Poly(Glycidyl Methacrylates)-grafted Zinc Oxide Nano- wire by Surface-initiated Atom Transfer Radical Poly- merization

1Key Laboratory for Thin Film and Microfabrication of the Ministry of Education, National Key Laboratory of Nano/Micro Fabrication Technology, Research Institute of Micro/Nano Science and Technology, Shanghai Jiao Tong University, Shanghai 200240, P. R. China 2Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China *Corresponding author. E-mail: yfzhang@sjtu.edu.cn Poly(Glycidyl Methacrylates)-grafted Zinc Oxide Nanowire by Surface-initiated Atom Transfer Radical Polymerization Bao Zhang1,2, Nantao Hu1, Yanfang Wang1, Zi Wang1, Ying Wang1, Eric S. Kong1 and Yafei Zhang1,*

ZnO nanowires are one of the most promising materials for optoelectronic applications due to their wide band gap of 3.37 eV and large exciton binding energy of 60 meV [1]. It has been recognized as one of the promising nanomaterials in a broad range of high-technology applications, such as photodetector [2], light-emitting diode [3], gas sensor [4], solar cell [5], and optical modulator waveguide [6], etc. Work in this area has focused on the synthesis and material properties of ZnO nanostuctures, and thus, a wide array of materials are available [7,8]. The properties of these nanostructures, and our ability to assemble them, depend largely on the surface functionalization of such structures.
Surface-initiated polymerization, generally called ""grafting from"", is an important tool to further develop their chemical and physical properties by covalently graft a wide range of polymer chains onto curved or flat surfaces [9][10][11][12]. In comparison with traditional processes used to prepare polymer coatings, surface-initiated polymerization methods provide numerous advantages, including chemical attachment of the polymer to the surface, [13] preparation of conformal coatings on objects of various shapes [14], and good control over film thickness and composition [15].
One of the most successful processes is ATRP [16][17][18], which offers efficient, well-controlled grafting and narrow molecular weight distributions of the polymers grown from the surfaces. The radical reactions involved in the ATRP process enable a wide range of monomers to be used, leading to polymer-modified surfaces with new functionality [16]. This, together with the halogen end-groups, can significantly enhance the physicochemical compatibility of the resulting composites, making the design and preparation of novel materials with DOI:10.3786/nml.v2i4.p285-289 http://www.nmletters.org tailorable structures and properties accessible. ATRP reactions have already been used effectively to modify the surfaces of many nanostructured, such as silica surfaces [19], the surfaces of gold [20], magnetic nanoparticles [21], and carbon nanotubes [22], in each case, providing stability and/or other desirable surface properties. In contrast to the large body of work detailing the modification of silica surfaces, we are aware of only a few reports of related chemistry with ZnO in which a silane was used to modify the surface [23,24]. was refluxed for 12 h in the presence of CaH 2 and distilled. All the reagents used in this study were of analytic grade.

Synthesis of ZnO nanowires
The synthesis of ZnO nanowires were performed according to the report described previously [25]. 0.3 g ZnCl 2 and 30 g Na 2 CO 3 were successively added into a 100 mL Telfon-lined stainless steel autoclave, which was then filled with distilled water up to 90% of the total volume. The obtained reaction mixture was stirred for an additional 30 min. The autoclave was sealed and maintained at 140C for 12 h. After the reaction was completed, the resulting white products were filtered off, washed with ethanol and hot distilled water for several times, and then dried in a vacuum at 60C for 4 h.

Techniques and measurement
The morphology and structure of the samples were

Synthesis of ZnO nanowires
The synthesis route of the ZnO nanowires was shown in scheme 1. Figure 1(A)

Immobilization of the initiator on ZnO surface
To prepare the polymer brush on the ZnO surface, a uniform and dense layer of initiators immobilized on the ZnO surface is indispensable. Scheme 1 outlines the route to generate the ATRP initiator on the ZnO surface. The α-bromoester initiator on the ZnO substrate was prepared by the self-assembly of 3-aminopropyl triethoxysilane, followed by amidization with 2-BPB. FTIR (Fig. 3 A)  To investigate the content of the polymer on the ZnO nanowires, we carried out the TGA characterization. In the TGA curve of the PGMA-ZnO nanowires (Fig. 4), the weight loss at near 100C is assigned to the release of moister adsorbed.
And the weight loss at the temperature range of 250-550C is assigned to the thermal degradation of the grafted PGMA. As far as the ZnO nanowires (Fig. 4A) is concerned, the weight was nearly not changed. As for the PGMA-ZnO nanowires (after the reaction was going on 12 h) (Fig. 4B), the weight decreased to 32%, which means that the content of the polymer in PGMA-ZnO nanowires was 68%. The kinetics of SI-ATRP Attempts were made to prepare polymer nanotube by removing the ZnO nanowires in hydrochloride acid ， but polymers failed to make well-formed tubes (Fig. 1C), instead forming disordered polymer thin films. We studied ZnO nanowires with different thickness of polymer, but they are never sufficient to give normal polymer nanotubes. We deduced that the soft polymer will be collapsed and adhered together after the template ZnO was removed. The FTIR spectrum of the products (Fig. 3C) is similar to PGMA-ZnO nanowires (Fig. 3B), which indicated that the polymer component was not changed. To prove the ZnO nanowires were removed completely, the product was investigated by TGA. The result (Fig. 4C) shows that the The grafted organic layer composed of PGMA could provide a platform for further surface modification by functionalization of the hydroxyl groups. It is also expected to be used for the assembly of the ZnO semiconductor devices.