407 research outputs found
Heteroatom doped-carbon nanospheres as anodes in lithium ion batteries
No full textLong cycle performance is a crucial requirement in energy storage devices. New formulations and/or improvement of “conventional” materials have been investigated in order to achieve this target. Here we explore the performance of a novel type of carbon nanospheres (CNSs) with three heteroatom co-doped (nitrogen, phosphorous and sulfur) and high specific surface area as anode materials for lithium ion batteries. The CNSs were obtained from carbonization of highly-crosslinked organo (phosphazene) nanospheres (OPZs) of 300 nm diameter. The OPZs were synthesized via a single and facile step of polycondensation reaction between hexachlorocyclotriphosphazene (HCCP) and 4,4′-sulphonyldiphenol (BPS). The X-ray Photoelectron Spectroscopy (XPS) analysis showed a high heteroatom-doping content in the structure of CNSs while the textural evaluation from the N2 sorption isotherms revealed the presence of micro- and mesopores and a high specific surface area of 875 m2/g. The CNSs anode showed remarkable stability and coulombic efficiency in a long charge–discharge cycling up to 1000 cycles at 1C rate, delivering about 130 mA·h·g−1. This study represents a step toward smart engineering of inexpensive materials with practical applications for energy devices
Synthesis and evaluation of partly fluorinated polyelectrolytes as components in 19F MRI-detectable nanoparticles
No full textA series of partly fluorinated polyelectrolytes were synthesized by transition metal mediated living radical polymerization and evaluated for their applicability as corona-forming components in F-19 MRI-detectable nanoparticles in aqueous solutions. The polymers were statistical and block copolymers of trifluoroethyl methacrylate (TFEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The polymers were either directly dissolved in water (statistical copolymers), or assembled into aqueous nanoparticles with PTFEMA cores and P(TFEMA-co-DMAEMA) coronas (block copolymers). The polymer composition, polymer charge density, solution ionic strength and solution pH were varied. The F-19 spin-lattice (T-1) and spin-spin (T-2) relaxation times and F-19 image intensities of solutions of the polymers were measured and related to polymer structure and aqueous conformation. The F-19 NMR T-2 relaxation times were found to be highly indicative of the F-19 imaging performance. Maintaining sufficient mobility of the F-19 nuclei was important for obtaining images of high intensity. F-19 mobility could be increased by preventing their aggregation in water by exploiting electrostatic repulsion between monomer units
PK/PD modelling of comb-shaped PEGylated salmon calcitonin conjugates of differing molecular weights
No full textSalmon calcitonin (sCT) was conjugated via cysteine-1 to novel comb-shaped end-functionalised (poly(PEG) methyl ether methacrylate) (sCT-P) polymers, to yield conjugates of total molecular weights (MW) inclusive of sCT: 6.5, 9.5, 23 and 40 kDa. The conjugates were characterised by HPLC and their in vitro and in vivo bioactivity was measured by cAMP assay on human T47D cells and following intravenous (i.v.) injection to rats, respectively. Stability against endopeptidases, rat serum and liver homogenates was assessed. There were linear and exponential relationships between conjugate MW with potency and efficacy respectively, however the largest MW conjugate still retained 70% of Emax and an EC50 of 3.7 nM. In vivo, while free sCT and the conjugates reduced serum [calcium] to a maximum of 15–30% over 240 min, the half-life (T1/2) was increased and the area under the curve (AUC) was extended in proportion to conjugate MW. Likewise, the polymer conferred protection on sCT against attack by trypsin, chymotrypsin, elastase, rat serum and liver homogenates, with the best protection afforded by sCT-P (40 kDa). Mathematical modelling accurately predicted the MW relationships to in vitro efficacy, potency, in vivo PK and enzymatic stability. With a significant increase in T1/2 for sCT, the 40 kDa MW comb-shaped PEG conjugate of sCT may have potential as a long-acting injectable formulation
The 'double dendron' approach to host free phosphorescent poly(dendrimer) OLEDs
No full textThe addition of dendrons to iridium(III) complexes attached to a poly(styrene) backbone is shown to improve the physical and optoelectronic properties of the phosphorescent materials. The iridium(III) complexes have two 2-phenylpyridyl ligands and one phenyltriazolyl ligand, with the latter providing the attachment point to the polymer backbone. It was found that by increasing the number of dendrons (from zero to two) per 2-phenylpyridyl ligand, the intra-and interchain interactions could be more effectively controlled. The poly(dendrimer) with two dendrons per ligand had solution and solid-state photoluminescence quantum yields of 67% and 47%, respectively. Organic light-emitting diodes containing the doubly dendronised (two dendrons per ligand) poly(dendrimer) had a low turn on voltage of 3.6 V (>1.0 cd m(-2)), a maximum luminance of 6 700 cd m(-2) (at 12.2 V), and 100 cd m(-2) was achieved at 6.0 V with an external quantum efficiency (EQE) of 9.2% (28.1 cd A-1) and power efficiency of 14.7 lm/W. A solution of the doubly dendronised poly(dendrimer) in N-methyl-2-pyrolidinone was found to have a viscosity of 4.6 mPa s, which falls in the range of solutions that can be inkjet printed
Gas barrier polymer nanocomposite films prepared by graphene oxide encapsulated polystyrene microparticles
No full textThe dispersion and orientation of two-dimensional (2D) inorganic nanoplatelets in polymers are technical challenges faced in polymer nanocomposite manufacturing. This work demonstrates an effective way to facilitate the dispersion and orientation of graphene oxide (GO) nanoplatelets in a polymer matrix through encapsulating the polymer within a nanoplatelet shell. Briefly, few-layered GO nanoplatelets encapsulated polystyrene (PS) microparticles were synthesized by a Pickering suspension polymerization method. The synthesis conditions, morphologies, and barrier properties of the GO encapsulated PS spheres and the melt-compressed films are characterized. The addition of salt induces flocculation of GO onto the surface of the styrene monomer droplet, resulting in the formation of a multilayered GO shell as well as the sedimenting of the PS/GO particles during polymerization. The obtained GO encapsulated PS microspheres were purified, dried, and melt-compressed to form composite films. The oxygen permeability (expressed as transmission rate) of the PS/GO composite film containing 2 wt % GO was 526.02 ± 55.78 cm3 m–2 24 h–1—a reduction of 96% relative to the PS control film and 34% lower than the solution mixed PS/GO composite film. This indicates that the encapsulated PS spheres act as an effective carrier to facilitate the dispersion of GO. The orientation was realized by the following melt-compression process, which creates tortuous pathways hindering the permeation of gases through the PS matrix
Synthesis of polymeric microcapsules by interfacial-suspension cationic photopolymerisation of divinyl ether monomer in aqueous suspension
No full textPolymeric microcapusles have been synthesised with a markedly more hydrophillic monomer than previously reported, triethylene glycol divinyl ether, using cationic photopolymerisation in an aqueous environment. Characterisation by NMR and SEM show that the particles are formed with low dispersity with a size of approximately 1 μm in spite of the expected inhibition in aqueous conditions. Furthermore, supercritical carbon dioxide has been used to generate silver nanoparticles which distribute throughout the shell of the microcapsules further illustrating the structure of these capsules with characterisation by TEM and SAXS
Polymer chemistry : rooftop reactions
No full textDesigning a molecule that acts as both an initiator for a photo-controlled radical polymerization and as a reactive end-group for polymer chain crosslinking has enabled the preparation of polymeric gels whose properties can be controlled by exposure to sunlight
Enlightening the mechanism of copper mediated photoRDRP via high-resolution mass spectrometry
No full textThe initiation mechanism of photochemically mediated Cu-based reversible-deactivation radical polymerization (photoRDRP) was investigated using pulsed-laser polymerization (PLP) and high-resolution mass spectrometry. The variation of the catalyst composition and ESI-MS analysis of the resulting products provided information on how initiator, ligand, copper species, and monomer are interacting upon irradiation with UV light. A discussion of the results allows for a new postulation of the mechanism of photoRDRP and–for the first time–the unambiguous identification of the initiating species and their interactions within the reaction mixture. One pathway for radical generation proceeds via UV light-induced C–Br bond scission of the initiator, giving rise to propagating radicals. The generation of copper(I) species from copper(II) can occur via several pathways, including, among others, via reduction by free amine ligand in its excited as well as from its ground state via the irradiation with UV light. The amine ligand serves as a strong reducing agent and is likely the main participant in the generation of copper(I) species
Polymerization of methyl acrylate mediated by copper(0)/Me-6-TREN in hydrophobic media enhanced by phenols ; single electron transfer-living radical polymerization
No full textPhenol has been used as an additive to enhance the rate of SET-LRP in toluene at ambient temperature. A direct relationship between reaction time and amount of phenol added has been found with the optimum amount being similar to 20 equiv. of phenol with respect to initiator. Polymerization of methyl acrylate (MA) has been carried out in the presence of varying amounts of phenol and the rate of polymerization depends on the concentration of phenol relative to initiator. With a 20-fold excess 93% conversion is observed after 218 min (PDI = 1.06, M-n = 11,500 g mol(-1)) when compared with 80% conversion with a 5-fold excess (PDI = 1.21, M-n = 5310 g mol(-1)). When nonsterically hindered phenols are employed in a 20 molar excess with respect to the initiator the polymerizations have good linear first-order kinetics and give polymers with PDI between 1.06 and 1.16. When a highly hindered phenol is employed there is a significant induction period prior to polymerization taking place which is similar to when using no phenol. Less hindered phenols accelerated the polymerization when compared with polymerizations with no added phenol. Increasing steric hindrance at the -OH prevents this coordination which indicates that the role of phenol is different with either copper(0) or copper(I). Aliphatic and aromatic esters and amides were used successfully as initiators giving polymers with M-n close to that predicted at similar to 10,000 g mol(-1) and PDI typically less than 1.10. An induction period is observed in most cases which can be removed by a pre-equilibrium step before the addition of monomer. This results in excellent first-order kinetics being observed in the polymerization of MA in toluene solution (50 vol %). Here Cu(0) (powder)/Me-6-TREN with 20 equiv. of phenol and all of the reactants, except the monomer, were added to the reaction flask and stirred for 45 min at 25 degrees C. The structure of the polymer is shown by MALDI TOF MS to contain bromide chain ends derived from the alkyl bromide initiator. The retention of this end group is consistent with living radical polymerization. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym. Chem 46: 7376-7385, 200
CH and SiH activation reactions of (η5-C5H5)Rh(C2H4)CO in low-temperature matrices and in solution
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