calcd Found Corrb
Moisture intake (%)a
C
H
N
62.18 60.00 62.28 69.28 67.42 69.24 65.09 63.00 64.71 65.09 63.39 64.25 65.63 66.92 68.12 68.89 63.73 65.32
4.91 5.09 4.89 5.65 5.76 5.60 5.47 5.64 5.48 5.47 5.64 5.57 5.70 5.67 5.57 5.45 5.75 5.60
8.54 8.36 8.68 9.24 8.91 9.15 10.85 9.92 10.19 10.85 10.20 10.32 10.56 9.10 9.30 9.46 10.04 10.29
3.8 2.7 2.7 1.2 1.8 2.5
a Moisture intake % W W0W0 100, W weight of polymer sample after standing at room temperature and W0 weight of polymer sample after drying in vacuum at 100°C for 10 h. b Corrected value for C and N found value 100 moisture intake=100, and corrected value for H found value 100 moisture intake=100.
Fig. 1. IR (KBr) spectrum of PAIs (7d).
2440
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
730 cm 1 , that show the presence of the imide heterocycle in these polymers. The polymer (7a) showed characteristic absorptions at 1320 and 1100 cm 1 due to the sulfone moiety (SO2 stretching). Fig. 1 shows a typical IR spectrum PAIs (7d). All polymers are soluble in aprotic polar solvents such as N,N-dimethylacetamide (DMAc), DMF, NMP, dimethylsulfoxide (DMSO) and protic solvents such as sulfuric acid and are insoluble in organic solvents such as tetrahydrofuran (THF), chloroform, acetone and benzene. 5.4. Thermal properties The thermal decomposition temperature of three PAIs (7a), (7b) and (7d) were evaluated by means of thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) under nitrogen atmosphere at a rate of heating of 10°C/min respectively. Table 3 summarizes the thermal properties of three PAIs (7a), (7b) and (7d). The PAIs (7a), (7b) and (7d) exhibited good resistance to thermal decomposition up to 300°C in nitrogen with minimum decomposition, but above this temperature the decomposition is faster. The temperature of 5% weight loss for all these polymers ranged from 218°C to 365°C and the temperature of 10% weight loss for these polymers ranged from 370°C to 412°C. The residual
Table 3 Thermal properties of PAIs (7a), (7b) and (7d) Polymer
Decomposition temperature (°C) T5 a
Decomposition temperature °C T10 b
Char yield (%)c
7a 7b 7d
365 270 218
412 380 370
36.95 39.82 24.27
a
Temperature at which 5% weight loss was recorded by TGA at heating rate of 10°C/min in N2 . b Temperature at which 10% weight loss was recorded by TGA at heating rate of 10°C/min in N2 . c Percentage weight of material left undecomposed after TGA analysis at maximum temperature 600°C in N2 .
weight for these polymers at 600°C ranged from 24.27% to 39.82% (Figs. 2±4).
6. Summary and conclusions The present work has shown that N,N 0 -(pyromellitoyl)-bis-L -leucine diacid chloride (5) is an interesting monomer which contains both a pyromellitimide group as well as chiral L -leucine groups. Thus, a series of new optically active PAIs having inherent viscosities of 0.28± 0.46 dl/g were synthesized by microwave assisted polycondensation reaction of the optically active monomer
Fig. 2. TGA and DTG curves of PAIs (7a) under nitrogen atmosphere.
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
2441
Fig. 3. TGA and DTG curves of PAIs (7b) under nitrogen atmosphere.
Fig. 4. TGA and DTG curves of PAIs (7d) under nitrogen atmosphere.
(5) with six dierent aromatic diamine (6a±f). These aromatic PAIs are optically active and are soluble in various organic solvents and have good thermal stability. The resulting novel polymers have potential to be
used in a column chromatography technique for the separation of enantiomeric mixtures. Furthermore, the above results demonstrate that microwave heating is an ecient method (shorter reaction time and high
2442
S.E. Mallakpour et al. / European Polymer Journal 37 (2001) 2435±2442
eciency of energy) for the polycondensation reactions. We are currently using this method for the synthesis of novel polymers and modi®cation of polymers. Acknowledgements We wish to express our gratitude to the Research Aairs Division Isfahan University of Technology (IUT), Isfahan, for ®nancial support. We thank Amine Pharmaceutical center, Isfahan, I.R, Iran for recording optical rotations. References [1] Gedye R, Smith F, Westaway HA, Baldisera L, Laberge L, Rousell J. Tetrahedron Lett 1986;27:279. [2] Abramovich RA. Org Prep Proceed Int 1991;23:683. [3] Caddick S. Tetrahedron 1995;51:10403. [4] Hajipour AR, Mallakpour SE, Afrousheh A. Tetrahedron 1999;55:2311.
[5] Hajipour AR, Mallakpour SE, Imanzadeh G. J Chem Res 1999:228. [6] Hajipour AR, Mallakpour SE, Khoee S. Synlett 2000;5:740. [7] Mallakpour SE, Hajipour AR, Khoee S. J Polym Sci Polym Chem Ed 2000;38:1154. [8] Mallakpour SE, Hajipour AR, Khoee S. J Appl Polym Sci 2000;77:3003. [9] Mallakpour SE, Hajipour AR, Faghihi K. Polym Int 2000;49:1383. [10] Mallakpour SE, Hajipour AR, Zamanlou MR. J Polym Sci Polym Chem Ed 2001;39:177. [11] Mallakpour SE, Hajipour AR, Faghihi K. Eur Polym J 2001;37:119. [12] Okamoto Y, Nakano T. Chem Rev 1994;94:349. [13] Mallakpour SE, Hajipour AR, Khoee S, Sheikholeslami B. Polym Int 1998;47:193. [14] Mallakpour SE, Hajipour AR, Mahdavian AR, Khoee S. J Polym Sci Polym Chem Ed 1999;37:1211. [15] Mallakpour SE, Hajipour AR, Mahdavian AR, Ra®emanzelat F. Polym Int 1999;48:109. [16] Mallakpour SE, Hajipour AR, Khoee S. Polym Int 1999;48:1133.