Hairy nanotubes DOI: 10.1002/smll.200600688 “Hairy” Single-Walled Carbon Nanotubes Prepared by Atom Transfer Radical Polymerization Wei Wu, NicolayV. Tsarevsky, JaredL. Hudson, James M. Tour,* Krzysztof Matyjaszewski,* and Tomasz Kowalewski* “Hairy nano-objects” are hybrid nanostructures comprising a core sur- rounded by a “hairlike” corona of flexible polymer chains, the role of which is typically to improve the solubility of the core material or to improve its dispersability and adhesion in other polymer matrices. Both aspects could be particularly useful with carbon nanotubes, especially in their applications as reinforcing agents. The controlled synthesis of hairy carbon nanotubes is accomplished by chemical modification with 2-bro- mopropionate followed by extension with poly(n-butyl acrylate) through atom transfer radical polymerization. The obtained hairy nanotubes are visualized at nearly molecular resolution with tapping-mode atomic force microscopy, providing insight into the uniformity of grafted chain lengths and grafting density. The grafting densities vary from  1.0– 10.0chainsnm 1 along the nanotubes. Such a wide range of grafting density may indicate some chemical heterogeneity along and between the nanotubes; it may be also an indication of the challenges associated with carrying out chemical modification of nano-objects having high tendency to aggregate. Keywords: · atomic force microscopy · carbon nanotubes · polymerization · hairy nano-objects 1. Introduction The high tensile strength and electronic properties of single-walled carbon nanotubes (SWCNTs) [1–3] make them attractive for various applications for nanoelectronics, [4–6] biomedical devices, [7] sensors, [8] and high-strength fibers. [9,10] However, due to the poor miscibility of SWCNTs with sol- vents and polymers, solution processing and the preparation of nanotube-containing composite materials both remain a challenge.Anotherchallengeisrelatedtothepooradhesion between nanotubes and typical polymer matrices. One strat- egy to address the above issues is to modify SWCNT surfa- ces through covalent attachment of functional groups. [11] Of particular interest are the groups that can initiate polymeri- zation and yield “hairy” nanotubes. Indeed, some recent re- ports indicate that such polymer–nanotube hybrids could be prepared by atom transfer radical polymerization (ATRP) [14,15] from the surfaces of CNTs functionalized with various alkyl halides. [16–20] However, whereas the surface [*] W. Wu, N.V. Tsarevsky, Prof. K. Matyjaszewski, Prof. T. Kowalewski Department of Chemistry, Carnegie Mellon University 4400 Fifth Avenue, Pittsburgh, PA 15213 (USA) Fax:(+ 1)412-268-6897 E-mail: km3b@andrew.cmu.edu tomek@andrew.cmu.edu J. L. Hudson, Prof. J. M. Tour Department of Chemistry and Smalley Institute for Nanoscale Science and Technology Rice University MS 222, 6100 Main Street, Houston, TX 77005 (USA) Fax:(+ 1)713-348-6250 E-mail: tour@rice.edu Supporting information for this article is available on the WWW under http://www.small-journal.com or from the author. small 2007 , 3, No.10, 1803–1810 # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 1803 J. Tour, K. Matyjaszewski, T. Kowalewski, et al.