Synthesis and Self-Assembly of Mixed-Graft Block Copolymers

Article abstract of DOI:10.1002/chem.201900520

Mixed-graft block copolymers (mGBCPs) consist of two or more types of polymeric side chains grafted on a linear backbone in a random, alternating, or pseudo-alternating sequence. They can phase-separate with the backbone serving as the interface of the bl

Full text of DOI:10.1002/chem.201900520

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Title: Synthesis and self-assembly of mixed graft block copolymers
Authors: Mingjiang Zhong, An N. Le, and Ruiqi Liang
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
Synthesis and self-assembly of mixed graft block copolymers
An N. Le, Ruiqi Liang, and Mingjiang Zhong*[a]
[
[
a]
b]
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Institution
Address 1
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Chemistry - A European Journal
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CONCEPT
One of the most accessible complex architectures that we
can explore is a graft polymer. Graft polymers consist of polymeric
side chains attached to a linear backbone and include both comb
and bottlebrush polymers. They have attracted interest due to
their unique rheological properties and dynamics. For example,
graft polymers with high grafting density have high entanglement
Abstract: Mixed graft block copolymers (mGBCPs) consist of two
or more types of polymeric side chains grafted from a linear
backbone in
a random, alternating, or pseudo-alternating
sequence. They can phase separate with the backbone serving
as the interface of the blocks, and the side chains dominate their
self-assembly behavior. mGBCPs are an accessible polymer
architecture for exploring the idea of encoding polymer properties
through macromolecular architecture, as there are two distinct
structural components that can be tuned: the backbone and the
side chains. In this Concept article, the current literature on the
synthesis of mGBCPs is reviewed, and advantages and
disadvantages of each synthetic method are noted. Self-
assembly of the mGBCPs is also discussed where possible.
Finally, directions for future research on mGBCP synthesis and
self-assembly are suggested.
molecular weights and extended backbone conformations due to
steric repulsion of the side chains.[6] Several copolymer variations
of graft polymers have also been investigated, including
backbone graft block copolymers (GBCPs) (Figure 1a, top),
mixed GBCPs (mGBCPs) (Figure 1a, middle), and core-shell
GBCPs (Figure 1a, bottom). There are three general synthetic
strategies for the synthesis of graft polymers: grafting-to (Figure
1b, top), grafting-from (Figure 1b, middle), and grafting-through
(
Figure 1b, bottom). Briefly, in grafting-from methods, side chains
are grown from a macroinitiator, which forms the backbone of the
graft polymer. Grafting-to methods involve attachment of pre-
synthesized side chains to a multi-functional backbone. In
grafting-through methods, the backbone is formed directly
through the polymerization of macromonomers. More
comprehensive summaries of graft polymer synthesis, physical
properties, self-assembly, and applications can be found in other
reviews.[6-7]
Introduction
Polymers with complex architecture, i.e., non-linear ones, have
been studied extensively since properties of the polymer,
including thermal properties[1] and mechanical properties are
highly dependent on the chain topology. Block copolymers
[2]
(
BCPs) with complex architecture are especially intriguing, as
their self-assembly can result in new morphologies and unique
interfaces.[ Furthermore, through rational design, polymer
architecture can provide a new handle for encoding specific
properties into a polymeric material. For example, the mechanics
of biological materials could be mimicked by a bulk ABA triblock
linear-b-graft-b-linear copolymer, in which the graft block
composed of polydimethylsiloxane (PDMS) provided softness,
the linear poly(methyl methacrylate) (PMMA) blocks provided
extensibility, and the combination of the chain topologies in the
3]
“
hard-soft-hard” triblock copolymer resulted in strain-stiffening
behavior.[
2b, 4]
Different architectural components of the molecular
design, the linear and graft blocks, contributed different properties
to the resulting material, allowing for precise tailoring of its
mechanical properties. In another example of architecturally-
encoded polymer properties, dendritic polybutadiene with three
generations of branching showed hierarchical relaxation behavior
in which each generation of the dendritic structure had a distinct
relaxation time that could be tuned by the volume fraction of the
generation.[5] This example demonstrates that through
architecture design alone, without changing the chemical
composition of the polymer, different parts of the macromolecule
could be encoded with specific viscoelastic properties.
Harnessing polymer architecture may be the key to developing
new polymeric materials with multiple functionalities and tailored
properties.
Figure 1. (a) Cartoon of backbone GBCP (top), mixed GBCP (middle), and
core-shell GBCP (bottom) and (b) cartoon of general synthetic strategies to
graft polymers: grafting-to (top), grafting-from (middle), and grafting-through
(bottom).
[
a]
A. N. Le, R. Liang, Prof. Dr. M. Zhong
Department of Chemical and Environmental Engineering, Yale
University, New Haven, CT 06511 (USA)
E-mail: mingjiang.zhong@yale.edu
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Chemistry - A European Journal
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CONCEPT
Graft copolymers may be ideal candidates for initial studies
on architecturally-encoded properties since, in some ways, they
can be viewed similarly to linear BCPs, the behavior of which has
been well-documented. Backbone GBCPs can be considered
BCPs in which the blocks are graft polymers instead of single
linear chains.[7c, 8] Sequence-defined mGBCPs in which two side
chains emanate from the same grafting junction, also known as
double-brush[9] or Janus[9a, 10] GBCPs, can be viewed as linear
diblock copolymers polymerized along the block junction.[9a, 10b, 11]
Core-shell graft copolymers may also be thought of as a series of
linear ABA triblock copolymers linked at the center of the B
block.[12] Therefore, familiar self-assembly principles and
synthetic approaches may be applied to the study of graft
copolymers, while the complex architecture opens up
opportunities for encoding specific properties into the polymer.
In this Concept article, we will focus on the synthesis and
self-assembly behaviors of mGBCPs, which consist of two or
more types of polymeric side chains grafted from a linear
the block interfaces. In this architecture, the side chains and
backbone can be separately controlled, offering two independent
handles for the tuning of polymer properties.[
As the self-assembly of mGBCPs can be affected by the
side chain sequence along the backbone, as well as the grafting
density of the side chains, examples presented in this Concept
article will be arranged based on the synthetic methods used to
obtain the mGBCPs. In the first section, general synthetic
strategies to mGBCPs, including grafting-to methods, random
11]
copolymerization
of
macromonomers,
alternating
copolymerizations, and other strategies involving grafting-from,
are discussed. The second section focuses on synthetic
strategies in which full grafting density and controlled side chain
sequence in the mGBCPs can be ensured. mGBCPs with
nontraditional side chains are reviewed in the last section.
Advantages and disadvantages of each synthetic strategy will be
noted throughout the Concept article. Although there is a wealth
of information regarding synthesis of two-component mGBCPs,
their self-assembly behavior and novel properties remain under-
researched, but we will attempt to highlight any relevant work
where possible. This Concept article will end with some directions
for future work in this emerging research area.
backbone in
a random, alternating, or pseudo-alternating
sequence. By incorporating side chains of different chemical
compositions into the polymers, various functionalities and
physical properties of the side chain polymers can be integrated
into the GBCP, while still retaining the distinct, intrinsic properties
of those polymers as well as the unique features of a graft polymer
architecture (Figure 2c). This is in contrast to copolymerization in
a linear polymer, which has traditionally been used to incorporate
additional functionalities into polymers or to modify their
properties (Figure 2a).[13] Copolymerization of small-molecule
monomers results in a polymer with properties between those of
the homopolymers or with a mixture of functionalities, but other
characteristics of the polymer, such as molecular-scale
heterogeneity, may be altered due to the change in the chemical
structure of the polymer chain. Another key distinction is that the
repeating chemical units in an mGBCP, i.e., the side chains, are
macromolecular. Thus, they retain the ability of BCPs to form
phase separated nanostructures. mGBCPs can self-assemble
into nanostructures in which the backbones of the GBCPs form
General synthetic routes to mGBCPs
Synthesis of mGBCPs based solely on grafting-to methods
Synthetic routes to mGBCPs involving grafting-to strategies
typically rely on “click” reactions or other highly efficient coupling
reactions,[14] as these reactions can proceed to high conversion,
even for reactions between macromolecular species. For
example, a straightforward route to synthesizing an mGBCP with
randomly distributed side chains is to use copper-catalyzed azide-
alkyne cycloaddition (CuAAC) click reactions between alkyne
end-functionalized polymer side chains and an azide-
functionalized poly(glycidyl methacrylate) backbone, PGMA-
N
3
.[15] Using poly(n-butyl acrylate) (PnBA) and poly(2-
cinnamoyloxyethyl methacrylate) (PCEMA) side chains (M
7.9 kDa and 31.4 kDa, respectively) and grafting densities <30%,
n
=
1
the grafting-to reactions proceeded quantitatively, and the grafting
densities could be varied by changing the feed ratio of the
3
PnBA/PCEMA side chains to the PGMA-N backbone in the click
reaction.[15b] The grafting density was found to impact the domain
size and ordering of the self-assembly. Due to diminished side
chain stretching, decreasing the grafting density from 29.5% to
9.8% at a fixed ratio of PnBA/PCEMA decreased the domain
spacing from 26 nm to 17 nm. Improved long-range ordering of
the self-assembled lamellae with decreased grafting density could
be explained by an increase in side chain mobility in these
mGBCPs with relatively long side chains. It is important to note
that in this work, as is typical with synthetic routes involving
grafting-to strategies, the grafting density was relatively low; for a
20% grafting density, the side chains were separated by an
average of 5 monomer units, or 10 C–C bonds. Nevertheless, the
advantage of this synthetic strategy is its simplicity. The synthesis
Figure 2. Comparison of copolymerization in linear polymers with linear BCPs
and mGBCPs.
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
could be readily modified to incorporate three different side chains, to syntheses. Note that the purification of these GBCPs can also
and a “random” distribution of side chains could be achieved
despite differences in reactivity of the alkyne-functionalized side
chains by utilizing a multi-step reaction sequence.[15c]
be challenging due to the need to remove unreacted
macromolecular species.
Better control over side chain sequence in a grafting-to
strategy can be realized by utilizing v-shaped side chains, which
incorporate two different polymeric side chains linked with an
alkyne functionality.[16] By grafting these v-shaped diblock
Grafting-through random copolymerization of macro-
monomers
Although still limited by steric hindrance, grafting-through
methods can offer improvement on the grafting density, compared
to grafting-to strategies. This subsection summarizes works in
which mGBCPs were synthesized via grafting-through random
copolymerizations of macromonomers of similar reactivities. In
the examples presented here, the side chain sequence was not
confirmed to be controlled, unlike in the alternating
copolymerizations discussed in the next subsection. However, in
all cases, NMR analysis was used to verify that the two
macromonomers were consumed at the same rate throughout the
reaction or that the macromonomers had similar polymerization
rates in homopolymerizations. Both are evidence that the
copolymerizations were statistical, not blocky or gradient.
3
copolymer side chains to a PGMA-N backbone via CuAAC click,
an mGBCP could be synthesized in which one of each side chain
was present at every grafting point, ensuring a 1:1 ratio and even
distribution of side chains along the backbone. Significant steric
hindrance due to the branched side chain structure decreased the
efficiency of the click reaction, especially for side chains of higher
molecular weight. However, compared to the previously
introduced grafting-to method, higher grafting densities were
obtained since double the number of side chains were introduced
per click reaction. For an mGBCP containing polycaprolactone
(
PCL) and polystyrene (PS) side chains, PGMA100-g-v(PCL10-b-
PS24), a grafting density of 80.6% was achieved.
An
early
example
of
randomly
copolymerized
The Thayumanavan group recently demonstrated another
elegant way to ensure a controlled sequence of side chains via a
grafting-to strategy by utilizing sequential nucleophilic additions to
an alkyne-functionalized methacrylate-based backbone (Scheme
macromonomers involved the free radical polymerization (FRP)
of poly(2-vinylpyridine) (PVP) and PMMA side chains end-
functionalized with methacrylate.[
18]
The conversions of the
macromonomers were low (26–50%), likely due to their relatively
high molecular weights (>3.7 kDa) causing excessive steric
hindrance. This work draws attention to the difficulty of
overcoming steric hindrance in grafting-through strategies. Other
examples of copolymerizations of methacrylate-based
macromonomers utilized shorter side chains, reducing the steric
hindrance concern.[19] For example, atom transfer radical
polymerization (ATRP) was used to synthesize an mGBCP with
1
).[17] The first nucleophilic addition of a thiol end-functionalized
side chain was based on thiol-yne click chemistry catalyzed by
triethylamine. The reaction resulted in quantitative conversion of
the alkyne, but the mildly basic conditions prevented a second
addition to the alkene. The second thiol end-functionalized side
chain could then be introduced via a Michael-type addition
catalyzed by a stronger organic base such as triazabicyclodecene
(
TBD). The conversion of alkene was quantitative, resulting in a
hydrophobic PDMS (M
n
n
= 1.0 kDa) and hydrophilic PEO (M = 1.1
kDa) side chains (Scheme 2a).[ This mGBCP showed a phase-
19a]
fully grafted mGBCP with controlled side chain sequence.
Although different polymer side chains, including PS and
poly(ethylene oxide) (PEO), were introduced as the second side
chain, this work only explored octane-1-thiol as the first side chain
to be introduced. Future work using this synthetic strategy may
demonstrate that a broader scope of polymer side chains can be
used.
separated bulk morphology, as the differential scanning
calorimetry (DSC) analysis indicated
a
glass transition
temperature (T ) feature corresponding to amorphous domains of
g
PDMS and a melting peak corresponding to the semi-crystalline
domains of PEO. Wide-angle X-ray scattering and small-angle X-
ray scattering (SAXS) also indicated a loss of crystallinity and
order in the phase separated structures above the melting point
of PEO. Below the melting point of PEO, the domain spacings
ranged from 10.0–12.5 nm, depending on the PEO/PDMS
composition. Another study was reported by the same group in
which both side chains, an octadecyl methacrylate and PEO-
These three examples highlight the importance of using
highly efficient reactions for the synthesis of mGBCPs via grafting-
to methods, as steric hindrance is an important consideration. As
such, grafting density is a major concern and limitation in grafting-
n
methacrylate (M = 1.1 kDa), were (semi)crystalline, but packing
frustration caused by the grafted architecture was suggested to
result in amorphous domains of the octadecane.[ Similar work
by the Terashima group studied the bulk and solution self-
20]
n
assembly of random GBCPs with PEO (M = 480 Da) and
octadecane side chains synthesized via ruthenium-catalyzed
living radical copolymerization or free radical copolymerization of
the acrylate-functionalized side chains (Scheme 2b).[21] Due to the
lower molecular weight of the PEO block, compared to the
previous example, and the flexibility of the acrylate backbone,
phase separation of the side chains resulted in amorphous
Scheme 1. Synthetic route to mGBCPs via sequential nucleophilic additions: (i)
thiol-yne click reaction with octyl thiol with triethylamine catalyst and (ii) Michael-
type addition with other thiol-functionalized reagents with TBD catalyst. Adapted
from Ref. [17] with permission from the Royal Society of Chemistry.
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Chemistry - A European Journal
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CONCEPT
regions containing PEO and the acrylate backbone and crystalline
regions of the octadecane side chains. Depending on the molar
ratio of PEO/octadecane macromonomers, spherical or lamellar
morphologies (d* = 5–6 nm) were obtained, and the lamellar d-
spacings could be tuned based on this molar ratio (50-80 mol%
octadecyl acrylate) while the side chain molecular weights were
fixed. Spherical micelles and vesicles were also formed by
aqueous solution self-assembly, and reverse micelles with size
dependent on the copolymer composition were observed in
hexanes. Although the copolymerization of methacrylate and
acrylate functionalized monomers is a versatile method of
synthesizing mGBCPs, this method is still limited by the
requirement of low molecular weight side chains.
High conversions of macromonomers with relatively large
molecular weight can be obtained by using ring opening
metathesis polymerization (ROMP) of norbornene-functionalized
macromonomers to synthesize mGBCPs. Ring strain in the
norbornene functionality, along with a highly active Ru-based
Grubbs catalyst, contribute to the efficiency of the grafting-
through reaction.[22] For example, ROMP copolymerization of
norbornene-functionalized poly(lactic acid) (PLA) (M
and PnBA (M = 4.0 kDa) reached >97% conversion (Scheme
c). SAXS analysis of these mGBCPs with different numbers
n
= 4.7 kDa)
n
[8d]
2
of PLA/PnBA side chains revealed that only symmetric random
copolymers, i.e., the number of PLA side chains equaled the
number of PnBA side chains, phase separated to form ordered
lamellar morphologies. The d-spacings for all symmetric GBCPs
were 14.3 ± 0.3 nm, regardless of the backbone lengths,
indicating that the polynorbornene backbone formed the interface
of the blocks. Likewise, the order-disorder transition temperature
Scheme 2. Synthetic routes to mGBCPs based on grafting-through random
copoolymerizations of macromonomers: (a) methacrylate-functionalized PDMS
and PEO; (b) acrylate-functionalized PEO and octadecane; (c) norbornene-
functionalized PLA and PnBA. Adapted from Refs. [19], [21], and [8d] with
permission from the American Chemical Society.
(TODT) was consistent for all backbone lengths, at 80 ± 5 °C,
suggesting that the TODT was determined by the side chain length,
not backbone length, further evidence of the phase separation
along the backbone of the GBCP. Meanwhile, asymmetric
random copolymers (fPLA = 0.63, 0.79) displayed a disordered
morphology. The inability of the GBCPs to form well-ordered non-
lamellar morphologies at asymmetric volume fractions was
attributed to the rigidity of the backbone due to the densely grafted
side chains, which prevented the GBCP from coiling.
While studies of phase separation in mGBCPs based on
random copolymerization of macromonomers have been
informative, a better defined synthesis with controlled side chain
sequence may be more conducive to theoretical modeling and
elucidation of structure-property relationships.
respectively. Ishizu et al. synthesized an alternating GBCP with
PS and PMMA side chains starting from the alternating
copolymerization of vinylbenzyl (VB)-functionalized PS (M = 5.0
n
kDa) and MI bearing a phenol moiety (Scheme 3).[23] After the free
radical copolymerization, α-bromoisobutyryl bromide (BiBB) was
installed on the phenol groups through esterification, and PMMA
was subsequently grafted from the ATRP initiator. In another case
combining grafting-from and grafting-to methods with an
alternating copolymerized backbone, MI functionalized with an
ATRP initiator was copolymerized with 4-vinylbenzyl azide to form
a macroinitiator backbone, which was first used for the grafting-
from polymerization of PMMA (DP ~ 12).[24] Next, alkyne-
n
functionalized poly(N-isopropylacrylamide) (PNIPAM) (M = 2.8
kDa) side chains were linked to the PMMA grafted polymer
through CuAAC click to form the mGBCP. In water, the GBCPs
self-assembled into spherical micelles (30–40 nm diameter) with
a PMMA interior and a thermoresponsive PNIPAM corona. It is
worthwhile to note that the grafting efficiency of the click reaction
was only ~80%, likely due to steric hindrance between the grafted
PMMA and PNIPAM side chains. While the side chain sequence
is controlled in methods involving alternating copolymerization
followed by grafting-from or grafting-to routes, full grafting density
cannot be ensured, as the initiation efficiency and quantitative
coupling between the side chain and backbone cannot be
guaranteed.
Synthesis
copolymerizations
of
mGBCPs
based
on
alternating
One way to obtain a sequence-defined backbone in
mGBCPs is to utilize alternating copolymerizations. For example,
the copolymerization of styrene and maleimide (MI) based
monomers can be combined with grafting-through, grafting-from,
and/or grafting-to strategies to synthesize alternating GBCPs.
This is accomplished by functionalizing the styrene or MI
monomers with polymeric side chains, initiators for side chain
polymerizations, or reaction sites for side chain tethering,
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Chemistry - A European Journal
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CONCEPT
Scheme 3. Synthetic route to mGBCP based on an alternating copolymerization of VB-functionalized PS and phenol-functionalized MI, followed by modification
with ATRP initiators and grafting-from polymerization of MMA. Adapted from Ref. [23] with permission from the American Chemical Society.
Synthesis of mGBCPs based on grafting-from methods
combining grafting-through and grafting-from reactions,
This subsection will focus on other grafting-from syntheses
of mGBCPs besides those involving alternating copolymerization.
As mentioned in the previous subsection, one difficulty with
grafting-from strategies is that if the initiation efficiency is not
extremely high, the grafting density will not be 100% and grafted
side chains may have a broad molecular weight distribution.[25]
Therefore, these GBCPs may not be as well-defined as those
synthesized from grafting-through reactions of macromonomers,
for instance. Grafting-from reactions through radical-mediated
polymerizations also typically require dilute conditions and low
conversions to minimize the risk of intermolecular coupling, which
would lead to crosslinking between the GBCPs.[26] On the other
hand, an advantage of a grafting-from method is that side chains
with functionalities or solubilities that are not amenable to grafting-
through reactions can be incorporated, and there is less concern
for steric hindrance. These GBCPs can also be easier to purify
since only small-molecule monomers must be removed.
n
poly(ethylene glycol) methyl ether acrylate (PEOMEA) (M = 454
Da) was first polymerized by ATRP into a grafted homopolymer
with PEO side chains (PPEOMEA) (Scheme 4).[ ATRP initiators
were then installed directly on the grafted backbone in a
sequence-controlled manner using lithium diisopropylamide
(LDA) and α-bromopropionyl chloride without side reactions with
other functionalities on the PPEOMEA. Importantly, compared to
other methods of introducing ATRP initiators into the backbones
of grafted polymers, this method resulted in the formation of C–C
bonds, which are more stable than ester linkages. NMR analysis
also indicated that the introduction of ATRP initiators was
quantitative. PS side chains (DP = 10–25) were then grafted from
the macroinitiator. Solution self-assembly in water showed that
spherical micelles of 150–300 nm formed, and the critical micelle
concentrations were ~ 10-7 g/mL, lower than those of linear BCPs,
which was speculated to be a result of the BCP architecture and
asymmetric composition. While the side chain sequence and
macroinitiator synthesis were well-controlled in this work, the
initiation efficiency and grafting density were still not confirmed.
Other works have combined grafting-from with grafting-to
strategies.[10a, 30] One such synthetic route that was particularly
29]
In one example of the synthesis of an mGBCP that relied
solely on grafting-from, a poly(2-hydroxyethyl methacrylate)
(
PHEMA) backbone was synthesized and randomly esterified
with BiBB to obtain a macroinitiator with initiation sites for both
ATRP and ring opening polymerization (ROP).[27] Tin(II) 2-
ethylhexanoate served a dual role as a catalyst for ROP and a
reducing agent in the activator generated by electron transfer
efficient combined grafting-to and grafting-from reactions
simultaneously.[
10a]
An acrylate-based backbone was synthesized
from an alkyne and 2-bromopropionate containing monomer. This
macroinitiator backbone ensured that two side chains would be
linked to each backbone repeat unit, maintaining a controlled
(
AGET) ATRP, allowing for the simultaneous grafting of poly(L-
lactic acid) (PLLA) and PS side chains from the macroinitiator to
obtain an mGBCP with random side chain sequence. Although
the initiation efficiency was not formally studied, the relatively high
dispersities (Ð = 1.41–1.80), especially for GBCPs with lower
molecular weight, may be an indication of poor initiation efficiency.
Nevertheless, the advantage of only utilizing grafting-from
reactions is the facile purification; the GBCP could be effectively
purified by simple precipitation, avoiding fractionation
precipitation, column chromatography, and preparative gel
permeation chromatography that are usually necessary to remove
excess macromolecular reactants in other synthetic strategies.
A grafting-from strategy can also be combined with grafting-
through or grafting-to methods.[28] In a clever synthetic route
sequence. Since both CuAAC click and ATRP utilize
a
Cu(I)/ligand catalyst system, azide-functionalized PEO (M = 775
n
Da) could be grafted to the backbone while ethyl acrylate (and
other vinyl monomers) was grafted from the 2-bromopropionate
ATRP initiator in a one-shot fashion. The efficiency of the grafting-
3
to reaction as evaluated by the conversion of the PEO-N was
found to be 92%. Initiation efficiency was also determined to be
complete through 13C NMR analysis of a model ATRP reaction. A
key point to remember is that while full grafting density oftentimes
cannot be achieved in grafting-from (and grafting-to) methods, it
is important to carefully characterize the GBCP products to fully
understand their macromolecular structures.
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Chemistry - A European Journal
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CONCEPT
Scheme 4. Synthetic route to mGBCP with PS and PEO side chains via grafting-through and grafting-from strategies. Adapted from Ref. [29] with permission from
the American Chemical Society.
Synthetic routes resulting in mGBCPs with through the grafting-through synthesis of VB-functionalized and
controlled grafting density and side chain MI-functionalized side chains. For example, of VB-PEO (M
n
= 870
= 1.7 and 2.2 kDa)
were confirmed to have low reactivity ratios (r = r = 0.08),
sequence
Da) and MI-poly(ε-caprolactone) (PCL) (M
n
1
2
indicating that the free radical copolymerization was indeed
alternating, despite the styrene and MI functionalities being
appended with macromolecules.[ Crystallization behavior of the
GBCP was studied, revealing a dynamically confined crystalliza-
tion process in which the PCL side chains crystallized within a
confined domain concurrently with the formation of PCL
spherulites (Figure 4).[ These processes occurred simultane-
ously because, unlike in linear crystalline BCPs, the rigidity of the
GBCP architecture required a parallel alignment of the backbones
for crystallization to take place within the confined lamellae.
Grafting-through
macromonomers
alternating
copolymerization
of
33]
The most well-defined mGBCPs exhibit a sequence-defined
backbone as well as full grafting density, which typically can be
achieved only via grafting-through methods. Alternating
copolymerization of macromonomers can be an effective strategy
to fulfill both of these requirements. Ishizu et al. have developed
a method of obtaining alternating copolymerizations from VB- and
methacryloyl (MC)-functionalized side chains by introducing
34]
tin(IV) tetrachloride (SnCl
4
) into the FRP as a Lewis acid (Figure
[
31]
3a). The Lewis acid increased the electron-accepting ability of
Grafting-through polymerizations of branched macro-
monomers
the MC functionality, allowing for the formation of 1:1 donor-
acceptor complexes between the MC and VB side chains. The
alternating copolymerization thus proceeded through
homopolymerization of these complexes. The aqueous solution
self-assembly of an mGBCP with VB-PS (M = 2.3 kDa) and MC-
PEO (M = 800 Da) side chains, as well as with VB-PEO (M
.0 kDa) and MC-poly(propylene oxide) (PPO) (M = 1.2 kDa) side
The mGBCPs self-assembled into
rod-shaped aggregates with high aspect ratios due to the
remarkably long backbone lengths (DP = 890–3030 for PS/PEO
and DP = 806 for PEO/PPO) of the GBCPs, enabled by the FRP
a
The grafting-through polymerization of branched
macromonomers (BMMs) to obtain mGBCPs has recently gained
popularity. Branched macromonomers can be viewed as linear
diblock copolymers with a polymerizable functionality at the block
junction. Typically, norbornene is used as the polymerizable
functionality since it is highly active in ROMP, but a synthetic route
based on an itaconate-functionalized BMM has also been
reported.[9c] As with the alternating copolymerization of
macromonomers, the advantage of this synthetic strategy is that
a full grafting density can be ensured and side chain sequence is
also controlled in a pseudo-alternating fashion, resulting in a
GBCP with a defined structure. The pseudo-alternating sequence
ensures that the side chain composition is relatively homogene-
n
n
n
=
2
n
[
32]
chains, was then studied.
(
Figure 3b,c).
As mentioned previously, copolymerization of styrene and
maleic anhydride is well-established alternating
a
copolymerization that also does not require the addition of a Lewis
acid. This reaction can be adapted to obtain alternating mGBCPs
Figure 3. (a) Synthetic route to mGBCP based on alternating copolymerization of VB-PEO and MC-PPO; (b) Cartoon depicting aqueous solution self-assembly of
mGBCPs synthesized via alternating copolymerizations of VB-PS and MC-PEO or VB-PEO and MC-PPO; (c) SEM images of rod-shaped aggregates of an mGBCP
3
synthesized from VB-PEO and MC-PPO in aqueous solution at 0.001 kg/m . Adapted from Ref. [32b] with permission from Kluwer Academic Publishers.
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
while the remaining hydroxyl group was used as an initiator for
n
the ROP of lactide to form the BMM with M = 4.3–8.9 kDa
Scheme 5a).[ The conversions of the BMMs in ROMP were
9b]
(
markedly lower for BMMs of increasing molecular weight and for
longer backbone lengths (up to DP = 250), evidence of the ROMP
being limited by steric hindrance. Compared to the corresponding
BMMs, the GBCPs were less disposed to form intermolecularly
self-assembled structures in both organic and aqueous solution,
instead forming unimolecular micelles. Presumably, the rigid
backbone of the GBCPs prevented them from ordering efficiently
in solution.
It is worthwhile to mention that the structure of the
norbornene derivatives has a significant impact on the success of
the ROMP. While Cheng et al. reduced steric hindrance effects
by including a spacer chain in the design of the BMM, work by the
Fontaine group illustrated the limitations of ROMP when the
BMMs are too crowded at the norbornene junction.[36] When PEO
and PCL side chains were directly linked to the norbornene
n
without a spacer (Scheme 5b), the conversion of the BMM (M =
4
5
.0 kDa) in ROMP was very limited (45% for a backbone DP of
0). As a comparison, conversion of the highest molecular weight
= 8.9 kDa) reached a conversion
BMM studied by Cheng et al. (M
n
of 84% for the same backbone DP. Besides the inclusion of a
spacer chain, the nature of the anchor group on the norbornene
derivative has also been found to affect the activity of the
macromonomers.[37]
Making use of a spacer chain in their BMM synthesis, the
Johnson group developed a synthetic method to allow for ROMP
of BMMs of M
n
up to 20 kDa.[10b] The norbornene derivative also
Figure 4. Cartoon depicting steps in the dynamically confined crystallization
process of mGBCPs with PCL and PEO side chains: (a) alignment of mGBCPs
at the front of the crystals; (b) formation of a confined space between GBCP
backbones; (c) crystallization of PCL within the confined space. Adapted from
Ref. [34] with permission from Elsevier.
allowed for different side chains to be readily incorporated through
CuAAC click and esterification reactions, and the self-assembly
behavior of GBCPs with a range of side chain compositions was
studied. In a series of GBCPs with PS and PDMS side chains of
varying molecular weight, the bulk morphologies ranged from
hexagonal cylinders (fPS = 0.30, 0.38) to lamellae (fPS = 0.46, 0.54)
to a coexistence of lamellae and gyroids (fPS = 0.60, 0.63) to
hexagonal cylinders of PDMS (fPS = 0.66, 0.74). Similarly to
previously discussed studies of self-assembly of GBCPs, the side
chain composition, not the backbone lengths, dictated the
morphologies observed, indicating that the side chains were
phase separated along the length of the backbone. The
coexistence of phases was speculated to originate from the broad
molecular weight distribution of the GBCP backbone, but this
effect was not investigated further. Other features of the self-
assembly that were unique to the molecular architecture were
rapid self-assembly kinetics due to limited chain entanglement
and a slight increase in domain spacings of the GBCPs compared
to the corresponding BMMs, attributed to chain stretching due to
the densely grafted backbone. The thin film self-assembly of the
PS-branch-PDMS GBCPs was also investigated for potential
applications in lithography and nanopatterning.[
ous, as while AB-, AA-, and BB- side chain sequences are all
possible, block lengths greater than 2 (i.e., AAA- or BBB-
sequences) are avoided.[11] The synthetic route also allows for
facile characterization of the side chains, i.e., BMMs,
independently of the backbone polymerization and comparison of
the BMM to the corresponding GBCP. However, major drawbacks
include steric hindrance in the backbone polymerization and
challenging purification to remove unreacted BMMs.
The polymerization of diblock BMMs was first conceived by
Cheng and Yang in a study in which a norbornene-based BMM
(
n
M = 2.3 kDa) containing PS and PVP side chains was
[
35]
synthesized via anionic polymerization.
A 10 C–C spacer
between the norbornene and the branching point, along with side
chains with relatively low molecular weight, reduced steric
hindrance and allowed for reasonable conversions of the BMMs
(
77% and 94% for a backbone DP of 50 and 10, respectively).
38]
Extending their method to utilize more accessible polymerization
reactions, the same group later designed a BMM based on
norbornene linked with a tetraethylene oxide spacer to a
branching point with two hydroxyl groups.[9a, b] One hydroxyl group
could be used for an esterification reaction with PEO-COOH,
As noted by the Johnson and Ross groups, a distinctive
attribute of mGBCP self-assembly is that the domain size is
decoupled from the thermodynamic tendency for phase
separation, the segregation strength χN.[
10b, 38]
In linear BCPs, the
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
Scheme 5. Synthetic routes to mGBCPs via grafting-through polymerization of branched macromonomers based on norbornene (a) with a tetraethylene oxide
spacer and (b) with PCL and PEO side chains directly appended. Adapted from Refs. [9b] and [36] with permission from the American Chemical Society and Wiley
Periodicals, respectively.
degree of polymerization N determines the domain size and also
contributes to this segregation strength, thereby setting a lower
limit on the domain sizes that can be obtained through phase
separation.[39] In contrast, for mGBCPs, ultra-small nanodomain
sizes can be achieved, as the side chain length, which determines
the domain size, can be decreased, while still maintaining a high
enough molecular weight to ensure phase separation. In fact, the
stability of phase separation has been found to increase upon
formation of the GBCP backbone, as the block interfaces are
n
chains were relatively short (M < 1 kDa), high BMM conversions
could be obtained despite the side chains being tethered directly
to the norbornene. Similarly to previous work, SAXS data of
GBCPs and their corresponding BMMs showed that the domain
spacings were dependent on the side chain lengths. Besides a
slight increase in domain spacing after polymerization of the
GBCP backbone due to side chain stretching, the domain
spacings and morphologies were otherwise unchanged by the
g
backbone length (Figure 5c). At the same time, the T and storage
covalently linked, decreasing the entropic penalty of self-
modulus both increased with increasing backbone length (Figure
5d). The backbone-dependent thermomechanical properties were
reflected by the physical states of the samples; the sample with a
backbone DP of 1, i.e., the BMM, was a viscous liquid, while a
backbone DP of 10 gave a soft solid, and a backbone DP of 50
formed a free-standing film (Figure 5e). This systematic study
confirmed that BCP nanostructures and thermomechanical
properties could be independently encoded into two different
features of the mGBCP architecture, the side chain length and
backbone length, respectively.
assembly.[
10b]
This effect enables GBCPs to phase separate,
while their corresponding BMMs may be disordered. Furthermore,
work by the Zhong and Johnson groups indicated that the GBCP
architecture decreased the dependence of the segregation
strength on χ, allowing for phase separation with small
nanodomains to be obtained from polymer combinations of
relatively low χ, such as PS/poly(tert-butyl acrylate) (PtBA) (d* =
1
1.1 nm), PDMS/PEO (d* = 7.0 nm), and PDMS/PtBA (d* =10.1
nm).[
11]
The same work also elaborated on the concept of
Although synthetic routes based on grafting-through
polymerization of branched macromonomers must be carefully
designed to minimize steric hindrance, this method provides well-
defined mGBCP products that can be reliably investigated in
systematic structure-property studies.
independently tuning polymer nanostructures and bulk properties
via the mGBCP architecture. A series of mGBCPs of varying
backbone lengths and side chain lengths was synthesized by
ROMP of norbornene-functionalized BMMs consisting of
oligomeric PDMS and PLA side chains (Figure 5a). Since the side
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
Figure 5. (a) Synthetic route to mGBCPs with oligomeric PDMS and PLA side chains; (b) transmission electron microscopy image of (PDMS15-branch-PLA16
c) SAXS profiles of BMM and GBCPs of PDMS15-branch-PLA16; (d) backbone length, [BMM] /[G3] , dependent bulk properties of PDMS-branch-PLA GBCPs; (c)
macroscopic appearance of BMM (viscous liquid, left), corresponding GBCP with [BMM] /[G3] = 10 (tacky solid, middle), and [BMM] /[G3] = 50 (glassy solid, right).
G3: Grubbs third generation catalyst. Adapted from Ref. [11] with permission from Wiley-VCH.
200
) ;
(
0
0
0
0
0
0
mGBCPs with untraditional side chains
The cyclopolymerization resulted in multicyclic GBCPs with cyclic
PEO and PLLA side chains (Figure 6a). The self-assembly
behavior and novel properties of these GBCPs are still under
investigation. A study on supramolecularly formed mGBCPs
utilized a loosely grafted polymer with a PEO backbone (300 Da,
mGBCPs with nonlinear side chains
6
00 Da and 1 kDa segments between grafts) with two docosyl
side chains emanating from each grafting junction (Figure 6b).[
Crystallization of the docosyl side chains drove the PEO
backbone segments to fold, resulting in a sequence-controlled
mGBCP with linear docosyl side chains and looped PEO side
chains (Figure 6c). These mGBCPs self-assembled into lamellae
with domain spacings dependent on the PEO segment lengths (d*
= 4–6.4 nm). However, since a model system in which the repeat
units were not linked also phase-separated in a similar manner,
this self-assembly was more crystallization-driven than
architecture-driven. The combination of different polymer
architectures into the mGBCP architecture is in its early stages,
but these hierarchical architectures may be a new avenue for
encoding novel properties into BCPs.
41b]
While all of the previous examples have been limited to mGBCPs
containing linear side chains, a few examples have explored the
synthesis and self-assembly of mGBCPs with dendritic or cyclic
side chains. An early example reported the grafting-through
synthesis via Suzuki polycondensation of a branched Suzuki-type
monomer bearing dendritic hydrophobic and hydrophilic side
chains.[
40]
Langmuir-Blodgett experiments indicated that the
amphiphilic mGBCPs self-assembled on the surface of the water
with the hydrophilic domains in contact with water and
hydrophobic domains exposed to the air. mGBCPs with dendritic
and linear side chains have also been synthesized by alternating
copolymerization of a styryl dendron with maleic anhydride
functionalized with an ATRP initiator, followed by a grafting-from
reaction of PtBA and subsequent hydrolysis to poly(acrylic acid).
The dendritic side chains were hypothesized to increase the
rigidity of the backbone.
mGBCPs with mesogen side chains
There have been several reports of mGBCPs with cyclic
side chains either covalently or supramolecularly formed.[41] The
covalently formed mGBCPs were synthesized by random
copolymerization of α,ω-norborneneyl end-functionalized PEO
A couple of studies have incorporated mesogen side chains into
mGBCPs to open up possibilities for magnetic field alignment of
the GBCP self-assembled structures or for their use in functional
= 5.0 kDa) side chains by ROMP.[41a]
[42]
(
M
n
= 5.1 kDa) and PLLA (M
n
materials. In one example, a liquid-crystalline (LC) mGBCP
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
Figure 6. (a) mGBCPs with cyclic side chains synthesized via random copolymerization of α,ω-norborneneyl end-functionalized PEO and PLLA; (b) Synthetic route
to a loosely grafted polymer with PEO backbone and docosyl side chains; (c) Crystallization-driven self-assembly of the loosely grafted polymer into an mGBCP
with looped side chains. Adapted from Refs. [41a] and [41b] with permission from the American Chemical Society and Wiley Periodicals, respectively.
was synthesized by random copolymerization of norbornene-
chains are not entangled.[45] Although the effect of grafting density
on the self-assembly of mGBCPs has not yet been systematically
studied, various examples presented above preliminarily
demonstrated that a densely grafted backbone can decrease the
ability of mGBCPs to self-assemble into morphologies with
interfaces of high curvature, hinder their long-range ordering,
increase their self-assembled domain sizes due to side chain
stretching, and speed self-assembly kinetics due to a lack of chain
entanglement. It should be noted that the chemical structure of
the GBCP backbone itself influences the grafting density, which
can be defined as a ratio of the number of side chains per atoms
in the backbone, z. For polynorbornene backbones based on
norbornene macromonomers with a single side chain, z = 0.2,
whereas for polyacrylate or polymethacrylate backbones with a
single side chain per repeating unit, z = 0.5. Likewise, z = 0.4 for
n
functionalized PEO (M = 2.0 kDa) and cholesteryl mesogen side
chains.[43] Like other mGBCP examples, the domain size of the
phase separation was dependent on the chain length, leading to
12–15 nm domain spacings. However, due to the mesogen side
chains, ordering at a second length scale was also observed, and
SAXS data also indicated LC layer spacings of 3–7 nm
corresponding to smectic mesophases. The incorporation of LC
mesogens into the mGBCPs enabled the development of a
material with hierarchical ordering on multiple length scales,
which can be exploited in potential applications in photonics and
stimuli-responsive materials.
Outlook
norbornene BMMs, and
z
=
1
for polyacrylate and
polymethacrylate backbones with two side chains per repeating
unit. Lower grafting densities can be obtained by
copolymerization with a diluent that does not contain a side chain,
while higher grafting densities might be obtained by increasing the
number of branches in a BMM. Systematic studies on a well-
defined mGBCP system to investigate the effect of grafting
density on self-assembly behaviors would be extremely
informative, albeit challenging to synthesize and fully
characterize.
Throughout this Concept paper, the control over the
macromolecular structure of mGBCPs was emphasized since
different synthetic methods offer varying degrees of control over
the grafting density and side chain sequence. The grafting density
is particularly important for the conformation of the GBCPs and
their entanglement.[44] Two distinct regimes can be defined: in the
comb regime, low grafting density allows the backbone to coil and
side chains to overlap, while in the densely grafted bottlebrush
regime, the backbone and side chains are extended and side
The influence of side chain sequence on mGBCP self-
assembly also has not yet been fully investigated and understood.
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
However,
preliminary
work
has
indicated
that
a
architecture could be integrated into a higher order architecture.
For example, one such architecture that has been investigated
combined backbone and mixed GBCPs in a structure comprising
one grafted block with A/C mixed side chains and another block
with B/C mixed side chains (grafted A/C-b-B/C) in which A was a
hydrophobic alkyl side chain, B was a fluorinated side chain, and
C was a hydrophilic PEO side chain.[ In aqueous solution,
orthogonal self-assembly of the hydrophobic and fluorinated side
chains led to the formation of double core micelles and
multicompartment micelles. Another architecture that is currently
being investigated combines two-component mGBCPs with a
grafted homopolymer into a backbone-compartmentalized GBCP
(grafted A/B-b-C). Like the previous example, this architecture
combines interfaces oriented along the GBCP backbone and
interfaces oriented perpendicularly to the backbone, and these
orthogonal interfaces may yield novel bulk or thin-film self-
assembled morphologies that are potentially useful for nano-
patterning purposes.
(
pseudo)alternating side chain sequence may be important for
[
11]
obtaining well-controlled and predictable phase separation.
The controlled side chain sequence avoids possible formation of
nonuniform microdomains resulting from compositional
heterogeneity along the backbone, which may occur with
randomly grafted side chains.
53]
Numerous studies presented in this Concept paper have
shown that the side chain molecular weights and compositions
dominate the self-assembly behaviors of mGBCPs, but the
backbone has been speculated to play a small role in a few cases,
such as in the coexistence of two morphologies. Furthermore, the
length of the backbone may be critical in the self-assembly
behavior of mGBCPs in the limit of low backbone degree of
polymerization, i.e., when the side chain lengths are much longer
than the backbone length.[46] In this limit, the mGBCPs become
increasingly similar to miktoarm star polymers, and the self-
assembly behaviors are nearly identical to those of backbone
GBPCs with short backbones (degree of polymerization of 6). The
role of the backbone molecular weight distribution remains an
open question, as does the role of the chemical structure of the
backbone structure in the self-assembly of mGBCPs. The
backbone can be expected to become of increasing importance
as the side chain lengths become shorter since the backbone then
represents a larger volume fraction of the mGBCP.[47] Especially
for a more rigid backbone, such as a polynorbornene backbone,
or one with a lengthy spacer chain, there is ambiguity as to where,
exactly, the backbone resides at the block interface and how its
structure affects how the ability of the side chains to phase
separate at that interface.
The scaling up of the synthesis of mGBCPs is another
challenge that needs to be addressed in order to be able to utilize
these polymers in any practical applications. For instance, scaling
up can be problematic for GBCPs synthesized via grafting-
through polymerization of a BMM, as the purity requirements are
stringent and the multi-step synthetic route to the BMMs can be
complex. The Johnson group has taken steps towards addressing
the scalable synthesis of BMMs by introducing an efficient
modular synthetic procedure towards a norbornene precursor.[48]
Simple modifications to this precursor allowed facile installation of
various polymeric side chains. Another potential approach to
producing GBCPs in a scalable manner is to combine steps of the
synthesis, as in the one-shot/pot synthesis of the side chains and
backbone or both of the side chains, thereby eliminating some
purification steps.[10a, 26b, 27]
While there has been great progress in the synthesis of
mGBCPs in the past two decades, there are still gaps remaining
in our fundamental understanding of mGBCPs and their self-
assembly behavior in bulk, thin-film, and solution. Thorough
knowledge of the relationships between structural parameters
such as backbone and side chain lengths, grafting density, and
side chain sequence and self-assembly behaviors, including TODT
,
morphologies, domain spacings, and dynamics, will be central to
the development of functional materials based on an mGBCP
design. There are many opportunities for the creative utilization of
polymer architecture to program multiple functionalities into
BCPs, and we hope that this Concept paper will not only provide
a framework for the rational design of mGBCPs but also spur
researchers to address the open questions that remain.
Acknowledgements
Financial support was provided by Yale University. A.N.L. thanks
the National Science Foundation Graduate Research Fellowships.
The authors thank Prof. Jeremiah A. Johnson for insightful
discussions.
Keywords: block copolymers • self-assembly • nanostructures •
graft polymers • polymer architectures
[
1]
a) M. Trollsås, B. Atthof, A. Würsch, J. L. Hedrick, J. A. Pople, A. P. Gast,
Macromolecules 2000, 33, 6423-6438; b) E. J. Shin, W. Jeong, H. A.
Brown, B. J. Koo, J. L. Hedrick, R. M. Waymouth, Macromolecules 2011,
As discussed in the introduction, one of the motivations to
study mGBCPs is the possibility of encoding properties or
functionalities into the polymer through its architecture. For
example, ion-conducting[49] or electron-conducting[50] side chains
may be combined with other side chains that induce phase
44, 2773-2779; c) H. Sun, D. M. Yu, S. Shi, Q. Yuan, S. Fujinami, X. Sun,
D. Wang, T. P. Russell, Macromolecules 2019, 52, 592-600.
a) W. F. M. Daniel, J. Burdyńska, M. Vatankhah-Varnoosfaderani, K.
Matyjaszewski, J. Paturej, M. Rubinstein, A. V. Dobrynin, S. S. Sheiko,
Nat. Mater. 2015, 15, 183; b) M. Vatankhah-Varnosfaderani, W. F. M.
Daniel, M. H. Everhart, A. A. Pandya, H. Liang, K. Matyjaszewski, A. V.
Dobrynin, S. S. Sheiko, Nature 2017, 549, 497; c) P. Deshmukh, H. Yoon,
S. Cho, S. Y. Yoon, O. V. Zore, T. Kim, I. Chung, S. K. Ahn, R. M. Kasi,
J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3424-3433; d) D. Lee, H.
Y. Jung, M. J. Park, ACS Macro Lett. 2018, 7, 1046-1050.
[2]
separation or that provide mechanical support[51]
; such a
molecular design may be advantageous for polymeric electrolyte
and ion-selective membrane applications, amongst others. While
two-component mGBCPs are an obvious first step towards this
goal, mGBCPs incorporating three or more components may be
an avenue for encoding more complex properties or multiple
functionalities into a polymer.[15c, 52] Likewise, the mGBCP
[
3]
a) G. Polymeropoulos, G. Zapsas, K. Ntetsikas, P. Bilalis, Y. Gnanou, N.
Hadjichristidis, Macromolecules 2017, 50, 1253-1290; b) M. W. Matsen,
Macromolecules 2012, 45, 2161-2165.
[4]
S. S. Sheiko, M. H. Everhart, A. V. Dobrynin, M. Vatankhah-
Varnosfaderani, Science Robotics 2018, 3.
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
[
[
[
5]
6]
7]
E. van Ruymbeke, K. Orfanou, M. Kapnistos, H. Iatrou, M. Pitsikalis, N.
Hadjichristidis, D. J. Lohse, D. Vlassopoulos, Macromolecules 2007, 40,
[27] D. Wu, Y. Yang, X. Cheng, L. Liu, J. Tian, H. Zhao, Macromolecules 2006,
39, 7513-7519.
[28] M. Xie, J. Dang, H. Han, W. Wang, J. Liu, X. He, Y. Zhang,
Macromolecules 2008, 41, 9004-9010.
[29] L. Gu, Z. Shen, S. Zhang, G. Lu, X. Zhang, X. Huang, Macromolecules
2007, 40, 4486-4493.
[30] a) H. Luo, M. Szymusiak, E. A. Garcia, L. L. Lock, H. Cui, Y. Liu, M.
Herrera-Alonso, Macromolecules 2017, 50, 2201-2206; b) T. Palacios-
Hernandez, H. Luo, E. A. Garcia, L. A. Pacheco, M. Herrera-Alonso,
Macromolecules 2018, 51, 2831-2837.
5941-5952.
a) R. Verduzco, X. Li, S. L. Pesek, G. E. Stein, Chem. Soc. Rev. 2015,
44, 2405-2420; b) S. S. Sheiko, B. S. Sumerlin, K. Matyjaszewski, Prog.
Polym. Sci. 2008, 33, 759-785.
a) G. Xie, M. R. Martinez, M. Olszewski, S. S. Sheiko, K. Matyjaszewski,
Biomacromolecules 2018, 20, 27-54; b) J. Rzayev, ACS Macro Lett. 2012,
1, 1146-1149; c) T. Pelras, S. Mahon Clare, M. Müllner, Angew. Chem.
Int. Ed. 2018, 57, 6982-6994; d) C. Feng, Y. Li, D. Yang, J. Hu, X. Zhang,
X. Huang, Chem. Soc. Rev. 2011, 40, 1282-1295; e) I. I. Potemkin, V. V.
Palyulin, Polymer Science, Ser. A. 2009, 51, 123-149.
a) T.-P. Lin, A. B. Chang, S.-X. Luo, H.-Y. Chen, B. Lee, R. H. Grubbs,
ACS Nano 2017, 11, 11632-11641; b) S. J. Dalsin, T. G. Rions-Maehren,
M. D. Beam, F. S. Bates, M. A. Hillmyer, M. W. Matsen, ACS Nano 2015,
[31]
[32]
K. Ishizu, X. X. Shen, K. I. Tsubaki, Polymer 2000, 41, 2053-2057.
a) K. Ishizu, J. Satoh, K. Tsubaki, J. Mater. Sci. Lett. 2001, 20, 2253-
2256; b) K. Ishizu, N. Sawada, J. Satoh, A. Sogabe, J. Mater. Sci. Lett.
2003, 22, 1219-1222.
[
8]
[33] H. Zhu, G. Deng, Y. Chen, Polymer 2008, 49, 405-411.
9
, 12233-12245; c) W. Gu, J. Huh, S. W. Hong, B. R. Sveinbjornsson, C.
[34]
N. Xia, G. Zhang, T. Li, W. Wang, H. Zhu, Y. Chen, G. Deng, Polymer
2011, 52, 4581-4589.
Park, R. H. Grubbs, T. P. Russell, ACS Nano 2013, 7, 2551-2558; d) Y.
Xia, B. D. Olsen, J. A. Kornfield, R. H. Grubbs, J. Am. Chem. Soc. 2009,
[35]
[36]
C. Cheng, N.-L. Yang, Macromolecules 2010, 43, 3153-3155.
D. A. Nguyen, V. Montembault, S. Piogé, S. Pascual, L. Fontaine, J.
Polym. Sci., Part A: Polym. Chem. 2017, 55, 4051-4061.
S. C. Radzinski, J. C. Foster, R. C. Chapleski, D. Troya, J. B. Matson, J.
Am. Chem. Soc. 2016, 138, 6998-7004.
131, 18525-18532; e) J. Rzayev, Macromolecules 2009, 42, 2135-2141.
[
[
9]
a) Y. Li, E. Themistou, J. Zou, B. P. Das, M. Tsianou, C. Cheng, ACS
Macro Lett. 2012, 1, 52-56; b) Y. Li, J. Zou, B. P. Das, M. Tsianou, C.
Cheng, Macromolecules 2012, 45, 4623-4629; c) S. Chakraborty, S. G.
Ramkumar, S. Ramakrishnan, Macromolecules 2017, 50, 5004-5013.
[37]
[38] L.-C. Cheng, K. R. Gadelrab, K. Kawamoto, K. G. Yager, J. A. Johnson,
10] a) B. Xu, C. Feng, X. Huang, Nat. Commun. 2017, 8, 333; b) K.
Kawamoto, M. Zhong, K. R. Gadelrab, L. C. Cheng, C. A. Ross, A.
Alexander-Katz, J. A. Johnson, J. Am. Chem. Soc. 2016, 138, 11501-
A. Alexander-Katz, C. A. Ross, Nano Lett. 2018, 18, 4360-4369.
C. Sinturel, F. S. Bates, M. A. Hillmyer, ACS Macro Lett. 2015, 4, 1044-
1050.
[39]
[40]
11504.
Z. Bo, J. P. Rabe, A. D. Schlüter, Angew. Chem. Int. Ed. 1999, 38, 2370-
[
[
[
11] Z. H. Guo, A. N. Le, X. Feng, Y. Choo, B. Liu, D. Wang, Z. Wan, Y. Gu,
J. Zhao, V. Li, C. O. Osuji, J. A. Johnson, M. Zhong, Angew. Chem. Int.
Ed. 2018, 57, 8493-8497.
12] a) S. Onbulak, J. Rzayev, Polym. Chem. 2015, 6, 764-771; b) K. Huang,
J. Rzayev, J. Am. Chem. Soc. 2009, 131, 6880-6885; c) K. Huang, D. P.
Canterbury, J. Rzayev, Macromolecules 2010, 43, 6632-6638.
13] a) L. S. Boffa, B. M. Novak, Chem. Rev. 2000, 100, 1479-1494; b) B.
Obermeier, F. Wurm, C. Mangold, H. Frey, Angew. Chem. Int. Ed. 2011,
2372.
[41] a) T. Isono, T. Sasamori, K. Honda, Y. Mato, T. Yamamoto, K. Tajima, T.
Satoh, Macromolecules 2018, 51, 3855-3864; b) S. Chakraborty, S.
Ramakrishnan, J. Polym. Sci., Part A: Polym. Chem. 2018, 0, 1554-1563.
[42] Y. Rokhlenko, K. Kawamoto, J. A. Johnson, C. O. Osuji, Macromolecules
2018, 51, 3680-3690.
[43]
P. Deshmukh, S.-k. Ahn, M. Gopinadhan, C. O. Osuji, R. M. Kasi,
Macromolecules 2013, 46, 4558-4566.
5
0, 7988-7997; c) C. Mangold, F. Wurm, H. Frey, Polym. Chem. 2012, 3,
[44]
a) I. N. Haugan, M. J. Maher, A. B. Chang, T.-P. Lin, R. H. Grubbs, M.
A. Hillmyer, F. S. Bates, ACS Macro Lett. 2018, 7, 525-530; b) H. Liang,
Z. Cao, Z. Wang, S. S. Sheiko, A. V. Dobrynin, Macromolecules 2017,
50, 3430-3437; c) J. Paturej, S. S. Sheiko, S. Panyukov, M. Rubinstein,
Science Advances 2016, 2, e1601478; d) S. Lecommandoux, F. Chécot,
R. Borsali, M. Schappacher, A. Deffieux, A. Brûlet, J. P. Cotton,
Macromolecules 2002, 35, 8878-8881.
1714-1721; d) J. Herzberger, K. Niederer, H. Pohlit, J. Seiwert, M. Worm,
F. R. Wurm, H. Frey, Chem. Rev. 2016, 116, 2170-2243.
[
[
14] Q. Fu, C. Liu, W. Lin, J. Huang, J. Polym. Sci., Part A: Polym. Chem.
2008, 46, 6770-6779.
15] a) J. Sun, J. Hu, G. Liu, D. Xiao, G. He, R. Lu, J. Polym. Sci., Part A:
Polym. Chem. 2011, 49, 1282-1288; b) C. Hou, J. Hu, G. Liu, J. Wang,
F. Liu, H. Hu, G. Zhang, H. Zou, Y. Tu, B. Liao, Macromolecules 2013,
[45] H. Liang, B. J. Morgan, G. Xie, M. R. Martinez, E. B. Zhulina, K.
Matyjaszewski, S. S. Sheiko, A. V. Dobrynin, Macromolecules 2018, 51,
10028-10039.
[46] A. E. Levi, J. Lequieu, J. D. Horne, M. W. Bates, J. M. Ren, K. T. Delaney,
G. H. Fredrickson, C. M. Bates, Macromolecules 2019, 52, 1794-1802.
[47] S. Ramakrishnan, R. Sarkar, B. Gowd, Polym. Chem. 2019.
[48] H. V. T. Nguyen, N. M. Gallagher, F. Vohidov, Y. Jiang, K. Kawamoto, H.
Zhang, J. V. Park, Z. Huang, M. F. Ottaviani, A. Rajca, J. A. Johnson,
ACS Macro Lett. 2018, 472-476.
46, 4053-4063; c) F. Liu, J. Hu, G. Liu, C. Hou, S. Lin, H. Zou, G. Zhang,
J. Sun, H. Luo, Y. Tu, Macromolecules 2013, 46, 2646-2657; d) P. Zhao,
Y. Yan, X. Feng, L. Liu, C. Wang, Y. Chen, Polymer 2012, 53, 1992-2000.
16] Y. Wu, Q. Tang, M. Zhang, Z. Li, W. Zhu, Z. Liu, Polymer 2018, 143, 190-
[
[
1
99.
17] H. He, B. Liu, M. Wang, R. W. Vachet, S. Thayumanavan, Polym. Chem.
018, 10, 187-193.
2
[
[
18] T. Stephan, S. Muth, M. Schmidt, Macromolecules 2002, 35, 9857-9860.
19] a) D. Neugebauer, Y. Zhang, T. Pakula, K. Matyjaszewski,
Macromolecules 2005, 38, 8687-8693; b) X. Chang, H. Mao, G. Shan, Y.
Bao, P. Pan, ACS Macro Lett. 2019, 357-362.
20] D. Neugebauer, M. Theis, T. Pakula, G. Wegner, K. Matyjaszewski,
Macromolecules 2006, 39, 584-593.
[49] P. Gavelin, P. Jannasch, B. Wesslén, J. Polym. Sci., Part A: Polym.
Chem. 2001, 39, 2223-2232.
[50] a) N. Ranieri, G. Ruggeri, F. Ciardelli, Polym. Int. 1999, 48, 1091-1098;
b) L. Fang, P. Liu, B. R. Sveinbjornsson, S. Atahan-Evrenk, K. Vandewal,
S. Osuna, G. Jiménez-Osés, S. Shrestha, G. Giri, P. Wei, A. Salleo, A.
Aspuru-Guzik, R. H. Grubbs, K. N. Houk, Z. Bao, J. Mater. Chem. C 2013,
1, 5747-5755.
[
[
[
21] G. Hattori, M. Takenaka, M. Sawamoto, T. Terashima, J. Am. Chem. Soc.
2
018, 140, 8376-8379.
22] Y. Xia, J. A. Kornfield, R. H. Grubbs, Macromolecules 2009, 42, 3761-
766.
K. Ishizu, H. Yamada, Macromolecules 2007, 40, 3056-3061.
24] J. Yin, Z. Ge, H. Liu, S. Liu, J. Polym. Sci., Part A: Polym. Chem. 2009,
7, 2608-2619.
25] B. S. Sumerlin, D. Neugebauer, K. Matyjaszewski, Macromolecules 2005,
8, 702-708.
[51]
C. M. Bates, A. B. Chang, N. Momčilović, S. C. Jones, R. H. Grubbs,
Macromolecules 2015, 48, 4967-4973.
a) Y. Mo, G. Liu, Y. Tu, S. Lin, J. Song, J. Hu, F. Liu, J. Polym. Sci., Part
A: Polym. Chem. 2017, 55, 1021-1030; b) S. Lin, S. Feng, Y. Mo, Y. Tu,
Y. Guo, J. Hu, G. Liu, Z. Zhong, L. Miao, H. Zou, F. Liu, J. Polym. Sci.,
Part A: Polym. Chem. 2017, 55, 1536-1546.
3
[
[
23]
[52]
4
[
[
3
[53]
M. Matsumoto, M. Sawamoto, T. Terashima, ACS Macro Lett. 2019, 8,
320-325.
26] a) K. L. Beers, S. G. Gaynor, K. Matyjaszewski, S. S. Sheiko, M. Möller,
Macromolecules 1998, 31, 9413-9415; b) C. Cheng, E. Khoshdel, K. L.
Wooley, Nano Lett. 2006, 6, 1741-1746; c) D. Neugebauer, Y. Zhang, T.
Pakula, S. S. Sheiko, K. Matyjaszewski, Macromolecules 2003, 36,
6746-6755.
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Chemistry - A European Journal
10.1002/chem.201900520
CONCEPT
Entry for the Table of Contents
CONCEPT
An N. Le, Ruiqi Liang, Mingjiang Zhong*
Page No. – Page No.
Title
A platform for architecturally encoded properties: This Concept article provides
an overview of current literature on mixed graft block copolymers, highlighting
control over grafting density and side chain sequence in each of the synthetic
routes. The unique polymer architecture allows for encoding of multiple properties
into the mixed graft block copolymer material.
This article is protected by copyright. All rights reserved.