Historical perspective
Functionalization of carbon nanotubes by combination of controlled radical polymerization and “grafting to” method

https://doi.org/10.1016/j.cis.2020.102126Get rights and content

Highlights

  • Non-covalent and covalent tethering of small molecules and polymer chains onto CNT

  • Non-covalent grafting by hydrogen bonding and π-π stacking interactions

  • Covalent grafting by condensation, cycloaddition, and addition reactions

  • Combination of CRP and “grafting to” methods for controlled tethering of CNT

  • Applications of polymer-modified CNT in sensors, filtration, solar cells, etc.

Abstract

This paper reviews the recent advances in non-covalent and covalent tethering of small molecules and polymer chains onto carbon nanotube (CNT) and its derivatives. The functionalized CNT has recently attracted great attention because of an increasing number of its potential applications. In non-covalent functionalization of CNT, the sp2-hybridized network plays a crucial role. The non-covalent grafting of small molecules and polymers can mainly be carried out through hydrogen bonding and π-stacking interactions. In covalent functionalization of CNT, condensation, cycloaddition, and addition reactions play a key role. Polymer modification has been reported by using three main methods of “grafting from”, “grafting through”, and also “grafting to”. The “grafting from” and “grafting through” rely on propagation of polymer chains in the presence of CNT modified with initiator and double bond moieties, respectively. In “grafting to” method, which is the main aim of this review, the pre-fabricated polymer chains are mainly grafted onto the surface using coupling reactions. The coupling reactions are used for grafting pre-fabricated polymer chains and also small molecules onto CNT. Recent studies on grafting polymer chains onto CNT via “grafting to” method have focused on the pre-fabricated polymer chains by conventional and controlled radical polymerization (CRP) methods. CRP includes reversible activation, atom transfer, degenerative (exchange) chain transfer, and reversible chain transfer mechanisms, and could result in polymer-grafted CNT with narrow polydispersity index of the grafted polymer chains. Based on the mentioned mechanisms, nitroxide-mediated polymerization, atom transfer radical polymerization, and reversible addition-fragmentation chain transfer are known as the three commonly used CRP methods. Such polymer-modified CNT has lots of applications in batteries, biomedical fields, sensors, filtration, solar cells, etc.

Introduction

Carbon nanotube (CNT) as one of carbon allotropes has attracted large attentions due to its special properties. CNT is imagined as a cylinder obtained from rolling-up graphene sheets around a central hollow core structure [1,2]. Single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) are two common types of CNT. The SWCNT is twisted single graphene layers, while the MWCNT is composed from two or more graphene layers packed by van der Waals forces and π-π stacking interactions. CNT has commonly been used in thermal conductors, energy storage materials, conductive adhesives, thermally-stable materials, structural materials, fibers, catalyst supports, biological applications, air and water filtration, ceramics, and other applications [3,4]. Well-dispersion of CNT in a matrix requires its functionalization with small or even long chain chemicals. Physical and chemical functionalization methods are used for modification of CNT with different molecules. Functionalization of CNT with pre-synthesized polymer chains are carried out by using coupling reactions between the functionalized polymer chains with the bear or modified CNT.

Functionalized polymer chains are commonly synthesized by controlled radical polymerization (CRP) with different mechanisms [5]. CRP methods are mainly based on reversible termination or transfer reactions, where nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer polymerization (RAFT) are the three main methods of CRP. Control of polymerization in NMP method is carried out by a dynamic equilibration between the macroradicals and nitroxide radical-terminated dormant species [[6], [7], [8], [9], [10]]. In ATRP method, transition metal complex is used as the controlling agent of its equilibrium, where the polymer chains are reversibly terminated with a halide end. In RAFT method, different chain transfer agents of dithioester, dithiocarbamate, trithiocarbonate, and xanthate are needed to achieve reversible chain transfer equilibrium between the growing macroradicals. The polymer chains with nitroxide, halide, and chian transfer agent functional groups respectively in NMP, ATRP, and RAFT systems can be grafted to the bare or modified CNT using different coupling reactions, which are commonly known as “grafting to” reactions.

In “grafting to” reactions, the bear CNT can react with polymer macroradicals with radical addition reaction. In addition, CNT can be modified with different small molecules which are needed in the coupling reaction with functinalized polymer chains. Therefore, this review has focused on small-molecule functionalization of CNT with different methods based on physical and chemical methods. After that, polymer-functionalization of the bear and modified CNT with the polymers synthesized with three common CRP methods are reviewed in detail. By using the “grafting to” method, well-defined polymers with narrow molecular weight distribution synthesized by CRP methods can form uniform layers on CNT. Moreover, synthesis of polymer brushes on CNT with different grafting densities can be achieved [[11], [12], [13], [14], [15]]. Such polymer-functionalized CNT can be used in lots of applications, such as polymer composites, Pickering emulsions, stimuli-responsive materials, etc. Functionalization of CNT with small molecules and polymer chains are investigated in this study. The most prominent studies on functionalization of CNT by small molecules using physical and chemical functionalization methods are summarized in Table 1, Table 2, respectively. In addition, the most important studies on covalent and non-covalent functionalization of CNT with polymer chains synthesized by ATRP, RAFT, and NMP methods with the focus on “grafting to” methods are presented in Tables 3 and 4, respectively.

Section snippets

Physical functionalization methods

Physical adsorption of small molecules on CNT is a promising approach for its functionalization. Physical functionalization enhances dispersibility and preserves the extended π networks of CNT. This type of functionalization is commonly carried out by some different methods such as π-π interaction and electrostatic interactions.

Physical functionalization of CNT by π-π interaction is among the most important methods, in which the π electrons on the surface of CNT interact with π electrons of

Polymer-functionalization of CNT by covalent “grafting to” method

CRP is considered as a highly applicable method to synthesize well-defined polymers with controlled molecular weight and narrow polydispersity index. Controlling reactivity of growing radicals in radical polymerization results in appearance of the CRP methods as modern polymerizations. In CRP methods, NMP, ATRP, and RAFT polymerization are highly efficient in synthesis of polymer brushes on CNT. NMP, ATRP, and RAFT polymerization rely on dissociation-combination, atom transfer, and reversible

Polymer-functionalization of CNT by non-covalent “grafting to” method

In non-covalent method, polymers could attach to the CNT surface without sharing any electrons. Hydrogen bonding and π-π interaction are the prominent kinds of non-covalent interactions. The recent and important studies of polymer grafting via “grafting to” method through the non-covalent interaction are reviewed in the following.

Applications

High surface area, high functionalization ability, enhanced cellular uptake, and possibility of conjugation of CNT with many therapeutics result in its application in enhancing storage of batteries, biomedical applications, sensors, filtration, solar cells, etc. Conductivity enhancement of CNT results in its higher practical usage in wide variety of applications like batteries. Thermal conductivity of CNT decreases in most of the chemical functionalization processes [12,15,16]. Thermal

Conclusion, outlook, and challenges

Unique structure and properties of CNT introduced it as a promising material in diverse research fields. Its potential applications in novel materials are restricted due to some drawbacks such as limited solubility in aqueous and organic solvents, limited processability, and limited compatibility with polymer matrices. Functionalization of CNT with small molecules and also polymers is considered as a major key in circumventing these issues. Covalent and non-covalent functionalization of CNT

Declaration of Competing Interest

None.

Acknowledgment

Iran National Science Foundation (INSF) is greatly appreciated for its financial support (Grant Number: 96013220).

References (177)

  • L. Stobinski

    Multiwall carbon nanotubes purification and oxidation by nitric acid studied by the FTIR and electron spectroscopy methods

    J Alloys Compd

    (2010)
  • Y. Shao et al.

    Comparative investigation of the resistance to electrochemical oxidation of carbon black and carbon nanotubes in aqueous sulfuric acid solution

    Electrochim Acta

    (2006)
  • J.L. Delgado et al.

    The first synthesis of a conjugated hybrid of C60-fullerene and a single-wall carbon nanotube

    Carbon N Y

    (2007)
  • G. Modugno

    A comparative study on the enzymatic biodegradability of covalently functionalized double- and multi-walled carbon nanotubes

    Carbon N Y

    (2016)
  • S. Cosnier et al.

    Design of carbon nanotube-polymer frameworks by electropolymerization of SWCNT-pyrrole derivatives

    Electrochim Acta

    (2008)
  • N.T. Dintcheva

    Multi-functional polyhedral oligomeric silsesquioxane-functionalized carbon nanotubes for photo-oxidative stable ultra-high molecular weight polyethylene-based nanocomposites

    Eur Polym J

    (2016)
  • G. Liang et al.

    Molecularly imprinted monolithic column based on functionalized β-cyclodextrin and multi-walled carbon nanotubes for selective recognition of benzimidazole residues in citrus samples

    Microchem J

    (May 2019)
  • M. Holzinger

    [2+1] cycloaddition for cross-linking SWCNTs

    Carbon N Y

    (2004)
  • N. Kong et al.

    Carbohydrate conjugation through microwave-assisted functionalization of single-walled carbon nanotubes using perfluorophenyl azides

    Carbohydr Res

    (2015)
  • E.T. Mickelson et al.

    Fluorination of single-wall carbon nanotubes

    Chem Phys Lett

    (1998)
  • E.T. Mickelson et al.

    Fluorination of single-wall carbon nanotubes

    Chem Phys Lett

    (1998)
  • H. Touhara

    Property control of carbon materials by fluorination

    Carbon Alloy Nov Concepts Dev Carbon Sci Technol

    (2003)
  • P.J. Boul

    Reversible sidewall functionalization of buckytubes

    Chem Phys Lett

    (1999)
  • H. Muramatsu

    A selective way to create defects by the thermal treatment of fluorinated double walled carbon nanotubes

    Chinese J Catal

    (2014)
  • Y. Lin

    Advances toward bioapplications of carbon nanotubes

    (2004)
  • P.T. Lillehei et al.

    A quantitative assessment of carbon nanotube dispersion in polymer matrices

    Nanotechnology

    (2009)
  • Pulickel M. Ajayan et al.

    Nanocomposite science and technology

    (2006)
  • Peng-Cheng Ma et al.

    Carbon nanotubes for polymer reinforcement

    (2011)
  • H. Fischer

    The Persistent Radical Effect in Controlled Radical

    (1999)
  • H. Roghani-mamaqani et al.

    In situ controlled radical polymerization: a review on synthesis of well-defined nanocomposites

    Polym Rev

    (2012)
  • A. Goto et al.

    Comparative study on decomposition rate constants for some alkoxyamines

    Macromolecules

    (2002)
  • Kohji Ohno et al.

    Mechanism and Kinetics of Nitroxide-Controlled Free Radical Polymerization. Thermal Decomposition of 2,2,6,6-Tetramethyl-1-polystyroxypiperidines

    Macromolecules

    (1997)
  • I. Luzinov et al.

    Responsive brush layers: from tailored gradients to reversibly assembled nanoparticles

    Soft Matter

    (2008)
  • A.T. Cate

    Progress in organic coatings high density hydrophilic and hydrophobic brush coatings using a polymeric primer layer

    Prog Org Coat

    (2009)
  • K.S. Iyer et al.

    Polystyrene layers grafted to macromolecular anchoring layer

    Macromolecules

    (2003)
  • B. Zdyrko et al.

    Polymer Brushes by the “Grafting to” Method

    Macromol Rapid Commun

    (2011)
  • G. Pagona

    Electronic interplay on illuminated aqueous carbon nanohorn−porphyrin ensembles

    J Phys Chem B

    (Oct. 2006)
  • N. Lalaoui et al.

    Fully oriented bilirubin oxidase on porphyrin-functionalized carbon nanotube electrodes for electrocatalytic oxygen reduction

    Chem Eur J

    (2015)
  • P. Du et al.

    Rapid functionalization of carbon nanotube and its electrocatalysis

    Front Chem China

    (2007)
  • N. Lalaoui

    Enzymatic versus electrocatalytic oxidation of NADH at carbon-nanotube electrodes modified with glucose dehydrogenases: application in a Bucky-paper-based glucose enzymatic fuel cell

    ChemElectroChem

    (Dec. 2016)
  • A. Le Goff

    Facile and tunable functionalization of carbon nanotube electrodes with ferrocene by covalent coupling and π-stacking interactions and their relevance to glucose bio-sensing

    J Electroanal Chem

    (2010)
  • A. Suri et al.

    A facile, solvent-free, noncovalent, and nondisruptive route to functionalize single-wall carbon nanotubes using tertiary phosphines

    Chem Mater

    (2008)
  • U. Hahn et al.

    Immobilizing water-soluble dendritic electron donors and electron acceptors-phthalocyanines and perylenediimides-onto single wall carbon nanotubes

    J Am Chem Soc

    (2010)
  • P. Zhang

    Dispersion of muti-walled carbon nanotubes modified by rosemary acid into poly (vinyl alcohol) and preparation of their composite fibers

    RSC Adv

    (2015)
  • H.Y. Zheng et al.

    Electrostatic gating in carbon nanotube aptasensors

    Nanoscale

    (2016)
  • C. Ehli

    Interactions in single wall carbon nanotubes/pyrene/porphyrin Nanohybrids

    J Am Chem Soc

    (2006)
  • C. Bosch-Navarro et al.

    Electrostatic anchoring of Mn4 single-molecule magnets onto chemically modified multiwalled carbon nanotubes

    Adv Funct Mater

    (2012)
  • Y. Dang

    Hole extraction enhancement for efficient polymer solar cells with Boronic acid functionalized carbon nanotubes doped hole transport layers

    ACS Sustain Chem Eng

    (Apr. 2018)
  • S.J. Pastine

    A facile and patternable method for the surface modification of carbon nanotube forests using perfluoroarylazides

    J Am Chem Soc

    (2008)
  • N.G. Sahoo et al.

    Specific functionalization of carbon nanotubes for advanced polymer nanocomposites

    Adv Funct Mater

    (Dec. 2009)
  • Cited by (0)

    View full text