A novel and simple procedure to synthesize chitosan-graft-polycaprolactone in an ionic liquid

Article abstract of DOI:10.1016/j.carbpol.2013.01.090

An ionic liquid, 1-ethyl-3-methylimidazolium acetate (EMIMAc), was synthesized and employed as a homogeneous and green reaction media to prepare chitosan-graft-polycaprolactone (CS-g-PCL) via ring-opening polymerization, using stannous octoate (Sn(Oct)₂) as a catalyst. The structures and compositions of copolymers could be facilely controlled by the reaction conditions and feed ratios. The grafting content of polycaprolactone (PCL) could reach as high as 630%. The chemical structures of the copolymers were systematically characterized by ¹H NMR, Fourier transform infrared spectroscopy (FTIR) and wide-Angle X-ray diffraction (WAXD), while thermal properties were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal stability and glass transition temperature (T_g) of the graft copolymers vary regularly with the change of PCL grafting content.

Full text of DOI:10.1016/j.carbpol.2013.01.090

Carbohydrate Polymers 94 (2013) 505–510
Contents lists available at SciVerse ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
A novel and simple procedure to synthesize
chitosan-graft-polycaprolactone in an ionic liquid
Zhaodong Wanga,b, Liuchun Zhenga,∗, Chuncheng Lia,∗, Dong Zhanga, Yaonan Xiaoa,
Guohu Guana, Wenxiang Zhua
a Beijing National Laboratory for Molecular Sciences, Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences (ICCAS),
Beijing, PR China
b Graduate University of the Chinese Academy of Sciences, Beijing 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
An ionic liquid, 1-ethyl-3-methylimidazolium acetate (EMIMAc), was synthesized and employed as a
homogeneous and green reaction media to prepare chitosan-graft-polycaprolactone (CS-g-PCL) via ring-
opening polymerization, using stannous octoate (Sn(Oct)2) as a catalyst. The structures and compositions
of copolymers could be facilely controlled by the reaction conditions and feed ratios. The grafting content
of polycaprolactone (PCL) could reach as high as 630%. The chemical structures of the copolymers were
systematically characterized by 1H NMR, Fourier transform infrared spectroscopy (FTIR) and wide-angle
X-ray diffraction (WAXD), while thermal properties were studied by thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC). The thermal stability and glass transition temperature (Tg)
of the graft copolymers vary regularly with the change of PCL grafting content.
Received 15 September 2012
Received in revised form
12 December 2012
Accepted 17 January 2013
Available online 4 February 2013
Keywords:
Ionic liquid
Homogeneous reaction
Chitosan
© 2013 Elsevier Ltd. All rights reserved.
Graft
Polycaprolactone
1. Introduction
hydrogen bonds between hydroxyl groups and amino groups
(Hirase, Higashiyama, Mori, Takahara, & Yamane, 2010; Martino,
Chitosan (CS), with a repeating structure unit of ␤-(1,4)-
2-amino-2-deoxy-␤-d-glucose, is a fully or partly deacetylated
product of chitin, which is abundant natural resource. Recently,
chitosan has attracted much attention for its favorable proper-
ties such as good biocompatibility, biodegradability, biological
activity and non-toxicity. In particular, the unique polycationic
nature endows the chitosan with various charming functions,
including antibacterial activity and remarkable affinity to pro-
teins and DNA. Therefore, chitosan has been widely used in
many fields such as removal of metal ions from waste water
(Ravi Kumar, 2000), tissue engineering scaffolds (Duan, Dong,
Yuan, & Yao, 2004), packaging (Sébastien, Stéphane, Copinet,
& Coma, 2006), cosmetics, drug carriers and wound healing
accelerator (Kweon, Song, & Park, 2003). Unfortunately, the appli-
cation of chitosan suffers greatly from many drawbacks such
as insufficient mechanical properties, especially the brittleness,
poor solubility (low solubility in aqueous and insolubility in
common organic solvents) and processability (nonthermal plastic-
ity), resulting from the strong intramolecular and intermolecular
Pollet, & Avérous, 2011; Qian & Zhang, 2010; Wu, Yu, Mi, Wu, &
Shyu, 2004).
Thus, various chitosan based graft copolymers have been
developed, such as chitosan-g-poly(methylmethacrylate) (Singh,
Tripathi, Tiwari,
& Sanghi, 2006) chitosan-g-polyacrylonitrile
(Yuan & Jiang, 2011), chitosan-g-poly(vinyl acetate), chitosan-g-
poly(l-lactic acid) (Jayakumar, Prabaharan, Reis, & Mano, 2005),
chitosan-g-poly(vinyl alcohol) (Xiao, Gao,
chitosan-g-poly(1,4-dioxan-2-one) (Liu, Zhai, Wang,
&
Gao, 2010), and
Wang,
&
2008). Graft of aliphatic polyester onto chitosan is regarded as
the most effective method to extend the applications of chitosan
as a functional biomaterial because it can combines the mer-
its of both CS and polyesters. Moreover, the CS can effectively
buffer the acidity of degradation products of polyesters due to its
basic characteristics. PCL, as promising aliphatic polyester, is fully
biodegradable, biocompatible and nontoxic (Liu, Li, Garreau, & Vert,
2000; Williams et al., 2005). Therefore, PCL has been widely used
in biomedical area. It has been reported that the grafting with PCL
can substantially improve the solubility and mechanical properties
of chitosan (Liu, Wang, Shen, & Fang, 2005; Zhou, Huang, Xu, & Fan,
2009).
However, conventional technique to synthesize CS-g-PCL
copolymers usually carries out in heterogeneous reaction
∗
Corresponding authors. Tel.: +86 10 62562292; fax: +86 10 62562292.
E-mail addresses: hubeizlc@iccas.ac.cn (L. Zheng), lichch@iccas.ac.cn (C. Li).
0144-8617/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carbpol.2013.01.090

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Z. Wang et al. / Carbohydrate Polymers 94 (2013) 505–510
mediums and involves large quantity of volatile organic solvents,
which seriously pollute our environment. These heterogeneous
reactions have many other disadvantages such as time consuming,
uneven grafting and wide grafting distributions since the graft
reactions tend to take place at the surface of chitosan. An effective
alternative to solve these problems is to prepare organic soluble
chitosan derivatives as intermediate of the graft reaction, and the
most common is phthaloylchitosan (Cai, Jiang, Chen, et al., 2009;
Cai, Jiang, Tu, Wang, & Zhu, 2009; Liu et al., 2005). However, this
method complicates the preparation procedure and increases the
production cost.
2.2. Preparation of EMIMAc
1-Ethyl-3-methylimidazolium bromine (0.2 mol) and lead (II)
acetate trihydrate (0.1 mol) were dissolved in 30 mL of dis-
tilled water and 70 mL of distilled water, respectively. After
they were completely dissolved, 1-ethyl-3-methylimidazolium
bromine solution was poured into lead (II) acetate trihydrate
solution under vigorous mechanical stirring. The reaction was car-
ried out at 35 ◦C for 48 h under nitrogen atmosphere. Then the
reaction system was refrigerated at 3 ◦C for 12 h and the precip-
itates were filtered off. The filtrates were distilled under reduced
pressure to remove the water. The obtained EMIMAc (moisture con-
tent < 0.02%; bromide content < 0.004%) was light yellow viscous
liquid and the yield was 93%.
Ionic liquids (ILs), as a new generation of green solvents,
have attracted increasing attention recently owing to their low
vapor pressure and tunable solvability by varying the structure
of cations and anions (Klingshirn, Broker, Holbrey, Shaughnessy,
& Rogers, 2002; Zhao, Jackson, Song, & Olubajo, 2006). Recently,
imidazole based ionic liquids have been reported to success-
fully dissolve polysaccharide such as chitosan, chitin and cellulose
(Liao, Liu, Zhang, & Gong, 2006; Xiao, Chen, Wu, Wu, & Dai,
2011), and were regarded as green solvents to replace the volatile
organic solvents traditionally used in processing and synthe-
sis industries. Guo, Wang, Shen, Shu, & Sun (2013) prepared
cellulose-g-PCL nanomicelles by homogenous ring-opening poly-
merization in the ionic liquid of 1-N-butyl-3-methylimidazolium
chloride. Dong et al. (2008) and Yan et al. (2009) synthe-
sized cellulose-graft-poly(l-lactide) copolymers in the ionic liquid
of 1-allyl-3-methylimidazolium chloride with Sn(Oct)2 and 4-
dimethylaminopyridine as catalyst, respectively. Although many
novel cellulose-based hybrid biomaterials have been prepared in
ionic liquids (Barthel & Heinze, 2006; Heinze, Schwikal, & Barthel,
2005), up to now, very little information is available on the modifi-
cation of chitosan or chitin in ionic liquid, except the acetylation of
␣-chitin (Mine, Izawa, Kaneko, & Kadokawa, 2009), to the best of
our knowledge. In this work, PCL was grafted onto the unmodified
CS in the ionic liquid of EMIMAc for the first time. The main working
objective is to gain CS-g-PCL with high grafting content in a short
time in the homogeneous media of ionic liquid. The structures of
the copolymer were systematically investigated by FTIR, 1H NMR,
DSC, and WAXD.
2.3. Synthesis of CS-g-PCL in EMIMAc
CS-g-PCL was synthesized in EMIMAc according to the follow-
ing procedure. In a dry 100 mL of three-neck flask, which was
evacuated and purged with nitrogen for three times, 8 g of EMI-
MAc and 0.4 g of CS were introduced under nitrogen atmosphere.
Then the temperature was raised to 100 ◦C and the reaction sys-
tem was gradually reduced to 5–15 Pa, and maintained for 6 h to
get a homogenous solution. Subsequently, the system was cooled
to room temperature and a predetermined amount of ␧-CL and
0.5 wt% of Sn(Oct)2 (with respect to ␧-CL) were added. After that,
the exhausting-refilling process was repeated for 3 times. Then the
reaction was carried out at 100 ◦C for predetermined time under
nitrogen atmosphere. After that, the product was purified by repre-
cipitation in ethanol and filtered. The EMIMAc, unreacted ␧-CL
monomer and PCL homopolymer were removed by Soxhlet extrac-
tion with acetone for 24 h. The dried CS-g-PCL powder was obtained
under vacuum oven at 60 ◦C for 12 h. The whole synthesis procedure
of CS-g-PCL is shown in Scheme 1.
2.4. Characterization
2.4.1. Element analysis
The contents of carbon, hydrogen and nitrogen were measured
with a FLASH EA1112 element analyzer (EA). Since the absolute
content of nitrogen was constant, the grafting content can be cal-
culated according to the following equation:
2. Materials and methods
2.1. Materials
NCS
= NCS-g-PCL
Chitosan (degree of deacetylation = 85%, determined by 1H NMR
analysis, Mw = 52 kDa) was supplied by Golden-shell Biochemi-
cal Co. Ltd. (Zhejiang, China) and dried in vacuum at 60 ◦C for
12 h before use. Stannous octoate and ␧-caprolactone (␧-CL) were
purchased from Alfa Aesar (USA), and ␧-CL was distilled under
reduced pressure from calcium hydride before use. 1-Ethyl-3-
methylimidazolium bromine was obtained from Chengjie Chemical
Reagent Co. Ltd. (Shanghai, China). Lead (II) acetate trihydrate
was bought from Sinopharm Chemical Reagent Co. Ltd. (Shanghai,
China). All the other chemicals and solvents were analytical grade
and used as received without further purification.
1 + x
where NCS and NCS-g-PCL are the contents of the nitrogen element in
chitosan and CS-g-PCL, respectively; and x is the weight percentage
of PCL relative to chitosan.
2.4.2. FTIR spectroscopy
FTIR spectra of neat chitosan and all the CS-g-PCL powder were
recorded with a Nicolet 6700 FT-IR spectrometer from 650 to
4000 cm−1 at room temperature. The sample was scanned 32 times
and the resolution ratio was 4 cm−1
.
Scheme 1. Synthesis scheme of CS-g-PCL.

Z. Wang et al. / Carbohydrate Polymers 94 (2013) 505–510
507
Table 1
Results of the graft copolymerization under different conditions.
Sample
Solvent
CL/CS (mol/mol)
t (h)
Yielda (g)
PCL-Hb (g)
Grafting contentc (%)
Grafting efficiencyd (%)
0
1
2
3
4
5
6
7
8
9
DMSO
10
5
5
5
5
2
5
10
20
5
10
20
0.45
0.52
0.50
0.53
0.54
0.94
1.89
1.36
2.50
3.86
0.05
0.09
0.10
0.06
0.07
0.16
0.34
0.42
0.97
1.62
8
56
86
38
63
65
76
80
76
77
58
54
54
EMIMAc
EMIMAc
EMIMAc
EMIMAc
EMIMAc
EMIMAc
EMIMAc
EMIMAc
EMIMAc
10
20
20
20
20
50
50
50
68
140
199
317
160
311
630
a
The weight of samples recovered.
b
c
The weight of PCL homopolymer removed by acetone extraction.
Grafting content (%) = 100 × (Wgraft copolymer − Wchitosan of graft copolymer)/Wchitosan of graft copolymer (determined by EA).
d
Grafting efficiency (%) = 100 × Wgraft copolymer × PCL content (%)/(Wgraft copolymer × PCL content (%) + PCL-H), where Wgraft copolymer = Yield − PCL-H; PCL content (%) = Grafting
content (%)/(100 + Grafting content (%)).
2.4.3. NMR
collision and reaction between ␧-CL monomers and d-glucosamine
(GlcN) units increases when more ␧-CL is introduced. In con-
trast, the grafting efficiency of the copolymers increased with the
increasing feed ratio of CL/CS and achieved a maximum value when
feed ratio of CL/CS is 20, then decreased with further increasing feed
ratio of CL/CS. Another conspicuous tendency among samples 3–6
and 7–9 was that the grafting content of PCL also increases substan-
tially with increasing reaction time. When the feed ratio of CL/CS
was 50 and the reaction time was 20 h, the grafting content of PCL
can achieve as high as 630%, which was greatly higher than the
values reported by most literatures (Liu, Chen, & Fang, 2006; Liu
et al., 2005; Zhou et al., 2009). The high grafting content of PCL is
attributed to the fact that chitosan dissolves well in EMIMAc and
the grafting copolymerization takes place in homogeneous condi-
tion. Due to the highly insoluble nature of chitosan, the traditional
technique to modify chitosan always needs to synthesize chitosan
precursor to enhance the solubility and thus involves large quan-
tity of organic solvent which seriously pollute the environment. As
contrast, the present strategy is a much more simple and highly
efficient procedure to prepare chitosan graft copolymers with high
grafting content.
1H NMR spectra were performed using a Bruker DMX-400 NMR
spectrometer using CDCl3 as solvent for PCL, and D2O/CF3COOD
(95:5, v/v) for the rest samples.
2.4.4. Differential scanning calorimetry (DSC)
DSC analysis was carried out with a TA Q2000 differential
scanning calorimeter (TA Instruments) under nitrogen atmosphere
(50 mL min−1). The samples were first heated to 180 ◦C and main-
tained for 5 min to eliminate the thermal histories. Then they were
cooled to −80 ◦C at a rate of 20 ◦C min−1 and held there for 10 min.
After that, the samples were reheated to 180 ◦C with the same rate.
Both of the cooling and reheating scans were recorded for analysis.
2.4.5. Wide-angle X-ray diffraction (WAXD) analysis
The WAXD measurements were determined with a Ragaku
Model D/max-2B X-ray diffractometer (Japan) with a Cu/k␣ radia-
tion (40 kV, 20 mA), and the experimental data were collected from
3◦ to 60◦ at a scanning rate 2◦ min−1
.
2.4.6. Thermogravimetric analysis (TGA)
TGA was conducted with a Perkin-Elmer TGA-7 under nitrogen
atmosphere at a rate of 20 ◦C min−1
.
3.2. FTIR analysis of CS-g-PCL
Fig. 1 displays the FTIR spectra of chitosan, PCL and CS-g-PCL
3. Results and discussion
copolymers with various grafting contents. As shown in the FTIR
3.1. Synthesis of CS-g-PCL
The CS-g-PCL copolymer was synthesized by grafting the PCL
onto chitosan through ring-opening polymerization of ␧-CL in EMI-
MAc with Sn(Oct)2 as the catalyst (Scheme 1). Since ethanol is good
solvent for EMIMAc but poor solvent for graft polymers, the poly-
mers can be directly recovered from alcohol coagulants. The results
of the graft copolymerization under various reaction conditions are
summarized in Table 1.
DMSO was a common solvent employed to swell chitosan for
chitosan modification (Cai, Jiang, Chen, et al., 2009; Cai, Jiang, Tu,
et al., 2009). However, the grafting content of PCL was as low as 8%
(Table 1) when DMSO was used as the solvent, suggesting that het-
erogenous reaction is not beneficial to the graft copolymerization.
In contrast, the grafting content of PCL was much higher in EMI-
MAc due to the homogenous nature. Therefore, it can be concluded
that the homogenous graft copolymerization of ␧-CL in ionic liquid
of EMIMAc is much more efficient than that in common solvent of
DMSO.
The effect of feed ratios and reaction times on the grafting con-
tent is shown in Table 1. It can be found from samples 1, 2, 4, 7 that
the grafting content of PCL increases evidently with the increasing
feed ratio of CL/CS. This trend can be explained as that probability of
Fig. 1. FTIR spectra of chitosan (a), sample 1 (b), sample 8 (c), and PCL (d).

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Z. Wang et al. / Carbohydrate Polymers 94 (2013) 505–510
Fig. 2. 1H NMR spectra of chitosan (a), PCL (b) and sample 1 (c).
Fig. 3. DSC thermograms of chitosan (a), sample 1 (b), sample 2 (c), sample 4 (d),
sample 8 (e), sample 9 (f) and PCL (g) in the second heating run.
spectrum of native CS (Fig. 1a), the characteristic peak at 897 cm−1
is assigned to the C O stretching of glycoside linkage, the peak
at 1160 cm−1 is attributed to the asymmetric C O stretching of
that graft copolymerization is highly effective, which is ascribed to
the homogeneous reaction nature.
C
O
C bridge and the peak at 1590 cm−1 belongs to the N H defor-
mations of amino group. The peaks at 1650 cm−1 and 1380 cm−1 are
associated with the C O stretching and the C H bending of amide
group, indicating the incomplete deacetylation of the chitosan. The
characteristic peaks of PCL can be detected in the spectra of CS-
g-PCL (Fig. 1b and c). The strong peak at 1725 cm−1 is assigned to
the stretching vibration of C O on PCL ester group, while the peaks
at 2865 cm−1 and 2940 cm−1 are arising from the stretching vibra-
tion of C H of CH2 group on PCL. Hence, the presence of PCL side
chains in the modified chitosan can be confirmed.
Furthermore, it can be found from Fig. 1 that the peak at
1725 cm−1, attributing to ester carbonyl, became stronger with the
increase of grafting content of PCL in the copolymer. At the same
time, the intensity of the peak at 1650 cm−1 (amide I) increases and
a new peak at 1560 cm−1 (amide I) appears after grafting, imply-
ing that PCL has been grafted to CS backbone at the amino groups.
It is well known that the hydrophilic groups on chitosan such as
hydroxyl and amino groups exhibit broad peaks in the range of
3000–3500 cm−1 due to their strong hydrogen interactions. The
intensity of these peaks decreases obviously after the graft copo-
lymerization, indicating the reduction of number of hydroxyl and
amino groups in the chitosan derivative.
3.4. Differential scanning calorimetry
The DSC thermograms of chitosan, PCL and CS-g-PCL are pre-
sented in Fig. 3. It is well regarded that, owing to the strong
inter/intramolecular hydrogen bonds between OH and NH2, the
melting point of chitosan is much higher than its decomposition
temperature. Thus, chitosan cannot melt and lacks thermoplastic-
ity. It is regarded that the variation in heat capacity, arising from
the change in specific volume near Tg, is too small to be detected
by DSC. As a result, no obvious glass transition attributing to CS can
be observed in Fig. 3. In contrast, the molecular chains of PCL are
much more flexible and the glass transition is more prominent. The
Tg of copolymer is almost invisible for CS-g-PCL with low grafting
content. However, with increasing grafting content of PCL, the Tg of
copolymer gradually becomes evident and decreases steadily from
16.1 ◦C to −59.9 ◦C to gradually approach to the Tg of pure PCL.
Interestingly, there is an evident endothermic peak for CS-g-PCL
with highest grafting content, arising from the melting of PCL side
chains. It indicates that when the side chain length of PCL increases
to some extent, some fascinating thermal behaviors transformation
would happen. Nevertheless, the endothermic peak appeared at a
much lower temperature region (11.9 ◦C, lower than room tem-
perature) as compared to pure PCL, suggesting very poor crystal
structure of PCL side chains in CS-g-PCL. It may be original from
the fact that the chain length of PCL side chains is not long enough.
Furthermore, the crystallization of PCL side chains has been greatly
restrained by CS main chains.
3.3. 1H NMR spectra of CS-g-PCL
The 1H NMR spectra of CS, PCL and CS-g-PCL are shown in
Fig. 2. The characteristic signals of chitosan protons were observed
at 4.72 ppm for H-1, 3.02 ppm for H-2, 1.92 ppm for H-7 and
3.3–3.8 ppm for H-3, -4, -5, -6 in Fig. 2a. As indicated in Fig. 2b, the
signals occurring at 1.20, 2.23, 3.48 and 1.4–1.6 ppm are assigned to
H-␥, H-␣, H-␧, H-␤, -␦ of PCL, respectively. Obviously, the spectrum
of the graft copolymer (Fig. 2c) demonstrates all the proton signals
of chitosan and PCL. Thus, the structure of PCL-g-CS can be verified.
Moreover, the intensity of signals at 4.45 ppm attributed to H-1ꢀ
increases, while the signal at 4.72 ppm arising from H-1 decreases
after copolymerization. It suggests that PCL was grafted onto the CS
skeleton through NH2. The variation of the intensity of the peaks
at 3.5–3.8 ppm implied that the graft reaction also occurs on the
OH. Thus, the grafting of CS by PCL takes place at random along
the CS backbones and produces a random copolymer. The simulta-
neous grafting of PCL on reactive groups of NH2 and OH suggests
3.5. Wide-angle X-ray diffraction
WAXD was performed to study the crystal structure and the
corresponding results are given in Fig. 4. As far as chitosan is
regarded, whose crystal form was rhombic (Dung, Milas, Rinaudo,
& Desbrieres, 1994), the peak at ca 11◦ was assigned to crystal form
I, while the strong peak at ca 20◦ was ascribed to crystal form II
(Zhang, Ping, Zhang, & Shen, 2003). Upon grafted by PCL, the peak
at ca 11◦ disappeared and the peak at ca 20◦ became widened and
weaken. It indicates that the degree of crystallinity of chitosan in the
copolymer is reduced upon graft copolymerization. These results
can be explained as that the PCL side chains disturbed the regularity

Z. Wang et al. / Carbohydrate Polymers 94 (2013) 505–510
509
Table 2
The data of thermogravimetric analysis of chitosan and CS-g-PCL copolymers.
Chitosan
Sample 1
Sample 2
Sample 4
Sample 8
Sample 9
PCL
Tmax (◦C)
318.78
38.84
267.78
37.18
274.34
31.99
306.32
22.46
327.52
11.75
328.94
5.67
330.89
0.36
Residue at 700 ◦C (%)
of packing between chitosan chains, decreasing its crystallizability
as well as the ability to form hydrogen bonds. However, characteris-
tic peaks arising from PCL are undetectable for the graft copolymers,
even for the sample with highest grafting content. It may be arising
from the fact that the crystallizability of PCL side chains is very poor.
Furthermore, the testing temperature for WAXD experiment was
carried out at room temperature, which is higher than the melting
point of graft copolymers, thus no crystals were formed at room
temperature.
two-stage degradation. Similar results have been reported by Feng
and Dong (2006). The first stage located at 20–170 ◦C with a slight
weight loss about 5% is due to the vaporization of water and elim-
ination of unstable fragments. The second one, the primary stage,
starts at 170 ◦C, corresponds to the degradation of chitosan main
chains. The basic data of thermogravimetric analysis are listed in
Table 2. Chitosan has the highest weight residue at 700 ◦C (38.8%),
while the PCL homopolymer has the lowest weight residue. The
weight residue decreases significantly with increasing graft content
of PCL and approaches to that of PCL. The residue is as low as 5.67%
when the grafting content of PCL is 630%. This result can be reason-
able interpreted as that the PCL chains dominate the decomposition
process when the grafting content of PCL is high enough.
3.6. Thermogravimetric analysis
The TGA thermograms of chitosan and CS-g-PCL copolymers are
presented in Fig. 5. It can be found that native chitosan go through a
Furthermore, the maximal decomposition temperature (Tmax
)
increases steadily and gradually approaches to that of PCL with
the increase of grafting content because PCL becomes the main
composition of copolymer. It consists well with the results for
chitosan-graft-poly(p-dioxanone) (Wang et al., 2009). The Tmax of
sample 1, sample 2 and sample 4 is lower than that of chitosan
while the Tmax of sample 8 and sample 9 is higher than that of chi-
tosan. This result can be explained by the fact that the introduction
of PCL partially destroys the hydrogen bonds of chitosan (Wu et al.,
2005) when the grafting content is low, causing a depressed ther-
mal stability. With further increase in the grafting content of PCL,
PCL becomes the main composition of copolymer, and the thermal
stability is close to that of PCL homopolymer.
4. Conclusions
In conclusions, a novel, convenient, and efficient procedure
to prepare CS-g-PCL was proposed in this contribution by ring-
opening polymerization of ␧-caprolactone, using EMIMAc as a
homogenous reaction media and stannous octoate as the catalyst.
It is much more effective to realize the graft copolymerization in
EMIMAc than in conventional solvent of DMSO. Both of the OH
and NH2 participates in the reaction and the grafting contents of
PCL surprisingly achieve as high as 630%. With increasing grafting
content of PCL, the Tg of copolymer gradually becomes evident and
decreases steadily to approach to the Tg of pure PCL. The melting
behavior of grafted side PCL segment emerges when the graft-
ing content approaches a certain extent. In summary, this article
provides a novel, convenient, and efficient method to synthesize
CS-g-PCL. The obtained graft copolymers are expected to have the
advantageous properties of two polymers and are promising to
have some applications in many fields, such as tissue engineering
or drug and gene delivery.
Fig. 4. WAXD patterns of chitosan (a) and sample 4 (b).
Acknowledgements
Financial support from National Science Fund of China (Grant
No. 21104087) and Cultivation Project of Institute of Chemistry,
Chinese Academy of Science (ICCAS) (Grant No. CMS-PY-201239)
is gratefully acknowledged.
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