Macromolecular Nanotechnolgy Surface initiated ring-opening polymerization of L-proline N-carboxy anhydride from single and multi walled carbon nanotubes Manos Gkikas a , Biswa P. Das b , Marina Tsianou b , Hermis Iatrou a,⇑ , Georgios Sakellariou a,⇑ a University of Athens, Chemistry Department, Panepistimiopolis, Zografou 15771, Athens, Greece b Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260-4200, USA article info Article history: Received 14 April 2013 Received in revised form 12 June 2013 Accepted 1 July 2013 Available online 17 July 2013 Keywords: Surface-initiated ring-opening polymerization Carbon nanotubes Poly(L-proline) Diels–Alder cycloaddition abstract Ring-opening surface initiated polymerization of L-proline N-carboxyanhydride was per- formed from amine functionalized single (SWNTs) and multi walled carbon nanotubes (MWNTs). The primary amines were grafted on the surfaces via a well-studied Diels–Alder cycloaddition. The initiator attachment helped the debundling of carbon nanotubes as shown by atomic force microscopy (AFM) studies where only small aggregates were observed. Thermogravimetric analysis revealed high wt% of grafted polyproline on the car- bon nanotubes surface after the ring-opening polymerization. AFM studies showed a rather uniform layer of grafted polyproline from both MWNTs and SWNTs. The grafting of PLP on the surface was also verified by FTIR and Raman spectroscopy as well as 1 H NMR in CDCl 3 / d-TFA. The polyproline grafted carbon nanotubes (CNTs) were readily dissolved in organic solvents in contrast to the insoluble pristine and amine-functionalized CNTs. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Carbon nanotubes [1] (CNTs) have attracted great atten- tion in both academic and industrial research due to their exotic properties. High surface area and high aspect ratio (1000), very high flexibility [2], low mass density [3], combination of electrical and thermal properties and extraordinary mechanical properties with high tensile strength (70 GPa), elastic modulus (200 MPa), and Young’s modulus (1.5 TPa) [2,3], make them suitable can- didates for applications in a wide range of technologies [2,3]. Lately, much effort has been devoted to use these materials in the field of nanobiotechnology. Therefore, designing biologically significant [4] CNT surfaces is of par- amount importance since functionalized CNTs have the ability to penetrate mammalian cell membranes, rendering them highly promising novel delivery systems. In addition, their high surface area provides multiple attachment sites for drugs, genes, targeting moieties and fluorescent mark- ers. Pristine CNTs appear to be non-toxic to cells at low concentrations [5], while their physicochemical character- istics (length and diameter) are critical for their toxicolog- ical profile [6,7]. Carbon nanotubes functionalized with short peptides [8,9] and, more recently, with polypeptides [10–18] have been introduced, where the modification has been achieved by surface initiated ring-opening polymeri- zation [10–12] or via the grafting to methodology [13–18], though the number of polypeptides utilized is strictly lim- ited only to two. In efforts to enhance the dispersion properties of carbon nanotubes, polypeptide conjugates have been used in aqueous media by tethering, through the polypeptide side chain, aromatic hydrophobic groups [14] in random copolypeptides or by labeling poly(L-lysine), PLL, with MACROMOLECULAR NANOTECHNOLOGY 0014-3057/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2013.07.002 ⇑ Corresponding authors. Tel.: +30 2107274768 (G. Sakellariou). E-mail addresses: iatrou@chem.uoa.gr (H. Iatrou), gsakellariou@ chem.uoa.gr (G. Sakellariou). European Polymer Journal 49 (2013) 3095–3103 Contents lists available at SciVerse ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj