Synthesis and characterization of a hybrid material from self-assembling colloidal particles and carbon nanotubes

The work describes the synthesis of a hybrid material starting from surface-modified colloidal particles of styrene (ST)-acrylic acid (AA) copolymer and carbon nanotubes (CNTs). Vinyl double bonds have been chemically grafted on the surface of the ST-AA copolymer particles in order to be able to copolymerize with acrylamide (AM). The hybrid material was obtained by reaction between the free radicals resulted from both copolymerization and AM homopolymerization and the superficial groups of modified CNTs. Due to the difference between the diameter of the polymer particles and the one of the CNTs, a change in the CNTs shape is to be expected (disentanglement due to steric effects). The products thus obtained have been characterized using IR, SEM, XPS, Raman, and AFM techniques.     

Atom transfer radical emulsion polymerization (emulsion ATRP) of styrene with water-soluble initiator

This study presents styrene emulsion polymerization initiated in aqueous media through an atom transfer radical polymerization (ATRP) mechanism. The water-soluble initiator employed in this process has been synthesized by our team by reacting diethanolamine with α-bromoisobutyryl bromide. The complexation of CuBr was realized by using a bicomponent complexation system comprised of 2,2′-bipyridine and N,N,N′,N′,N″-pentamethyldiethylenetriamine. The initiator ratio influence on the obtained emulsion was studied. The obtained latexes and polymer particles have been characterized by dynamic light scattering, scanning electron microscopy, and gel permeation chromatography.     

Glass Transition Temperature Improvement for Polychloroprene by One-Step ATRP Reaction

Polymethyl methacrylate (PMMA) polymer chains were grafted on neoprene W (NW) by a one-step ATRP reaction. The thermal properties of the products were analyzed by DSC. Improvement of T _g was a result of the PMMA grafted chains. Also, the melting point (T _m ) changed from 42°C for NW to 142°C for modified NW. Using different solvents for the resulting copolymers, aggregates were obtained. Phase separation was influenced by the grafting degree of PMMA and the employed solvent. The copolymers were analyzed by GPC, FT-IR, DSC, and SEM.     

Mechanisms of water oxidation catalyzed by ruthenium diimine complexes

(18)O-isotope-labeling studies have led to the conclusion that there exist two major pathways for water oxidation catalyzed by dimeric ruthenium ions of the general type cis, cis-[L2Ru(III)(OH2)]2O(4+). We have proposed that both pathways involve concerted addition of H and OH fragments derived from H 2O to the complexes in their four-electron-oxidized states, i.e., [L2Ru(V)(O)]2O(4+), ultimately generating bound peroxy intermediates that decay with the evolution of O2. The pathways differ primarily in the site of addition of the OH fragment, which is either a ruthenyl O atom or a bipyridine ligand. In the former case, water addition is thought to give rise to a critical intermediate whose structure is L2Ru(IV)(OH)ORu(IV)(OOH)L2(4+); the structures of intermediates involved in the other pathway are less well defined but may involve bipyridine OH adducts of the type L2Ru(V)(O)ORu(IV)(OH)(L(*)OH)L(4+), which could react further to generate unstable dioxetanes or similar endoperoxides. Published experimental and theoretical support for these pathways is reviewed within the broader context of water oxidation catalysis and related reactions reported for other diruthenium and group 8 monomeric diimine-based catalysts. New experiments that are designed to probe the issue of bipyridine ligand "noninnocence" in catalysis are described. Specifically, the relative contributions of the two pathways have been shown to correlate with substituent effects in 4,4'- and 5,5'-substituted bipyridine complexes in a manner consistent with the formation of a reactive OH-adduct intermediate in one of the pathways, and the formation of OH-bipyridine adducts during catalytic turnover has been directly confirmed by optical spectroscopy. Finally, a photosensitized system for catalyzed water oxidation has been developed that allows assessment of the catalytic efficiencies of the complex ions under neutral and alkaline conditions; these studies show that the ions are far better catalysts than had previously been assumed based upon reported catalytic parameters obtained with strong oxidants in acidic media.     

Organic photovoltaic devices with colloidal TiO2 nanorods as key functional components

We report on a novel approach to integrate colloidal anatase TiO(2) nanorods as key functional components into polymer bulk heterojunction (BHJ) photovoltaic devices by means of mild, all-solution-based processing techniques. The successful integration of colloidal nanoparticles in organic solar cells relies on the ability to remove the long chain insulating ligands, which indeed severely reduces the charge transport. To this aim we have exploited the concomitant mechanisms of UV-light-driven photocatalytic removal of adsorbed capping ligands and hydrophilicization of TiO(2) surfaces in both solid-state and liquid-phase conditions. We have demonstrated the successful integration of the UV-irradiated films and colloidal solutions of TiO(2) nanorods in inverted and conventional solar cell geometries, respectively. The inverted devices show a power conversion efficiency of 2.3% that is a ca. three times improvement over their corresponding cell counterparts incorporating untreated TiO(2), demonstrating the excellent electron-collecting property of the UV-irradiated TiO(2) films. The integration of UV-treated TiO(2) solutions in conventional devices results in doubled power conversion efficiency for the thinner active layer and in maximum power conversion efficiency of 2.8% for 110 nm thick devices. In addition, we have demonstrated, with the support of device characterizations and optical simulations, that the TiO(2) nanocrystal buffer layer acts both as electron-transporting/hole-blocking material and optical spacer.     

Room temperature asymmetric Pd-catalyzed methoxycarbonylation of norbornene: highly selective catalysis and HP-NMR studies

Palladium complexes bearing monodentate and bidentate phosphine ligands (1-7) were synthesised and used as catalyst precursors in the methoxycarbonylation of norbornene. The catalytic systems bearing ligands 1, 3 and 4 afforded excellent conversions (>99%) and selectivity of the ester (>99%). NMR investigations showed that using complex 1a as the precursor resulted in the protonated phosphine, 1-H(+), being formed under catalytic conditions and thus the addition of acid is not required for the activation of this system since the reaction involving the precursor with methanol under CO pressure produces 2 equivalents of HCl and leads to the formation of the active species. The protonation of ligand 4 under methoxycarbonylation conditions was also observed and the diprotonated diphosphine was isolated and characterised. This compound was tested as a ligand and acid source in a catalysis and provided excellent conversion and high selectivity to the ester.     

Design,synthesis and structure of new dendritic melamines. First use of a tandem C-2-substituted serinol—O,O-masked 4-piperidone as a peripheral unit in iterative synthesis

The iterative chemoselective amination of cyanuric chloride to dimers of new G-2 dendritic N-substituted-2,4,6-triamino-s-triazines (melamines) having C-2-substituted 2-aminopropane-1,3-diols (‘serinols’) in tandem with the ethylene ketal of 4-piperidone as peripheral units is reported. The structure as a function of increasing molecular size was studied by NMR spectroscopy, DFT calculation and AFM imaging. A concise nomenclature defining the restricted rotational phenomena about the newly created C(s-triazine)–N(exocyclic) partial double bonds, seen as axes of (pro)diastereomerism, is used. We propose a new form of frontier rotamerism for the dendrimer surface, which operates over a long range.     

Interaction between the conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the lecithin mimic 1-O-(l-Arginyl)-2,3-O-dilauroyl-sn-glycerol in aqueous solution

In this paper, the interaction between the water-soluble conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the amino acid glyceride conjugate 1-O-(L-arginyl)-2,3-O-dilauroyl-sn-glycerol dichlorohydrate (a mimic for the phospholipid lecithin) has been studied in aqueous solution by electronic spectroscopy (absorption and fluorescence) and small-angle neutron scattering (SANS). A significant increase in the polymer fluorescence and blue shift in its emission are observed on association with the surfactant. This is suggested to be due to breakup of polymer aggregates. In addition, the spectroscopic and photophysical data suggest this is followed by the vesicle to ribbon transition characteristic of this surfactant, leading to incorporation of single chains of the polymer within mixed polymer-surfactant aggregates. Support for this comes from preliminary SANS measurements, from which evidence for polymer dissolution and formation of two-dimensional structures has been obtained.     

Prediction and observation of isostructurality induced by solvent incorporation in multicomponent crystals

The crystal structures of two pharmaceutical molecules-carbamazepine and its 10,11-dihydro derivative-with acetic acid have been successfully predicted by computational methods. While the crystalline structure of the former was known a priori, no structural information was available for the latter. Possible crystal structures were generated in silico before any experimental work was performed. Although the crystal structures of the pure drug molecules are very different, incorporation of acetic acid in their crystal lattices results in isomorphic products.