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Terminal Groups (terminal + groups)
Selected AbstractsFunctionalized Multi-Wall Carbon Nanotubes for Lipase Immobilization,ADVANCED ENGINEERING MATERIALS, Issue 5 2010I. V. Pavlidis Abstract We examine the immobilization of lipase B from Candida antarctica on functionalized multi-wall carbon nanotubes (MWCNTs) through physical adsorption. MWCNTs functionalized with carboxyl-, amine- and ester- terminal groups on their surface are used as immobilization carriers. Dispersion of the nanotubes and the immobilization procedure take place in aqueous and low-water media. High enzyme loadings are attained, up to 25% of the weight of the carbon nanotubes. These novel biomaterials are characterized though FT-IR and Raman spectroscopy. The MWCNT,lipase bioconjugates exhibit high catalytic activity and increased storage and operational stability. The biomaterials retain more than 55% of their initial activity after 6 months at 4,°C, while they retain approximately 25% of their initial activity after 30 d of incubation in hexane at 60,°C. The catalytic behaviour of the immobilized enzyme depends on the terminal group of the carbon nanotubes, the concentration of the enzyme and the immobilization method employed. [source] Improved Auxiliary for the Synthesis of Medium-Sized Bis(lactams)EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2008Jasper Springer Abstract Our auxiliary-based method for the synthesis of bis(lactams) has been optimized. A novel auxiliary is described that is inserted in the backbone of a linear peptide facilitating the mutually reactive terminal groups to approach one another for a cyclization reaction. A subsequent ring contraction mechanism leads to the bis(lactams) with the remainings of the auxiliary still attached. Functionalized seven- and eight-membered bis(lactams) have been prepared that are difficult to access using traditional methods. Removal of the auxiliary from the bis(lactams) has been described with the possible side reactions that can occur.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Molecular Origins of the Mechanical Behavior of Hybrid GlassesADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Mark S. Oliver Abstract Hybrid organic-inorganic glasses exhibit unique electro-optical properties along with excellent thermal stability. Their inherently mechanically fragile nature, however, which derives from the oxide component of the hybrid glass network together with the presence of terminal groups that reduce network connectivity, remains a fundamental challenge for their integration in nanoscience and energy technologies. We report on a combined synthesis and computational strategy to elucidate the effect of molecular structure on mechanical properties of hybrid glass films. We first demonstrate the importance of rigidity percolation to elastic behavior. Secondly, using a novel application of graph theory, we reveal the complex 3-D fracture path at the molecular scale and show that fracture energy in brittle hybrid glasses is fundamentally governed by the bond percolation properties of the network. The computational tools and scaling laws presented provide a robust predictive capability for guiding precursor selection and molecular network design of advanced hybrid organic-inorganic materials. [source] Air-Stable n-Type Organic Field-Effect Transistors Based on Carbonyl-Bridged Bithiazole DerivativesADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Yutaka Ie Abstract An electronegative conjugated compound composed of a newly designed carbonyl-bridged bithiazole unit and trifluoroacetyl terminal groups is synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements reveal that carbonyl-bridging contributes both to lowering the lowest unoccupied molecular orbital energy level and to stabilizing the anionic species. X-ray crystallographic analysis of the compound shows a planar molecular geometry and a dense molecular packing, which is advantageous to electron transport. Through these appropriate electrochemical properties and structures for n-type semiconductor materials, OFET devices based on this compound show electron mobilities as high as 0.06,cm2 V,1 s,1 with on/off ratios of 106 and threshold voltages of 20,V under vacuum conditions. Furthermore, these devices show the same order of electron mobility under ambient conditions. [source] Super-Stable, High-Quality Fe3O4 Dendron,Nanocrystals Dispersible in Both Organic and Aqueous SolutionsADVANCED MATERIALS, Issue 11 2005M. Kim High-quality Fe3O4 nanocrystals coated with stearate groups are successfully converted to dendron-coated nanocrystals (dendron,nanocrystals). Poly(ethylene glycol) oligomers are used as major terminal groups for the dendron ligands, which afford excellent dispersibility of the dendron,nanocrystals in a broad spectrum of solvents, ranging from dichloromethane to water (see Figure). [source] Towards Control of Dendrimer Properties by Reversible Exchange of Termini: Synthesis and Characterization of Diverse Porphyrin DendrimersISRAEL JOURNAL OF CHEMISTRY, Issue 1 2009Meital Shema-Mizrachi Porphyrin dendrimers with boronic ester, aldehyde, and pyridil termini were synthesized and fully characterized. These dendrimers have the potential to change their physical and chemical properties by reversible alteration of the reactive terminal groups. [source] Character of long-chain branching in highly purified natural rubberJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Sureerut Amnuaypornsri Abstract The nature of long-chain branching in natural rubber (NR) from Hevea brasiliensis was analyzed for NR purified by enzymatic deproteinization in the latex state followed by acetone extraction in the solid state to remove the proteins and neutral lipids, respectively. The treatment of purified NR in a toluene solution with a polar solvent, such as methanol or acetic acid, resulted in a clear decrease in the molecular weight, gel content, and Huggins' constant; this was caused by the decomposition of branch points in the purified rubber. This finding clearly showed that long-chain branching in the purified NR was mainly derived from the association of phospholipids linked with both terminal groups in the rubber chain via hydrogen bonds. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Structural and photooxidation studies of poly(styrene oxide) prepared with Maghnite-H+ as cationic catalystJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Aïcha Hachemaoui Abstract The nature of irregularities and end-groups in poly(styrene oxide) samples prepared using Maghnite-H+ as a cationic catalyst were studied by 1H- and 13C-NMR at 200 MHz. Head-to-head (H-H) and tail-to-tail (T-T) irregularities are detected in all the samples studied. Secondary hydroxyl terminal groups are identified in polymers prepared with Maghnite-H+. Poly(styrene oxide) was found to undergo chain scission by aging at 25°C. It was confirmed that oxidation of this type of polymers results from the important sensitivity of the polyether soft segment to oxidative degradation. For this reason, the scissions due to the oxidation of the material lead to notable quantities of low molecular weight photoproducts. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified by MALDI-TOF-MS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] FTIR, 1H-NMR spectra, and thermal characterization of water-based polyurethane/acrylic hybridsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008O. R. Pardini Abstract Polyurethane (PU) polymer was synthesized following a prepolymer mixing process, by polyaddition of isophorone diisocyanate (IPDI), poly(propylene glycol) (PPG), 2-hydroxyethyl methacrylate (HEMA), and 2,2-bis(hydroxymethyl)propionic acid (DMPA). The PU anionomer having 2-ethoxymethacrylate terminal groups was dispersed in water by prior neutralization of carboxylic acid groups of DMPA with triethylamine (TEA), chain extended with hydrazine (HZM) in water and a dispersion polymerization with methyl methacrylate/n -butyl acrylate/acrylic acid mixture was performed. The above polymerization reactions lead to the formation of PU/acrylic hybrids having a chemical bond between PU and acrylic moieties. Acrylic content was varied from 0 to 50 wt % and samples were purified to eliminate oligomers and impurities before characterization. The FTIR and 1H-NMR spectra of these purified hybrid samples were obtained and bands and peaks assignments were discussed. Thermal properties (DSC and TGA) were also discussed. Breaking hydrogen bonds is the main reason for changes in properties with increasing acrylic content. Particle size data of dispersions is also presented and discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis and chiroptical properties of L -valine-containing poly(phenylacetylene)s with (a)chiral pendant terminal groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006Lo Ming Lai Abstract Poly(phenylacetylene)s containing L -valine residues (P1) with (a)chiral pendant terminal groups R(*) [,(HCC{C6H4CONHCH[CH(CH3)2]COOR(*)})n,]; R(*) = 1-octyl (P1o), (1S,2R,5S)-(+)-menthyl [P1(+)], (1R,2S,5R)-(,)-menthyl [P1(,)] are designed and synthesized. The polymers are prepared by organorhodium catalysts in high yields (yield up to 88%) with high molecular weights (Mw up to ,6.4 × 105). Their structures and properties are characterized by NMR, IR, TGA, UV, and circular dichroism analyses. All the polymers are thermally fairly stable (Td , 320 °C). The chiral moieties induce the poly(phenylacetylene) chains to helically rotate in a preferred direction. The chirality of the pendant terminal groups affects little the helicity of the polymers but their bulkiness stabilizes the helical conformation against solvent perturbation. The backbone conjugation and chain helicity of the polymers can be modulated continuously and reversibly by acid. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2117,2129, 2006 [source] Dendrimer-star polymer and block copolymer prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization with dendritic chain transfer agentJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005Chun-Yan Hong Abstract A new reversible addition-fragmentation chain transfer (RAFT) agent, dendritic polyester with 16 dithiobenzoate terminal groups, was prepared and used in the RAFT polymerization of styrene (St) to produce star polystyrene (PSt) with a dendrimer core. It was found that this polymerization was of living characters, the molecular weight of the dendrimer-star polymers could be controlled and the polydispersities were narrow. The dendrimer-star block copolymers of St and methyl acrylate (MA) were also prepared by the successive RAFT polymerization using the dendrimer-star PSt as macro chain transfer agent. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6379,6393, 2005 [source] Synthesis and characterization of epoxidized polybutadiene/polyaniline graft conducting copolymerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2004F. R. De Risi Abstract In this article the synthesis and characterization of an elastomeric conducting material, obtained by grafting polyaniline (EB) on commercial cis -1,4-polybutadiene (PB), are described. PB was first partially epoxidized in chloroform solution using meta-chloroperbenzoic acid (MCPBA). The conducting polymer was then grafted to the activated polybutadiene (EPB) via the aminolysis reaction between the polyaniline NH2 terminal groups and the oxirane rings. The material so obtained (EPBPAN) and the epoxidized intermediate product were characterized by 1H NMR, 13C NMR, Fourier transform infrared, and ultraviolet,visible spectroscopy, thermal and mechanical analysis, and electrical conductivity measurements. The effect of the sample deformation on conductivity also was analyzed. The HCl doping of the EPBPAN film induced crosslinking reactions, generated by the acid cleavage of unreacted oxirane groups. The electrical conductivity of the doped material reached values of about 10,5 ,,1 cm,1. The key characteristics of our elastomeric conducting material are its simple synthesis, its starting as a commercial product, and the solubility of its undoped form in a common low-boiling organic solvent like chloroform. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3082,3090, 2004 [source] Synthesis and characterization of 2,2-bis(methylol)propionic acid dendrimers with different cores and terminal groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2004Michael Malkoch Abstract Three sets of aliphatic polyester dendrimers based on 2,2-bis(methylol)propionic acid (bis-MPA) were synthesized. Two of the sets had benzylidene terminal groups and either a trimethylolpropane or triphenolic core moiety. The last set had acetonide terminal groups and a triphenolic core moiety. Benzylidene-[G#1]-anhydride and acetonide-[G#1]-anhydride were used as the reactive building blocks in the construction of all dendrimers. The large excess of building blocks used in the coupling reactions initially resulted in considerable material loss. This waste was eliminated through the development of a recycling method. 1H and 13C NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis were used to verify the purity of all compounds. Size exclusion chromatography (SEC) was used, as well as MALDI-TOF, for molecular weight determinations. The SEC measurements were conducted with a universal calibration method and an online right-angle laser light scattering detector. Measured dendrimer molecular weights were close to their theoretical molar masses. Observations were also made of the hydrodynamic radius and intrinsic viscosity for the different dendrimers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1758,1767, 2004 [source] Fabrication of Aromatic-Aliphatic Aminoketone Polymers with Terminal Fluorine GroupsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2010Susann Anders Abstract A procedure for synthesis aromatic-aliphatic PAK, completely functionalized with p- fluorophenyl terminal groups, is presented. This synthesis uses the nucleophilic aromatic substitution of DFB with various secondary aliphatic diamines [CH3NH(CH2)mNHCH3] (m,=,3, 6, and 8) and cesium fluoride as the base catalyst in the melt. The linearity and the complete functionalization of the PAK compounds with p- fluorophenyl terminal groups are demonstrated with the aid of MALDI TOF mass spectrometry. PAK compounds are semi-crystalline as shown by WAXS and DSC measurements. The degree of crystallinity ranges between 2 and 25%. Nucleophilic aromatic substitution reactions in the fluorine end groups are demonstrated by reaction of PAK (m,=,6) with the strong S- nucleophile mercaptoacetic acid. [source] Melt Mixing of Ethylene/Butyl Acrylate/Glycidyl Methacrylate Terpolymers with LDPE and PETMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2009Aida Benhamida Abstract The chemical modification by melt-mixing of an EBAGMA terpolymer with LDPE and PET was investigated with the aim to use these EBAGMA/LDPE and EBAGMA/PET blends (in equal weight quantities) as compatibilizer master batches to improve the compatibility of the LDPE/PET system. It is shown that when the EBAGMA terpolymer is melt blended with LDPE, almost 40% of the initial amount of EBAGMA is linked to the LDPE backbone. In contrast, in the case of EBAGMA/PET, FT-IR spectra indicate the total reactivity between the two components through the reaction of the epoxy group of EBAGMA with the PET terminal groups. SEM analysis shows that both master batches present two well-interconnected phases. [source] Modeling of Semibatch Esterification Process for Poly(ethylene terephthalate) SynthesisMACROMOLECULAR REACTION ENGINEERING, Issue 4 2007Himanshu Patel Abstract The esterification kinetics of terephthalic acid (TPA) and ethylene glycol (EG) in poly(ethylene terephthalate) (PET) synthesis were studied using a semibatch reactor. Rate constants were optimized by data fitting with the oligomeric chain length, the fraction of carboxyl groups in the terminal groups (,) and the water generation curve for different EG/TPA feed ratios. The influence of the TPA particle size distribution on the solid-liquid mass transfer rate and on acid conversion (,) was investigated. It was observed that conversion became more sensitive towards TPA particle size as the EG/TPA feed ratio was lowered. It is advantageous to use the model based on TPA particle size for mass transfer limited esterification reactors. The effect of the monomer feed ratio on conversion, chain length and system heterogeneity can be predicted with this model. [source] Atomic study of molecular wires composed of thiophene oligomersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007P. Bai Abstract In this paper, we study the electron conductance of thiophene oligomers based molecular wires through atomic structures using the first principles method based on density functional theory and nonequilibrium Green's function. The molecular wires are built by sandwiching various thiophene oligomers between two metal electrodes via terminal groups at atomic levels. The effects of alkyl substituents on the thiophene oligomers are modelled by varying inter-ring angles of the oligomers. Thiophene dimers, tetramers and hexamers are used to studied thiophene size effects. The projected orbitals, energy gaps, transmission functions and current,voltage characteristics of the molecular wires are calculated and analyzed. Results show that the molecular wires with the planar structures of thiophene oligomers have larger electron transmission functions, hence better electronic conductance than those with twist structures. The conductance of molecular wires decreases when the chain length of the thiophene oligomer increases. The results can provide guidance for design of thiophene molecular electronic wires and other devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dendrimeric Oligo(phenylenevinylene)-Extended Dithieno[3,2- b:2,,3,- d]phospholes,Synthesis, Self-Organization, and Optical PropertiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2009Carlos Romero-Nieto Abstract A boost from the branches: Incorporation of the dithieno[3,2- b:2,,3,- d]phosphole system as a core in oligo(phenylenevinylene) dendrimers (an example is shown here) provides materials that exhibit energy-transfer features relaying incoming photons from the dendrons towards the core, which in turn shows enhanced emission intensity. The optical properties and self-assembly features of the dendrimers can be impacted by the terminal groups (-H, -CF3, or -NPh2) employed. To establish this system as a fluorescent core in ,-conjugated dendrimers, a series of oligo(phenylenevinylene) (OPV)-extended dithieno[3,2- b:2,,3,- d]phospholes has been prepared by means of a Wittig,Horner protocol with a dithienophosphole dialdehyde and appropriately functionalized phosphonates. The "zero-generation" model compounds have provided the general accessibility of OPV-functionalized dithienophospholes, and show varying emission colors covering the optical spectrum from green to red. Expansion of the synthetic strategy towards the corresponding first-generation dendrimers has provided materials that show intriguing self-organization features in case of the phenyl-terminated dendrimer, forming large one-dimensional microfibres, as well as desirable energy-transfer processes from the dendrons to the dithienophoshole core resulting in an enhanced emission intensity for the latter. The present study has revealed that the terminal end-groups of the OPV branches have significant impact on the optical features of the OPV dendrimers as a whole. [source] | |||||||||||||||||||||||||