Synthesis and characterization of new optically active poly(azo-ester-imide)s via interfacial polycondensation

Abstract

N,N′-Pyromelliticdiimido-di-L-amino acids (1a–1d) were prepared from the reaction of pyromellitic dianhydride with the corresponding L-amino acids in a solution of glacial acetic acid/pyridine (3:2) at refluxing temperature. 4,4′-sulfonyl bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol, 4,4′-oxy bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol and 4,4′-methylene bis(4,1-phenylene) bis(diazene-2,1-diyl) diphenol, were prepared from 4,4′-diamino diphenyl sulfone, 4,4′-diamino diphenyl ether, 4,4′-diamino diphenyl methane, sodium nitrite and phenol following the general procedure of diazo coupling. Interfacial polycondensation method was used to prepare the corresponding poly(azo-ester-imid)s (PAEI_1–12) in biphasic solution of water/dichloromethane. The resulting polymers (PAEIs) have been obtained in high yields having good inherent viscosities (0.32–0.57 dl g⁻¹), optical activities and thermal stabilities.

Introduction

Chiral polymers including those bearing main- or side-chain amino acid units are used widely in the pharmaceutical industry for enantio-selective separation of drugs. This is achieved mainly via the use of chiral polymers as the stationary phase in chromatography or electrophoresis. Apart from chiral separation, biocompatible amino acid containing polymers are used in drug delivery systems (Feng et al. 2007; Bluhm et al. 2005; Billiot and Warner 2000).

Bifunctional colorants can be used as monomers in synthesis of functional polymers, so designing and synthesis of these compounds is important (Xin et al. 2001). Recently azo polymers have become important due to their potential uses in various optical applications. Photochemical trans-cis isomerization induced by UV or visible light is one of the most important properties of them (Kumar and Neckers 1989; Zollinger 1961; Wu et al. 2001). Azo compounds are highly colored and have been used as dyes and pigments for a long time. They have also been used in many practical applications such as coloring fibers, photoelectronic applications, and analytical chemistry (Koh and Greaves 2001; Hallas and Choi 1999; Gup et al. 2007).

Aromatic poly(imide-ester)s are one of the most important classes of high-performance polymers and attract attention for outstanding properties and potential liquid crystalline nature (Kurita et al. 1991). Poly imides are a class of high-temperature polymers which have gained considerable importance in many engineering applications due to their excellent electrical, thermo-oxidative, and mechanical properties at elevated temperatures. However, applications for polyimides are often limited due to their intractability and insolubility as well as high melting temperatures, which cause a variety of processing problems (Ghassemi and Hay 1993; Wilson 1990; Takekoshi 1990; Sroog 1990; Kaplan and Hirsch 1974). Interfacial polymerization has been used to prepare various condensation polymers, particularly polyamides, polyesters, polyurethanes, and polyureas (Provatas et al. 2000; Chen et al. 1995; Kim et al. 1995; Wang and Nakamura 1995; Morgan 1965; Noll 1968). Interfacial polymerization allows the synthesis of condensation polymers at low temperature with limited side reactions. This method can directly generate finished products such as films, fibers, membranes, etc. and has seen widespread acceptance in many fields, ranging from microencapsulation of pharmaceutical products (Finch 1993) to conducting polymer films (Lando and Rickert 1987).

Materials and methods

All chemicals and solvents were purchased from Fluka, Aldrich or Merck chemical Co. and were used without further purification.

IR spectra were recorded on a FT/IR-680 plus spectrophotometer using KBr pellets. Band intensities are assigned as week (w), medium (m), and strong (s). Band shapes assigned as shoulder (sh), sharp (s), and broad (br). Inherent viscosities were measured by a standard procedure using a Cannon Fenske routine viscometer at 25°C using DMF as solvent. ¹H NMR spectra were recorded on 300 MHz instrument, using DMSO-d₆ as solvent and tetramethylsilane as shift reference (tube diameter 5 mm). Specific rotations were measured by a JASCO P-1030 Polarimeter. Thermal gravimetric analysis (TGA) was obtained by a Mettler TGA-50 under air atmosphere at a rate of 5°C/min. Differential scanning calorimetry (DSC) was obtained by a Mettler DSC-30 under nitrogen atmosphere. Elemental analyses were performed with a Perkin Elmer CHNS elemental analyzer. Melting points were measured in open capillaries with a Gallenkamp instrument.

Monomer synthesis

Synthesis of diacids (1a–1d): general procedure

Into a 25 ml round-bottomed flask equipped with a condenser and an electric stirrer, 1.0 mmol (0.218 g) of pyromellitic dianhydride (1), 2 mmol of the corresponding L-amino acid, 10 ml of acetic acid/pyridine (3:2) and a stirring bar were placed. The mixture was stirred at room temperature for 2 h and then refluxed for 8 h. The solvent was removed under reduced pressure, and 5 ml of cold concentrated HCl was added. The formed precipitate was filtered off, washed with hot water and vacuum dried.

Diacid (1a)

White; Yield (%) = 92; m.p. (°C) > 250; ${[\alpha ]}_D^{25}=+3.54$ (0.050 g in 10 ml DMF); IR (KBr): 3500–2800 (br, s), 2950 (s, s), 1780 (sh, w), 1720 (s, s), 1590 (s, m), 1390 (s, s), 1380 (sh, w), 1290 (s, w), 1210 (s, w), 1160 (s, w), 920 (s, w), 810 (s, w), 720 (s, m), 640 (s, w) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 0.9 (t, 12H), 1.52 (m, 2H), 1.9 (td, 2H), 2.2 (td, 2H), 4.88 (dd, 2H), 13.4 (s, 2H) ppm; Elemental analysis: calculated for C₂₂H₂₄N₂O₈: C (59.45%), H (5.44%), N (6.30%); found C (59.10%), H (5.80%), N (6.71%).

Diacid (1b)

White; Yield (%) = 96; m.p. (°C) > 250; ${[\alpha ]}_D^{25}=+5.18$ (0.050 g in 10 ml DMF); IR (KBr): 3600–2500 (br, s), 2900 (s, m), 1780 (sh, s), 1720 (sh, s), 1700 (s, s), 1590 (sh, w), 1460 (s, s), 1390 (s, s), 1380 (sh, s), 1260 (s, s), 1160 (s, m), 1140 (sh, w), 1080 (s, s), 1010 (s, s), 910 (s, s), 850 (s, s), 800 (sh, w), 720 (s, s), 600 (s, m) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 1.6 (d, 6H), 4.9 (q, 2H), 8.3 (s, 2H), 13.4 (s, 2H) ppm; Elemental analysis: Calculated for C₁₆H₁₂N₂O₈: C (53.34%), H (3.36%), N (7.77%); found C (52.90%), H (3.40%), N (7.30%).

Diacid (1c)

White; Yield (%) = 89; m.p. (°C) > 250; ${[\alpha ]}_D^{25}=+20.86$ (0.050 g in 10 ml DMF); IR (KBr): 3400–2700 (br, s), 2900 (s, s), 1750 (sh, m), 1700 (s, s), 1580 (sh, w), 1450 (sh, w), 1390 (s, s), 1350 (sh, m), 1250 (sh, w), 1190 (s, m), 1120 (sh, w), 1060 (sh, w), 890 (s, w), 720 (s, m) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 0.95 (t, 6H), 1.09 (d, 6H), 1.2 (m, 4H), 2.4 (m, 2H), 4.65 (d, 2H), 8.4 (s, 2H), 13.2 (s, 2H) ppm; Elemental analysis: Calculated for C₂₂H₂₄N₂O₈: C (59.45%), H (5.44%), N (6.30%); found C (59.20%), H (5.70%), N (5.90%).

Diacid (1d)

White; Yield (%) = 90; m.p. (°C) > 250; ${[\alpha ]}_D^{25}=+1.56$ (0.050 g in 10 ml DMF); IR (KBr): 3600–2800 (br, s), 2900 (sh, w), 1760 (sh, w), 1720 (s, s), 1560 (s, m), 1490 (s, w), 1370 (s, s), 1350 (sh, m), 1220 (sh, w), 1180 (sh, w), 1090 (s, m), 900 (sh, w), 800 (s, w), 720 (s, m), 690 (s, w) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 3.32 (dd, 2H), 3.52 (dd, 2H), 5.2 (dd, 2H), 7.2 (m, 10H), 8.23 (s, 2H) ppm; Elemental analysis: Calculated for C₂₈H₂₀N₂O₈: C (65.62%), H (3.93%), N (5.46%); found C (65.30%), H (4.10%), N (5.30%).

Synthesis of diacyl chlorides: general procedure (Banihashemi and Pourabbas 2000)

Finely powdered diacid (0.5 g) was placed into a 50 ml round-bottomed flask and redistilled thionyl chloride (30 ml) was added. The mixture was refluxed for 3 h with stirring. The unreacted thionyl chloride was distilled off by an ordinary distillation and the remaining was driven out by rotary evaporation. Solids were treated with n-hexane, and collected after filtration. The diacyl chloride was dried in a vacuum oven at 40°C.

Diacid chloride (1′a)

White; Yield (%) = 70; m.p. (°C) = 168 (d); ${[\alpha ]}_D^{25}=+3.18$ (0.050 g in 10 ml DMF); IR (KBr): 3482 (s, w), 3224 (br, w), 3108 (s, w), 2958 (s, s), 2933 (sh, w), 2872 (s, m), 1811 (s, s), 1776 (s, m), 1720 (s, s), 1468 (s, m), 1383 (s, s), 1366 (s, s), 1272 (s, w), 1231 (s, w), 1172 (s, m), 1155 (s, m), 1077 (s, s), 1047 (sh, w), 992 (s, s), 939 (s, m), 921 (sh, m), 876 (s, m), 840 (s, s), 819 (sh, m), 765 s, s), 719 (s, m), 663 (s, w), 603 (s, s), 563 (s, m), 481 (s, m), 417 (s, m) cm⁻¹.

Diacid chloride (1′b)

White; Yield (%) = 78; m.p. (°C) = 173 (d); ${[\alpha ]}_D^{25}=+5.50$ (0.050 g in 10 ml DMF); IR (KBr): 3489 (br, m), 2940 (s, m), 1778 (sh, s), 1731 (s, s), 1456 (s, s), 1381 (s, s), 1364 (s, s), 1275 (s, w), 1181 (s, m), 1156 (s, m), 1126 (s, m), 1082 (s, m), 1065 (s, m), 1015 (s, m), 942 (s, s), 901 (s, m), 842 (s, s), 736 (s, s), 712 (s, m), 663 (s, w), 624 (s, m), 601 (s, s), 562 (s, m), 443 (s, w), 405 (s, m) cm⁻¹.

Diacid chloride (1′c)

White; Yield (%) = 70.45; m.p. (°C) = 165 (d); ${[\alpha ]}_D^{25}=+14.08$ (0.050 g in 10 ml DMF); IR (KBr): 3481 (br, m), 2969 (s, m), 2936 (sh, w), 2879 (sh, w), 2360 (sh, w), 1795 (s, s), 1775 (sh, m), 1721 (s, s), 1475 (s, m), 1377 (s, s), 1360 (s, s), 1152 (sh, w), 1110 (sh, w), 1086 (s, m), 1046 (s, w), 1001 (s, w), 962 (s, w), 891 (s, m), 854 (s, m), 817 (s, m), 740 (s, s), 637 (s, m), 561 (s, m) cm⁻¹.

Diacid chloride (1′d)

White; Yield (%) = 68; m.p. (°C) = 162 (d); ${[\alpha ]}_D^{25}=+4.56$ (0.050 g in 10 ml DMF); IR (KBr): 3063–2926 (br, m), 1773 (s, s), 1728 (s, s), 1603 (sh, w), 1497 (s, m), 1455 (s, m), 1378 (s, s), 1363 (sh, s), 1330 (sh, w), 1201 (s, w), 1157 (s, w), 1131 (sh, m), 1105 (sh, m), 1078 (s, w), 1027 (s, m), 966 (s, m), 919 (s, m), 888 (s, w), 847 (s, s), 827 (sh, s), 773 (s, m), 735 (s, s), 700 (s, s), 621 (s, m), 606 (s, m), 565 (s, m) cm⁻¹.

Preparation of monomer 2a: general procedure

Into a 50 ml round-bottomed flask, a stirring bar, 1.0 mmol (0.248 g) of 4,4′-diamino diphenyl sulfone, 0.366 ml of HCl (Conc.) and 10 ml of water were added. The solution was then cooled to 0–5°C in an ice bath. A solution of 2.0 mmol (0.138 g) sodium nitrite in 5 ml of water was prepared and then added dropwise to the mixture. Stirring was continued for 10 min at the same temperature. This solution was added portion wise to the coupling component solution prepared by mixing a solution of 2.0 mmol (0.188 g) of phenol, 2.0 mmol (0.080 g) of NaOH and 10 ml of water. During the reaction, the temperature was maintained at 0–5°C. After 1 h, the colorful precipitate was filtered off, washed with cold water, and vacuum dried.

The other monomers (2b, 2c) were synthesized following the same procedure using 1.0 mmol (0.200 g) of 4,4′-diamino diphenyl ether or 1.0 mmol (0.198 g) of 4,4′-diamino diphenyl methane correspondingly.

Monomer 2a

Dark red; Yield (%) = 86.9; m.p. (°C) = 227; IR (KBr): 3600–3300 (br, s), 2925 (sh, w), 2361 (sh, w), 1585 (s, s), 1504 (s, m), 1464 (sh, w), 1430 (s, s), 1401 (sh, w), 1325 (s, w), 1301 (s, m), 1255 (sh, m), 1138 (s, s), 1101 (s, s), 1067 (s, w), 1008 (s, m), 923 (s, w), 848 (s, s), 795 (s, m), 738 (s, m), 720 (s, m), 703 (s, w), 642 (sh, w), 610 (s, s), 577 (s, s), 545 (sh, w) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 7.00 (d, 4H), 7.88 (d, 4H), 8.00 (d, 4H), 8.19 (d, 4H), 10.6 (s, 2H) ppm; Elemental analysis: Calculated for C₂₄H₁₈N₄O₄S: C (62.87%), H (3.96%), N (12.22%), S (6.99%); found C (62.60%), H (4.20%), N (11.90%), S (6.70%).

Monomer 2b

Dark red; Yield(%) = 69.3; m.p. (°C) = 216; IR (KBr): 3600–3400 (br, m), 2800 (sh, w), 2360 (sh, w), 2239 (s, w), 1581 (s, s), 1489 (s, m), 1435 (sh, m), 1384 (sh, w), 1240 (s, s), 1145 (s, s), 1096 (s, m), 1006 (s, w), 874 (sh, m), 842 (s, s), 781 (sh, w), 727 (sh, w), 649 (sh, m), 619 (sh, w), 551 (s, m), 517 (sh, w), 482 (sh, m) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 7.00 (d, 4H), 7.27 (d, 4H), 7.81 (d, 4H), 7.92 (d, 4H), 10.70 (s, 2H) ppm; Elemental analysis: Calculated for C₂₄H₁₈N₄O₃: C (70.23%), H (4.42%), N (13.65%); found C (70.00%), H (4.60%), N (13.40%).

Monomer 2c

Dark brown; Yield(%) = 75.5; m.p. (°C) = 195; IR (KBr): 3600–3100 (br, s), 2922 (sh, m), 1600 (br, w), 1587 (s, s), 1502 (s, s), 1463 (s, m), 1432 (s, s), 1410 (sh, m), 1384 (sh, m)m 1235 (s, s), 1138 (s, s), 1098 (s, m), 1101 (s, m), 924 (sh, w), 870 (sh, m), 837 (s, s), 802 (sh, m), 774 (sh, w), 724 (s, w), 647 (s, w), 621 (s, m), 547 (s, m), 529 (sh, m), 477 (s, m), 417 (sh, w) cm^{−1; 1}H NMR (300 MHz, DMSO-d₆) δ: 4.12 (s,2H), 6.96 (d, 4H), 7.45 (d, 4H), 7.78 (d, 4H), 7.81 (d, 4H), 10.4 (s, 2H) ppm; Elemental analysis: Calculated for C₂₅H₂₀N₄O₂: C (73.51%), H (4.93%), N (13.71%); found C (73.40%), H (5.10%), N (13.90%).

Interfacial polycondensation: general procedure

Into a 100 ml round-bottomed flask, a stirring bar, 1.0 mmol of a corresponding diacyl chloride (1′a–1′d), and 10 ml of dichloromethane were placed. The mixture was stirred for 5 min. A solution of 1.0 mmol of diazo compound (2a–2c), 20 ml of NaOH (0.1 N), and catalytic amount of tetraethylammonium bromide (0.1 g) in 10 ml of H₂O was prepared. This solution was added dropwise to the flask, while stirring vigorously in an ice bath. After 1 h, the formed polymer was filtered off, washed with methanol, and vacuum dried.

PAEI₁

IR (KBr): 3600–3100 (br, s), 2959 (sh, m), 2871 (sh, w), 1779 (sh, s), 1725 (s, s), 1593 (s, s), 1495 (s, m), 1468 (sh, m), 1437 (sh, w), 1383 (s, s), 1363 (sh, m), 1301 (s, m), 1195 (sh, m), 1142 (sh, m), 1100 (sh, m), 1010 (s, m), 918 (s, w), 849 (s, m), 797 (s, w), 728 (s, m), 617 (sh, m), 576 (s, m), 561 (sh, w), 415 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₆H₃₈N₆O₁₀S: C (63.73%), H (4.42%), N (9.69%), S (3.69%); found C (63.50%), H (4.60%), N (9.40%), S (3.50%).

PAEI₂

IR (KBr): 3600–3100 (br, s), 1750 (sh, m), 1723 (s, s), 1635 (sh, w), 1590 (sh, m), 1559 (sh, w), 1496 (sh, m), 1457 (sh, m), 1384 (s, s), 1300 (s, m), 1193 (sh, m), 1141 (sh, m), 1101 (s, m), 1076 (sh, w), 849 (s, m), 796 (sh, w), 729 (s, m), 611 (sh, w), 559 (sh, w), 468 (sh, w), 419 (s, w) cm⁻¹. Elemental analysis: Calculated for C₄₀H₂₆N₆O₁₀S: C (61.38%), H (3.35%), N (10.74%), S (4.09%); found C (61.40%), H (3.60%), N (10.60%), S (4.00%).

PAEI₃

IR (KBr): 3600–3300 (br, s), 2968 (sh, m), 2360 (sh, w), 1800 (sh, w), 1779 (sh, m), 1724 (s, s), 1635 (sh, w), 1495 (s, m), 1457 (s, m), 1384 (s, s), 1359 (sh, m), 1141 (sh, m), 1101 (sh, m), 1000 (sh, w), 728 (s, m), 575 (sh, w), 561 (sh, w), 419 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₆H₃₈N₆O₁₀S: C (63.73%), H (4.42%), N (9.69%), S (3.69%); found C (63.60%), H (4.50%), N (9.40%), S (3.80%).

PAEI₄

IR (KBr): 3600–3300 (br, s), 2360 (sh, m), 2342 (sh, w), 1774 (sh, m), 1725 (s, s), 1578 (s, s), 1495 (s, m), 1418 (sh, m), 1383 (s, s), 1192 (sh, m), 1140 (sh, m), 1104 (s, m), 1010 (sh, w), 829 (sh, w), 727 (s, m), 699 (s, m), 618/ (sh, m), 461 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₅₂H₃₄N₆O₁₀S: C (66.80%), H (3.66%), N (8.98%), S (3.43%); found C (66.5%), H (3.80%), N (8.70%), S (3.50%).

PAEI₅

IR (KBr): 3600–3400 (br, s), 2924 (sh, m), 1773 (s, m), 1725 (s, s), 1582 (s, s), 1488 (s, s), 1382 (s, m), 1239 (s, s), 1145 (s, s), 841 (sh, m), 726 (s, m), 548 (s, m) cm⁻¹. Elemental analysis: Calculated for C₄₆H₃₈N₆O₉: C (67.47%), H (4.67%), N (10.26%); found C (67.40%), H (4.70%), N (10.10%).

PAEI₆

IR (KBr): 3600–3300 (br, m), 2850 (sh, w), 1750 (sh, w), 1722 (s, s), 1580 (s, s), 1488 (s, m), 1383 (s, s), 1364 (sh, w), 1238 (s, m), 1192 (sh, w), 1146 (s, m), 1078 (sh, w), 1012 (s, w), 925 (s, w), 843 (s, m), 725 (s, m), 620 (sh, w), 550 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₀H₂₆N₆O₉: C (65.39%), H (3.56%), N (11.44%); found C (65.30%), H (3.70%), N (11.20%).

PAEI₇

IR (KBr): 3600–3400 (br, s), 2965 (sh, m), 2361 (sh, m), 1778 (sh, w), 1725 (s, s), 1583 (s, s), 1488 (s, s), 1381 (s, s), 1357 (s, s), 1239 (s, m), 1192 (s, m), 1146 (s, m), 1009 (s, w), 841 (sh, w), 728 (s, m), 548 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₆H₃₈N₆O₉: C (67.47%), H (4.67%), N (10.26%); found C (67.20%), H (4.80%), N (10.40%).

PAEI₈

IR (KBr): 3600–3400 (br, m), 1834 (s, m), 1777 (sh, w), 1725 (s, s), 1584 (s, m), 1479 (s, m), 1455 (sh, w), 1389 (s, s), 1363 (sh, w), 1240 (s, m), 1147 (s, w), 1106 (s, m), 993 (sh, w), 843 (sh, w), 727 (s, m), 700 (s, m) cm⁻¹. Elemental analysis: Calculated for C₅₂H₃₄N₆O₉: C (70.42%), H (3.86%), N (9.47%); found C (70.20%), H (3.70%), N (9.30%).

PAEI₉

IR (KBr): 3600–3300 (br, s), 2960 (sh, m), 2931 (sh, w), 2872 (sh, w), 2362 (sh, w), 1777 (sh, m), 1725 (s, s), 1578 (s, s), 1491 (sh, w), 1414 (sh, w), 1382 (s, s), 1364 (sh, w), 1195 (sh, m), 1152 (sh, m), 1011 (s, m), 923 (s, m), 865 (s, w), 826 (s, w), 727 (s, m), 648 (s, w), 620 (s, w), 563 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₇H₄₀N₆O₈: C (69.10%), H (4.93%), N (10.28%); found C (68.80%), H (5.10%), N (10.00%).

PAEI₁₀

IR (KBr): 3600–3300 (br, s), 2850 (sh, w), 1760 (sh, w), 1721 (s, s), 1578 (s, s), 1491 (s, m), 1417 (sh, m), 1383 (s, s), 1364 (sh, w), 1194 (s, m), 1152 (s, m), 1077 (s, m), 1012 (s, m), 925 (s, w), 846 (s, w), 728 (s, m), 648 (sh, w), 620 (sh, w), 562 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₁H₂₈N₆O₈: C (67.21%), H (3.85%), N (11.47%); found C (67.40%), H (4.10%), N (11.30%).

PAEI₁₁

IR (KBr): 3600–3400 (br, m), 2965 (sh, m), 1778 (sh, m), 1725 (s, s), 1591 (s, m), 1492 (s, m), 1458 (s, m), 1381 (s, s), 1357 (s, s), 1195 (sh, m), 1152 (s, w), 1011 (s, w), 833 (sh, w), 727 (s, m), 549 (sh, w) cm⁻¹. Elemental analysis: Calculated for C₄₇H₄₀N₆O₈: C (69.10%), H (4.93%), N (10.28%); found C (68.90%), H (5.00%), N (10.00%).

PAEI₁₂

IR (KBr): 3600–3400 (br, w), 2360 (sh, w), 1834 (s, m), 1777 (sh, m), 1725 (s, s), 1590 (sh, m), 1496 (s, m), 1455 (s, m), 1382 (s, s), 1362 (sh, m), 1193 (sh, w)1106 (s, m), 992 (sh, w), 916 (sh, w), 828 (s, w), 727 (s, m), 699 (s, m), 620 (s, w), 563 (s, w) cm⁻¹. Elemental analysis: Calculated for C₅₃H₃₆N₆O₈: C (71.94%), H (4.10%), N (9.49%); found C (71.60%), H (4.20%), N (9.30%).

Results and discussion

Monomer synthesis

We synthesized the diimide-diacids [N,N′-pyromellitic-diimido-di-L-aminoacids (1a–1d)] by the condensation reaction of pyromellitic dianhydride with L-aminoacids (a–d) (1:2 molar ratio) in a solution of refluxing acetic acid/pyridine (3:2), and then treating the residue with cold concentrated HCl to get the corresponding diacid (Scheme 1). The mixture of reaction was allowed to stir for 2 h, in this part amic acid formation occurs. Refluxing for 8 h causes the dehydration and cyclic imide formation. Refluxing a diacid with an excess amount of thionyl chloride allows the diacyl chloride formation. After removing the thionyl chloride by distillation under reduced pressure, the residue was washed with n-hexane to remove the remaining thionyl chloride. Compounds (2a–2c) were synthesized by the reaction of a diamine such as 4,4′-diamino diphenyl sulfone, 4,4′-diamino diphenyl ether or 4,4′-diamino diphenyl methane (1.0 mmol), sodium nitrite (2.0 mmol) and HCl in water. The mixture was stirred for 10 min. A solution of phenol (2.0 mmol), and NaOH (0.1 M, 20 ml) in 10 ml of water was prepared and added dropwise to the first solution and then the mixture was stirred for 1 h (Scheme 1). The chemical structure and the purity of optically active monomers (1a–1d, 2a–2c) were proved by FT-IR and ¹H NMR spectroscopy, and elemental analysis. Figure 1 represents the ¹H NMR spectra of diacid (1b) and monomer (2a).

Scheme 1.

Preparation of monomers

Fig. 1.

¹H NMR spectra of diacid 1b and compound 2a

Polymer synthesis

The PAEIs (1–12) were synthesized by the interfacial polycondensation reaction between an equimolar mixture of one of the diacyl chlorides and one of the diphenols (2a–2c) using tetraethylammonium bromide as a phase transfer catalyst in a biphasic solution (water/CH₂Cl₂) (Scheme 2). Interfacial polymerization behaves more like the chain polymerization since the monomer diffusion to the interface layer is much faster than to the second phase. This method allows the reaction to proceed much faster and at lower temperature, so it is a very good method to prepare chiral polymers. The synthesis and some physical properties of these novel optically active PAEIs are given in Table 1.

Scheme 2.

Interfacial polymerization

Table 1.

Synthesis and some physical properties of PAEIs

Diacid chloride	Diazo compound	PAEI	Yield (%)	ηinh (dl g−1)a	${[\alpha ]}_D^{25}$ b	Color
1′a	2a	1	77	0.32	−7.94	O
1′b	2a	2	72	0.32	−7.96	O
1′c	2a	3	80	0.38	+1.76	O
1′d	2a	4	85	0.39	−7.86	O
1′a	2b	5	84	0.46	−8.08	LB
1′b	2b	6	78	0.50	−8.00	LB
1′c	2b	7	90	0.49	−7.64	DY
1′d	2b	8	88	0.52	−8.44	LB
1′a	2c	9	91	0.33	−8.12	DY
1′b	2c	10	84	0.43	−8.2	LB
1′c	2c	11	82	0.57	−8.66	LB
1′d	2c	12	85	0.52	−8.24	DY

O orange, LB light brown, DY dark yellow

^aMeasured at a concentration of 0.5 dl g⁻¹ in NMP (5% LiCl) at 25°C

^bMeasured at a concentration of 0.5 dl g⁻¹ in NMP (5% LiCl) at 25°C

All the polymers were obtained in good yields with good inherent viscosities (0.32–0.57 dl g⁻¹), and show optical rotation and therefore are optically active.

Polymer characterization

The formation of PAEIs was confirmed by the FT-IR spectroscopy and elemental analysis. As an example, Fig. 2 shows the IR spectrum of PAEI₇ with the characteristic absorptions at 1778 (C=O, asymmetric, imidic), 1725 (C=O, symmetric, imidic), 1583 (N=N, azo), 1509 (C–N, imide), 1381 and 726 (imidic ring). The colors of PAEIs range from dark yellow to light brown. The solubility of PAEIs was tested qualitatively in various organic solvents and the results are summarized in Table 2. All of the PAEIs are soluble or partially soluble in organic solvents such as DMF, DMSO, NMP and H₂SO₄ at room temperature, and are partially soluble or insoluble in solvents such as methylene chloride and acetone.

Fig. 2.

IR spectrum of PAEI₇

Table 2.

Solubility of PAEIs(1–12)

PAEI	NMP (5%LiCl)	THF	Cyclohexane	EtOH	DMSO	DMF	NMP	H2SO4	CH2Cl2	Acetone
1	+	+	−	−	P	+	P	+	−	−
2	+	P	−	−	P	P	+	+	−	−
3	+	+	−	−	P	P	+	+	P	−
4	+	P	−	−	P	P	P	+	−	−
5	+	P	−	−	P	P	P	+	−	−
6	+	+	−	−	+	+	+	+	P	−
7	+	P	−	−	P	P	−	+	P	−
8	+	P	−	−	+	P	P	+	−	−
9	+	P	−	−	P	P	+	+	P	−
10	+	P	−	−	P	P	P	+	−	−
11	+	P	−	−	P	P	P	+	P	−
12	+	P	−	−	+	+	P	+	P	−

+ soluble, − insoluble, P partially soluble

Thermal properties

The thermal properties of PAEI₇ were evaluated by means of TGA/DTG (under air atmosphere) and DSC (under nitrogen atmosphere). The temperatures of 5 and 10% weight loss are 295 and 320°C, correspondingly, and the Tg is about 105°C. TGA/DTG thermogram of PAEI₇ is represented in Fig. 3.

Fig. 3.

TGA/DTG thermogram of PAEI₇

Conclusions

A series of optically active PAEIs having inherent viscosities in the range of 0.32–0.57 dl g⁻¹ were synthesized for the first time by the interfacial polycondensation of optically active N,N′-pyromelliticiimido-di-L-amino acid chlorides (1′a–1′d) as an acidyl chloride with aromatic diphenols containing azo groups (2a–2c). These aromatic PAEIs show optical rotation and can be used in chiral separation, via the use of chiral polymers as the stationary phase. They are readily soluble in various organic solvents and have a good thermal stability. These polymers can potentially be used as liquid crystals, dyes and pigments, in photoelectronics, in optical light storage due to the characteristics of the azo functional group. These polymers also have amino acid groups in the main chain, and so may be biocompatible with applications in drug delivery systems and biodegradable materials.