# Assessment of Catalyst Selectivity in Carbon-Nanotube Silylesterification
## 1 Introduction  
Carbon nanotubes (CNTs) [1] have exceptional electrical, mechanical, and physical properties [2]. However, their major drawbacks are their insolubility in most common solvents, and their tendency to form aggregates due to strong \(\pi\)-\(\pi\) and van der Waals interactions. Therefore, due to the chemical functionalization of CNTs, it is often necessary in order to exfoliate and solubilize them before their practical application [3, 4]. Moreover, their use as reinforcement in polymers requires anchoring groups that must be introduced by chemical functionalization. Many different methods for the chemical functionalization of CNT sidewalls were reported [5]. One approach consists of the direct functionalization of the CNT sidewall using, for example, carbenes, nitrenes, the Diels-Alder reaction, and diazonium [6]. This option has the advantage of preserving the aspect ratio of CNTs, as well as their mechanical and electrical properties [7]. However, this depends on the number of defects created in the outermost aromatic layer. A second approach concerns thederivatization of oxidized functional groups introduced by acidic treatments [8] at the extremities or defective areas of CNTs. Derivatization reactions include amidation [9; 10], esterification, and reactions with silicon derivatives such as hydrosilanes and chlorosilanes [11]. Among the various options for the derivatization of oxidized functional groups, silylesterification is a powerful way to modify the CNT surface using silane compounds [12]. This functionalization allows for modification by many silane derivatives bearing various side chains. Hydrosilanes have the advantage of being less reactive than their chlorosilane counterparts, which allows for the use of less stringent experiment conditions. Usually, the coupling of hydrosilanes with oxygen-containing molecules requires the presence of a catalyst. Depending on the catalyst's nature, hydrosilanes react differently with oxygenated molecules. CNT modification with an Si-O-C bond creates opportunities for the addition of different functional groups for various applications. These include the filling of silicone composites, rubbers [13], ceramics, and epoxides [14]. In a previous study [11], our group reported on the functionalization of oxidized CNTs (using oxidative acid treatment) with hydrosilane as an anchoring molecule. Specifically, we used a fluorine-bearing hydrosilane, diisopropyl(3,3,4,4,5,5,6,6,6-nonafluorohexyl) silane, which is also referred to as R\({}_{\text{f}}\)(iPr)\({}_{2}\)SiH. We compared two different catalysts--zinc chloride (ZnCl\({}_{2}\)) and [PERSON]'s catalyst (1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum (0) complex). CNTs oxidized by concentrated acids, bearing several different oxygenated functional groups, reacted differently with each catalyst. We hypothesized that the zinc chloride catalyst allowed for reactions involving only carboxyl groups, while [PERSON]'s catalyst facilitated reactions of both alcohol and carboxyl groups that were introduced during oxidative acid treatment. The aim of this study was to assess the selectivity of silylesterification reactions on CNTs by using CNTs modified by derivatives of aryl diazonium salts as a starting material. In contrast to products obtained after oxidation using concentrated acid mixtures, diazonium-mediated modification allows for the preparation of CNTs with controlled surface chemistry [15; 16; 17]. In addition, the advantage of using diazonium modification is that oxidative treatment can affect CNT conductivity. This has been proven in a previous study by measuring the electrical conductivity of buckypaper (a thin sheet of aggregated CNTs) [7] prepared from diazonium-modified CNTs and oxidized CNTs. Using a silylesterification reaction [11], the selectivity of both catalysts for various oxygenated functional groups on aryl diazonium derivatives was investigated (Table 1).