Acessibilidade / Reportar erro

New optically active and thermally stable poly(amide-imide)s containing N,N'-(Bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)-bis-L-alanine and aromatic diamines: synthesis and characterization

Abstracts

Five new optically active poly(amide-imide)s (PAIs) 6a-e were prepared by direct polycondensation reaction of the newly synthesized N,N´-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic)-bis-L-alanine 4 with various aromatic diamines 5a-e using polar aprotic solvents such as N-methyl-2-pyrrolidone (NMP). In this technique triphenyl phosphite (TPP) and pyridine were used as condensing agents to form poly(amide-imide)s through the N-phosphonium salts of pyridine. All of the polymers were obtained in quantitative yields with inherent viscosities between 0.29-0.46 dL g-1 and were highly soluble in polar aprotic solvents such as N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP) and solvents such as sulfuric acid. They were fully characterized by means of ¹H NMR, FTIR spectroscopy, elemental analyses, inherent viscosity, solubility test, specific rotation and thermal properties of these polymers were investigated using thermogravimetric analysis techniques (TGA and DTG).

Poly(amide-imide)s; optically active polymers; L-alanine


Cinco novas poliamidas-iminas (PAIs) oticamente ativas 6a-e foram preparadas pela reação de policondensação direta da N,N´-(biciclo[2,2,2]octa-7-eno-2,3,5,6-tetracarboxila)-bis-L-alanina 4 com várias diaminas aromáticas 5a-e usando solventes polares apróticos como a N-metil-2-pirrolidona (NMP). Neste procedimento, trifenil fosfito (TPP) e piridina foram usados como agentes de condensação para formar poliamidas-imidas através dos sais de N-fosfônio-piridina. Todos os polímeros foram obtidos com rendimentos quantitativos com uma viscosidade intrínseca entre 0,29-0,46 dL g-1, sendo altamente solúveis em solventes polares apróticos como N,N-dimetil acetamida (DMAc), N,N-dimetilformamida (DMF), dimetil sulfóxido (DMSO), N-metil-2-pirrolidona (NMP) e ainda em solventes como o ácido sulfúrico. Os compostos foram caracterizados por espectroscopia de RMN ¹H, espectroscopia no infravermelho, análise elementar, viscosidade intrínseca, testes de solubilidade, rotação específica e as propriedades térmicas desses polímeros foram investigadas usando técnicas termogravimétricas de análise (TGA e DTG).


SHORT REPORT

New optically active and thermally stable poly(amide-imide)s containing N,N'-(Bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)-bis-L-alanine and aromatic diamines: synthesis and characterization

Khalil Faghihi* * e-mail: k_faghihi@araku.ac.ir ; Morteza Absalar; Mohsen Hajibeygi

Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Faculty of Science, Arak University, 38158 Arak, Iran

ABSTRACT

Five new optically active poly(amide-imide)s (PAIs) 6a-e were prepared by direct polycondensation reaction of the newly synthesized N,N´-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic)-bis-L-alanine 4 with various aromatic diamines 5a-e using polar aprotic solvents such as N-methyl-2-pyrrolidone (NMP). In this technique triphenyl phosphite (TPP) and pyridine were used as condensing agents to form poly(amide-imide)s through the N-phosphonium salts of pyridine. All of the polymers were obtained in quantitative yields with inherent viscosities between 0.29-0.46 dL g-1 and were highly soluble in polar aprotic solvents such as N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP) and solvents such as sulfuric acid. They were fully characterized by means of 1H NMR, FTIR spectroscopy, elemental analyses, inherent viscosity, solubility test, specific rotation and thermal properties of these polymers were investigated using thermogravimetric analysis techniques (TGA and DTG).

Keywords: Poly(amide-imide)s; optically active polymers; L-alanine

RESUMO

Cinco novas poliamidas-iminas (PAIs) oticamente ativas 6a-e foram preparadas pela reação de policondensação direta da N,N´-(biciclo[2,2,2]octa-7-eno-2,3,5,6-tetracarboxila)-bis-L-alanina 4 com várias diaminas aromáticas 5a-e usando solventes polares apróticos como a N-metil-2-pirrolidona (NMP). Neste procedimento, trifenil fosfito (TPP) e piridina foram usados como agentes de condensação para formar poliamidas-imidas através dos sais de N-fosfônio-piridina. Todos os polímeros foram obtidos com rendimentos quantitativos com uma viscosidade intrínseca entre 0,29-0,46 dL g-1, sendo altamente solúveis em solventes polares apróticos como N,N-dimetil acetamida (DMAc), N,N-dimetilformamida (DMF), dimetil sulfóxido (DMSO), N-metil-2-pirrolidona (NMP) e ainda em solventes como o ácido sulfúrico. Os compostos foram caracterizados por espectroscopia de RMN 1H, espectroscopia no infravermelho, análise elementar, viscosidade intrínseca, testes de solubilidade, rotação específica e as propriedades térmicas desses polímeros foram investigadas usando técnicas termogravimétricas de análise (TGA e DTG).

Introduction

Aromatic polyimides are widely employed in the aerospace, microelectronics, optoelectronics and composites for their excellent balance of thermal and mechanical properties.1-2 However their applications have been limited in some fields because the aromatic polyimides are normally insoluble in common organic solvents and have extremely high glass transition or melting temperatures. It is well known that the chemical composition and chain structure of aromatic polyimides were responsible for their prominent properties and responsible for their poor processibility. Therefore one of the targets of polyimide chemistry is to incorporate new functionalities to make polyimides more easily processing without decreasing their many desirable properties such as excellent thermal stability and good mechanical resistance.3-4 For this purpose many efforts on chemical modifications of polyimides have been done, such as introduction of flexible linkages in their backbone, or incorporation of bulky side groups which results in good solubility and processability of the polyimides.5-11 Synthesis of poly(amide-imide)s (PAIs) by incorporating amide functionality at regular intervals in the polyimide main chain is also used. Replacement of polyimides by copolyimides such as poly(amide-imide)s (PAIs) may be useful to tackle the intractability of polyimides12-13 and among them poly(amide-imide)s (PAIs) can improve the solubility. Recently we have synthesized thermally stable PAIs by different methods.14-18

Also polymers with optically active properties have been found interesting applications such as chiral stationary phase for enantiomeric separation in chromatography methods or chiral media for asymmetric synthesis.19-24 In the polycondensation reactions we use amino acids as chiral inducting agents. These materials are naturally occurring compounds and synthetic polymers based on amino acids are expected to be biodegradable and biocompatible. Recently optically active polymers by the reaction of an optically active monomer with several diamines via solution polymerization have been synthesized.25-29

In this article, we described synthesis and characterization of a series of novel poly(amide-imide)s 6a-e containing rigid segments such as bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic diimide in the main chain. The resulting polymers were prepared by the direct polycondensation reaction of N,N´-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)-bis-L -alanine 4 with 4,4´-diamino diphenyl ether 5a, 4,4´-diamino diphenyl sulfone 5b, 3,3´-diamino diphenyl sulfone 5c, 1,4-diamino benzene 5d, 1,5-diamino naphthalene 5e in a medium consisting of N-methyl-2-pyrrolidone (NMP), triphenyl phosphite (TPP), calcium chloride (CaCl2) and pyridine.

Experimental

Reagents

Bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride 1, L-alanine 2, 4,4'-diaminodiphenylether 5a, 4,4'-diaminodiphenylsullfone 5b, 3,3'-diaminodiphenylsulfone 5c, 1,4-phenylenediamine 5d, 1,5-diamino naphthalene 5e, N-methyl-2-pyrrolidone (NMP), pyridine and triphenyl phosphite (TPP) were purchased from Merck Chemical Company and used without previous purification. Commercially available calcium chloride (CaCl2) was purchased from Merck Chemical Company and dried under vacuum at 150 °C for 6 h.

Techniques

1H NMR and 13C NMR spectra were recorded on a Bruker 300 MHz instrument, (Germany). Fourier transform infrared (FTIR) spectra were recorded on Galaxy series FTIR 5000 spectrophotometer (England) as solid by using KBr pellets. Vibration transition frequencies were reported in wave number (cm-1) and band intensities were assigned as weak (w), medium (m), shoulder (sh), strong (s) and broad (br). Inherent viscosities were measured by a standard procedure using a Technico Regd Trad Mark Viscometer. Specific rotations were measured by an A-Kruss polarimeter. Thermal Gravimetric Analysis (TGA and DTG) data for polymers were taken on a Mettler TA4000 System under N2 atmosphere at rate of 10 °C min-1. Elemental analyses were measured by Vario EL equipment by Arak University.

Monomer synthesis

N,N´-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetra carboxylic)bis-L-alanine 4

Into a 100 mL round-bottomed flask with a stirring bar were placed (1.24 g, 5.0 mmol) of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride 1, (0.89 g, 10.0 mmol) of L-alanine 2 and 30 mL of concentrated acetic acid. The mixture was stirred at room temperature for 8 h and then refluxed for 5 h. The solvent was removed under reduced pressure and then 5 mL cold concentrated HCl was added to the residue until a white precipitate formed. The precipitate was washed with cold water and dried under reduced pressure to give 1.79 g (92%) of compound 4, m.p. 248-251 °C; [α]D25= -58.35° (0.05g in 10 mL DMF); IR (KBr, νmax/ cm-1): 2400-3400 (m, br), 1770 (w), 1705 (s), 1628 (w), 1396 (m), 1309 (w), 1207 (m), 1126 (m), 976 (w), 819 (w), 675 (w), 611 (w), 353 (w); 1H NMR (300 MHz, DMSO-d6, TMS ): d 13.01(s, br, 2H), 5.95-5.98 (t, 2H), 4.50-4.57 (q, 2H), 3.37 (s, 2H), 3.22 (s, 4H), 1.23-1.25 (d, 6H); 13C NMR (300 MHz, DMSO-d6): d 176.82, 170.61, 130.64, 47.55, 42.47, 33.89, 14.49. Elemental Anal. Calc. for C18H18N2O8 : C, 55.39; H, 4.65; N, 7.18; Found: C, 55.04; H, 4.46; N, 7.14.

Polymer synthesis

As a typical example, PAI 6c was prepared as follows: Into a 50 mL round-bottom flask with a stirring bar were placed (0.100 g, 0.326 mmol) diimide-diacid 4, (0.065 g, 0.326 mmol) of 3,3´´-diamino diphenyl sulfone 5c, 0.10 g of calcium chloride, 1.0 mL of NMP, 0.8 mL of triphenyl phophite and 0.3 mL of pyridine. The mixture was stirred at room temperature for 2 h and then was heated while stirring at 120-130 °C for 8 h. At the end of the reaction, for quenching growth of the polymer chain, the polymer solution was slowly trickled into a stirred methanol, giving a stringy precipitate. Then polymeric product was washed with hot methanol, collected by filtration and dried at 80 °C for 12 h under vacuum to leave 0.163 g (91%) of solid polymer 6c.

Results and Discussion

Monomer synthesis

The asymmetric diimide-diacid 4 was synthesized by the condensation reaction of one equimolar of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride 1 with two equimolars of L- alanine 2 in an acetic acid solution (Scheme 1).

The chemical structure and purity of diimide-diacid 4 were proved by using elemental analysis, 1H NMR, 13C NMR and FTIR spectroscopy. The measured results in elemental analyses were closely corresponded to the calculated ones, demonstrating that the expected compound was obtained. Figure 1 displays FTIR spectrum of diimide-diacid 4. Peaks appearing at 2400-3400 cm-1 (acid O-H stretching), 1770 cm-1 (C=O asymmetric imide stretching), 1705 cm-1 (C=O acid and symmetric imide stretching), 1396 and 675 cm-1 (imide characteristic ring vibration) confirmed the presence of imide rings and carboxylic groups in this compound.


The 1H NMR spectrum of diimide-diacid 4 showed in Figure 2. H(a) protons relevant to O-H carboxylic groups, H(b) protons relevant to olefin hydrogens that appeared in region of 5.95-5.98 ppm. Peaks in the region 4.50-4.57 ppm as a quartet were assigned to the CH(c) proton which is a chiral center.


The 13C NMR spectrum of diimide-diacid 4 showed 7 signals including C(b) in carboxylic group that appeared in region of 176.82 ppm, C(d) was relevant to chiral carbon atom that appeared in region of 47.55 ppm (Figure 3).


13C NMR and 1H NMR spectra along with elemental analyses data confirmed the proposal structure of compound 4.

Polymer synthesis

PAIs 6a-e were synthesized by direct polycondensation reaction of an equimolar mixture of monomer 4 with five different derivatives of aromatic diamine 5a-e as shown in Scheme 2.

Synthesis and some physical properties of PAIs 6a-e are summarized in Table 1. These polymers have inherent viscosities in range of 0.29-0.46 dL g-1. All of the resulting polymers show optical rotations and have optical activities. Results show that PAIs 6b and 6c have higher inherent viscosities in comparing to other PAIs because they have a rigid and polar moiety in the diamine structure such as sulfone moiety (Table 1).

Polymer characterization

The structures of these polymers were confirmed as PAIs by mean of FTIR, 1H NMR spectroscopy and elemental analyses. FTIR spectroscopy of all PAIs are listed in Table 2.

The representative FTIR spectrum of PAI 6e was shown in Figure 4. The polymer exhibited characteristic absorption bands at 1707-1774 cm-1 to the imide ring (asymmetric and symmetric C=O stretching vibration) and 1384 cm-1 (C-N stretching vibration). The absorption bands of amide groups appeared at 3286 cm-1 (N-H stretching).


Figure 5 displays 1H NMR spectrum of PAI 6d. Peak at 9.60 ppm related to NH of amide groups in the polymer chain, aromatic protons related to 1,4-phenylene appeared in the region of 7.41 ppm and the peak in the region of 6.06 ppm related to olefin protons.


The elemental analyses of the resulting PAIs 6a-e were in good agreement with the calculated values for the proposed structure (Table 3).

The solubility of PAIs 6a-e was investigated by 0.01g of polymeric sample in 2.0 mL solvent. All of the polymers are soluble in organic solvents such as N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), NMP (N-methyl-2-pyrrolidone), sulfuric acid and are insoluble in solvents such as chloroform, methylene chloride, methanol, ethanol and water (Table 4).

Thermal properties

The thermal properties of PAIs 6a and 6c were investigated by TGA and DTG in a N2 atmosphere at a heating rate of 10 °C min-1 as model for prepared polymers and the thermal data are summarized in Table 5 (Figure 6). The initial decomposition temperatures of 5% and 10% weight losses (T5 and T10) and the char yield at 600 °C are summarized in Table 5. These polymers exhibited good resistance to thermal decomposition up to 320 to 340 °C in nitrogen and began to decompose gradually above those temperatures. T5 for these polymers ranged from 320 to 340 °C and T10 for two polymers ranged from 345 to 355 °C and the residual weights for these polymers at 600 °C ranged from 38 and 58% in nitrogen. Results show that PAI 6c containing sulfone moiety has higher thermal stability in comparing to PAI 6a because this polymer has a rigid and polar moiety in the diamine structure such as sulfone moiety (Table 5).


Conclusions

A new series of PAIs 6a-e containing bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic diimide were synthesized by direct polycondensation reaction of N,N´-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)bis-L-alanine 4 with various aromatic diamins 5a-e using triphenyl phosphite, NMP, calcium chloride and pyridine as condensing agents. The high char yields of these polymers showed that the introduction of bicyclo and aromatic rings into the polymer backbone increased the thermal stability and solubility in polar amidic solvents. Since these optically active polymers have amino acid in the polymer architecture and they are expected to be biodegradable. Optically active and thermal stability properties can make these polymers attractive for practical applications such as processable high-performance engineering plastics used as chiral stationary phase and chiral media for asymmetric synthesis.

Received: December 22, 2008

Web Release Date: November 6, 2009

  • 1. Ghosh, M. K.; Mittal, K. L.; Polyimide: Fundamental and Applications, Dekker: New York, 1996.
  • 2. Wilson, D.; Stenzenberger, H. D.; Hergenrother, P. M.; Polyimides, Chapman and Hall: New York, 1990.
  • 3. Kripotou, S.; Pissis, P.; Sysel, P.; Sindelar, V.; Bershtein, V. A.; Polymer 2006, 47, 357.
  • 4. Liaw, D. J.; Chang, F. C.; Liu, J. H.; Wang, K. L.; Faghihi, K.; Huang, S. H.; Lee, K. R.; Lai, J. Y.; Polym. Degrad. Stab 2007, 92, 323.
  • 5. Williams, M. K.; Holland, D. B.; Melendez, O.; Weiser, E. S.; Brenner, J. R.; Nelson, G. L.; Polym. Degrad. Stab 2005, 88, 20.
  • 6. Maya, E. M.; Lozano, A. E.; Campa, J. G.; Abajo, J.; Macromol. Rapid Commun 2004, 25, 592.
  • 7. Yang, C. P.; Hsiao, S. H.; Wu, K. L.; Polymer 2003, 44, 7067.
  • 8. Hariharan, R.; Bhuvana, S.; Anitha, M. M.; Sarojadevi, M.; J. Appl. Polym. Sci 2004, 93, 1846.
  • 9. Liaw, D. J.; Hsu, P. N.; Chen, W. H.; Lin, S. L.; Macromolecules 2002, 35, 4669.
  • 10. Patil, P. S.; Pal, R. R.; Salunkhe, M. M.; Maldar, N. N.; Wadgaonkar, P. P.; Eur. Polym. J. 2007, 43, 5047.
  • 11. Liaw, D. J.; Huang, C. C.; Chen, W. H.; Polymer 2006, 47, 2337.
  • 12. Chang, Y. T.; Shu, C. F.; Macromolecules 2003, 36, 661.
  • 13. Liaw, D. J.; Chen, W. H.; Polym. Degrad. Stab 2006, 91, 1731.
  • 14. Faghihi, K.; Naghavi, H.; J. Appl. Polym. Sci 2005, 96, 1776.
  • 15. Faghihi, K.; Hajibeygi, M.; J. Appl. Polym. Sci 2004, 92, 3447.
  • 16. Faghihi, K.; Zamani, K.; Mirsamie, A.; Mallakpour, S.; J. Appl. Polym. Sci 2004, 91, 516.
  • 17. Faghihi, K.; J. Appl. Polym. Sci 2008, 109, 74.
  • 18. Faghihi, K.; Hagibeygi, M.; Macromol. Res 2005, 13, 14.
  • 19. Akekah, A.; Sherrington, D. S.; Chem. Rev 1981, 81, 557.
  • 20. Aglietto, M.; Chiellini, E.; Antone, S. D.; Ruggeri, G.; Solaro, R.; Pure Appl. Chem 1988, 60, 415.
  • 21. Yuki, H.; Okamoto, Y.; Okamoto, I.; J. Am. Chem. Soc 1980, 102, 6358.
  • 22. Okamoto, Y. E.; Yashima, E.; Angew. Chem., Int. Ed. 1999, 37, 1020.
  • 23. Soai, K.; Niwa, S.; Chem. Rev 1992, 92, 833.
  • 24. Subramanian, G.; Chiral Separation Techniques, Wiley: New York, USA, 2001.
  • 25. Mallakpour, S. E.; Hajipour, A. R.; Zamanlou, M. R.; Eur. Polym. J 2002, 38, 475.
  • 26. Mallakpour, S. E.; Hajipour, A. R.; Zamanlou, M. R.; Polym. Sci., Ser. A 2002, 44, 243.
  • 27. Faghihi, K.; Macromol. Res 2004, 12, 258.
  • 28. Faghihi, K.; Zamani, K.; Mirsamie, A.; Mallakpour, S. E.; Polym. Int 2004, 53, 1226.
  • 29. Mallakpour, S.; Kowsari, E.; Polym. Bull 2005, 53, 169.
  • *
    e-mail:
  • Publication Dates

    • Publication in this collection
      14 Oct 2011
    • Date of issue
      2009

    History

    • Accepted
      06 Nov 2009
    • Received
      22 Dec 2008
    Sociedade Brasileira de Química Instituto de Química - UNICAMP, Caixa Postal 6154, 13083-970 Campinas SP - Brazil, Tel./FAX.: +55 19 3521-3151 - São Paulo - SP - Brazil
    E-mail: office@jbcs.sbq.org.br