Synthesis and hierarchical self-assembly of rod-rod block copolymers via click chemistry between mesogen-jacketed liquid crystalline polymers and helical polypeptides

Article abstract of DOI:10.1021/ma1007418

A series of novel rod-rod diblock copolymers containing poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PMPCS) and poly(γ-benzyl-L-glutamate) (PBLG) were synthesized by click chemistry from alkyne-and azide-functionalized homopolymers. The α-alkyne PMPCS homopolymers were synthesized by copper-mediated atom transfer radical polymerization with a bromine-containing α-alkyne bifunctional initiator, and α-azido PBLG homopolymers were synthesized by ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride with an amino-containing α-azide initiator. The molecular structures of the rod-rod block copolymers were confirmed by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography analysis. The self-assembling behavior of the rod-rod block copolymers in bulk was investigated using differential scanning calorimetry, polarized light microscopy, wide-angle X-ray diffraction, and transmission electron microscopy techniques. A lamellar structure was observed with f_PBLG of ～0.50, in which PMPCS was in a columnar nematic phase and PBLG assignedto a hexagonally packed-cylinder structure (Φ_H). Accordingto the TEM micrographs and simulated lengths of the copolymers, a stacked bilayer structure in a hexagon in lamella morphology for the selfassembly of the rod-rod block copolymers was proposed. Finally, by increasing f_PBLG to ～0.69, a microphase-separated hexagon in cylinder morphology was found, in which PMPCS formed the core of the cylinders surrounded by PBLG in Φ_H phase and both rods were in an interdigitated packing.

Full text of DOI:10.1021/ma1007418

Macromolecules 2010, 43, 5637–5646 5637
DOI: 10.1021/ma1007418
Synthesis and Hierarchical Self-Assembly of Rod-Rod Block Copolymers
via Click Chemistry between Mesogen-Jacketed Liquid Crystalline
Polymers and Helical Polypeptides
Qing-Han Zhou, Ju-Kuan Zheng, Zhihao Shen,* Xing-He Fan,* Xiao-Fang Chen, and
Qi-Feng Zhou*
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of
Ministry of Education, College of Chemistry and Molecular Engineering, Peking University,
Beijing 100871, China
Received April 6, 2010; Revised Manuscript Received June 1, 2010
ABSTRACT: A series of novel rod-rod diblock copolymers containing poly{2,5-bis[(4-methoxyphenyl)-
oxycarbonyl]styrene} (PMPCS) and poly(γ-benzyl-L-glutamate) (PBLG) were synthesized by click chemistry
from alkyne- and azide-functionalized homopolymers. The R-alkyne PMPCS homopolymers were synthe-
sized by copper-mediated atom transfer radical polymerization with a bromine-containing R-alkyne
bifunctional initiator, and R-azido PBLG homopolymers were synthesized by ring-opening polymerization
of γ-benzyl-L-glutamate N-carboxyanhydride with an amino-containing R-azide initiator. The molecular
1
structures of the rod-rod block copolymers were confirmed by H NMR spectroscopy, Fourier transform
infrared spectroscopy, and gel permeation chromatography analysis. The self-assembling behavior of the
rod-rod block copolymers in bulk was investigated using differential scanning calorimetry, polarized light
microscopy, wide-angle X-ray diffraction, and transmission electron microscopy techniques. A lamellar
structure was observed with fPBLG of ∼0.50, in which PMPCS was in a columnar nematic phase and PBLG
assigned to a hexagonally packed-cylinder structure (Φ ). According to the TEM micrographs and simulated
H
lengths of the copolymers, a stacked bilayer structure in a hexagon in lamella morphology for the self-
assembly of the rod-rod block copolymers was proposed. Finally, by increasing fPBLG to ∼0.69, a
microphase-separated hexagon in cylinder morphology was found, in which PMPCS formed the core of
the cylinders surrounded by PBLG in ΦH phase and both rods were in an interdigitated packing.
Introduction
researches into rod-rod BCPs have been greatly intensified
during recent years.
Block copolymers (BCPs) have attracted tremendous attention
for their self-assembling properties in bulk or in selective solvents,
forming various periodic patterns on the nanometer scale due
Generally, for rod-rod BCPs, due to the rigid nature and
higher persistence length of each block, low-curvatured aggre-
gates, such as vesicles in selective solvents and lamellar structures
1
-3
to microphase separation. These morphologies, such as lamellae,
cylinders, gyroids, and spheres, are determined by the volume
fraction of one component f, the total degree of polymerization N
of the block copolymer, and the Flory-Huggins interaction
parameter χ. Coil-coil block copolymers have already gained
an enormous interest from scientists since a couple of decades ago
and have been practically used as materials in nowadays life
attributed to the successful establishment of their experimental
1
3
in solid state, will be formed. Rod-rod block copolymers solely
1
4-16
based on polypeptides have been already synthesized.
Vesi-
cular structures were observed in water by self-assembly of
polyleucine-b-poly(hydroxylated glutamate) copolymer which
could mimic the assembly conformation of protein as a novel
17
biomaterial in medical use. In addition, the so-called schizo-
phrenic vesicles were found by zwitterionic diblock copolymer
18
2-4
poly(L-glutamic acid)-b-poly(L-lysine), so were micelles by
and theoretical phase diagrams.
Compared with coil-coil
1
9
miktoarm star copolymers, which would likely find potential
diblock copolymers, for rod-coil BCPs, the aggregation between
rigid-rod blocks and high Flory-Huggins interaction parameter
χ can allow microphase separation to occur at relatively low
degrees of polymerization and at a rather short length of a few
use in controlled drug delivery systems. Kros at al. synthesized
polyisocyanide-b-poly(γ-benzyl-L-glutamate) diblock copoly-
mers and observed vesicles with a diameter of >5 μm by using
2
0
5
-7
laser scanning confocal and optical microscopes. Lamellar
morphologies, including hexagon in lamella (HL) structure, in
bulk were investigated for peptide-containing copolymers as
nanometers.
Unique and nonpredicted morphologies from
rod-coil BCPs have been found, which have been widely investi-
gated and reviewed during the past decade.
synthesis and self-assembly of rod-rod block copolymers is still a
relatively new research area; however, it promises real-world
applications, such as biosensors, scaffolds for tissue engineering,
8-10
In contrast, the
2
1,22
well.
Rod-rod BCPs containing polypeptide and π-conju-
gated polymer blocks were also studied, and samples showed
different nanostructures depending on the blockcomposition and
the polypeptide secondary structure.
23
11,12
heterojunction solar cells, and photodetectors.
Accordingly,
On the other hand, mesogen-jacketed liquid crystalline poly-
mers (MJLCPs) represent a special class of liquid crystalline
polymers (LCPs) which attracted increasing interest in recent
*To whom correspondence should be addressed. E-mail: (Z.S.)
zshen@pku.edu.cn; (X.-H.F.) fanxh@pku.edu.cn; (Q.-F.Z.) qfzhou@
pku.edu.cn.
24,25
years.
In this kind of liquid crystalline polymers mesogenic
r 2010 American Chemical Society
Published on Web 06/14/2010
pubs.acs.org/Macromolecules

5
638 Macromolecules, Vol. 43, No. 13, 2010
Zhou et al.
pendants are considered to be densely packed around the back-
bone, and force the backbone to adopt a rigid or semirigid
bath. Methylene chloride (50 mL) and KOH (2.2 g) were added,
with the temperature remaining under 10 °C while being stirred.
After filtration, the aqueous phase was extracted with diethyl
ether three times. The combined organic layers were dried with
26
conformation. Rod-like MJLCPs have good tunability in rod
length, while the rod diameter can also be altered by varying the
lengths of both the rigid core and flexible tails in the mesogenic
Mg
1
2
2
SO
.2 g (78%). H NMR (CDCl
H, CH NH ), 1.73 (q, 2H, CH CH CH ), and 1.17 (s, 2H,
4
and concentrated to afford an oil by distillation. Yield:
1
27
3 2 3
): δ 3.38 (t, 2H, CH N ), 2.81 (t,
side chains. Because of the above properties, MJLCPs have
been widely used as rod blocks in synthesizing well-defined rod-
2
2
2
2
2
2
8-32
NH2).
coil diblock and triblock copolymers.
However, rod-rod
Polymerization Reactions. Synthesis of r-Alkyne PMPCS.
The monomer of PMPCS, {2,5-bis[(4-methoxyphenyl)oxycar-
bonyl]styrene} (MPCS), was prepared as described in the
diblock copolymers containing MJLCP building blocks have
never been reported so far. Study on this kind of copolymers will
greatly enrich the liquid crystalline and self-assembling behaviors
of MJLCPs. On the other hand, polypeptides have shown char-
ming properties for their self-assembling properties and potential
39
literature. In a typical experiment for polymerization, MPCS
(
0.202 g, 50 μmol), propargyl 2-bromoisobutyrate (2.05 mg, 10
μmol), CuBr (1.43 mg, 10 μmol), PMDETA (1.73 mg, 10 μmol),
and chlorobenzene (2.02 mL) were charged into a polymeriza-
tion tube under ambient atmosphere. After stirred and degassed
by three freeze-thaw cycles, the tube was sealed under vacuum.
Subsequently, the tube was immerged into a thermostated oil
bath at 90 °C for 12 h, and then quenched in cold THF to room
temperature. The solution was passed through a neutral alumina
column in order to remove copper salt. The polymer was pre-
cipitated in a large volume of methanol, and dried in a vacuum
overnight.
3
3-35
real-world applications for decades.
Therefore, we are
specifically interested in the synthesis, self-assembly behavior,
and potential applications of rod-rod diblock copolymers con-
taining both MJLCPs and polypeptides.
Recently, we have designed and obtained a new kind of rod-
rod diblock copolymer poly{2,5-bis[(4-methoxyphenyl)oxycar-
bonyl]styrene}-b-poly(γ-benzyl-L-glutamate) (PMPCS-b-PBLG).
In this contribution, we describe here the synthesis of these block
copolymers by combining atom transfer radical polymerization
(
ATRP) of 2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene, ring-
Synthesis of r-Azido PBLG. γ-Benzyl-L-glutamate N-carboxy-
anhydride (Bz-L-GluNCA) was prepared according to a literature
opening polymerization (ROP) of γ-benzyl- -glutamate N-car-
L
40
boxyanhydride, and a subsequent copper-catalyzed click che-
mistry to form a series of rod-rod BCPs with different volume
fractions of the two blocks. The phase behavior of the rod-rod
BCPs with different volume fractions were investigated in this
study, and hierarchical self-assembling structures on nanometer
scale were analyzed by differential scanning calorimetry (DSC),
polarized light microscopy (PLM), wide-angle X-ray diffraction
procedure. In a typical experiment, Bz-L-GluNCA (0.789 g, 3.0
mmol), 1-azido-3-aminopropane (3.0 mg, 30 μmol), and 2.63 mL
of anhydrous DMF were introduced into a dry Schlenk flask.
After degassed by three freeze-thaw cycles, the solution was
stirred for 3 days at room temperature under Ar atmosphere.
The polymer was precipitated in diethyl ether and dried under
vacuum.
Synthesis of PMPCS-b-PBLG Block Copolymers by Huisgen’s
(
WAXD), and transmission electron microscopy (TEM) techni-
1
(
1
,
3-Dipolar Cycloaddition. Typically, R-alkyne PMPCS
0.168 g, 24 μmol, 1.2 equiv), R-azido PBLG (0.216 g, 20 μmol,
equiv), and PMDETA (6.93 mg, 40 μmol, 2 equiv) were
ques. To the best of our knowledge, this is the first example of
utilizing a facile and efficient click coupling reaction to prepare
rod-rod diblock copolymers containing an R-helical polypeptide
and a rigid vinylic polymer, although syntheses of rod-coil BCPs
introduced into a Schlenk flask in 2 mL anhydrous DMF. After
degassed by one freeze-thaw cycle, CuBr (5.74 mg, 40 μmol,
36,37
by click chemistry have been reported in literature.
2
equiv) was added rapidly. The Schlenk flask was immerged
into a thermostated oil bath at 35 °C for 24 h. The reaction
mixture was passed through a neutral alumina column in order
to remove copper salt, and precipitated in excess of diethyl ether.
The product was filtered and washed with a mixed solvent of
methanol and acetone to remove excess of PMPCS. Table 1
summarized the molecular characteristics of the homopolymers
and diblock copolymers presented in this work.
Experimental Section
Materials. 2-Bromo-2-methylpropionyl bromide (98%, Acros),
-chloropropylamine hydrochloride (98%, Acros), propargyl
3
0
00
00
alcohol (99%, Aldrich), sodium azide (99%), N,N,N ,N ,N -
pentamethyl diethylenetriamine (PMDETA) (98%, TCI), and
triethylamine (98%) were used as received. N,N-Dimethylfor-
mamide (DMF) and tetrahydrofuran (THF) (Beijing Chemical
Reagents Co., A.R. grade) were used after distilled. Chloro-
benzene was purified by washing with concentrated sulfuric acid
to remove residual thiophenes, followed by washing with a 5%
sodium carbonate solution, and again with water, then dried
with anhydrous calcium chloride and finally distilled.
Synthesis of r-Functionalized Initiators. Synthesis of Propar-
gyl 2-Bromoisobutyrate. Propargyl alcohol (1.1 g, 19.6 mmol)
and triethylamine (3.5 g, 23.5 mmol) were dissolved in methy-
lene chloride (20 mL), and 2-bromo-2-methylpropionyl bro-
mide (3.0 g, 23.5 mmol) was added dropwise slowly.
Characterization. The molar masses were determined with the
combination of gel permeation chromatography (GPC),
1
H
NMR, and matrix-assisted laser desorption/ionization time-of-
flight mass spectrometry (MALDI-TOF MS) measurements.
GPC experiments were conducted on a Waters 2410 instrument
equipped with a Waters 2410 RI detector and two Waters
˚
μ-Styragel columns (103, 104 A), with THF or DMF as eluent
(1.0 mL/min) in presence of LiBr (1 g/L). The calibration curve
1
was obtained with linear polystyrenes as standards. H NMR
spectra were obtained with a Bruker 400 MHz spectrometer.
MALDI-TOF MS measurements were performed on a Bruker
Autoflex high-resolution tandem mass spectrometer. Thermo-
gravimetric analysis (TGA) was performed on a TA Q600 SDT
instrument in nitrogen atmosphere. DSC examination was
carried out on a TA Q100 DSC calorimeter in nitrogen atmo-
sphere. PLM observation was performed on a Nikon DS-Ri1
microscope with an Instec HCS302 hot stage. One-dimensional
(1D) WAXD experiments were carried out on a Philips X’Pert
Pro diffractometer with a 3 kW ceramic tube as the X-ray source
(Cu KR) and an X’celerator detector. Two-dimensional (2D)
WAXD patterns were obtained using a Bruker D8Discover
diffractometer with a GADDS as a 2D detector calibrated
with silicon powder and silver behenate. The oriented films by
mechanical shearing were mounted on the sample stage with the
The reaction mixture was cooled in an ice-water bath, and
was stirred at 0 °C for 30 min and then at room temperature for
4
and distilled under vacuum. A purified product was easily
h. The filtered solution was washed with water for three times,
obtained by passing through a silica gel column. Yield: 3.09 g
O), 2.53 (t, 1H,
1
77%). H NMR (CDCl
(
CtCH), and 1.96 (s, 6H, (CH ) C).
3
): δ 4.78 (d, 2H, CH
2
3
2
Synthesis of 1-Azido-3-aminopropane. This compound was
A
3
8
synthesized following an already published procedure.
solution of 3-chloropropylamine hydrochloride (2 g, 15.4 mmol)
and sodium azide (3.8 g, 58.5 mmol) in water (20 mL) was heated
at 80 °C for 15 h. After water was almost removed by distillation
under vacuum, the reaction mixture was cooled in an ice-water

Article
Macromolecules, Vol. 43, No. 13, 2010 5639
point-focused X-ray incident beam either parallel (X direction)
or perpendicular (Y or Z direction) to the shear direction
(X direction). The background scattering was recorded and sub-
tracted from the sample patterns. TEM was used to investigate
the microphase separation of samples on a Hitachi H-800
electron microscope. The solution-cast and ultramicrotomed
sample films were stained by RuO vapor to enhance contrast.
4
Results and Discussion
Table 1. Molecular Characteristics of r-Functionalized PMPCS and
PBLG Homopolymers and PMPCS-b-PBLG Block Copolymers
Synthesis of PMPCS-b-PBLG Rod-Rod Diblock Copoly-
mers by Click Chemistry from Homopolymers. The synthesis
of rod-rod diblock copolymers is outlined in Schemes 1 and 2,
which was started with the preparation of R-alkyne-terminated
PMPCS by copper-mediated atom transfer radical polymeriza-
tion and that of R-azide-functionalized PBLG by ring-opening
polymerization of Bz-L-GluNCA, followed by Huisgen’s 1,3-
dipolar cycloaddition (click chemistry) to connect the two rigid-
rod blocks. The R-alkyne initiator was prepared by commer-
cially available regents, 2-bromo-2-methylpropionyl bromide
c
n
d
e
sample
M
n
(g/mol)
DP
PDI
f
PBLG (%)
a
alkyne-PMPCS42
azido-PBLG19
azido-PBLG49
azido-PBLG80
azido-PBLG112
17 300
4 300
10 900
17 700
42
19
49
80
112
173
-
-
-
-
-
1.16
1.26
1.28
1.27
1.25
1.25
1.28
1.31
1.28
1.33
1.33
b
b
b
b
24 700b
38 200b
21 600
azido-PBLG173
PMPCS42-b-PBLG19
PMPCS42-b-PBLG49
PMPCS42-b-PBLG80
PMPCS42-b-PBLG112
20
38
50
58
69
b
28 200
35 000
42 000
55 500
43
b
and propargyl alcohol, according to published procedure. The
b
R-alkyne initiator was used to trigger ATRP of MPCS in
chlorobenzene, using copper bromide (CuBr) complexed by
PMDETA, and the alkyne hydrogen did not interfere with the
polymerization. The proton of alkyne-terminated homopoly-
b
PMPCS42-b-PBLG173
a
n
M value determined by GPC in THF (calibrated with polystyrene
standards) is 11 400 g/mol. However, a PMPCS sample with an M
n
-
1
(GPC) value of 6 050 g/mol is found to have an absolute molecular
mer was clearly identified by H NMR (shown in Figure 1a),
and GPC analysis was utilized to confirm the R-functionalized
PMPCS precursor as well. Figure 1a shows the H NMR
weight of 9 220 g/mol by using MALDI-TOF MS, which leads to a
factor of 1.52 between these two molecular weights. Assuming that the
shape of PMPCS does not change dramatically, the molecular weight of
1
b
spectrum of alkyne-PMPCS42 in CDCl . The resonance signals
3
alkyne-PMPCS42 should be 17 300 g/mol (11 400 g/mol ꢀ1.52). The
of protons of trisubstituted phenyl (f, g, and h), disubstituted
phenyl (i and j), methyl group (k), and vinyl backbone (d and e)
appeared at δ = 7.2-8.0, 6.4-7.0, 3.4-3.9, and 1.6-1.9 ppm,
respectively. Signals of alkyne (a) and methylene (b) protons
related to the initiator appeared at δ = 2.2 and 3.9 ppm,
respectively.
molecular weights of the copolymers and their corresponding PBLG
n
blocks were calculated from the M of alkyne-PMPCS42 and the area
ratio of characteristic resonance (methyl group) of PMPCS to that
(
1
methylene group of benzyl) of the PBLG block in H NMR spectra.
c
d
Degree of polymerization of homopolymers. Determined by GPC in
e
DMF in presence of LiBr at 1 g/L. Volume fraction of PBLG;
calculated using the number-average degrees of polymerization of the
PMPCS segment and the PBLG block in combination with the following
It is well-known that primary amine residues can be em-
38
ployed for the ROP of R-amino acid N-carboxyanhydride.
3
41
3 42
densities: PMPCS, F = 1.26 g/cm ; PBLG, F = 1.28 g/cm .
Scheme 1. Synthesis of PMPCS-b-PBLG Diblock Copolymers by Click Chemistry
Scheme 2. Synthetic Pathway to r-Functionalized Homopolymers

5
640 Macromolecules, Vol. 43, No. 13, 2010
Zhou et al.
Figure 2. Representative texture of PMPCS42-b-PBLG19 at 135 °C
from PLM observation.
35 °C using CuBr complexed by PMDETA in a Schlenk
44 1
flask. GPC measurements in DMF (LiBr, 1 g/L) and H
NMR experiments (CDCl /TFA with 15% TFA) were
3
carried out to verify the completion of the coupling reaction.
The corresponding resonance signals of protons in each
block are shown in Figure 1c. Moreover, FTIR was also
used to monitor the azide vibrational band for the comple-
tion of the click coupling reaction. The FTIR spectrum of
azido-PBLG clearly revealed the presence of the vibrational
-
1
band at 2098 cm , which was characteristic of azide moi-
eties (Figure S1 in Supporting Information, see spectrum of
azido-PBLG19 as an example), and the disappearance of the
azide band in the spectra of the copolymers evidenced
the completion of the coupling reactions. On the other hand,
-
1
the amide I and amide II bands at 1655 and 1550 cm are
characteristic of the peptidic R-helical secondary structure.
45
For polypeptides possessing a β-sheet conformation, posi-
tion of the amide I band for parallel β-sheet is in the range of
-
1
1
636-1640 cm , and for the antiparallel β-sheet in the
-1 46
range of 1622-1632 cm
mers, amide I bands around 1655 cm and the increase in
the absorbance of the amide II bands at 1550 cm were dis-
tinctively observed for the copolymers with increasing con-
tent of PBLG, in which the PBLG block had an R-helical
conformation as indicated by the FTIR spectra. For the
.
In the spectra of the copoly-
-
1
-
1
-
1
sample of azido-PBLG , a shoulder band at 1625 cm was
1
9
also observed in the FTIR spectrum, indicating that anti-
parallel β-sheet structure was in coexistence with the R-helical
structure of PBLG with a low degree of polymerization.
47
Phase Structure and Self-Assembly in Bulk. DSC was used
to study the thermal transitions of the diblock copolymers.
Glass transitions were observed at ∼15 °C for PBLG blocks
and ∼130 °C for PMPCS blocks during the first cooling and
subsequent heating scans of the copolymers. PLM was used
to observe birefringence of the copolymers. Sample films
were cast from THF solutions by drying at room tempera-
ture. The liquid crystalline birefringence was observed at
around 135 °C. The texture of PMPCS -b-PBLG is shown
in Figure 2 as an example. The birefringence did not dis-
appear when the sample was heated to 190 °C, which was
near the limit of thermal stability for PBLG, and subse-
quently cooled to room temperature, which implied that the
samples formed their liquid crystalline phases at high tem-
peratures (above 135 °C) and these phases remained un-
changed upon cooling.
1
Figure 1. H NMR spectra of alkyne-PMPCS42 (a), azido-PBLG19 (b),
3
and PMPCS42-b-PBLG19 (c) in a CDCl /TFA mixture with 15% TFA.
In the present work, 1-azido-3-aminopropane was used to
facilitate the polymerization of polypeptide from Bz-L-GluN-
CA. GPC analysis in DMF verified the synthesis of the
homopolymer, in which LiBr was added to minimize polymer
aggregation. The azido-functioned group of the PBLG pre-
cursor was clearly evidenced by H NMR in CDCl with 15%
4
2
19
1
3
trifluoroacetic acid (TFA). In Figure 1b, the resonance signals
of protons of amide group (d), phenyl group (i), methylene
group of benzyl (h), R-methine group (e), and β- and
γ-methylene groups (g and f) appeared at δ = 7.9, 7.2-7.3,
5
.1, 4.6, and 1.9-2.5 ppm, respectively. The signals of R-, β-, and
γ-methylene protons (a, b, and c) adjacent to the azide group
were observed at δ = 3.35, 1.85, and 2.53 ppm, respectively.
The following was the “click chemistry” between the
azido-PBLG and the alkyne-PMPCS. The 1,3-dipolar cy-
cloaddition coupling reaction was performed in DMF at
In order to account for the self-assembly of the copoly-
mers, films with about 30 mg of samples were prepared from
solution-casting for 1D WAXD experiments which were
performed at different temperatures from 40 to 190 °C.

Article
Macromolecules, Vol. 43, No. 13, 2010 5641
arrangement (Φ ) of R-helical PBLG, and the Φ phase was
H
H
4
7
developed upon first heating at about 130 °C. It indicated that
following the increase of volume fraction to ∼50%, the Φ
H
phase was well developed, i.e., the structure of the PBLG blocks
transformed from a poorly ordered hexagonal arrangement
into an ordered one. The existence of such ordered packing
of PBLG indicated the microphase separation of the block
copolymers. The columnar diameters of PBLG helices for
PMPCS -b-PBLG and PMPCS -b-PBLG were 1.58 and
42
80
42
112
1.56 nm, respectively. The decrease in the columnar diameter of
the PBLG block indicated that the helices were packed into a
more ordered hexagonal arrangement for longer PBLG due to
the increasing hydrogen-bonding effect. On the other hand,
47
the peaks attributed to the Φ phase of PMPCS were partially
N
embedded in the strong, first-order reflection of the Φ phase of
H
PBLG in sample PMPCS -b-PBLG due to the decrease in
the volume fraction of PMPCS. The diffuse halo at 14 nm
42
112
-1
with a corresponding d-spacing of 0.46 nm, which was a small
decrease compared to 0.48 nm from the 1D WAXD patterns
of PMPCS -b-PBLG and PMPCS -b-PBLG , could be
42
19
42
49
Figure 3. 1D WAXD patterns of PMPCS42-b-PBLG19 (a) and
PMPCS42-b-PBLG49 (b) copolymers during the first heating at 170 °C.
attributed to the increase in the amount of amorphous, smaller
side chains of PBLG (compared to those of PMPCS). And the
diameter of PMPCS columns was 1.56 nm for PMPCS -b-
42
Figure 3 shows the 1D WAXD patterns of PMPCS -b-
4
PBLG112.
2
PBLG19 and PMPCS -b-PBLG . In the sample PMPCS -
42
To further confirm the phase structure of the block co-
polymers, 2D WAXD experiments were carried out on
mechanically sheared samples. Parts a and b of Figure 5
show the 2D WAXD patterns taken with the X-ray beam
along Y and Z directions at room temperature, respectively.
In Figure 5a, two pairs of strong diffraction arcs could be
observed on the meridian in the low-angle region, which were
42
49
b-PBLG , one diffuse halo at larger q values (q = 4π(sin θ)/λ,
1
9
where q is the scattering vector, θ the scattering angle in
WAXD experiments, and λ the wavelength of X-ray) and a
relatively sharp peak at lower q values were observed. The
-
1
peak with q* at 3.97 nm (corresponding to a d-spacing of
.58 nm) could be attributed to the columnar nematic phase
1
-
1
(
(
Φ ) of PMPCS, while the diffuse halo with q** at ∼13 nm
N
attributed to the Φ phase of PMPCS and the Φ phase of
N H
corresponding to a d-spacing of about 0.48 nm) was attri-
PBLG, respectively. In Figure 5c, a set of Bragg reflections
from the hexagonally ordered packing of PBLG at q = 4.7,
8.3, 9.8, and 12.6 nm was observed with a scattering vector
buted to the distances between mesogens, polymer backbones,
and other parts of the BCP. The 1D WAXD pattern of
4
8
-1
1/2 1/2 1/2
ratio of 1:3 :4 :7
PMPCS -b-PBLG exhibited rather similar profile to that
4
in the integration at a 30°-angle
2
49
of PMPCS -b-PBLG for the Φ phase of PMPCS with a
centered at the meridian shown in Figure 5a, which was
consistent with the 1D WAXD results. The columnar dia-
meter of PBLG helices was 1.54 nm. In Figure 5d, only a pair
of diffraction arcs could be observed on the meridian, in
which the reflection from the ΦN phase of PMPCS was
embedded in the first-order reflection of the ΦH phase of
PBLG as mentioned above in the 1D WAXD results. The 2D
WAXD results indicated that the long axes of the PMPCS
and PBLG rods were both aligned parallel to the X direction
and to the lamellar normal. In other words, the PMPCS rods
were aligned parallel to the PBLG rods. For the 2D WAXD
patterns of the sample of PMPCS -b-PBLG112, a set of
4
2
19
N
d-spacing of 1.56 nm, and the reflection for PBLG was
-
1
also found at 4.48 nm with a d-spacing of 1.40 nm, which
corresponded to a columnar diameter of 1.62 nm. The appea-
rance of reflections from both PMPCS and PBLG indicated
the microphase separation of the block copolymer. How-
ever, contrary to a well ordered, tight hexagonal columnar
packing of polypeptides in R-helical conformation, absence
of higher-order Bragg reflections in the WAXD pattern of
PMPCS -b-PBLG indicated that the PBLG helices were
4
2
49
4
7,49,50
in a poorly ordered packing.
A relatively low volume
fraction of the PBLG block might be the reason for this
point. Annealing at high temperatures was reported to help
4
2
Bragg reflections from the hexagonally ordered packing of
PBLG at q = 4.8, 8.6, 10.1, and 12.7 nm was also observed
5
1
-1
improve the level of ordering in some rod-coil systems.
1
/2 1/2 1/2
However, it worked little in this rod-rod system probably
because of the rigid nature of each block. The microphase
separation of the copolymers was investigated using TEM.
However, no patterned structure was observed in both
samples, which was possibly caused by the low composition
of PBLG blocks and the poorly ordered PBLG helices for
PMPCS -b-PBLG and PMPCS -b-PBLG .
with a scattering vector ratio of 1:3 :4 :7 in the integra-
tion at a 30°-angle centered at the meridian shown in
Figure 5d, in which the columnar diameter of the PBLG
hexagon was 1.52 nm from the data above (shown in
Figure 5f).
The morphology of an alternating lamellar structure was
observed by using TEM. Observations were performed on
solution-cast films from solutions at a low concentration of
4
2
19
42
49
The phase transition and self-assembling behavior of
samples PMPCS -b-PBLG and PMPCS -b-PBLG
4
2
80
42
112
0.5 mg/mL. The film samples were stained by RuO vapor to
4
were also investigated. 1D WAXD was facilitated to inves-
tigate the phase behavior of samples at different tempera-
tures from 40 to 170 °C (shown in Figure 4). Upon the first
heating and cooling procedures, the Bragg reflections were
enhance contrast after annealing at 170 °C for 10 h. TEM
micrographs revealed that the distances between lamellae of
alternating PMPCS layer (dark parts) and PBLG layer (light
parts) were about 49 nm for PMPCS -b-PBLG and 58 nm
4
2
80
1
/2 1/2 1/2
found at scattering vectors with a ratio of 1:3 :4 :7 for
PMPCS -b-PBLG at q of 4.60, 8.12, 9.43, and 12.17 nm
for PMPCS -b-PBLG
4
(shown in Figure 6). The above
2
112
-
1
,
and for PMPCS -b-PBLG at q of 4.65, 8.13, 9.39, and
1
results indicated that the formation of liquid crystalline (LC)
phases did not destroy the microstructure regardless of the
change in the diameter of the PMPCS or PBLG rod.
4
2
80
4
2
112
-
1
2.20 nm , indicating the highly ordered hexagonal columnar
52

5
642 Macromolecules, Vol. 43, No. 13, 2010
Zhou et al.
Figure 4. 1D WAXD powder patterns of samples PMPCS42-b-PBLG80 and PMPCS42-b-PBLG112 during the first heating (parts a and c, respectively)
and first cooling (parts b and d, respectively).
However, the lamellar microstructures shown in the TEM
micrographs were not well ordered, which was probably
because the rigid rods had low chain mobility to form highly
ordered patterns.
interdigitated lamellar structure has a maximal layer distance
less than 30 nm by simulation. Therefore, we propose a stacked
bilayer structure in the HL morphology for the self-assembly of
PMPCS -b-PBLG and PMPCS -b-PBLG112.
42
80
42
According to the above data from FTIR, 1D WAXD, and
D WAXD experiments, the PBLG blocks could be assigned
WAXD and TEM techniques were also used to investigate
the self-assembling morphology of sample PMPCS -b-
2
42
to a tightly packed hexagonal domain in the lamellar struc-
ture, and were considered to be packed next to the columnar
nematic domain formed by the PMPCS blocks for sample
PMPCS -b-PBLG112. The proposed structure of the diblock
PBLG173. In the 1D WAXD patterns (shown in Figure 7,
parts a and b), upon the first heating and cooling procedures,
the Bragg reflections were found at scattering vectors with a
1
/2 1/2
-1
ratio of 1:3 :4 at 4.64, 8.06, and 9.25 nm , indicating the
42
copolymer is similar to the so-called HL or a cylinders-in-lamella
morphology which has been reported on PBLG-b-polyglycine
and PBLG-b-poly(L-lysine) peptide copolymers, and also in
some other rod-coil systems. The PBLG segment had a
hexagonal packing, with a columnar diameter of 1.56 nm for
hexagonal columnar arrangement (Φ ) of R-helical confor-
H
mation of PBLG with a columnar diameter of 1.56 nm, and
the ΦH phase of PBLG was developed upon first heating at
about 140 °C. Again, the existence of such an ordered pack-
ing of PBLG indicated the microphase separation of the
block copolymer. The peak attributed to the columnar
nematic phase of PMPCS was difficult to observe because
it was embedded in the strong, first-order reflection of the
ΦH phase of PBLG at a high fPBLG. The cylinder morpho-
logy was found in the TEM micrographs on thin, ultrami-
21,35,49
sample PMPCS -b-PBLG112. Twice of the molecular lengths of
the copolymers (47 nm for PMPCS -b-PBLG and 56 nm for
42
42
80
PMPCS -b-PBLG112) on the basis of the molecular length
42
simulation agreed well with the TEM observations, and the
difference between the layer distances (about 9 nm) of the two
samples was close to twice of the increase in length (4.8 nm ꢀ 2)
of the PBLG block, in which the polypeptide segments adopted
an 18/5 R-helical conformation and the PMPCS was pre-
sumed to have an extended chain conformation of the vinyl
backbone. A bilayer structure appears more reasonable since the
crotomed films. RuO vapor was used to stain the thin
4
sample sections to enhance contrast after the sample was
annealed at 130 °C for 3 days and sheared. Layer-like struc-
tures formed by alternating dark (PMPCS) and light (PBLG)
strips were clearly observed in Figure 7c, and the average

Article
Macromolecules, Vol. 43, No. 13, 2010 5643
Figure 5. 2D WAXD patterns of sheared film samples of PMPCS42-b-PBLG80 (a and b) and PMPCS42-b-PBLG112 (d and e) with X-ray incident beam
along Y and Z directions, respectively. Integration at a 30°-angle centered at the meridian shown in parts a (c) and d (f). Schematic drawing of the
shearing geometry with X-axis the shear direction (g).
PBLG (light) matrix, and an average circle-to-circle distance
of about 42 nm could be estimated from this figure. The
TEM results indicated a cylinder morphology with the
PMPCS domain as cylinders and PBLG domain as the ma-
trix. The simulated molecular length of the copolymer (about
3
7 nm) was consistent with the estimated distance between
the PMPCS cylinders from the TEM micrographs, which
indicated that PMPCS and PBLG rods were packed in an
interdigitated manner in their respective domains. Some
areas in Figure 7d showed a 6-fold symmetry, although the
cylinders did not pack in a perfect hexagonal lattice through-
out the whole domain. The lack of a high order in the micro-
structures shown in the TEM micrographs might also be
attributed to the rigidity and the low chain mobility of the
PMPCS and PBLG rods. However, to the best of our knowl-
edge, no similar morphology (hexagonally packed cylinders
with hexagonally packed helices, which can be called hexagon
in cylinder) has been observed in rod-rod BCP systems.
2D WAXD patterns of the samples with X-ray beam along X
(shear direction), Y, and Z directions are shown in Figure 7f-h,
respectively. In parts f and g of Figure 7, a pair of strong
diffraction arcs could be observed on the meridian in the low-
angle region, in which the reflection from the ΦN phase of
PMPCS was embedded in the first-order reflection of the ΦH
phase of PBLG, and higher-order reflections from the hexago-
nal columnar arrangement of PBLG were visible in Figure 7f. A
ring pattern at low angles could be observed in Figure 7h
with X-ray beam along the X direction, indicating polydomain
nature of the hexagonal arrangement of PBLG in the direction
Figure 6. TEM micrographs of PMPCS42-b-PBLG80 (a) and
PMPCS42-b-PBLG112 (b) stained by RuO after 10-h annealing at
70 °C.
4
1
distance between layers was about 38 nm estimated from this
figure. In Figure 7d, the dark circles were packed within the

5
644 Macromolecules, Vol. 43, No. 13, 2010
Zhou et al.
Figure 7. 1D WAXD powder patterns of PMPCS42-b-PBLG173 during first heating (a) and cooling (b) experiments. TEM micrographs of
ultramicrotomed films of PMPCS42-b-PBLG173 (c and d). Schematic drawing of the shearing geometry with X-axis the shear direction (e). 2D
WAXD patterns of a sheared film sample of PMPCS42-b-PBLG173 with X-ray beam along Y (f), Z (g), and X (h) directions.
Figure 8. Schematic representation of the proposed model for the self-assembly of the rod-rod diblock copolymer in poorly ordered packing (a),
hexagon in lamella (b), and cylinder (d) structures, respectively. Schematic drawings of the shearing geometry with the X-axis being the shear direction
(c and e).
perpendicular to the shear direction. These results also indicated
that after mechanical shearing the PMPCS rods and the PBLG
rods were both aligned parallel to the shear direction
polymer backbones aligned along the shear direction and the
cylinders of the microstructure perpendicular to the shear
direction. However, the development of the cylinder morpho-
logy suggested that the alignment of the rods along the shear
direction was far from perfect, which is evident from Figure 7g.
A schematic representation is shown in Figure 8 which exhibits
(X direction). Therefore, according to the TEM micrographs
and the 2D WAXD patterns, the mechanical shearing forced the
orientation of the self-assembling morphology, with the
53

Article
Macromolecules, Vol. 43, No. 13, 2010 5645
different hierarchical self-assembling structures of the copoly-
mers with different volume fractions of PBLG. In summary, the
copolymer with a low volume fraction of PBLG adopted a
poorly ordered packing, in which the detailed packing schemes
of the PMPCS and PBLG rods were unclear, although a
bilayer-type packing was drawn in Figure 8 for the ease of
drawing. With the increase in fPBLG, the morphology trans-
formed first into a stacked bilayer structure in an HL morpho-
logy, and then into a hexagon in cylinder morphology with the
PMPCS domain as cylinders and the PBLG domain as the
matrix at the relatively high content of the PBLG block.
It will be more interesting to know how the self-assembling
structure changes when the two rods in the rod-rod BCPs
have more different diameters. The additional benefit of
using rods with more different diameters is the clear separa-
tion of characteristic reflections from each rod in WAXD
patterns, which facilitates easier structural analysis. On the
other hand, the larger difference in the area of projection
along the long axis of the rods will affect the curvature of the
microphase-separated structure. To this end, further re-
search is currently underway.
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