Modification of multiwall carbon nanotubes by grafting from controlled polymerization of styrene: Effect of the characteristics of the nanotubes

Linear polystyrene chains were grown from the convex surface of two commercially available multiwall carbon nanotubes (MWCNTs) with similar diameter but different lengths. The MWCNTs were supplied from Bayer Material Science® (purity >95%, external diameter = 13–16 nm, length = 1–10 μm, denoted MWCNT_BMS⁹⁵) and FutureCarbon GmbH (purity >99%, external diameter = 15 nm, length = 5–50 μm, denoted MWCNT_FC⁹⁹). The MWCNTs were oxidized with nitric acid, consecutively reacted with thionyl chloride, glycol or poly(ethylene glycol), 2‐bromo‐2‐methylpropionyl bromide and finally with styrene under atom transfer radical polymerization (ATRP) conditions. The content of polystyrene grafted from the surface of the MWCNTs can be controlled by adjusting the molecular weight of the poly(ethylene glycol), the initiator concentration and the monomer to carbon nanotube weight ratio. Under comparable experimental conditions, a higher amount of polystyrene is grafted from the MWCNT_BMS⁹⁵ than from MWCNT_FC⁹⁹. The difference in dimensions and the state of aggregation of the carbon nanotubes influence the grafting from polymerization reactions, where relative shorter and tightly aggregated carbon nanotubes promote higher polymerizations yields than longer and less aggregated carbon nanotubes. The increase of the viscosity of the carbon nanotube dispersion decreases the polymer grafting content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1035–1046, 2010     

Preparation of poly(styrene‐co‐acrylonitrile)‐grafted multiwalled carbon nanotubes via surface‐initiated atom transfer radical polymerization

The in situ grafting‐from approach via atom transfer radical polymerization was successfully applied to polystyrene, poly(styrene‐co‐acrylonitrile), and polyacrylonitrile grafted onto the convex surfaces of multiwalled carbon nanotubes (MWCNTs) with (2‐hydroxyethyl 2‐bromoisobutyrate) as an initiator. Thermogravimetric analysis showed that effective functionalization was achieved with the grafting approach. The grafted polymers on the MWCNT surface were characterized and confirmed with Fourier transform infrared spectroscopy and nuclear magnetic resonance. Raman and near‐infrared spectroscopy revealed that the grafting of polystyrene, poly(styrene‐co‐acrylonitrile), and polyacrylonitrile slightly affected the side‐wall structures. Field emission scanning electron microscopy showed that the carbon nanotube surface became rough because of the grafting of the polymers. Differential scanning calorimetry results indicated that the polymers grafted onto MWCNTs showed higher glass‐transition temperatures. The polymer‐grafted MWCNTs exhibited relatively good dispersibility in an organic solvent such as tetrahydrofuran. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 460–470, 2007     

Polymer coating of carboxylic acid functionalized multiwalled carbon nanotubes via reversible addition‐fragmentation chain transfer mediated emulsion polymerization

In this work, successful polymer coating of COOH‐functionalized multiwalled carbon nanotubes (MWCNTs) via reversible addition fragmentation chain transfer (RAFT) mediated emulsion polymerization is reported. The method used amphiphilic macro‐RAFT copolymers as stabilizers for MWCNT dispersions, followed by their subsequent coating with poly(methyl methacrylate‐co‐butyl acrylate). Poly(allylamine hydrochloride) was initially used to change the charge on the surface of the MWCNTs to facilitate adsorption of negatively charged macro‐RAFT copolymer onto their surface via electrostatic interactions. After polymerization, the resultant latex was found to contain uniform polymer‐coated MWCNTs where polymer layer thickness could be controlled by the amount of monomer fed into the reaction. The polymer‐coated MWCNTs were demonstrated to be dispersible in both polar and nonpolar solvents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis,characterization, and heterogeneous catalysis of polymer‐supported poly(propyleneimine) dendrimer stabilized gold nanoparticle catalyst

We report here, the synthesis of two types of heterogeneous nanoparticle catalysts viz., polymer‐supported poly(propyleneimine)‐G2 dendrimer stabilized gold nanoparticle catalysts using crosslinked poly(4‐vinylpyridine) matrix (PSP4VP) as support material. The grafting of dendrimer on the surface of P4VP beads was characterized by FTIR spectrophotometer and CHN analyses. The immobilization of AuNPs was characterized by UV‐Vis spectrum, SEM, and HRTEM studies. The resultant polymer‐supported dendrimer stabilized AuNPs were used as a heterogeneous catalyst for the reduction of 4‐nitrophenol. The catalytic activity is found to be excellent and it can also be reused many times by simple filtration and activity remains maintained. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2525–2532, 2010     

Synthesis of polyethylene‐grafted multiwalled carbon nanotubes via a peroxide‐initiating radical coupling reaction and by using well‐defined TEMPO and thiol end‐functionalized polyethylenes

Polyethylene (PE), alkoxyamine‐ and thiol‐terminated PEs (PE‐TEMPO and PE‐SH, respectively) can be converted to macroradicals using a peroxide, a thermal cleavage of the alkoxyamine and a hydrogen transfer reaction of the thiol, respectively. The addition of these macroradicals to multiwalled carbon nanotubes (MWCNTs) were compared by performing grafting reactions at 160 °C in 1,3‐dichlorobenzene as solvent. Raman spectroscopy was utilized to follow the introduction of PE on the MWCNTs' surface while thermogravimetric and elemental analysis indicated the extent of this grafting. The grafting ratio was found to be in the range of 19–36 wt %. PE‐functionalized MWCNTs were imaged by transmission electronic microscopy showing a PE layer with various thicknesses covering the surface of nanotubes. It was found that higher levels of grafting were obtained using PE‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy and PE‐SH rather than a radical grafting reaction in which dicumyl peroxide, PE, and MWCNTs were reacted. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of pyrene bearing amphiphilic miktoarm star polymer and its noncovalent interactions with multiwalled carbon nanotubes

A novel amphiphilic miktoarm star polymer, polystyrene‐poly(ethylene glycol)‐poly(methyl methacrylate), bearing a pyrene group at the end of PS arm (Pyrene‐PS‐PEG‐PMMA) was successfully synthesized via combination of atom transfer radical polymerization and click chemistry. The structure and composition of the amphiphilic miktoarm star polymer were characterized by gel permeation chromatography and ¹H NMR. The functionalization of multiwalled carbon nanotubes (MWCNTs) via “π–π” stacking interactions with pyrene‐PS‐PEG‐PMMA miktoarm star polymer was accomplished and the resulting polymer‐MWCNTs hybrid was analyzed by using ¹H NMR, UV–vis, fluorescence spectroscopy, and thermal gravimetric analysis. The high‐resolution transmission electron microscopy and analytical techniques aforementioned confirmed that the noncovalent functionalization of MWCNT's with the amphiphilic miktoarm star polymer was successfully achieved. The MWCNT/pyrene‐PS‐PEG‐PMMA exhibited significant dispersion stability in common organic solvents such as dimethyl formamide, chloroform, and tetrahydrofuran. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Grafting of poly(ε‐caprolactone) onto maghemite nanoparticles

We report the coating of maghemite (γ‐Fe₂O₃) nanoparticles with poly(ε‐caprolactone) (PCL) through a covalent grafting to technique. ω‐Hydroxy‐PCL was first synthesized by the ring‐opening polymerization of ε‐caprolactone with aluminum isopropoxide and benzyl alcohol as a catalytic system. The hydroxy end groups of PCL were then derivatized with 3‐isocyanatopropyltriethoxysilane in the presence of tetraoctyltin. The triethoxysilane‐functionalized PCL macromolecules were finally allowed to react on the surface of maghemite nanoparticles. The composite nanoparticles were characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Effects of the polymer molar mass and concentration on the amount of polymer grafted to the surface were investigated. Typical grafting densities up to 3 μmol of polymer chains per m² of maghemite surface were obtained with this grafting to technique. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6011–6020, 2004     

Functionalized multi‐walled carbon nanotubes with poly(N‐(2‐hydroxypropyl)methacrylamide) by RAFT polymerization

In this study, we grafted water‐soluble biocompatible polymer, poly(N‐(2‐hydroxypropyl)methacrylamide) (PHPMA), onto the surface of multi‐walled carbon nanotubes (MWNTs). The reversible addition‐fragmentation chain transfer (RAFT) agents, dithioesters, were successfully immobilized onto the surface of MWNTs first, PHPMA chains were then subsequently grafted onto MWNTs via RAFT polymerization by using dithioesters immobilized on MWNTs as RAFT agent. FTIR, XPS, ¹H NMR, Raman and TGA were used to characterize the resulting products and to determine the content of water‐soluble PHPMA chains in the product. The MWNTs grafted with PHPMA chains have good solubility in distilled water, PBS buffer, and methanol. TEM images of the samples provide direct evidence for the formation of a nanostructure that MWNTs coated with polymer layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2419–2427, 2006     

Peroxide initiated maleic anhydride grafting: Structural studies on an ester‐containing copolymer and related substrates

Maleic anhydride (MAn) was grafted onto the low molecular weight esters methyl decanoate (MD) and methyl 2‐ethylhexanoate (MEH) using the free‐radical initiators Lupersol‐101 and ‐130; the esters were used as model compounds for the copolymer poly(ethylene‐co‐methyl acrylate). The grafted products in both cases were isolated from the unreacted ester and were subjected to extensive analysis using spectroscopic and chromatographic techniques. Analysis of the grafted material indicated the presence of one or more succinic anhydride (SAn) residues grafted to the ester. In the case of the multiply grafted material it has been established conclusively by ¹³C‐NMR using 2,3‐¹³C₂ labeled MAn that the multiple grafts exist as single units. A limited number of grafting experiments was performed on the copolymer in the melt and the graft‐modified copolymer was characterized spectroscopically. Single graft units were observed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1609–1618, 1999     

Polyelectrolyte‐grafted carbon nanotubes: Synthesis,reversible phase‐transition behavior,and tribological properties as lubricant additives

A novel polyelectrolyte‐grafted multiwalled carbon nanotubes (MWCNTs‐g‐PILs) which possesses a hard backbone of MWCNTs and a soft shell of brush‐like poly (ionic liquids) (PILs) has been synthesized via the surface atom transfer radical polymerization (ATRP). Chemical structure and the grafted PILs quantities of MWCNTs‐g‐PILs were determined by FTIR, TGA, and XPS. TEM and FE‐SEM observations indicate that the nanotubes were coated with a PILs layer, exhibiting core‐shell nanostructures with the PILs chains as the brush‐like or hairy shell and the MWCNTs as the hard backbone. Furthermore, the effect of counter‐anions on the solubility of MWCNTs‐g‐PILs was investigated. The results indicate that relative solubility of MWCNTs‐g‐PILs in various solvents could be switched by anion exchange. This tunable solubility results in the formation of the cycle of reversible phase‐transition. Tribological property of MWCNTs‐g‐PILs as additives in base lubricant 1‐methyl‐3‐butylimidaaolium hexafluorophosphate (LP104) was evaluated using an Optimol SRV oscillating friction and wear tester, confirming that MWCNTs‐g‐PILs are the excellent antiwear and friction‐reducing additives, which can amend the tribological properties of base lubricant significantly. This is attributed to the good dispersibility and core‐shell structure of MWCNTs‐g‐PILs. These results reported in this work may open primarily toward constructing a bridge among carbon nanotues (CNTs), ILs, and lubricant additives and secondarily to prove that CNTs (modified CNTs) as lubricant additives are promising candidates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7225–7237, 2008     

Thermal and electrical properties of poly(l-lactide)-graft-multiwalled carbon nanotube composites

The dispersion of the nanometer-sized carbon nanotubes in a polymer matrix leads to a marked improvement in the properties of the polymer. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt compounded with multiwalled carbon nanotubes (MWCNTs). A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The morphology of the composite was observed with scanning electron microscopy. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The thermal stability of the composites was studied using thermogravimetric analysis and their activation energy during thermal degradation was determined using the Kissinger and Flynn-Wall-Ozawa methods. The activation energy of PLLA/PLLA-g-MWCNT was higher than that of PLLA/MWCNT, which indicates that the composite made with the PLLA-g-MWCNTs was more thermally stable than the composite made with the MWCNTs.     

Terpyridine‐modified poly(vinyl chloride): Possibilities for supramolecular grafting and crosslinking

Commercially available poly(vinyl chloride) (PVC) was covalently modified with terpyridine supramolecular binding units in a two‐step reaction. First, PVC was modified with aromatic thiols to introduce OH functionalities into the polymer backbone, which were subsequently reacted with an isocyanate‐functionalized terpyridine binding unit. The resulting functionalized material contained metal‐ion binding sites, which could be used for grafting and crosslinking reactions. A grafting experiment was performed with a small organic terpyridine ligand. The complexation of the modified PVC with several transition‐metal ions was studied with ultraviolet–visible spectroscopy and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2964–2973, 2003     

Covalent functionalization of multiwalled carbon nanotubes with poly(styrene-co-acrylonitrile) by reactive melt blending

A small amount of cyano groups in poly(styrene-co-acrylonitrile) (SAN) was converted to oxazoline groups through reaction with 2-aminoethanol. Reactive melt blending of oxazoline-containing SAN and acidified multiwalled carbon nanotubes (MWCNTs) leads to the grafting of polymer chains onto MWCNTs arising from reactions between oxazoline and carboxylic acid groups. Spectroscopic, thermal and microscopic techniques confirmed the successful grafting of SAN onto MWCNTs. This method is comparatively simpler and greener than a previously reported method, and can be adopted to graft other acrylonitrile-containing polymers onto MWCNTs.     

Novel Amphiphilic Degradable Poly(ε‐caprolactone)‐graft‐poly(4‐vinyl pyridine), Poly(ε‐caprolactone)‐graft‐poly(dimethylaminoethyl methacrylate) and Water‐Soluble Derivatives

New amphiphilic graft copolymers that have a poly(ε‐caprolactone) (PCL) biodegradable hydrophobic backbone and poly(4‐vinylpyridine) (P4VP) or poly(2‐(N,N‐dimethylamino)ethyl methacrylate) (PDMAEMA) hydrophilic side chains have been prepared by anionic polymerization of the corresponding 4VP and DMAEMA monomers using a PCL‐based macropolycarbanion as initiator. The water solubility of these amphiphilic copolymers is improved by quaternization, which leads to fully water‐soluble cationic copolymers that give micellar aggregates in deionized water with diameters ranging from 65 to 125 nm. In addition, to improve the hydrophilicity of PCL‐g‐P4VP, grafting of poly(ethylene glycol) (PEG) segments has been carried out to give a water‐soluble double grafted PCL‐g‐(P4VP;PEG) terpolymer.

     

Enhanced dielectric properties of polymer composite films induced by encapsulated MWCNTs with a one core‐two shell structure

Multiwalled carbon nanotubes (MWCNTs) can endow high dielectric constant to polymer‐based composites. However, the accompanying poor dispersion of MWCNTs and high dielectric loss for composites severely limit their application in dielectric field. Herein, a modified acid‐treated MWCNTs encapsulated by the polyaniline/poly(sodium 4‐styrenesulfonate) layers (aMWCNTs@PANI‐PSS) with a one core‐two shell structure was fabricated by in situ polymerization followed by electrostatic self‐assembly technique. Furthermore, the composite films based on aMWCNTs@PANI‐PSS/poly(vinylidenefluoride‐hexaflouropropylene) (PVDF‐HFP) were fabricated by a solution‐casting method. An ultrathin insulating PSS shell is wrapped onto aMWCNTs@PANI, resulting in the improvement of dispersibility for aMWCNTs@PANI and the decrease of dielectric loss for composite films. When the content of aMWCNTs@PANI‐PSS is 5.0 wt %, the dielectric constant of aMWCNTs@PANI‐PSS/PVDF‐HFP reaches 430 (100 Hz), which is about 55 times of pure PVDF‐HFP and 1.7 times of aMWCNTs@PANI/PVDF‐HFP (247). Besides, the responding dielectric loss of aMWCNTs@PANI‐PSS/PVDF‐HFP composite film is only 0.67, much lower than that of aMWCNTs@PANI/PVDF‐HFP (25) and aMWCNTs/PVDF‐HFP (3185). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 948–956     

Synthesis of dual‐functional poly(6‐azidohexylmethacrylate) brushes by a RAFT agent carrying carboxylic acid end groups

Novel types of dual‐functional surface‐attached polymer brushes were developed by interface‐mediated reversible addition‐fragmentation chain transfer (RAFT) polymerization of 6‐azidohexylmethacrylate using the surface‐immobilized RAFT agent and the free initiator. The interface‐mediated RAFT polymerization produced silicon substrate coated with dual‐functional (azido groups from monomer and carboxylic acid groups from RAFT agent) poly(6‐azidohexylmethacrylate) [poly (AHMA)] with a grafting density as high as 0.59 chains/nm². Dual‐functional polymer brushes can represent an attractive chemical platform to deliberately introduce other molecular units at specific sites. The azido groups of the poly(AHMA) brushes can be modified with alkyl groups via click reaction, known for their DNA hybridization, while the carboxylic acid end groups can be reacted with amine groups via amide reaction, known for their antifouling properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1696–1706     

Switchable thin‐film surface prepared via a simple grafting‐to method using a polystyrene‐b‐poly(2‐vinylpyridine) copolymer

A polystyrene‐b‐poly(2‐vinylpyridine) block copolymer containing a methylhydridosilane linking group was chemically grafted to an 8‐trichlorosilyloctene monolayer via a simple one‐step hydrosilylation reaction. The resulting Y‐shaped thin film exhibited a low grafting density, which was characteristic of the grafting‐to technique. To further reduce the miscibility of the two arms, methyl iodide was reacted with the poly(2‐vinylpyridine) block to produce quaternary ammonium groups. The surfaces before and after quaternization were both solvent‐switchable when subjected to block‐selective solvents. Tensiometry, ellipsometry, attenuated total reflection/Fourier transform infrared, and atomic force microscopy were used to characterize the properties and morphology of both unquaternized and quaternized samples. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5608–5617, 2006     

Synthesis of well‐defined pH‐responsive PPEGMEA‐g‐P2VP double hydrophilic graft copolymer via sequential SET‐LRP and ATRP

A series of well‐defined double hydrophilic graft copolymers containing poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA) backbone and poly(2‐vinylpyridine) (P2VP) side chains were synthesized by successive single electron transfer living radical polymerization (SET‐LRP) and atom transfer radical polymerization (ATRP). The backbone was first prepared by SET‐LRP of poly(ethylene glycol) methyl ether acrylate (PEGMEA) macromonomer using CuBr/tris(2‐(dimethylamino)ethyl)amine as catalytic system. The obtained homopolymer then reacted with lithium diisopropylamide and 2‐chloropropionyl chloride at ?78 °C to afford PPEGMEA‐Cl macroinitiator. poly(poly(ethylene glycol) methyl ether acrylate)‐g‐poly(2‐vinylpyridine) double hydrophilic graft copolymers were finally synthesized by. ATRP of 2‐vinylpyridine initiated by PPEGMEA‐Cl macroinitiator at 25 °C using CuCl/hexamethyldiethylenetriamine as catalytic system via the grafting‐ from strategy. The molecular weights of both the backbone and the side chains were controllable and the molecular weight distributions kept relatively narrow (M_w/M_n ≤ 1.40). pH‐Responsive micellization behavior was investigated by ¹H NMR, dynamic light scattering, and transmission electron microscopy and this kind of double hydrophilic graft copolymer aggregated to form micelles with P2VP‐core while pH of the aqueous solution was above 5.0. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Isomer‐dependent properties of poly(vinyl pyridine)‐based films grown on copper surfaces

The effect of poly(2‐vinyl pyridine) (P2VP) and poly(4‐vinyl pyridine) (P4VP) isomers on the growth of surface films on copper substrates was studied by electrochemical, spectroscopic, thermogravimentric, and microscopic methods. In acid environment (3% v/v acetic acid) and in the presence of KSCN, electrochemically generated copper cations reacted rapidly with SCN^? and P2VP or P4VP, yielding coordination compounds, which deposited onto copper surfaces as films. The characteristics of such polymer–metal complexes (films) were markedly isomer‐dependent. Cu(I)/P2VP/SCN^? complexes with monovalent cations and sulfur‐coordinated thiocyanate were obtained in the presence of P2VP, whereas the formation of Cu(II)/P4VP/SCN^? complexes with divalent cations and nitrogen‐coordinated thiocyanate was observed in the presence of P4VP. Interestingly, similar physical–chemical properties (electronic structure, stoichiometry, and thermal behavior) were observed for materials synthesized by electrochemical and chemical methods. These results suggest, therefore, that control over the surface properties of copper substrates can be achieved using electrosynthesized films based on different PVP isomers. Besides acting as effective protective barriers against aggressive media and thus reducing the metal dissolution (corrosion) kinetics, these materials are potentially attractive for other applications in which surface properties are paramount, such as in catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 215–225, 2009     

Surface modification of multiwalled carbon nanotubes via nitroxide‐mediated radical polymerization

The nitroxide‐mediated radical polymerization of styrene was carried out on the surfaces of multiwalled carbon nanotubes (MWNTs) initiated by an MWNT‐supported initiator multiwalled carbon nanotube–2″,2″,6″,6″‐tetramethylpiperidinyloxy (MWNT–Tempo). The content of polystyrene grafted from the surface was controlled by changes in the polymerization conditions, such as the reaction times or the ratios of monomers to initiators. The obtained polystyrene‐grafted multiwalled carbon nanotubes (MWNT–PSs) were further used to initiate the polymerization of 4‐vinylpyridine to get polystyrene‐b‐poly(4‐vinylpyridine)‐grafted multiwalled carbon nanotubes (MWNT–PS‐b‐P4VPs). In contrast to unmodified MWNTs, MWNT–PSs had relatively good dispersibility in various organic solvents, such as tetrahydrofuran, CHCL₃, and o‐dichlorobenzene. The structures and properties of MWNT–PSs and MWNT–PS‐b‐P4VPs were characterized and studied with several methods, including thermogravimetric analysis, Fourier transform infrared, ultraviolet–visible, and transmission electron microscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4656–4667, 2006