RESUMEN
A soluble poly(tetrazine) polymer was prepared via Suzuki polycondensation of 3,6-bis(5-bromofuran-2-yl)-1,2,4,5-tetrazine and a fluorene diboronate derivative. It can undergo efficient and quantitative post-polymerization inverse-electron-demand Diels-Alder click reactions with a variety of trans-cyclooctene (TCO) derivatives. The resulting polymers were oxidized to convert dihydropyridazine rings into pyridazines. The absorption spectra of the product polymers, both before and after oxidation, showed hypsochromic shifts that correlated with steric hindrance of the appended side chains. They also exhibited a significantly enhanced fluorescence intensity relative to the original poly(tetrazine). While gel-permeation chromatography indicated that the product polymers exhibited longer retention times, NMR end-group analysis showed that the polymers retained relatively constant degrees of polymerization. Graft copolymers were easily prepared via reaction with TCO-functionalized poly(ethylene glycol) chains and a cross-linked foam was produced by reacting the poly(tetrazine) with a bis-TCO crosslinker.
RESUMEN
Control of single-walled carbon nanotube dispersion properties is of substantial interest to the scientific community. In this work, we sought to investigate the effect of a macrocycle, pillar[5]arene, on the dispersion properties of a polymer-nanotube complex. Pillar[5]arenes are a class of electron-rich macrocyclic hosts capable of forming inclusion complexes with electron-poor guests, such as alkyl nitriles. A hydroxyl-functionalized pillar[5]arene derivative was coupled to the alkyl bromide side chains of a polyfluorene, which was then used to coat the surface of single-walled carbon nanotubes. Noncovalent functionalization of carbon nanotubes with the macrocycle-containing conjugated polymer significantly enhanced nanotube solubility, resulting in dark and concentrated nanotube dispersions (600 µg mL-1), as evidenced by UV-vis-NIR spectroscopy and thermogravimetric analysis. Differentiation of semiconducting and metallic single-walled carbon nanotube species was analyzed by a combination of UV-vis-NIR, Raman, and fluorescence spectroscopy. Raman spectroscopy confirmed that the concentrated nanotube dispersion produced by the macrocycle-containing polymer was due to well-exfoliated nanotubes, rather than bundle formation. The polymer-nanotube dispersion was investigated using 1H NMR spectroscopy, and it was found that host-guest chemistry between pillar[5]arene and 1,6-dicyanohexane occurred in the presence of the polymer-nanotube complex. Utilizing the host-guest capability of pillar[5]arene, the polymer-nanotube complex was incorporated into a supramolecular organogel.
RESUMEN
A conjugated poly(phenyl-co-dibenzocyclooctyne) Schiff-base polymer, prepared through polycondensation of dibenzocyclooctyne bisamine (DIBO-(NH2)2) with bis(hexadecyloxy)phenyldialdehyde, is reported. The resulting polymer, which has a high molecular weight (M(n)>30â kDa, M(w)>60â kDa), undergoes efficient strain-promoted alkyne-azide cycloaddition reactions with a series of azides. This enables quantitative modification of each repeat unit within the polymer backbone and the rapid synthesis of a conjugated polymer library with widely different substituents but a consistent degree of polymerization (DP). Kinetic studies show a second-order reaction rate constant that is consistent with monomeric dibenzocyclooctynes. Grafting with azide-terminated polystyrene and polyethylene glycol monomethyl ether chains of varying molecular weight resulted in the efficient syntheses of a series of graft copolymers with a conjugated backbone and maximal graft density.
RESUMEN
Tris(pentafluorophenyl)boron B(C6F5)3 is an effective catalyst for the hydrosilylative reduction of tertiary and N-phenyl secondary amides. It allows for the mild reduction of a variety of these amides in near quantitative yield, with minimal purification, at low temperatures, and with short reaction times. This reduction shows functional group tolerance for alkenes, nitro groups, and aryl halides, including aryl iodides.