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Polymer International 43 (1997) 8È12
Synthesis and Characterisation of
Polyamides and Polyimides from
Amino/Methylene bis[Benzenamine]
Styryl Pyridines
Venkateswarlu Peesapati,* U. Narasimha Rao
Department of Chemistry, Osmania University, Hyderabad-7, India
& Richard A. Pethrick
Department of Pure and Applied Chemistry, Thomas Graham Building, 295 Cathedral Street, University of Strathclyde, Glasgow
G1 1XL, UK
(Received 21 May 1996 ; revised version received 8 November 1996 ; accepted 25 November 1996)
Abstract : Polyamides and polyimides containing diamines, with potential nonlinear optical characteristics, were prepared using (E)-4,4@-[[[2-(4-pyridinyl)
ethenyl]phenyl]amino]bis[benzenamine] and (E)-4-4@-[[[2-(4-pyridinyl)ethenyl]
2-methyl phenyl]amino]bis[benzenamine] condensed with pyromellitic dianhydride to obtain poly(amic acid)s. The poly(amic acid)s were soluble in polar
aprotic solvents, such as dimethylformamide, dimethylsulphoxide and dimethylacetamide, and could be cast into transparent, tough, Ñexible Ðlms. Amorphous
thermally stable polyimides were formed by cyclodehydration. Similarly, (E)-4,4@[[[2-(4-pyridinyl)ethenyl]phenyl]methylene]bis[benzenamine] and (E)-4,4@-[[[2(4-pyridinyl)ethenyl]phenyl]methylene]bis[N-ethylbenzenamine]
condensed with 3-methyladipoyl chloride to obtain other new polyamides. Characterisation using infra-red and nuclear magnetic resonance spectroscopy, X-ray
di†raction and thermogravimetric analysis are reported.
Key words : poly(amic acid)s, polyimides, polyamides, styryl pyridines, synthesis,
molecules investigated, styryl molecules in solution have
been found to exhibit some of the highest values of the
second order non-linear optical coefficient x2 so far
In our earlier communications,7,8 we reported the
synthesis and characterisation of polyamides and polyimides from two diamines, with non-linear properties,
containing a styryl pyridine moiety. The results revealed
that the compounds prepared, whilst meeting the
requirement for a curable monomer, did not appear to
have the required non-linear activity. The lack of a
detectable signal was probably a result of the e†ects of
The various approaches which may be adopted for the
production of materials with second order non-linear
optical properties have been recently reviewed.1h3
Single crystals of molecules, which form noncentrosymmetric crystalline forms and have a molecular
structure that contains a donor and acceptor group
connected by a conjugated backbone, have the capability of frequency doubling of light. Of the many organic
* To whom all correspondence should be addressed.
( 1997 SCI. Polymer International 0959-8103/97/$17.50
Printed in Great Britain
Synthesis of polyamides and polyimides
readsorption of the light at 532 nm, even for spun Ðlms,
or dipolar pairing removing possible non-linear e†ects.
Recently, polyamides and polyimides have been
shown to be poled to form high temperature non-linear
s2 materials.9 This paper describes the synthesis of new
thermally stable polyamides/imides by the insertion of a
styryl pyridine group into a polymer backbone. The
advantage with the design presented here is that the
nitrogen bridged structure allows sufficient electron
transfer for hyperpolarisation to be achieved, which is
not possible with the carbon bridged molecules that we
reported earlier.7 These polymers, like those reported
recently,9 have high values of the glass transition temperature (T ) and hence meet the requirements for prog
cessing into device structures.
As an illustration of the polymerisation process, we
report the reaction of (E)-4,4@-[[[2-(4-pyridinyl)ethenyl]
phenyl]amino]bis[benzenamine] (2a) with PMDA
(Scheme 2).
Preparation of poly(amic acid) (3a). Diamine (2a) (0É37 g,
0É001 mol) was dissolved in 15 ml DMAC and cooled to
10¡C. To this clear solution was added PMDA
(0É2189 g, 0É001 mol) by stirring in 20 mg batches over a
period of 1 h ; the viscosity increased as the solid dissolved. The mixture was then stirred under nitrogen
atmosphere for 2 h at 10¡C. The poly(amic acid) (3a)
was precipitated by pouring one-third of the reaction
mixture into a large excess of methyl alcohol ; the precipitate was washed with methanol, Ðltered and dried in
vacuum, whereupon orange red Ñakes of polymer were
N,N-Dimethylacetamide (DMAC) was fractionally distilled under reduced pressure after it was dried over
P O for 24 h. Pyromellitic dianhydride (PMDA) was
2 5
sublimed prior to use. Other chemicals used were of
laboratory reagent grade. In our earlier paper,10 the
synthesis of 4,4@-[(4-bromophenyl)amino]bis[benzenamine] (1a) and its methyl analogue (1b) and related
compounds were described, and these molecules were
used as precursors for the generation of the polymers
(Scheme 1).
(E)-4,4@-[[[2-(4-Pyridinyl)ethenyl]phenyl]amino]bis[benzenamine] (2a) was prepared from 4,4@[4-bromophenyl)amino]bis[benzenamine] (1a) (4É15 g,
0É01 mol)
earlier.7,10 Yield 3É4 g (70%) ; m.p. 105È106¡C.
(E) - 4, 4@ - [[[2 - (4 - Pyridinyl)ethenyl]2 - methylphenyl]amino]bis[benzenamine] (2b) was prepared under conditions similar to those described earlier for the synthesis of (2a), starting from 4,4@-[(4-bromo, 3-methylphenyl)
amino]bis[benzenamine] (1b) (4É29 g, 0É01 mol). Yield
3É55 g (75%) ; m.p. 123È125¡C.
Preparation of polyamide (4a) by imidisation reaction.
(thermal cyclisation). The reaction mixture of poly(amic
acid) (3a) was poured onto a glass plate and the solvent
removed under vacuum. The tough Ðlm so obtained
was cyclised by heating in vacuum at 260¡C for 3 h to
give a tough orange-red Ðlm. The polyimides obtained
showed similar IR spectra and the absence of amic acid
The other polymers, namely poly(amic acid) (3b) and
polyimide (4b), were prepared in a similar manner as
described in Scheme 2).
Scheme 1
Scheme 2
V . Peesapati, U. Narasimha Rao, R. A. Pethrick
the mixture, followed by 0É197 g (0É001 mol) of 3methyladipoyl chloride. The solution thus obtained was
poured into water. The precipitated polymer was collected by Ðltration and dried under vacuum. The yield
of the polymer (6a) was 0É476 g (95%).
Following the above procedure, condensation of (E)4,4@-[[[2-(4-pyridinyl)ethenyl]phenyl]methylene]bis[Nethylbenzenamine] (5b) (0É433 g, 0É001 mol) and 3methyladipoyl chloride (0É197 g, 0É001 mol) gave the
other polyamide (6b) in 95% yield (Scheme 3).
The poly(amic acid)s and polyimides and polyamides
were amorphous in nature, as evidenced by their X-ray
di†raction pattern taken by the powder method using
nickel-Ðltered CuKa radiation on a Phillips X-ray unit
(Phillips generated PW-1730). The thermal stability of
the polymers was studied by thermogravimetric analysis
(TGA) on a Netsch 409 thermal analyser. Thermograms
were obtained by heating the samples in a nitrogen
atmosphere at a heating rate of 10¡C min~1 (Fig. 1).
Scheme 3
Preparation of polyamide (6a ) from (E )-4 ,4 ¾-ÍÍÍ2 (4 -pyridinyl )ethenyl Ëphenyl Ëmethylene Ëbis Íbenzenamine Ë (5a )
By direct polycondensation. A mixture of diamine (5a)
(0É377 g, 0É001 mol), 3-methyladipic acid (0É160 g,
0É001 mol), calcium chloride (dried) (0É5 g), triphenylphosphine in 2É5 ml of pyridine and N-methyl-2pyrrolidone (NMP) (8 ml) was heated with stirring at
100¡C for 3 h under nitrogen. The reaction mixture was
poured into water. The precipitated polymer was collected by Ðltration, washed thoroughly with water and
dried under vacuum. The yield of the polymer (6a) was
0É45 g (90%).
By low temperature solution polycondensation. A solution of diamine (0É377 g, 0É001 mol) (5a) in 8 ml of NMP
was cooled to [ 25 to [ 30¡C in a dry iceÈacetone
bath. Then 0É7 ml of propylene oxide was added to
Fig. 1. TGA curves of polyimides (4a) and (4b) and (6a) and
(6b) in nitrogen at a heating rate of 10¡C min~1.
In the present work, two new polyimides and two polyamides containing styryl pyridine linkage were prepared
by the polycondensation of diamines (2a) and (2b) with
PMDA and (5a) and (5b) with 3-methyladipoyl chloride.
These materials were characterised by IR, X-ray di†raction, viscosity and TGA analysis.
The diamines containing styryl pyridine linkages were
synthesised by the condensation of 4-vinylpyridine with
4,4@-[(4-bromophenyl)amino]bis[benzenamine] (1a) and
its methyl analogue (1b) adopting HeckÏs reaction11 as
illustrated in Scheme 1 and characterised by IR, 13C
nuclear magnetic resonance (NMR) and mass spectroscopy.
Synthesis of polyimides by polycondensation of
dianhydrides and diamines involves two steps, the ringopening polyaddition reaction of the dianhydride with
diamine to form the poly(amic acid) (3a), and subsequent imidisation to polyimide (4a). The ring-opening
polyaddition reaction of dianhydride with diamine was
carried out at low temperature in polar solvents in a
slow stream of dry nitrogen.
Diamines (2a) and (2b) were highly soluble in DMAC.
Solutions of these amines were reacted with PMDA at
0¡C to give poly(amic acid)s (3a) and (3b), respectively,
which could be isolated by adding methanol. Cyclodehydration of the poly(amic acid)s (3a) and (3b) to
polyimides (4a) and (4b) could be achieved both chemically and thermally. In the present study, thermal cyclisation was used, which gave better results.
The IR spectrum of poly(amic acid) (3a), (Fig. 2)
showed distinctive peaks at 3243 cm~1 for NwH
stretching, 1720 and 1650 cm~1 for CxO stretching of
carboxylic acid and CxO stretching of amide, respectively, and 3243È3450 cm~1 broad peaks for OwH
Synthesis of polyamides and polyimides
Fig. 2. IR spectra of polyamic acid (3a) (ÈÈ) and (2) (È È È) showing the characteristic carbonyl and amide absorptions.
TABLE 1. Percentage weight loss of polyimides at
different temperaturesa
Weight loss (%)
a Heating rate, 10¡C minÉ1.
b Initial decomposition temperature.
stretching. The IR spectra of the polyimides (4a) and
(4b) showed characteristic bands which established the
presence of imide rings in these polymers. They were
strong absorption bands in the regions near 1719 cm~1
(asymmetric carbonyl stretching), 1367 cm~1 (imide II,
imide axial vibration), 1115 cm~1 (imide III, imide ring
transverse vibration) and 718 cm~1 (imide IV, imide
ring vibration out of plane).
The 1H NMR spectra in dimethylsulphoxide/
(DMSO-d ) (200 MHz) of poly(amic acid)s (3a) and (3b)
showed signals between d 6É9È8É5 ppm for aromatic
protons. The acid proton appeared as a broad peak at d
Fig. 3. NMR spectrum of polyamide (6a) (in DMSO-d ) showing characteristic methane proton resonance at d 5É45.
10É5 ppm. The methyl protons of (3b) resonated at d
2É1 ppm.
The poly(amic acid)s (3a) and (3b) had inherent viscosities of 0É58 and 0É42 dl g~1 which were determined
in dimethylformamide (DMF) at a concentration of
0É1 g/100 ml. Similarly, the low temperature solution
polycondensation a†orded the aramides (6a) and (6b),
which had higher viscosities of 0É25 and 0É32 dl g~1
compared with those from the direct polycondensation.
The polyimides (4a) and (4b) were stable up to 350¡C
in nitrogen, and the temperatures at 10% weight loss
were above 475¡C on the TGA curves (Fig. 1). The
thermal behaviour of the other polymers was also
evaluated by means of TGA (Fig. 1). Polyamides (6a)
and (6b) were stable up to 250¡C in nitrogen and the
temperature at 10% weight loss was 300¡C (Table 1).
The chemical structures of the polyamides (6a) in
DMSO-d and (6b) in CDCl were analysed by 1H
NMR (Fig. 3). From the 1H NMR spectrum, the characteristic triphenyl methane proton resonated at d 5É45
(CwH). The two a-protons of the pyridine ring resonated at d 8É5 and the b-protons resonated at d 7É6, as
broad peaks. All the other protons clustered in the d
6É9È7É2 ppm region. The aliphatic protons resonated
between d 0É6È3É8 ppm. The structures of the polymers
were also conÐrmed by their 13C NMR spectra.
X-ray di†raction studies revealed that the polyamides
and polyimides were amorphous. The amorphous
nature was reÑected in their excellent solubility in
NMP, DMSO, DMF, pyridine and H SO .
2 4
Four new polyimides and polyamides containing styryl
pyridine linkages were prepared by the poly condensation of the requisite diamines with dianhydride
(PMDA) and 3-methyladipoylchloride. Poly(amic acid)s
were soluble in DMAC and could be cast into a tough
V . Peesapati, U. Narasimha Rao, R. A. Pethrick
Ðlm, but the polyimides were sparingly soluble and
showed good thermal stability. The polyamides prepared also showed good solubility in various solvent
systems. These materials failed to exhibit any non-linear
properties. However, the failure to detect such properties reÑects the fact that the materials were not poled
prior to formation of the rigid backbone structure and
hence a random distribution of the dipoles, producing a
self-cancellation situation, most probably existed within
the polymer. Further work will be carried out to investigated the way in which alignment and orientation can
be induced in the polymers prior to the Ðnal stage in the
synthesis, with the anticipation that a non-linear
material can be generated.
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