## 1 Introduction  
Nanoscience and nanotechnology have brought us the excellent development of many novel categories of functional materials and have become remarkable fields of study [1; 2]. Recently, carbon nanotubes (CNTs) have acquired increasing importance and popularity in membrane science and technology due to their high permeability and selectivity, which they owe to the rapid flux through the hollow interior and nano-scale diameter of CNTs [3; 4; 5; 6; 7]. For instance, multiwalled carbon nanotubes (MWCNTs) with outer diameters (2-100 nm) exhibit a significantly high permeability in membrane process applications because of the large surface area [6]. The MWCNT hybrid nanostructure and composite materials with the introduction of polymer chemistry have dramatically attracted attention [8; 9]. These nanocomposite materials complement the characteristics of functional polymers and thus provide improved nano-scale dispersing, hydrophilicity, electric properties, etc. [10]. Someresearchers have directly immobilized MWCNTs into a polymeric membrane by the blending method due to its easy manipulation and mild conditions [11; 12]. However, despite the outstanding properties of MWCNT composite materials, the tendency to be polymerized caused by the big inherent van der Waals forces of MWCNTs restricts its application to the fabrication of nanocomposites. [13].  
Among the surface modification method, the \"grafting to\" technique is one of the most convenient techniques to cap polymer chains which can adjust the dispersibility of nanoparticles in polymer matrices [14]. In this approach, functional group-terminated polymer chains can graft onto the surface of nanoparticles in a highly efficient reaction, resulting in the formation of tethered polymer chains [15]. To achieve dense polymer layers attached to the MWCNT surface, strong interactions between polymer chains and the MWCNT surface are required. Poly(methyl methacrylate) (PMMA) is usually studied as a compatibilizer agent for polymer/nanoparticle composites [16]. Recently, \"click chemistry\" has attracted more attention in surface modification for nanoparticles due to its high yields without byproducts [17; 18; 19; 20]. When combined with reversible addition-fragmentation chain transfer (RAFT), the precise predesign of the molecular weight, structure, and functionality of polymers can be controlled by living polymerizations [21]. For example, [PERSON] and co-workers synthesized a hydrophilic MWCNT based upon the Diels-Alder (DA) click reaction by one step [22]. Nonetheless, few have been reported in the field of PMMA-functioned MWCNTs, synthesized through the click reaction.  
In this work, by using azide/alkyne end groups, PMMA with an azide end group can effectively graft onto the MWCNT surface. To do this, the RAFT agent 2-dodecylsulfanylthiocarbonylsulfanyl-2-methylpropionic acid 3-azidopropyl ester (DMP-N\({}_{3}\)) was used in the polymerization of PMMA. Then, azide-terminated PMMA was attached to the surface of alkyne-terminated MWCNTs via the \"grafting to\" approach. Due to the PMMA chain on the MWCNT surface, the nanohybrids can be stably dispersed in water and have potential for the preparation of MWCNT composite materials.