Current Organic Chemistry - Volume 17, Issue 17, 2013

The effect of the G to D band intensity (IG/ID) ratio, percentage of Sp2 hybridization and percent of impurities on the electrical resistivity of nanocomposites reinforced with multi-walled carbon nanotubes (MWCNT) has been studied. The MWCNT were purified by reflux, selective oxidation, sonication and mixed oxidative method. The IG/ID ratio was determined by RAMAN spectroscopy, the percent of impurities was determined by TGA whereas the percentage of Sp2 hybridization and carbons bonds by XPS. The resistivity measurements showed how nanocomposites prepared with MWCNTs treated by the mixed oxidative method has the lowest volumetric resistivity values; fact ascribed to the structural changes on the outer shells resulted from the mixed method along to the formation of conductive aggregates where the number of contacts per fiber increases. Hence, for electrical conductivity in CNT/polymer composites, Sp2 hybridization couples with an agglomerated structure have a beneficial effect on electrical conductivity.

One of the most frequent questions in the manufacture of composites with carbon nanotubes (CNT) is the interfacial interaction between the CNT and the matrix. In order to improve this interaction, multi-wall carbon nanotubes (MWCNT), after prior oxidation, were functionalized with amine groups by a novel route for CNT, using hexabromoacetone (HBA). MWCNT were characterized, before and after functionalization procedures, by elemental analysis, high resolution electron scanning microscopy (FEG) and TGA. Epoxy (DGEBA) matrix composites were manufactured with pristine, oxidized and amino-MWCNT, in concentrations of MWCNT ranging from 0.042 to 0.083 wt%. The composites were characterized by mechanical tests in flexural mode, differential scanning calorimetry (DSC) and thermogravimetry (TGA). Elemental analyses confirmed the increases in the contents of oxygen, after the oxidation procedure, and nitrogen, after amination using HBA, proving the efficiency of both methods for the functionalization of MWCNT. Flexural tests show there were no changes in moduli and maximum flexural strength for the composites with functionalized MWCNT when compared to the pure resin. The glass transition temperature (Tg) of composites with 0.1 wt% of aminated- MWCNT increased 18°C when compared with the Tg of the neat resin.

This work was aimed to explore the state-of-the-art in the field of carbon nanotubes exploring the different and more commonly used synthesis, purification and characterization methods. The diversification of techniques to elaborate, purify and analyze the diverse types of carbon nanotubes has driven to the development of their structures and to the growth of their applications. The historical analysis revealed an initial increase in the number of publications that has caused a deceleration in recent years; nonetheless, the scientific research in this field still presents a number of challenges.

In this review we focus on the current status of using carbon nanotube (CNT) as a filler for polymer nanocomposites. Starting with the historical background of CNT, its distinct properties and the surface functionalization of the nanotube, the three different surface polymerization techniques, namely grafting “from”, “to” and “through/in between” were discussed. Wider focus has been given on “grafting from” surface initiated polymerizations, including atom transfer radical polymerization (ATRP), reversible addition fragmentation chain-transfer (RAFT) Polymerization, nitroxide mediated polymerization (NMP), ring opening polymerization (ROP) and other miscellaneous polymerization methods. The grafting “to” and “through / in between” also discussed and compared with grafting from polymerization. The merits and shortcomings of all three grafting methods were discussed and the bottleneck issue in grafting from method has been highlighted. Furthermore the current and potential future industrial applications were deliberated. Finally the toxicity issue of CNTs in the final product has been reviewed with the limited available literature knowledge.

Carbon nanotubes (CNTs) are considered to be the ultimate reinforcing agent for high performance polymer composites and many potential applications have been proposed. However, processing difficulties in obtaining homogeneous dispersions of CNTs or the potentially weak interfacial interaction between the CNTs and different media have resulted in systems with properties that fall short of the expectations associated with the promise of CNTs. In order to overcome these difficulties and fully explore the exceptional properties of CNTs their functionalization has become a fundamental step. Although there are many methods available for the treatment of CNTs, most of them are not attractive for application in an industrial scale. Plasma modification of CNTs on the other hand is a green and fast method which has gained great attention recently due to its many advantages. In this review we summarize the results reported on plasma modification of CNTs to date. Analysis of the types of plasma generation methods, gases and experimental conditions used in the literature is presented. The spectroscopy techniques more often used to characterize the chemical groups attached to the CNT surfaces treated via plasma are briefly presented.

The Staudinger reaction of various β-carboline derivatives with aryloxyacetyl chlorides led to novel fused tetracyclic compounds containing two biologically considerable cores, such as the β-carboline and the β-lactam units. The reaction is stereoselective, giving exclusively the cis cycloadducts as racemates. The mechanism and the 100% stereoselectivity of this cycloaddition was studied by high level quantum chemical calculations.

A series of N-protected non-proteinogenic α-amino acid esters have been prepared. The key step in this synthesis is the treatment of trichloroacetimidate 3, 8 or acetate 4, 9 derivatives with Lewis acid and C-active nucleophiles to afford the desired products via C-C bond formation and the introduction of substituents at the α-position of the amino acid in good yields and short reaction time.