4. Polymerization

The CNTs have excellent thermal and electrical conductivities and reported to be used as fillers in polymer based advanced composites. However due to poor solubility of CNTs, homogeneous dispersion is difficult task. The polymer functionalized CNTs are prepared following three approaches:

1. A non-covalent functionalization method in which polymers are produced by ring opening metathesis polymerization. The coating of hyper branched polymers on MWCNTs has been obtained via cationic ring opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane with a BF₃ .Et₂O catalyst [14]
   
   
2. A covalent functionalization performed by, first grafting polymerization initiators onto the tubes through covalent bond and then exposing these CNT based macro-initiators to the monomer. The polymer is obtained by atom transfer radical polymerization. The polyethylene-MWCNT composite has been produced using catalyst grafting procedure by polymerization of ethylene on [ZrCl₂C_p2] MAO/MWCNT where C_p = C₅H₅ and MAO = methylaluminoxane [15].
   
   
3. Olefin polymerization via anchored metallocenes catalysts. It has been proposed that MWCNT play a key role in increasing the molecular mass. Supporting the catalytic system on MWCNTs increases the polymerization rate of ethylene. Syndiotactic polypropylene-MWCNT composites have been prepared by propylene polymerization on zirconocene-MAO catalysts [16].

 

5. Fuel cell electrocatalysts

CNTs are used as catalysts supports for anode or cathode catalysis in direct methanol fuel cells or proton exchange membrane fuel cells. The structure and properties of carbon supports which constitute the electrode material have a direct impact on performance of fuel cells. The most studied reactions are methanol oxidation (anode catalyst), oxygen reduction (cathode catalyst) and hydrogen oxidation (anode catalyst). The Pt is most used metal followed by Pt-Ru system. The general observation is that CNT based catalysts are more active and better resistant to poisoning compared to conventional carbon black support. The advantage of CNT supports for fuel cell applications is attributed to:

1. Higher metal dispersion and higher electroactive surface area
2. Higher mesopores 3D network facilitating mass transport
3. Excellent conducting properties which improve electron transfer