430 research outputs found
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
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
David Sherrington commemorative issue
No full textThis themed issue of Polymer Chemistry was commissioned following the passing, in October 2014, of Professor David Colin Sherrington, FRS. It was commissioned as a dedication to the memory of a world-class polymer chemist of international renown, as well as a celebration of a subject area that was very close to Dave's heart and upon which he founded his career and made his name. It is entirely appropriate that this collection of papers is published in a leading international journal that bears the name of the subject field with which Dave's name is synonymous and to which he contributed so much – Polymer Chemistry – and that this collection be published in the UK by his own professional chemical society, the Royal Society of Chemistry
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
Highly efficient, stoichiometric radical exchange reactions using isoindoline profluorescent nitroxides
No full textExchange reactions between the isoindoline profluorescent nitroxide 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) and a TEMPO capped polystyrene were carried out. High conversions to the desired products were achieved using only stoichiometric ratios of nitroxide relative to polymer. The scope of this study was expanded by exploiting a di-nitroxide 9,10-bis(5-[1,1,3,3-tetramethylisoindolin-2-yloxy])anthracene (BTMIOA) as a connector between two polymer chains forming PS-nitroxide-PS systems
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
The effect of dendronisation of arylamine centred chromophores on field effect transistor performance
No full textWe report the design and synthesis of new dendronised hole transport materials and their first use in organic field effect transistors (OFETs) as solution processed amorphous channels. The dendrimers were comprised of a triphenylamine centre, core chromophores containing one or two thiophene units per arm, and first generation biphenyl dendrons with 2-ethylhexyloxy surface groups attached. The dendronised materials were found to be more easily processed than their non-dendronised equivalents. Top contact OFETS were fabricated and found to have hole mobilities in the saturated regime of 1.7 x 10(-6) cm(2) V(-1) s(-1) and 1.1 x 10(-5) cm(2) V(-1) s(-1) for dendrimers with one and two thiophene units in each arm of the chromophore, respectively. The devices had threshold voltages of around 10 V and ON/OFF ratios in the range 10(2) to 10(3). The OFET results demonstrate that for amorphous films it is important that the chromophore is as large as possible to allow for maximal intermolecular interactions
Water vapour transmission in butadiene-MMA-methacrylic acid latex films
No full textBatch emulsion copolymerizations of butadiene, methyl methacrylate (MMA), methacrylic acid (MAA) and hydroxyethyl methacrylate were performed in RCle reactor, and the product vulcanized to form a film typical of those used for barrier products (gloves and condoms). The water vapour transmission (WVT) or breathability and physical properties (such as tensile strength and elongation at break) of the films were measured. Factorial design was used to vary the concentration of monomers in the copolymerizations. Methacrylic acid is a hydrophilic monomer and its distribution in or on the particles would be expected to affect WVT. Characterization by ultracentrifugation, nuclear magnetic resonance and infrared spectroscopy showed that most of the methacrylic acid units were buried inside the particles. This appears to be responsible for a relatively low WVT rate, probably due to the absence of hydrophilic (MAA-rich) domains inside the film. When centrifuged, the latex shows two particle-containing layers; characterization of the latex revealed the presence of MMA-rich domains in one layer, probably arising from secondary particle formation late in the polymerization. The butadiene-to-MMA ratio probably dominates tensile strength through vulcanization with sulfur. The elongation at break was independent of both the butadiene-to-MMA ratio and the MAA concentration over the range studied (ascribed to competing effects), but dependent upon the total crosslinker concentration. (c) 2007 Elsevier Ltd. All rights reserved
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
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
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