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Polymeric Systems (polymeric + system)
Selected AbstractsPolymeric systems for amorphous ,9 -tetrahydrocannabinol produced by a hot-melt method.JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2006Part II: Effect of oxidation mechanisms, chemical interactions on stability Abstract The objectives of the present research investigations were to (i) elucidate the mechanism for the oxidative degradation of ,9 -tetrahydrocannabinol (THC) in polymer matrix systems prepared by a hot-melt fabrication procedure, and (ii) study the potential for controlling these mechanisms to reduce the degradation of THC in solid dosage formulations. Various factors considered and applied included drug-excipient compatibility, use of antioxidants, cross-linking in polymeric matrices, microenvironment pH, and moisture effect. Instability of THC in polyethylene oxide (PEO)-vitamin E succinate (VES) patches was determined to be due to chemical interaction between the drug and the vitamin as well as with the atmospheric oxygen. Of the different classes and mechanisms of antioxidants studied, quenching of oxygen by reducing agents, namely, ascorbic acid was the most effective in stabilizing THC in PEO-VES matrices. Only 5.8% of the drug degraded in the ascorbic acid-containing patch as compared to the control (31.6%) after 2 months of storage at 40°C. This coupled with the cross-linking extent and adjustment of the pH microenvironment, which seemed to have an impact on the THC degradation, might be effectively utilized towards stabilization of the drug in these polymeric matrices and other pharmaceutical dosage forms. These studies are relevant to the development of a stable transmucosal matrix system for the therapeutic delivery of amorphous THC. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:2473,2485, 2006 [source] Amphiphilic Block Polypeptide-Type Ligands for Micellar Catalysis in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Shlomi Elias Abstract Novel amphiphilic block polypeptide ligands were synthesized and showed excellent behavior in the metal-catalyzed organic transformations in pure water. The catalytic activity and/or recycling properties of the catalysts are the result of the micellar structure of the polymeric system in water. [source] Investigation of electrical conduction mechanism in double-layered polymeric systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Prashant Shukla Abstract The electrical conduction in solution-grown polymethylmethacrylate (PMMA), polyvinylidenefluoride (PVDF) and PMMA-PVDF double-layered samples in the sandwich configuration (metal-polymer-metal) was investigated at different fields in the range 100,120 kV/cm as a function of temperature in the range 293,423 K for samples of constant thickness of about 50 ,m. Certain effects which lead to a large burst of current immediately after the application of field were observed in double-layered samples. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories on electrical conduction. The observed linear I-V characteristics show that the electrical conduction follows Pool-Frenkel mechanism in PMMA and PVDF samples. Whereas, the non-linear behavior of current-voltage measurements in PMMA-PVDF double-layered samples have been interpreted on the basis of space charge limited conduction (SCLC) mechanism. The conductivity of the polymer films increased on formation of their double-layer laminates. The polymer-polymer interface act as charge carrier trapping centres and provides links between the polymer molecules in the amorphous region. The interfacial phenomenon in polymer-polymer heterogeneous system has been interpreted in terms of Maxwell-Wagner model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Synthesis, characterization and application of poly[(1-vinyl-2-pyrrolidone)- co -(2-hydroxyethyl methacrylate)] as controlled-release polymeric system for 2,4-dichlorophenoxyacetic chloride using an ultrafiltration techniquePOLYMER INTERNATIONAL, Issue 7 2008Guadalupe del C Pizarro Abstract BACKGROUND: Polymers supporting chemicals used in agriculture have recently been developed to overcome the serious environmental problems of conventional agrochemicals. The success of these formulations is based on a suitable choice of polymer support. Degradable polymeric hydrogels are of particular interest. The gradual release of the bioactive agent can be achieved by hydrolytic or enzymatic cleavage of the linking bond. RESULTS: In this context, poly[(1-vinyl-2-pyrrolidone)- co -(2-hydroxyethyl methacrylate)] [poly(NVP- co -HEMA)] has been used as a bioactive carrier reagent. Herein, we report a controlled-release system with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) using an ultrafiltration system. Hydrolysis was studied by testing the release at various pH values. A high release with poly(NVP- co -HEMA),2,4-D was observed at pH = 7 and 10 after two days (Z = 2). The release percentage of copolymer,herbicide increased at pH = 10. It showed release values between 79.0 and 94.5%. Poly(NVP- co -HEMA),herbicide can release a bioactive compound in aqueous solution at pH = 3, 7 and 10. CONCLUSION: Based on the results of homogeneous hydrolysis, it is argued that the herbicide release rate depends on the pH of the reaction environment. This functional polymer could be employed as a biodegradable material for applications in agrichemical release. Copyright © 2008 Society of Chemical Industry [source] C3 -symmetrical self-assembled structures investigated by vibrational circular dichroism,CHIRALITY, Issue 9 2008Maarten M. J. Smulders Abstract We demonstrate by using vibrational circular dichroism (VCD) spectroscopy that it is possible to investigate the chirality of a supramolecular polymeric system in relatively dilute solutions. Chiral C3 -symmetrical discotic molecules, based on a trialkylbenzene-1,3,5-carboxamide, form supramolecular columnar stacks with a right-handed helical structure in solution due to intermolecular hydrogen bonds. The handedness of the supramolecular chirality is determined using electronic spectroscopy measurements. Under dilute conditions (at 10,3 M concentrations), it was also possible to probe the hydrogen bonding moieties with IR and VCD spectroscopy on these self-assembled structures. In combination with density functional theory (DFT) calculations, we could verify the preference for a right-handed chirality in the helical stacks and the nonplanar orientation of the carbonyl groups present in the molecule. This chiral arrangement is in agreement with the structure determined for a related benzene-1,3,5-tricarboxamide by X-ray diffraction. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source] Tunable Colors in Opals and Inverse Opal Photonic CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Carlos I. Aguirre Abstract Colloidal photonic crystals and materials derived from colloidal crystals can exhibit distinct structural colors that result from incomplete photonic band gaps. Through rational materials design, the colors of such photonic crystals can be tuned reversibly by external physical and chemical stimuli. Such stimuli include solvent and dye infiltration, applied electric or magnetic fields, mechanical deformation, light irradiation, temperature changes, changes in pH, and specific molecular interactions. Reversible color changes result from alterations in lattice spacings, filling fractions, and refractive index of system components. This review article highlights the different systems and mechanisms for achieving tunable color based on opaline materials with close-packed or non-close-packed structural elements and inverse opal photonic crystals. Inorganic and polymeric systems, such as hydrogels, metallopolymers, and elastomers are discussed. [source] Nanoparticle Electroluminescence: Controlling Emission Color Through Förster Resonance Energy Transfer in Hybrid ParticlesADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Christopher F. Huebner Abstract Electroluminescent (EL) polymers are attractive for developing all-organic light-emitting devices (OLEDs) due to the potential advantages that polymeric systems may offer in the large-scale manufacturing of electronics. Nonetheless, many of these EL , -conjugated polymers are inherently insoluble in the solvents employed in the intended solution-based manufacturing processes. One such polymer is poly(2,5-dioctyl-1,4-phenylenevinylene) (POPPV), where the inherent lack of solubility of POPPV in organic solvents has frustrated its widespread application in devices and no OLEDs have been presented that exploit its electroluminescence characteristics. In this effort, a unique strategy is presented for the preparation of hybrid nanoparticles composed of POPPV, a green emitter (,em,=,505,nm) and poly(9,9-di- n -octylfluorenyl-2,7-diyl) (PFO), a blue emitter (,em,=,417,nm). The aqueous-based nanoparticle dispersion composed of these hybrid particles is stable to aggregate and can be employed in the construction of OLEDs. The color characteristics of the electroluminescence for the devices can be tuned by exploiting the Förster resonance energy transfer between the polymers within a particle, while suppressing energy transfer between the particles. These aqueous-based nanoparticle dispersions are amenable to being printed into devices through high-throughput manufacturing techniques, for example, roll-to-roll printing. [source] Porous epoxies by reaction induced phase separation of removable alcohols: Control of spheroidal pore size by mass fraction, cure temperature, and reaction rate,JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Robert J. Klein Abstract Porous organic and inorganic materials with both random and controlled microstructures have utility in a variety of fields including catalysis, sensors, separations, optical platforms, tissue engineering, hydrogen storage, micro-electronics, medical diagnostics, as well as other applications. This work highlights a simple and general technique for tuning the pore size in crosslinking polymeric systems by adding a solvent poragen that phase separates during the curing process (reaction induced phase separation). The pore size can be controlled over large length scales ranging from microns to well below 100 nanometers. In this system an amine cured epoxy resin was reacted in the presence of the sacrificial poragen octadecanol, which is removed by vacuum-assisted evaporation once the epoxy components have reacted to form a solid, porous matrix. The importance of the present approach is based on the simplicity of the chemical formulation, the ease by which other epoxide or amine chemistries may be substituted for the two reactive components, and the control of pore size down to the nanometer scale by the addition of a small amount of catalyst. © 2010 Wiley Periodicals, Inc., J Appl Polym Sci, 2010 [source] Stochastic generator of chemical structure.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2001Abstract A novel computational technique to generate close-to-equilibrium crosslinked polymeric systems is proposed. Compared to the current state-of-the-art equilibration methods, the new technique appears to be faster by several orders of magnitude. The main advantage of the technique is that one can circumvent the bottlenecks in configuration space that inhibit relaxation in molecular dynamics or Monte Carlo simulations. The problem of polymer equilibration described by continuous equations in molecular dynamics is reduced to a discrete representation where solutions are approximated by simple algorithms. In the current study, a series of coarse-grained, united-atom, and fully atomistic crosslinked networks has been generated. Network statistics and topology, X-ray scattering intensities, and elastic properties are tested vs. experimental results and similar models generated using molecular dynamics and Monte Carlo simulations. The results demonstrate the efficiency of this new method for generating large realistic polymeric systems up to 1.4 M atoms. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 580,590, 2001 [source] A study of phase separation in peptide-loaded HPMC films using Tzero -modulated temperature DSC, atomic force microscopy, and scanning electron microscopyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2004Samana Hussain Abstract Despite the widespread use of drug-loaded polymeric systems, there is still considerable uncertainty with regard to the nature of the distribution of the drug within the polymer matrix. The aim of this investigation was to develop thermal and microscopic techniques whereby the miscibility and spatial distribution of a model peptide, cyclosporin A (CyA), in hydroxypropyl methylcellulose (HPMC) films may be studied. The new technique of Tzero -modulated temperature differential scanning calorimetry (Tzero MTDSC), scanning electron microscopy (SEM), and pulse force mode atomic force microscopy (PFM-AFM) were used in conjunction to study films prepared using a solvent evaporation process, with a solvent extraction study performed to elucidate the nature of the observed phases. Tzero MTDSC studies showed glass transitions for both the HPMC and CycA, with the Tg for the HPMC and CycA seen for the mixed systems. SEM showed two spherical phases of differing electron density. PFM-AFM also showed spheres of differing adhesion that increased in size on addition of drug. Pixel intensity analysis indicated that the smaller spheres corresponded to CycA. Exposure of the films to dichloromethane, in which CycA is soluble but HPMC is not, resulted in the presence of voids that corresponded well to the spheres suggested to correspond to the drug. It was concluded that the system had undergone extensive or complete phase separation, and that the thermal and microscopic techniques outlined above are an effective means by which this issue may be studied. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1672,1681, 2004 [source] Advances and potential applications of chitosan derivatives as mucoadhesive biomaterials in modern drug deliveryJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 8 2006Shruti Chopra Pharmaceutical technologists have been working extensively on various mucoadhesive polymeric systems to create an intimate and prolonged contact at the site of administration. Chitosan is one of the most promising polymers because of its non-toxic, polycationic biocompatible, biodegradable nature, and particularly due to its mucoadhesive and permeation enhancing properties. Due to its potential importance in controlled drug delivery applications, pharmaceutical scientists have exploited this mucoadhesive polymer. However, chitosan suffers from limited solubility at physiological pH and causes presystemic metabolism of drugs in intestinal and gastric fluids in the presence of proteolytic enzymes. These inherent drawbacks of chitosan have been overcome by forming derivatives such as carboxylated, various conjugates, thiolated, and acylated chitosan, thus providing a platform for sustained release formulations at a controlled rate, prolonged residence time, improved patient compliance by reducing dosing frequency, enhanced bioavailability and a significant improvement in therapeutic efficacy. We have explored the potential benefits of these improved chitosan derivatives in modern drug delivery. [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] Cellular Adhesion, Proliferation and Viability on Conducting Polymer SubstratesMACROMOLECULAR BIOSCIENCE, Issue 12 2008Luis J. del Valle Abstract This work reports a comprehensive study about cell adhesion and proliferation on the surface of different electroactive substrates formed by ,-conjugated polymers. Biological assays were performed considering four different cellular lines: two epithelial and two fibroblasts. On the other hand, the electroactivity of the three conducting systems was determined in physiological conditions. Results indicate that the three substrates behave as a cellular matrix, even though compatibility with cells is larger for PPy and the 3-layered system. Furthermore, the three polymeric systems are electro-compatible with the cellular monolayers. [source] Polymer Foams Stabilized by Particles Adsorbed at the Air/Polymer InterfaceMACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2008Prachi Thareja Abstract In aqueous systems, partially hydrophobic particles are known to stabilize foams even in the absence of any added surfactant. This paper shows that the same principle can be applied to polymeric systems: particles that are partially wetted by a polymer melt can stabilize a foam of that polymer. The foam stability is attributable to the adsorption of the particles at the air/polymer interface. Remarkably, stable foams are realized even from polymers that are liquid at room temperature, and hence are otherwise unfoamable. The implications of this result to practical foaming operations are discussed. [source] Cluster secondary ion mass spectrometry of polymers and related materials,MASS SPECTROMETRY REVIEWS, Issue 2 2010Christine M. Mahoney Abstract Cluster secondary ion mass spectrometry (cluster SIMS) has played a critical role in the characterization of polymeric materials over the last decade, allowing for the ability to obtain spatially resolved surface and in-depth molecular information from many polymer systems. With the advent of new molecular sources such as , , , and , there are considerable increases in secondary ion signal as compared to more conventional atomic beams (Ar+, Cs+, or Ga+). In addition, compositional depth profiling in organic and polymeric systems is now feasible, without the rapid signal decay that is typically observed under atomic bombardment. The premise behind the success of cluster SIMS is that compared to atomic beams, polyatomic beams tend to cause surface-localized damage with rapid sputter removal rates, resulting in a system at equilibrium, where the damage created is rapidly removed before it can accumulate. Though this may be partly true, there are actually much more complex chemistries occurring under polyatomic bombardment of organic and polymeric materials, which need to be considered and discussed to better understand and define the important parameters for successful depth profiling. The following presents a review of the current literature on polymer analysis using cluster beams. This review will focus on the surface and in-depth characterization of polymer samples with cluster sources, but will also discuss the characterization of other relevant organic materials, and basic polymer radiation chemistry. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:247,293, 2010 [source] Association between plasticized starch and polyesters: Processing and performances of injected biodegradable systemsPOLYMER ENGINEERING & SCIENCE, Issue 5 2001Luc Avérous Different formulations of wheat thermoplastic starch (TPS) have been processed with various plasticizer/starch ratios and moisture contents. The biodegradable polyesters tested are polycaprolactone (PCL), polyester amide (PEA), polybutylene succinate adipate (PBSA) and polybutylene adipate co terephtalate (PBAT). TPS and polyesters are melt blended in different proportions by extrusion and then injected to obtain dumbbell specimens. Various properties are evaluated such as the mechanical properties (tensile and impact tests), and the hydrophilic character with contact angle measurements. Additionally, uniaxial shrinkage is evaluated. Results show that the addition of polyester to TPS increases the dimensional post-injection stability. Blend modulus values are close to the results of the classical rule of mixture. Elongation at break, resilience values and SEM observations seem to give some indications about the compatibility between both polymeric systems. PBAT and PEA present better results than PCL and PBSA. Contact angle measurement show that we have a drastic increase of the hydrophobic character from 10% of polyester in the blend. The different combinations of TPS and polyesters give a wide range of mechanical behavior for compostable materials, to be developed in specific applications. [source] Control of stereochemical structures of silicon-containing polymeric systems,POLYMER INTERNATIONAL, Issue 3 2009Yusuke Kawakami Abstract Various optically active silicon compounds have been synthesized or separated, and used to synthesize silicon-containing polymers with well-controlled stereochemical structures. Hydrosilylation, anionic ring-opening polymerization and cross-coupling reactions have been used to synthesize optically active and/or stereoregular silicon-containing polymers. Copyright © 2009 Society of Chemical Industry [source] Photodegradation mechanism and stabilization of polyphenylene oxide and rigid-rod polymersPOLYMER INTERNATIONAL, Issue 2 2006Ying-Hung So Abstract Poly(2,4-dimethyl-1,4-phenylene oxide) (PPO), poly(benzo[1,2- d:5,4- d,]bisoxazole-2,6-diyl-1,4-phenylene) (PBO) and poly(benzo[1,2- d:4,5- d,]bisthiazole-2,6-diyl-1,4-phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self-sensitized photo-induced electron-transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo-induced electron-transfer mechanism. Methods to stabilize these polymers against photo-oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry [source] Polymers as functional components in batteries and fuel cells,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9-10 2006Gerhard Wegner Abstract The recent 10 years have seen an unprecedented development in the area of portable electronic devices: mobile phones, laptops, PDAS, and digital cameras have all become commodities on a large scale. All of these devices need a power supply in terms of a battery acceptable capacity, possibly rechargeable. This demand has triggered research and development in polymer materials science for lithium ion conducting polymers that could replace or avoid organic liquids as a supporting electrolyte. Moreover, polymers need to be optimized that act in the form of "gels" as framework and/or membrane materials to achieve mechanical integrity of the electrode compartments. Ionic conductivity for protons in polymeric systems is also the key issue in the development of so-called polyelectrolyte-membrane fuel cells (PEMFCs) that are supposed to work as power sources for mobile applications, e.g. in hybrid cars. A liquid fuel such as methanol would be converted to CO2 and H2O with concomitant production of electricity. Novel proton conducting polymer systems are required that work at temperatures between 150,200°C, that is under more or less water-free conditions. These requirements find an echo in the academic world in terms of renewed interest in the mechanisms of ionic transport phenomena in polymeric systems and in studies that aim for optimization of materials. In this article there will be a report on both lithium-ion and proton conducting polymers that have been recently developed in the authors' laboratory. The results will be discussed in the context of the demands that need to be met for advanced technologies. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||