Synthesis of a new pyridine-containing diamine and related polyimide

Article abstract of DOI:10.1016/j.cclet.2009.11.004

A new kind of aromatic diamine monomer containing pyridine unit, 2,6-bis[4-(4-aminophenoxy)phenoxy]pyridine (BAPP), was synthesized in three steps, using hydroquinone as starting material. A novel pyridine-containing polyimide was prepared from the resulting diamine BAPP with 4,4′-oxydiphthalic anhydride (ODPA) via a conventional two-step thermal imidization method. The resulting polyimide exhibits excellent solubility, film-forming capability and high thermal resistance.

Full text of DOI:10.1016/j.cclet.2009.11.004

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Chinese Chemical Letters 21 (2010) 277–278
www.elsevier.com/locate/cclet
Synthesis of a new pyridine-containing diamine and
related polyimide
*
Jiu Jiang Zhao, Chen Liang Gong, Shu Jiang Zhang, Yu Shao, Yan Feng Li
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering,
Institute of Biochemical Engineering & Environmental Technology, Lanzhou University, Lanzhou 730000, China
Received 15 June 2009
Abstract
A new kind of aromatic diamine monomer containing pyridine unit, 2,6-bis[4-(4-aminophenoxy)phenoxy]pyridine (BAPP), was
synthesized in three steps, using hydroquinone as starting material. A novel pyridine-containing polyimide was prepared from the
resulting diamine BAPP with 4,40-oxydiphthalic anhydride (ODPA) via a conventional two-step thermal imidization method. The
resulting polyimide exhibits excellent solubility, film-forming capability and high thermal resistance.
# 2009 Yan Feng Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Pyridine; Aromatic polyimide; Pyridine-containing diamine
Aromatic polyimides have been widely used in aerospace, electrical and electronic applications, composite
material and optoelectronical industries because of their excellent thermal, mechanical and electrical properties as
well as outstanding chemical resistance [1–3]. Despite their outstanding properties, most of them have high melting
temperatures or softening temperatures and limited solubility in most solvents because of their rigid backbones and
strong interactions between chains, which restrict their application in corresponding fields [4]. To overcome these
problems, much research effort has been focused on the synthesis of soluble and processable polyimides in fully
imidized form without deterioration of their own excellent properties. Several approaches to soluble polyimides
including introduction of flexible linkage and heteroaromatic rings into the polymer backbone have been developed in
the past decade [5,6]. The pyridine rings with heteroaromatic structure have excellent stabilities derived from its
molecular symmetry and aromaticity, introduction of aryl–ether linkage into the polymer chains can improve the
solubility, so the incorporation of aryl–ether linkage and pyridine rings into polyimide backbone would improve the
solubility without deterioration of their own excellent properties.
In this work, a new pyridine-containing diamine, 2,6-bis[4-(4-aminophenoxy)phenoxy]pyridine (BAPP) 3, was
synthesized by a three step procedure, as shown in Scheme 1. Firstly, 4-(4-nitrophenoxy)phenol 1 was synthesized
through the nucleophilic etherification of 4-chloronitrobenzene (0.8 equiv.) with potassium phenolate of
hydroquinone (1.0 equiv.) in dimethylformamide (DMF). Then the dinitro compound, 2.6-bis[4-(4-nitrophenox-
y)phenoxy]pyridine 2 was synthesized by nucleophilic substitution reaction of 1 (2.1 equiv.) and 2.6-dichloropyridine
* Corresponding author.
E-mail address: liyf@lzu.edu.cn (Y.F. Li).
1001-8417/$ – see front matter # 2009 Yan Feng Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2009.11.004

278
J.J. Zhao et al. / Chinese Chemical Letters 21 (2010) 277–278
Scheme 1. Synthesis of 2,6-bis[4-(4-aminophenoxy)phenoxy]pyridine (BAPP). (a) DMF, K2CO3, 100 8C, 10 h; (b) DMAC, K2CO3, 150 8C, 24 h;
(c) NH2NH2ꢁH2O, Pd/C, CH3CH2OH, 80 8C, 6 h.
(1.0 equiv.) in the presence of anhydrous potassium carbonate (2.1 equiv.) in dimethylacetamide (DMAc). Finally 2
was converted to the corresponding diamine monomer 3 by hydrazine Pd/C-catalyzed reduction, the corresponding
yield was 66%, 50% and 95%. The MS(ESI) of 3, m/z, shows (M+1)+: 478.1. Its 1H NMR (400 MHz, CDCl3, d) data
were at d 7.60 (t, 1H, J = 8.0 Hz, H-a), 7.01 (d, 4H, J = 9.2 Hz, H-c), 6.87 (m, 8H, H-d, H-e), 6.65 (d, 4H, J = 8.8 Hz,
H-f), 6.47 (d, 2H, J = 8.0 Hz, H-b), 3.40 (broad, 4H, H-g), and 13C NMR (400 MHz, CDCl3, d) absorption peaks
appeared at d 162.68(C3), 155.43(C7), 148.86(C4), 148.32(C8), 142.60(C11), 141.99(C1), 122.27(C5), 120.76(C6),
118.02(C9), 116.22(C10), 103.63(C2). Elem. Anal. Calcd. for C29H23N3O4 (477.17): C 72.94%, H 4.85%, N 13.40%.
Found: C 72.90%, H 4.87%, N 13.38%. The data agree with the structure of BAPP.
The related polyimide was synthesized by polycondensation of BAPP and aromatic dianhydride ODPAvia previous
method [7]. The inherent viscosity of the resulting polyimide in the DMF solution with a 0.5 g/dL concentration at
30 8C was 0.46 dL/g. FT-IR spectra of the resulting polyimide revealed strong bands at 1776 cmꢀ1 (asymmetrical
C O stretch), 1717 cmꢀ1 (symmetrical C O stretch), 1376 cmꢀ1 (C–N stretch) and 1111 and 745 cmꢀ1 (imide ring
deformation), which indicated that imide ring was fully formed. The value of 5% gravimetric loss and 10% gravimetric
loss in nitrogen of the resulting polyimide is 501 8C and 527 8C, and its Tg is 274 8C, which showed the polyimide has
excellent thermal stability. It also exhibited good solubility in common organic solvents such as DMF, DMAc,
dimethyl sulfoxide and tetrahydrofuran. Meanwhile, the resulting polyimide has excellent film-forming capability; a
strong and flexible film could be obtained. The polyimide film has tensile strength of 101.2 MPa, elongation at break of
9.6%, and tensile modulus of 1.43 GPa. According to the above experimental results, the new pyridine-containing
diamine BAPP holds good polymerizability.
Acknowledgment
The authors acknowledge the financial support from the Research Foundation of the State Key Laboratory of
Applied Organic Chemistry.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at doi:10.1016/
j.cclet.2009.11.004.
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