bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tracheal transplant with a prefabricated microsurgical flap
Authors: Icibaci Alexan , de Mello‐Filho Francisco Veríssimo 
Published: September 2009

AbstractObjective:To test the viability of a tracheal autotransplant, with an original technique using a prefabricated flap from a complete tracheal neovascularized segment (CTNVS) of the sternohyoid muscle anastomosed by a microsurgical technique.Study Design:An experimental study using dogs as an animal model.Methods:Ten mongrel dogs weighing 23 to 40 kg were divided into two groups: group I (control), five animals submitted to autotransplant of the CTNVS without a microsurgical vascular anastomosis; and group II, five dogs submitted to autotransplant of the CTNVS with a microsurgical vascular anastomosis.Results:All group I dogs developed respiratory insufficiency and died because of necrosis and stenosis of the autotransplanted CTNVS, whereas all group II dogs completed a minimum period of 90 days of observation without any clinical changes. Macro‐ and microscopic analysis revealed intact tracheal structures.Conclusions:The present clinical and morphological findings demonstrate that the CTNVS autotransplant is viable, when a microsurgical vascular anastomosis is used. Laryngoscope, 2009
Poly[ethylene‐co‐(vinyl alcohol)]‐graft‐poly(ε‐caprolactone) Synthesis by Reactive Extrusion, 1 ‐ Structural and Kinetic Study
Authors: Becquart Frédéric , Chalamet Yvan , Chen Jianding , Zhao Yanchao , Taha Mohamed 
Published: September 2009

AbstractChemical modification of EVOH in the molten state at 185 °C by a grafting from process of poly(ε‐caprolactone) in batch was studied. 1H NMR was used to characterize the structure evolutions of PCL grafts. In addition to grafting reactions, dynamic covalent transesterification reactions between EVOH residual alcohols and the polyester grafts led to a redistribution of the PCL grafts length. $\mathop {\overline {Dp} }\nolimits_n $ up to 27 and SR up to 80% were obtained. Experiments made in a corotating mini twin‐screw extruder also confirmed these results. The effect of the alcohol to caprolactone ratio and catalyst concentration (SnOct2) on kinetic evolution showed that few minutes were necessary to complete the polymerization. A kinetic model was proposed and adequate conditions for the synthesis by reactive extrusion were defined.magnified image
Squishy Non‐Spherical Hydrogel Microparticles
Authors: Haghgooie Ramin , Toner Mehmet , Doyle Patrick S. 
Published: September 2009

AbstractRecent advances in the synthesis of polymeric colloids have opened the doors to new advanced materials. There is strong interest in using these new techniques to produce particles that mimic and/or interact with biological systems. An important characteristic of biological systems that has not yet been exploited in synthetic polymeric colloids is their wide range of deformability. A canonical example of this is the human red blood cell (RBC) which exhibits extreme reversible deformability under flow. Here we report the synthesis of soft polymeric colloids with sizes and shapes that mimic those of the RBC. Additionally, we demonstrate that the mechanical flexibility of the colloids can be reproducibly varied over a large range resulting in RBC‐like deformability under physiological flow conditions. These materials have the potential to impact the interaction between biological and synthetic systems.magnified image
Effect of Gold Nanoparticles on the Thermosensitivity, Morphology, and Optical Properties of Poly(acrylamide–acrylic acid) Microgels
Authors: Echeverria Coro , Mijangos Carmen 
Published: September 2009

AbstractNovel positive thermosensitive microgels of poly(acrylamide–acrylic acid) with embedded gold nanoparticles have been synthesized and characterized by means of dynamic light scattering, UV‐vis spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These systems show temperature (upper critical solution temperature‐like volume phase transition) and optical responsiveness making them externally triggered systems.magnified image
Polyethylene Obtained by Plasma Polymerization of Hexene
Authors: Morales Pilar , Gómez Lidia M. , Olayo M. Guadalupe , Cruz Guillermo J. , Palacios Cuauhtemoc , Morales Juan , Ordoñez Eduardo 
Published: September 2009

AbstractThis work presents the synthesis by plasma of polyhexene (PHe) as an alternative to produce thin films of polyethylene (PE) without catalysts or other chemical compounds. PHe was obtained using 1‐Hexene in glow discharges at 13.5 MHz, 10−1 mBar and power between 40 and 120 W. The results showed that plasma PHe had the typical CC and CH bonds of PE with other bonds, as CC and CO, that indicate unsaturation and oxidation in the polymers. The thermal degradation of PHe starts at 250 °C, 100 °C lower than in PE. However, at T > 500 °C, PHe has more residual mass than PE. In the interval of 20–100 °C, the electrical conductivity of PHe was calculated between 10−11 and 10−8 S/cm. These results suggest that the structures of PHe and PE are similar and that the plasma polymerization of 1‐hexene is an alternative route to obtain oxidized and unsaturated varieties of PE as thin films on different surfaces.
Microemulsion Copolymerization Modeling Study Via a Combined Integral‐Differential Experimental Data Processing Approach
Authors: López‐Serrano F. , Mendizábal E. , Puig J.E. , Álvarez J. 
Published: September 2009

AbstractOn the basis of the data processing technique associated with the integro‐differential (ID) modeling assessment methodology, the styrene‐acrylonitrile microemulsion copolymerization system is studied, with a three‐state (conversion, active particles and micelles) and four‐parameter model (entrance and exit of radicals to and from particles, monomer transport from micelles to growing particles and initial micelle number), in conjunction with experimental conversion measurements. Comparing with the standard regression method, employed in previous studies, the ID approach incorporates additional information contained in the smooth conversion measurement derivative and does not require relying on a constant number of particles, as the slope‐and‐intercept method does. The resulting model, tested at three initiator concentrations, temperatures and comonomer feed, describes the S‐shaped conversion and the bell‐shaped active particles evolutions. This last finding is contrary to previous assumptions on linear growth with time of active particles. As expected, the entry and exit rate coefficients increase with initiator and styrene concentration and temperature. The surfactant transport from micelles decreases with initiator concentration and the initial micelles concentration value only affects the entry rate.
Evaluation of the Final Morphology of HIPS Based on the Architecture of the Compatibilizer Graft Copolymer PBd‐g‐PS
Authors: de Anda Carlos , Morales Graciela , Acuña Pablo , Sosa José , Knoeppel Dave , Mays Jimmy W. 
Published: September 2009

AbstractHigh Impact Polystyrene (HIPS) was synthesized by radical bulk polymerization at 70 °C using 6% w/w of total rubber and 0.01% w/w of azobisisobutyronitrile (AIBN) as radical initiator, where the total rubber was composed by polybutadiene (PBd) and model graft copolymers PBd‐g‐PS. Different ratios in weight percent of PBd to PBd‐g‐PS were used in order to evaluate the effect of the graft copolymers on the morphology development of the rubber particles during the HIPS synthesis reaction. The morphology of the final material was evaluated by Transmission Electron Microscopy (TEM). The model graft copolymers used with controlled architecture and molecular weight were synthesized previously by high vacuum anionic polymerization. Results show that increasing the content and changing the architecture of the graft copolymer significantly affects the phase inversion point.
Photochromic Block Copolymer Poly(styrene‐b‐azo monomer) by ATRP
Authors: Vázquez Y. , Elizalde L.E. , Nájera M.A. , Santos G. de los , Telles J.G. 
Published: September 2009

AbstractPhotoactive monomers [(E)‐1(4‐methacryloxyphenyl)‐2‐(nitrophenyl) diazene] (azo 1) and (E)‐1‐(4‐methacryloxyethyl‐phenyl)‐2‐phenyl‐diazene (azo2) were synthesized. The azo 1 monomer showed poor reactivity under the evaluated polymerization method. The Azo 2 monomer was used in the block copolymerization with polystyrene by the normal ATRP methodology. Several polystyrene macroinitiators were prepared with molecular weights of 10, 20 and 30 k g/mol. The end functionality was increased by the addition of 0.1 equivalents of copper II chloride. Block copolymers in 30% yield and low polydispersity were synthesized by ATRP from the polystyrene macroinitiators and the azo monomer. The block copolymer exhibits good photochromic activity.
The Use of the RAFT‐Technique for the Preparation of Temperature/pH Sensitive Polymers in Different Architectures
Authors: Licea‐Claveríe Angel , Alvarez‐Sánchez Jesús , Picos‐Corrales Lorenzo A. , Obeso‐Vera Claudia , Flores Mercedes C. , Cornejo‐Bravo José Manuel , Hawker Craig J. , Frank Curtis W. 
Published: September 2009

AbstractIn this contribution we report the use of the RAFT‐technique for the preparation of three types of responsive polymeric materials with a high potential of application in the biomedical field: 1.‐Diblock copolymers with reversible self‐assembly capacity as a function of pH based on N,N′‐diethylaminoethyl methacrylate (DEAEM) and 2‐methacryloyloxy benzoic acid (MAOB); 2.‐Diblock copolymers with reversible self‐assembly capacity as a function of temperature, based N‐isopropylacrylamide (NIPAAm) and n‐hexyl acrylate (HA); and 3.‐Polymeric stars with random number of arms consisting either in NIPAAm‐arms or copolymeric NIPAAm‐arms and hydrophobic core.
Anionic Syntheses of Chain‐End and In‐Chain Functionalized Polymers by Silyl Hydride Functionalization and Hydrosilylation Chemistry
Authors: Quirk Roderic P. , Janoski Jonathan , Olechnowicz Michael , Kim Hoon , Dabney David E. , Wesdemiotis Chrys 
Published: September 2009

AbstractA new general anionic functionalization methodology is described based on (a) the quantitative silyl hydride functionalization of well‐defined polymeric organolithium compounds with either dimethylchlorosilane (ω‐chain end functionalization) or dichloromethylsilane (in‐chain functionalization) and (b) reaction of the silyl hydride‐functionalized polymer with a functionalized alkene using Karstedt's Pt(0) hydrosilylation catalyst.
Poly(D‐lactide)–Poly(menthide)–Poly(D‐lactide) Triblock Copolymers as Crystal Nucleating Agents for Poly(L‐lactide)
Authors: Wanamaker Carolyn L. , Tolman William B. , Hillmyer Marc A. 
Published: September 2009

AbstractPoly(d‐lactide)–poly(menthide)–poly(d‐lactide) (PDLA–PM–PDLA) triblock copolymers were explored as novel nucleating agents for the crystallization of poly‐ (l‐lactide) (PLLA). PLLA/PDLA‐PM‐PDLA blends containing ≥85 wt% PLLA were prepared in a batch melt mixer. SAXS analysis was consistent with the ability of PDLA–PM–PDLA to form micelles when mixed with atactic polylactide. The presence of the stereocomplex in the PLLA matrix was confirmed by differential scanning calorimetry (DSC). The effectiveness of the putative stereocomplexed micelle crystallites for nucleating PLLA crystallization was also confirmed by DSC. Nucleation efficiencies near 100% were obtained when using a triblock copolymer with 15 kg/mol PDLA end blocks. In addition, fast crystallization kinetics were observed in isothermal crystallization experiments at 140 °C. Compared to PLLA/PDLA homopolymer blends, improvements in nucleation efficiency were observed when blending PLLA with PDLA‐containing triblock copolymers.
One‐Pot Biocatalytic Synthesis of Sugar Based Poly (ε‐caprolactone)
Authors: Barrera‐Rivera Karla A. , Martínez‐Richa Antonio 
Published: September 2009

AbstractThe one‐pot biocatalytic synthesis of amphiphilic polymers consisting of an isosorbide headgroup and a hydrophobic polyester chain is described. The immobilized lipase of Yarrowia lipolytica (YLL) catalyzed ring‐opening polymerization of ε‐caprolactone (ε‐CL) initiated by the multifunctional initiator isosorbide. Polymerizations were carried out in bulk at 70, 80, 90 and 120 °C. The highest reaction rates for ε‐CL polymerization resulted for YLL immobilized on macroporous resins: Lewatit VP OC 1026 at 80 °C, and the strongly acidic Lewatit K‐2629 at 90 °C. Structural analyses were made by MALDI‐TOF, 1H, and 13C‐NMR.
Rapid Starch Acetylation at Low Temperature Using Iodine as Catalyst
Authors: Ramírez‐Arreola Daniel E. , Robledo‐Ortiz Jorge R. , Arellano Martín , González‐Núñez Rubén , Rodrigue Denis 
Published: September 2009

AbstractSummary: A method to prepare starch acetate using acetic anhydride (AA) is presented. The process was carried out at temperatures below 100 °C using iodine (I) as a catalyst. The effect of reaction temperatures, as well as AA/starch and I/starch weight ratio was analyzed. The results show that high degrees of substitution can be reached by this method and the initial amount of acetic anhydride has a substantial effect on reaction efficiency. For a weight ratio of acetic anhydride to native starch (AA/AN) equal to two, a substitution degree of 3 was reached for 30 min and 70 °C.
Adsorption of Chitosan into SiO2 Monoliths Materials: Physical and Chemical Properties
Authors: Flores Norma I. Hinojosa , Ramírez Nelly Flores , Valencia Jaime Espino , García Salomón R. Vásquez , Bárcenas Gabriel Luna , García‐González Leandro 
Published: September 2009

AbstractThe dispersion of biopolymer chitosan on silica polymer matrix, prepared by the sol‐gel method under conditions of nearly linear chain growth, has allowed us obtain the beneficial properties of the large surface area of the dispersed SiO2 porous substrates. This study primarily aims to explore the chitosan adsorption in different weight ratios on silica monoliths by means solvent‐aided dispersion. The chitosan on SiO2 system has been investigated to know certain polymer properties, such as morphology, structure and thermal stability. The surface of the SiO2 monolith disks calcined (500 °C) employed as matrixes for chitosan were fractures free. SBET surfaces areas of these monoliths range from 452.99 m2/g. According to the FTIR analysis, the hydrogen bond there is an attractive intermolecular force between chitosan and SiO2. In contrast, the amino groups of the biopolymer are still accessible as active sites for heterogeneous catalysis. In addition, the thermostability of chitosan deposited on the monoliths was better than chitosan isolate.
Polymer Chain Collapse in Supercritical Fluids. 1. Molecular Simulation Results
Authors: Ortiz‐Estrada C. H. , Luna‐Bárcenas G. , Alvarado F. Javier , Gonzalez‐Alatorre G. , Sanchez I. C. , Castillo‐Tejas J. , Manero‐Brito O. , Ramírez N. Flores , García Salomón R. Vásquez 
Published: September 2009

AbstractA few years ago we reported the first observation, by computer simulations, of polymer chain collapse near the lower critical solution temperature (LCST).1 In the present work, we extended the above study to understand the underlying physics of a single polymer chain collapse near LCST and its relationship to phase boundaries in the T‐x plane. Effects of solvent and monomer sizes, and solvent and monomer energetic interactions are studied. Using Monte Carlo simulations, the mean end‐to‐end distance (R) and gyration radius (Rg) are calculated for a single chain in a supercritical fluid solvent over a broad range of densities, pressures and temperatures. In general, the chain collapses as temperature increases at constant pressure. Upon a further temperature increase, the chain expands again to approach the athermal limit provided that the temperature is sufficiently high. The collapse is related to an LCST phase boundary while the expansion represents the signature of an upper‐critical solution temperature (UCST) suggesting the existence of a closed‐immiscibility loop. By manipulating the strength of the energetic interactions as well as the solvent‐to‐monomer size ratio, the size of the size of the immiscibility loop can be fine‐tuned. The relationship among size and the segment‐solvent energetic interaction are correlated by a conformational parameter (Ψ) for the first time. By monitoring the Ψ behavior, it is possible to predict solution's phase behavior, transition zone from LCST‐UCST in a closed‐loop miscibility behavior. The above relationship between chain conformation to phase boundaries may be useful in understanding phase stability in compressible polymer‐solvent mixtures.
Shelf Stability of Isocyanate‐Functionalized Vinyl Acrylic Latexes
Authors: Treviño María E. , Ramírez Jorge C. , Saade Hened , López Raúl G. , Ríos Leonardo 
Published: September 2009

AbstractCopolymerization of vinyl acetate (VA) with butyl acrylate (BA) and dimethyl meta‐isopropenyl benzyl isocyanate (TMI) was carried out at 40 °C in emulsions stabilized with sodium dodecyl sulfate (SDS) or sodium dodecyl benzene sulfonate (SDBS). Regardless of the type of surfactant employed, latexes were very unstable during storage. Moreover, the hydrolysis of TMI and undesirable premature crosslinking of the polymeric chains did occur at room temperature during latexes storage.
Preparation and Characterization of Stable Aqueous Ferrofluids Using Low Molecular Weight Sulfonated Polystyrene
Authors: Ledezma Raquel , Bueno Darío , Ziolo Ronald F. 
Published: September 2009

AbstractSummary: One of the most optically transparent magnetic materials known at room temperature consists of nanocrystalline γ‐Fe2O3 dispersed in a DVB cross‐linked sulfonated polystyrene (PS) matrix. When attrited dry or in water without surfactant and subsequently processed in water or water miscible liquids, the nanocomposite leads to a highly stable, low optical density ferrofluid with unique properties and uses in a variety of applications. We have heretofore identified the stabilizing agent in the ferrofluid as low molecular weight (∼6000) sulfonated PS, which results from attrition of the cross linked polystyrene nanocomposite. We report on the synthesis of low molecular weight (LMW) PS by atom transfer radical polymerization (ATRP) followed by sulfonation with acetyl sulfate and on the one‐step synthesis of a stable ferrofluid of nanocrystalline Fe3O4 using the newly synthesized LMW sulfonated PS. Physicochemical analyses and characterizations include GPC, GC‐MS, GPC, NMR, FTIR, XRD, TEM and magnetic data.
Monovalent Salt Effects on the Membrane Activity of Antimicrobial Polymers
Authors: Som Abhigyan , Choi Yeon , Tew Gregory N. 
Published: September 2009

AbstractSynthetic mimics of antimicrobial peptides (SMAMPs) are known to disrupt cellular membranes in aqueous media. The impact of ionic strength, or the salt concentration, on membrane activity of these SMAMPs is an important issue since some AMPs are known to lose their activity at higher salt concentrations. In this report, the effect of salt concentration on membrane activity was evaluated using fluorescence dye leakage assays. Salt concentration did not affect the membrane activity of these SMAMPs significantly except for the 100% anionic vesicles (phosphatidylglycerol (PG) or phosphatidylserine (PS) only), where membrane activity decreased with increasing salt concentration. The results also indicated that the membrane activity of SMAMPs with monoamine side chains is independent on ionic strength against cardiolipin (CL) vesicles; however, SMAMPs containing bis‐ or tris‐ amines exhibited salt concentration dependent membrane activity for CL liposomes.
Recent Optical Applications of Perfluorocyclobutyl Aryl Ether Polymers
Authors: Mujkic Monika , Iacono Scott T. , Neilson Andrew R. , Smith Dennis W. 
Published: September 2009

AbstractSummary: Perfluorocyclobutyl (PFCB) aryl ether polymers have various applications in the field of optics due to their synthetic versatility and availability, solution and melt processability, high temperature and photo stability, excellent optical transparency. Nanoparticle matrix materials, encapsulants, and chemical sensors are just a few examples of recent developments.
Obtainment of Graded Index Preforms by Combined Frontal Co‐Polymerization of MMA and BzMA
Authors: Villegas Armando García , Ocampo Miguel A. , Luna‐Bárcenas Gabriel , Saldívar‐Guerra Enrique 
Published: September 2009

AbstractSummary. A simple system to obtain preforms with graded refraction index (GI) is presented. Index profiles with cylindrical symmetry are developed by introduction of a uniform rod of Poly Methylmethacrylate (65%)‐co‐Benzilmethacrylate (35%) (Poly‐(MMA‐co‐BzMA)) during mass copolymerization of an 80% MMA – 20% BzMA solution of the same monomers. The obtained preforms present a gradual variation of the refraction index with approximate radial symmetry. Dripping of the central bar produces moderate variations of the index profile along the preform axis, but a large enough fraction of the obtained preforms have potential to produce graded index (GI) polymer optical fibers (POF) by subsequent drawing and to obtain flat polymeric lenses by slicing.
Coarsening of PS/SAN Blends with Cocontinuous Morphology Studied with 3D Image Analysis
Authors: Lopez‐Barron Carlos R. , Macosko Christopher W. 
Published: September 2009

AbstractGeometrical parameters of the interface in fluorescently labeled polystyrene (FLPS)/styrene‐ran‐acrylonitrile compolymer (SAN) blends with cocontinuous morphology were obtained on the basis of differential geometry of 3D images. Images were analyzed for time evolution of interfacial area, average mean and Gaussian curvatures, curvature distributions and topology. Annealing of a symmetric (50/50 FLPS/SAN w/w) and a non symmetric (35/65) blend was monitored. For the symmetric blend a linear time evolution of the characteristic length along with a self similar growth of the microstructure, evidenced by the dynamic scaling of the curvature probability densities, were observed. For the non symmetric blend, the more elongated domains of the minor phase, namely FLPS, broke up producing zones with droplet‐matrix structures coexisting with cocontinuous domains. Due to this morphological transition, dynamic scaling failed for the non symmetric blends. The number of holes on the interface, described by the genus, in a fixed sample volume decreases with time due to the growth of the microstructures and the formation of droplets.
The Transient Flow of the PET‐PEN‐Montmorillonite Clay Nanocomposite
Authors: Calderas F. , Sanchez‐Solis A. , Maciel A. , Manero O. 
Published: September 2009

AbstractPolyethylene terephthalate (PET) and polyethylene 2, 6 naphthalene dicarboxylate (PEN) nanocomposites were prepared by an extrusion process with organic‐modified montmorillonite clay. The steady‐state viscosity of all blends diminished as compared to the system with no clay added. A rheological study was conducted to know more about the complex structure formed by the polymer matrix‐clay interactions. Instantaneous stress relaxation curves are presented for the PEN, PEN‐PET and PET‐PEN‐1phr clay systems. A Fourier Transform (FT) frequency response was obtained from the relaxation curves and compared to the linear oscillatory data, which lead to an extended frequency region. The results were modeled by a rheological equation of state which accounts for the formation‐destruction dynamics of the microstructure during flow. Relaxation time spectra are presented and compared for both rheological tests, namely, instantaneous stress relaxation and linear oscillatory flow. Additional studies using scanning electron microscopy (SEM) are presented, which reveal the presence of a slip layer in capillary flow for the system with added clay.