OPTIMIZING CU(I) CATALYSTS ONTO NANOPARTICLES FOR
ENHANCED REACTIVITY IN SELF-HEALING POLYMERS
A. Stojanovic1, A. Shaigan Nya1, S. Rana1and W. H. Binder1
1Institute of Chemistry, Chair of Macromolecular Chemistry, Faculty of Natural Sciences II
(Chemistry, Physics and Mathematics), Martin-Luther University Halle-Wittenberg, von Danckelmann-Platz 4, Halle 06120, Germany– e-mail: wolfgang.binder@chemie.uni-halle.de Keywords: copper(I) catalyst, nanoparticles, alkyne-azide “click” reaction
ABSTRACT
The concept of self-healing polymers requires fast and efficient crosslinking processes, ideally based on catalytic reactions. Recently, we have developed a click-based concept to enable self-healing properties in polymeric materials, with a focus on fast crosslinking processes. Basically, liquid reagents were encapsulated and thus can be activated by a catalytic system, inherently present within the polymer-matrix. As especially the combination of self-healing properties of nanocomposite-materials in aerospace industry deems valuable in terms of property-optimization, we focus on crosslinking processes under mild conditions, based on the copper(I)-catalyzed alkyne-azide "click" cycloaddition reaction (CuAAC). Thus we have immobilized copper(I) catalysts onto the surface of nanoparticles, on the one hand to increase the stability of the catalyst and to stimulate the self-healing processes, on the other hand to enhance the properties of the polymeric nanocomposites via the presence of the nanoparticles. For this purpose the surface of different types of nanoparticles has been chemically modified, in the subsequent step immobilizing the corresponding Cu(I) catalyst coordinatively onto their surfaces. The prepared immobilized Cu(I) were extensively characterized via TGA, XRD and TEM, furthermore demonstrating and optimizing the activity of the immobilized catalyst for all types of "click"-reactions. 1. INTRODUCTION
Polymers with self-healing [1] or self-repairing properties [2], often including capsule-based concepts [3], mechanophores [2] and supramolecular concepts [4] have gained increasing intention in the past years. In all cases the basic concept of such materials relies on the use of crosslinking processes which enables repair of a mechanically induced damage by subsequent network-formation [5]. Recently, we have developed a click-based concept to enable self-healing properties in polymeric materials, with a focus on fast, “click-chemistry-based” crosslinking processes [6]. Basically, liquid reagents were encapsulated and thus can be activated by a catalytic system, inherently present within the polymer-matrix (see Figure 1).
Figure 1: The self-healing process based on the combination of “click”-crosslinking and encapsulation.
For many applications e.g. in aerospace industry the crosslinking processes under mild conditions are of an especial interest. Hence, we focus on the crosslinking processes based on the copper(I)-catalyzed alkyne-azide "click" cycloaddition reaction (CuAAC). The features of CuCAAC such as high efficiency and substrate insensitivity, make this type of reactions suitable for crosslinking processes under moderate condition, both in homogenous and heterogeneous systems [7].
In present work we focus on the immobilization of copper(I) catalysts onto the surface of nanoparticles, with the aim to on the one hand increase the stability of the catalyst and to stimulate the self-healing processes, and on the other hand to enhance the properties of the polymeric nanocomposites via the presence of the nanoparticles. 2. RESULTS AND DISCUSSION
For the purpose of the effective immobilization of Cu(I) onto the surface of nanoparticles the surface of the selected nanoparticles was modified in the multiple-step synthetic route in order to be able to coordinatively bound the corresponding Cu(I) catalyst. The schematic representation of the synthetic route is presented in figure 2. The obtained functionalized nanoparticles have been intensively characterized via TGA, FTIR and EDX.
Figure 2: Scheme of the immobilization of Cu(I) catalyst
In the next step the selected Cu(I) catalyst is coordinatively attached to the surface of the nanoparticles. After suitable immobilization of the corresponding Cu(I) catalyst, the amountof the coordinatively bonded Cu(I) was determined and the prepared nanoparticles were extensively characterized via TGA, XRD and TEM. Furthermore
the activity of the immobilized catalyst for all types of "click"-reactions has been investigated.
3. CONCLUSION
Our preliminary results have shown that the selected Cu(I) catalysts can be effectively bounded on the surface of nanoparticles. Furthermore, the concept of the use of immobilized Cu(I) catalyst for the crosslinking processes based on alkyne-azide "click" cycloaddition reaction seems to be very promising.
ACKNOWLEGDEMENT
The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement n° 313978.
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