Preparation and characterization of biodegradable electrospun polyanhydride nano/microfibers

Article abstract of DOI:10.1166/jnn.2010.2535

The biodegradable polyanhydride copolymers P(CPP-SA) composed of p-carboxyhenoxy propane (CPP) and sebacic acid (SA) at weight ratios of 20:80, 35:65 and 50:50 were polymerized by a melt polycondensation process without catalyst. The copolymers were chara

Full text of DOI:10.1166/jnn.2010.2535

Copyright © 2010 American Scientific Publishers
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Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 10, 6369–6375, 2010
Preparation and Characterization of Biodegradable
Electrospun Polyanhydride Nano/Microfibers
Qiuxiang Su, Aijun Zhao, Hongsen Peng, and Shaobing Zhou∗
School of Materials Science and Engineering, Key Laboratory of Advanced Technologies of Materials,
Ministry of Education, Southwest Jiaotong University, Chengdu, 610031, P. R. China
The biodegradable polyanhydride copolymers P(CPP–SA) composed of p-carboxyhenoxy propane
(CPP) and sebacic acid (SA) at weight ratios of 20:80, 35:65 and 50:50 were polymerized by a melt
polycondensation process without catalyst. The copolymers were characterized by fourier transform
infrared spectroscopy (FT-IR), 1H-nuclear magnetic resonance (1H-NMR), Ubbelohde viscometer,
differential scanning calorimetry (DSC) and wide angle X-ray powder-diffraction (XRD). P(CPP–SA)
nano/microfibers were the first time to be fabricated by electrospinning. The copolymers hold an
excellent fibre-forming performance and the diameter range of 80–3,200 nm can be obtained. The
in vitro degradation of the polyanhydride copolymers was evaluated in form of the nano/microfibers
by investigating the change of fibrous morphology, weight loss and pH change of degradation
medium. The experimental results showed that degradation rate was fast in the fist day and slow in
the following period, furthermore the degradation rate decreased with the increase of the content
of CPP in copolymers. Therefore, the electrospun polyanhydride nano/microfibers exhibited strong
potential as drug delivery vehicle and tissue engineering scaffold.
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Keywords: PolyanIhPyd: r1id1e4,.2X7-r.a6y7D.7if6fraOcntio: nW, Uedltr,a1fi4neO, cFtib2e0rs1,5D0e9g:r0ad6a:4ti0on.
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1. INTRODUCTION
the melt polycondensation method as reported by Hill and
Carothers.19ꢀ20 Since polyanhydrides with high molecular
weight have been often obtained by melt polycondensation
compared to other methods such as interfacial condensa-
tion, dehydrative coupling agents, solution polymerization
and so on.21–27
Polyanhydrides as a new class of biodegradable poly-
mers have been developed since 1980s’ by the group of
Langer,1 which now have been used widely in a num-
ber of applications for controlled release devices for drugs
treating anticancer agents,2ꢀ3 local anesthetics,4 chemo-
therapeutic agents,5ꢀ6 anticoagulants,7 peptides and pro-
tein therapeutic.8–11 Based on the outlined advantage of
degradable polymers there have been numerous polymers
explored, while polyanhydrides can be used widely in
biomedical field for good biocompatibility and variable
degradation properties. Compared with the bulk erosion
process of polylactide (PLA) and polylactide-co-glycolide
(PLGA),12–14 polyanhydrides are believed to predomi-
nantly undergo surface erosion which is also termed
heterogeneous erosion for hydrolytic instability of the
anhydride bond and hydrophobicity.15–17 The outer drug
can be released by steady speed from the polymers and
the inner drug has been protected from biological environ-
ment throughout the surface erosion process, which made
polyanhydride have particular advantages as drug delivery
carriers.18 Polyanhydrides are most commonly prepared by
Polymer processing techniques are being explored for
the incorporation of drug molecules into delivery vehicles
of various geometries. As framework controlled release
polymer, sustained-release wafers, beads and microspheres
using plyanhydrides loaded with appropriate drug can be
prepared by relevant processing techniques in previous
research.3ꢀ28–31 While in our study, we choose polyan-
hydride nano/microfibers for controlled release device,
which have not been reported yet. The main advantages
of polyanhydrides nano/microfibers are as follows. Firstly,
they have excellent fiber forming property.32 Secondly,
the locally delivery and controlled release profiles make
electrospun nano/microfibers potential as implantable drug
carriers and functional coating of medical devices. The
very large surface area to volume ratio, flexibility in sur-
face functionalities, superior mechanical performance, and
versatility of design are some of the characteristics that
make the polymer nanofibers optimal candidates for many
important applications.33ꢀ34 Therefore, we can anticipate
∗Authors to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2010, Vol. 10, No. 10
1533-4880/2010/10/6369/007
doi:10.1166/jnn.2010.2535
6369

Preparation and Characterization of Biodegradable Electrospun Polyanhydride Nano/Microfibers
Su et al.
that the nano/microfibers have potential in drug controlled
release system.
solution was added into and refluxed again for 1 h, and the
obtained solution was stirred to receive white precipitate.
After filtration the collection was washed with anhydrous
ethanol. The residue was dissolved in water, extracted with
dried ether and neutralized with 6NH2SO4. After wash-
ing with water and drying in vacuum, CPP product was
In this study, we synthesized biodegradable poly-
anhydrides composed of sebacic acid (SA) and 1, 3-bis
(p-carboxyphenoxy) propane (CPP) via melt poly-
condensation. The copolymers were characterized by
FT-IR, 1H-NMR, XRD, DSC and Ubbelohde vscosity
technique. Polyanhydride nano/microfibers were also fab-
ricated using electrospinning, since it is one of the few
techniques to prepare long fibers with nano- to micrometer
diameter.33ꢀ35–44 The in vitro degradation of polyanhydride
nano/microfibers was further studied.
1
obtained. Its yield was about 50%. H-NMR (CDCl3ꢃ: ꢄ
12.54 (s, COOH), 7.87, 7.04 (d, 4H, ArH), 4.21 (t, 4H,
CH2O), 2.21 (m, 2H, CH2ꢃ. IR (KBr, cm−1ꢃ: 2954, 2889
(CH2), 1693 (C O).
2.3.2. Preparation of Acylated Prepolymers
Preweighted sebacic acid was refluxed in acetic anhydride
for 1 h under nitrogen atmosphere and excess acetic anhy-
dride was removed by drying under vacuum at 65 C. The
2. MATERIALS AND METHODS
ꢀ
2.1. Materials
crude prepolymer was recrystallized from dried toluene.
The crystals were washed with the mixed solvent of dried
ether and petroleum ether (v/v = 50/50) to remove traces
of acetic anhydride and toluene. Then, the final prod-
ucts were dried under vacuum. Its yield was about 87%.
1H-NMR (CDCl3ꢃ: ꢄ 2.46 (t, 4H, C( O)CH2ꢃ, 1.67 (m,
4H, CH2ꢃ, 1.31 (m, 8H, CH2ꢃ. IR (KBr, cm−1ꢃ: 1806, 1740
(anhydride C O).
Sebacic acid was recrystallized three times from
ethanol. Acetic anhydride was distilled from magne-
sium. 1, 3-Dibromopropane, p-hydroxybenzoic acid and
all other solvents were used as received without fur-
ther purification. All the other chemicals were analytical
reagent grade.
2.2. Characterization
Preweighed CPP was refluxed in 100 mL acetic anhy-
dride for 25 min under nitrogen atmosphere and then,
Infrared spectra were obtained using a Nicolet 5700 spec-
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unreacted diacid was removed by filtration. The CPP pre-
trometer. The samples were pressed into KBr pellets for
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ꢀ
polymer was deposited with dry ethyl ether at 0 C and
1
Copyright: American Scientific Publishers
analysis. H-NMR spectra were obtained on a Bruker AM
300 apparatus using CDCl3 as a solvent and TMS as an
internal reference. Intrinsic viscosity ([ꢁ]) of polymers was
measured in a chloroform solution (polymer concentra-
1
dried under vacuum. Its yield was about 79%. H-NMR
(CDCl3ꢃ: ꢄ 7.99, 7.12 (d, 4H, Ar-H), 4.26 (t, 4H, CH2O),
2.35 (s, 6H, CH3ꢃ, 2.27 (m, 2H, CH2ꢃ. IR (KBr, cm−1ꢃ:
1801, 1720 (anhydride C O).
ꢀ
tion 1% w/v) at 23 C using a Ubbelohde viscometer. The
thermal properties of polymer were determined by differ-
ential scanning calorimetry (DSC) (Netzsch STAꢀ449 C,
Bavaria, Germany) from room temperature to 300 C with
2.3.3. Preparation of Copolymer
CPP prepolymer and SA prepolymer were mixed in
defined ratio in a three-necked flask under nitrogen. The
flask was immersed in an oil bath and the prepolymers
were allowed to melt after reaching 180 ꢀC, and then,
the pressure was reduced to 50∼60 mmHg. The acetic
anhydride condensed as byproduct was collected in a liq-
uid nitrogen trap. After a defined time, the crude poly-
mer was allowed to cool, dissolved in dichloroformethane,
precipitated in petroleum ether. The precipitate was then
washed with anhydrous ether and dried under vacuum at
roomꢀtemperature. The polymers obtained were stored at
ꢀ
a heating rate of 10 C/min under a nitrogen atmosphere.
The crystallinity of copolymer was characterized using an
X-ray diffractometer (XRD) (Phlips, X’Pert PRO, Nether-
lands) and scanning was done in the 2ꢂ angle range of
5–45ꢀ. The morphology of the polyanhydride fibers was
investigated by using scanning electron microscope (SEM)
(FEI, Quanta200, America) equipped with field-emission
gun (10 kV) and robinson detector after 2 min of gold
coating to minimize a charging effect.
1
2.3. The Synthesis of P(CPP–SA) Copolymers
−20 C. H-NMR (CDCl3ꢃ: ꢄ 7.98, 6.95 (d, ArH), 4.25
(t, CH2O), 2.44 (t, C( O)CH2ꢃ, 2.33 (m, CH2ꢃ, 1.64 (m,
CH2ꢃ, 1.31 (m, CH2ꢃ. IR (KBr, cm−1ꢃ: 1810, 1740, 1720
(anhydride C O).
2.3.1. Preparation of p-Carboxyhenoxy Propane
Preweighted sodium hydroxide, p-hydroxybenzoic and
distilled water were added into a three-necked flask
equipped with mechanical stirrer, reflux condenser and
dropping funnel. The mixture was heated at reflux and 1,
3-Dibromopropane was dropped into for 1 h, followed by
keeping on reflux for 5 h. Then sodium hydroxide water
2.4. Preparation of Polyanhydride Nano/Microfibers
The electrospinning apparatus was equipped with a high-
voltage statitron (Tianjing High Voltage Power Supply Co.,
6370
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Su et al.
Preparation and Characterization of Biodegradable Electrospun Polyanhydride Nano/Microfibers
Tianjing, China). The copolymer was dissolved in chloro-
form solvent and then added in a 5 mL syringe attached
to a circular-shaped metal capillary. The circular orifice of
the capillary has an inner diameter of 0.6 mm. An oblong
counter electrode is located about 15–18 cm from the cap-
illary tip. The flow rate of the polymer and drug solu-
tion was controlled within 1 mL/h by a precision pump
(Zhejiang University Medical Instrument Co., Hangzhou,
China) to maintain a steady flow from the capillary out-
let. The applied voltage was controlled within the range
15–20 kV.47
sharp rise in Tm as the CPP content increased to 50 wt%.
The result is in agreement with previous report.46 Based
on the literature, we can know that meltꢀing point of SA
and CPP homopolymers is 86 and 240 C, respectively.
When CPP content in copolymer is near 50 wt%, its melt-
ing point will be gradually close to Tm of CPP homopoly-
mer. The factual weight percentages of SA and CPP in the
copolymers were in good agreement with the feed ratio.
The amount of SA in the copolymer was slightly higher
than the amount fed, while the CPP amount was slightly
less than fed. Furthermore, the molecular weight decreases
with increasing CPP content in the same experimental con-
ditions. The reason is that aromatic acid has lower reactiv-
ity than aliphatic acid. Reactivity decreases with increased
the CPP amount, which results in depressing chain inter-
actions with CPP in polymerization, and subsequently
reducing the content of CPP, the molecular weight of
polyanhydride increases.
2.5. Degradation of Polyanhydride Nano/Microfibers
80 mg of P(CPP–SA) nano/microfibers was placed indi-
vidually in test tube containing 10 mL of 0.1 M phosphate-
buffered saline (PBS) at pH 7.4. The tubes were kept
in a thermo-stated incubator (Haerbin Dongming Medi-
ꢀ
cal Equipment Company) which was maintained at 37 C
and 100 cycles/min. At predetermined time intervals,
the remaining fibers were collected by centrifugation,
washed with distilled water and freeze-dried. Samples then
weighed to determine the weight loss due to degradation
of copolymer. The pH values of the degradation medium
were measured using an Orion pH meter with a pH glass
electrode. The meter was calibrated using KCl standard
3.2. Fourier Transform Infrared Spectra (FT-IR)
FT-IR spectra of P(CPP–SA) copolymers show typical
three characteristic anhydride carbonyl peaks at 1810,
1740 and 1720 cm−1, the C–H stretching vibrations of
long aliphatic alkyl at 2900 and 2850 cm−1, and the C–O
stretching of anhydride group at 1070 cm−1 and 1040 cm−1
(see Fig. 1). With the amount of CPP in the copoly-
solutions.
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−1
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mer increasing the intensity of peaks at 1720 cm also
−1
Copyright: American Scientific Publishers
increased while the intensity of the peak at 1740 cm
decreased.
3. RESULTS AND DISCUSSION
3.1. Polyanhydride Synthesis
3.3. Nuclear Magnetic Resonance (NMR)
The polyanhydrides were synthesized in a melt poly-
condensation process in accordance with the protocol
established by Domb et al.21 Firstly, aromatic monomer
CPP monomer was synthesized with p-hydroxybenzoic
acid and 1, 3-dibromopropane. Later, acetic mixed anhy-
dride prepolymers were prepared by heating corresponding
diacids in acetic anhydride. Finally, P(CPP–SA) copoly-
mers with CPP/SA weight ratios of 20:80, 35:65 and 50:50
were synthesized by melt-polycondensation of CPP pre-
polymer and SA prepolymer. Table I summarizes the prop-
erties of P(CPP–SA) copolymers with different ratios of
CPP and SA. From DSC data, we can find that the melting
temperature (Tm) of these copolymers was almost simi-
lar when CPP content is below 35 wt%, but there was a
Figure 2 shows the 1H-NMR spectrum of P(CPP–SA)
copolymer obtained by melt polycondensation. The well
resolved chemical shifts at ꢄ = 1ꢅ3ꢀ1ꢅ6ꢀ and 2.4 ppm
belong to the hydrogen atoms of individual functional
groups on poly(sebacic anhydride) and chemical shifts
at 2.33, 4.25, 6.95, and 7.98 ppm ascribed to the pro-
tons of CPP. The peak at 7.25 ppm corresponds to
the d-chloroform. The spectrum also confirmed that the
polyanhydrides were provided with anticipant structure.
The actual weight percentages of SA and CPP in the poly-
mer were estimated by integration and comparison of the
corresponding NMR peaks, which were in good agreement
with the monomer feed ratios, also as shown in Table I.
Table I. Characterization of P(CPP–SA) copolymers.
CPP:SA in the feed
(wt%)
CPP:SA 1H-NMR
(wt%)a
Yield
(%)
Intrinsic viscosity
Viscosity weight
averagec
Tm
(ꢀC)d
Crystallinity
(%)e
([ꢁ])b
20:80
35:65
50:50
17.8:82.2
33.5:66.5
43.6:56.4
82
76
58
0.3805
0.2441
0.2154
35187
17922
14819
63ꢅ6
57ꢅ5
185ꢅ1
37.9
28.8
16.2
296
k
3
aCalculated by 1H-NMR. bDetermined using a Ubbelohde viscometer at 23 ꢀC. cCalculated by the formula as follow.18 ꢆꢁꢇ
DSC. eCalculated using XRD.
= 3ꢅ88 × 10−4M0ꢅ658
.
dDetermined by
CHCl
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Preparation and Characterization of Biodegradable Electrospun Polyanhydride Nano/Microfibers
Su et al.
erosion. The crystallinity was determined by X-ray diffrac-
tion based the reported methods.48ꢀ49 In general, the peaks
of amorphous and crystalline overlap each other partially
or fully for the crystalline polymers. Therefore, it is impor-
tant to realize that distinguishing between the two different
types of peaks is a very meaningful work. The analysis
method is derived from Gauss-Cauchy Compound func-
tion, which was put forward by Hindeleh etc.50 to char-
acterize the curve of X-ray diffraction. An amorphous
intensity curve and multiple peaks separation program
based on XRD pattern were employed (Fig. 3). The degree
of crystallinity calculated from the pattern was shown in
Table I. The data show that the crystallinity of polyanhy-
dride reduces to the low-water mark while the monomer
content of CPP/SA tends to 1:1, which may lead to an
increase in the confusion degree and a decline in the struc-
tural regularity. Thus, it further resulted in the depression
of the degree of crystallinity.
(A)
(B)
(C)
Fig. 1. FT-IR spectra of P(CPP–SA) (A) 20:80; (B) 35:65; (C) 50:50.
3.5. Degradation of P(CPP–SA) Ultrafine Fibers
After P(CPP–SA) copolymers were dissolved in methylene
chloride solvent, the nano/microfibers were prepared by
electrospinning. Figures 4(a, b and c) show original fibrous
morphology of P(CPP–SA) copolymers observed by SEM.
There was no obvious change on fibrous morphology
of the copolymers with different CPP/SA weight ratios.
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P(CPP–SA) copolymers have good fibre-forming perfor-
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Copyright: American Scientific Publishers
mance, and the nano/microfibers are straightforward and
have smooth external surfaces without visible nodes. The
size distribution of the fibers before degradation is from
80 nm to 3200 nm. The average fiber diameter of P(CPP–
SA) with CPP/SA weight ratios of 20:80, 35:65 and 50:50
is 1030 380 nm, 1690 670 nm and 1310 360 nm
shown in Figures 4(a, b and c), respectively. Consequently,
from these results a conclusion can be made that the mor-
phology and diameter of the fibers are not affected basi-
cally by the monomer ratios of copolymers.
Figure 5 shows the weight loss profiles of P(CPP–SA)
copolymers with different monomer ratios. There are two
phases through our investigation of degradation. For one
thing, copolymers degrade rapidly in the first day and
Fig. 2. 1H-NMR spectra of 20:80 P(CPP:SA) copolymer.
3.4. X-ray Diffraction (XRD)
For degradable polymers, the erosion behavior is based on
the polymer microstructure which is composed of amor-
phous and crystalline polymer parts, and the amorphous
structures erode faster than crystalline ones. Therefore,
crystallinity is an important factor that controls polymer
CPP: SA = 20:80
CPP: SA = 35:65
CPP: SA = 50:50
10
15
20
25
30
10
15
20
25
30
10
15
20
25
30
2θ/ (°)
2θ/ (°)
2θ/ (°)
Fig. 3. Curve analysis of P(CPP–SA) X-ray diffraction.
6372
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Su et al.
Preparation and Characterization of Biodegradable Electrospun Polyanhydride Nano/Microfibers
(a)
(d)
(g)
(b)
(e)
(h)
(c)
(f)
(i)
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Fig. 4. SEM photos of 20:80 P(CPP–SA) after: (a) 0; (d) 7; (g) 13 d and 35:65 P(CPP–SA) after: (b) 0; (e) 7; (h) 13 d and 50:50 P(CPP–SA) after:
(c) 0; (f) 1; (i) 13 d degradation in PBS at 37 ꢀC.
weight loss up to 50%, which may be strongly related to
their geometry and the composing of copolymer. Due to
high specific surface area and porous structure of polyan-
hydride ultrafine fibers, the progress of degradation can be
accelerated. Furthermore, in the first phase, SA segments
would be prior to degrade compared with CPP segments
owing to more hydrophilic for SA than CPP. And in the
following period, the degradation presented slow-motion
moment. The degradation rate is dependent on the content
of CPP monomer, slower degradation rate were observed
for more CPP content. The weight percentage of residue
after 13 days was almost equal to the corresponding con-
tent of CPP in copolymers in all cases, which further sug-
gested that the monomer CPP ratio in copolymer can affect
the degradation rate.
it was the first time to directly observe the degradation
process. Compared with SEM photos in Figures 4(d–f),
we can see that there were almost no fibers and only
some sheet residue for 20:80 P(CPP–SA), but for 35:65
P(CPP–SA) and especially for 50:50 P(CPP–SA) some
short fibers could be found. After 13 days’ degradation,
only sheet residue could be observed for all copolymers
(Figs. 4(g–i)). Especially for 80:20 P(CPP–SA) copolymer,
the outermost layer of fibers was first peeling off during
degradation, which caused the diameter of internal layer
become thinner. On the contrary, some layer peeled off
exhibited bigger owing to the perimeter of outside layer
of the fibers as shown in Figures 4(d and g). The phe-
nomenon is similar to that cortex desquamated from a tree
trunk. It indicated that the degradation occurred on fibers
surface first. The degradation mechanism belonged to sur-
face erosion. The results further confirmed that the degra-
dation rate of the copolymer decreased with CPP content
increasing. It is well known that during the degradation
the weight of biodegradable polymers would lose because
For the in vitro degradation study, the nano/microfibers
ꢀ
were degraded in PBS (pH 7.4) at 37 C for 13 days.
SEM photos show that the surface morphology of P(CPP–
SA) fibers with CPP/SA ratios of 20:80, 35:65 and 50:50
changed during the degradation. To the best our knowledge
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Preparation and Characterization of Biodegradable Electrospun Polyanhydride Nano/Microfibers
Su et al.
100
80
60
40
20
0
7.4
7.2
7.0
6.8
6.6
6.4
20:80
35:65
50:50
20:80
35:65
50:50
0
2
4
6
8
10
12
14
0
2
4
6
8
10
12
14
Time (day)
Time (day)
Fig. 5. Weight loss of 20:80, 35:65, 50:50 P(CPP–SA) nano/microfibers
Fig. 6. The pH change of medium for 20:80, 35:65, 50:50 P(CPP–SA)
incubated in PBS at 37 ꢀC.
nano/microfibers incubated in PBS at 37 ꢀC.
their some degradation product dissolved in degradation
medium. For P(CPP–SA) copolymers, their degradation
products, only SA can be dissolved in water. It also indi-
cated that the component of the sheet residue was mainly
CPP, which could also be proved by the weight loss pro-
files in Figure 5. The mass of fibers decreased sharply in
the initial 1 day, and then, only a slight mass loss was
observed in the following period. Degradation of the poly-
4. SUMMARY
The copolymers of CPP and SA can be synthesized by
melt polycondensation without any catalyzer. The poly-
mers with anticipant structure were proven by FT-IR
and 1H-NMR analysis. The crystallinity of P(CPP–SA)
copolymers was in reverse to the content of CPP from
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the investigation. In order to widen biomedical applica-
mer designates the process of a polymer chain cleavage,
IP: 114.27.67.76 On: Wed, 14 Oct 2015 09:06:40
tion of the polymer, we successfully prepared P(CPP–SA)
nano/microfibers by electrospinning for the first time to
the best of our knowledge. The fibers exhibited an excel-
lent fibre-forming performance. The in vitro degradation
of P(CPP–SA) nano/microfibers showed two phases: near
50% fast degradation in the fist day and followed grad-
ual degradation and furthermore the rate decreased with
CPP component increase. The degradation rate can be
controlled by adjusting the molar ratios of CPP and SA.
Therefore, P(CPP–SA) may be potential in form of fiber
for biomedical application as drug controlled release car-
rier and tissue engineering scaffold.
Copyright: American Scientific Publishers
while erosion is the sum of all processes that lead to mass
loss from polyanhydride matrix.51 The mass loss of fibers
in the initial phase might result from low molecular weight
part of copolymer dissolving into the degradation media
and the cleaving of the more labile SA–SA bonds. In the
following phase, the mass loss may be due to the hydrol-
ysis of high molecule weight copolymer into oligomers
or monomers.52 The XRD patterns of the residue were
almost similar with that of PCPP homopolymer,46 which
further suggested that the residue was mainly low molec-
ular weight PCPP and CPP crystals.
There are three kinds of bonds in P(CPP–SA) copoly-
mers: SA–SA bonds, CPP–CPP bonds and SA–CPP
bonds. David et al. reported that the following order
of anhydride bond lability was determined: SA–SA
≈ SA–CPP ꢁ CPP–CPP by using solution-state 1H-
NMR spectroscopy,26 leading to preferential hydrolysis of
aliphatic blocks within the copolymer chain. Therefore, the
more CPP content, the more CPP–CPP bonds in polyan-
hydride copolymer and the slower degradation rate, which
is consistent with the experimental results (Figs. 4–6).
The pH values of the degradation medium were also
measured to investigate the degradable property of the
copolymer as shown in Figure 6. P(CPP–SA) degraded
into CPP and SA monomers, which diffused into degra-
dation medium resulted in pH decrease. The pH change
profiles were similar with weight loss change. The reason
is same as above description.
Acknowledgments: This work was partially supported
by National Natural Science Foundation of China
(50773065, 30970723), Programs for New Century Excel-
lent Talents in university, Ministry of Education of China
(NCET-07-0719) and Sichuan Prominent Young Talent
Program (08ZQ026-040).
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Received: 28 June 2009. Accepted: 1 November 2009.
J. Nanosci. Nanotechnol. 10, 6369–6375, 2010
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