Preparation of defect-free nanocaterpillars via in situ nanoparticlisation of a well-defined polyacetylene block copolymer

Article abstract of DOI:10.1039/c4ra10325d

Previously we reported a one-pot preparation of nano-objects resembling a caterpillar (nanocaterpillar) from polyacetylene (PA) diblock copolymers, via the in situ nanoparticlisation of conjugated polymers (INCP) approach. However, they showed the following limitations: micro-structure of PA block was stereo-random containing mixtures of E and Z polyenes, and their nanostructures were contaminated by nanosphere defects. Herein, we report strategies to prepare not only defect-free nanocaterpillars, but also the stereo-regular PA diblock copolymers. By altering the ROMP temperature, we can control the stereochemistry (E/Z) of the PA block, the degree of chain-transfer reaction and molar mass dispersity. As a result of a suppressed chain-transfer reaction at low temperature, ROMP of cyclooctatetraene (COT) at 0 °C produced defect-free nanocaterpillars containing cis-major PAs and they can be transformed into those containing trans-major PAs by thermal isomerisation. Compared to previously reported ill-defined block copolymers, these well-defined block copolymers lead to an increase in the length of nanocaterpillars and narrower length distribution. This journal is

Full text of DOI:10.1039/c4ra10325d

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Preparation of defect-free nanocaterpillars via in
situ nanoparticlisation of a well-defined
polyacetylene block copolymer†
Cite this: RSC Adv., 2014, 4, 49180
Ki-Young Yoon, In-Hwan Lee and Tae-Lim Choi*
Previously we reported a one-pot preparation of nano-objects resembling a caterpillar (nanocaterpillar)
from polyacetylene (PA) diblock copolymers, via the in situ nanoparticlisation of conjugated polymers
(INCP) approach. However, they showed the following limitations: micro-structure of PA block was
stereo-random containing mixtures of E and Z polyenes, and their nanostructures were contaminated by
nanosphere defects. Herein, we report strategies to prepare not only defect-free nanocaterpillars, but
also the stereo-regular PA diblock copolymers. By altering the ROMP temperature, we can control the
stereochemistry (E/Z) of the PA block, the degree of chain-transfer reaction and molar mass dispersity.
As a result of a suppressed chain-transfer reaction at low temperature, ROMP of cyclooctatetraene
Received 17th July 2014
Accepted 25th September 2014
ꢀ
(
COT) at 0 C produced defect-free nanocaterpillars containing cis-major PAs and they can be
transformed into those containing trans-major PAs by thermal isomerisation. Compared to previously
reported ill-defined block copolymers, these well-defined block copolymers lead to an increase in the
length of nanocaterpillars and narrower length distribution.
DOI: 10.1039/c4ra10325d
www.rsc.org/advances
together is relatively weak. Chemists can take advantages of this
by utilizing these supramolecules as smart materials.
Introduction
Self-assembly of block copolymers in solution has received great
Recently, we reported an alternative approach known as in
attention, because the block copolymers form not only spheres, situ nanoparticlisation of conjugated polymers (INCP). The
cylinders, and vesicles, but also various intriguing nano- synthesis of polyacetylene (PA) diblock copolymers via ring-
structures such as undulating cylinders, disklike micelles, and opening metathesis polymerisation (ROMP) of cyclo-
multicompartment structures. However, in most cases, these octatetraene (COT) is a good example of this process, because
6,7
1
2
3
unique nanostructures were not directly formed aer their the introduction of insoluble PA due to effective p–p interaction
synthesis because the intermolecular forces holding the unim- between PA chains generate the strong attractive force to
ers were not sufficient to form supramolecules in the reaction molecular self-assembly system. Furthermore, long PA blocks
media. For this reason, post-synthetic treatments such as form nano-objects resembling caterpillars (nanocaterpillars in
selective solvent addition, dialysis, temperature change, aging, Fig. 1c), conrmed by atomic force microscopy (AFM), dry
or introduction of glue molecules were required to induce the transmission electron microscopy (TEM), and cryo-TEM. Within
1
–4
self-assembly processes. Such additional processes may limit the nanocaterpillar structures, the individual spheres were held
the mass production of polymeric nanostructures, narrowing tightly together by p–p interaction between PA segments, and
their potential applications. This problem was overcome to these unique structures are very stable under heat and
5
6
some extent by polymerisation-induced self-assembly (PISA).
mechanical force.
6
Amphiphilic block copolymers prepared by aqueous dispersion/
This process, however, suffered from following limitations.
emulsion polymerisation could form supramolecules in situ During the formation of nanocaterpillars, defects in the nano-
during polymerisation. Nevertheless, these supramolecules are structure were observed. At least more than 10% of the nano-
not thermodynamically stable adducts, and they are fragile spheres failed to transform into nanocaterpillars. Also the PA
when environment changes (for example, changes in tempera- core block consisted of non-uniform microstructures of poly-
ture or solvents), because the driving force holding the unimers enes comprised of a mixture of E and Z stereoisomers. These
defects existed because at room temperature, a chain-transfer
reaction catalysed by a highly active catalyst 2 inevitably
occurred on the PA block. This resulted in the formation of not
Department of Chemistry, Seoul National University, Seoul, 151-747, Korea. E-mail:
only stereo-random polyenes (Fig. 1a) but also PA blocks with
tlc@snu.ac.kr
broad molar mass dispersity (Đ), which produced block
copolymers containing short PA chains. These nanospheres
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra10325d
1
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(
Table 1, entries 1–3). Even using toluene, a relatively poor
6,8
solvent for the ROMP of COT, the conversion reached 84%
within 5 h at 55 C. However, this condition produced a large
amount of undesired benzene (34% at 55 C and 21% at 40 C),
resulting in relatively short PA incorporated into the diblock
copolymer, while the least amount of benzene (4%) was formed
ꢀ
ꢀ
ꢀ
ꢀ
at 0 C (Table 1, entries 1–4). In short, the reactions at higher
temperatures not only had a positive inuence on the PA
synthesis by increasing the COT conversion but also a negative
effect by promoting the depolymerisation that released the
benzene at the same time. Clearly the benzene formation was a
thermodynamically driven process. Thus, the fact that benzene
ꢀ
formation was minimised at 0 C implied that the chain-
transfer reaction, another thermodynamically favoured process,
ꢀ
could be minimised at 0 C as well.
To further investigate how temperature affected the degree
of chain-transfer reaction, we determined the E/Z ratio on the
PA block. In the absence of the chain-transfer reaction, PA
produced by ROMP of COT should contain Z olen as the major
isomer, because only one out of four Z-olens in COT undergoes
the metathesis reaction, and three Z olens remain untouched.
Furthermore, since the Grubbs catalyst kinetically produces
Fig. 1 (a) Chain-transfer reaction during ROMP of COT. PN: poly-
norbornene (b) in situ nanoparticlisation from the block copolymers almost equal amounts of E and Z isomers for ROMP, we
containing the broad disperse PA core vs. those from the well-defined expected that the ideal ROMP of COT, in the absence of the
block copolymers containing the narrow disperse PA core. (c) AFM and
TEM images for nanocaterpillar.
chain-transfer reaction, would produce cis-major PA. In
contrast, an increase in the degree of chain-transfer reaction on
the PA block would produce more of the enthalpically favoured
E olens, even leading to the trans-major PA diblock copolymer
with broader Đ at the end (Fig. 1a). Therefore, the investigation
of the relationship between the temperature and E/Z ratio of PA
contaminated by the short PA core would not undergo the
structural evolution to nanocaterpillars or prevent the elonga-
tion of nanocaterpillars by acting as end-cappers (Fig. 1b). In
would indicate the degree of chain-transfer reaction. To deter-
order to produce materials with well-dened nanostructures
mine the E/Z ratio, we used cross-polarisation/magic-angle-
and microstructures, the underlying problem—the chain-
transfer reaction on PA—should be suppressed (Fig. 1a and b).
Herein, we report on our investigation of how reaction
temperatures affect rates of ROMP, depolymerisation, chain-
transfer reaction during ROMP of COT, and ratio of E and Z
stereochemistry of the polyene. Aer optimising the ROMP
conditions that suppress the chain-transfer reaction, we obtain
longer nanocaterpillars containing either cis- or trans-major PA
selectively without nanosphere defects. During the course of
these investigations, evidences supporting the mechanism for
the nanoparticlisation are obtained as well.
13
spinning (CP/MAS) C solid-state NMR spectroscopy since
1
liquid H NMR spectroscopy provided no information on the PA
6
block, which spontaneously formed the unsolvated core. CP/
13
MAS C solid-state NMR spectra showed that the trans-PA
signal at 138 ppm increased and the cis-PA signal at 128 ppm
8
decreased with the increase in the temperature (Fig. 2a). As a
ꢀ
result, the PA block produced at 0 C showed a very weak signal
ꢀ
for E olens, whereas that produced at 55 C showed a weak
signal for Z olens. UV/vis spectroscopy provided another
denitive conclusion on the stereoisomer for the PA blocks. PA
ꢀ
diblock copolymer produced at 0 C revealed a spectrum with
the onset point at 630 nm, whereas that of the polymer syn-
ꢀ
thesised at 55 C was 800 nm (Fig. 2b). These onset points
Results and discussion
translated into band-gaps of 2.0 eV and 1.6 eV, respectively, and
9
To prepare well-dened diblock copolymers containing a PA these values perfectly matched those of cis-PA and trans-PA.
block with narrow Đ, we initially investigated the effect of
l
max showed good correlation with the degree of polymerisation
reaction temperatures on chain-transfer reaction during the (DP) of COT (See Table 1, entries 1–4). IR spectroscopy provided
ROMP of COT. By using 1 as a monomer for the rst block and a additional insight, since it vividly showed a sharp signal at
ꢁ
1
catalyst 2, the fundamental factors for the synthesis of the 1010 cm , corresponding to trans-PA from the polymer syn-
ꢀ
second block such as COT conversion and benzene formation thesised at 55 C, while that signal totally disappeared in the
8
1
ꢀ
8
(
as a result of depolymerisation), were monitored by crude H case of the polymer prepared at 0 C (Fig. S2†). From these
ꢀ
NMR analysis at various temperatures (Table 1). As expected, characterisations, we successfully veried that ROMP at 0 C
the ROMP of COT was much faster at 40 C than at room resulted in the cis-major PA diblock copolymer and that ROMP
temperature, resulting in complete conversion in 4.5 h, whereas at 55 C produced the trans-major PA. This conclusion implied
only 35% conversion was observed at 0 C even aer 24 h
ꢀ
ꢀ
ꢀ
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Table 1 Synthesis of the PA diblock copolymer by ROMP of COT at various conditions
a
ꢀ
b
c
d
e
Entry
Solvent
Conc (M)
Temp ( C)
Time (h)
Conv [yield] (%)
PhH (%)
DPCOT
f
1
DCM
DCM
DCM
Toluene
0.1
0.1
0.1
0.1
r.t.
0
40
55
16
24
4.5
5
93 [92]
35 [84]
99 [89]
84 [88]
12
4
21
34
ꢂ25
ꢂ10
ꢂ24
ꢂ17
2
3
4
a
b
c
d
Based on [COT]. Conversion of COT. Isolated yield aer precipitation. Yield of benzene formation calculated on the basis of the total number
of double bonds from the converted COTs. Degree of polymerisation of COT. Ref. 6.
e
f
Based on the conclusions from several analyses, ROMP of
ꢀ
COT at 0 C was optimised to obtain the diblock copolymers
containing a long PA block with narrow Đ, because the polymers
with the actual COT DP of at least 30 would have sufficient
6
driving force to form well-dened nanocaterpillars. To increase
the DP of COT, a large feed ratio of COT (>100 eq.) was used to
ꢀ
compensate for the conversion penalty at 0 C: the DP doubled
to 19 (Table 2, entry 1). In order to optimise ROMP of COT, we
10
changed to more active catalyst 3. Indeed, model kinetic
studies conducted at room temperature conrmed that the
ROMP of COT using 3 was much faster than 2 (Fig. 3). Likewise,
13
Fig. 2 (a) CP/MAS C solid-state NMR spectra and (b) UV/vis spectra
in chloroform for PA diblock copolymers synthesised at various
temperatures.
ꢀ
changing from 2 to 3 enhanced the rate of ROMP at 0 C with
shortened reaction time (24 h / 12 h) (Table 2, entry 2). By
further increasing the COT concentration to 1 M and monomer-
to-initiator (M/I) ratio to 200, and by optimising the solvent
system by adding a co-solvent, chloroform, which increased the
polymer solubility, diblock copolymers containing a long PA
block of up to 52-mers of COT was obtained (Table 2, entries 3–5).
Aer characterising the polymer by the same methods described
above, we concluded that these polymers contained a long cis-
major PA block with narrow Đ (Table S1, Fig. S2 and S4†).
With the successful synthesis of PA diblock copolymers with
narrow Đ, their nanostructures were imaged by atomic force
microscopy (AFM), showing the well-dened nanocaterpillars
without any post-treatment (Fig. S5†). Compared to the nano-
caterpillars with ill-dened polymers (synthesised at r. t.), the
well-dened nanocaterpillars with well-dened polymers (syn-
that chain-transfer reaction on the PA or secondary metathesis
reactions on the cis-major PA would be minimised at 0 C.
ꢀ
Another supportive analysis for determining the degree of
chain-transfer reaction is by measuring Đ by size exclusion
chromatography (SEC). However, SEC traces for the diblock
copolymers showed two sets of traces: the major trace corre-
sponding to the self-assembled nanoparticles with high
molecular weight and the minor trace corresponding to the
single chains of diblock copolymers, which were disassembled
under the shear pressure of SEC conditions (see Fig. S3† for the
6,7
details). Although the major traces of SEC offered no infor-
mation on the degree of chain-transfer reaction because the
signals were from the collections of supramolecules, we could
analyse the minor traces to infer the dispersity in the block
copolymers. SEC analysis of PN50-b-PA40 (10 equiv. of COT)
ꢀ
thesised at 0 C, Table 2, entry 5) showed almost no nano-
spheres (Fig. 4a vs. b). Furthermore, the average lengths (L
the two sets of nanocaterpillars were calculated using statistics
Fig. S6†). L for well-dened nanocaterpillars was greater than
that of nanocaterpillars prepared at room temperature (154 nm
vs. 101 nm) with the smaller standard deviation (s/L , 0.411 vs.
.561). Length distribution (L /L ) was also narrower (1.17 vs.
n
) of
ꢀ
produced at 55 C showed the broadest minor trace, while that
(
n
produced at room temperature showed a narrower minor trace.
ꢀ
Finally, PN50-b-PA40 synthesised at 0 C showed the narrowest
n
and unimodal minor trace (Fig. S3†). All these analyses
demonstrated that the degree of chain-transfer reaction
0
1
w
n
.32, Fig. 4a and b). Moreover, the AFM height prole showed
depended on the temperature, and as a result, ROMP of COT at
ꢀ
ꢀ
that the average height of nanocaterpillars prepared at 0
C
0
C resulted in minimal chain-transfer reaction.
statistically had a lower standard deviation (13.9% vs. 16.1%) at
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Table 2 Optimisation for synthesis of the PA diblock copolymer by ROMP of COT at 0 C
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ꢀ
a
ꢀ
b
c
d
e
Entry
Cat.
Y
Solvent
Conc (M)
Temp ( C)
Time (h)
Conv [yield] (%)
PhH (%)
DPCOT
1
2
3
4
5
2
3
3
3
3
100
100
200
200
200
DCM
DCM
DCM
DCM/CHCl
DCM/CHCl
0.9
0.9
1.0
1.0
1.0
0
0
0
0
0
24
12
12
12
12
22 [60]
32 [70]
20 [45]
27 [47]
30 [52]
12
9
11
12
12
ꢂ19
ꢂ29
ꢂ35
ꢂ46
ꢂ52
3
3
¼ 1
¼ 4
a
b
c
d
Based on [COT]. Conversion of COT. Isolated yield aer precipitation. Yield of benzene formation calculated on the basis of the total number
e
of double bonds from the converted COTs. Degree of polymerisation of COT.
9
0% condence level, indicating that the PA blocks with narrow
Đ were likely to form the core with more uniform sizes
Fig. S7c†). Lastly, dynamic light scattering (DLS) analysis of
(
nanoparticles in chloroform revealed that the polymers with
broader Đ showed two distinct populations of average hydro-
dynamic diameter (D ) for nanospheres (21 nm) and nano-
h
caterpillars (148 nm), while a denite unimodal population of
well-dened nanocaterpillars (167 nm) was observed (Fig. 4c,
see ESI† for the detailed condition). Because results from both
AFM and DLS analyses were in excellent agreement, one can
conclude that the polymers with the narrow Đ undergo self-
assembly to form longer nanocaterpillars with narrower length
distribution without nanosphere defects, thus supporting the
11
models in Fig. 1b. Some divarications of nanocaterpillars were
observed in Fig. 4a. We believe that there are due to stacking of
individual nanocaterpillars because their heights were much
higher than others (Fig. S8a and b†).
Fig. 3 Kinetic studies for the ROMP of COT at room temperature
using 2 and 3 (feeding ratio, [NB] : [2 or 3] : [COT] ¼ 50 : 1 : 50).
Fig. 4 (a) AFM image (inset: zoom-in image) of the nanocaterpillars from the PA diblock copolymer with narrow Đ (DPCOT ¼ 52) (b) that with
broad Đ (DPCOT ¼ 50). (c) DLS intensity profiles for those with narrow Đ (blue) and broad Đ (green).
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Since well-dened nanocaterpillars containing cis-major PA supported that thermal isomerisation produced well-dened
were prepared, our next efforts focused on producing the well- nanocaterpillars containing trans-PA whose core size and length
dened nanocaterpillars containing trans-major PA core, slightly increased as a result of the elongated PA block.
because trans-PA has different electronic properties such as
8
much higher conductivity. However, diblock copolymers con-
Conclusions
taining trans-major PA block with high DP and narrow Đ could
ꢀ
not be prepared directly using ROMP of COT at 55 C, because it In summary, we have synthesised the PA diblock copolymers
would enhance both benzene formation, thereby lowering DP, containing long cis-major PA cores with narrow Đ by ROMP of
ꢀ
and chain-transfer reaction, thereby broadening Đ. Hence, we COT at 0 C. Suppressing the chain-transfer reaction resulted in
chose an alternative strategy to detour to a trans-major PA by the formation of longer nanocaterpillars without nanosphere
12
isomerisation of cis-major PA. Heating the polymer in toluene defects. Furthermore, by thermal isomerisation, well-dened
ꢀ
at 100 C for 20 min successfully produced trans-major PA, and nanocaterpillars containing long trans-major PA cores with
1
3
its stereochemistry was conrmed by CP/MAS C solid-state narrow Đ were also prepared. This cis-to-trans conversion on PA
NMR and spectroscopic analyses (Fig. 5a and b and S2†). increased both the core size and length of the nanocaterpillars.
The change in stereochemistry by isomerisation to trans-PA These results demonstrate how one can control not only the
altered the nanostructure. Firstly, the isomerisation increased stereochemistry on PA and the dispersity of the PA block but
the average core size of nanocaterpillars because trans-PA was also the core size, nanoparticle length, and electronic proper-
more stretched than cis-PA. Transmission electron microscopy ties, such as band gap, by manipulating the reaction conditions
(TEM) analysis, which showed the nano-objects resembling of the catalysis.
caterpillars by revealing the electron-rich PA core only even
without staining, conrmed that the average core diameter for
cis-major PA (12.5 nm) increased to 20.2 nm aer isomerisation
Acknowledgements
(Fig. 5c). This change induced slight increase in the overall size The nancial support from Basic Science Research Program, the
n
of the nanocaterpillars as well. Measuring L by AFM revealed Nano-Material Technology Development Program, and BRL
the increase in the length from 154 nm to 170 nm, while the through NRF is acknowledged. We thank NCIRF and NICEM at
length dispersity barely changed as 1.19 (Fig. S7†). DLS analysis SNU for generous support of the TEM, EA, and Solid-state NMR
in chloroform also showed that Dh of nanocaterpillars also experiments. K.-Y.Y. thanks Hyun Ju Song and Jihye Lee for help
increased by isomerisation from 167 nm to 188 nm (Fig. 5d).
Similarly, the nanocaterpillars from a diblock copolymer
with shorter DP of COT (30) showed the same trend with the
previous one with the longer PA block (DP of COT 52, Fig. S8c–e†).
The nanocaterpillars prepared at 0 C showed a unimodal trace
under the DLS analysis while those prepared at r.t. showed a
with illustration.
Notes and references
ꢀ
1 (a) H. Cui, Z. Chen, S. Zhong, K. L. Wooley and D. J. Pochan,
Science, 2007, 317, 647; (b) Z. Li, J. Ma, N. S. Lee and
K. L. Wooley, J. Am. Chem. Soc., 2011, 133, 1228; (c) S. Jain
and F. S. Bates, Science, 2003, 300, 460; (d) Q. Ma,
E. E. Remsen, C. G. Clark, T. Kowalewski and K. L. Wooley,
Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 5058.
bimodal trace. Also, isomerisation increased the D measured
h
by DLS from 130 nm to 155 nm. All these observations clearly
2
3
L. Yin and M. A. Hillmyer, Macromolecules, 2011, 44, 3021.
(a) A. O. Moughton, M. A. Hillmyer and T. P. Lodge,
Macromolecules, 2011, 45, 2; (b) Z. Li, E. Kesselman,
Y. Talmon, M. A. Hillmyer and T. P. Lodge, Science, 2004,
3
06, 98; (c) A. H. Gr ¨o schel, F. H. Schacher, H. Schmalz,
O. V. Borisov, E. B. Zhulina, A. Walther and
A. H. E. M u¨ ller, Nat. Commun., 2012, 3, 710; (d) B. Fang,
A. Walther, A. Wolf, Y. Xu, J. Yuan and A. H. E. M u¨ ller,
Angew. Chem., Int. Ed., 2009, 48, 2877; (e) J. Dupont and
G. Liu, So Matter, 2010, 6, 3654.
4
(a) P. A. Rupar, L. Chabanne, M. A. Winnik and I. Manners,
Science, 2012, 337, 559; (b) W. Xiaosong, G. Guerin, W. Hal,
W. Yishan, I. Manners and M. A. Winnik, Science, 2007,
317, 644; (c) S. K. Patra, R. Ahmed, G. R. Whittell,
D. J. Lunn, E. L. Dunphy, M. A. Winnik and I. Manners, J.
Am. Chem. Soc., 2011, 133, 8842; (d) E. Lee, B. Hammer,
J.-K. Kim, Z. Page, T. Emrick and R. C. Hayward, J. Am.
Chem. Soc., 2011, 133, 10390.
(a) Y. Li and S. P. Armes, Angew. Chem., Int. Ed., 2010, 49,
4042; (b) S. Sugihara, A. Blanazs, S. P. Armes, A. J. Ryan
13
Fig. 5 (a) CP/MAS C solid-state NMR spectra, (b) UV/vis spectra, (c)
TEM images, and (d) DLS intensity profiles of the well-defined nano-
caterpillars before and after cis/trans isomerisation.
5
49184 | RSC Adv., 2014, 4, 49180–49185
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and A. L. Lewis, J. Am. Chem. Soc., 2011, 133, 15707; (c)
RSC Advances
see; (d) R. S. Saunders, R. E. Cohen and R. R. Schrock,
Macromolecules, 1991, 24, 5599–5605; (e) R. R. Schrock,
S. Luo, J. C. Lee, N. C. Zanetti and W. M. Davis, J. Am.
Chem. Soc., 1996, 118, 3883–3895; (f) M. Buchmeiser and
R. R. Schrock, Macromolecules, 1995, 28, 6642–6649.
9 K. Yoshino, Synth. Met., 1989, 28, 669.
A. Blanazs, J. Madsen, G. Battaglia, A. J. Ryan and
S. P. Armes, J. Am. Chem. Soc., 2011, 133, 16581; (d)
B. Charleux, G. Delaittre, J. Rieger and F. D'Agosto,
Macromolecules, 2012, 45, 6753; (e) W.-M. Wan and
C.-Y. Pan, Polym. Chem., 2010, 1, 1475.
6
7
K.-Y. Yoon, I.-H. Lee, K. O. Kim, J. Jang, E. Lee and T.-L. Choi, 10 (a) J. A. Love, J. P. Morgan, T. M. Trnka and R. H. Grubbs,
J. Am. Chem. Soc., 2012, 134, 14291.
Angew. Chem., Int. Ed., 2002, 41, 4035; (b) E.-H. Kang,
I. S. Lee and T.-L. Choi, J. Am. Chem. Soc., 2011, 133, 11904.
(a) J. Kim, E.-H. Kang and T.-L. Choi, ACS Macro Lett., 2012, 1,
1090; (b) I.-H. Lee, P. Amaladass, K.-Y. Yoon, S. Shin, 11 It should be noted that the average Dh for the sample
Y.-J. Kim, I. Kim, E. Lee and T.-L. Choi, J. Am. Chem. Soc.,
prepared at r. t. should be lower than 150 nm, because
DLS clearly shows bimodal distribution, but it does not
2013, 135, 17695; (c) I.-H. Lee, P. Amaladass and T.-L. Choi,
Chem. Commun., 2014, 50, 7945.
h
give the average D for the whole population. Also the
8
(a) F. L. Klavetter and R. H. Grubbs, J. Am. Chem. Soc., 1988,
dispersity in length is still inevitable due to intrinsic step-
growth-like mechanism of the nanocaterpillar formation.
110, 7807; (b) O. A. Scherman and R. H. Grubbs, Synth. Met.,
2001, 124, 431; (c) O. A. Scherman, I. M. Rutenberg and 12 T. Ito, H. Shirakawa and S. Ikeda, J. Polym. Sci., Polym. Chem.
R. H. Grubbs, J. Am. Chem. Soc., 2003, 125, 85105. For the
Ed., 1975, 13, 1943.
previous synthesis of PA by two-step Durham methods,
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