ARTICLE
copolymer, leading to the formation of Janus-like conforma-
2 Blencowe, A.; Tan, J. F.; Goh, T. K.; Qiao, G. G. Polymer
4
0
tion. As for PS-PEG miktoarm star copolymer, nothing has
been reported on the formation of Janus structures. Thus,
here we direct our attention to the self-assembly of the
obtained miktoarm star copolymer in cyclohexanone. The
polymer–solvent interaction parameters (vp-s) at room tem-
perature are 0.4638 and 0.3469 for the PS–cyclohexanone
2009, 50, 5–32.
3
Higashihara, T.; Sakurai, T.; Hirao, A. Macromolecules 2009,
2, 6006–6014.
4
4
Hadjichristidis, N. J Polym Sci Part A: Polym Chem 1999, 37,
57–871.
8
4
1
5 Gao, H.; Matyjaszewski, K. Macromolecules 2006, 39,
154–3160.
and PEG–cyclohexanone pairs, respectively. According to
the Flory–Huggins theory criterion, the polymer and solvent
3
are miscible over the entire composition range when vp-s
<
6 Bosman, A. W.; Heumann, A.; Klaerner, G.; Benoit, D.; Fre-
chet, J. M. J.; Hawker, C. J. J Am Chem Soc 2001, 123,
6461–6462.
0.5. Cyclohexanone, therefore, is a good solvent for both PS
and PEG blocks. However, there is a small difference
between the vp-s values for the PS–cyclohexanone and PEG–
cyclohexanone pairs. Such subtle difference demonstrates
that cyclohexanone has preferential affinity to PEG block,
which may promote phase segregation in the miktoarm star
7
Liu, J. Q.; Liu, H. Y.; Jia, Z. F.; Bulmus, V.; Davis, T. P. Chem
Commun 2008, 6582–6584.
8
Gao, H.; Matyjaszewski, K. Prog Polym Sci 2009, 34, 317–350.
4
0,41
copolymer and lead to the formation of Janus structure.
Figure 5 shows the AFM images of (PS) -polyEVBA-(PEG)
40
9 Ouchi, M.; Terashima, T.; Sawamoto, M. Chem Rev 2009,
1
09, 4963–5050.
1
4
1
0 Zhang, W. D.; Zhang, W.; Zhu, J.; Zhang, Z. B.; Zhu, X. L.
miktoarm star copolymer, spin-coated from a 0.1 wt % cyclo-
hexanone solutions on a mica wafer. Intriguingly, both the
height and phase images show dumbbell-like (hetero-dou-
blets) shapes with strong phase contrast, where the dark cir-
cular domains with ꢁ80 nm diameters and ꢁ3 nm heights
correspond to the rigid PS arms, while the light circular
domains with ꢁ170 nm diameters and ꢁ7 nm heights corre-
J Polym Sci Part A: Polym Chem 2009, 47, 6908–6918.
11 Gao, H.; Matyjaszewski, K. J Am Chem Soc 2007, 129,
11828–11834.
1
2 Du, J. Z.; Chen, Y. M. J Polym Sci Part A: Polym Chem
2
004, 42, 2263–2271.
4
2
13 Li, C. H.; Ge, Z. S.; Liu, H. W.; Liu, S. Y. J Polym Sci Part A:
spond to the softer PEG arms. The diameter of the dumb-
bell-like object is much larger than the hydrodynamic radius
Polym Chem 2009, 47, 4001–4013.
(
R ) of the single miktoarm star polymer molecule (ꢁ20 nm
14 Gozgen, A.; Dag, A.; Durmaz, H.; Sirkecioglu, O.; Hizal, G.;
h
Tunca, U. J Polym Sci Part A: Polym Chem 2009, 47, 497–504.
obtained by DLS, Fig. 6). On the basis of these results, we
may speculate that in cyclohexanone an intramolecular seg-
regation of PS and PEG arms likely occurs, leading to Janus-
like miktoarm star copolymers that may further aggregate
on mica into large entities with Janus structure due to the
incompatibility of PS and PEG arms (Scheme 3).
1
5 Zhang, Y. F.; Liu, H.; Dong, H. F.; Li, C. H.; Liu, S. Y. J Polym
Sci Part A: Polym Chem 2009, 47, 1636–1650.
1
6 Fu, Q.; Wang, G. W.; Lin, W. C.; Huang, J. L. J Polym Sci
Part A: Polym Chem 2009, 47, 986–990.
1
7 Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew Chem Int
Ed 2001, 40, 2004–2021.
CONCLUSIONS
1
8 Durmaz, H.; Dag, A.; Erdogan, E.; Demirel, A. L.; Hizal, G.;
In summary, a facile synthetic pathway to miktoarm star
copolymers with multiple arms has been developed using a
combination of RAFT arm-first technique and aldehyde–ami-
nooxy ‘‘click’’ coupling reaction. As an initial attempt of this
new methodology, star PS bearing multiple aldehyde func-
tionalities in the core was initially prepared by RAFT arm-
first technique via crosslinking of the preformed linear
macro-RAFT agents using a newly designed aldehyde-con-
taining divinyl compound EVBA. The aldehyde groups pre-
served in the star core were then allowed to simply click
with aminooxy-terminated PEGs to form PS-PEG miktoarm
star copolymers. The obtained miktoarm star copolymer may
show a Janus-like segregated structure in cyclohexanone.
Tunca, U. J Polym Sci Part A: Polym Chem 2010, 48, 99–108.
1
9 Gou, P. F.; Zhu, W. P.; Zhu, N.; Shen, Z. Q. J Polym Sci Part
A: Polym Chem 2009, 47, 2905–2916.
20 Zhang, Y. F.; Li, C. H.; Liu, S. Y. J Polym Sci Part A: Polym
Chem 2009, 47, 3066–3077.
2
1 Dag, A.; Durmaz, H.; Sirkecioglu, O.; Hizal, G.; Tunca, U.
J Polym Sci Part A: Polym Chem 2009, 47, 2344–2351.
2
2 Gao, H.; Matyjaszewski, K. Macromolecules 2006, 39,
4
960–4965.
23 Zhu, J.; Zhu, X. L.; Kang, E. T.; Neoh, K. G. Polymer 2007,
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8, 6992–6999.
2
4 Gungor, E.; Durmaz, H.; Hizal, G.; Tunca, U. J Polym Sci
Financial support by Natural Science Foundation of China (pro-
ject no. 20874115) is greatly acknowledged.
Part A: Polym Chem 2008, 46, 4459–4468.
2
5 Heredia, K. L.; Tolstyka, Z. P.; Maynard, H. D. Macromole-
cules 2007, 40, 4772–4779.
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MIKTOARM STAR COPOLYMERS VIA RAFT AND CLICK REACTION, WU ET AL.
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