bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surviving Radicals: Promises of a Microwave Effect on Miniemulsion Polymerization for Technical Processes
Authors: Holtze Christian , Tauer Klaus 
Published: February 2007

AbstractRapid heating in a microwave oven has unexpected effects on free radical miniemulsion polymerization: After a temperature pulse of less than 20 s, ultra‐high molecular weight polystyrene was yielded at a conversion larger than 40%. These results may be explained with the model of “surviving radicals” according to which single radicals remain active inside the confined reaction space of latex particles even after the emulsion has left the microwave oven. In the pure environment of a 100 nm droplet, they cannot terminate and will polymerize all the monomer within a droplet. In this contribution, we summarize the concept of “surviving radical polymerization” and present recent results on the effects of radical‐active additives and the development of a tube reactor for continuous microwave‐assisted processing. These investigations highlight the potential of this method for industrial applications.magnified image
Synthesis of Polytriarylamines via Microwave‐Assisted Palladium‐Catalysed Amination
Authors: Shen I‐Wen , McCairn Mark C. , Morrison John J. , Turner Michael L. 
Published: February 2007

AbstractA new synthetic route to polytriarylamines by microwave‐assisted palladium‐catalysed amination between 2,4‐dimethylaniline and 4,4′‐dibromobiphenyl is reported. The use of microwave heating significantly reduces the polymerisation time from days to around five minutes when conducted at 100 °C. However, prolonged microwave irradiation (20 min) can cause chain degradation of these polymers. Reactive amino and bromo end‐groups can be removed by sequential reaction with 4‐bromoanisole and diethylamine to generate polytriarylamines that are suitable for the fabrication of organic electronic devices.magnified image
Microwave‐Assisted Polymer Synthesis: Recent Developments in a Rapidly Expanding Field of Research
Authors: Hoogenboom Richard , Schubert Ulrich S. 
Published: February 2007

AbstractThe use of microwave irradiation has become a common heat source in organic chemistry. Inspired by this enormous success, the use of microwave irradiation is also increasingly studied for polymerization reactions. The present review discusses developments in this rapidly growing field of research. The main areas in which the use of microwave irradiation has been explored in the recent years are step‐growth polymerizations, ring‐opening polymerizations as well as radical polymerizations. These different areas will be addressed in detail, whereby special attention will be given to observed improvements resulting from the use of microwave irradiation as well as the occurrence of non‐thermal effects.magnified image
Microwave‐Assisted Preparation of Semiconducting Polymers
Authors: Galbrecht Frank , Bünnagel Torsten W. , Scherf Ullrich , Farrell Tony 
Published: February 2007

AbstractPolymeric semiconducting materials are being utilized as components in a new generation of electronic devices. The generation of high quality polymeric semiconductors often involves transition metal‐catalyzed cross‐coupling reactions, which require long reaction times. Microwave heating can be very efficient in reducing reaction times and consequently leads to increased reaction yields and concomitantly reduces the amount of side products. This microreview aims to summarize the use of microwave heating to prepare conjugated polymers, which are specifically tailored towards applications in optoelectronic and electronic devices. Moreover, microwave heating is a valuable investigative tool for the screening towards novel materials, especially when optimizing the backbone arrangement of unsaturated building blocks.magnified image
Single‐Mode Microwave‐Assisted Atom Transfer Radical Polymerization Catalyzed by [RuCl2(p‐cymene)(PCy3)]
Authors: Delfosse Sébastien , Borguet Yannick , Delaude Lionel , Demonceau Albert 
Published: February 2007

AbstractIn the atom transfer radical polymerization (ATRP) of methyl methacrylate in the presence of [RuCl2(p‐cymene)(PCy3)] (p‐cymene = 4‐isopropyltoluene, PCy3 = tricyclohexylphosphine), a microwave effect is noted which strikingly depends on both the temperature and the method used (conventional microwave synthesis (CMS, i.e., without simultaneous cooling) or enhanced microwave synthesis (EMS, with simultaneous cooling)). Thus, between 85 and 120 °C under CMS conditions, microwave‐assisted polymerizations take place in a controlled fashion, and at 120 °C the microwave‐assisted polymerization is three times faster than the conventionally heated protocol. However, from 130 °C, microwave irradiation has a deleterious effect and the polymerizations are no longer controlled. Likewise, using the EMS method in the temperature range of 85–120 °C results in uncontrolled processes, as indicated by the unsuccessful resumption of the polymerizations. These failures might be attributed to a significantly high concentration of radical species, which results in enhanced propagation and termination ‐ mostly disproportionation ‐ rates.magnified image
Microwave‐Assisted Free Radical Copolymerizations of Styrene and Methyl Methacrylate
Authors: Stange Heiner , Greiner Andreas 
Published: February 2007

AbstractFree radical copolymerizations of styrene and MMA were performed in toluene and DMF as solvents using different peroxide initiators with and without microwave irradiation. A general trend showed significant solvent dependence of monomer conversion rate only for copolymerizations initiated by tert‐butyl perbenzoate in DMF compared to toluene but nearly no impact for copolymerizations initiated by dicumyl peroxide and dibenzoyl peroxide. Significant variations in copolymer composition were not observed for reactions under conventional heating compared to microwave irradiation. It was concluded that enhanced initiator decomposition under microwave irradiation in DMF accelerate polymerization of styrene and MMA by formation of larger amount of initiator radicals.magnified image
The Thermoviscoelastic Constitutive Equation of PP and PA Blends and Its Rate Temperature Equivalency at High Strain Rates
Authors: Shaoqiu Shi , Bing Yu , Lili Wang 
Published: February 2007

AbstractBy using Instron 1342 testing system and an improved SHPB technique, PP/PA blends are tested at a wide range of strain rates from 10−4 up to 103 s−1 and at a temperature range of 25–80 °C. Their mechanical responses are shown to be sensitive both to the strain rate and temperature. Based on the experimental data of 113 blends at a wide range of strain rates from 10−4 up to 103 s−1 and at a temperature range of 25–80 °C, it is shown that the mechanical behavior of this PP/PA blends can be described with ZWT thermoviscoelastic constitutive equation. The corresponding thermoviscoelastic parameters for 113 blends are obtained. The predicted theoretical results coincide quite well with the experimental data.The experimental results also reveal that the rate/time‐temperature equivalence relation is shown for PP/PA blends. Raising the temperature is equivalent to the increasing of time (the decreasing of strain rate). Conversely, decreasing the temperature is equivalent to the decreasing of time (the increasing of strain rate). Through introducing a dimensionless parameter $Z = {{\dot \varepsilon \eta _0 } \over E}\exp \left( {{A \over {kT}}} \right)$, two characteristic parameters: strain rate $\dot \varepsilon$ and temperature T are put together to this unified parameter Z. From experimental results, A/k is fitted, A/k = 8.595 °C, and a unified curve characterizing the rate/time –temperature equivalence relation is obtained.
Effect of Molecular Weight on Enthalpy Relaxation in Syndiotactic Poly(Methyl‐Methacrylate)
Authors: Sciucca Stefania Della , Penco Maurizio , Sartore Luciana 
Published: February 2007

AbstractThe structural relaxation behaviour of narrow fractions (Mw/Mn < 1.1) of syndiotactic poly(methyl methacrylate) with molecular masses ranging from 2,000 to 200,000 Daltons have been studied by DSC with two classical procedures, namely: the rate of cooling and the isothermal approaches. The apparent activation energy (Δh*) of enthalpy relaxation was evaluated from the dependence of the glass transition temperature on the cooling rate while a comparison of the apparent relaxation rates was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (Ta = Tg − 10 °C). As expected, the increase of molecular weights gives rise to both a continuous increase of Δh* and a decrease of the apparent isothermal relaxation rate. More interestingly, both Δh* and the apparent isothermal relaxation rate showed abrupt changes around the syndiotactic PMMA entanglement mass (Me
).
Synthesis and Characterization of Conductive Polypyrrole/Montmorillonite Nanocomposites via One‐pot Emulsion Polymerization
Authors: Peighambardoust S. J. , Pourabbas Behzad 
Published: February 2007

AbstractA series of electrically conductive polypyrrole/clay nanocomposites were synthesized in this work by using one‐pot emulsion oxidative polymerization of pyrrole in the presence of unmodified clay and using DBSNa as the surfactant. The effect of surfactant on the morphological and electrical properties of PPy also were investigated and discussed in some extent. Electrical conductivity of the samples was measured by using samples in which the conductive materials was sandwiched between two Ni electrodes at room temperature. PPy/MMT nanocomposites were characterized by using XRD, TEM, TGA and DSC means of investigation. Intercalated structures were determined for the nanocomposites as confirmed by XRD and TEM studies. Electrical conductivity of the nanocomposites was measured to be dependent to the clay content, and the methods of preparation. Measurement also showed that polymerization of pyrrole monomers pre‐intercalated between the clay gallery spaces of the clay led to higher conductivity for the nanocomposite in the same level of clay content. Thermal property measurements showed a lower thermal decomposition rate for the PPy/MMT nanocomposites with respect to the PPy.
Study on the Effect of Uniaxial Elongational Flow on Polyamide Based Nanocomposites
Authors: Garofalo Emilia , Russo Giovanna Maria , Di Maio Luciano , Incarnato Loredana 
Published: February 2007

AbstractThis work focuses on the study of uniaxial elongational flow and its effects on morphology and stiffness of polyamide‐6 based nanocomposites prepared by melt compounding. The elongational flow characterization was realized by converging flow method and fiber spinning technique. During the haul‐off tests, fibers of the neat polyamide‐6 and the hybrids (at 3 and 6 wt% of silicate) were collected at different draw ratios. Mechanical properties of the produced fibers were investigated and correlated to their nanostructure through analytical techniques sensitive to different aspects of morphology, such as DSC and TEM analysis. Rheological results, obtained with a capillary rheometer, indicate that the shear viscosity decreases with the silicate loading, while the extentional viscosity increases. Moreover, the presence of the silicate in polymer matrix leads to enhancements of draw‐down force and reduction of the breaking draw ratio. In hybrid fibers an enhanced degree of exfoliation of the filler was observed upon drawing. Moreover, DSC analyses suggest that the crystalline structure of the fibers is the result of two opposite effects: the presence of the silicate which stabilizes the γ form and the drawing which promotes the α crystal phase. The degree of silicate exfoliation and the amount of the different crystal phases strongly affect the tensile properties of the fibers.
PMMA Based Nanocomposites Filled with Modified CaCO3 Nanoparticles
Authors: Avella Maurizio , Errico Maria Emanuela , Gentile Gennaro 
Published: February 2007

AbstractPMMA based nanocomposites filled with calcium carbonate nanoparticles (CaCO3) have been prepared by in situ polymerization approach. In order to improve inorganic nanofillers/polymer compatibility, PBA chains have been grafted onto CaCO3 nanoparticle surface. Morphological analysis performed on nanocomposite fractured surfaces has revealed that the CaCO3 modification induces homogeneous and fine dispersion of nanoparticles into PMMA as well as strong interfacial adhesion between the two phases. Mechanical tests have shown that both unmodified and modified CaCO3 are responsible for an increase of the Young's Modulus, whereas only PBA‐grafted nanoparticles allow to keep unchanged impact strength, strongly deteriorated by adding unmodified CaCO3. Finally, the presence of CaCO3 nanoparticles significantly improves the abrasion resistance of PMMA also modifying its wear mechanism.
Thermal Properties of E‐beam Cured Epoxy/Thermoplastic Matrices for Advanced Composite Materials
Authors: Alessi S. , Dispenza C. , Spadaro G. 
Published: February 2007

AbstractThe aim of this work is to investigate the possibility to improve the thermal behaviour of epoxy based systems, cured by ionizing radiation, in order to produce matrices for advanced carbon fibres composites. Blends of two epoxy monomers, difunctional and trifunctional, have been polymerized by e‐beam irradiation and the dynamic mechanical thermal properties have been investigated. The increase of the concentration of the trifunctional epoxy monomer in the blend causes a marked increase of the Tg, but strongly decreases the reactivity. Subsequently, blends of the same epoxy monomers with a high Tg thermoplastic toughening agent have been considered and their reactivity and the thermal properties of the obtained materials have been also studied. The experimental results show that the thermoplastic component increases the reactivity of the difunctional/trifunctional blends, without a significant decrease of the glass transition temperature which still satisfies the requirements for advanced composite materials.
Mechanical and Thermal Analysis of Composites Based on Rubbers From Used Tires
Authors: Acierno Domenico , Ciccarelli Ireneo , Romano Vittorio , Russo Pietro 
Published: February 2007

AbstractSummary: Reuse and recycling of tires at the end of their useful life is an environmental challenge owing to the huge volumes discarded all over the world. This paper tries to give a scientific contribution toward the mechanical recycling of elastomers derived from pre treatment of tires to produce anti‐shock tiles and heat‐insulating panels for civil applications. Thermal and mechanical results herein reported satisfactorily justify the interest devoted by now to this topic.
Deposition of Super‐Hydrophobic and Oleophobic Fluorocarbon Films in Radio Frequency Glow Discharges
Authors: Laguardia L. , Ricci D. , Vassallo E. , Cremona A. , Mesto E. , Grezzi F. , Dellera F. 
Published: February 2007

AbstractFluorocarbon films using a monomer, 1H, 1H, 2H‐perfluoro–1‐dodecene were deposited in a continuous radio frequency (RF) glow discharge, the process was carried out in a parallel‐plate RF discharge onto stainless steel reactor in order to produce coating with a water‐and oil–repellent surface. Fourier‐Transform Infrared spectroscopy (FT‐IR) and X‐ray Photoelectron Spectroscopy (XPS) revealed that the films obtained contain mainly perfluoromethylene (CF2) species. Film wettability was tested using water and hydrocarbon liquids for contact angle measurements, furthermore surface energy was also calculated. Oil‐repellency was found to increase as the amount of CF2 species increases in the film structure. Film morphology was studied by Atomic Force Microscopy (AFM), films showing an usual morphology from that typical of Plasma Polymerised Fluorocarbon (PPFC) films. The combination of the low surface energy coating and the surface morphology produces materials which are both water and oil repellency.
Methylsiloxane Oligomers with Oxyalkyl Fragments in the Side Chain
Authors: Mukbaniani O. , Zaikov G. , Tatrishvili T. , Titvinidze G. , Mukbaniani N. 
Published: February 2007

AbstractThe dehydrocondensation reactions of α,ω–bis(trimethylsiloxy)methylhydridesiloxane with saturated primary n‐alcohols in the presence of anhydrous powder‐like potassium hydroxide or platinum on the carbon (Pt/C‐5%) at 1:30 ratio of initial compounds, at various temperature (40–60 °C) was carried out, and methylsiloxane oligomers with n‐alkyloxy substituted groups in the side chain were obtained. It was shown that completely dehydrocondensation of all active SiH groups do not take place. Dehydrocondensation reaction order, activation energy and rate constants were found. The synthesized oligomers were characterized by 1H, 13C NMR, Cosy and FTIR spectra data. Gel‐permeation chromatography, differential scanning calorimetric, thermogravimetric and wide‐angle X‐ray investigations of synthesized oligomers were carried out.
Molecular analysis of mutations induced in human cells by N‐ethyl‐N‐nitrosourea
Authors: Eckert Kristin A. , Ingle Caroline A. , Klinedinst Donna K. , Drinkwater Norman R. 
Published: February 2007

AbstractMutational activation of cellular proto‐oncogenes is an important event in the pathogenesis of chemically induced tumors. We have used the on P‐tk shuttle vector, pHET, to analyze the types of DNA sequence changes induced after treating mammalian cells with the carcinogen N‐ethyl‐N‐nitrosourea (ENU). This shuttle vector contains the putative replication origin of the Epstein‐Barr virus (EBV) and is stably maintained as a plasmid in EBV‐transformed human lymphoblastoid cells. Populations of plasmid‐bearing cells were treated with ENU, and plasmid DNA was isolated approximately 7–8 population doublings after treatment for analysis of mutations induced at the herpes simplex virus type 1 thymidine kinase (HSV‐tk) target gene. After ENU treatment, frequencies of four of the six possible base substitution mutations significantly increased. Transition mutations were the most common sequence change: 48% of the 46 mutants sequenced were GC→Ã transitions and 17% were AT→GC transitions. In addition, the number of AT→TA (20%) and AT→CG (9%) transversion mutations significantly increased after ENU treatment. Based on the comparison of mutations induced by ENU in human cells with the types of base pair changes previously reported for other alkylating agents, we propose that the O2‐ethylthymine adduct may be a significant premutagenic lesion in mammalian cells, capable of resulting in AT base pair transversion mutations. Studies from other laboratories have demonstrated the importance of AT→TA transversion mutations in the activation of cellular proto‐oncogenes by ENU.
Phenobarbital specifically reduces gap junction protein mRNA level in rat liver
Authors: Mesnil Marc , Fitzgerald D. James , Yamasaki Hiroshi 
Published: February 2007

AbstractThe gene expression of liver major gap junction (GJ) protein was studied in rats systemically administered phenobarbital, a rat liver tumor promoter. Using a GJ protein cDNA and northern blot analysis, the level of GJ protein mRNA in liver was observed to be markedly reduced at 4 and 11 wk of phenobarbital exposure (0.1% in drinking water). However, the level of GJ protein mRNA was not altered in kidney at 11 wk of exposure. In liver, phenobarbital did not induce expression of the neoplasm‐associated marker genes glutathione S‐transferase (placental form) and γ‐glutamyltranspeptidase, while in kidney the observed expression of these genes was not changed. These in vivo results indicate that phenobarbital reduces GJ protein gene expression specifically in rat liver without altering expression of genes often altered during liver carcinogenesis, and they support assigning a role for the impairment of gap junctional intercellular communication in phenobarbital‐mediated liver tumor promotion.
Activated Ki‐ras genes in bladder epithelial cell lines transformed by treatment of primary mouse bladder explant cultures with 7,12‐dimethylbenz[a]anthracene
Authors: Brookes Peter , Cooper Colin S. , Ellis Moira V. , Warren William , Gardner Emily , Summerhayes Ian C. 
Published: February 2007

AbstractDNA from five lines of transformed bladder epithelial cells derived from cultures of primary cells that had been treated with 7,12‐dimethylbenz[a]anthracene (DMBA) can transform NIH 3T3 mouse fibroblasts in DNA transfection experiments. Southern analysis of DNA from NIH 3T3 primary and secondary transformants established that four of the DMBA‐transformed cell lines contained activated cellular Ki‐ras, while the remaining cell line contained a transforming gene that is unrelated to Ki‐ras, N‐ras, and Ha‐ras. The point mutations responsible for Ki‐ras activation were detected using oligonucleotide probes following selective amplification of Ki‐ras specific sequences using the polymerase chain reaction. The results showed that activation of Ki‐ras invariably involved a GC → AT transition mutation of the first position of codon 12. Surprisingly, a Ki‐ras gene that was activated by a GC → AT transition mutation at the same position was also detected in a single transformed bladder urothelial cell line derived from control cultures of mouse bladder cells. Together, our results indicate that Ki‐ras activation in the DMBA‐transformed bladder cell lines may not be a direct consequence of interaction of activated DMBA metabolites with the Ki‐ras gene.
Modified responsiveness of v‐Ha‐ras‐transfected rat fibroblasts to growth factors and a tumor promoter
Authors: Huang Ming , Kamata Nobuyuki , Nose Kiyoshi , Kuroki Toshio 
Published: February 2007

AbstractThe correlation of the phenotypic changes of v‐Ha‐ras transfected cells with the expression of p21ras and the modified responses to growth factors and a tumor promoter were examined. Transfection of the v‐Ha‐ras gene together with the neomycin‐resistance gene into 208F rat fibroblasts yielded transformed clones characterized by morphological changes, anchorage‐independent growth, and tumorigenicity in nude mice. The degrees of these biological alterations were parallel with the expression of mRNA and protein of the ras gene. In rastransformed cells, anchorage‐independent growth was stimulated by epidermal growth factor (EGF), insulin, bombesin, and fibroblast growth factor, whereas in the parental 208F cells, anchorage‐independent growth was observed only in the presence of EGF, and there were many fewer EGF‐induced colonies than those in the ras‐transformed clones. A tumor promoter, 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) also augmented anchorage‐independent growth of ras‐transformed cells and induced morphological changes in monolayer cultures without altering the expression of the ras gene or phosphorylation of the p21ras protein. Retinoic acid inhibited the TPA‐induced anchorage‐independent growth. These results showed a good correlation of the expression of p21ras with the phenotypic changes and the increased sensitivity of the p21ras‐expressing cells to the stimulation of growth factors and tumor promoter.