Journal of the American Chemical Society
COMMUNICATION
the peak at 2100 cmÀ1, ascribed to the azide group, was clearly
present, and Figure S10 shows its GPC curve, which is well
defined, monomodal, and symmetrical. The Mn and Mw/Mn
were measured as 1000 g/mol and 1.1, respectively. PS Polymer
brush 3 was produced under the same synthesis conditions as
cyclic PEG Polymer brush 2. From the GPC shown in Figure 1B
(blue), it can be seen that the monomodal peak shape of the
precursor, Poly-2, was preserved, and a complete peak shift to the
higher MW was observed. This confirms that, by combining the
Poly-2 template with ATRP, a wide range of cyclic polymer
brushes can be prepared.
’ ACKNOWLEDGMENT
Generous support was primarily provided from DMR-
0820506, CMMI-0531171. Partial support was provided from
ARO W911NF-09-1-0373 and ONR N00014-10-1-0348. Shared
facilities support also comes from DMR-0820506. The authors
thank Dr. A. J. Boydston, Dr. Y. Xia, and Prof. R. H. Grubbs for
valuable discussions about the synthesis of cyclic catalyst UC-6
and Michael Lis for assistance in preparing the manuscript.
’ REFERENCES
Additionally, by introducing a chemical agent with two or more
reactive groups as a cross-linker, novel network materials with
cyclic molecular structures can be prepared by cross-linking the
cyclic templates. To demonstrate this concept, 1,6-hexanedi-
amine was used as a model cross-linker for Poly-1 (Scheme 1(vi))
and 1,6-hexanediazide was used for Poly-2 (Scheme 1(vii)). By
using a molar ratio of 1:5 between reactive groups in the cross-
linkers and clickable side groups in the templates, both Cyclic gel
1 and Cyclic gel 2 were obtained in less than 5 min at room
temperature. Figures 3D and S11 show representative photos of
the resulting gels in inverted vials. Compared to conventional
gels that are formed by cross-linking linear polymer chains, the
novel cyclic gels should possess unique properties, as the cyclic
polymer chains serve as a form of secondary topological cross-
links.24 Rather than the uncontrolled free radical coupling
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tries described here will enable more freedom to manipulate the
internal structure of these novel cyclic gels and should lead to an
even wider array of network properties.
In conclusion, the synthesis and application of two universal
cyclic polymer templates were demonstrated, combining REMP
and click chemistry. Using activated ester chemistry, cyclic
Poly-1, bearing pentafluorophenol ester side groups, was post-
functionalized by amine functional agents. By virtue of copper(I)-
catalyzed click chemistry, cyclic Poly-2, with alkyne side groups,
was modified by azide functional agents. Based on these clickable
cyclic polymer templates, several diverse novel materials with
cyclic molecular topologies were developed, including functional
cyclic polymers, microscopic cyclic polymer brushes, and macro-
scopic cyclic gels. Theoretically, the use of these universal cyclic
polymer templates could be expanded to incorporate other types
of click chemistry, such as thiolÀene coupling and DielsÀAlder
click reactions, following the same concept. Further, due to the
high selectivity of click chemistry and orthogonal reaction me-
chanisms, these individual templates could be combined. This
provides practical methods to explore novel materials not only
bearing cyclic main-chain topologies but also having an advanced
hierarchy, such as new double-network materials containing two
independent cyclic macromolecules. Current investigations of
these and other possibilities are ongoing.
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’ ASSOCIATED CONTENT
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S
Supporting Information. Experimental details and
b
Figures S1ÀS11. This material is available free of charge via
’ AUTHOR INFORMATION
Corresponding Author
6909
dx.doi.org/10.1021/ja2007559 |J. Am. Chem. Soc. 2011, 133, 6906–6909