Synthesis, analysis and possibility application of cyclic and linear forms of poly(aspartic acid) synthesized under microwave irradiation

Article abstract of DOI:10.1080/15421401003719860

In this paper a new original method of synthesis of poly(aspartic acid) (PAA) from aspartic acid (AA) or maleic anhydride under microwave irradiation is presented. The syntheses carried out mainly without the catalyst, received higher yield in comparison for conventional method. PAA has been characterized by nuclear magnetic resonance (¹H NMR, ¹³C NMR), infrared spectroscopy (FT-IR) and termogravimetric analysis (Tg). Obtained polymer we used for several diversified applications, such as, medicine, agriculture and catalyst for oxidation reactions. Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421401003719860

This article was downloaded by: [Colorado College]
On: 03 November 2014, At: 17:26
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Synthesis, Analysis and Possibility
Application of Cyclic and Linear Forms
of Poly(Aspartic Acid) Synthesized Under
Microwave Irradiation
J. Pielichowski a , J. Polaczek a & E. Hebda a
a Department of Chemistry and Technology of Polymers , Cracow
University of Technology , Krakow, Poland
Published online: 28 May 2010.
To cite this article: J. Pielichowski , J. Polaczek & E. Hebda (2010) Synthesis, Analysis and
Possibility Application of Cyclic and Linear Forms of Poly(Aspartic Acid) Synthesized Under
Microwave Irradiation, Molecular Crystals and Liquid Crystals, 523:1, 120/[692]-127/[699], DOI:
10.1080/15421401003719860
To link to this article: http://dx.doi.org/10.1080/15421401003719860
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Mol. Cryst. Liq. Cryst., Vol. 523: pp. 120=[692]–127=[699], 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421401003719860
Synthesis, Analysis and Possibility Application of
Cyclic and Linear Forms of Poly(Aspartic Acid)
Synthesized Under Microwave Irradiation
J. PIELICHOWSKI, J. POLACZEK, AND E. HEBDA
Department of Chemistry and Technology of Polymers, Cracow
University of Technology, Krakow, Poland
In this paper a new original method of synthesis of poly(aspartic acid) (PAA) from
aspartic acid (AA) or maleic anhydride under microwave irradiation is presented.
The syntheses carried out mainly without the catalyst, received higher yield in
comparison for conventional method. PAA has been characterized by nuclear
magnetic resonance (1H NMR, 13C NMR), infrared spectroscopy (FT-IR) and
termogravimetric analysis (Tg). Obtained polymer we used for several diversified
applications, such as, medicine, agriculture and catalyst for oxidation reactions.
Keywords Microwave irradiation; poly(aspartic acid); polyethylene; polymer
catalyst
Introduction
The emergence of microwave-enhanced chemistry as an more efficient alternative
and environmentally friendly way of performing chemical synthesis promises to be
one of the most significant events of the 1990s with tremendous potential for
the 21st century. Polymer synthesis can greatly benefit from the unique featured
offered by modern microwave technology, which was demonstrated in many success-
ful applications [1]. Fundamental difference in the heat transfer during material
processing in thermal and microwave fields is that microwave energy in contrast
to thermal heating, is supplied directly to a large volume, thus avoiding the thermal
lags associated with conduction and convection [2].
Over the last three decades, polyesters and polyamides have received the most
attention as biodegradable polymers from researchers. Polylactide (PLA), typical
biodegradable polyester, has been demonstrated to possess good mechanical proper-
ties and the necessarily biodegradability and biocompatibility to be used in the areas
of tissue engineering and drug delivery. However, various control and modification
aspects of some of the properties of PLA have proven difficult [3–5]. The avoid these
problems, various other possibilities to obtain the biodegradable and biocompatible
compound have been investigated. Polypeptides consisting of a-amino acids are
Address correspondence to J. Polaczek, Department of Chemistry and Technology of
Polymers, Cracow University of Technology, 24 Warszawska Street, Krakow 31-155, Poland.
E-mail: jpolacze@riad.pk.edu.pl
120=[692]

Cyclic and Linear Forms of Poly(Aspartic Acid)
121=[693]
intriguing polyamides because of their hydrophilic nature and diversity in the
various side-chain groups. Polymers having the amino acid moiety in the main chain
or in the side chain find a variety of useful applications, such as chelating agents for
metal ions, ion-exchange resins, polymer catalysts with enzyme like behavior, and
promoieties for preparing polymeric prodrugs [6,7].
To this group of polymers due their advantages e.g., belongs poly(aspartic acid)
(here: PAA), which is biologically inert polyamino acid. The name ‘‘poly(aspartic
acid)’’ treats to the whole group of polymers differing the structure or molecular weight.
In dependence from kind of parent substances, the way of guidance of polyreaction
as well as modification chemical or physical it comes into being the well-fitting here
into the polymer about diverse proprieties, finding sequence proprieties of uses.
Poly(aspartic acid) – (PAA) shows such specific properties as a toxicity, water
solubility, hygroscopicity and its degradation gives amino acids. Owing to unique
characteristics PAS and its derivatives it can be exploited for a range of uses both
in science and industry e.g., medicine, pharmacology, cosmetics, agriculture, metal-
lurgy, paper processing and others [8]. Well known, are conventional syntheses of
PAA from aspartic acid and maleic acid ammonium derivatives [9,10], but these
kinds of reaction are carried out at high temperature (150–300ꢀC) for several hours
(2–10 h) [11]. Considering the reaction conditions, these processes are not favour-
able, especially in technological processes. Additionally, the polymerization process
requires a catalyst, for example phosphorus acid, which causes impracticability of
PAA e.g., in medicine or pharmacology.
In this paper, we report a new and simple method of obtaining poly(aspartic acid)
by using microwave irradiation method, and the next, we present several diversified
applications this polymer. First reports about application of this method to pro-
duction of biopolymers appeared by the end of the 20th century. Harada et al. used
microwaves to manufacture poly(amino acids) [12]. Since then there has been hardly
any research about application microwave in synthesis of polymers of amino acid.
Experimental
Materials
The following materials were used in this work:
. D, L-Aspartic acid, propylene carbonate (Sigma-Aldrich)
. Maleic anhydride, ammonium hydroxide (POCh, Poland)
A new original method of synthesis of PAS from maleic acid and aspartic acid
derivatives under microwave irradiation was worked. The process was carried out
using a microwave reactor ‘‘MicroSYNTH’’ from Milestone S. R. L. brand by
applying 1000 W power. The main advantage of this monomer is its availability
and price. Maleic anhydride is almost three times cheaper than aspartic acid and
is also a by-product in some processes [13].
The Synthesis of PAA Using Maleic Anhydride
The reaction required a few steps. Firstly, maleic anhydride was hydrolyzed in water
to give maleic acid (step I), then it was converted into ammonium derivatives by
addition of ammonium hydroxide (step II). The stages I and II require an increased
temperature 100ꢀC. In this way, there is possible to obtain ammonium salt or=and

122=[694]
J. Pielichowski et al.
Table 1. Compared reaction parameters in PAA preparation
Time of
cycle [min]
Temperature
[ꢀC]
Substrate
Power [W]
Colour
Maleic acid ammonium
5
3
3
3
3
3
3
3
3
3
7
5
3
14
130
150
170
190
210
230
176
186
196
200
215
220
230
230
200
250
300
350
400
450
380
380
380
380
390
390
390
390
Colourless
Pink
Dark pink
Dark pink
Dark pink
Dark red
White
Aspartic acid
White
Light pink
Light pink
Light pink
Light brown
Brown
Dark brown
amide of maleic acid. It is not very important which transitional product is formed
because polymerization of both gives the same cyclic product, namely anhydropo-
ly(aspartic acid) – APAA (step III). The temperature of polymerization is raised
gradually in order to achieve high yield of polycondensation- Table 1. Water from
the reaction is removed by means of distillation. Finally, linear PAA is obtained after
hydrolysis of its cyclic form at room temperature (step V). The hydrolysis of the
APAA leads to poly(aspartates) containing a and b-peptide bonds. It is explained
by nucleophilic attack of the hydroxide ions at the CꢁN bonds (Fig. 1, step V).
Figure 1. The synthesis of cyclic and linear PAA using maleic anhydride and aspartic acid.

Cyclic and Linear Forms of Poly(Aspartic Acid)
The Synthesis of PAA Using Aspartic Acid
123=[695]
Polycondensation of cyclic PAA (Fig. 1, step 4) was realized at the temperature
range from 176ꢀC to 230ꢀC, carbonate propylene was used as solution. Water was
removed from the system by an azeotropic distillation under normal pressure. In
Table 1 the reaction parameters for two ways of obtaining the products are presented
comparatively.
Cyclic PAA was precipitated with methanol, washed in water and dried. The
reaction efficiency was above 93%. PAA sodium salts has been obtained during
the reaction of hydrolysis of cyclic forms of PAA, water solutions of sodium
(Fig. 1, step 5). The process of hydrolysis was carried out in solution with
pH ¼ 8.5 to 13.0.
Results and Discussion
1) Analysis of PSI
Infrared Spectroscopy (FT-IR). FT-IR spectrum of cyclic PAA (Fig. 2) shows
=
intensive absorption band of stretching vibrations of C O group cyclic imide ring
in the range from 1690 cmꢁ1 to 1720 cmꢁ1. Strong absorption band of NH
stretching vibrations is in the range of 3500–3100 cmꢁ1
.
Proton Nuclear Magnetic Resonance (1H NMR). 1H NMR spectrum of cyclic PAA
in DMSO-d6 is characterized signals of the methine proton in the range from
4.5 ppm to 5.4 ppm. The methylene is observed at 3.3 and 2.8 ppm.
Carbon Nuclear Magnetic Resonance (13C NMR). 13C NMR spectrum of cyclic
PAA in DMSO-d6 is characterized two carbonyl peaks, which are observed at 173
and 174 ppm, representing the two inequivalent carbonyls of the succinimide
repeat unit. The repeat unit methylene and methine are observed at 32 and
47 ppm, respectively [2–4].
Termogravimetric Analysis (TG). TG profile is shown that decomposition process
of cyclic PAA proceed in two steps, leaving 35% of residue. TG analysis have
Figure 2. Spectrum of cyclic PAA using aspartic acid as reagent.

124=[696]
J. Pielichowski et al.
Figure 3. TG curve of PAA.
been showed, that PAA is resistant to temperatures 230ꢀC. Figure 3 is shown TG
curves of PSI.
2) Application of Cyclic and Linear of Poly(Aspartic Acid)
a) Modification of HD-polyethylene using poly(aspartic acid) for total artificial
joints. Owing to its toxicity and biodegradability to amino acids, poly(aspartic acid)
has already established its position in the field of medical engineering. This polymer
is characterized by high thermal stability (300ꢀC) and could be safely used to modify
PEHD. The first experiments have shown that addition of poly(aspartic acid) results
in an improvement of mechanical and tribologic properties comparing to the pure
PE [14,15].
Modification of HD PE using PAA in amount of 5 and 10 mass % were carried
out. The components were added into granulated polyethylene and this mixture was
used to manufacture paddles by injection processing. The results of mechanical
properties are shown in Table 2.
Degradation of Modified Polyethylene. As poly(aspartic acid) degrades easily,
analyses of modified polyethylene samples under degradation conditions were
carried out. The samples were kept to physiological NaCl solution at 70ꢀC for 30
days. After removing the extracts mechanical analyses were performed. The results
are shown in Table 3 and Figure 4.
In spite of that after 30 days of incubation hardness and abrasion resistance
of analyzed samples have decreased by their values were still higher than those of
polyethylene without modification. However, for some samples durability after
incubation was better than before.
Table 2. Mechanical properties of HD PE modified whit PAA
Tensile
strength
[MPa]
Young
module
[MPa]
Elongation
at break
[%]
Hardness
[N=mm2]
Abrasion
[mm2=m]
Sample
PEHD
PEHD þ 5% PAA
11.10
13.10
15.06
2.19
1.62
2.09
21.74
20.51
19.11
1.14
1.13
1.11
10.40
10.96
10.49
PEHD þ 10% PAA

Cyclic and Linear Forms of Poly(Aspartic Acid)
125=[697]
Table 3. Mechanical properties of HD PE modified PAA after 30 days of incubation
Tensile
strength
[MPa]
Young
module
[MPa]
Hardness
[N=mm2]
Abrasion
[mm2=m]
Elongation
at break [%]
Sample
PE HD
11.01
12.42
12.60
2.24
1.83
2.25
22.04
22.38
21.06
1.06
1.00
1.11
12.39
10.94
10.03
The pH measurements of physiological NaCl solution have indicated that after
48 hours of incubation the value of pH change from 6 to 3. during this time the
most abundant degradation products, probable oligomers, were passed through into
solution. Later, in the next 28 days the value of pH decreased much slower. After 30
days in vitro tests mass loss of all samples was observed to occur higher for samples
containing 5 and 10% of PAA was a results of mowing into solution of some
decomposition products or migration of a modifying agent.
b) Linear of PAA as addition to cement – correction of cement prolix, reduction of
‘‘make-up water’’ amount in cement mixtures. We have studied the influence of
sodium polyaspartate on rheological properties flow of Portland cement depends
on pH salt and amount water in cement mixtures. We also performed investigations
of the influence addition of sodium polyaspartate with pH ¼ 11.20 on the amount of
water in cement mixture at different ratio water=cement- Table 4. Addition of PAA
salt to cement is (0.35–0.40 w=w %) results in obtaining a plasticized cement, charac-
terized by good flow properties.
Figure 4. Change of pH values of solution after 30 days of incubation.

126=[698]
J. Pielichowski et al.
Table 4. Relation of cement mixtures flow to water=cement
ratio of linear PAA
Water=cement
Flow [cm]
0.40
72
0.36
50
0.35
46
Addition of sodium polyaspartate with pH ¼ 11.20 causes maximum reduction
of water (12.5%, w=c ¼ 0.35) with preservation of appropriate consi-stency. Sodium
salt of PAA with pH ¼ 11.20 causes the best cement flow (an increase from 48 to
112 cm in relation to standard sample) and makes it possible to decrease the amount
of water in cement water by 12.5%.
C) Linear PAA as carrier from metals – prepare catalysts. Complex of sodium
salt PAA with cobalt(II) or copper(II) acetate was carried out by mixing of 1.00 g
of PAA-Na with corresponding amount of metal acetate in water (Fig. 5).
It in this way a catalyst:was obtained
– PAA-Na þ cobalt acetate – PAA-Co
– PAA-Na þ copper acetate – PAA-Cu
Further, it was applied for oxidation reactions of aliphatic and aromatic hydro-
carbons that were carried out in the presence of molecular oxygen at the atmospheric
pressure.
Figure 5. Synthesis of poly(aspartic acid)-based catalysts.

Cyclic and Linear Forms of Poly(Aspartic Acid)
127=[699]
The complex of sodium salt PAA with cobalt or copper are very effective in
oxidizing of alkenes under mild conditions. We obtained ketone and epoxide as a
products reaction of alkene oxidation.
Conclusion
Our work is focused on evaluation of the influence of microwave irradiation on the
PAA properties. Optimization of the process conditions results in shortening of
the reaction time (about 1 hour) without using the catalyst. The optimization results
also in increasing of yield comparing to the conventional method. Polymer obtained
in such a way is characterized by high purity which is of crucial importance in
e.g., biomedical applications.
References
[1] Bogdał, D., Penczek, P., & Pielichowski, J. (2003). Adv. Polym. Sci., 163, 193.
[2] Parodi, F. (1999). Polym. Liquid Cryst., 2, 4017.
[3] Langer, R. (2000). Acc. Chem. Res., 33, 9.
[4] Kricheldorf, R. H. & Kreiser-Samders, I. (1996). Macromol. Symp., 103, 85.
[5] Bucholz, F. L. (1996). J. Chem. Ed., 73, 512.
[6] U.S. Pat. No. 5, 116, 513.
[7] U.S. Pat. No. 5, 152, 902.
[8] Polaczek, J., Dziki, E., & Pielichowski. (2003). Polimery, 1, 61.
[9] Roweton, S., Huang, S. J., & Swift, G. (1997). J. Environ. Polym. Degrad., 5, 175.
[10] Schwamborn, M. (1997). Polymer Degradation and Stability, 5, 1.
[11] U.S. Patent 6,093,789.
[12] U.S. Patent 4,696,981.
[13] Polaczek, J., Pielichowski, J., Pielichowski, K., Tylek, E., & Dziki, E. (2005). Polimery,
50(11–12), 812.
[14] Pielichowski, J., Polaczek, Dziki, E., & Wa˛s, M. (2004). Eng. Biomat., 38–43, 99–102.
[15] Pielichowski, J. & Polaczek, J. (2003). Eng. Biomat., 26, 5–9.