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)

Conducting polymer/SWCNTs modular hybrid materials via Diels-Alder ligation

The development of a facile covalent strategy for the fabrication of organic conducting polymers (OCPs)/carbon nanotubes (CNTs) based molecular hybrid materials remains a challenge and is expected to address the detrimental intrinsic bundling issue of CNTs. In view of the pristine CNTs' ability to undergo Diels-Alder reactions with dienes, we report the synthesis of a novel poly(3-hexylthiophene) (P3HT) based organic conducting polymer (OCP) with terminal cyclopentadienyl (Cp) groups. The synthetic strategy employed is based on a combination of in situ end group functionalization via Grignard metathesis (GRIM) polymerization and a subsequent end group switching via reaction with nickelocene. Characterization data from Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) fully support the successful synthesis of monofunctional Cp-capped P3HT, which was found to be highly reactive toward dienophile end-capped polystyrene (PS). The Cp -capped P3HT was subsequently ligated to the surface of pristine single walled CNTs (SWCNTs). The resulting P3HT/SWCNTs molecular hybrid material was characterized using thermogravimetric analysis (TGA), elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), and high resolution transmission electron microscopy (HRTEM). The data from TGA, EA, and XPS were used to quantitatively deduce the grafting density. P3HT/SWCNTs prepared with Cp capped P3HT was found to contain 2 times more P3HT than the reference sample, featuring a grafting density of 0.0510 chains·nm-2 and a periodicity of 1 P3HT chain per 748 carbon atoms of the SWCNTs. HRTEM revealed individual SWCNTs wrapped with P3HT whereas in the reference sample P3HT was adsorbed on the bundles of the SWCNTs. The results presented here provide a new avenue for designing novel materials based on CNTs and OCPs

Hetero diels-alder chemistry for the functionalization of single-walled carbon nanotubes with cyclopentadienyl end-capped polymer strands

Single-walled carbon nanotubes (SWCNTs) are pre-functionalized with a pyridinyl-based dithioester to undergo a hetero Diels-Alder (HDA) reaction with cyclopentadienyl end-capped poly(methyl)methacrylate (Mn = 2700 g mol-1, PDI = 1.14). Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis (EA), and X-ray photoelectron spectroscopy (XPS) evidence the success of the grafting process. The estimated resulting grafting density (from XPS and EA) via the HDA reaction increases by a factor of more than two (0.0774 chains·nm-2 via XPS) compared with typical values obtained via a direct cyclopentadiene driven Diels-Alder conjugation onto non-functional SWCNTs under similar conditions. Cyclopentadienyl end-capped polymer strands react at the surface of pre-functionalized single-walled carbon nanotubes with a pyridine-based dithioester through a hetero Diels-Alder reaction. Elemental analysis and X-ray photoelectron spectroscopy are employed to det ermine the grafting density

Unexpected aqueous UCST behavior of a cationic comb polymer with pentaarginine side chains

Thermoresponsive polymers, undergoing a reversible chemical or physical change using temperature as stimulus, attract increasing interest in particular as adaptable biomaterials. Except for zwitterionic polymers, fully charged polymers require the presence of specific ions to exhibit an upper critical solution temperature (UCST) in water. Herein, we report the discovery of an UCST in pure water for fully cationic comb polymers based on oligoarginine pendent grafts. These polymers were prepared using an original strategy based on solid-phase peptide synthesis of pentaarginine methacrylate-based macromonomer and its polymerization through reversible addition-fragmentation chain transfer. Despite their cationic nature, guanidinium groups from the arginine have the ability to self-associate at low temperature through hydrophobic interactions into stacked pair configuration defying the expected Coulomb interactions. These results pave the way to biomedical applications such as antimicrobial materials and drug delivery systems through the tuning of the polymer structure