ChemComm
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Fig. 3 Left: GPC trace for polymer 4 in chloroform, calibrated against PEG standards;
the two peaks correspond to single-length and double-length chains arising from
association via the ‘‘Roman Handshake’’. Right: transmission electron micrograph
showing micellar nanoparticles of polymer 4 on a graphene oxide support.
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[
PEG–‘‘Roman Handshake’’–PEG]. Conversely, in DMF-LiBr as
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eluent, only a single peak corresponding to unassociated
chains was observed, confirming the conclusion from NMR
analysis that, in the present system, dipolar aprotic solvents are
powerful inhibitors of supramolecular dimerisation.
In aqueous solution, dimerisation of polymer 4 is clearly evident
from the strong charge-transfer absorption in the visible at 570 nm
(
ESI,† Fig. S11), but 4 also seems to aggregate to form micellar-type
structures in water. Aqueous GPC thus shows peaks at Mn
500 Da (unimers) and E 120 000 Da (self-assembled nanostruc-
9
S. V. Kolotuchin and S. C. Zimmerman, J. Am. Chem. Soc., 1998,
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E
1
4
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0 F. Ouhib, M. Raynal, B. Jouvelet, B. Isare and L. Bouteiller, Chem.
Commun., 2011, 47, 10683 and references therein.
1 (a) S. Burattini, H. M. Colquhoun, B. W. Greenland and W. Hayes,
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tures; ESI,† Fig. S12). However, no GPC peak associated with the
dimer is observed in water, suggesting that in aqueous solution the
dimers themselves undergo a further assembly process to form
micelles. This is corroborated by unstained TEM analysis (Fig. 3)
of dried samples on graphene oxide supports, which shows
well-defined, spherical assemblies with diameters in the size-
range 6–8 nm. Analysis by dynamic light scattering also con-
firmed that nanoscale structures (ca. 20 nm) were present in
aqueous solution although, as is often found for PEO-based
systems, larger aggregates (ca. 200 nm) were also found.
We have thus demonstrated a powerful new self-assembling
molecular motif based on electronically-complementary p–p-
stacking interactions and hydrogen bonding, and have shown
its potential for effective enhancement of polymer molar mass.
This work was supported by EPSRC (EP/G026203/1 and EP/
C533526/1), the Royal Society (travel grant to CJC) and the
1
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(c) S. Burattini, B. W. Greenland, W. Hayes, M. E. Mackay, S. J. Rowan
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56 Chem. Commun., 2013, 49, 454--456
This journal is c The Royal Society of Chemistry 2013