Paper
Green Chemistry
∼7 nm. The hydrodynamic sizes of the CCS polymers were
found to increase significantly. For example, an increase of
hydrodynamic radius from ∼7 nm for the block copolymer P2a
in THF to 58 nm and 26 nm was observed for the CCS poly-
mers with 20 mol% of CL-1 and CL-2, respectively. A similar
change in hydrodynamic radius due to the formation of core
cross-linked networks was also observed by Sumerlin et al.,8
Fulton et al.,9 Stenzel et al.,20 Lee et al.21 Also, a larger hydro-
dynamic radius was observed in the case of CL-1 compared to
CL-2 at the same concentration (mol%) which relates to a
more effective cross-linking leading to higher incorporation of
arms by CL-1, which correlates with molecular weight data as
discussed earlier. Although it is a fact that a more precise
characterization of these synthesized star-branched polymers
is possible by using a multi-angle light scattering detector, yet
our results based on 1H NMR, FTIR, GPC and DLS grossly hint
to the formation of core cross-linked star polymers via the for-
mation of an isoxazoline ring using ‘click chemistry’.
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Conclusion
In conclusion, this study may be envisaged as an effort to in-
troduce a green methodology for the synthesis of CCS polymers
through isoxazoline ring formation in a rapid, convenient, one-
pot nitrile oxide-acrylate 1,3-DC reaction. Unlike conventional
Cu-catalyzed reactions that are associated with the risk of con-
tamination by the metal beyond threshold level, rendering them
particularly unfavorable for biological applications, this process
does not require the use of Cu, thus ensuring the development
of a hazardless product. The synthesis of acrylate functionalized
triblock copolymers of well-defined structures were made possi-
ble by the versatile RAFT technique. A reasonably good control
on the molecular weight and PDI of the linear block copolymer
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A. Takahara, J. Am. Chem. Soc., 2007, 129, 13298;
(b) Y. Amamoto, T. Maeda, M. Kikuchi, H. Otsucka and
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M. Kikuchi, H. Masunaga, S. Sasaki, H. Otsucka and
A. Takahara, Macromolecules, 2010, 43, 1785.
allowed the formation of
a well-defined CCS polymer.
Such advanced technologies based on metal-free chemistry are
of utmost significance, as they may be effectively applied for
developing new materials for diverse applications, particularly
in the field of biological sciences.
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J. T. Koberstein and N. J. Turro, Chem. Commun., 2008,
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Acknowledgements
Financial support from the Department of Science and Tech-
nology, Government of India, New Delhi, (Project ref. no. SR/
FTP/CS-79/2007) is acknowledged. R. Banerjee and S. Maiti
acknowledge UGC and CSIR, New Delhi, respectively, for
Research Fellowships. The authors are also thankful to Prof.
Nilmoni Sarkar for providing help in DLS measurements.
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1372 | Green Chem., 2014, 16, 1365–1373
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