Synthesis of soluble poly(amide-ether-imide-urea)s bearing amino acid moieties in the main chain under green media (ionic liquid)

Article abstract of DOI:10.1007/s00726-010-0660-x

In this study, an optically active diamine, N,N′-(pyromellitoyl)- bis{N-[4(4-aminophenoxy)phenyl]-2-(4-methyl)pentanamide} (1) containing amino acid l-leucine was prepared in three steps. The step-growth polymerization of this chiral diamine with several diisocyanates in room temperature ionic liquid (IL), 1,3-dipropylimidazolium bromide as an environmentally friendly solvent and in a volatile organic solvent, is investigated. The polymerization yields and inherent viscosities of the resulting poly(amide-ether-imide-urea)s are compared in both solvents. The results show that the IL to be the superior polymerization media. All of the obtained polymers exhibited good solubility in some polar aprotic organic solvents such as N,N-dimethyacetamide, N,N-dimethyformamide, dimethyl sulfoxide while thermal stability was not disturbed based on thermogravimetric analysis and differential scanning calorimetry experiments. X-ray diffraction analysis of polymers shows that they are amorphous. The observation of optical rotation confirms the optical activity of prepared polymers.

Full text of DOI:10.1007/s00726-010-0660-x

Amino Acids (2011) 40:487–492
DOI 10.1007/s00726-010-0660-x
ORIGINAL ARTICLE
Synthesis of soluble poly(amide-ether-imide-urea)s bearing amino
acid moieties in the main chain under green media (ionic liquid)
Shadpour Mallakpour
Received: 22 March 2010 / Accepted: 11 June 2010 / Published online: 23 June 2010
Ó Springer-Verlag 2010
Abstract In this study, an optically active diamine,
N,N0-(pyromellitoyl)-bis{N-[4(4-aminophenoxy)phenyl]-2-
(4-methyl)pentanamide} (1) containing amino acid L-leucine
was prepared in three steps. The step-growth polymeriza-
tion of this chiral diamine with several diisocyanates in
room temperature ionic liquid (IL), 1,3-dipropylimidazo-
lium bromide as an environmentally friendly solvent and in
a volatile organic solvent, is investigated. The polymeri-
zation yields and inherent viscosities of the resulting
poly(amide-ether-imide-urea)s are compared in both sol-
vents. The results show that the IL to be the superior
polymerization media. All of the obtained polymers
exhibited good solubility in some polar aprotic organic
solvents such as N,N-dimethyacetamide, N,N-dimethyfor-
mamide, dimethyl sulfoxide while thermal stability was not
disturbed based on thermogravimetric analysis and differ-
ential scanning calorimetry experiments. X-ray diffraction
analysis of polymers shows that they are amorphous. The
observation of optical rotation confirms the optical activity
of prepared polymers.
Introduction
The synthesis of artificial chiral polymers and oligomers has
recently been attracting considerable attention due to their
various advanced functions. The application of optically
active polymers in chiral recognition, liquid crystals,
asymmetric catalysis, and linear optical devices has made
them one of the most motivating material categories (Zhai
et al. 2005; Zhong et al. 2005; Gasparrini et al. 2005; Lee
et al. 2003; Lindholm and Forstedt 2005; Ikeuchi et al. 2009).
Furthermore, the chemistry of polyureas (PU)s may poten-
tially be in the interesting correlation with optical activity,
since they are known as excellent candidates for the micro-
encapsulation purposes (Ley et al. 2003) and their chiral
structure may lead to the asymmetric recognition behavior.
PUs are commercialized since 1989 and may simply be
prepared via the polymerization of diamines with diisocy-
anates (Li and Chen 2008; Jewrajka et al. 2009; Tamami
et al. 2005). The adoptable mechanical properties of PUs
caused by the tailoring of hard and/or soft moieties in the
structures, in conjunction with excellent hydrolysis resis-
tances, make them appropriate for plenty of various
applications such as coating, roofs, bridges, etc. (Roland
and Casalini 2007; Roland et al. 2007; Sarva et al. 2007; Ni
et al. 2000; Du et al. 2001). In addition, the application of
PUs as piezoelectric and ferroelectric polymers, second-
order optical nonlinear polymers, biodegradable polymers,
and polymer microcapsules has already been reported (Du
et al. 2001; Sakai et al. 2008; Hong and Park 2000; Tao
et al. 1995). On the other hand, chiral PUs an advanced
category of macromolecules are useful precursors for
preparation of polymeric chiral stationary phases in HPLC
techniques (Huang et al. 2007).
Keywords Chiral diamine ꢀ L-Leucine ꢀ Polyurea ꢀ
Optically active polymers ꢀ Imidazolium ionic liquid ꢀ
Green chemistry
S. Mallakpour (&)
Organic Polymer Chemistry Research Laboratory,
Department of Chemistry, Isfahan University of Technology,
Isfahan 84156-83111, Islamic Republic of Iran
e-mail: mallak@cc.iut.ac.ir; mallak777@yahoo.com;
mallakpour84@alumni.ufl.edu
However, the use of PUs is associated with some serious
drawbacks as a consequence of their limited solubility and
123

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S. Mallakpour
high glass transition or softening temperatures which have
been attributed to the high polarity of urea functions and
the construction of strong interchain hydrogen bond lattice
(Sarva et al. 2007; Huang et al. 2007; Kurita et al. 1994;
Sendijarevic et al. 2004; Yang et al. 1998). Generally, it
has been accepted that the utilization of aromatic low
molecular weight diamines make the resulting PUs highly
stiff and poorly soluble in organic solvents, while the
existence of further fractions with superior flexibilities,
such as ether functionalities and aliphatic moieties cause
major improvements in both rigidity and solubility
behaviors (Sakai et al. 2008; Yang et al. 1998; Luo et al.
1996). Although the aforementioned soft functional groups
may diminish the thermal resistance of PUs, it can be
restored by the incorporation of further intrinsic thermo-
resistance functions, such as amide or imide groups in the
polymer backbone.
WI, USA), Riedel–deHaen AG (Seelze, Germany) and
Merck Chemical Co. Pyromellitic dianhydride (benzene-
1,2,4,5-teracarboxilic dianhydride) was recrystallized from
acetic anhydride and then dried in a vacuum oven at 125°C
overnight. N,N-Dimethylacetamide (DMAc) was dried
over barium oxide, followed by fractional distillation. 4,40-
Oxydianiline (ODA) was purified by sublimation and then
dried in a vacuum oven at 125°C overnight. 2,4-Tolylene
diisocyanate (TDI) (a) (Merck), hexamethylene diisocya-
nate (HDI) (b) (Merck), 4,40-methylene-bis-(4-phenyliso-
cyanate) (MDI) (Aldrich) (c) and isophorone diisocyanate
(IPDI) (d) (Fluka) were employed as received. IL, 1,3-
dipropylimidazolium bromide ([1,3-(pr)2im]Br) was pre-
pared according to the literature procedure (Lindholm and
Forstedt 2005).
Instruments
Many chemical processes involve volatile organic sol-
vents (VOS)s that evaporate into the atmosphere with
detrimental effects on human health and the environment.
Obviously, considerable efforts have focused on the
reduction and often elimination of VOSs as major envi-
ronmental pollutants (Long and Hunt 1998). Ionic liquids
(IL)s exhibit great promise as solvents for polymerization
of a wide range of monomers. Their low volatility, high
thermal and chemical stability, and potential to be recycled
make ILs attractive as an environmentally friendly alter-
native to organic solvents (e.g., N,N-dimethylformamide,
N,N-dimethylacetamide, N-methyl-2-pyrrolidone, toluene,
xylene, dichloromethane) utilized in many industrial
polymerization processes (Johnston-Hall et al. 2009;
Andrzejewska et al. 2009; Kubisa 2009; Mallakpour and
Kolahdoozan 2008).
Proton nuclear magnetic resonance (1H-NMR, 500 MHz
and 13C-NMR, 125 MHz) spectra were recorded in
DMSO-d6 solution using a Bruker (Germany) Avance
500 instrument. Proton resonances are designated as
singlet (s), doublet (d), and multiplet (m). FT-IR spectra
were recorded on 400D IR spectrophotometer (Japan).
The spectra of solids were obtained using KBr pellets.
The vibrational transition frequencies are reported in
wavenumbers (cm-1). Band intensities are assigned as
weak (w), medium (m), strong (s) and broad (br).
Inherent viscosities were measured using a Cannon–
Fenske Routine Viscometer (Germany) at concentration
of 0.5 g dL-1 at 25°C. Specific rotations were measured
by a Jasco Polarimeter (Japan). Quantitative solubility
was determined using 0.05 g of the polymer in 0.5 mL
of solvent. Thermogravimetric analysis (TGA) data for
polymers were taken on Perkin Elmer in nitrogen
atmosphere at a heating rate of 20°C min-1 by the Ira-
nian Polymer and Petrochemical Institute of Iran (IPPI).
Differential scanning calorimetry (DSC) data were
recorded on a DSC-PL-1200 instrument at a heating rate
of 20°C min-1 in nitrogen atmosphere by IPPI. Glass-
transition temperatures (Tg) were read at the middle of
the transition in the heat capacity taken from the heating
DSC traces. The X-ray diffraction (XRD) patterns were
recorded by employing a Philips X’PERT MPD diffrac-
tometer (Cu Ka radiation: k = 0.154056 nm at 40 kV
and 30 mA) over the 2h range of 20–80° at a scan rate
Following the extensive investigation of the synthesis
and characterization of the new optically active macro-
molecules (Mallakpour and Seyedjamali 2008; Mallakpour
and Rafiee 2008, 2009; Mallakpour and Zadehnazari 2010;
Mallakpour and Khani 2010; Mallakpour and Shamoa-
hammadi 2004), in this article, we wish to report the syn-
thesis and characterization of a series of optically active,
poly(amide-ether-imide-urea)s, (PAEIU)s, with modified
solubility and thermal properties via the IL-mediated
polymerization of high molecular weight chiral diamine
containing natural amino acid, L-leucine moieties in the
polymer backbone with several diisocyanates.
of 0.05° min-1
.
Experimental
Monomer synthesis
Materials
N,N0-(Pyromellitoyl)-bis{N-[4(4-aminophenoxy)phenyl]-2-
(4-methyl)pentanamide} (1) was synthesized according to
previous work (Mallakpour and Seyedjamali 2010).
All chemicals were purchased from Fluka Chemical Co.
(Buchs, Switzerland), Aldrich Chemical Co. (Milwaukee,
123

Synthesis of soluble poly(amide-ether-imide-urea)s bearing amino acid
489
Polymerization of diamine 1 with MDI in IL
Polymerization of diamine 1 with MDI in organic
solvent media
A 25 mL three neck round bottomed flask was charged
with 0.300 g (3.71 9 10-4 mol) of diamine 1 and 0.15 g of
[1,3-(pr)2im]Br, the nitrogen atmosphere was equipped,
0.093 g (3.71 9 10-4 mol) of MDI was added and the
temperature was slowly raised up to 80°C. The mixture was
stirred mechanically for 2 h. After that time, the viscose
solution was poured into the 30 mL of methanol, polymer
precipitated rapidly as a white solid, filtered-off to yield
0.373 g (95%) of PAIEU3c.
PAIEU3a–PAIEU3c were synthesized according to pre-
vious work (Mallakpour and Seyedjamali 2010).
Results and discussion
Monomer synthesis
PAIEU3c: Off-white solid; FT-IR (KBr): 3,477 (m),
3,374 (s), 2,967 (m), 2,933 (m), 2,875 (w), 1,774 (m),
1,723 (s), 1,626 (m), 1,593 (s), 1,525 (m), 1,503 (m), 1,383
(m), 1,349 (m), 1,312 (m), 1,148 (s), 1,105 (s), 1,075 (m)
Optically active diamine 1 was prepared according to the
synthesis sequence illustrated in Scheme 1. Dehydration of
pyromellitic dianhydride and excess L-leucine in acetic
acid reflux led to the preparation of corresponding imide
acid. In continuation, imide acid was converted to its acid
chloride derivative using thionyl chloride and then was
dissolved in dry THF and added very slowly to the slightly
excess amount of ODA to avoid polymerization as an
unwanted side reaction. Resulting chiral diamine was
characterized by means of FT-IR, 1H-NMR, 13C-NMR and
elemental analysis techniques.
1
553 (m) cm-1. H NMR (500 MHz, DMSO-d6): d 0.87–
0.88 (d, 3H, CH3, J = 6.7 Hz), 0.89–0.90 (d, 3H, CH3,
J = 6.7 Hz), 1.52 (m, 1H, CH), 1.87–1.92 (m, 1H, CH2),
2.16–2.21 (m, 1H, CH2), 3.81 (s, 1H, CH2), 4.85–4.88 (dd,
1H, CH chiral, J1 = 11.1, J2 = 3.91), 6.72 (d, 1H, Ar–H,
J = 4.8), 6.84 (d, 1H, Ar–H, J = 4.6), 6.91–6.93 (d, 2H,
Ar–H, J = 8.3), 7.10–7.12 (d, 2H, Ar–H, J = 7.7), 7.35–
7.36 (d, 2H, Ar–H, J = 7.67), 7.42–7.43 (d, 2H, Ar–H,
J = 8.52), 8.33 (s, 1H, Ar–H), 8.50–8.54 (d, 1H, Ar–H,
J = 4.6) 8.50–8.53 (s, broad, 2H, NH), 8.78–8.83 (s, broad,
2H, NH), 8.90 (s, 2H, NH) ppm. Elemental analysis cal-
culated for C61H54N8O10 (1,059.13 g mol-1): C, 69.18%;
H, 5.14%; N, 10.58%. Found: C, 68.61%; H, 5.92%; N,
10.74%.
Polymer synthesis in IL media
Equal molar ratios of diamine 1 and different diisocyanates
(2a–2d) were polymerized in IL medium as an advanced
alternate for VOS (Scheme 1). The reaction time and
temperature were optimized separately and the optimum
conditions were preferred by means of the superior reaction
yields and the viscosity of resulted macromolecules.
The use of [1,3-(pr)2im]Br as the best IL was base on
the optimization data in our previous work (Mallakpour
and Kolahdoozan 2008). Synthesis and some physical
properties of obtained polymers are collected in Table 1.
The other PAEIUs derived from different diisocyanates
such as TDI, HDI and IPDI were prepared in this IL
according to the procedure described above.
PAEIU3a: off-white solid; FT-IR (KBr): 3,275 (br),
2,800–3,000 (br), 1,773 (w), 1,695 (m), 1,600 (m), 1,537
(s), 1,448 (m), 1,223 (m) cm-1
.
1
PAEIU3b: off-white solid; FT-IR (KBr): 3,353 (br),
2,932 (m), 2,856 (m), 1,791 (m), 1,745 (s), 1,613 (m), 1,524
FT-IR spectrum of PAEIU3c and H-NMR spectrum of
PAEIU3d as typical examples are illustrated in Figs. 1
and 2.
(s), 1,421 (m), 1,357 (m), 1,253 (m), 1,187 (m) cm-1
.
PAEIU3d: off-white solid; FT-IR (KBr): 3,364 (br),
2,954 (s), 2,925 (s), 2,900 (m), 1,775 (m), 1,736 (m), 1,639
According to the optical activity of synthesized PAE-
IUs, they may be potentially suitable materials for column
packing in HPLC techniques as chiral stationary phases.
The magnitude and the sign of specific rotation of PAEIUs
were not predictable since optical rotation is extremely
reliant on the chemical structure and a tiny variance in the
configuration as well as molecular weight of polymers has
significant random consequence on the optical rotation.
1
(s), 1,558 (s), 1,462 (m), 1,239 (m), 747 (m) cm-1. H
NMR (500 MHz, DMSO-d6): d 0.86–0.93 (m, 18H, CH3),
1.05 (s, 3H, CH3), 1.49–1.52 (m, 2H, CH), 1.87–1.94 (m,
4H, CH2), 2.15–2.21 (m, 4H, CH2), 2.70 (s, 2H, CH2),
3.29–3.32 (t, 2H, CH2, J = 7.08), 3.78–3.81 (m, 1H, CH)
4.85–4.88 (dd, 2H, CH chiral, J1 = 11.30, J2 = 4.41),
6.56–6.58 (d, 2H, Ar–H, J = 7.668), 6.70–6.72 (d, 4H, Ar–
H, J = 6.77), 6.75–6.78 (d, 4H, Ar–H, J = 6.80), 7.27–
7.31 (d, 4H, Ar–H, J = 6.77) 7.33–7.36 (d, 4H, Ar–H,
J = 6.97), 8.32 (s, 2H, NH), 8.43 (s, 2H, NH), 8.54 (s, 2H,
NH) ppm. Elemental analysis calculated for C58H62N8O10
(1,031.16 g mol-1): C, 67.56%; H, 6.06%; N, 10.87%.
Found: C, 66.80%; H, 5.25%; N, 10.67%.
Polymer synthesis in organic solvent media
In order to make a reasonable comparison, the polycon-
densation reactions were compared with those progressed
in organic solvent which have been reported recently
(Mallakpour and Seyedjamali 2010). According to the
123

490
S. Mallakpour
Br
N
N
IL:
O
O
O
O
80 oC / 2 h
*
*
N
H2N
O
N
N
+
NH2
OCN
R
NCO
N
H
O
H
or
H
H
2a-2d
Dry DMAc
O
O
1
O
O
O
O
O
O
*
*
HN
R
NH
HN
O
N
N
N
N
O
C
C
H
H
n
H
H
O
O
PAEIU3a-PAEIU3d
CH3
CH3
H
H
,
,
,
C
H
C
R =
6
CH3
H
H3C
IPDI
d
TDI
a
HDI
b
MDI
c
Scheme 1 Polymerization reactions of monomer 1 with several aromatic and aliphatic diisocyanates in IL or organic solvent
Table 1 Synthesis and some physical properties of polymers pre-
pared in IL
Entry Polymer Diisocyanate Yield
(%)
ginh
25; a
Na; 589
½aꢁ
(dL g-1 a
)
1
2
3
4
a
PAEIU3a TDI
PAEIU3b HDI
PAEIU3c MDI
PAEIU3d IPDI
94
92
95
91
0.53
0.49
0.55
0.44
-28.4
-23.2
-39.5
-29.1
Measured at a concentration of 0.5 g dL-1 in DMF at 25°C
Fig. 2 1H-NMR spectrum of PAEIU3d
also due to the cleaner reaction conditions and concurrent
green chemistry issues. Morphology of the resulting mac-
romolecules via both methods has been evaluated by means
of XRD technique and confirmed to have amorphous
structures.
Solubility behaviors
Fig. 1 FT-IR spectrum of PAEIU3c as a typical example
referenced publication, the yields and inherent viscosities
of resulting macromolecules ranged between 85–91% and
0.37–0.46 dL g-1, respectively.
Solubility of PAEIU3s was examined in common organic
solvents quantitatively and it was confirmed that all of
them are soluble in solvents such as DMF, NMP, DMAc,
or dimethyl sulfoxide at room temperature, and found
insoluble in acetone, cyclohexane, chloroform, and meth-
anol. The isobutyl side group in the structure of monomer
may be the cause of observed good solubility as they can
depress the strong H-bond interaction, which is the com-
mon origin of limited PUs solubility. On the other hand, the
incorporation of ether moieties along the polymer chains
Induction of chirality into the polymer backbone was
proved by the specific rotation measurement. A comparison
between the data presented in Table 1 and previously
reported data, confirms that polycondensation of chiral
diamine 1 with various diisocyanates proceeds more
effectively in IL media, because of not only the higher
reaction yields and the viscosity of resulted polymers but
123

Synthesis of soluble poly(amide-ether-imide-urea)s bearing amino acid
491
increases the flexibility of polymer backbone and facilitates
their solubility as well as processability.
contrasted to the fact that: low molecular weight aromatic
diamine monomers provide rigid PUs (Long and Hunt
1998). The application of synthesized polymers of micro-
encapsulation purposes may be the subject of further
investigations.
Thermal properties
Generally, the solubility enhancement agents are associated
with reduction of the thermal stability of final products as
an unwanted side effect. In the present study, this problem
has been removed due to the existence of additional imide
and amide functional groups which are known by their
hardness and tolerance toward thermal shocks. It may be
concluded that elastic soft divisions have regulated the
rigidity of each amide, imide and urea functional groups,
thus improving the solubility behaviors, and conversely
such hard groups have improved the thermal stability of
polymers.
Acknowledgments Research Affairs Division, Isfahan University
of Technology (IUT), Center of Excellency in Sensors and Green
Chemistry Research IUT and National Elite Foundation (NEF) are
gratefully acknowledged for financial support. Special thanks to Mrs.
Carolyn S. Coolidge for her excellent proofreading of this manuscript.
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been reported. The polymerization of this chiral diamine
with several aromatic and aliphatic diisocyanates was
performed via an IL-mediated polycondensation as a green
process and the results have been compared with organic
solvent analogous. Accordingly, the IL showed to be a
superior polymerization media with higher reaction yields,
elevated inherent viscosity of obtained polymer and the
adjustment with environmental and biological concerns.
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stability, especially in the case of aromatic issues.
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