Synthesis and structural characterization of dendritic-linear PMA-APM-r-PS copolymers for a self-assembled microporous matrix

Article abstract of DOI:10.1002/pola.24113

A set of dendritic-linear copolymers, poly(maleic anhydride-grafted-3, 3′-dimethyl-(4-aminophenylazanediyl)bis(2methylpropanoate)) -random-polystyrene (PMA-APM-r-PS), was successfully prepared by copolymerization of the novel dendritic macromonomer, 4-(4-

Full text of DOI:10.1002/pola.24113

Synthesis and Structural Characterization of Dendritic-Linear
PMA-APM-r-PS Copolymers for a Self-Assembled Microporous Matrix
1
2
1
SHANG-JU HSIEH, CHENG-CHIEN WANG, CHUH-YUNG CHEN
1
Department of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
2
Department of Chemical and Materials Engineering, Southern Taiwan University, Tainan 710, Taiwan
Received 21 January 2010; accepted 29 April 2010
DOI: 10.1002/pola.24113
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A set of dendritic-linear copolymers, poly(maleic an-
dritic-linear copolymer film as functions of dendritic GMA-
HPAM segments in the content using SEM. Self-assembly of
the dendritic-linear PMA-APM-r-PS copolymer in the MG2-X
system, which represented the second generation dendron
0
hydride-grafted-3,3 -dimethyl-(4-aminophenylazanediyl)bis(2-
methylpropanoate))-random-polystyrene (PMA-APM-r-PS), was
successfully prepared by copolymerization of the novel dendritic
macromonomer, 4-(4-(bis(3-(4-(bis(3-methoxy-2-methyl-3-oxopro-
pyl)amino)phenylamino)-2-methyl-3-oxopropyl)amino)phenyl-
amino)-4-oxobut-2-enoic acid (MA-APM), with styrene mono-
containing X wt % of the dendritic MA-APM segment,
resulted in submicron phase segregation. Interestingly, the
submicron phase segregation morphology of the MG2–43
sample presented a uniform size distribution of ordered-array
structures. The results of this study demonstrate that control-
0
mer. The dendritic MA-APM macromonomer dendron 3,3 -di-
methyl-(4-aminophenylazanediyl)bis(2-methylpropanoate)
(
APM) was then grafted by using the divergent growth
ling the appropriate macromonomer content via the grafting
of a three-dimensional structure results in a self-assembly
process that is capable of providing an ordered-array micropo-
rous morphology in a polymer film. VC 2010 Wiley Periodicals,
1
13
method. FTIR, H NMR, and C NMR spectra were used to
identify the structures of the dendron, the dendritic macromo-
nomer, and the dendritic-linear PMA-APM-r-PS copolymer.
Furthermore, microporous dendritic-linear PMA-APM-r-PS co-
polymer films were prepared by using solvent-induced phase
separation at room temperature. We investigated the phase
separation behavior and morphological structures of the den-
Inc. J Polym Sci Part A: Polym Chem 48: 3290–3301, 2010
KEYWORDS: dendrimers; dendritic-linear copolymer; hexago-
nally-ordered structure; macromonomers; self-assembly
INTRODUCTION Microporous thin film materials with perfect
arrangements of ordered structures (10 lm = pore size =
self-assembling block copolymer solutions. After complete
evaporation of the solvent, the water droplets remain in the
50 nm) have attracted significant interest in recent year due
copolymer films, forming a perfectly ordered microporous
1
14–19
to their great potential as templating materials, membrane
copolymer structure.
Many studies have discussed the
2
3
4–6
filters, optical filters, electronic and optical devices,
cata-
structure of three-dimensional films and submicron films by
means of the water-assisted method, and according to their
results, the pore sizes of the ordered structures are influ-
enced by several key factors, such as the properties of the
block copolymer and the relative humidity and air-flow ve-
locity. Film preparation is challenging because of the need
for a special block copolymer polymerization treatment.
7
8
lytic supports, and biosensors. Until recently the modes of
preparation of these types of microporous materials were
through the ‘‘top-down’’ approaches using photolithographic
9
techniques or through ‘‘bottom-up’’ approaches using the
self-assembly of materials as templates around which mate-
rial assemblies take place. In addition, the templating
method and ‘‘breath figure’’ approach are two of the most
widely used techniques for the fabrication of ordered micro-
porous films through the ‘‘bottom-up’’ approach. In the tem-
Dendronized, or dendritic-grafted copolymers, are linear
polymers that bear pendant dendrons along the repeated
units. The two main synthetic routes to dendronized copoly-
1
0
plating method, uniform spherical particles (usually silica
mers include the ‘‘coupling to’’ approach and the ‘‘macromo-
1
1
20,21
or polymer spheres ) are used as a template, and ordered
microporous structure films are formed when the templates
nomer’’ approach.
In the ‘‘coupling to’’ approach, the
copolymer that becomes the core in the final product serves
as a starting material. The anchor groups of the copolymer
are used to either divergently or convergently attach a dense
sequence of dendrons. In contrast, in the ‘‘macromonomer’’
approach, a monomer already carrying dendrons is subjected
1
2,13
are removed.
Alternatively, a template-free method called
the ‘‘breath figure’’ approach, or water-assisted method, uti-
lizes a moist air-flow to create microdroplets of water that
work as a template for the micropores in condensing and
Correspondence to: C.-Y. Chen (E-mail: ccy7@ccmail.ncku.edu.tw)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 3290–3301 (2010) V
2010 Wiley Periodicals, Inc.
C
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to polymerization or polycondensation. The obvious advantage
of the ‘‘macromonomer’’ approach over the ‘‘coupling to’’ strat-
egy lies in the fact that it does not involve a postpolymeriza-
tion reaction, and can offer accurate control over the dendritic
rene and methyl methacrylate (MMA) (Merck Co.) were puri-
fied using a distillation method under reduced pressure.
They were stored at 5 C before use.
ꢀ
22
side groups, however, it becomes difficult to get copolymers
with higher degrees of polymerization (DP) for the dendritic
macromonomers of three or greater generations due to steric
hindrance. Nevertheless, one may say that, judging by the num-
ber of articles, polymerization using the ‘‘macromonomer’’
route is the most successful approach thus far. In addition,
because of the steric hindrance imposed by the bulky dendritic
side groups due to the rod-like shape of the copolymers, many
microporous films are made using dendritic-linear copolymers.
Polymerization Procedure for the Dendritic-Linear
Copolymer
Synthesis of the 4-(4-(bis(3-(4-(bis(3-methoxy-2-methyl-
3-oxopropyl)amino)phenylamino)-2-methyl-3-oxopropyl)
amino)phenylamino)-4-oxobut-2-enoic Acid (MA-APM)
Macromonomer
The macromonomer 4-(4-(bis(3-(4-(bis(3-methoxy-2-methyl-3-
oxopropyl)amino)phenylamino)-2-methyl-3-oxopropyl)amino)-
phenylamino)-4-oxobut-2-enoic acid (MA-APM) was synthe-
sized as part of this study. A solution of maleic anhydride (MA)
in DMF was added dropwise to a vigorously stirred solution
of p-phenylenediamine in DMF under a nitrogen atmosphere at
23
Xi et al. have prepared honeycomb macroporous films on the
basis of amphiphilic dendronized block copolymers using and
on-solid surface spreading method and an on-water spreading
method on the basis of the self-organization of water droplets.
ꢀ
ꢀ
0
C. Next, the mixture was stirred for 30 min at 0 C and then
24
In addition, Ishizu et al. have reported the fabrication of
highly ordered microporous films using emulsion micelles of
the amphiphilic PEO-b-PMMA diblock copolymer using the cur-
further stirred for 24 h at room temperature. The feed ratio of
p-phenylenediamine to MA was 10:1 (molar ratio). After reac-
tion was complete, the solvent was removed under a reduced
24
ꢀ
rent water-assisted method.
pressure at 60 C using a rotary evaporator, and the resulting
black powder was extracted by the mixed solution of toluene
and chloroform, the ratio of toluene to chloroform was 1.5:1
More recently, we have demonstrated a new method for con-
structing hexagonally-ordered microporous matrices using
dendritic-linear random copolymers via solvent-induced
phase separation. According to our results, the micelle
domains and the interaction of each segment in the dendri-
tic-linear copolymer control the surface morphology of the
matrix. Therefore, controlling the appropriate macromono-
mer content by grafting three-dimensional structures can
directly promote self-assembly and provide a hexagonally
ordered microporous matrix.
(
volumetric ratio), three times. After filtration, the solvent was
2
5
removed under reduced pressure at room temperature by
using rotary evaporator, and the resulting gray power was
dried in a vacuum oven overnight to yield the final amine-ter-
1
minated product (MA-APM-G0.5). Yield: 77%.
H NMR
(
400MHz, CDCl , 300K, TMS, d , ppm): 6.42 and 6.85 (s, 2H,
3 H
ACH ¼¼ CHA), 6.64 and 7.38 (m, 4H, ANAArHANA), 8.05
ꢁ
1
(
(
(
ANH). FTIR (KBr pellet, cm ): 1546 (NH, amide II), 1640
C ¼¼ C), 1658 (C ¼¼ O, amide I), 1696 (C ¼¼ O), 3200 (NH
2
) 3400
In this study, we announce the synthesis and characteriza-
tion of the dendritic macromonomer, 4-(4-(bis(3-(4-(bis(3-
methoxy-2-methyl-3-oxopropyl)amino)phenylamino)-2-methyl-
NH), 3600 (OH).
A solution of freshly distilled MMA in ethanol was added drop-
wise to the solution of MA-G0.5 precursor in methanol under a
nitrogen atmosphere over a period of 2 h, which was then
3
-oxopropyl)amino)phenylamino)-4-oxobut-2-enoic acid (MA-
0
APM), and the dendritic-linear copolymer, 3,3 -dimethyl-(4-
aminophenylazanediyl)bis(2-methylpropanoate))-random-poly-
styrene (PMA-APM-r-PS) (PMA-APM-r-PS). In addition, various
microporous films over an area of more than 2 cm were cre-
ated via solvent-induced phase separation
ꢀ
stirred for 1 hr at 0 C. Next, the mixture was further stirred
for 5 days at room temperature. The feed ratio of MMA to MA-
APM-G0.5 was 10:1 (molar ratio). After reaction was complete,
the solvent and unreacted MMA were removed under a
2
2
6,27
and the mor-
ꢀ
reduced pressure at 40 C using a rotary evaporator, and the
phologies of these copolymer films were characterized using
scanning electron microscopy (SEM). Furthermore, we demon-
strate how a hexagonally-ordered microporous structure with
a 1.9–2.5 lm micropore size can form on the film surface of a
dendritic-linear copolymer. We investigated the influence of
the dendritic segment to the dendritic-linear copolymer sys-
tem weight ratio on the number of ordered/disordered states,
the number density of micropores, and the uniformity of the
micropore size. We demonstrate that this experimental pro-
cess is significantly different from the mechanism of micropo-
rous formation under moist air-flow conditions.
resulting dark-brown oil was dried in a vacuum oven overnight
to yield the final ester-terminated product (MA-APM-G1). Yield:
1
8
6
6
0%. H NMR (400 MHz, CDCl , 300 K, TMS, d , ppm): 1.26 (t,
3
H
H, ACH ), 2.57 (s, 2H, NACH ACH(ACH )ACOAOA), 3.71 (s,
3
2
3
H, AC( ¼¼ O)AOACH
3
)
3.51 and 3.83 (m, 4H, Ar-
N(ACH A)ACH ACHA), 6.42 and 6.85 (s, 2H, ACH ¼¼ CHA),
2
2
6
.89 and 7.41 (m, 4H, ANAArHANA). FTIR (KBr pellet,
ꢁ
1
cm ): 1546 (NH, amide II), 1640 (C ¼¼ C), 1658 (C ¼¼ O, amide
I), 1700 (C ¼¼ O), 1740 (C ¼¼ O), 3400 (NH), 3600 (OH).
A solution of p-PDA in ethanol was added dropwise to the so-
lution of MA-G1 precursor in methanol under a nitrogen
atmosphere over a period of 2 h, which was then stirred for
EXPERIMENTAL
ꢀ
Materials
1 h at 0 C. Next, the mixture was further stirred for 5 days at
Reagents were purchased from Aldrich and Fluka Co. and
used without further purification. Maleic anhydride (MA)
and p-phenylenediamine (p-PDA) were used as received. Sty-
room temperature. The feed ratio of p-phenylenediamine to
MA-APM-G1 was 10:1 (molar ratio). After reaction was com-
plete, the solvent was removed under a reduced pressure at
DENDRITIC-LINEAR PMA-APM-r-PS COPOLYMERS, HSIEH, WANG, AND CHEN
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SCHEME 1
ꢀ
1
40
C by using a rotary evaporator, and the resulting black
APM-G1.5). Yield: 78%. H NMR (400 MHz, CDCl , 300 K, TMS,
3
power was extracted by the mixed solution of toluene and
chloroform, the ratio of toluene to chloroform was 1:4 (volu-
metric ratio), three times. After filtration, the solvent was
removed under reduced pressure at room temperature by
using rotary evaporator, the resulting dark-brown oil was dried
in a vacuum oven overnight to yield the final product (MA-
d , ppm): 1.28 (m, 18H, ACH ACHACH ), 2.57 (s, 2H,
H
2
3
ACH ACH(ACH )ACOA), 3.52 and 3.81 (m, 4H, Ar-
2
3
NACH
2
ACHA), 6.47 and 6.81 (s, 2H, ACH ¼¼ CHA), 6.90 and
ꢁ
1
7.39 (m, 4H, ANAArHANA). FTIR (KBr pellet, cm ): 1546
(NH, amide II), 1640 (C ¼¼ C), 1658 (C ¼¼ O, amide I), 1700
(C ¼¼ O), 3200 (NH ) 3400 (NH), 3600 (OH).
2
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1
13
to conventional calibration methods (CC). H NMR and
C
NMR spectra were recorded using a Bruker 400-MHz FT-
NMR instrument, and the chemical shifts were recorded in
parts per million with tetramethylsilane as an internal stand-
ard. Fourier transfer infrared (FTIR) spectra were recorded
using a Varian 2000 FTIR analyzer, which was operated from
ꢁ
1
7
00 to 4000 cm at room temperature. FTIR spectra were
ꢁ
1
obtained using a resolution of 4 cm
and were averaged
over 32 scans. The samples were thoroughly mixed with po-
tassium bromide (KBr) at approximately 3 wt %, and the
resulting powders were pressed into a transparent pellet.
Elemental analysis (EA) was performed using an Elementar
Vario EL III elemental analyzer and X-ray photoemission
spectrometry (XPS) was performed using a Kratos Axis Ultra
DLD ESCA machine. The thermal properties of the polymers
were measured by thermogravimetric analysis (TGA) per-
formed using a TA TGA-Q50 thermogravimetric analyzer.
ꢀ
Samples were heated from room temperature to 800 C at a
FIGURE 1 FTIR spectra of (a) MA monomer, (b) MA-APM-G0.5,
and (c) MA-HPAM-G1.0. [Color figure can be viewed in the
online issue, which is available at www.interscience.
wiley.com.]
ꢀ
heating rate of 20 C/min in a nitrogen purge system. Tg
was determined by DSC from the midpoint of the inflection
tangent with a second heating at 10 C/min. TGA and DSC
ꢀ
data were analyzed using TA Instruments Universal Analysis
software. A Hitachi S4200 field emission scanning electron
microscope (FE-SEM) was used to observe the morphology
of the dendritic-linear PMA-APM-r-PS copolymer.
The intended product with higher generations of the MA-
APM dendritic macromonomer was obtained by repeating
the previous procedure.
RESULTS AND DISCUSSION
Synthesis of the Dendritic-Linear Copolymer
The solution of the MA-APM macromonomer in N,N-dimethy-
lacetamide was added dropwise to a three-neck 250 mL
round-bottom flask, which contained the mixed solution of
initiator, azobisisobutyronitrile (AIBN) and styrene monomer
in N,N-dimethylacetamide, whereas mixing well in a nitrogen
purge system. The mixture was stirred for 1 h at room tem-
Synthesis and Characterization
Synthesis of the MA-APM Dendritic Macromonomer
Preparation of the dendritic-linear copolymers can be carried
out in a number of ways, including: (a) polymerization of the
dendron-functionalized macromonomers, (b) grafting of den-
drons to a linear polymer backbone, or (c) divergent dendro-
nization of appropriately functionalized linear polymers. In
this research, we used a combination of methods (a) and (b)
to obtain our dendritic-linear copolymers. The MA-APM den-
dritic macromonomer was directly synthesized by subjecting
it to a ring-opening reaction and repeated alkylation and
amidation using a divergent growth approach. It was then
ultimately polymerized with a styrene monomer.
ꢀ
perature and then heated to 80 C for 48 h. Finally, the den-
dritic-linear copolymers (PMA-APM-r-PS) were precipitated
in a methanol solution, separated by filtration, and then
1
dried in a vacuum oven. Yield: 85%. H NMR (400 MHz,
CDCl , 300 K, TMS, d , ppm): 0.50–3.90 (m, ACHA, ACH A,
3
H
2
ACH
3
), 3.69 (m, ACOAOACH
3
), 6.65–7.45 (m, benzene),
7.08 (m, ACOANHA).
The overall preparation procedure is illustrated in Scheme 1.
Synthesis of the MA-APM Macromonomer
Dendritic MA-APM macromonomers were synthesized
Preparation of the PMA-APM-r-PS Copolymer Films
Microporous films were prepared by casting the 30 wt %
PMA-APM-r-PS copolymer solution in tetrahydrofuran (THF)
at room temperature in a glove box under a nitrogen atmos-
phere onto a variety of substrates, such as glass slides, alu-
minum plates, metal wafers, and mica.
1
13
according to Scheme 1, and characterized by H NMR,
C
NMR, and FTIR, respectively. Figure 1 presents the FTIR
spectra of the MA monomer, MA-APM-G0.5 and MA-APM-G1
macromonomer signals. The MA-APM-G0.5 spectrum
ꢁ
1
depicted in Figure 1(b) indicates that signals at 1853 cm
ꢁ
1
and 1782 cm , corresponding to the symmetric and asym-
metric stretching vibrations of C ¼¼ O, cannot be observed;
however, three significant peaks at 1696, 1658, and 1546
Characterization
The molecular weight of the raw sample and its distribution
were determined by gel permeation chromatography (GPC),
using a Postnova 1021 solvent delivery pump, Viscotek 270
dual detector, Viscotek VE 3580 RI detector, and American
Polymer Standards Corporation 10 lm AM Gel GPC columns
ꢁ
1
cm , corresponding to the stretching vibrations of C ¼¼ O in
the carboxylic acid group, amide I band, and amide II band,
can be observed. These peaks demonstrate that the ring of
the MA monomer is opened and that the dendritic MA-APM-
G0.5 was successfully synthesized. Furthermore, as the gen-
eration of the dendritic MA-APM macromonomer increases
from [G ¼ 0.5] to [G ¼ 1], we can see in Figure 1(b) the
3
4
5
(
AM Gel 10 Å, 10 Å, and 10 Å) with linear polystyrene (PS)
standards. THF (HPLC grade) was used for elution at a flow
rate of 1 mL/min. The GPC results were calibrated according
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1
FIGURE 2 H NMR spectra of (a)
MA-APM-G0.5, (b) MA-APM-
G1.0, and (c) MA-APM-G2.0 in
CDCl
3
.
ꢁ
1
clear characteristic peak at 1740 cm that corresponds to
the stretching vibrations of C ¼¼ O in the ester. Moreover, the
C ¼¼ C stretching vibration signal of the macromonomer at
MA-APM-G1.0 macromonomer was synthesized by reacting
the amine-terminated MA-APM-G0.5 macromonomer with
methyl methacrylate, and the higher generation dendritic
macromonomers were obtained by repeating the procedure.
ꢁ
1
1640 cm
still exists in each generation of the dendritic
MA-APM macromonomer.
1
The H NMR spectra of the dendritic MA-APM-G0.5 and MA-
Figure 2 depicts 1H NMR spectra of the dendritic MA-APM-
G0.5, MA-APM-G1.0, and MA-APM-G2.0 macromonomers. The
formation of the amine-terminated MA-APM-G0.5 macromo-
nomer proceeded as expected with the addition of p-phenyl-
enediamine to the Maleic anhydride. The ester-terminated
APM-G1.0 macromonomers [Fig. 2(a,b)], as well as a signifi-
cant appearance of methyl ester protons (AOCH A) at 3.69
3
ppm during the formation of the ester-terminated MA-APM-
G1 dendritic macromonomer, indicate that close to a 100%
substitution occurred for each generation. The chemical shift
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1
3
3
FIGURE 3 C NMR spectrum of the G2 MA-APM in CDCl .
of the proton in the amide group (ACOANHA) is apparent
at 7.08 ppm, and the chemical shifts of the proton in the
phenyl group (N-ArH-N) are apparent at 6.90 ppm and 7.39
ppm, respectively. In addition, the chemical shifts of the pro-
fore, the MA-APM macromonomer was successfully synthe-
sized as identified via 1H NMR, C NMR, and FTIR.
1
3
Synthesis of the Dendritic-Linear PMA-APM-r-PS
Copolymer
tons from the double bond (CH ¼¼ CA) are significantly appa-
2
The dendritic-linear PMA-APM-r-PS copolymers were synthe-
sized via free radical polymerization involving the styrene
monomer and the dendritic MA-APM macromonomer. The
rent across the different generations at 6.42 and 6.85 ppm,
respectively. The integration values of these signals can be
used to determine the arm number of the dendritic macro-
monomer. On the basis of the calculated results, the MA-APM
dendritic macromonomers were defined as MA-GX, where X
indicates the number of generations associated with the MA-
APM dendritic macromonomer. Therefore, G2 represents the
second generation and has four arms of the methyl ester
1
13
products were characterized by H NMR, C NMR, and EA.
1
13
Figure 4 depicts the H NMR and C NMR spectra for the
1
dendritic-linear PMA-APM-r-PS copolymer. H NMR was used
to determine the content of the dendritic MA-APM segment
for the dendritic-linear PGMA-HPAM-r-PS copolymer by com-
paring the peak integration values. Specifically, the integra-
tion value from the dendritic MA-APM segment ester group
1
3
group in the dendritic macromonomer. Furthermore, the
C
NMR spectrum of the MA-APM macromonomer (Fig. 3) fea-
tures double bond (C ¼¼ C) signals at 136.3 and 138.8 ppm,
respectively. Signals related to the carboxylic acid structures
appear at 166.2 ppm. This result is consistent with the
notion that the ring of the MA monomer is opened. There-
3
(ACOAOCH ), which was apparent at around 3.69 ppm, was
compared to the integration values from the proton of the
amide group (ACOANHA), consistent with chemical shifts in
the dendritic MA-APM segment at 7.08 ppm. We also took
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13
FIGURE 4 (a) H NMR and (b)
C
NMR spectra of the dendritic-lin-
ear PMA-APM-r-PS copolymer in
3
CDCl .
into account the phenyl group’s chemical shift in the context
of the styrene segment and the dendritic MA-APM segment
at 6.6–7.4 ppm. On the basis of the calculated results, the
dendritic-linear PMA-APM-r-PS copolymers were defined as
MG2-Y, where Y represents the weight percentage of the den-
dritic MA-APM segment in PMA-APM-r-PS copolymers.
Therefore, MG2–15 represents the second generation dendri-
tic macromonomer in each dendritic segment, and accounts
for 15 wt % of the entire dendritic-linear PMA-APM-r-PS co-
polymer. The series of percentages in this research includes
MG2–15, MG2–23, MG2–34, MG2–43, MG2–49, and MG2–54.
Moreover, the results of the elemental analysis, as listed in
Table 1, do seem to confirm the weight percentage of the
dendritic segments for each PMA-APM-r-PS copolymer. From
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TABLE 1 PMA-APM-r-PS Molecular Characteristics and Morphology
Designation
(
Generation
MA-APM-
Segment
Elemental Analysis
b
no. – MA-APM
Segment wt %)
M
w
a
3
wt %
(10 g/mol)
PDI
Morphology (SEM)
C%
N%
H%
a
MG2-macromonomer
MG2–15
–
0.958
–
–
62.58
87.88
85.96
83.72
82.14
81.19
80.47
8.87
1.32
1.89
2.56
3.02
3.30
3.52
6.91
7.54
7.48
7.40
7.35
7.31
7.29
14.6
23.2
34.1
42.9
49.4
53.8
45.4
36.6
28.1
31.8
35.3
41.6
1.957
1.864
1.794
1.813
1.878
2.103
Phase separation/disordered
Phase separation/disordered
Phase separation/pseudo-disordered
Phase separation/honeycomb-ordered
Phase separation/disordered
Phase separation/disordered
MG2–23
MG2–34
MG2–43
MG2–49
MG2–54
a
1
b
Calculated by H NMR
Determined by GPC
1
3
the C NMR analysis depicted in Figure 4(b), we note the
chemical shift at 38 ppm, which is linked with the main
chain ACACA bonds of the styrene segment. These data
may indicate the formation of the PMA-APM-r-PS copolymer.
tional oxygen that is single bonded to carbon. This yields a
3
6
total shift of about 4 eV. Moreover, the shift arising from
replacing a carbon or hydrogen with a nitrogen that is
directly attached to the carbon atom under consideration is
3
5
about 1 eV. As can be seen in Figure 5(a), the C 1s signal
of the PMA-APM-r-PS copolymer can be decomposed into
four peaks. The peaks located at 283.7–285.4 eV, according
to the internal energy standard, can be interpreted as the
Table 1 summarizes GPC results for the PMA-APM-r-PS
copolymers, with the data calibrated according to conven-
tional calibration methods (CC) and using linear polystyrene
standards. The polydispersity indexes (PDI) of the PMA-APM-
r-PS copolymers seem slightly broadened, around 1.8 ~2 .2. This
phenomenon can be ascribed to the structure of the dendri-
tic-linear copolymers, because of their different hydrodynamic
2
3
combination of the sp C ¼¼ C and sp CAC structures of the
bulk and surface carbons of the PMA-APM-r-PS copolymers.
The peak at 286.4–286.6 eV originates from the ACANA
and ACAOA, and the peak at 288.8–289.4 eV is associated
with AC( ¼¼ O)ANA and AC( ¼¼ O)AOA structures. The last
peak located at 292.3 eV represents the shake-up structure
associated with p to p* transitions of the phenyl rings.
2
8,29
30–33
volumes
and side chain effects,
in comparsion to a
linear polymer of the same molecular weight.
XPS was utilized to analyze the compositions of the PMA-
APM-r-PS copolymer samples. In each case, a broad initial
scan was performed (1100–0 eV) to establish the gross ele-
mental composition on the surface of the samples. The PMA-
APM-r-PS membranes exhibited distinct carbon (C 1s, C
KLL), oxygen (O 1s, O KLL) and nitrogen (N 1s) peaks, repre-
senting the major constituents of the sample surface; how-
ever the N 1s peak at a binding energy of around 400 eV,
Figure 5(b) shows that the N 1s peak is composed of two
peaks, located at 399.7, and 399.9 eV, which originate from
the AC( ¼¼ O)ANHA, and Ar-N structures, respectively. Fur-
thermore, the O 1s peak at 532.1 eV in Figure 5(c) is attrib-
uted to C ¼¼ O in the AC( ¼¼ O)AN and AC( ¼¼ O)AO structures,
and the peak at 533.7 is associated with CAO, including
C( ¼¼ O)AOH and C( ¼¼ O)AOAC structures. These graphs pro-
vide evidence that the dendritic PMA-APM-r-PS copolymers
were successfully synthesized, and these data are consistent
with the above NMR and FTIR results.
3
4
which reflects the presence of the amine structure, con-
firms the structure of the PMA-APM-r-PS membranes. The
results of the XPS experimental data are consistent with the
1
FTIR analysis and H NMR spectra. Furthermore, detailed
1
13
A review of the experimental FTIR, H NMR, C NMR, and
GPC results reveals that the dendritic macromonomer and
the dendritic-linear PMA-APM-r-PS copolymers were success-
fully synthesized in this study. For each MG2-X copolymer,
Table 1 lists the generation number, molecular weight,
weight percentage of the dendritic MA-APM segment, PDI,
and elemental analysis results.
analysis of the XPS spectra offers clear evidence that the
dendritic PMA-APM-r-PS copolymers were successfully syn-
thesized. Before discussing the C 1s spectra, it is important
to note that the short-range nature of substituent effects can
3
5
lead to additive rules for the C 1s shift. Thus, the degree of
shifting of the characteristic peak for the C 1s of carbon,
which is single bonded to oxygen (alcohols, ethers, and
3
5
esters), is about 1.6 eV. For carbon that is single bonded to
two oxygen atoms, the degree of shifting of the characteristic
peak for C 1s is about 2.8 eV, approximately twice the effect
of a single substituent. For carbon double bonded to oxygen
in simple carbonyl compounds, the characteristic shift is
Thermal Behavior
TGA and DSC analyses were used to determine the thermal
properties of the dendritic-linear PMA-APM-r-PS copolymer.
TGA is a technique used to accurately track the in situ
weight changes of the sample during heating. Figure 6 shows
the TGA thermograms of the various PMA-APM-r-PS
3
6
about 2.6 eV. For a carbonyl to carbonyl group, there is a
.4 eV change in binding energy associated with the addi-
1
DENDRITIC-LINEAR PMA-APM-r-PS COPOLYMERS, HSIEH, WANG, AND CHEN
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
3
6–38
homopolymer in the thermal decomposition.
When poly-
merized with the dendritic segment (MA-APM) at 15 wt %,
the thermal degradation temperature of the dendritic-linear
ꢀ
ꢀ
copolymer is 39 C higher at 360 C than would be the case
ꢀ
for the PS homopolymer at 321 C (curves a and b in Fig. 6).
As a function of increasing dendritic segment (MA-APM)
wt %, the thermal degradation temperature of the dendritic-
ꢀ
linear PMA-APM-r-PS copolymer was elevated by 38 C from
ꢀ
ꢀ
3
60 C for MG2–15 to 398 C for MG2–54. In addition, we
note that the dendritic-linear MG2–54 copolymer (PMA-
ꢀ
APM-r-PS) is thermally stable up to 398 C.
On the other hand, the thermal behaviors of the PMA-APM-r-
PS copolymers were monitored using differential scanning
calorimetry (DSC), as shown in Figure 7. Theoretically, the
glass transition temperature (T ) of the copolymers should
g
decrease with increased branching. We considered the fact
that the presence of a side group is known to influence the
Tg of a particular copolymer by an amount that depends on
the flexibility and bulk of the side group. Usually, flexible
side chains and/or pendent groups increase the flexibility of
the backbone chain and lead to a decrease in the glass tran-
sition temperature. In principle, the glass transition of car-
bon-backbone copolymers reflects the rotational energy bar-
riers about r bonds of the main chain and lower glass
transition temperatures resulting from lower energy barriers.
While the dominating effect of flexible side chains is to
increase free volume, thus lowering T , the rigid side chains
g
may restrict torsion about r bonds in the main chain, increas-
ing T . In our system, the dendritic MA-APM segment, which
g
has a high degree of extension and three-dimension structure,
can be undoubtedly considered a flexible group. Therefore, the
Tg value also depends on the free volume of the dendritic seg-
ment of the PMA-APM-r-PS copolymers. In the MG2-X system,
for polymerization with the dendritic segment (MA-APM) at a
15 wt % content, the glass transition temperature of the den-
dritic-linear copolymer is significantly lower than would be the
ꢀ
case for the PS homopolymer: we note a 7 C decrease, from
ꢀ
9
4 to 87 C [curves a and b in Fig. 8(a)]. By increasing the
FIGURE 5 XPS core level spectra of (a) C 1s, (b) N 1s, and (c) O
1s of the PMA-APM-r-PS copolymer.
copolymers, notated as PS, MG2–15, MG2–23, MG2–34,
MG2–43, MG2–49, and MG2–54. The dendritic segments
(
MA-APM) have a significant effect on the resulting dendri-
FIGURE 6 TGA curves of the (a) MG2-X PMA-APM-r-PS series
tic-linear PMA-APM-r-PS copolymers in comparsion to the PS
copolymers.
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ARTICLE
g
FIGURE 8 Variation of glass transition temperature (T ) for the
G2 dendritic-linear PMA-APM-r-PS copolymers as a function of
the G2 dendritic MA-APM segment content. [Color figure can
be viewed in the online issue, which is available at www.
interscience.wiley.com.]
FIGURE 7 DSC curves of the (a) MG2-X PMA-APM-r-PS series
copolymers. [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com.]
between each segment is slightly disrupted, leading the varia-
tion of the T to a different condition (the third trend). This
g
phenomenon coincides with the copolymer morphology
observed via SEM, which is discussed later.
dendritic segment (MA-APM) contents, the T value of the den-
g
ꢀ
dritic-linear PMA-APM-r-PS copolymers decreased by 16 C,
ꢀ
ꢀ
from 87 C for MG2–15 to 71 C for MG2–54. The reduced
degree of the T value in the PMA-APM-r-PS system is more
g
less than that of the PGMA-HPAM-r-PS system reported in our
previous report, which is due an increase in the number of
phenyl groups in the MA-APM structure that make the flexibil-
ity and mobility lower than that of the GMA-HPAM structure.
For each dendritic-linear PMA-APM-r-PS copolymer, the decom-
Polymer Morphology
Our dendritic-linear PMA-APM-r-PS microporous copolymer
films were prepared at room temperature by casting the THF
solution onto the substrate. Figure 9 depicts SEM images of
the microporous PMA-APM-r-PS copolymer films with different
dendritic MA-APM segment contents. In particular, the forma-
tion of ordered packed micropores with a uniform size distri-
bution can be observed for MG2–43 in the SEM images
depicted in Figure 9. The formation mechanism of the
ordered/disordered microporous surface structures has been
described in our previous report. The resulting micropores in
the self-assembled film matrix can be ascribed to the aggrega-
tion of the dendritic MA-APM segment of the dendritic-linear
PMA-APM-r-PS copolymer. The continuous or dispersed condi-
tion of each styrene and dendritic segment micelle control the
surface morphologies of the PMA-APM-r-PS copolymer films. In
this case, because the entanglement and mobility of the dendri-
tic MA-APM segment are constrained by the main chain in the
position temperature (T ) and the glass transition temperature
d
(Tg) are listed in Table 2.
Furthermore, we were able to use the variation of the glass
transition temperature to quickly find the critical equilibrium,
which resulted in the hexagonally-ordered microporous struc-
ture in our previously reported PGMA-HPAM-r-PS system. In
the MG-X system, we still found three trends in the wt % plot
of the dendritic MA-APM vs. glass transition temperature (Tg)
depicted in Figure 8. The first trend occurred at 0–23 wt %,
and second at 23–43 wt % and third at 43–54 wt %. The vari-
g
ation of T in the dendritic-linear PMA-APM-r-PS copolymers
results from two effects: the free volume of the dendritic seg-
ment and the interaction of the dendritic and styrene seg-
ments. Because the dendritic MA-APM segments are flexible
structures, they are expected to increase the free volume, low-
TABLE 2 The Thermal Stability of PMA-APM-r-PS
ering T . A manifested decrease in T at the lower content of
g
g
a
ꢀ
b
ꢀ
Sample
Dendron
T
d
( C)
T
g
( C)
the dendritic MA-APM segment (the first trend) was observed.
When the weight percentage of the dendritic MA-APM segment
was set to a specific value, the intermolecular interactions
between each segment were significant enough to affect copol-
PS
–
321
360
369
380
388
394
398
94
87
84
82
80
75
71
MG2–15
MG2–23
MG2–34
MG2–43
MG2–49
MG2–54
a
G2
G2
G2
G2
G2
G2
ꢀ
ymer chain motion and result in an enhancement in T . There-
g
fore, the change in T , influenced by the free volume and inter-
g
molecular interactions, begin to flatten out (the second trend).
Moreover, we can observe an ordered structure on the copoly-
mer film surface when the interaction between the dendritic
segment and the styrene segment approximately reach a criti-
cal equilibrium (the intersection). Afterward, the balance
Condition: Heating rate 20 C/min under N
2
purge.
2
purge.
b
ꢀ
Condition: Heating rate 10 C/min, under N
DENDRITIC-LINEAR PMA-APM-r-PS COPOLYMERS, HSIEH, WANG, AND CHEN
3299

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 9 SEM photographs of the microporous PMA-APM-r-PS copolymer film given different dendritic MA-APM segment con-
tents. (a) PS, (b) MG2–15, (c) MG2–23, (d) MG2–34, (e) MG2–43, (f) MG2–49, and (g) MG2–54.
PMA-APM-r-PS copolymer, the shapes and the volumes of the
dendritic MA-APM segment micelle domains are related to the
number of styrene segments in solution. The dendritic MA-
APM segment domains should prefer to form spherical shapes,
consistent with thermodynamics, because the styrene segment
content is much greater than the dendritic segment content. It
follows that the PMA-APM-r-PS copolymer films, which exhibit a
spherical microporous matrix, are formed after solvent evapora-
tion, as shown in the SEM images. With several different dendri-
tic segment contents, this formation mechanism can be catego-
rized into three routes: (i) the morphologies of the PMA-APM-r-
PS copolymer films are controlled by the continuous phase of the
styrene segment in the copolymers; (ii) the surface morphologies
of the PMA-APM-r-PS copolymer films are gradually affected by
the dendritic segment micelles; and (iii) surface data regarding
the PMA-APM-r-PS copolymer films are jointly controlled by the
styrene and the dendritic segments. As shown in the SEM photo-
graphs, the average diameters of the self-assembled micropores
were estimated to range from 1.9 lm to 2.5 lm for the MG2–43
system. Moreover, the average interval distance of the ordered-
array structures in the MG2–43 system was found to range from
the volumetric fraction of the hexagonally-ordered structures in
the dendritic-linear PMA-APM-r-PS film. According to the litera-
39,40
ture,
the relationship between volumetric fraction (u), radius
(R) and repeating distance (L) of ordered arrays is given by:
ꢀ
ꢁ
2
R
L
u ¼ p
Given that L ¼ 5–5.4 lm and R ¼ 0.95–1.25 lm, the volu-
metric fraction of the micropores u is 0.11 to 0.17 for the
MG2–43 system. The dendron is a dimensional architecture,
and its configuration can be broadly reworked and reinter-
preted. This may explain the values of the volumetric frac-
tions for MG2–43. Additionally, the morphologies of the vari-
ous dendritic proportions of the PMA-APM-r-PS MG2-X
copolymers are listed in Table 1.
CONCLUSION
New kinds of dendritic MA-APM macromonomer and dendri-
tic-linear PMA-APM-r-PS copolymers were successfully syn-
thesized by a coupling reaction using the divergent method.
1
13
5.1 to 5.4 lm, respectively. From these results, we can calculate
H NMR, C NMR, FTIR, EA, and XPS analyses confirmed the
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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
structure and characteristics of the MA-APM macromono-
mers and the PMA-APM-r-PS copolymers. In addition, micro-
porous structure films were successfully manufactured by
casting a series of the PMA-APM-r-PS copolymers and using
a THF solution at room temperature via the solution induced
phase separation method. Of note, at 43 wt % of the dendri-
tic MA-APM segments in the MG2–43 copolymer, the dendri-
tic segment micelle displayed self-assembling behavior that
resulted in a ordered-array microporous copolymer matrix.
Our research confirms that controlling the appropriate mac-
romonomer content via the grafting of a three-dimensional
structure, like MA-APM, can promote self-assembly and pro-
duces a ordered-array microporous copolymer matrix.
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