Effect of partial hydrogenation on the phase behavior of poly(isoprene-b-styrene-b-methyl methacrylate) triblock copolymers

Article abstract of DOI:10.1021/ma301739j

We studied the effect of selective hydrogenation of the polyisoprene block in poly(isoprene-b-styrene-b-methyl methacrylate) (ISM) triblock copolymers on nanoscale network phase formation. The morphologies of the resulting poly((ethylene-alt-propylene)-b-styrene-b-methyl methacrylate) (EPSM) triblock copolymers and several EPSM copolymer/homopolymer blends were investigated using a combination of small-angle X-ray scattering and transmission electron microscopy, where well-ordered HEX, S_A, and Q²³⁰ (network) nanostructures were identified. Variations in the nanoscale morphologies and phase boundaries between EPSM copolymers and their corresponding ISM precursors can be attributed to the differences in conformational asymmetry and block interactions. Of particular interest, the growth in the gyroid network region in the EPSM relative to the ISM is highlighted as the expansion of this region could further enable the creation of network-forming nanoporous membranes made from materials that are expected to demonstrate improved resistance against thermal and oxidative degradation.

Full text of DOI:10.1021/ma301739j

Article
pubs.acs.org/Macromolecules
Effect of Partial Hydrogenation on the Phase Behavior of
Poly(isoprene‑b‑styrene‑b‑methyl methacrylate) Triblock
Copolymers
Maeva S. Tureau and Thomas H. Epps, III*
̈
Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States
S
* Supporting Information
ABSTRACT: We studied the effect of selective hydro-
genation of the polyisoprene block in poly(isoprene-b-
styrene-b-methyl methacrylate) (ISM) triblock copolymers
on nanoscale network phase formation. The morphologies of
the resulting poly((ethylene-alt-propylene)-b-styrene-b-methyl
methacrylate) (EPSM) triblock copolymers and several EPSM
copolymer/homopolymer blends were investigated using a
combination of small-angle X-ray scattering and transmission
electron microscopy, where well-ordered HEX, SA, and Q230
(network) nanostructures were identified. Variations in the
nanoscale morphologies and phase boundaries between EPSM
copolymers and their corresponding ISM precursors can be
attributed to the differences in conformational asymmetry and block interactions. Of particular interest, the growth in the gyroid
network region in the EPSM relative to the ISM is highlighted as the expansion of this region could further enable the creation of
network-forming nanoporous membranes made from materials that are expected to demonstrate improved resistance against
thermal and oxidative degradation.
by ABC triblock melts have been reported. The major
morphologies include two-domain and three-domain LAM
morphologies,14−16 core−shell versions of cylinders (HEX) and
spheres (S),2,15,17−20 three equilibrium network phases (core−
shell gyroid Q230, alternating gyroid Q214, and orthorhombic
O70),14,16,18,20−29 and other complex nanostructures.2,21,30−36
Among these nanoscale morphologies, ABC network phases are
interesting, as they possess multidimensional cocontinuous
domains with high degrees of internal interfacial area per
specimen volume. This feature provides materials with
enhanced mechanical properties (e.g., enhanced structural
stability due to higher mechanical strength and toughness in
comparison to their two-dimensional [lamellae or cylindrical]
counterparts).24,37
Unfortunately, many of these ABC materials are polydiene-
containing copolymers. Polydiene-containing BCPs are known
to exhibit poor thermal stability as well as degradation in the
presence of oxygen and UV irradiation, making them unsuitable
for many applications.38,39 To overcome these limitations, a
postpolymerization modification such as hydrogenation of
carbon−carbon double bonds of the polydienes has been
employed to enhance the polymers’ resistance to thermal,
oxidative, and radiation-induced degradation and to improve
INTRODUCTION
■
Block copolymers (BPCs) are versatile macromolecules that
demonstrate unique properties based on their distinctive
molecular architecture.1 The chemical connectivity between
each block, the composition and length of the copolymer
chains, as well as the degree of incompatibility between the
blocks, drive block copolymers to self-assemble on nanometer
length scales.2 As a result, BCP materials can exhibit well-
defined and periodic nanostructures with tailored chemical and
physical properties that can be applied to advanced
technologies such as nanotemplating (e.g., electronics,3−5
lithographic masks,6−8 and solar cells9) and nanoseparation
devices (e.g., nanofiltration membranes).10−13
In AB diblock copolymers, the mechanism of nanoscale
phase separation of two covalently-bound homopolymer
blocks, A and B, is governed by two major parameters: the
component volume fraction (fA, where f B = 1 − fA) and the
segregation strength (χABN), which is the product of the Flory−
Huggins segment−segment interaction parameter (χAB) and
the degree of polymerization (N).2 Upon the addition of a third
block, ABC triblock copolymers give rise to increased
morphological complexity due to additional tunable parameters,
including three χ-parameters (χAB, χBC, and χAC), two
independent volume fractions (fA and f B, where f C = 1 − fA
− f B), and the overall degree of polymerization (N).2 Over the
past few decades, numerous theoretical and experimental
studies dedicated to the morphological characterization and
compositional mapping of the complex morphologies exhibited
Received: August 17, 2012
Revised: September 22, 2012
Published: October 3, 2012
© 2012 American Chemical Society
8347
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
the physical properties of the resulting saturated materials (e.g.,
superior tensile strength and elongation at break).38−47
In previous work, the morphological behavior of the
poly(isoprene-b-styrene-b-methyl methacrylate) (ISM) triblock
copolymer system was studied experimentally, and several
network-like nanostructures were reported.25,26,48 However, to
reduce the thermal and oxidative degradation of the
polyisoprene (PI) block, these ISM polymers could benefit
from the hydrogenation of the PI block to create tougher and
more environmentally resistant materials.
The hydrogenation of unsaturated polymers is typically
accomplished through catalytic or noncatalytic methods.
Catalytic hydrogenation methods can produce large batches
of hydrogenated copolymers43 and are thus, a preferred route
on the industrial scale. The hydrogenation can be either
heterogeneous44,49,50 or homogeneous30,43,47,51 in nature, and
the effectiveness of the catalytic process toward the selective
hydrogenation of unsaturated polymers is a function of the
catalyst activity and hydrogenation conditions.47 For heteroge-
neous catalysis, highly effective PI hydrogenation may be
achieved, but it usually requires harsh conditions that can
induce polymer degradation and branching.43 Additionally,
most heterogeneous catalysts can become ineffective over time
due to the absorption of the polymer chains onto the catalyst
and have low selectivity in many cases.44 On the other hand,
homogeneous catalysts, including Wilkinson’s catalyst30,43,47,51
or other soluble catalysts such as Ni/Al,52 are typically effective
under milder reaction conditions that minimize side reactions.
Such catalysts also have shown to have better selectivity and
tolerance toward the presence of functional groups.47,53,54
However, homogeneous catalytic hydrogenations accomplished
using the Wilkinson’s catalyst typically require high-pressure
autoclaves43,55 and often are time-intensive reaction processes
(>3 days).51,55
Unlike catalytic hydrogenation methods that typically require
higher pressures,30,43−45,51 a low-pressure noncatalytic ap-
proach was utilized in this study.38,39,41,56 Here, fully or
partially hydrogenated poly(ethylene-alt-propylene-b-styrene-b-
methyl methacrylate) (ESPM) triblock copolymers were
produced from the selective PI hydrogenation of ISM
precursors using diimide intermediates, generated in situ from
the thermal decomposition of p-toluenesulfonyl hydrazide
(TSH).38 Upon hydrogenation of the PI block, the EPSM
triblock system becomes a promising candidate for the creation
of nanoporous separation membranes due to the toughness
given by the combined interactions of the glassy polystyrene
(PS) and rubbery poly(ethylene-alt-propylene) (PEP) blocks,
the mechanical strength provided by the PS block, and the ease
of removal of the poly(methyl methacrylate) (PMMA) block.
We note that nanoporous membranes made from partially
hydrogenated materials contain remaining double bonds in the
PI block that can be chemically cross-linked to improve solvent
resistance in addition to the thermal and oxidative resistance
imparted by the PI hydrogenation.
Previous work on the ISM triblock system demonstrated the
discovery of three multidimensional and cocontinuous nano-
scale networks that are potentially desirable for separation
membranes due to their well-defined diffusion pathways and
high structural stability.25,26 This article focuses on the
nanoscale characterization of selected EPSM materials that
were generated with the goal of preserving the network-like
nanostructures found in their ISM triblock precursors. A
comparison of the morphological behavior of neat and triblock/
homopolymer blends between the ISM triblock precursors and
EPSM materials is discussed based on the differences in
interaction parameters (χij) and statistical segment length ratios
(bi/bj) between the ISM and EPSM systems, which results in a
noticeable network phase extension and slight shifts in the
phase boundaries.
EXPERIMENTAL SECTION
■
Material Synthesis. The poly(isoprene-b-styrene-b-methyl meth-
acrylate) (ISM) triblock copolymers were synthesized using anionic
polymerization techniques. Synthetic protocols are detailed else-
where.25,26,57,58
ISM Hydrogenation. ISM triblock copolymers were chemically
modified by the selective hydrogenation of the polyisoprene (PI) block
with diimide in toluene, produced in situ by the thermal
decomposition of p-toluenesulfonyl hydrazide (TSH).38,39,46,56 TSH
(97%, Sigma-Aldrich) was initially purified by recrystallization from
ethanol and dried under vacuum prior to use. Toluene (ACS certified,
Fisher Scientific) was degassed by sparging with argon for 30 min and
then dried by passage through an alumina column and a Q5 column.
The hydrogenation reaction was carried out under a nitrogen blanket
in a round-bottom flask equipped with a reflux condenser, nitrogen
inlet port, and glass connectors fitted with a needle port capped by a
Teflon-coated septum. The connector ports were used to bleed out
excess nitrogen built up during the reaction. The reaction mixture was
continuously stirred and brought to reflux by slowly heating to ∼80−
90 °C to allow for the complete dissolution of TSH in toluene and
then heated to 120 °C for 4 h and 135 °C for 3 h. Upon completion of
the reaction, the hydrogenated samples were precipitated into cold
methanol and thoroughly washed ∼3 times with methanol/distilled
water mixtures (∼75 vol % methanol) to remove any excess TSH and
byproducts of the TSH decomposition. Finally, the purified EPSM
copolymers were dissolved in toluene, precipitated into methanol, and
dried under vacuum.
Chemical Characterization. Number-average molecular weight
(Mn) and polydispersity index (PDI) for ISM and EPSM triblocks
were determined by gel permeation chromatography (GPC), using
polystyrene standards with tetrahydrofuran (THF) as the mobile
phase. The GPC traces were obtained on a Viscotek VE 2001
equipped with a Viscotek VE 3580 refractive index detector and
Waters Styragel HR1 and HR4 columns (7.8 × 300 mm each) in
series. No chemical degradation or cross-linking was detected in the
powdered hydrogenated materials. Most Mn values, as determined
from GPC using PS standards, were found to be slightly higher upon
hydrogenation, likely due to the different hydrodynamic volume of the
PEP versus the PI block. The component mole fractions of the ISM
1
precursors and EPSM copolymers were calculated from integrated H
NMR peak intensities using a Bruker AV-400 instrument and were
further converted to volume fractions using homopolymer densities at
140 °C (0.83, 0.969, 1.13, and 0.79 g mL−1 for PI, PS, PMMA, and
PEP, respectively59). We note that all ISM triblock copolymers
showed ∼94% 1,4-PI addition (and ∼6% 3,4-PI addition), as expected
under the anionic polymerization conditions.60 The degree of
hydrogenation of the EPSM materials was obtained by calculating
1
the mole percentage reduction in the PI units based on the H NMR
spectra of the ISM triblock precursor and resulting hydrogenated
(EPSM) analogue. No significant TSA byproducts were incorporated
to the PI double bonds of the hydrogenated EPSM materials,
corresponding to the fraction of incorporated tosyl groups (i.e., −CH3
38,55
1
group found at ∼2.3−2.4 ppm in the H NMR spectra).
Small-Angle X-ray Scattering (SAXS). Lab source SAXS
experiments were conducted at the University of Delaware (UD) on
a Rigaku SAXS instrument as described elsewhere.26 These data are
referred to as “UD-SAXS data”. SAXS data were acquired at 30 °C and
plotted as azimuthally integrated scattered intensity versus scattering
vector modulus, q = 4πλ−1 sin(θ/2), where θ is the scattering angle.
Details on the thermal annealing conditions for each sample are
reported in Table S2 of the Supporting Information. SAXS patterns
8348
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
a
Scheme 1. Reactions Occurring During the Hydrogenation of the PI Units in the ISM Triblock Copolymer Using Diimide
a
Reactions: (1) diimide generation from the thermal decomposition of TSH at a decomposition temperature Td ∼ 107 °C; (2) hydrogenation of
ISM triblocks with diimide, leading to EPSM triblock materials; (3) disproportion reaction of diimide, generating hydrazine (N2H4) and nitrogen
(N2).
Table 1. Characterization Data for ISM Precursor Triblocks, EPSM Triblocks, and Associated Blends
a
volume composition
polymer
precursor
f EP/I
f S
f M
Mn (g mol−1
)
PDI
% hydrogenation (molar basis)
phase
LAM
ISM triblocks
T1
T2
T3
T4
0.00/0.13
0.00/0.24
0.00/0.25
0.00/0.29
0.43
0.59
0.57
0.66
0.44
0.17
0.18
0.05
28 100
31 200
20 100
31 100
1.07
1.11
1.09
1.04
b
HEX → Q230
DIS
HEX
EPSM triblocks
HT1
T1
0.13/0.01
0.25/0.00
0.23/0.03
0.29/0.02
0.43
0.58
0.56
0.64
0.43
0.17
0.18
0.05
27 400
31 500
20 700
30 500
1.09
1.15
1.09
1.07
90
100
86
Q230
SA
HT2
T2
T3
T4
HT3
HEX
HEX
HT4
95
c
EPSM blends
bHT1_1
bHT1_2
bHT3
HT1/PS
0.10/0.01
0.10/0.01
0.28/0.03
0.31/0.02
0.37/0.02
0.27/0.01
0.57
0.34
0.55
0.62
0.57
0.58
0.32
0.55
0.14
0.05
0.04
0.14
Q230
HT1/PMMA1
HT3/PS/PEP
HT4/PEP
HEX
HEX
HEX
HEX
HEX
bHT4_1
bHT4_2
bHT4_3
HT4/PEP
HT4/PMMA2
a
Volume fractions of hydrogenated materials are calculated based on their respective mole percent hydrogenation and volume fractions of ISM
b
c
triblock precursors. HEX-to-Q230 transition on cooling. EPSM blends refer to blends of EPSM triblocks with constituent homopolymers.
Homopolymer Mn’s for PS, PMMA1, PMMA2, and PEP are 13.7, 11.3, 1.1, and 6.0 kg mol−1, respectively, with corresponding PDIs of 1.06, 1.30,
1.07, and 1.12. Blend bHT1_1 is a mixture of triblock HT1 with 26 vol % PS content, while blend bHT1_2 is a mixture of HT1 with 21 vol %
PMMA1. bHT3 is a blend of triblock HT3 with 10 vol % PS and 9 vol % PEP. bHT4_1, bHT4_2, and bHT4_3 are blends of triblock HT4 with 3
vol % PEP, 11 vol % PEP, and 9 vol % PMMA2, respectively.
presented herein are vertically shifted for clarity, and unidentified, but
expected, peak locations are indicated by dashed arrows.
Transmission Electron Microscopy (TEM). TEM micrographs
were obtained at the W.M. Keck Electron Microscopy Facility at UD
using a JEOL JEM-2000FX transmission electron microscope
operating at 200 kV. The annealed SAXS samples were cut on a
Leica Reichart Ultracut cryo-microtome at temperatures ranging from
−60 to −75 °C (depending on the PI or PEP copolymer content)
using a Diatome diamond knife. The ISM sample preparation is
described elsewhere.25,26 The microtomed slices (70−100 nm in
thickness), cut from hydrogenated (PEP-containing) materials, were
placed on 400 mesh copper grids and vapor-stained using a 0.5%
aqueous solution of RuO4 for 1.5 min to enhance the electron density
contrast.
Synchrotron SAXS experiments were performed on the DND-CAT
beamline at the Argonne National Laboratory (Advanced Photon
Source - APS) and on the X27C beamline at the Brookhaven National
Laboratory (National Synchrotron Light Source - NSLS). At the APS
facility, two setups were used with an incident beam of wavelength λ =
0.729 Å and a Mar CCD detector at a sample-to-detector distance of
4.0 and 6.5 m, while the setup at the NSLS facility used an incident
beam of wavelength λ = 1.371 Å and a Mar CCD detector at a sample-
to-detector distance of 1.8 m. The synchrotron SAXS data from the
APS and NSLS facilities are referred to as “APS-SAXS” and “NSLS-
SAXS” data, respectively.
8349
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
RESULTS
■
The EPSM triblock materials were generated from the selective
PI hydrogenation of neat ISM triblock copolymers with
diimide, produced in situ by the thermal decomposition of p-
toluenesulfonyl hydrazide (TSH), according to reaction 1 of
Scheme 1.39,41 The hydrogenation of the PI block in ISM
triblock materials produces an alternating ethylene and
propylene unit and leads to the formation of fully or partially
hydrogenated EPSM materials, depending on the TSH:PI
molar ratio and reaction conditions (see reaction 2 in Scheme
1). Theoretically, an equimolar ratio of TSH:PI repeat unit
should lead to complete hydrogenation. However, previous
studies have shown this does not occur, as not all of the diimide
intermediates formed during the thermal decomposition
process react with sites of unsaturation in polydienes.39,41,61 It
is known that diimide can simultaneously undergo dispropor-
tionation during the hydrogenation process, forming nitrogen
(N2) and hydrazine (N2H4), as shown in reaction 3 of Scheme
1.39,61 The rate of disproportionation (k2) was found to be
faster than the rate of hydrogenation (k1) of diene repeat
units.39,41,46 Conversely, the thermal decomposition of TSH is
known to form sulfur-containing byproducts (i.e., mainly p-
toluenesulfinic acid and bis(p-tolyl) disulfide), capable of
competing with the diimide products by also reacting with
CC bonds in the PI block.38,61 Therefore, favoring complete
hydrogenation while minimizing byproducts substitutions
required a slow thermal decomposition of TSH, which was
accomplished by finding a balance between the amount of
excess TSH and the reaction temperature (i.e., above the
toluene boiling point).41,46 As a result, a nearly complete
hydrogenation of the ISM triblock materials was obtained using
a solution of 3 wt % polymer in toluene with a 4:1 molar ratio
of TSH:PI repeat units. Additional details regarding the PI
hydrogenation of ISM materials can be found in the
Experimental Section.
Figure 1. SAXS data acquired at 30 °C for triblock T1, HT1, and
associated blends bHT1_1 and bHT1_2, from mixing HT1 with PS
and PMMA1, respectively. Triblock T1 exhibits a LAM morphology.
HT1 and associated blend bHT1_1 suggest the Ia3d space group
̅
symmetry, characteristic of a Q230 network nanostructure. Blend
bHT1_2 suggests a hexagonal symmetry, indicative of a hexagonally
packed cylinder (HEX) morphology.
assignment for ISM triblock precursor, T1 (Figure 2a), and
reveal two complementary projections of the Q230 network
morphology for hydrogenated EPSM triblock, HT1: the
“wagon-wheel pattern”, characteristic of the [111] projection
(Figure 2b) and an additional orientation resembling the Q230
The phase behavior of the parent ISM materials used in this
hydrogenation study was described previously.25,26,48 To
facilitate the comparison between ISM precursors and hydro-
genated EPSM materials, the characterization data of neat ISM
materials and hydrogenated triblock analogues are summarized
in Table 1. Additionally, blends between select hydrogenated
triblocks and their constituent homopolymers were prepared to
probe the differences in phase behavior between the ISM26 and
EPSM systems. The characterization data for the blended
materials also are reported in Table 1.
Extensive Q230 Network Phase Region in the EPSM
Triblock Copolymer System. ISM triblock T1 was subjected
to two consecutive PI hydrogenations (first hydrogenation
yielded an 88 mol % hydrogenated EP/I block) to produce a 90
mol % hydrogenated triblock HT1. UD-SAXS data (Figure 1)
for T1 show diffraction peaks at q*, 2q*, 3q*, and 4q*,
suggestive of a lamellar morphology (LAM). Although the
SAXS data for the ISM triblock (T1) show peaks characteristic
of a LAM morphology, the hydrogenated EPSM triblock
analogue (HT1) shows a different APS-SAXS signature with
distinct reflection peaks located at √6q*, √8q*, √16q*,
√20q*, √22q*, √24q*, √26q*, √30q*, √32q*, √34q*,
√38q*, √42q*, √46q*, √48q*, and √50q*. Although the
peaks at √14q* and √40q* (indicated by dashed arrows) are
Figure 2. TEM micrographs obtained from (a) T1 (LAM), (b) HT1
(Q230 network), (c) bHT1_1 (Q230 network), and (d) bHT1_2
(HEX): (a) the PI domains (dark) of sample T1 are stained with
OsO4; (b−d) the PS domains (dark gray) and PS/PEP interfaces are
stained with RuO4. Scale bars are 100 nm.
not identifiable, this peak sequence is consistent with the Ia3d
̅
space group, indicative of a Q230 network morphology (Figure
1). The corresponding TEM images support the LAM phase
8350
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
network [125] projection (inset image of Figure 2b). Two
blends were generated from mixing the hydrogenated Q230
network-forming material HT1 with either 26 vol % PS content
(blend bHT1_1) or 21 vol % PMMA1 content (blend
bHT1_2). Blend compositions for bHT1_1 and bHT1_2
were chosen to match composition-equivalent blends from the
ISM precursor system (i.e., blends of ISM triblock T1 with the
same PS and PMMA homopolymers, respectively).26 Blend
bHT1_1 revealed a similar APS-SAXS pattern to that of the
hydrogenated material HT1 but showed less apparent ordering
than the HT1 precursor material (Figure 1). The correspond-
ing TEM image for blend bHT1_1 (Figure 2c) provides
support for the Q230 network assignment. Upon addition of 21
vol % PMMA1 to HT1, blend bHT1_2 shows a different APS-
SAXS signature with reflections at q*, √3q*, √4q*, √7q*,
√9q*, √12q*, √16q*, √19q*, and √21q*, consistent with a
hexagonal symmetry (Figure 1). The TEM micrographs
confirm a well-defined core−shell HEX morphology, as
illustrated in the parallel (Figure 2d) and perpendicular (inset
of Figure 2d) orientations, where PEP cylinders are surrounded
by a shell of PS in a matrix of PMMA. Additionally, two blends
were generated from mixing HT1 with ∼9 vol % PS content
(bHT1_3) and ∼18 vol % PS content (bHT1_4), in order to
assess the extent of the Q230 network phase region, at
intermediate compositions between the Q230 network-forming
HT1 and bHT1_1 specimens. The UD-SAXS patterns for
blends bHT1_3 and bHT1_4, shown in the Supporting
Information (Figure S1), also are indexed according to the
Ia3d space group, characteristic of the Q230 morphology.
̅
Alternating Spheres in the EPSM Triblock Copolymer
System. ISM triblock T2, exhibiting a likely HEX-to-Q230
phase transition on cooling, was nearly 100% hydrogenated to
produce the EPSM sample HT2. Details on the characterization
of the ISM triblock T2 can be found in the Supporting
Information (UD-SAXS data in Figures S2 and S3 and TEM
micrographs in Figure S4). APS-SAXS data and a TEM
micrograph, acquired at 30 °C for sample T2, are presented in
Figures 3a and 3b, respectively, in order to allow for a direct
comparison with the EPSM triblock analogue HT2. The APS-
SAXS pattern for sample HT2, provided in Figure 3a, shows
Bragg reflection peaks at consecutive integer square roots q*,
√2q*, √4q*, √5q*, √6q*, ..., up to √27q*, suggestive of a
body-centered cubic spherical symmetry.15,62 However, several
higher order peaks were not located at √3q*, √7q*, √15q*,
√18q*, √19q*, √22q*, and √23q* (dashed arrows). The
corresponding TEM micrograph in Figure 3c further supports
an alternating spherical morphology (SA) of PEP (light dots
with dark outlines) and PMMA (light dots) spheres in a
continuous PS matrix (gray).
Inducing Order from a Disordered ISM Copolymer
upon Hydrogenation. ISM triblock T3 was characterized as a
disordered melt (DIS) using a combination of SAXS and TEM
analysis.48 APS-SAXS data for triblock T3 reveal a broad
primary peak over the entire range of temperatures explored
(Figure 4). This lack of ordering was confirmed in a
corresponding TEM micrograph (Figure 5a). Upon 86 mol
% hydrogenation of the PI block in triblock T3, the resulting
hydrogenated material, HT3, showed a well-defined APS-SAXS
pattern with Bragg peaks located at q*, √3q*, √4q*, √7q*,
and √9q*, suggestive of a hexagonal symmetry (Figure 4).
TEM micrographs support a HEX assignment in HT3 (Figure
5b). We note that, as this material was only partially
hydrogenated and had an appreciable PI content, osmium
Figure 3. (a) APS-SAXS data for triblock T2 and HT2 (hydrogenated
T2) acquired at 30 °C. Triblock T2 was identified as a possible HEX/
Q
230 mixed-morphology resulting from a HEX-to-Q230 phase transition
on cooling (see Supporting Information). Sample HT2 is indicative of
a possible spherical symmetry. TEM micrographs obtained from (b)
T2 (HEX/Q230 mixed-morphology) and (c) HT2 (alternating spheres
- SA). (b) Dark regions represent the PI domain (stained with OsO4)
and lighter regions correspond to the unstained PS and PMMA
domains. (c) Gray region represents the PS matrix (stained by RuO4),
the lighter spheres with black outline represent the PEP domain
(contours stained with RuO4), and the brighter spheres correspond to
the unstained PMMA domains. An illustration of the SA morphology is
provided in the inset of (c) for clarity. TEM scale bars are 100 nm.
tetroxide (OsO4) was used to preferentially stain the remaining
unsaturated repeat units on the randomly hydrogenated PI
chains. Using this staining agent provided better contrast than
staining with RuO4. The resulting TEM images show
perpendicular (Figure 5b) and parallel (inset of Figure 5b)
orientations of the HEX morphology, in which the stained
PEP/PI cylinders appeared dark in a matrix of unstained (and
indistinguishable) PS and PMMA domains (light). Lastly, blend
bHT3 was obtained by blending the hydrogenated material
HT3 with 10 vol % PS and 9 vol % PEP. This sample retained a
HEX morphology, as indicated by the NSLS-SAXS data in
Figure 4, with well-defined peaks at q*, √3q*, √4q*, √7q*,
√9q*, √12q*, √13q*, √16q*, and √19q*. The TEM images
for blend bHT3 support this HEX morphology assignment
(Figure 5c).
Additionally, EPSM triblock material HT4, situated in the
vicinity of triblock HT3 on the PMMA-poor side of the EPSM
phase diagram, was produced by 95 mol % PI hydrogenation of
8351
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
DISCUSSION
■
In this study, EPSM triblock copolymers were generated by
hydrogenating the PI block in ISM triblock precursors. The
anionically synthesized ISM precursors provided materials with
narrow molecular weight distributions that assembled into
distinctive network structures.26 Furthermore, the chemically
modified EPSM triblock analogues presented in this study will
offer materials with improved chemical and physical properties
that will facilitate the removal of the PMMA block, while also
preventing the collapse of the nanoscale structure for the
creation of tough yet flexible nanoporous membranes.
As noted previously,25,26 the ISM copolymers are non-
frustrated with statistical segment length ratios close to unity
(bM/bI = 0.95, bI/bS = 1.11, and bS/bM = 0.95)59,63 and a χ-
64,65
66
67
parameter sequence of χIM
≫ χIS > χSM (at 100 °C).
Figure 4. SAXS data for triblock T3, HT3, and bHT3 (a blend of HT3
and PS/PEP homopolymers). All SAXS patterns were acquired at 30
°C. Sample T3 shows a broad primary peak, indicative of a disordered
specimen. Sample HT3 reordered upon hydrogenation to a hexagonal
symmetry. Blend bHT3 retained the hexagonal symmetry.
Therefore, a direct comparison could be made between the
nearly ideal ISM system and a symmetric model ABC phase
diagram by Tyler et al.68 Upon hydrogenation, the resulting
EPSM triblock system is substantially more asymmetric with
appreciably different statistical segment length ratios, in
comparison to the ISM precursor system (bM/bEP = 0.85,
bEP/bS = 1.25, and bS/bM = 0.95).59,63 Additionally, although
the chemical modification of the PI block in the ISM system
does not significantly alter the overall degree of polymerization
(NEP ≈ NI and hence, NEPSM ≈ NISM = NI (or NEP) + NS + NM)
in the hydrogenated materials, it will affect the interaction
parameters involving the PEP block (χEPS and χEPM). These
changes in effective segregation strengths (χEPSN and χEPMN vs
χISN and χIMN, respectively) and segment length ratios (bM/bEP
and bEP/bS vs bM/bI and bI/bS, respectively) are expected to
affect the phase behavior of the EPSM system with respect to
that of the ISM triblock precursors and the Tyler et al. model
ABC system.68 The temperature-dependent expressions for χIS
and χEPS were reported by Sakurai et al. (χIS = 0.042 and χEPS
=
0.069 at 140 °C)69 and as expected, χEPS > χIS (Table S1 in the
Supporting Information). To the best of the author’s
knowledge, no temperature-dependent equation for χEPM have
been reported in the literature, but we believe that χEPM > χIM
based on estimations from solubility parameter theory (χIM
=
0.1425 and χEPM = 0.2079 at 140 °C; see Table S1 in the
Supporting Information). To assess quantitative differences in
χ-parameters between the EPSM and ISM systems, the
associated χ-parameters were estimated using solubility
Figure 5. TEM micrographs obtained from (a) T3 (DIS), (b) HT3
(HEX), and (c) bHT3 (HEX). (a, b) Stained with OsO4. (c) Stained
with RuO4. The TEM micrographs of (b) and (c) support the HEX
morphology assignment, where both perpendicular and parallel (inset)
orientations are noted. Scale bars represent 100 nm.
parameter theory (based on regular solution theory), χ12
=
V0(δ2 − δ1)2/RT, where the molar volume of the component
pair (V0) is calculated from the geometric mean of the
component molar volumes: V0 = (V1V2)1/2, δ is the solubility
parameter for each polymer, R is the gas constant, and T is the
temperature in kelvin.17 We note that a modified equation to
the regular solution theory can be applied, which includes an
entropic interaction term (usually a constant ranging between
0.3 and 0.4).70 In this study, however, the entropic
contributions are neglected as we are interested in the relative
differences between the estimated χ-parameters of the ISM and
EPSM triblock systems. Details regarding the calculation of χ-
parameters (see Table S1 in the Supporting Information)
indicate that the difference in the neighboring blocks (EP/S vs
I/S) χ-parameters is larger in EPSM than in the ISM precursor.
However, the EPSM system still follows the same χ-parameter
a HEX-forming ISM triblock precursor (T4). Three blends
(bHT4_1, bHT4_2, and bHT4_3) also were prepared by
mixing hydrogenated material HT4 with 3 vol % PEP, 11 vol %
PEP, and 9 vol % PMMA2, respectively, to probe the EPSM
phase space at similar compositions to ISM triblock/
homopolymer blend analogues.26 Based on SAXS and TEM
analyses, triblock HT4 and associated blends retained the HEX
morphology of the ISM materials. SAXS data (Figure S5) and
TEM micrographs (Figure S6) for T4, HT4, and blended
materials are reported in the Supporting Information, and these
samples will be discussed further in the Discussion section.
1,35
1,35
sequence as for the ISM system (i.e., χEPM
> χEPS
≫
χSM1), which implies that this nonfrustrated and asymmetric
8352
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
EPSM system also should favor the formation of network
structures as the EP and M blocks are unlikely to mix.71
To investigate the differences in phase behavior between the
EPSM and ISM systems near network phase regions, judicious
blends made from EPSM triblocks and corresponding
homopolymers were targeted to match their non-hydrogenated
analogue blends (i.e., ISM triblock/homopolymer blends) at
similar compositions.26 Using this approach, several morpho-
logical differences were revealed between the ISM precursor
and the hydrogenated EPSM systems.
Three blends were generated by mixing Q230 network-
forming HT1 with incremental amounts of PS homopolymer
(bHT1_3, bHT1_4, and bHT1_1 with 9, 18, and 26 vol % PS
content, respectively) to probe the extent of the Q230 network
phase region in the EPSM system. The blend composition for
bHT1_1 was chosen to match a composition-equivalent Q230
network-forming ISM blend, reported in a previous publica-
tion.26 Although a HEX morphology is expected in the Tyler et
al. ABC phase diagram at similar compositions, blend bHT1_1
retained a Q230 network structure. The additional blends
bHT1_3 and bHT1_4, generated at intermediate compositions
between EPSM triblock HT1 and blend bHT1, appeared to
retain a Q230 network morphology. This latter finding provides
possible evidence of an extended Q230 network phase in the
EPSM system, when compared to the ISM system at similar
compositions. The general trend depicted by the shift of the
phase boundaries of the EPSM system resembles that of a less
idealized poly(isoprene-b-styrene-b-ethylene oxide) (ISO) tri-
block copolymer system, as seen in the work by Epps et al. and
later in the self-consistent field theory (SCFT) theoretical
predictions based on the ISO system by Tyler et al.14,68 In
contrast to the ISM phase map reported previously,26
conformational asymmetries (bEP/bM = 1.18)59,63 resulted in
a shift in the phase boundaries toward the EP-rich corner, along
the EP/M edge of the EPSM phase map, which likely
contributed to the enlargement of the Q230 network phase
region toward the M-rich corner. An illustration of the
extended Q230 network phase region in the EPSM system
(dashed-green region) as compared to that of the ISM
precursor system (bottom green-colored region) is shown in
a partial phase map depicting the change in phase boundaries
upon hydrogenation (Figure 6).
Additional exploration of network phase regions was carried
out in the EPSM system at similar compositions to noncubic
network-forming ISM/PMMA blends. To this end, a blend,
bHT1_2 was made from mixing HT1 with 21% PMMA1. This
material was targeted to match blends located in the O70
orthorhombic network region of the ISM system.26 Instead of
exhibiting an O70 orthorhombic network structure, blend
bHT1_2 exhibited a well-defined HEX morphology (Figure
6). Although this blend lies near the PMMA-rich LAM region
of Tyler et al. ABC phase diagram and at close proximity to the
Q230 network phase region, a HEX-forming blend at such
compositions is not unexpected as the conformational
asymmetries of the EPSM system may affect the Q230-to-HEX
phase sequence predicted in the Tyler et al. ABC model phase
diagram.68 Furthermore, the increase in χ-parameters between
the PEP block and the PS and PMMA blocks is reminiscent of
the lithium salt doping of the ISO system, which led to a
morphological transition from O70 to HEX upon doping.72
Similar results were obtained from simulation efforts;73
however, we note that the change in χ-parameters is not
nearly as dramatic in this work.
Figure 6. Partial phase map depicting the estimated ISM phase regions
of LAM, HEX, DIS, and three network structures (Q214 alternating
gyroid, Q230 core−shell gyroid, and O70 orthorhombic).25,26,48 The
phase diagram is overlaid with EPSM triblock copolymers (fully or
partially hydrogenated HT1, HT2, HT3, and HT4 materials analogue
to the ISM triblock precursors, represented by colored circles with
black outline) and associated blends (colored circles). The dashed
colored contours highlight the approximate change in phase
boundaries in the hydrogenated (EPSM) triblock system based on
the samples investigated in this work. We note that the phase
boundaries may expand (or contract) as additional samples are
examined.
To further probe the phase behavior, sample T2 (assigned to
possible HEX/Q230 phase-mixed morphology) was hydro-
genated to sample HT2, which exhibited an alternating
spherical morphology (SA), as shown in Figure 6. A small SA
region was stable along the fA = fC isopleth of the Tyler et al.
model ABC phase diagram, and this SA-forming sample HT2 is
located in the HEX region of the model phase diagram, but
very close to the HEX/SA boundary. This SA finding for HT2
further indicates that the EPSM system, while similar to the
ISM system, does not behave as symmetrically with respect to
the f EP = f M isopleth as the ABC model system, likely due to
the greater difference in the neighboring block χ-parameters
(χEPS > χSM), as well as the difference in statistical segment
length ratios.1,35,68
Finally, a morphological shift from a DIS state in the ISM
triblock precursor T3 to a HEX morphology in triblock HT3
was noted upon hydrogenation. This HEX-forming triblock
HT3 is found to be qualitatively consistent with the Tyler et al.
ABC phase behavior, as sample HT3 is located in close
proximity to the network/HEX phase boundary.68 Blend
bHT3, made by mixing HT3 with PS/PEP homopolymers,
was targeted to similar compositions to a Q230 network-forming
ISM/PS/PI blend analogue;26 however, the hydrogenated
blend retained a HEX morphology (Figure 6). Additionally,
blends bHT4_1 (3 vol % PEP) and bHT4_3 (9 vol %
PMMA2) were targeted to match the compositions of a Q230
8353
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
network-forming ISM blend and HEX-forming blend ana-
logues, respectively;26 however, these blends also retained the
HEX morphology (Figures S5 and S6 in the Supporting
Information). The bHT4_3 blend may imply that the HEX-to-
Q230 phase boundary in the EPSM system occurs at higher PEP
contents than in the ISM system (i.e., PI content), as shown in
Figure 6. Again, this phenomenon likely arises from the
considerable conformational asymmetries in the EPSM system,
which results in an expanded HEX phase region as the phase
boundaries tend to shift toward compositions richer in PEP as
bEP/bS = 1.25 in EPSM.59,63,74
(FA9550-09-1-0706). M. Tureau acknowledges an Air Products
and Chemicals, Inc., Fellowship. Use of the DuPont−
Northwestern−Dow Collaborative Access Team (DND-CAT)
located at Sector 5 of the Advanced Photon Source (APS) was
supported by E. I. DuPont de Nemours & Co., the Dow
Chemical Company, and the State of Illinois. Use of the APS
was supported by the U.S. Department of Energy, Office of
Science, Office of Basic Energy Sciences, under Contract DE-
AC02-06CH11357. Portions of this work also were performed
at the National Synchrotron Light Source (NSLS), Brookhaven
National Laboratory. NSLS is supported by the U.S. Depart-
ment of Energy, Office of Science, Office of Basic Energy
Sciences, under Contract DE-AC02-98CH10886. NMR spectra
were obtained with instrumentation supported by NSF
CRIF:MU, CHE 0840401. We acknowledge the W.M. Keck
Electron Microscopy Facility at the University of Delaware for
the use of their JEOL JEM-2000FX TEM instrument. We also
thank E. Kelley for the synthesis of the PS homopolymer.
CONCLUSIONS
■
In summary, four EPSM triblock copolymers were generated by
hydrogenation of PI repeat units in ISM triblock copolymer
precursors, using diimide as a hydrogenating agent. In view of
creating nanoporous templates, the combination of the strong
PS and flexible PEP blocks is expected to enhance mechanical
integrity as well as environmental resistance, while also
facilitating the removal of the PMMA domains. The
morphological characterization of the EPSM triblock copoly-
mers and associated EPSM copolymer/homopolymer blends
has been investigated using a combination of SAXS and TEM
techniques, where well-ordered HEX, SA, and Q230 network
morphologies were identified. This hydrogenation study
provides experimental understanding for how changing χ-
parameters and statistical segment length ratios impact network
formation in an ABC triblock copolymer system. The variations
in phase behavior between the EPSM system and the ISM
precursor system arise from the significant differences in
conformational asymmetry between the two systems (larger
statistical segment length ratios bEP/bS > bI/bS and bEP/bM > bI/
bM and segregation strengths χEPSN > χISN and χEPMN > χIMN).
Particularly, this study presents an initial assessment on the
location of an extended Q230 network window in the PMMA-
rich region of the EPSM system, which gives further insight
into the universality of the phase behavior of nonfrustrated
ABC triblock copolymer systems.
REFERENCES
■
(1) Young, R. J.; Lovell, P. A. Introduction to Polymers, 2nd ed.;
Chapman & Hall: London, 1991.
(2) Bates, F. S.; Fredrickson, G. H. Phys. Today 1999, 52, 32−38.
(3) Gobius, d. S. G.; Vukovic, I.; Vukovic, Z.; Polushkin, E.;
Hiekkataipale, P.; Ruokolainen, J.; Loos, K.; ten, B. G. Macromol. Rapid
Commun. 2011, 32, 366−370.
(4) Lee, D. H.; Park, S.; Gu, W.; Russell, T. P. ACS Nano 2011, 5,
1207−1214.
(5) Kim, H.-C.; Park, S.-M.; Hinsberg, W. D. Chem. Rev. 2010, 110,
146−177.
(6) Olson, D. A.; Chen, L.; Hillmyer, M. A. Macromolecules 2008, 20,
869−890.
(7) Hillmyer, M. A.; Abetz, V. Adv. Polym. Sci. 2005, 190, 137−181.
(8) Darling, S. B. Prog. Polym. Sci. 2007, 32, 1152−1204.
(9) Crossland, E. J. W.; Kamperman, M.; Nedelcu, M.; Ducati, C.;
Wiesner, U.; Smilgies, D. M.; Toombes, G. E. S.; Hillmyer, M. A.;
Ludwigs, S.; Steiner, U.; Snaith, H. J. Nano Lett. 2008, 9, 2807−2812.
(10) Phillip, W. A.; Rzayev, J.; Hillmyer, M. A.; Cussler, E. L. J.
Membr. Sci. 2006, 286, 144−152.
(11) Phillip, W. A.; Amendt, M.; O’Neill, B.; Chen, L.; Hillmyer, M.
A.; Cussler, E. L. ACS Appl. Mater. Interfaces 2009, 1, 472−480.
(12) Phillip, W. A.; O’Neill, B.; Rodwogin, M.; Hillmyer, M. A.;
Cussler, E. L. ACS Appl. Mater. Interfaces 2010, 2, 847−853.
(13) Li, L.; Schulte, L.; Clausen, L. D.; Hansen, K. M.; Jonsson, G. E.;
Ndoni, S. ACS Nano 2011, 5, 7754−7766.
ASSOCIATED CONTENT
* Supporting Information
■
S
χ-parameters for ISM and EPSM triblock systems (Table S1);
thermal annealing conditions for the reported neat and blended
ISM and EPSM materials (Table S2); SAXS patterns for two
additional Q230 network-forming blends produced from EPSM
triblock (HT1) and PS homopolymer (Figure S1); detailed
characterization of triblock T2 (SAXS and TEM in Figures S2,
S3, and S4); characterization of HEX-forming ISM triblock
(T4), EPSM triblock (HT4), and associated blends of HT4 and
homopolymers (SAXS and TEM in Figures S5 and S6,
respectively). This material is available free of charge via the
Internet at http://pubs.acs.org.
(14) Epps, T. H., III.; Cochran, E. W.; Bailey, T. S.; Waletzko, R. S.;
Hardy, C. M.; Bates, F. S. Macromolecules 2004, 37, 8325−8341.
(15) Chatterjee, J.; Jain, S.; Bates, F. S. Macromolecules 2007, 40,
2882−2896.
(16) Bailey, T. S.; Hardy, C. M.; Epps, T. H., III.; Bates, F. S.
Macromolecules 2002, 35, 7007−7017.
(17) Huckstadt, H.; Gopfert, A.; Abetz, V. Polymer 2000, 41, 9089−
̈
̈
̈
9094.
(18) Huckstadt, H.; Goldacker, T.; Gopfert, A.; Abetz, V.
̈
̈
̈
Macromolecules 2000, 33, 3757−3761.
(19) Tang, P.; Qiu, F.; Zhang, H.; Yang, Y. Phys. Rev. E 2004, 69,
031803/1−031803/8.
AUTHOR INFORMATION
Corresponding Author
*E-mail: thepps@udel.edu.
Notes
■
(20) Shefelbine, T. A.; Vigild, M. E.; Matsen, M. W.; Hajduk, D. A.;
Hillmyer, M. A.; Cussler, E. L.; Bates, F. S. J. Am. Chem. Soc. 1999,
121, 8457−8465.
(21) Bailey, T. S.; Pham, H. D.; Bates, F. S. Macromolecules 2001, 34,
6994−7008.
The authors declare no competing financial interest.
(22) Matsushita, Y.; Suzuki, J.; Seki, M. Physica B 1998, 248, 238−
242.
ACKNOWLEDGMENTS
This work was supported by NSF-NER (CBET-0707507),
NSF-CAREER (DMR-0645586), and AFOSR-PECASE
■
(23) Epps, T. H., III.; Chatterjee, J.; Bates, F. S. Macromolecules 2005,
38, 8775−8784.
8354
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355

Macromolecules
Article
(24) Meuler, A. J.; Hillmyer, M. A.; Bates, F. S. Macromolecules 2009,
42, 7221−7250.
(58) Varshney, S. K.; Jacobs, C.; Hautekeer, J. P.; Bayard, P.; Jerome,
R.; Fayt, R.; Teyssie, P. Macromolecules 1991, 24, 4997−5000.
(59) Fetters, L. J.; Lohse, D. J.; Richter, D.; Witten, T. A.; Zirkel, A.
Macromolecules 1994, 27, 4639−4647.
(25) Tureau, M. S.; Epps, T. H., III. Macromol. Rapid Commun. 2009,
30, 1751−1755.
(60) Odian, G. Principles of Polymerization; John Wiley & Sons:
Hoboken, NJ, 2004; p 692.
(26) Tureau, M. S.; Rong, L.; Hsiao, B. S.; Epps, T. H., III.
Macromolecules 2010, 43, 9039−9048.
(27) Kuan, W.-F.; Roy, R.; Rong, L.; Hsiao, B. S.; Epps, T. H. ACS
Macro Lett. 2012, 1, 519−523.
(28) Epps, T. H., III.; Cochran, E. W.; Hardy, C. M.; Bailey, T. S.;
Waletzko, R. S.; Bates, F. S. Macromolecules 2004, 37, 7085−7088.
(29) Epps, T. H., III; Bates, F. S. Macromolecules 2006, 39, 2676−
2682.
(61) Hahn, S. F. J. Polym. Sci., Part A: Polym. Chem. 1992, 30, 397−
408.
(62) Epps, T. H., III. Locating Network Phases in Linear ABC
Triblock Copolymers. Doctoral Thesis, University of Minnesota,
Minneapolis, 2004.
(63) Cochran, E. W.; Morse, D. C.; Bates, F. S. Macromolecules 2003,
36, 782−792.
(64) Tcherkasskaya, O.; Ni, S.; Winnik, M. A. Macromolecules 1996,
29, 610−616.
(30) Breiner, U.; Krappe, U.; Abetz, V.; Stadler, R. Macromol. Chem.
Phys. 1997, 198, 1051−1083.
(31) Beckmann, J.; Auschra, C.; Stadler, R. Macromol. Rapid
Commun. 1994, 15, 67−72.
(65) Yang, J.; Lu, J.; Rharbi, Y.; Cao, L.; Winnik, M. A.; Zhang, Y.;
Wiesner, U. B. Macromolecules 2003, 36, 4485−4491.
(66) Hanley, K. J.; Lodge, T. P. J. Polym. Sci., Part B: Polym. Phys.
1998, 36, 3101−3113.
(32) Stadler, R.; Auschra, C.; Beckmann, J.; Krappe, U.; Voigt-
Martin, I.; Leibler, L. Macromolecules 1995, 28, 3080−3097.
(33) Breiner, U.; Krappe, U.; Thomas, E. L.; Stadler, R. Macro-
molecules 1998, 31, 135−141.
(67) Russell, T. P.; Hjelm, R. P.; Seeger, P. A. Macromolecules 1990,
23, 890−893.
(34) Kloninger, C.; Rehahn, M. Macromol. Chem. Phys. 2007, 208,
833−840.
(68) Tyler, C. A.; Qin, J.; Bates, F. S.; Morse, D. C. Macromolecules
2007, 40, 4654−4668.
(35) Kaneko, T.; Suda, K.; Satoh, K.; Kamigaito, M.; Kato, T.; Ono,
T.; Nakamura, E.; Nishi, T.; Jinnai, H. Macromol. Symp. 2006, 242,
80−86.
(69) Sakurai, S.; Hashimoto, T.; Fetters, L. J. Macromolecules 1995,
28, 7947−7949.
(70) Kelly, J. Y.; Albert, J. N. L.; Howarter, J. A.; Stafford, C. M.;
Epps, T. H., III; Fasolka, M. J. J. Polym. Sci., Part B: Polym. Phys. 2012,
50, 263−271.
(36) Ott, H.; Abetz, V.; Altstadt, V. Macromolecules 2001, 34, 2121−
̈
2128.
(37) Dair, B. J.; Honeker, C. C.; Alward, D. B.; Avgeropoulos, A.;
Hadjichristidis, N.; Fetters, L. J.; Capel, M.; Thomas, E. L.
Macromolecules 1999, 32, 8145−8152.
(71) Bailey, T. S. Morphological Behavior Spanning the Symmetric
AB and ABC Block Copolymer. Doctoral Thesis, University of
Minnesota, Minneapolis, 2001.
(38) Mango, L. A.; Lenz, R. W. Makromol. Chem. 1973, 163, 13−36.
(39) Phinyocheep, P.; Pasiri, S.; Tavichai, O. J. Appl. Polym. Sci. 2003,
87, 76−82.
(72) Epps, T. H.; Bailey, T. S.; Waletzko, R.; Bates, F. S.
Macromolecules 2003, 36, 2873−2881.
(73) Nagpal, U.; Detcheverry, F. A.; Nealey, P. F.; de Pablo, J. J.
Macromolecules 2011, 44, 5490−5497.
(40) Santin, C.; Jacobi, M.; Schuster, R.; Santoso, M. J. Therm. Anal.
Calorim. 2010, 101, 273−279.
(74) Matsen, M. W.; Bates, F. S. J. Polym. Sci., Part B: Polym. Phys.
1997, 35, 945−952.
(41) Santin, C. K.; Jacobi, M. M.; Alegre, P.; Schuster, R. H. KGK
2007, 60, 331−335.
(75) Hashimoto, T.; Ijichi, Y.; Fetters, L. J. J. Chem. Phys. 1988, 89,
2463−2472.
(42) De Sarkar, M.; De, P. P.; Bhowmick, A. K. J. Appl. Polym. Sci.
1999, 71, 1581−1595.
(76) Balsara, N. P.; Fetters, L. J.; Hadjichristidis, N.; Lohse, D. J.;
Han, C. C.; Graessley, W. W.; Krishnamoorti, R. Macromolecules 1992,
25, 6137−6147.
(43) Balsamo, V.; Muller, A. J.; von G, F.; Stadler, R. Macromol.
̈
Chem. Phys. 1998, 199, 1063−1070.
(44) Gehlsen, M. D.; Bates, F. S. Macromolecules 1993, 26, 4122−
4127.
(77) Lin, C. C.; Jonnalagadda, S. V.; Kesani, P. K.; Dai, H. J.; Balsara,
N. P. Macromolecules 1994, 27, 7769−7780.
(78) Brandrup, J.; Immergut, E. H.; Grulke, E. A.; Abe, A.; Bloch, D.
R. Polymer Handbook, 4th ed.; John Wiley & Sons: New York, 1999; p
2005.
(45) Bhattacharjee, S.; Rajagopalan, P.; Bhowmick, A. K.; Avasthi, B.
N. J. Appl. Polym. Sci. 1993, 49, 1971−1977.
(46) Harwood, H. J.; Russell, D. B.; Verthe, J. J. A.; Zymonas, J.
Makromol. Chem. 1973, 163, 1−12.
(47) Mohammadi, N. A.; Rempel, G. L. Macromolecules 1987, 20,
2362−2368.
(48) Tureau, M. S.; Kuan, W.-F.; Rong, L.; Hsiao, B. S.; Epps, T. H.
Macromolecules 2012, 45, 4599−4605.
(49) Gotro, J. T.; Graessley, W. W. Macromolecules 1984, 17, 2767−
2775.
(50) Rangarajan, P.; Register, R. A.; Fetters, L. J. Macromolecules
1993, 26, 4640−4645.
(51) Schmalz, H.; Boker, A.; Lange, R.; Krausch, G.; Abetz, V.
̈
Macromolecules 2001, 34, 8720−8729.
(52) Tierney, N. K.; Register, R. A. Macromolecules 2003, 36, 1170−
1177.
(53) Hadjichristidis, N.; Pispas, S.; Floudas, G. Block Copolymers:
Synthetic Strategies, Physical Properties, and Applications; John Wiley &
Sons: Hoboken, NJ, 2003.
(54) Yu, J. M.; Yu, Y.; Dubois, P.; Teyssie,
1997, 38, 3091−3101.
́
P.; Robert, J. Polymer
(55) Auschra, C. Polym. Bull. 1993, 30, 257−264.
(56) Kimishima, K.; Jinnai, H.; Hashimoto, T. Macromolecules 1999,
32, 2585−2596.
(57) Allen, R. D.; Long, T. E.; McGrath, J. E. Polym. Bull. 1986, 15,
127−134.
8355
dx.doi.org/10.1021/ma301739j | Macromolecules 2012, 45, 8347−8355