Journal of Biomaterials and Nanobiotechnology, 2011, 2, 561-566
doi:10.4236/jbnb.2011.225067 Published Online December 2011 (http://www.scirp.org/journal/jbnb)
561
Biodegradable Blend Nanoparticles of
Amphiphilic Diblock Copolymers Prepared
by Nano-Precipitation Method
Wichuda Nanthakasri, Mangkorn Srisa-Ard, Yodthong Baimark*
Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahasarakham University,
Mahasarakham, Thailand.
Received September 30th, 2011; revised November 15th, 2011; accepted November 26th, 2011.
ABSTRACT
Nanoparticles of biod egradable methoxy poly (ethylene glycol)-b-polyester amphiphilic d iblock copolymers have widely
investigated for use as con trolled release drug delivery carriers. In th is work, blend nanoparticles o f methoxy poly(eth-
ylene glycol)-b-poly(D,L-lactid e) (MPEG-b-PDLL) and m ethoxy poly(ethylene glycol)-b-poly(  -caprolacton e) (MPEG-
b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant dif-
ference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios
can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape
with smooth surface. Average size of the blend nanoparticles obtained from light-sca ttering analysis slightly d ecreased
with increase in blend ratio of MPEG -b-PCL. The MPEG-b-PDLL and MPEG- b-PCL were amorphous and semi-crys-
talline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning
calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased
and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio
increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend
nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decom-
position steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two
temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b-
PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend
ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by
varying the blend ratio.
Keywords: D,L-Lactide,  -Caprolactone, Diblock Copolymers, Blend Nanoparticles, Nano-Precipitation
1. Introduction
Amphiphilic diblock copolymer nanoparticles of meth-
oxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-
PDLL) and methoxy poly(ethylene glycol)-b-poly(
 -
caprolactone) (MPEG-b-PCL) have attracted much atten-
tion in drug delivery applications in the human body due
to their biocompatibility and biodegradability [1-4]. The
hydrophilic MPEG layer coated on the nanoparticle sur-
faces can increase blood circulation time of these nano-
particles [5,6]. Their thermal, biodegradation and drug
release properties can be controlled through several ap-
proaches including block length adjustment [7-10] and
copolymerization [11]. The physical blending is an al-
ternative method that has been widely used to adjust the
properties of polymers such as crystallinity, mechanical
properties and biodegradation properties [12-15]. These
properties strongly affected the drug release behaviors.
In addition, the MPEG segments attached to polyester
segments can improve miscibility between PDLL and
PCL blends to reduce the phase separation [12]. Thus,
unique properties of polymer blends quite different from
their origin polymers were obtained. However, the pre-
paration of blend nanoparticles of the amphiphilic
diblock copolymers has been scarcely published.
The present work describes the preparation of blend
nanoparticles of amorphous MPEG-b-PDLL and semi-

Biodegradable Blend Nanoparticles of Amphiphilic Diblock Copolymers Prepared by Nano-Precipitation Method 562
crystalline MPEG-b-PCL. The blend nanoparticle were
prepared by nano-precipitation method, which were then
investigated by transmission electron microscopy (TEM)
for particle morphology, 1H-NMR spectroscopy for
chemical composition and light-scattering analysis for
particle size and size distribution. Thermal properties of
the blend nanoparticles were also determined by differ-
ential scanning calorimetry (DSC) and thermogravimet-
ric analysis (TGA).
2. Materials and Methods
2.1. Materials
D,L-lactide (DLL) monomer was synthesized by thermal
decomposition reaction of low molecular weight poly
(D,L-lactic acid) (PDLLA) at 220˚C under reduced pres-
sure. The low molecular weight PDLLA was obtained
from polycondensation of D,L-lactic acid solution (90%,
Fluka) at 160˚C. Crude DLL was purified by repeated
re-crystallization from ethyl acetate and dried in vacuo at
50˚C for 48 h befo re use.
 -Caprolactone (CL) monomer
(99%, Acro, USA) was purified by drying with CaH2
followed by distillation under reduced pressure before
storage over molecular sieves in a refrigerator. Methoxy
polyethylene glycol (MPEG) with a molecular weight of
5000 g/mol (Fluka) was used after it was dried in vacuo
at 120˚C for 4 h. Stannou s octoate (Sn(O ct)2, 95% Sigma)
was used without further purification. All solvents in
analytical grade were used.
2.2. Synthesis of Diblock Copolymers
Both MPEG-b-PDLL and MPEG-b-PCL diblock co-
polymers were synthesized by ring-opening polymeriza-
tion in bulk under nitrogen atmosphere at 130˚C for 24 h.
Feed mole ratios of MPEG/DLL and MPEG/CL were
1/416 and 1/526, respectively. MPEG and Sn(Oct)2 were
used as the initiating system. Sn(Oct)2 concentration was
kept constant at 0.02 mol%. The diblock copolymers
were dissolved in chloroform before precipitating in cool
n-hexane for purification. They were then dried to con-
stant weight in vacuo at room temperature. According to
this procedure, the purified diblock copolymers were
obtained with more than 95% yields.
2.3. Characterization of Diblock Copolymers
2.3.1. 1H-NMR Spectrometry
Chemical compositions of the copolymers were meas-
ured by 1H-NMR spectrometry using a Bruker Advance
DPX 300 1H-NMR spectrometer at 25˚C CDCl3 was used
as the solvent, and tetramethysilane was used as the in-
ternal standard.
2.3.2. Gel Per meation Chromato gra p h y
The number-average molecular weight (Mn) and molecu-
lar weight distribution (MWD) of the copolymers were
determined by gel permeation chromatography (GPC)
using a Waters 717 plus Autosampler GPC equipped
with an Ultrastyragel column operating at 35˚C and
employing a refractive index detector. Tetrahydrofuran
was used as the solvent at a flow rate of 1 mL/min.
2.3.3. Differential Scanning Calorimetry
Thermal transition properties of the copolymers were
carried out by non-isothermal differential scanning calo-
rimetry (DSC) using a Perkin-El mer Pyris D iamond DS C
The sample (10 mg) was heated at the rate of 10˚C/min
under helium flow.
2.4. Preparation of Blend Nanoparticles
Blend nanoparticles of diblock copolymers were pre-
pared by the nano-precipitation method. Briefly, 60 mg
mixed copolymer was dissolved in 6 mL acetone. The
blend solution was added drop-wise into 60 mL distilled
water in a 100 mL beaker with magnetic stirring at speed
of 800 rpm. The nanoparticle colloid was obtained after
evaporating acetone at room temperature for 6 h in a
fume hood. The nanoparticle aggregates were removed
by centrifugation at 5000 rpm at 4˚C for 30 min. The
blend nanoparticles with MPEG-b-PDLL/MPEG-b-PCL
blend ratios of 4/0, 3/1, 2/2, 1/3 and 0/4 (w/w) were pre-
pared. Dried nanoparticle sample was collected by cen-
trifugation at 15,000 at 4˚C for 2 h before freeze-drying
for over ni ght.
2.5. Characterization of Blend Nanoparticles
2.5.1. Transmission Electron Microscopy
Morphology of the blend nanoparticles was determined
by transmission electron microscopy (TEM) using a
JEOL JEM 1230 TEM. For TEM analysis, a drop of na-
noparticle suspension was placed on a formvar film
coated on the copper grid. The specimen on the copper
grid was not stai n ed.
2.5.2. Light-Scattering Particle Size Analysis
Particle size and size distribution of the blend nanoparti-
cles were measured from the nanoparticle colloids by
light-scattering analysis using a Coulter LS230 particle
size analyzer at 25˚C.
2.5.3. 1H-NMR Spectrometry
Chemical functional groups of the blend nanoparticles
were studied by 1H-NMR spectrometry using a Bruker
Advance DPX 300 1H-NMR spectrometer at 25˚C.
CDCl3 was used as the solvent, and tetramethysilane was
used as the internal standard.
2.5.4. Differential Scanning Calorimetry
Thermal transition properties of the blend nanoparticles
were determined by non-isothermal differential scanning

Biodegradable Blend Nanoparticles of Amphiphilic Diblock Copolymers Prepared by Nano-Precipitation Method 563
blend ratios. It can be clearly seen that the blend nano-
particles had nearly spherical in shape with smooth sur-
face. They had nanometer in size range. The blend ratio
did not affect on the morphology of nanoparticles. Aver-
age particle sizes of the blend nanoparticles measured
from light-scattering analysis are summarized in Table 1.
The size of MPEG-b-PCL nanoparticles was the smallest.
The average sizes of blend nanoparticles increased sig-
nificantly as the MPEG-b-PDLL blend ratio increased.
This may be due to the crystallisable PCL block en-
hanced more compact nanoparticles.
calorimetry (DSC) as described above.
2.5.5. Thermogravimetric Analysis
The thermal decomposition behaviours of the blend
nanoparticles were characterized by non-isothermal ther-
mogravimetric (TG) analysis using a TA-Instrument
SDT Q600 TG analyzer. For TG analysis, sample (5 mg)
was heated from 50˚C to 800˚C at the rate of 20˚C/min
under nitro gen atmosphere.
3. Results and Discussion
3.1. Characterization of Diblock Copolymers The chemical compositions of blend components in
the nanoparticles can be investigated from the 1H-NMR Chemical compositions of diblock copolymers were de-
termined from 1H-NMR spectra. For this purpose, the
ratio of integral peak areas was calculated corresponding
to the ethylene oxide (EO, repeating units of MPEG)
methylene protons at
 = 3.6 - 3.7 ppm, the DLL methine
protons at
 = 5.0 - 5.3 ppm and the CL  -methylene
protons at
 = 4.0 - 4.2 ppm. The chemical compositions
of MPEG-b-PDLL and MPEG-b-PCL were measured as
EO/DLL = 20/80 and EO/CL = 18/82 (mol%) corre-
sponding to the MPEG/DLL and the MPEG/CL mole
ratios of 1/452 and 1/515, respectively. These calculated
copolymer compositions are similar to MPEG/monomer
(DLL or CL) feed mole ratios (1/416 and 1/526 for
MPEG-b-PDLL and MPEG-b-PCL, respectively). This
suggests that the polymerization reactions were taken to
near-quantitative conversion.
The Mns of MPEG-b-PDLL and MPEG-b-PCL ob-
tained from GPC curves were 49,000 and 47,000 g/mol,
respectively. The MWD values were 1.8 and 1.6 for the
MPEG-b-PDLL and the MPEG-b-PCL, respectively. The
Mns obtained from GPC results were less than to that
calculated from the feed ratios (65,000 g/mol). The tran-
sesterification degradation side-reactions may occur dur-
ing polyme ri zat i on.
3.2. Characterization of Blend Nanoparticles Figure 1. TEM micrographs of blend nanoparticles with
MPEG-b-PDLL/MPEG-b-PCL blend ratios of (a) 4/0, (b)
3/1, (c) 2/2, (d) 1/3 and (e) 0/4 w/w. Bars = 100 nm for (a)
and (e), and bars = 50 nm for (b)-(d).
Figure 1 shows the TEM micrographs of various blend
nanoparticles at different MPEG-b-PDLL/MPEG-b-PCL
Table 1. Average particle sizes and thermal properties of blend nanoparticles.
MPEG-b-PDLL/MPEG-b-PCL blend ratio (w/w) Size (nm)a Tg (˚C)b Tm (˚C)c Hm (˚C)d Td,max (˚C)e
4/0 348  16 36 - - 367
3/1 176  16 34 48, 55 6.9, 2.9 334, 420
2/2 162  16 29 54 23.4 329, 420
1/3 98  15 25 55 56.9 319, 420
0/4 98  18 - 55 94.2 420
aAverage particle size measured by light-scattering analysis; bGlass transition temperature obtained from DSC thermograms; cMelting temperature obtained
rom DSC thermograms; dH eat of melting obtained from DSC thermograms; eTemperature of maximum decomposition rate measured from DTG thermograms. f

Biodegradable Blend Nanoparticles of Amphiphilic Diblock Copolymers Prepared by Nano-Precipitation Method 564
spectra, as illustrated in Figure 2. It was found that the
integral peak areas of DLL and CL units directly related
to their blend ratios. The integral area of peak b (methine
protons of DLL units) steadily decreased with decrease
in the MPEG-b-PDLL blend ratio. Meanwhile the inte-
gral areas of peaks d and h (methylene protons of CL
units) significantly increased as the MPEG-b-PCL blend
ratio increased. This supported that the blend nanoparti-
cles with different blend ratios can be prepared by na-
no-precipitation method of the blend solution.
The DSC thermograms of the MPEG-b-PDLL and
MPEG-b-PCL showed that they were amorphous and
semi-crystalline copolymers, respectively (DSC curves
did not show). The MPEG-b-PDLL exhibited a single
glass transition temperature (Tg) at 36˚C. The melting
temperature (Tm) and heat of melting (Hm) of MPEG-
b-PCL were 61˚C and 86.0 J/g, respectively. The DSC
thermograms of the blend nanoparticles are presented in
Figure 3 and the DSC results are also summarized in
Table 1. The DSC thermograms of blend nanoparticles
exhibited both Tg of MPEG-b-PDLL and Tm of MPEG-
b-PCL. The Tg of MPEG-b-PDLL in blend nanoparticles
significantly decreased as the MPEG-b-PCL blend ratio
Figure 2. 1H-NMR spectra of blend nanoparticles with
MPEG-b-PDLL/MPEG-b-PCL blend ratios of (a) 4/0, (b)
3/1, (c) 2/2, (d) 1/3 and (e) 0/4 w/w (Peak-proton assign-
ments as shown).
Figure 3. DSC thermograms of blend nanoparticles with
MPEG-b-PDLL/MPEG-b-PCL blend ratios of (a) 4/0, (b)
3/1, (c) 2/2, (d) 1/3 and (e) 0/4 w/w (heating rate = 10˚C un-
der helium flow).
increased, suggesting that the MPEG-b-PDLL and
MPEG-b-PCL exhibited miscible blended in the amor-
phous phase to reduce the Tg of MPEG-b-PDLL. The Tm
of MPEG-b-PCL in blend nanoparticles did not change.
It should be noted that the Hm values of the blend
nanoparticles decreased steadily as increasing the MPEG-
b-PDLL blend ratio. This may be explained that the
MPEG-b-PDLL interrupted crystallisability of MPEG-b-
PCL in the blend nanoparticles.
The blend nanoparticles with controllable thermal
transition properties (Tg and Hm) might be of interest for
controlled release drug delivery applications. Two mains
mechanisms of drug releasing from polymer matrix con-
sisted of drug diffusion due to matrix swelling and drug
release due to erosion of polymer matrix. The swelling
and erosion rates of polymeric matrix strongly depended
upon the Tg and Hm, respectively. Thus drug release
may be adjusted by varying the Tg and Hm of the poly-
meric matrix.
Thermal stability of the blend nanoparticles was de-
termined from the TG thermograms, as shown in Figure
4. The weight losses of MPEG-b-PDLL and MPEG-b-
PCL started at approximate 300˚C and 350˚C, respec-
tively. The MPEG-b-PCL exhibited higher thermal sta-
bility than that of MPEG-b-PDLL. The thermal decom-
positions completely finished at approximate 400˚C and
450˚C for the MPEG-b-PDLL and the MPEG-b-PCL,
respectively. The blend nanoparticles showed two ther-
mal decomposition stages with the first MPEG-b-PDLL
decomposition following with the weight loss of MPEG-
b-PCL component. The weight loss behaviors of the
blend nanoparticles directly related to the blend ratio.
The weight remaining of the first decomposition step
decreased steadily with the MPEG-b-PDLL blend ratio.
The 2/2 (w/w) MPEG-b-PDLL/MPEG-b-PCL blend na-
noparticles showed remaining weight at approximately

Biodegradable Blend Nanoparticles of Amphiphilic Diblock Copolymers Prepared by Nano-Precipitation Method565
Figure 4. TG thermograms of blend nanoparticles with
MPEG-b-PDLL/MPEG-b-PCL blend ratios of (a) 4/0, (b)
3/1, (c) 2/2, (d) 1/3 and (e) 0/4 w/w (heating rate = 20˚C un-
der nitrogen flow).
50% by weight after MPEG-b-PDLL decomposition.
This indicating that the weight ratio of MPEG-b-PDLL/
MPEG-b-PCL was about 50/50 by weight corresponded
to the feed blend ratio (1/1 by weight). The TG results
supported that the blend nanoparticles with different
blend ratios can be prepared according to the 1H-NMR
analysis, as described above.
Thermal stability results can be clearly determined
from the derivative TG (DTG) thermograms, as shown in
Figure 5. The peak of DTG thermogram indicate a tem-
perature of maximum decomposition rate (Td, max). The
resulting Td, max are also reported in Table 1. The Td, max
values of MPEG-b-PDLL and MPEG-b-PCL were 367
and 420˚C, respectively supported the higher thermal
stability of MPEG-b-PCL than that of MPEG-b-PDLL.
The DTG thermograms of blend nanoparticles exhibited
two peaks (two Td, max) of MPEG-b-PDLL and MPEG-
b-PCL. It should be noted that the peak areas of DTG
thermograms depended on the blend ratios. The peak
area of the first peak of MPEG-b-PDLL decomposition
steadily decreased as the MPEG-b-PDLL blend ratio
decreased. The Td, max of MPEG-b-PCL in the b lend nano-
particles did not change. While, the Td, max of MPEG-
b-PDLL in the blend nanoparticles decreased slightly
with the MPEG-b-PDLL blend ratio. The DTG results
also supported that the blend nanoparticles with different
blend ratios exhibited difference in thermal decomposi-
tion beha viors.
4. Conclusions
The MPEG-b-PDLL/MPEG-b-PCL blend nanoparticles
with spherical in shape and smooth surface were suc-
cessfully prepared by nano-precipitation method. Blend
ratios of MPEG-b-PDLL/MPEG-b-PCL affects the ave-
Figure 5. DTG thermograms of blend nanoparticles with
MPEG-b-PDLL/MPEG-b-PCL blend ratios of (a) 4/0, (b)
3/1, (c) 2/2, (d) 1/3 and (e) 0/4 w/w (heating rate = 10˚C un-
der nitrogen flow).
rage particle size, thermal transition properties and ther-
mal decomposition behaviors. The average particle sizes
and glass transition temperatures of the blend nanoparti-
cles decreased and the heats of melting significantly in-
creased as the blend ratio of MPEG-b-PCL increased.
The blend ratio is an effective tool to modulate the parti-
cle size and thermal properties of the blend nanoparticles.
The thermal property control suggested in this work may
lead to rational manipulation of biodegradation and drug
release rates of the blend nanoparticles. These blend
nanoparticles might be interested in drug delivery appli-
cations.
5. Acknowledgements
The authors would like to acknowledge the financial
support from the Mahasarakham University and the Re-
search, Development and Engineering (RD&E) fund
through The National Nanotechnology Center (NANO-
TEC), The National Science and Technology Develop-
ment Agency (NSTDA), Thailand (Project No. NN-B-
22-EN4-30-52- 11) to Mahasarakham University. We also
gratefully acknowledge The Center of Excellence for
Innovation in Chemistry (PERCH-CIC), Commission on
Higher Education, Ministry of Education, Thailand for
providing a scholarship for one of us (W. Nanthakasri).
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