Single-Step in Situ Synthesis of Polymer-Grafted Single-Wall Nanotube Composites

Abstract

Single-wall carbon nanotubes (SWNTs) have been widely touted as attractive candidates for use as fillers in composite materials due to their extremely high Young's modulus, stiffness, and flexibility. 1 Successful applications of such composite systems require well-dispersed nanotubes with good adhesion with the host matrix, which, unfortunately, is not easily realized. Processing is rendered difficult by poor solubility of SWNTs, and the exfoliation of nanotube bundles is a major challenge. Moreover, inherently weak nanotube-polymer interactions result in poor interfacial adhesion, which can lead to nanotube aggregation within the matrix. Although a variety of chemical routes have been investigated to achieve nanotube solubility, 2 most methods either shorten the nanotubes or induce excessive functionalities that disrupt the original structure of the tubes. Polymer grafting, to improve the nanotube-polymer interface, has mainly been achieved on acidtreated nanotubes, 3 which may result in partial destruction of the tubular framework.Here, we report the development of a novel approach to in situ composite synthesis by attachment of polystyrene (PS) chains to full-length pristine SWNTs without disrupting the original structure, based on an established anionic polymerization scheme. 4 The process requires no nanotube pretreatment and works well with asproduced SWNTs. Both debundling of SWNT ropes and polymer attachment were achieved in a single step, and well-defined composites with a homogeneous dispersion of nanotubes were obtained.SWNTs produced by the HiPCO process 5 were used without further purification, as purification procedures might introduce functionalities that hinder carbanion formation. Dried pristine SWNTs were dispersed by sonication in purified cyclohexane. secButyllithium in slight excess of a predetermined amount (to ensure the removal of protic impurities on the SWNT surface) was added to this dispersion and sonicated in a bath for an hour. A homogeneous light yellow solution was obtained to which styrene monomer was added and polymerized at 48°C for 2 h under sonication. Carbanions are introduced on the SWNT surface by treatment with the anionic initiator that serves to exfoliate the bundles and provide initiating sites for the polymerization of styrene ( Figure 1). The negatively charged nanotubes are separated from the bundles and stay in solution due to mutual electrostatic repulsion between individual tubes, which was confirmed by long-term solution homogeneity. When styrene is added, both free secbutyllithium and the nanotube carbanions initiate polymerization, resulting in an intimately mixed composite system. The polymerization was terminated using degassed n-butanol, and the composite was recovered by precipitation with methanol. The composites were soluble in organic solvents such as dimethyl formamide, chloroform, and tetrahydrofuran.Composites with matrix molecular weights ranging from 1600 to 100 000 g mol -1 and polydispersities of ∼1.02 (determined using size exclusion chromatog...

Carbon nanotubes functionalized by salts containing stereogenic heteroatoms as electrodes in their battery cells

“…Sulfenylation and phosphonylation of carboanionic derivatives of carbon structures generated by the additions of alkyllithiums to native carbon nanotubes 21 . The fi rst system of the modifi ed MWCNT was obtained according to the process 23 .…”

“…These reactions should lead to modifi ed CNT carbon nanotubes with the general structure (R*)4. The joining of heteroatoms containing salt to native carbon tubes is based on the reaction of carbanions generated by the addition to them of the salts with oxidizing solvents 21 . This will lead to the creation of derivatives of the native nanotubes with a direct carbon-heteroatom bond [structured CNT = (R) (Z), where R = alkyl and Z = R 1 S (O) or R1 R2 P (O)]…”

Carbon Nanotube‐based Vectors for Delivering Immunotherapeutics and Drugs

“…It was also demonstrated that metallic SWNTs showed higher reactivity in these types of reactions than semiconductive SWNTs, which would allow CNT separation [134]. [135], CNTs were reacted with strong nucleophilic reagents such as nucleophilic carbene [128], sec-butyllithium [136], polymeric carbanions [137] and Birch reduction reagents (lithium/1,2-diaminoethane [108] or lithium/ammonia [138]) to form various f -CNTs (Scheme 3.4).…”

Electroactive shape memory performance of polyurethane composite having homogeneously dispersed and covalently crosslinked carbon nanotubes

“…Various methods have been examined in efforts to overcome this problem, such as mechanical mixing [3], chemical functionalization of the tubes [4][5][6], and the utilization of organic [7,8] and polymeric surfactants [9] via non-covalent interactions. An in-situ polymerization [10], where nanotubes are incorporated into the prepolymer during the polymerization process, has been utilized to provide carbon nanotubes-reinforced composites with enhanced mechanical properties. On the other hand, the functionalization of carbon nanotubes is also very effective in preparing soluble carbon nanotubes by generating structural defects in strong acid [11,12], and inducing a chemical reaction between alkyl groups and azide moieties [13], and π-π interaction with electron-rich molecules [6,14].…”