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Microwave-assisted synthesis and characterization of l-lysine-derived optically active poly (hydrazide-imide)s
⁎Corresponding author. Tel./fax: +987324225700. zahmatkesh1355@yahoo.com (Saeed Zahmatkesh)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
l-Lysine hydrochloride was transformed to ethyl l-lysine dihydrochloride. This salt was reacted with trimellitic anhydride to yield the corresponding diacid (1). Interfacial polycondensation results a series of novel poly (hydrazide-imide)s (PHIa–f). These polymers have inherent viscosities in the range of 0.10–0.37 dl g−1, display optical activity, and are readily soluble in polar aprotic solvents. They start to decompose (T10%) above 245 °C and display glass-transition temperatures at around 125.9 °C. All of the above polymers were fully characterized by UV, FT-IR and 1H NMR spectroscopy, elemental analysis, TGA, DSC, inherent viscosity measurement and specific rotation.
Keywords
Chiral
Optically active
l-Lysine
Poly (hydrazide-imide)
Microwave-assisted polymerization
1 Introduction
The interest for developing new biodegradable and/or biocompatible polymers has largely encouraged the use of monomers based on naturally occurring products (Gonsalves and Mungara, 1996; Steinbu, 2002). Both carbohydrate (Thiem and Bachmann, 1994; Varela and Orgueira, 1999) and aminoacid (Gonsalves and Mungara, 1996) derived monomers are being currently used as building blocks to generate novel polymeric structures with enhanced biodegradability.
l-Lysine in particular has been repeatedly used for making polyamides with potential as biomaterials (Gachard et al., 1997; Saotome and Schultz, 1967; Crescenzi et al., 1968; Katsarawa et al., 1985). For instance l-lysine with good functionalities has been used to prepare some polytartaramides (Majo et al., 2004).
Optically active polymers are one of the most important classes of high performance engineering materials which are suitable candidates for use as the chiral stationary phases in high performance liquid chromatography (HPLC) Nakano, 2001; Cirilli et al., 2003; Coa et al., 2007; Mallakpour and Kowsari, 2005; Yuan et al., 2005 as well as asymmetric catalysis applications (Itsuno, 2005; Hu et al., 2001, 2002; Hb et al., 2000; Canali et al., 1999). The synthesis and application of these polymers is a considerable topic, which has been paid more attention recently (Hajipour et al., 2005). Most of the natural polymers are optically active and have special chemical activities, such as catalytic properties that exist in genes, proteins and enzymes. Some other applications are construction of chiral media for asymmetric synthesis, chiral stationary phases for resolution of enantiomers in chromatographic techniques (Akelah and Sherrington, 1981), chiral liquid crystals in ferroelectrics and nonlinear optical devices (Wulff, 1989; Fontanille and Guyot, 1987). So, more considerations to improve different synthetic procedures of optically active polymers exist. Recently, we have synthesized optically active polymers by different methods (Hajipour et al., 2008, 2009; Zahmatkesh and Hajipour, 2009, 2010).
Polyhydrazides have been extensively studied since they increase dye ability of synthetic fibers and improve elasticity over other polymer types. They possess fair absorption characteristics when the hydrazide link is in the main chain or polymer backbone. They have been cyclized to give polyoxadiazoles and polytriazoles. They also provide a synthetic base for the chelate polymers, since the hydrazide group (–CO–NH–NH–CO–) can react with metal ions to form complexes. Moreover, the 1,3,4-oxadiazole ring has special interest owing to its superior thermostability in an oxaidative atmosphere (Hajipour et al., 2007). Aromatic polyhydrazides are generally synthesized by the low-temperature solution polycondensation of an aromatic dihydrazide with an aromatic diacid chloride in a solvent such as NMP in the presence of an inorganic salt like lithium chloride (Dobinson et al., 1979).
Organic reactions assisted by microwave irradiation have gained special attention. The reactions are very fast and are completed within short times. Recently we have used microwave irradiation to synthesize different types of macromolecules (Zahmatkesh and Hajipour, 2009, 2010).
The present work outlines a fast and effective procedure to synthesize six new atactic optically active polyhydrazides based on l-lysine through microwave-assisted polycondensation. A major aim of this work was to study the effect of inclusion of aliphatic or aromatic moieties in polymers, and their properties, were also investigated. These polymers showed good optical activity (+6.30 to +18.00). The outstanding characteristics of these polymers include thermal stability, good solubility, optical activity, potentially being ion exchangeable.
2 Material and methods
The trimellitic anhydride (Merck) was recrystallized from acetic anhydride. The other chemicals (Merck) were used as received. 1H NMR spectra were recorded on 300 or 500 MHz and 13C NMR on a 125 MHz (Bruker Avance) instrument, using DMSO-d6 as solvent and tetramethylsilane as shift reference (tube diameter, 5 mm). IR spectra were recorded on a Shimadzu FT-IR-680 instrument, using KBr pellets. UV spectra were recorded on a Perkin–Elmer lambada 5 instrument. Specific rotations were measured by an A. Kruss. Optronic P3002 RS (Germany) Polarimeter in DMF as solvent. Thermogravimetric analyses (TGA) were recorded on a Mettler TA4000 with a heating rate of 6 °C min−1 under air atmosphere. DSC analyses were preformed on a Mettler DSC-30 under nitrogen atmosphere. Inherent viscosities of polymers were measured by a standard procedure using a Cannon Fenske Routine Viscometer (Germany) at 25 °C using DMF as solvent. Melting points were measured in open capillaries with an IA9000 series digital Melting Point Apparatus.
2.1 Monomer synthesis
2.1.1 Synthesis of Ethyl l-lysine dihydrochloride (9)
In a 50 ml round-bottomed flask equipped with a reflux condenser and a stirring bar, 8 ml of thionyl chloride was added dropwise to the stirring absolute ethanol (2.5 ml) at −10 °C. l-lysine hydrochloride (7.3 g, 0.04 mol) was added to the mixture and refluxed for 6 h. The solvent was evaporated under reduced pressure and the residue was washed with diethyl ether three times. Yield: 87%; m.p.: 136–137 °C; IR (cm−1): 3421, 3350–2514, 2019, 1740, 1603, 1583, 1501, 1217, 851, 740; 1H NMR (D2O, ppm): 1.07 (3H), 1.29 (2H), 1.49 (2H), 1.76 (2H), 2.78 (2H), 3.91 (1H), 4.08 (2H); Elemental analysis for C8H18N2O2·2HCl, Calculated: C (38.87%), H (8.16%), N (11.33%), Found: C (38.62%), H (8.31%), N (11.40%).
2.1.2 Synthesis of Ethyl l-lysine-N,N′-ditrimellitoyl diacide (1)
Into a 25 ml round-bottomed flask, 2.000 g (10.42 mmol) of trimellitic anhydride, 1.282 g (5.21 mmol) of Ethyl l-lysine dihydrochloride, a mixture of acetic acid/pyridine (5 ml, 3:2) and a stirring bar were placed. The mixture was stirred at r.t. for 2 h and then refluxed for 6 h. The solvents were removed under reduced pressure. 5 ml of cold concentrated HCl was added. A white precipitate was formed and filtered off. The white diacid (1) was extracted from this crude product with chloroform. Yield: 2.32 g (79%); m.p.: 168 °C; = +3.14° (0.050 g in 10 ml DMF); IR (cm−1): 3400–2400, 1702, 1498, 1418, 1296, 1148, 1069, 1018, 916, 803, 750, 748; 1H NMR (500 MHz, CDCl3, ppm): 1.2 (3H), 1.3 (2H), 1.7 (1H), 1.8 (1H), 2.1 (1H), 2.2 (1H), 3.7 (2H), 4.2 (2H), 4.8 (1H), 7.9 (1H), 8.0 (1H), 8.1 (1H), 8.2 (1H), 8.4 (1H), 8.5 (1H); 13C NMR (125 MHz, CDCl3, ppm): δ 14.4, 23.6, 27.7, 28.2, 38.0, 52.4, 62.5, 123.8, 124.1, 124.8, 125.2, 132.2, 132.4, 134.9, 135.1, 136.2, 136.4, 136.5, 136.6, 166.8, 166.9, 167.6, 167.7, 169.3, 170.1, 170.2.
2.1.3 Synthesis of Ethyl l-lysine-N,N′-ditrimellitoyl diacylchloride (2)
Into a 25 ml round-bottomed flask were placed 0.558 g (1.0 mmol) of diacid (1), 5 ml (an excess amount) of thionyl chloride and two drops of DMF. The mixture was stirred for 20 min and then refluxed for 2 h. Unreacted thionyl chloride was removed under reduced pressure and the residue was washed with n-hexane, to leave 0.486 g (82%) of white crystals. dp: 175 °C; = +4.08° (0.050 g in 10 ml DMF). IR (KBr, cm−1): 3023, 2784, 1862, 1785, 1720, 1464, 1384, 1226, 1017, 922, 877, 754, 718, 680, 507.
2.1.4 Synthesis of dihydrazides (3–8)
General procedure: In a 25 ml round-bottomed flask equipped with a reflux condenser, a mixture of corresponding dimethyl ester (1.00 mol), hydrazine mono hydrate (2.50 mol), and ethanol (10 ml) was placed and refluxed for 5 h. Upon cooling, crystals separated, which were filtered and washed with ethanol.
2.1.4.1 Dihydrazide 3
White; Yield (%) = 95; m.p. (οC) > 300; IR (cm−1): 3324, 3033, 1623, 1605, 1540, 1489, 1340, 1291, 1103, 1016, 927, 886, 736, 713, 638; 1H NMR (300 MHz) δ: (ppm): 4.51 (s, 4H), 7.90 (s, 4H), 9.90 (s, 2H).
2.1.4.2 Dihydrazide 4
White; Yield (%) = 98; m.p. (οC) = 244–246; IR (cm−1): 3289, 3055, 1663, 1625, 1585, 1524, 1321, 1108, 996, 923, 819, 723, 687, 625; 1H NMR (300 MHz) δ: (ppm): 4.51 (s, 4H), 7.50 (t, 1H), 7.91 (dd, 2H), 8.30 (t, 1H), 9.80 (s, 2H).
2.1.4.3 Dihydrazide 5
White–Gray; Yield (%) = 75; m.p. (οC) = 240–241; IR (cm−1): 3282, 3181, 3007, 1679, 1611, 1534, 1360, 1269, 1097, 998, 793, 537; 1H NMR (300 MHz) δ: (ppm): 4.11 (s, 4H), 9.60 (s, 2H).
2.1.4.4 Dihydrazide 6
Yellow; Yield (%) = 80; m.p. (οC) = 148–149; IR (cm−1): 3304, 3201, 3131, 3034, 2873, 1667, 1647, 1532, 1363, 1248, 1203, 1052, 955, 788, 694; 1H NMR (300 MHz) δ: (ppm): 2.90 (s, 2H), 4.20 (s, 4H), 9.11 (s, 2H).
2.1.4.5 Dihydrazide 7
White; Yield (%) = 83; m.p. (οC) = 169–170; IR (cm−1): 3313, 3291, 3200, 3181, 3042, 2874, 2779, 1627, 1531, 1353, 1241, 1012, 949, 752, 664; 1H NMR (300 MHz) δ: (ppm): 2.30 (s, 4H), 4.11 (s, 4H), 8.90 (s, 2H).
2.1.4.6 Dihydrazide 8
White; Yield (%) = 87; m.p. (οC) = 176–177; IR (cm−1): 3315, 3180, 3046, 2965, 2927, 1636, 1532, 1379, 1330, 1157, 1016, 1001, 954, 711, 618; 1H NMR (300 MHz) δ: (ppm): 1.75 (quin, 2H), 2.00 (t, 4H), 3.51 (s, 4H), 8.90 (s, 2H).
2.2 Microwave-assisted polymerization
2.2.1 General procedure
Into a porcelain dish, a mixture of diacyl chloride (1.0 mmol) and DABCO (1.0 mmol) as a catalyst was placed. After grinding the reagents for 5 min, dihydrazide (1.0 mmol) was added and the mixture was ground for further 5 min. 0.25 ml of O-cresol as a solvent was added, and the mixture was ground for 5 min. The reaction mixture was irradiated in a microwave oven for 10 min (700 W, Interval: 10 s/min). The resulting homogenous glassy compound film was dissolved in DMF and then isolated by adding methanol/H2O (50:50) and triturating, followed by filtration. It was washed several times with methanol and vacuum dried.
2.2.1.1 PHIa
Yellow; yield (%) = 91; = +32.40; UV (λmax) = 298; IR (cm−1): 3640–3180, 2925, 1780, 1715, 1387, 1258, 864, 731; 1H NMR (500 MHz, DMSO-d6) δ: (ppm): 1.1 (3H), 1.2 (2H), 1.4 (2H), 1.7 (2H), 2.1 (2H), 4.1 (2H), 4.8 (1H), 7.2–8.5 (10H), 10.8 (4H).
2.2.1.2 PHIb
Yellow; yield (%) = 83; = +5.20; UV (λmax) = 268; IR (cm−1): 3630–3180, 2924, 1770, 1716, 1379, 726, 689; 1H NMR (500 MHz, DMSO-d6) δ: (ppm): 1.1 (3H), 1.2 (2H), 1.4 (2H), 1.7 (2H), 3.6 (2H), 4.2 (2H), 4.9 (1H), 7.6–8.5 (10H), 10.9 (4H).
2.2.1.3 PHIc
White; yield (%) = 87; = +10.30; UV (λmax) = 260; IR (cm−1): 3630–3170, 1780, 1716, 1389, 1243, 730, 689; 1H NMR (500 MHz, DMSO-d6) δ: (ppm): 1.1 (3H), 1.2 (2H), 1.4 (2H), 1.7 (2H), 2.1 (2H), 4.2 (2H), 4.8 (1H), 7.8–8.5 (6H), 11.2 (4H).
2.2.1.4 PHId
White–Gray; yield (%) = 82; = +15.50; UV (λmax) = 262; IR (cm−1): 3600–3200, 2942, 1770, 1716, 1387, 1294, 733; 1H NMR (500 MHz, DMSO-d6) δ: (ppm): 1.1 (5H), 1.6 (2H), 2.1 (2H), 3.6 (4H), 4.1 (2H), 4.8 (2H), 7.7–8.5 (6H), 10.4 (2H), 10.9 (2H).
2.2.1.5 PHIe
Pale yellow; yield (%) = 80; = +8.30; UV (λmax) = 268; IR (cm−1): 3630–3130, 1790, 1716, 1388, 1251, 731, 688; 1H NMR (500 MHz, DMSO-d6) δ: (ppm): 1.1 (3H), 1.2 (2H), 1.7 (2H), 2.2 (6H), 3.6 (2H), 4.2 (2H), 4.8 (1H), 7.9–8.5 (6H), 10.9–11.2 (4H).
2.2.1.6 PHIf
Yellow; yield (%) = 77; = +12.40; UV (λmax) = 269; IR (cm−1): 3630–3150, 1770, 1716, 1388, 1251, 731, 688; 1H NMR (500 MHz, DMSO-d6) δ: (ppm): 1.1 (3H), 1.2 (2H), 1.7 (4H), 2.1 (6H), 2.4 (2H), 4.2 (2H), 4.8 (1H), 7.7–8.4 (6H), 10.8 (2H).
3 Results and discussion
Ethyl l-lysine dihydrochloride was prepared with the reaction of a mixture of EtOH and thionyl chloride with l-lysine hydrochloride. l-Lysine hydrochloride was added to the mixture dropwise at −10 °C and then refluxed for 6 h. The dark solid was washed three times with diethyl ether to leave a bright white solid (87%). FT-IR spectroscopy shows a strong and broad peak at 3350–2514 cm−1 corresponding to the Ammonium N–H stretchings and a strong peak at 1740 cm−1 corresponding to the C≡O stretching of ester moiety. 1H NMR (D2O, ppm) spectroscopy shows the corresponding peaks such as 3.91 (1H) due to the chiral center and 1.07 (3H) and 2.78 (2H) peaks due to the ethyl moiety (Scheme 1). The best solvent to prepare Ethyl l-lysine-N,N′-ditrimellitoyl diacide (1) was acetic acid/pyridine mixture, since we have the salt form of chiral diamine as starting material here. The best method for purification of this synthetic diacid was found to be extraction with chloroform (Scheme 2). The chemical structure of diacid 1 was confirmed by spectroscopic analysis (Figs. 1–3). FT-IR spectroscopy shows a strong and broad peak at 3600–2700 cm−1 corresponding to the COOH stretchings, a strong peak at 1740 cm−1 corresponding to the C≡O stretching of ester moiety, a strong peak at 1702 cm−1 corresponding to the symmetric and unsymmetric C≡O stretching of imidic moiety and two peaks at 1411 and 750 cm−1 due to the cyclic imide groups. 1H NMR (CDCl3, ppm) spectroscopy shows 14 peaks and the corresponding peaks such as 4.8 (1H) due to the chiral center and 10.21 (2H) due to the acidic moiety. 13C NMR (CDCl3, ppm) spectroscopy shows 26 peaks due to the 26 different carbons. Corresponding white diacyl chloride (2) was prepared in refluxing SOCl2 for 2 h (Scheme 3). FT-IR spectroscopy shows the corresponding carbonyl stretching of acyl chloride at 1862 cm−1. Synthesis of dihydrazides (3–8) is presented in scheme 4. FT-IR spectroscopy shows the corresponding carbonyl stretching at 1663 cm−1 and that of NH at 3050–3289 cm−1.
Protection of l-lysine acidic group.
Diacid 1 synthesis.
IR spectrum of diacid 1.
1H NMR spectrum of diacid 1.
13C NMR spectrum of diacid 1.
Diacyl chloride 2 synthesis.
Synthesis of dihydrazides (3–8).
Microwave-assisted polymerization was applied to prepare the poly (hydrazide-imide)s (Scheme 5). The Microwave-assisted procedure provided a more satisfactory performance compared to the use of homogeneous systems since only about 10 min. of Microwave-assisted polycondensation was required for obtaining both yields and ηinh attained after 12 h by solution procedure. To optimize the polymerization conditions, we did six experiments on PHIa. The optimum condition is as follow: Power = 700 W; Time = 10 min with interval times of 10 s/min of running. It is found that at higher power, the lower viscosity and lower specific rotation are obtained; which can be attributed to polymer degradation. At lower power, the higher specific rotation but lower viscosity is obtained; the results are shown in Table 1. All of the very probable atactic polymers were obtained from an inexpensive starting material in quantitative yields with moderate inherent viscosities (0.10–0.37 dl g−1) and optical rotation (+6.30 to +18.00) (Table 2). In contrast to our previous papers, here there is no obvious regioselectivity between alpha and epsilon acyl chloride groups of the lysine ester containing diacid during the polymerization step then random orientation of lysine moieties along the polymer backbone can be predicted and the concept of “tacticity” cannot be addressed in this research. Head-to-tail regiorandomness may likely affect some physical properties of the polymers such as crystallinity. All polymers have been obtained in good yields (53–86%) and being thermally stable (T (10%): 248–301 °C). The color of these polymers was white to yellow. The resulting homogenous glassy compound films were isolated by adding methanol/H2O (80:20) and triturating, followed by filtration. It was washed several times with methanol and vacuum dried. Transparent, flexile, and tough films of these polymers were obtained which showed good mechanical strength of the films and consequently high molecular weight. High speed and high yield are the advantages of this polymerization method. One of the major objectives of this work is to study the solubility and the versatility of these polymers by incorporating the soft segment in the polymer backbone. These polymers are organo soluble in common polar aprotic solvents (Table 3). The novel polymers were fully characterized by spectroscopic analysis (UV, FT-IR, 1H NMR), thermal analysis (TGA, DSC), viscometric measurements, optical rotation measurements and solubility tests. As an example the corresponding spectra of PHIa are represented in Figs. 4–7, respectively. Thermal properties of these polymers are investigated by TGA/DTG under air atmosphere at 6 °C/min and by DSC under nitrogen atmosphere at 10 °C/min (Table 4). In FT-IR spectra of these polymers some characteristic peaks could be seen, including the N–H stretching of hydrazide group at around 3443 cm−1, C≡O asymmetric and symmetric stretching of imide groups at 1716 cm−1, C≡O stretching of hydrazide group at 1630 cm−1. All of these PHIs exhibited strong absorption at around 1380 and 720 cm−1, which shows the presence of the heterocyclic imide groups. The 1H NMR spectra of PHIs shows a peak at 4.8 ppm due to the chiral center. The polymers show a maximum absorption in UV spectra at around 248–262 nm.
Microwave-assisted polymerization.
Power
Time (min)
Interval (10 s/min)
ήinh (dl g−1)
900
15
−
0.31
+9.9
900
15
+
0.30
+8.4
700
10
+
0.37
+18
600
15
+
0.31
+6.3
300
20
+
0.29
+7.9
300
20
+
0.21
+8.5
Polymer code
Color
Yield (%)
ήinh (dl g−1)
Film qualitya
PHIa
Yellow
80
013
+16.20
Flexible
PHIb
Yellow
78
0.21
+6.30
Flexible
PHIc
White
86
0.10
+8.65
Flexible
PHId
White–gray
78
0.37
+18.00
Flexible
PHIe
Bright yellow
75
0.11
+7.28
Flexible
PHIf
Yellow
53
0.17
+11.00
Flexible
Solvents
PHIa
PHIb
PHIc
PHId
PHIe
PHIf
NMP
+
+
+
+
+
+
DMSO
+
+
+
+
+
+
DMAc
+
+
+
+
+
+
DMF
+
+
+
+
+
+
H2SO4
+
+
+
+
+
+
CH2Cl2
−
−
−
−
−
−
CHCl3
−
−
−
−
−
−
EtOH
−
−
−
−
−
−
MeOH
−
−
−
−
−
−
H2O
−
−
−
−
−
−
FT-IR spectrum of PHIa.
1H NMR spectrum of PHIa.
TGA spectrum of PHIa.
DSC spectrum of PHIa.
Polymer
Decomposition temperature (οC) T10%a
Char yield (%)b
PHIa
299.6
19.3
PHIb
292.6
21.22
PHIc
239.5
36
PHId
248
40.49
PHIe
301
13.22
PHIf
250
32.34
4 Conclusion
A fast and effective procedure to prepare a serious of optically active polyhydrazides has been introduced. Since there is no obvious regioselectivity between alpha and epsilon acyl chloride groups of the lysine ester containing diacid during the polymerization step then random orientation of lysine moieties along the polymer backbone can be predicted.
Acknowledgement
We gratefully acknowledge the funding support received for this project from Ardabil PNU.
References
- Application of functionalized polymers in organic synthesis. Chem. Rev.. 1981;81:557-587.
- [Google Scholar]
- Synthesis of resins with pendently-bound chiral manganese-salen complexes and use as heterogeneous asymmetric alkene epoxidation catalysts. React. Funct. Polym.. 1999;40:155-168.
- [Google Scholar]
- Enantioselective liquid chromatography of C3-chiral 2, 3-dihydro-1, 2, 5-benzothiadiazepin-4(5H)-one and thione 1,1-dioxides on polyacrylamide- and polysaccharide-based chiral stationary phases. J. Chromatog. A.. 2003;993:17-28.
- [Google Scholar]
- Helical polymers from optically active epoxides with bulky pendants. Polym. Bull.. 2007;59:481-490.
- [Google Scholar]
- High-strength, high-modulus fibers from hydrazide polymers and copolymers. J. Appl. Polym. Sci.. 1979;23:2189-2195.
- [Google Scholar]
- Fontanille M., Guyot M., eds. Recent advances in synthetic and mechanistic aspects of polymerization. Netherlands: Dordrecht; 1987.
- Synthesis and characterization of random and regular l-lysine-based polyamides. Macromol. Chem. Phys. 1997;198(5):1375-1389.
- [Google Scholar]
- Synthesis and properties of degradable polyamides and related polymers. Trends Polym. Sci.. 1996;4(1):25-31.
- [Google Scholar]
- Synthesis and characterization of novel optically active poly(amide–imide)s via direct amidation. Euro. Polym. J.. 2005;41:2290.
- [Google Scholar]
- Hajipour, A R., Zahmatkesh, S., Ruoho, A.E. 2007. Optically active polymer: Synthesis and Characterization of New Optically Active Poly (hydrazide-imide)s Incorporating l-Leucine. e-polymers, 088.
- Microwave-assisted synthesis and characterization of heterocyclic, and optically active poly(amide-imide)s incorporating l-amino acids. Polym. Adv. Technol.. 2008;19:1710-1719.
- [Google Scholar]
- Hajipour, A.R., Roosta, P., Zahmatkesh, S., Ruoho, A.E. 2009. Synthesis and characterization of novel optically active poly(ester-imide-imine)s. e-polymers, no. 011.
- Synthesis of a rigid and optically active poly(BINAP) and its application in asymmetric catalysis. Tetrahedron Lett.. 2000;41:1681-1685.
- [Google Scholar]
- Synthesis of optically active polymers with chiral units attached to rigid backbones and their application for asymmetric catalysis. Tetrahedron Lett.. 2001;42:7725-7728.
- [Google Scholar]
- Optically active dendronized polymers as a new type of macromolecular chiral catalysts for asymmetric catalysis. Tetrahedron Lett.. 2002;43:927-930.
- [Google Scholar]
- Chiral polymer synthesis by means of repeated asymmetric reaction. Prog. Polym Sci.. 2005;30:540-558.
- [Google Scholar]
- Heterochain polymers based on natural amino acids. Synthesis of polyamides from N,N'-bis(trimethylsilyl)lysine alkyl esters. Makromol. Chem.. 1985;186:939-954.
- [Google Scholar]
- Synthesis and characterization of polyamides obtained from tartaric acid and l-lysine. Euro. Polym. J.. 2004;40:2699.
- [Google Scholar]
- Synthesis of organosoluble and optically active poly(ester-imide)s by direct polycondensation with tosyl chloride in pyridine and dimethylformamide. Polym. Bull.. 2005;55:51-59.
- [Google Scholar]
- Optically active synthetic polymers as chiral stationary phases in HPLC. J. Chromatogr. A.. 2001;906:205-225.
- [Google Scholar]
- Optically active polyamides with regular structural sequences prepared from a-amino acid. Makromol. Chem.. 1967;109:239-249.
- [Google Scholar]
- Steinbu C.A., ed. Biopolymers. Vol Vols. 3–4 and 7–8. Weinheim: Wiley-VCH; 2002.
- Synthesis of chiral polyamides from carbohydrate-derived monomers. Adv. Carbohydr. Chem. Biochem.. 1999;55:137-174.
- [Google Scholar]
- Main-chain chirality and optical activity in polymers consisting of CC chains. Angew. Chem., Int. Engl. Ed.. 1989;28:21-37.
- [Google Scholar]
- Effect of chiral additive on formation of cellulose triacetate chiral stationary phase in HPLC. Anal. Chim. Acta. 2005;554:152-155.
- [Google Scholar]
- Zahmatkesh, S., Hajipour, A.R. 2009. Microwave-assisted synthesis and characterization of some optically active poly (ester-imide) thermoplastic elastomers. e-polymers, no. 068.
- Microwave-assisted synthesis and characterization of optically active poly (ester-imide)s incorporating l-alanine. Amino Acids. 2010;38:1253-1260.
- [Google Scholar]
