## 7 Polymer/CNT Composite Catalysts  
Since the discovery of carbon nanotubes (CNTs) in 1991 by [PERSON] [201] and due to their unique physical properties [202,203], many researchers have tried to fabricate advanced CNT composite materials that exhibit one or more of these remarkable physical and mechanical properties [204, 205, 206]. One of the topics of current interest is to use CNTs as a filler in polymer composite systems to obtain ultra-light structural materials with enhanced mechanical, electrical, thermal and optical characteristics [207, 208, 209, 210, 211, 212, 213]. The prospect of obtaining advanced nanocomposites with multifunctional features, e.g., materials used for structures and electrical conductors, has attracted great efforts from researchers in both academia and industry [214, 215, 216, 217]. Monoethylene glycol (MEG) is a necessary monomer for the production of polyester PET (polyethylene terephthalate), which is produced by hydration of ethylene oxide (EO). Non-catalytic and catalytic hydrations of EO are two well-known approaches to prepare MEG. Numerous catalysts, including anion exchange resins, quaternary phosphonium halides, polymeric organosilane ammonium salts and macrocyclic chelating compounds, have been used for the catalytic hydration of EO, and most of them use catalysts immobilized on ion exchange resin (IER) [218, 219, 220]. However, catalyst stability is a major challenge because the resins swell under the reaction conditions [221,222], and therefore there is an urgent demand for catalysts with high thermal stability while maintaining high selectivity and conversion. According to the papers published so far on heterogeneous catalytic hydration of ethylene oxide, polymeric ion exchange resins (IER), both strong acid and strong basic type, are the most effective catalysts. The acidic hydration process is accompanied with side reactions. On the other hand, alkaline hydration, with less byproducts, can increase the MEG selectivity, and is thus of greater research interest, but the intrinsic swelling problem of IER as the hydration proceeds restricts its application in the industrialization of catalytic hydration of ethylene oxide. Measures such as increasing the cross-linking density have been used to solve the swelling problem to some extent at the expense of reducing exchange capacity and the number of active sites of the resin. We have developed an ion exchange resin/CNT composite (PS-DVB/CNT) to handle the problem of swelling as mentioned above [223]. This resin/CNT composite was prepared via _in-situ_ suspension polymerization of styrene, divinylbenzene and multi-walled carbon nanotubes (MWNTs), followed by chloromethylation and amination. The pristine MWNTs, which acted as potential cross-linking agent,were dispersed well in the cross-linking network of PS-DVB polymer (Figure 12). The growing polymer chains, initiated by thermal decomposition of AIBN and subsequent polymerization, have tendency to add the double bonds on the surface of MWNTs, besides its tendency to add to the double bond of DVB, therefore we can readily functionalize the MWNTs through the \"grafting-onto\" mechanism. Taking the amount of double bonds into consideration, the MWNTs, together with DVB, might play the role of potential cross-linking agent. In our case, the content of MWNTs in the final resin composite reached 4% and the cross-linking density was 8%, equal to the industrialized non-functionalized ion exchange resin. It was found that the anti-swelling capability and thermal stability of resin/CNT composite are improved significantly after the addition of MWNTs while keeping the total number of active reaction sites, and the stability and the conductivity of the catalyst increased as well. It was also found that the glass transition temperature (\(T_{g}\)) increased from 125 \({}^{\circ}\)C to 132 \({}^{\circ}\)C when MWNTs were incorporated in the cross-linking network of PS-DVB.