Carbon Nanotube/Polymer Hybrid Material Design via Modular Ligation Techniques

Cyclopentadienyl end-capped poly(methyl)methacrylate, poly(N-isopropyl)acrylamide and poly(3-hexyl)thiophene are employed in a one-step Diels-Alder reaction to generate hybrid materials based on single-walled carbon nanotubes (SWCNTs). Variable analytical methods reveal the presence of the polymer strands after the ligation. The grafting density of the hybrid materials was compared to a conventional ligation technique involving an acidic pre-functionalization of the SWCNTs

Elements of fractal geometry in the 1H NMR spectrum of a copolymer intercalation-complex: Identification of the underlying Cantor set

Sequence-selective intercalation of pyrene into the chain-folds of a random, binary copolyimide under fast-exchange conditions results in the development of self-similar structure in the diimide region of the 1H NMR spectrum. The resulting spectrum can be described by the mathematics of fractals, an approach that is rationalised in terms of a dynamic summation of ring-current shielding effects produced by pyrene molecules intercalating into the chain at progressively greater distances from each "observed" diimide residue. The underlying set of all such summations is found to be a defined mathematical fractal namely the fourth-quarter Cantor set, within which the observed spectrum is embedded. The pattern of resonances predicted by a geometric construction of the fourth-quarter Cantor set agrees well with the observed spectrum

Grafting of adipic anhydride to carbon nanotubes through a Diels-Alder cycloaddition/oxidation cascade reaction

Accepted ManuscriptDifferent reactions have been reported for the successful functionalization of carbon nanotubes (CNT). The Diels-Alder cycloaddition is recognized as a plausible chemical approach, but few reports are known where this strategy has been used. In this study, the functionalization was performed by 1,3-butadiene generated from 3-sulfolene under heating conditions in diglyme. This simple and easily scalable method resulted in functionalized CNT with mass losses of 10 - 23 % by thermogravimetric analysis (nitrogen atmosphere). The functionalization was also supported by acid-base titration, elemental analysis, temperature programmed desorption and X-ray photoelectron spectroscopy. The high content in oxygen detected on the CNT surface was assigned to anhydride formation due to a cascade oxidation of the alkene groups generated in the cycloaddition reaction. The complete evolution of the alkene leads to a grafting density of 4.2 mmol g-1 for the anhydride moiety. Ab-initio calculations in CNT model systems indicate that the Diels-Alder addition of butadiene is a feasible process and that subsequent oxidation reactions may result in the formation of the anhydride moiety. The presence of the anhydride group is a valuable asset for grafting a multitude of complex molecules, namely through the nucleophilic addition of amines.Centro de Química and Instituto de Polímeros e Compósitos of the University of Minho and Fundação para a Ciência e Tecnologia (FCT) through the Portuguese NMR network (RNRMN), the Project F-COMP-01-0124-FEDER-022716 (ref. FCT PEst-C/QUI/UI0686/2011) FEDER-COMPETE, Project PEst-C/CTM/LA0025/2013 (Strategic Project - LA 25-2013-2014) and also Project Scope UID/CEC/00319/2013. TG Castro acknowledges FCT for a doctoral grant (SFRH/BD/79195/2011) RF Araújo for a Post-doc grant (SFRH/BPD/88920/2012) and MMF also acknowledges FCT through the program Ciência 2008. Access to computing resources funded by the Project "Search-ON2: Revitalization of HPC infrastructure of UMinho" (NORTE-07-0162-FEDER-000086) is also gratefully acknowledged

Nitrosocarbonyl Hetero-Diels–Alder Cycloaddition: A New Tool for Conjugation

It is demonstrated that nitrosocarbonyl hetero-Diels-Alder chemistry is an efficient and versatile reaction that can be applied in macromolecular synthesis. Polyethylene glycol functionalized with a hydroxamic acid moiety undergoes facile coupling with cyclopentadiene-terminated polystyrene, through a copper-catalyzed as well as thermal hetero-Diels-Alder reaction. The mild and orthogonal methods used to carry out this reaction make it an attractive method for the synthesis of block copolymers. The resulting block copolymers were analyzed and characterized using GPC and NMR. The product materials could be subjected to thermal retro [4 + 2] cycloaddition, allowing for the liberation of the individual polymer chains and subsequent recycling of the diene-terminated polymers. © 2014 American Chemical Society

Diels-Alder reactions for carbon material synthesis and surface functionalization

To meet the ever growing demand for carbon nanomaterials with tailored properties, Diels-Alder reactions are emerging as an efficient alternative to other synthetic methods. From an application perspective, the development of convenient surface functionalization strategies for carbon nanostructures is of paramount importance. Pristine carbon nanostructures display a natural tendency to undergo Diels-Alder reactions with a range of functional dienes and dienophiles without the need of a catalyst. This has sparked significant scientific interest in exploiting the Diels-Alder reaction as a powerful strategy for their synthesis as well as for their subsequent surface functionalization. The present review highlights the remarkable role of Diels-Alder reactions for the synthesis of fullerenes, carbon nanotubes and graphene, and its promise as a facile carbon nanostructure functionalization strategy with small molecules and polymer chains. A critical overview of the recent developments evidencing the potential of Diels-Alder reactions as an efficient route to carbon based functional materials is presented. © 2013 The Royal Society of Chemistry

Modular ambient temperature functionalization of carbon nanotubes with stimuli-responsive polymer strands

Cyclopentadienyl end-capped poly(N-isopropylacrylamide) (PNIPAM-Cp, M-n = 5400 g mol(-1), PDI = 1.13) was synthesized via a combination of RAFT (Reversible Addition-Fragmentation Chain Transfer) polymerization and modular conjugation (characterized via Nuclear Magnetic Resonance (NMR) as well as Electrospray Ionization-Mass Spectrometry (ESI-MS)), and reacted with untreated Single Walled Carbon Nanotubes (SWCNTs) as dienophiles in a Diels-Alder reaction with PNIPAM-Cp (diene) at ambient temperature in the absence of any catalyst. The obtained stimuli-responsive hybrid materials display thermo-responsive behaviour evidenced via UV-VIS-spectroscopy and Dynamic Light Scattering (DLS). The grafting density of the PNIPAM chains at the surface of the SWCNTs was determined via Thermogravimetric Analysis (TGA), Elemental Analysis (EA) and X-ray Photoelectron Spectroscopy (XPS), to be close to 0.0288 chains per nm(2)

One-step functionalization of single-walled carbon nanotubes (SWCNTs) with cyclopentadienyl-capped macromolecules via diels-alder chemistry

Without previous modification, single-walled carbon nanotubes (SWCNTs) react as dienophiles in a single-step Diels-Alder [4 + 2] cycloaddition with diene terminal polymer strands. Cyclopentadienyl-capped poly(methyl methacrylate) (Mn = 2900 g mol-1, PDI = 1.2) was grafted onto SWCNTs under mild conditions at ambient temperature as well as at 80 °C in the absence of any catalyst. Thermogravimetric analysis, elemental analysis, and X-ray photoelectron spectroscopy confirm the success of the reaction and allow to estimate the grafting density of the polymer chains on the SWCNTs via the above three independent methods (average grafting density of 0.064 mmol g-1 (0.029 chains nm-2) for samples reacted at ambient temperature and 0.086 mmol g-1 (0.039 chains nm-2) for samples reacted at 80 °C). In addition, high-resolution transmission electron microscopy images confirmed the presence of an amorphous polymer layer (∼3 nm) around the SWCNTs after functionalization. © 2011 American Chemical Society