Synthesis of biodegradable chiral poly(ester-imide)s derived from valine-, leucine- and tyrosine-containing monomers

Article abstract of DOI:10.1007/s00726-010-0799-5

The present demand for a drastic reduction in environmental pollution is extended to qualitative change in the approach to development of biodegradable polymers. The aim of this article is to focus on the synthesis of biodegradable optically active poly(ester-imide)s (PEI)s, which compose of different amino acids in the main chain as well as in the side chain. These polymers were synthesized by polycondensation of diacid monomers such as 5-(2-phthalimidyl-3- methyl butanoylamino) isophthalic acid (1), 5-(4-methyl-2-phthalimidyl pentanoylamino)isophthalic acid (2) with N,N0-(pyromellitoyl)-bis-L-tyrosine dimethyl ester (3) as a phenolic diol. The direct polycondensation reaction was carried out in a system of tosyl chloride, pyridine and N,N-dimethylformamide as a condensing agent under conventional heating conditions. The optically active PEIs were obtained in good yield and moderate inherent viscosity. The synthesized polymers were characterized by means of FT-IR, 1H-NMR, elemental and thermo gravimetric analysis techniques. In addition, in vitro toxicity and soil burial test were employed for assessing the sensitivity of these compounds to microbial degradation. To this purpose, biodegradability behavior of the monomers and polymers were investigated in culture media and soil condition. The results of this study revealed that synthesized monomers and their derived polymers are biologically active and probably microbiologically biodegradable. Springer-Verlag 2010.

Full text of DOI:10.1007/s00726-010-0799-5

Amino Acids (2011) 41:1215–1222
DOI 10.1007/s00726-010-0799-5
ORIGINAL ARTICLE
Synthesis of biodegradable chiral poly(ester-imide)s derived
from valine-, leucine- and tyrosine-containing monomers
•
Shadpour Mallakpour Parvin Asadi
•
Mohammad R. Sabzalian
Received: 14 August 2010 / Accepted: 26 October 2010 / Published online: 11 November 2010
Ó Springer-Verlag 2010
Abstract The present demand for a drastic reduction in
environmental pollution is extended to qualitative change in
the approach to development of biodegradable polymers.
The aim of this article is to focus on the synthesis of biode-
gradable optically active poly(ester-imide)s (PEI)s,
which compose of different amino acids in the main chain as
well as in the side chain. These polymers were synthesized
by polycondensation of diacid monomers such as
5-(2-phthalimidyl-3-methyl butanoylamino) isophthalic
acid (1), 5-(4-methyl-2-phthalimidyl pentanoylamino)iso-
phthalic acid (2) with N,N0-(pyromellitoyl)-bis-L-tyrosine
dimethyl ester (3) as a phenolic diol. The direct polycon-
densation reaction was carried out in a system of tosyl
chloride, pyridine and N,N-dimethylformamide as a con-
densing agent under conventional heating conditions. The
optically active PEIs were obtained in good yield and mod-
erate inherent viscosity. The synthesized polymers were
characterized by means of FT-IR, 1H-NMR, elemental and
thermo gravimetric analysis techniques. In addition, in vitro
toxicity and soil burial test were employed for assessing the
sensitivity of these compounds to microbial degradation. To
this purpose, biodegradability behavior of the monomers and
polymers were investigated in culture media and soil con-
dition. The results of this study revealed that synthesized
monomers and their derived polymers are biologically active
and probably microbiologically biodegradable.
Keywords Biodegradable polymers ꢀ Polymers
containing amino acid ꢀ Optically active material ꢀ
Poly(ester-imide)
Introduction
Today the urgency of reducing environmental pollution
with non-biodegradable plastics is a good reason for the
intensive efforts to develop new biodegradable polymers. It
is now widely accepted that the significance of polymers in
our life is unquestioned but the use of long-lasting poly-
mers for short-lived applications is not sustainable.
Therefore, biodegradable polymers are finding their way
into a variety of applications in material science. Biodeg-
radation is defined as an event in which enzymatic and/or
chemical decomposition takes place in associated with
living organisms (bacteria, fungi, etc.) or their secreted
products (Amass et al. 1998). Naturally occurring bio-
polymers formed in nature during the growth cycles of all
organisms such as polysaccharides, polypeptides and bac-
terial polyesters are first class of biodegradable polymers.
Polymer with hydrolysable backbones such as polyesters,
polycaprolactone, polyamides, polyurethanes and polyure-
as or polymer with carbon backbones such as poly(vinyl
alcohol) and polyacrylates are biodegradable synthesized
polymers (Chandra and Rustgi 1998). Poly (a-amino acid)s
(PAA)s as a new biomaterials have received much attention
S. Mallakpour ꢀ P. Asadi
Organic Polymer Chemistry Research Laboratory,
Department of Chemistry, Isfahan University of Technology,
Isfahan 84156-83111, Islamic Republic of Iran
S. Mallakpour (&)
Nanotechnology and Advanced Materials Institute,
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
M. R. Sabzalian
College of Agriculture, Department of Agronomy
and Plant Breeding, Isfahan University of Technology,
Isfahan 84156-83111, Islamic Republic of Iran
123

1216
S. Mallakpour et al.
because of incorporating a-amino acids in these com-
pounds. They have generated significant properties which
make them structurally tissue-compatible, easily metabo-
lized by living organisms and with nontoxic degradation
products (Pitarresi et al. 2008). However, due to their
unfavorable mechanical and thermal properties, all of
PAAs could not be considered as potential biomaterials
(Yu et al. 1999; Huang 2005). To improve the poor
physical-mechanical properties of most PAAs, amino acids
have been used to design monomers with a different
structure from conventional backbone found in peptides
containing amino acid. These materials are referred to as
‘non-peptide amino-acid-based polymers’ or as ‘amino-
acid-derived polymers’ with modified backbones. These
have previously been classified into four major groups by
Kenmitzer and Kohn (1997). It is worth pointing out that
the most important and diffusible biological polymers are
optically active. The presence of amino acid in the polymer
chains as a chiral group competent induces optical activity
into macromolecules (Mallakpour and Kolahdoozan 2008;
Mallakpour and Mirkarimi 2010; Mallakpour 2010).
Amino acids as constitutional components of proteins with
a high degree of functionality and chirality play crucial role
in the synthesis of biocompatible and biodegradable poly-
mers (Metselaar et al. 2007; Wezenberg et al. 2006). As an
example, poly(ester-amide)s containing amino acids, such
as phenylalanine, leucine, and alanine, have been synthe-
sized and they have been degraded by enzymes (Fan et al.
2001; Suarez et al. 1998; Tsitlanadzei et al. 2004). Of
these, macromolecules that contain amino acid units are
potentially useful in many different medical applications
such as bio-erodible sutures, tissue engineering scaffolds
and drug delivery matrices (Wathier et al. 2006; Gigante
et al. 2003; Guo et al. 2007; Yu et al. 2007; Tosi et al.
2007; Browna et al. 2003). Valine is an amino acid
obtained by hydrolysis of proteins. It is a branched-chain
amino acid (BCAA) that works with the other two BCAAs,
isoleucine and leucine, to promote normal growth, repair
tissues, regulate blood sugar, and provide the body with
energy. The importance of leucine as the primary amino
acid responsible for protein synthesis has been confirmed in
many studies. This amino acid has the capability to be
consumed to exert regulatory influences on carbohydrate
and protein metabolism, providing gluconeogenic precur-
sors via the formation of alanine in muscle, regulating
glucose homeostasis and decreasing protein breakdown. L-
Tyrosine is the only major natural nutrient amino acid
containing an aromatic hydroxyl group. This kind of the
amino acid has the ability to be used to improve memory
and mental alertness, to act as an appetite suppressant, to
control depression and anxiety and to enhance physical
performance (Garlick 2005; Layman and Baum 2004;
Eversloh et al. 2007).
Polyimides have attained a unique position in material
systems that can compete with other structural materials,
mechanical fasteners, higher voltage connectors and
chemically resistant parts because of their excellent ther-
mal, mechanical and physical properties (Wang and Chen
2010). However, some drawbacks remain to be addressed,
particularly in the perspective of their difficulties in melt-
ing processing. One way to decrease the melting point is by
adding of a flexible linking group in the main chain (Wang
and Leub 2000). Another approach involves the synthesis
of copolyimides such as poly(ester-imide)s (PEI)s (Hase-
gawa et al. 2010; Shabbir et al. 2010) and poly(amide-
imide)s by incorporating amide or ester functionality at
regular intervals in the polyimide chain (Chern et al. 1998;
Behniafar et al. 2009).
The direct step-growth polymerization reaction involves
the use of free carboxylic acid and diols under mild con-
ditions using activating reagents. Several condensing
agents suitable for the direct polycondensation reaction
such as diphenyl chlorophosphate and arylsulfonyl chlo-
rides have been developed in the past decades (Higashi
et al. 2001; Higashi and Mashimo. 1986). It was found that
Vilsmeier adduct derived from arylsulfonyl chlorides and
N,N-dimethylformamide (DMF) in pyridine (Py) was suc-
cessfully used as a suitable condensing agent for the syn-
thesis of aromatic polyesters by direct polycondensation of
aromatic dicarboxylic acids and bisphenols (Higashi et al.
1999).
Follow by our past success in generating optically active
polymers based on amino acids; we were encouraged to
consider the approach mentioned above to predict experi-
ment in order to address the question that can this method
succeed in yielding biodegradable polymers if we use two
biodegradable monomers. Our main interest in synthesiz-
ing biodegradable polymers relies on the fact that both
monomers have a-amino acids which can act as a biode-
gradable segment in the polymer chain. In this study the
amino acids are functionalized to produce diacid and diol
monomers. The structure of the resulting polymers was
1
investigated by FT-IR, H-NMR, elemental analysis tech-
niques and subsequently, their biodegradation and thermal
properties was evaluated.
Experimental
Materials
The amino acids of synthetic grade were used as purchased
from Merck Chemical without further purification.
N,N-Dimethylacetamide (DMAc), DMF, Py, N-methyl-2-
pyrrolidone (NMP) and triethylamine (TEA) were procured
from Fluka (dried over barium oxide (BaO) and then
123

Synthesis of biodegradable chiral poly(ester-imide)s
1217
distilled under reduced pressure). Pyromellitic dianhydride
(benzene-1,2,4,5-tetracarboxylic dianhydride) and phthalic
anhydride were the product of Merck Chemicals and
purified by recrystallization from a mixture of acetic
anhydride and acetic acid (1:4). 5-Aminoisophthalic acid
was obtained from Aldrich and recrystallized from H2O/
DMF (4/1) mixture.
solution was stirred at room temperature for 30 min and
then it was stirred at 120°C for 4 h. As the reaction was
proceeded, the solution became viscous and then at this
point the viscous liquid was precipitated in 20 ml of
methanol to give 0.20 g of PEI1 (86% yield). PEI2 was
prepared by a similar procedure (Mallakpour and Asadi
2010).
Instrument and measurement
Soil biodegradability test
The structure of PEIs was characterized by proton nuclear
magnetic resonance (1H-NMR, 500 MHz) and spectra were
recorded in dimethyl sulfoxide (DMSO)-d6 solution using a
Bruker Avance 500 instrument (Bruker, Germany) and FT-
IR spectra were also recorded on spectrophotometer (Jasco-
680, Japan). The spectra of solids were obtained using KBr
pellets. The vibrational transition frequencies are reported
in wavenumbers (cm-1). Band intensities were assigned as
weak (w), medium (m), strong (s) and broad (br). Inherent
viscosities were measured by 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 1 ml of solvent.
Thermal gravimetric analysis (TGA) data for polymers
were taken on Perkin Elmer at a heating rate of
10°C min-1 under argon (Ar) atmosphere. Elemental
analyses were performed by Leco, CHNS-932. Images
from cultured samples in Petri plate were captured using a
binocular equipped with a digital canon (DS126181, Japan)
camera.
To study of soil biodegradation, 30 mg of each compound
including 5-aminoisophthalic acid, diacid 5a and bisphenol
A (as reference) were separately mixed with 1.5 g clay-
loam soil. The mixture was transferred into 2-ml plastic
vials in three replications. Samples of soil without any
added compounds were also tested in these experiments as
negative controls. Vials were incubated at temperature of
23–25°C, with a saturated humidity and at dark condition
for 3 months. In this part of study days to 50% disap-
pearance of materials was recorded. Then water extracts of
soil samples were inoculated by streak culture on Potato
Dextrose Agar (PDA) as culture media. The number of
bacterial and fungal colonies formed on the media was
counted and noted as colony forming units (CFUs) per
100 ll of water extract.
Investigation of in vitro toxicity
In vitro assessment of polymeric compounds has been used
as a rapid, cost effective and reliable test for their toxicity
studies (Mallakpour et al. 2010a, b). In vitro toxicity of
5-aminoisophthalic acid, diacid (5a), PE1 and PE2 to air-
borne fungal saprophytes was evaluated on PDA as culture
media in three replications for 3 weeks. For this purpose,
20 to 50 mg of 5-aminoisophthalic, diacid 5a and obtained
polymers were put on PDA. Media were inoculated with
Monomer synthesis
Optically active diacid monomers such as: 5-(2-phthalim-
idyl-3-methyl butanoylamino)isophthalic acid (5a), 5-(4-
methyl-2-phthalimidylpentanoylamino)-isophthalicacid (5b)
and also N,N0-(pyromellitoyl)-bis-L-tyrosine dimethyl ester
(10) as a phenolic diol were prepared according to our pre-
viousworks (Mallakpour and Kolahdoozan2007; Mallakpour
and Dinari 2008; Mallakpour et al. 2010a, b).
O
O
O
O
N
O
O
R
H2N
H
+
AcOH
Reflux, 12h
SOCl2, CH2Cl2
OH
OH
R
H
O
(1)
(2)
O
O
O
O
O
Polymer synthesis
O
HO
OH
Dry DMAc
4h, 80o
+
Cl
HO
N
O
OH
R
H
The PEIs were prepared by the following procedure: a Py
(0.20 ml) solution of tosyl chloride (TsCl) (0.37 g;
1.94 9 10-3 mol), after 30 min stirring at room tempera-
ture was treated with DMF (0.14 ml; 1.94 9 10-3 mol) for
30 min and the resulting solution was added drop wise to a
solution of diacid (5a) (0.10 g; 2.44 9 10-4 mol) in Py
(0.20 ml). The mixture was maintained at room tempera-
ture for 30 min, after that diol 10 (0.14 g; 2.44 9
10-4 mol) was added to this mixture. Later on the whole
NH
H
NH2
(4)
O
(3)
R
O
N
O
CH3
for diacid 5a, R=
for diacid 5b, R=
CH3
H
H
(5a -5b)
CH3
CH3
Scheme 1 Preparation of amino acid containing diacid monomers
123

1218
S. Mallakpour et al.
Scheme 2 Preparation of N,N0-
(pyromellitoyl)-bis-(L-tyrosine
dimethyl ester) (10) as an
O
C
O
O
H3CO
H3CO
H
C
H
(8)
H
C
SOCl2/MeOH
-10 oC
HO
H2N
Et3N/CH2Cl2
0 oC
OH
OH
OH
H2N
optically active phenolic diol
ClH3N
(6)
(7)
O
O
OCH3
H
H3CO
O
O
O
O
C
C
H
DMF
Reflux
OH
HO
8
O
O
O
O
N
+
N
O
O
(9)
(10)
Table 1 Optimum conditions for preparation of PEIs
+
5a or 5b
10
Optimum conditions
TsCl/DMF/Py
TsCl/diacid (mmol/mmol)
Aging time (min)
8
30
4
O
O
O
H3CO
OCH3
H
O
O
O
C
C
H
Reaction time (h)
O
O
N
O
N
Temperature
120
8
DMF/diacid (mmol/mmol)
O
n
NH
H
O
R
O
CH3
CH3
N
O
CH3
CH3
Table 2 Reaction conditions for the polymerization of diacid
monomers with diol (10) and some physical properties of PEIsa
R=
R=
(PEI1)
(PEI2)
25
½aꢁD ðbÞ
Polymer
Diacid
Yield (%)
ginh (dL/g)b
Colorc
Scheme 3 Polycondensation reactions of diol (10) with diacids 5a
and 5b
PEI1
PEI2
a
5a
5b
86
90
0.33
0.35
-19.2
-17.7
PB
PY
TsCl/DMF/Py was used as a condensing agent
spores of Penicillium spp. and Aspergillus spp. saprophytic
fungi maintained at 28 1°C and material invasion by
fungi were noted and photographed using a binocular
equipped with a digital canon camera.
b
c
Measured at a concentration of 0.5 g/dl in DMF at 25°C
PB Pale-brown, PY Pale-yellow
methyl ester. This compound was reacted with pyromellitic
dianhydride in DMF under refluxing conditions to obtain
diol monomer 10.
Result and discussion
Monomer synthesis
Polymer synthesis
Diacid monomers were synthesized by the condensation
reaction of an equimolar amount of phthalic anhydride (1)
and different amino acids (S-valine and L-leucine) in reflux
acetic acid solution to obtain imide acid (2) which was
reacted with thionyl chloride in dichloromethane to get
related diacid chloride (3). At the final step, 3 was con-
verted to diacid compounds (5a and 5b) thorough reaction
with 5-amino isophthalic acid (4) in dry DMAc in the
presence of TEA. (Mallakpour and Kolahdoozan 2007;
Mallakpour and Dinari 2008) (Scheme 1).
N,N0-(Pyromelliticdiimido)-bis-L-tyrosine dimethyl ester
(10) was synthesized as described bellow (Scheme 2).
L-Tyrosine was added to a methanol solution containing
thionyl chloride and stirred at room temperature to obtain
white, powdery, L-tyrosine methyl ester hydrochloride
which was de-protected with TEA to obtain L-tyrosine
Vilsmeier adduct was used for the polycondensation of
aromatic diacids (5a and 5b) with diol (10) in the following
way: (Scheme 3) TsCl was dissolved in Py to yield sul-
fonium salt and after a certain period of time (aging time)
the solution was treated with DMF to form Vilsmeier
adduct. The reaction mixture was added to a solution of
diacid in Py to form activated acid. Then powder of diol
was added and after a period of time passed PEIs were
produced. All the reaction parameters such as aging times,
reaction time, temperature and molar ratio of chemical
additives to diacid had significant effect on the reaction
progress. The optimum conditions for the preparation of
PEIs are shown in Table 1.
The synthesis and some physical properties of these
novel optically active PEIs are listed in Table 2. The
inherent viscosities of PE1 and PEI2 under optimized
123

Synthesis of biodegradable chiral poly(ester-imide)s
1219
Table 3 1H-NMR, FT-IR and elemental analysis of PEIs
Polymer Spectra data
PEI1
PEI2
FT-IR Peaks (KBr): 3419 (m, br), 2954 (m), 1778 (m), 1724 (s), 1H-NMR (500 MHz, DMSO-d6): d 0.81 (s, CH3), 0.98 (s, CH3),
1678 (m), 1548 (w), 1505 (m), 1452 (m), 1382 (m), 1364 (s), 2.70 (m, CH), 3.32 (s, CH2), 3.67 (s, OCH3), 4.54 (s, CH, chiral
1215 (m), 1184 (w), 1167 (m), 1112 (m), 1018 (m), 917 (w, br), center), 5.32 (s, CH), 6.90 (s, 4H aromatic), 7.24 (s, 4H
887 (w), 833 (w), 712 (w), 633 (w), (cm-1).
aromatic), 7.87 (s, 4H aromatic), 8.48 (s, 3H aromatic), 8.58
(s, 2H aromatic), 10.35 (s, br, NH), (ppm).
(C51H38N4O15): calcd. C 64.69, H 4.02, N 5.91; Found: C 63.64, H
4.34, N 6.15.
PEI2: FT-IR Peaks (KBr): 3383 (m, br), 3074 (m), 2965 (m), 2930 1H-NMR (500 MHz, DMSO-d6): d 0.84 (s, CH3), 0.87 (s, CH3),
(m), 1777 (m), 1723 (s), 1605 (m), 1548 (w), 1507 (m), 1453 1.40 (m, CH2), 1.97 (m, CH2), 2.11 (m, CH), 3.4 (s, CH2), 3.68
(m), 1382 (m), 1365 (s), 1214 (m), 1193 (w), 1167 (m), 1112 (m) (s, OCH3), 4.91 (s, CH, chiral center), 5.32 (s, CH), 6.91 (s, 4H
1070 (m), 1017(m), 953 (w, br), 836 (w), 721 (w), 631 (w),
(cm-1).
aromatic), 7.08 (s, 4H aromatic), 7.87 (s, 4H aromatic), 8.2
(s, 3H aromatic), 8.56 (s, 2H aromatic),10.28 (s, br, NH), (ppm).
(C52H40N4O15): calcd. C 65.00, H 4.20, N 5.83; Found: C 65.69,
H 4.48, N 6.57.
Fig. 2 TGA thermograms of PEI1 and PEI2 under Ar atmosphere
and a heating rate of 10°C/min
polymers showed absorptions of amide N–H bonds appeared
around 3363–3419 cm-1 (hydrogen bond) and the peaks at
1778 cm-1 (C = O imide group), 1721 cm-1(C = O ester
group) and 1605 cm-1 (C = O, amide group) confirming the
presence of different carbonyl groups in the polymers
structure. Also these PEIs exhibited absorptions at 1382 and
712–721 cm-1 which indicate the presence of the imide
heterocycle in the polymers structures (Table 3).
1
The H-NMR (500 MHz) spectra of PEI1 is shown in
Fig. 1 1H-NMR (500 MHz) spectra of diol (10), diacid (5a) and
PEI1 in DMSO-d6 at R.T
Fig. 1. The appearance of the N–H proton of amide groups
around 10.30 ppm indicates the amide group in the poly-
mer’s chain. The proton of the chiral centers for S-valin
and L-tyrosine appeared at 4.54 and 5.32 ppm, respectively.
Furthermore, the other peaks in the spectrum confirmed
and prove the structure of PEI1 (Table 3).
conditions were 0.33 and 0.35 dl/g, respectively, and both
of polymerization reaction had a good yield. The incor-
poration of amino acids as a chiral unit into the polymer
backbone was confirmed by measuring the specific rota-
tions of the obtained polymers. As shown in Table 2, the
polymers demonstrate a relatively high optical rotation and
are therefore optically active.
The elemental analyses results for PEIs are also in
agreement with calculated values of carbon, hydrogen and
nitrogen in the polymers (Table 3).
Solubility of PEIs
Polymer characterization
The solubility properties of PEIs were studied quantita-
tively in various solvents. The results revealed that these
polymers are soluble in organic polar solvents such as
The structures of synthesized polymers were confirmed by
means of FT-IR spectroscopy. The FT-IR spectra of
123

1220
S. Mallakpour et al.
Fig. 3 Fungal colonies grown
from soil water extract, 6 days
after inoculation on PDA Petri
plates. a lack of fungal growth
from extract of soil containing
bisphenol A as a reference,
(b) 5-aminoisophthalic acid and
(c) diacid (5a)
Table 4 The number of
bacterial and fungal colony
forming units (CFUs) in water
extract of soil containing
bisphenol A, diacid (5a), and
5-aminoisophthalic acid
Compound
Bacterial CFUs (n/100 ll)
Fungal CFUs (n/100 ll)
BPA (positive control)
Diacid (5a)
0
8
0
0
0
14
80 12
98 16
5-Amino isophethalic
Soil (negative control)
36 18
32 10
74
8
Fig. 4 Invasion and growth of
saprophytic fungi 3 weeks
after inoculation on
(a) 5-aminoisophthalic acid,
(b) diacid (5a), (c) PEI1 and
(d) PEI2 in culture media
co-cultivated with Aspergillus
spp. and Penicillium spp.
fungal spores
Thermal properties
DMAc, DMF, NMP, and in sulfuric acid at room temper-
ature. These polymers are insoluble in solvents such as
chloroform, methylene chloride, acetone, cyclohexane,
tetrahydrofuran and water. The good solubility of these
PEIs is due to the presence of bulky group in side chain
which prevents the packing of the macromolecules and
facilitates the diffusion of solvent molecules among the
polymer chains.
The thermal properties of the PEIs were evaluated by TGA
techniques at a heating rate of 10°C/min under Ar atmo-
sphere (Fig. 2). Thermal stability of the polymer was
investigated based on 5% and 10% weight loss (T5, T10) of
the polymers and residue at 800°C (char yield). T10 of PEIs
was 367 and 356 for PEI1 and PEI2, respectively.
123

Synthesis of biodegradable chiral poly(ester-imide)s
1221
The amount of residue (char yield) in an Ar atmosphere
was around 27 at 800°C. TGA thermograms of above
polymers mention that they are thermally stable and this is
in agreement with wholly aromatic polymers backbone
which increases the stability of the polymers toward heat-
ing. Although the existence of pendant group may cause
the loss of thermal stability, but introducing of heat resis-
tant phthalimide groups as well as the presence of imide
and amide groups can counterbalance it.
Conclusions
In this study we investigated different polymer structures
that can be used to develop biodegradable polymers in order
to reduce environmental pollution and help mankind to
achieve sustainable developments. Thus, by applying amino
acids, two biodegradable optically active PEIs using TsCl/
DMF/Py as a condensing agent were synthesized and char-
acterized by different techniques. Due to the presence of
amino acids as biological chiral resources in these polymers
structures, we expected these polymers to be biodegradable.
To ensure real biodegradability and safe incorporation of
these materials in the geochemical life cycle, soil biode-
gradability and in vitro toxicity test was performed. The
results illustrated that synthesized polymers could be prob-
ably decomposed by soil microorganisms and therefore they
are biodegradable. The TGA measurements demonstrated
that the obtained polymers were stable up to 350°C under Ar
atmosphere. The introduction of the bulky pendent groups
into the PEIs backbone gave them remarkable solubility in
common organic solvents.
Soil biodegradability test
5-Aminoisophthalic acid and diacid (5a) were disappeared
to 50% after 1 month and they were often almost disap-
peared under experimental condition after 2 months. This
observation shows that both 5-aminoisophthalic acid and
diacid (5a) are biologically active and biodegradable under
soil burial. PDA Petri plates containing fungal colonies
grown from different soil water extract are shown in Fig. 3.
Results of counting fungal and bacterial colonies showed
that the highest number of colonies was counted from
water extracts of soil containing 5-aminoisophthalic acid.
Based on this result, it could be concluded that this com-
pound is more biologically active than diacid (5a). This can
be related to simpler and smaller structure of this com-
pound which makes nitrogen more available for microor-
ganism growth. Interestingly, there was no colonial growth
of fungal and bacterial saprophytes from water extracts of
BPA containing soil as a reference due to probable toxic
properties of this compound for soil microorganisms
(Table 4).
Acknowledgments We wish to express our gratitude to the
Research Affairs Division Isfahan University of Technology (IUT),
Isfahan, for partial financial support. Further financial support from
Center of Excellency in Sensors and Green Research (IUT) is
gratefully acknowledged. Special thanks to Mr. Iman E Mallakpour
(University of Arizona, USA) for his valuable time for excellent
proofreading of this manuscript.
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