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Linear Polymers (linear + polymer)
Selected AbstractsSelf-Assembly of Organodiphosphonate, Polyoxomolybdate and Diphenanthrolinecobalt(II) into Two Clusters and One Linear PolymerEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2003Rui-Biao Fu Abstract [{Co(1,10-phen)2}2{(Mo4O12)(O3PCH2CH2PO3)}·(H2O)] (1), [{Co(1,10-phen)2}2{(Mo4O12)(O3PCH2CH2CH2PO3)}·(1.5H2O)] (2) and [{Co(1,10-phen)2(H2O)2}{Co(1,10-phen)2(H2O)}{(Mo5O15)(O3PCH2CH2CH2CH2PO3)}·(6H2O)] (3) were synthesized by self-assembly of H2O3P(CH2)nPO3H2 (n = 2,4), polyoxomolybdate and [Co(1,10-phen)2]2+ (1,10-phen = 1,10-phenanthroline) under hydrothermal conditions. Compounds 1 and 2 are novel heterometallic hexanuclear clusters, while compound 3 is a new linear polymer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] A Materials Approach to the Dual-Site Isolation of Catalysts Bonded to Linear Polymers and Small, Ionic Molecules for Use in One-Pot Cascade Reactions,ADVANCED MATERIALS, Issue 21 2008A. Lee Miller II Site isolation of ionic catalysts and polymer-bound catalysts is achieved by placement on different sides of PDMS membranes. Ionic molecules and polymers do not flux through the PDMS membranes, but organic molecules can flux through the membranes and react with catalysts that are incompatible with each other. This is a general approach to site-isolate catalysts from each other. [source] Synthesis of hydroxy-terminated, oligomeric poly(silarylene disiloxane)s via rhodium-catalyzed dehydrogenative coupling and their use in the aminosilane,disilanol polymerization reaction,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2002Craig L. Homrighausen Abstract A series of oligomeric, hydroxy-terminated silarylene,siloxane prepolymers of various lengths were prepared via dehydrogenative coupling between 1,4-bis(dimethylsilyl)benzene [H(CH3)2SiC6H4Si(CH3)2H] and excess 1,4-bis(hydroxydimethylsilyl)benzene [HO(CH3)2SiC6H4Si(CH3)2OH] in the presence of a catalytic amount of Wilkinson's catalyst [(Ph3P)3RhCl]. Attempts to incorporate the diacetylene units via dehydrogenative coupling polymerization between 1,4-bis(dimethylsilyl)butadiyne [H(CH3)2SiCCCCSi(CH3)2H] and the hydroxy-terminated prepolymers were unsuccessful. The diacetylene units were incorporated into the polymer main chain via aminosilane,disilanol polycondensation between 1,4-bis(dimethylaminodimethylsilyl)butadiyne [(CH3)2NSi(CH3)2CCCC(CH3)2SiN(CH3)2] and the hydroxy-terminated prepolymers. Linear polymers were characterized by Fourier transform infrared, 1H and 13C NMR, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis, and they were thermally crosslinked through the diacetylene units, producing networked polymeric systems. The thermooxidative stability of the networked polymers is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1334,1341, 2002 [source] Bimolecular radical termination: New perspectives and insightsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2008Geoffrey Johnston-Hall Abstract The reversible addition-fragmentation chain transfer-chain length dependent termination (RAFT-CLD-T) method has allowed us to answer a number of fundamental questions regarding the mechanism of diffusion-controlled bimolecular termination in free-radical polymerization (FRP). We carried out RAFT-mediated polymerizations of methyl acrylate (MA) in the presence of a star matrix to develop an understanding of the effect of polymer matrix architecture on the termination of linear polyMA radicals and compared this to polystyrene, polymethyl methacrylate, and polyvinyl acetate systems. It was found that the matrix architecture had little or no influence on termination in the dilute regime. However, due to the smaller hydrodynamic volumes of the stars in solution compared to linear polymer of the same molecular weight, the gel onset point occurred at greater conversions, and supported the postulate that chain overlap (or c*) is the main cause for the observed autoacceleration observed in FRP. Other theories based on "short,long" termination or free-volume should be disregarded. Additionally, since our systems are well below the entanglement molecular weight, entanglements should also be disregarded as the cause of the gel onset. The semidilute regime occurs over a small conversion range and is difficult to quantify. However, we obtain accurate dependencies for termination in the concentrated regime, and observed that the star polymers (through the tethering of the arms) provided constriction points in the matrix that significantly slow the diffusion of linear polymeric radicals. Although, this could at first sight be postulated to be due to reptation, the dependencies showed that reptation could be considered only at very high conversions (close to the glass transition regime). In general, we find from our data that the polymer matrix is much more mobile than what is expected if reptation were to dominate. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3155,3173, 2008 [source] Synthesis of a model cyclic triblock terpolymer of styrene, isoprene, and methyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2002Dimitris Pantazis Abstract The synthesis of a model cyclic triblock terpolymer [cyclic(S- b -I- b -MMA] of styrene (S), isoprene (I), and methyl methacrylate (MMA) was achieved by the end-to-end intramolecular amidation reaction of the corresponding linear ,,,-amino acid precursor [S- b -I- b -MMA] under high-dilution conditions. The linear precursor was synthesized by the sequential anionic polymerization of S, I, and MMA with 2,2,5,5-tetramethyl-1-(3-lithiopropyl)-1-aza-2,5-disilacyclopentane as an initiator and amine generator and 4-bromo-1,1,1-trimethoxybutane as a terminator and carboxylic acid generator. The separation of the unreacted linear polymer from the cyclic terpolymer was facilitated by the transformation of the unreacted species into high molecular weight polymers by the evaporation of the reaction solvent and the continuation of the reaction under high-concentration conditions. The intermediate materials and the final cyclic terpolymer, characterized by size exclusion chromatography, vapor pressure osmometry, thin-layer chromatography, IR and NMR spectroscopy, exhibited high molecular weight and compositional homogeneity. Dilute-solution viscosity measurements were used as an additional proof of the cyclic structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1476,1483, 2002 [source] Effect of Reaction Conditions and Catalyst Design on the Rheological Properties of Polyolefins Produced in Gas-Phase Olefin Polymerization ReactorsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2008P. Pladis Abstract A model is developed to predict the viscoelastic behavior of polyolefins produced in catalytic polymerization reactors. The approach is based on the solution of different sub-models (e.g., a kinetic model, a single particle model, a macroscopic reactor model and a rheological model). From the calculated rheological curve, the polymer melt index is determined. The ability of the proposed model to predict the viscoelastic behavior of linear polymer melts quantitatively is examined for the operation of a catalytic olefin polymerization cascade-loop reactor process. In addition, the transient rheological properties of polyolefins produced in a Ziegler-Natta gas-phase olefin polymerization fluidized-bed reactor are calculated. [source] The dual roles of AlgG in C-5-epimerization and secretion of alginate polymers in Pseudomonas aeruginosaMOLECULAR MICROBIOLOGY, Issue 4 2003Sumita Jain Summary Pseudomonas aeruginosa strains causing chronic pulmonary infections in cystic fibrosis patients produce high levels of alginate, an exopolysaccharide that confers a mucoid phenotype. Alginate is a linear polymer of d -mannuronate (M) and variable amounts of its C-5-epimer, l -guluronate (G). AlgG is a periplasmic C-5-epimerase that converts poly d -mannuronate to the mixed M+G sequence of alginate. To understand better the role and mechanism of AlgG activity, a mutant was constructed in the mucoid strain FRD1 with a defined non-polar deletion of algG . Instead of producing poly mannuronate, the algG deletion mutant secreted dialysable uronic acids, as does a mutant lacking the periplasmic protein AlgK. High levels of unsaturated ends and the nuclear magnetic resonance spectroscopy pattern revealed that the small, secreted uronic acids were the products of extensive polymer digestion by AlgL, a periplasmic alginate lyase co-expressed with AlgG and AlgK. Thus, AlgG is bifunctional with (i) epimerase activity and (ii) a role in protecting alginate from degradation by AlgL during transport through the periplasm. AlgK appears to share the second role. AlgG and AlgK may be part of a periplasmic protein complex, or scaffold, that guides alginate polymers to the outer membrane secretin (AlgE). To characterize the epimerase activity of AlgG further, the algG4 allele of poly mannuronate-producing FRD462 was shown to encode a protein lacking only the epimerase function. The sequence of algG4 has a Ser-272 to Asn substitution in a serine,threonine-rich and conserved region of AlgG, which revealed a critical residue for C-5-epimerase activity. [source] Synthesis and magnetic properties of novel polymeric complexes containing bithiazole ringsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2007Weihong Lin Abstract A novel linear polymer (PFABT) containing bithiazole rings was synthesized by polycondensation of 2,2,-diamino-4,4,-bithiazole (DABT) and formaldehyde. The complexes of PFABT with two transition metal ions (Fe2+, Cu2+) were prepared for the first time. The polymer was determined through FT-IR, 1H-NMR and elemental analysis (EA), and the complexes were characterized by FT-IR. The magnetic behaviors of these complexes were measured as a function of magnetic field strength (0,50,kOe) at 4,K and as a function of temperature (4,300,K) under an applied magnetic field of 30,kOe. The results show that PFABT-Cu2+ is a ferromagnet while PFABT-Fe2+ is an anti-ferromagnet. Copyright © 2007 John Wiley & Sons, Ltd. [source] Preparation and Use of Microarrays Containing Synthetic Heparin Oligosaccharides for the Rapid Analysis of Heparin,Protein InteractionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2006Christian Noti Abstract Heparin is a highly sulfated, linear polymer that participates in a plethora of biological processes by interaction with many proteins. The chemical complexity and heterogeneity of this polysaccharide can explain the fact that, despite its widespread medical use as an anticoagulant drug, the structure,function relationship of defined heparin sequences is still poorly understood. Here, we present the chemical synthesis of a library containing heparin oligosaccharides ranging from di- to hexamers of different sequences and sulfation patterns. An amine-terminated linker was placed at the reducing end of the synthetic structures to allow for immobilization onto N -hydroxysuccinimide activated glass slides and creation of heparin microarrays. Key features of this modular synthesis, such as the influence of the amine linker on the glycosidation efficiency, the use of 2-azidoglucose as glycosylating agents for oligosaccharide assembly, and the compatibility of the protecting group strategy with the sulfation-deprotection steps, are discussed. Heparin microarrays containing this oligosaccharide library were constructed using a robotic printer and employed to characterize the carbohydrate binding affinities of three heparin-binding growth factors. FGF-1, FGF-2 and FGF-4 that are implicated in angiogenesis, cell growth and differentiation were studied. These heparin chips aided in the discovery of novel, sulfated sequences that bind FGF, and in the determination of the structural requirements needed for recognition by using picomoles of protein on a single slide. The results presented here highlight the potential of combining oligosaccharide synthesis and carbohydrate microarray technology to establish a structure,activity relationship in biological processes. [source] Blends of triazine-based hyperbranched polyether with LDPE and plasticized PVCJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Jyotishmoy Borah Abstract Triazine-based hyperbranched polyether was obtained by earlier reported method and blended with low density polyethylene (LDPE) and plasticized poly(vinyl chloride) (PVC) separately to improve some desirable properties of those linear polymers. The properties like processability, mechanical properties, flammability, etc. of those linear polymers were studied by blending with 1,7.5 phr of hyperbranched polyether. The mechanical properties were also measured after thermal aging and leaching in different chemical media. SEM study indicates that both polymers exhibit homogenous morphology at all dose levels. The mechanical properties like tensile strength, elongation at break, hardness, etc. of LDPE and PVC increase with the increase of dose level of hyperbranched polyether. The flame retardant behavior as measured by limiting oxygen index (LOI) for all blends indicates an enhanced LOI value compared to the polymer without hyperbranched polyether. The processing behavior of both types of blends as measured by solution viscosity and melt flow rate value indicates that hyperbranched polyether acts as a process aid for those base polymers. The effect of leaching and heat aging of these linear polymers on the mechanical properties showed that hyperbranched polyether is a superior antidegradant compared to the commercially used N -isopropyl- N -phenyl p -phenylene diamine. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 648,654, 2007 [source] Self-assembly of well-defined amphiphilic polymeric miktoarm stars, dendrons, and dendrimers in water: The effect of architectureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2009Daria E. Lonsdale Abstract Five polymeric architectures with a systematic increase in architectural complexity were synthesized by "click" reactions from a toolbox of functional linear polymers and small molecule linkers. The amphiphilic architectures ranged from a simple 3-miktoarm star block copolymer to the more complex third generation dendrimer-like block copolymer, consisting of polystyrene (PSTY) and polyacrylic acid (PAA). Micellization of these architectures in water at a pH of 7 under identical ionic strength gave spherical micelles ranging in size from 9 to 30 nm. Subsequent calculations of the PSTY core density, average surface area per PAA arm on the corona-core interface, and the relative stretching of the PAA arms provided insights into the effect of architecture on the self-assembly processes. A particular trend was observed that with increased architectural complexity the hydrodynamic diameter, radius of the core in the dry state and the aggregation number also increased with the exception of the third generation dendrimer. On the basis of these observations, we postulate that thermodynamic factors controlling self-assembly were the entropic penalty of forming PSTY loops in the core counterbalanced by the reduction in repulsive forces through chain stretching. This results in a greater number of aggregating unimers and consequently larger micelle sizes. The junction points within the architecture also play an important role in controlling the self-assembly process. The G3 dendrimer showed results contradictory to the aforementioned trend. We believe that the self-assembly process of this architecture was dominated by the increased attractive forces due to stretching of the PSTY core chains to form a more compact core. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6292,6303, 2009 [source] AB2 Functional Polyesters via Ring Opening Polymerization: Synthesis and CharacterizationMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2009Ingrid W. Velthoen Abstract Aliphatic AB2 functional polyesters were conveniently prepared by the ring opening polymerization of , -caprolactone and L -lactide in the presence of the AB2 functional initiator 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and Sn(Oct)2 as the catalyst. In L -lactide polymerization, both bis-MPA hydroxyl groups initiated the polymerization reaction, but for , -caprolactone polymerization this depended on the monomer to initiator to catalyst ratio. Initiation at two hydroxyl groups occurred at high monomer to initiator ([M]/[I]) ratio and at high Sn(Oct)2 to monomer ratio. The melting temperatures of the AB2 -functional PLLA and PCL polymers were comparable to linear polymers with a equal to the per arm in the polymer. [source] Solution Behavior of Temperature-Responsive Molecular Brushes Prepared by ATRPMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2007Joanna Pietrasik Abstract Molecular brushes, with side chains consisting of two copolymers: 2-(dimethylamino)ethyl methacrylate with methyl methacrylate, and N,N -dimethylacrylamide with butyl acrylate were prepared by grafting-from via atom transfer radical polymerization (ATRP). Poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) and poly(2-(2-bromopropionyloxy)ethyl methacrylate) were used as macroinitiators. Dynamic light scattering (DLS) studies were performed for aqueous solutions of molecular brushes below and above the lower critical solution temperature (LCST), and an unusual concentration-dependent LCST was observed. Due to the compact structure of molecular brushes, intramolecular collapse can occur when the average distance between molecules is much larger than the hydrodynamic dimensions of the individual macromolecules. However, if the concentration of the solution of molecular brushes is increased to the level in which the separation distance is comparable with the brush hydrodynamic dimensions, intermolecular aggregation occurs, as typically observed for solutions of linear polymers. [source] Organometallic Polymers of the Transition MetalsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2002Alaa S. Abd-El-Aziz Abstract This article provides a comprehensive review of the synthesis, properties and applications of organometallic polymers of the transition metals. The different classes of organometallic polymers are described according to their structural make-up, as well as by their methods of synthesis. A number of examples of each class are given to emphasize the richness and diversity in these areas of research. In addition to linear polymers, hyperbranched, crosslinked, star and dendritic polymers are also described. The properties that transition metal-containing organometallic polymers possess, as well as the applications that these materials have found in various domains are highlighted. [source] Mean-Square Radius of Gyration and Degree of Branching of Highly Branched Copolymers Resulting from the Copolymerization of AB2 With AB MonomersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2004Zhiping Zhou Abstract Summary: The evolution of the various structural units incorporated into hyperbranched polymers formed from the copolymerization of AB2 and AB monomers has been derived by the kinetic scheme. The degree of branching was calculated with a new definition given in this work. The degree of branching monotonously increased with increasing A group conversion (x) and the maximum value could reach 2r/(1,+,r)2, where r is the initial fraction of AB2 monomers in the total. Like the average degree of polymerization, the mean-square radius of gyration of the hyperbranched polymers increased moderately with A group conversion in the range x,<,0.9 and displayed an abrupt rise when the copolymerization neared completion. The characteristic ratio of the mean-square radius of gyration remained constant for the linear polymers. However, the hyperbranched polymers did not possess this character. In comparison with the linear polymerization, the weight average and z -average degree of polymerization increased due to the addition of the branched monomer units AB2 and the mean-square radius of gyration decreased quickly for the products of copolymerization. [source] Influence of the cross-linking density on the main dielectric relaxation of poly(methyl acrylate) networksPOLYMER ENGINEERING & SCIENCE, Issue 10 2005J.M. Meseguer Dueñas A series of polymer networks of varying cross-linking density was prepared by copolymerization of methyl acrylate and ethyleneglycol dimethacrylate. The aim of this work is to study the influence of cross-linking on the conformational mobility of the polymer chains using dielectric relaxation spectroscopy (DRS) in the temperature range of the main dielectric relaxation. As expected, the temperature range in which glass transition takes place became wider with increasing crosslinking density. DRS results were analyzed using the Havriliak-Negami equation. Master Cole-Cole arcs could be drawn for all the networks. The arcs become more symmetric as cross-linking density increases, as a consequence of the different effect of cross-links on large and small scale mobility. The conformational mobility that produces the main relaxation is drastically reduced when the cross-linking density increases what reduces the relaxation strength, but it also gives a qualitative change of behavior, as shown by the temperature dependence of the relaxation strength. In the loosely cross-linked networks the relaxation strength decreases monotonously as temperature increases, as in the main dielectric relaxation of linear polymers. Nevertheless, in highly cross-linked networks the curve of relaxation strength against temperature presents a maximum. POLYM. ENG. SCI., 45:1336,1342, 2005. © 2005 Society of Plastics Engineers [source] Electrospray mass spectrometry studies of macromolecules containing 1,3-oxazolidine moietiesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004J. Ma, ska-Solich The polycondensation of terephthalaldehyde with 2-amino-2-methyl-1,3-propanediol using acidic catalysts leads to the formation of linear polymers and macrocyclic compounds with 2-(1,,4,-phenylene)-5-methyl-1-aza-3,7-dioxabicyclo[3.3.0]octane as the repeating unit in all compounds. The structure of the polymer was determined by 1H- and 13C-NMR spectroscopy, and electrospray ionization mass spectrometric (ESI-MS) analysis. ESI-MS measurements were used to study the details of the polymer structure and support the equimolar alternating nature of bicyclo- O,N -acetals of terephthaldehyde in these macromolecules. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||