bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fühlen sich Chemielehrer gut genug ausgebildet?
Authors: Demuth Reinhard , Rumann Stefan , Brüchner Kirsten 
Published: July 2010

AbstractReinhard Demuth, Stefan Rumann, Kirsten BrüchnerErste Ergebnisse einer Befragung unter Berufsanfängern im Chemielehramt legen es nahe, die Curricula in der Erziehungswissenschaft und in Fachdidaktik zu überprüfen. Die besten Noten erhält die fachwissenschaftliche Ausbildung.
Neues von einem alten Bekannten
Authors: Zezschwitz Paultheo von 
Published: July 2010

AbstractPaultheo von ZezschwitzBereits vor 45 Jahren synthetisierten Elias J. Corey und Mitarbeiter das racemische â‐Caryophyllen.Nun gelang seiner Gruppe der enantioselektive Zugang über ein planar‐chirales Schlüsselintermediat. Jüngste In‐vivo‐Experimente zeigen, dass dieses Sesquiterpen als Cannabinoid wirkt und Entzündungen hemmt.
Dielectric relaxation of conductive carbon black reinforced chlorosulfonated polyethylene vulcanizates
Authors: Nanda Madhuri , Chaudhary R.N.P. , Tripathy D.K. 
Published: July 2010

AbstractThe frequency dependent dielectric relaxation behavior of conductive carbon black reinforced chlorosulfonated polyethylene (CSM) vulcanizates has been studied for different filler loadings in the frequency range of 102–106 Hz over a wide range of temperatures (30–120°C). The effects of filler loadings on the dielectric permittivity (ε′), dielectric loss tangent (tan δ), impedance, and electrical conductivity were studied. The variation of the dielectric permittivity with the filler loadings was explained on the basis of interfacial polarization of the filler in the polymer matrix. The frequency dependence of ac conductivity has been investigated using percolation theory. The effect of filler loading on the complex and real parts of impedance was clearly observed, which can be explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. The percolation threshold occurred near 30 phr of filler loading. Scanning electron microphotographs showed the agglomeration of the filler on and above these filler loadings. Additionally, the effect of temperature on dielectric loss tangent, dielectric permittivity, ac conductivity, and Nyquist plot of conductive black reinforced CSM vulcanizates has been studied. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Preparation of a novel heat stabilizer for poly(vinyl chloride)‐Zn, Mg, Al‐layered double hydroxide
Authors: Gu Zheng , Liu Weisheng , Dou Wei , Tang Fei 
Published: July 2010

AbstractA new zinc‐magnesium‐aluminum‐layered double hydroxide (ZnMgAl‐LDH) was prepared by one‐step coprecipitation using agents extracted from waste residue and intercalated with stearate anions. The X‐ray diffraction and Fourier transform infrared spectra show that the stearate anions have successfully intercalated into the interlayer of ZnMgAl‐LDH. The scanning electron microscopy shows the typical sand‐rose morphology of LDH. The enhanced thermal stability was confirmed by Congo red test. The poly(vinyl chloride) (PVC)/ZnMgAl‐LDH‐stearate nanocomposites have much more thermal stability time than PVC and PVC/ZnMgAl‐LDH composites. Thermal stability time of PVC containing 8 wt% ZnMgAl‐LDH‐stearate loading is 12 times of that of pure PVC. The tensile strength of the nanocomposites increases with the increase of ZnMgAl‐stearate content and exhibits excellent mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Crystallization behavior of poly(L‐lactic acid)‐based ecocomposites prepared with kenaf fiber and rice straw
Authors: Dobreva T. , Pereña J.M. , Pérez E. , Benavente R. , García M. 
Published: July 2010

AbstractSeveral composites of poly(L‐lactic acid) (PLLA) with natural fibers (kenaf and rice straw) and pigments have been prepared and analyzed. The study of the thermal behavior has shown a rather important nucleation ability of these fillers for the crystallization of the PLLA component in the composites. Thus, the cooling from the melt of pure PLLA at 10°C/min leads to an almost completely amorphous sample, while a high crystallinity (around 60%) is exhibited by the sample PLLA and rice straw (PLLA‐RS)‐yellow under those conditions. The analysis of the isothermal crystallization from the melt indicates that a maximum rate of crystallization is obtained for all the samples at around 105°C, although the rate is three times faster for samples PLLA and kenaf fiber (PLLA‐KF), PLLA‐KF‐red, and PLLA‐RS, in comparison with pure PLLA. The rate is increased by another factor of three for sample PLLA‐RS‐yellow. The analysis of the melting temperatures and crystallinities as a function of the crystallization temperature shows that there is a break at around 115°C, which seems to be related to the formation of ordered crystals at higher temperatures and disordered ones at lower temperatures. Besides, the natural fibers are environmentally friendly and nonexpensive materials, and the higher crystallization rates of the composites will result in shorter production cycles of end‐use articles. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers
Kinetics of methyl methacrylate polymerization initiated with n,n′‐bis[(4‐t‐butylazo‐4‐cyanovaleryl)‐oxyethyl]‐azo‐bis‐formamide
Authors: Simionescu Cristofor I. , Comǎniǎ Eugenia , Pǎstrǎvanu Mariana , Popa Aura Angelica 
Published: July 2010

AbstractThis paper deals with a kinetic study of methyl methacrylate polymerization in the presence of a bifunctional initiator, viz. N,N′‐bis[(4‐t‐butylazo‐4‐cyanovaleryl)The activation energy of the first step in thermal decomposition has been determined (Ed = 74.5 kJ/mol) using the gas chromatographic method. A dilatometric study led to the reaction order with respect to the initiator, as well as the overall activation energy of polymerization (E = 78.5 kJ/mol).
Chemistry of the modification of sulphur by the use of dicyclopentadiene and of styrene
Authors: Blight L. Bert , Currell Brian R. , Nash Brian J. , Scott R. Tony M. , Stillo Christopher 
Published: July 2010

AbstractDicyclopentadiene reacts with excess sulphur in the melt at 140°C to give initially cyclic tri‐ and pentathianes which then copolymerise with further sulphur to give initially chain polymers and then finally cross‐linked species, Styrene reacts under the same conditions to give rapid initial formation of relatively high molecular weight polymeric polysulphides which then depolymerise to give a mixture of short chain species and 2,4‐diphenylthiophene.
Solvent‐polymer interactions in the plasticisation of poly(ethylene terephthalate)
Authors: Ingamells Wilfred , Yanumet Nantaya 
Published: July 2010

AbstractThe effect of a range of chemically dissimilar solvents on the Tg of PET is dependent upon dispersion forces. A correlation is presented between the dispersion solubility parameters (δd) of the solvents and the reduction of the Tg which they cause. Two experimentally determed values for the (δd) of PET are presented as evidence to support the claim that aromatic and cyclic solvents solvate the aromatic part of the repeat unit and aliphatic solvents solvate the aliphatic part.
The Role of Crosslink Density in Influencing the Electrical Resistance Behaviour of Polymeric Coatings
Authors: Rais‐Ali Abdelhamid , Richardson Melvin O. W. 
Published: July 2010

AbstractPaint films used to protect metalic surfaces are commonly polymeric in nature. The extent of protection offered by film depends on many factors including the characteristic electrical resistance behaviou and its effect on impeding local electrochemical processes. In the present work a range of polymeric coatings have been produced with systematically varied crosslinked density using an ultra‐violet light curing technique. Their electrical resistance behaviour in an environment of varying concentrations of KC1 electrolyte has been examined. It is demonstrated that there are signs of the beginnings of a mechanism changeover from “D‐type” to “I‐type” behaviour at higher levels of crosslink density thus giving some tenuous support to previously unproven hypotheses in this area.
The Reaction of Naphthalene with Formaldehyde in the Presence of Sulphuric Acid
Authors: Robinson J. Gordon , Wardle David G. 
Published: July 2010

AbstractNaphthalene was reacted with various proportions of formaldehyde at different temperatures using sulphuric acid as the condensing agent. The products obtained in the early stages of the reaction consisted essentially of naphthalene units joined by ether and acetal bridges. However, as the reaction progressed the bridges lost oxygen, as water, to give methylene bridges while at the same time the softening points of the resins increased.
The Thermal Decomposition of Isocyanurates
Authors: Jiricny Josef , Reese Colin B. 
Published: July 2010

AbstractThe thermal decomposition of two isocyanurates and an MDI‐based polycarbodiimide was studied by high temperature infrared spectroscopy, thermogravimetric analysis and differential thermal analysis. The results (confirmed by large scale pyrolysis) show that the s‐triazine moiety decomposes above 400°C to generate free isocyanate groups. The latter may react further to give carbodiimides or ureas.
Hydrogels in Biomedical Applications
Authors: Pedley Derek G. , Skelly Peter J. , Tighe Brian J. 
Published: July 2010

AbstractThe nature of hydrogel polymers is described together with the range of biomedical applications in which their use has been suggested or described in the literature. The field of contact lens materials has provided the greatest variety of synthetic hydrogels and the material requirements for extended wear lenses present problems that are typical of those encountered in biomedical applications in general. The patient literature relating to contact lenses is reviewed and the development of the composition of hydrogel materials is thereby traced and compared with the range of lens materials currently available. In contrast the most commonly encountered, in fact almost the sole, hydrogel material in the literature relating to those areas more conventionally regarded as biomedical, is poly(2‐hydroxeythyl methacrylate) or polyHEMA. The use of this and related hydrogels in various applications including prostheses, ocular surgery, sature coatings, artificial internal organs and drug delivery systems is reviewed.
Effect of Polymer Molecular Weight on Colloidal Reinforcement
Authors: Kendall Kevin , Sherliker Frank R. 
Published: July 2010

AbstractThe tear strength of several thermoplastic polymers filled with colloidal silica has been determined as a function of polymer molecular weight. There were two regimes of behaviour. Low molecular weight materials were embrittled by a small amount, around 10% volume fraction, of filler. High molecular weight polymers, on the other hand, were not degraded at low filler concentrations, and some thermoplastics were actually reinforced, that is toughened, by the colloidal particles with a peak in crack resistance at 12% volume fraction. There was found to be a characteristic transition in toughness, similar to that observed with environmental stress cracking, between the low and high molecular weight regimes. It was concluded that a polymer molecular weight above the transition value was a necessary but not sufficient condition for colloidal reinforcement.
Modelling of Resole‐type Phenol Formaldehyde Polymerisation in Homogeneous, Continuous‐Flow, Stirred‐Tank Reactors
Authors: Pal Pralay K. , Kumar Anil , Gupta Santosh K. 
Published: July 2010

AbstractThe polymerisation kinetics of resoles has been modelled and numerical results obtained for an isothermal, homogeneous, continuous‐flow, stirred‐tank reactor. The different reactivities of the ortho and para hydrogens on the phenolic rings, both at the ‘ends’ of polymeric chains as well as at the shielded ‘internal’ locations, have been accounted for in the kinetic model and a sensitivity analysis has been carried out. The concentrations of phenol, formaldehyde, various sites, branch points and the number‐average chain length are obtained for various values of the rate constants, phenol to formaldehyde ratio in the feed stream and the average residence time in the reactor. It has been observed that the reactivity of the para‐hydrogen atom on an ‘end’ phenolic ring is the most important parameter.
On the Formation of a Low Viscosity State in Stiff Chain Polymers
Authors: Cogswell F. Neil 
Published: July 2010

AbstractFor a polymer to be capable of forming a nematic, liquid crystalline state the molecules must be nearly rigid and rod‐like. There are two main classifications of such liquid crystalline states: lyotropic ‐ generally applied to polymer solutions and implying the formation of a low viscosity state in a critical concentration range. and thermotropic ‐ usually applied to melts where the low viscosity mesophase appears over a limited temperature range.Lytropic —generally applied to polymer solutions and implying the formation of a low viscosity state in a critical concentration range. and thermotropic — usually applied to melts where the low viscosity mesophase appears over a limited temperature range.For polymers we further find that attaining this low viscosity state depends critically on the previous thermomechanical history of the mesophase and that, by appropriate thermo‐mechanical history, it is possible to induce a low viscosity state under conditions where such is not spontaneously formed. This extension of the liquid crystal state may also include polymers whose molecular flexibility is such that they do not naturally form liquid crystals.
Synthesis of Poly(p‐Benzenesulphonamide) Part II Solid State Polymerisation of Aniline‐4‐Sulphochloride via a Sulphene intermediate
Authors: Contreras Jordi , Jones J. Idris 
Published: July 2010

AbstractOn heating, aniline‐4‐sulphochloride undergoes a two‐stage solid state polymerisation with initial formation of an intermediate product, identical in composition with that of the starting material, which, at a higher temperature, eliminates hydrogen chloride to yield poly(p‐benzenesulphonamide). The intermediate product has been identified as 4‐imino‐cyclohexadiene sulphene hydrochloride and results from a rearrangement reaction of aniline‐4‐sulphochloride. On treatment with dry pyridine, this intermediate undergoes dehydrochlorination to yield transiently the monomeric sulphene, 4‐imino‐cylcohexadiene sulphene, which then polymerises to poly (p‐benzene sulphonamide). This reaction has been followed spectroscopically in an ultra‐violet cell.When a sample of aniline‐4‐sulphochloride was heated to 200°C in a sealed tube an acid catalysed rearrangement of the polysulphonamide occurred to give some units of p‐amino‐p‐phenylene sulphone in the polymer chain.Solid state polymerisation of aniline‐4‐sulphochloride hydrochloride also occurs on heating to 175°C under reduced pressure, with evolution of hydrogen chloride, but without the formation of an intermediate product. Here again, in a closed system, some acid catalysed rearrangemnt of the polymer was observed. N‐Methylaniline‐4‐sulphochloride hydrochloride similarly undergoes a solid state thermal polymerisation with evolution of hydrogen chloride to yield poly (p‐benzene‐N‐methyl‐sulphonamide).Considerable interest is attached to the discovery of the stable crystalline 4‐imino‐cyclohexadiene sulphene hydrochloride intermediate and the generation therefrom of the parent sulphene which serves as monomer in the polymerisation. The stability and reactivity of sulphenes generally are discussed.
Ultra‐drawing of High Molecular Weight Polyethylene
Authors: Lemstra Piet J. , Smith Paul 
Published: July 2010

AbstractThe effective drawability of solution‐cast or ‐spun high molecular weight polyethylene is enhanced significantly in comparison with an identical polymer sample that is crystallised from the melt.The maximum attainable draw ratio, which primarily determines the final mechanical properties, increases continuously with decreasing initial polymer concentration in solution. A tensile strength of 3.2 GPa and an axial Young's modulus of 120 GPa could be obtained by drawing high molecular weight polyethylene cast from a 1% polymer solution. This phenomenon of increased drawability is discussed in terms of a reduced number of entanglements per macromolecule in solution‐cast polyethylene.
The Quasi Ternary Eutectic System Polyethylene/Hexamethylbenzene/Adamantane
Authors: Smith Paul , Koningsveld Ronald , Schouteten Chretien J. H. , Pennings Albert J. 
Published: July 2010

AbstractThis paper describes the crystallisation and melting behaviour of the quasi ternary system composed of heterodisperse polyethylene, and the diluents hexamethylbenzene and adamantane. The simplified theory of melting point depression according to Flory and Huggins predicts a ternary eutectic point for this system, which was verified experimentally by differential scanning calorimetry. Morphological investigations revealed a complex rod‐like eutectic microstructure with characteristic dimensions in the micron range1.
Synthesis of di‐ and tri‐tertiary amine containing methacrylic monomers and their (co)polymerization via RAFT
Authors: Yu Bing , Lowe Andrew B. 
Published: July 2010

AbstractThe synthesis, reversible addition‐fragmentation chain transfer (RAFT) (co)polymerization, and aqueous phase behavior of three methacrylic monomers containing two or three pendent tertiary amine functional groups are described. Homopolymerizations were conducted with 1‐methyl‐1‐cyanoethyl dithiobenzoate (CPDB) under bulk conditions following standard RAFT procedures. All three monomers, 1,3‐bis(dimethylamino)propan‐2‐yl methacrylate (M1), 1‐(bis(3‐(dimethylamino)propyl) amino)propan‐2‐yl methacrylate (M2), and 2‐((2‐(2‐(dimethylamino)ethoxy)ethyl) methylamino)ethyl acrylate (M3), polymerized in a controlled manner as evidenced by the kinetic and molecular weight profiles. Homopolymerizations conducted at a lower ratio of CPDB:AIBN proceeded faster than those at a higher ratio. Subsequently, the facile copolymerization behavior of M1 and M3 was demonstrated via the synthesis of a range of statistical copolymers with hexyl and lauryl methacrylate comonomers containing 10–90 mol % hydrophobic comonomer. Finally, the aqueous‐solution characteristics of the M1–M3 homopolymers were briefly examined. All three homopolymers were shown to undergo phase transitions in aqueous media in response to changes in both temperature and pH. Specifically, 1 wt % solutions of polyM1 were shown to possess an LCST of ∼22 °C, that of polyM2 at ∼33 °C, and for polyM3 the observed cloud point was ∼63 °C. Additionally, all homopolymers became hydrophobic and phase separated at high solution pH. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1877–1890, 2009
End‐functionalization of semiconducting species with dendronized terpyridine–Ru(II)–terpyridine complexes
Authors: Pefkianakis Elefterios K. , Tzanetos Nikolaos P. , Chochos Christos L. , Andreopoulou Aikaterini K. , Kallitsis Joannis K. 
Published: July 2010

AbstractSemiconducting oligomers and polymers decorated with two or one dendronized tpy‐Ru(II)‐tpy metallocomplexes are presented. Initially, free terpyridine end‐functionalized semiconducting oligomers (distyrylanthracene, quinquephenylene, mono‐ and trifluorenes) were prepared while in a second approach, atom transfer radical polymerization was employed for the preparation of side‐chain oligomeric and polymeric (oxadiazole)s using a terpyridine initiator. These terpyridine‐bearing oligomers and polymers were complexated with a Percec‐type first‐generation (G1) dendronized terpyridine–Ru(III)Cl3 monocomplex, having two dodecyloxy groups. All oligomeric and polymeric metallocomplexes were characterized via NMR spectroscopies for their structural perfection and via UV‐Vis and PL spectroscopies for their optical properties. The existence of the organic semiconducting blocks in combination with the terpyridine–Ru(II)–terpyridine groups afforded hybrid metallo‐semiconducting species presenting the optical features of both their components. Moreover, their thin‐film morphologies were investigated through atomic force microscopy, revealing, in some cases, an organization tendency in the nanometer scale. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1939–1952, 2009
Molecular design, synthesis, and properties of Y‐type nonlinear optical polyester containing tricyanovinylthiophene with enhanced thermal stability of second harmonic generation
Authors: Lee Ga‐Young , Kim Jin‐Hyang , No Hyo Jin , Lee Ju‐Yeon , Rhee Bum Ku , Choi Hee‐dok 
Published: July 2010

Abstract1‐{3,4‐Di‐(2‐hydroxyethoxy)phenyl}‐2‐(2‐thiophenyl)ethene (5) was prepared and condensed with terephthaloyl chloride to yield polyester (6). Polymer 6 was reacted with tetracyanoethylene to give a new Y‐type polyester (7) containing 1‐(3,4‐dioxyethoxy)phenyl‐2‐{5‐(2,2,3‐tricyanovinyl)‐2‐thiophenyl)}ethenyl groups as NLO‐chromophores, which are components of the polymer backbones. Polyester 7 is soluble in common organic solvents such as N,N‐dimethylformamide and acetone. Polymer 7 showed a thermal stability up to 300 °C in thermogravimetric analysis with glass transition temperature (Tg) obtained from differential scanning calorimetry near 126 °C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at the 1560 nm fundamental wavelength was around 6.57 × 10−9 esu. The dipole alignment exhibited high thermal stability up to the Tg, and there was no SHG decay below 125 °C due to the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1911–1919, 2009
Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents
Authors: Lin Wentian , Niu Hui , Chung T. C. Mike , Dong Jin‐Yong 
Published: July 2010

AbstractThis article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl‐B‐9‐borabicyclononane (Me‐B‐9‐BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]‐catalyzed ethylene (Cp2ZrCl2 and rac‐Me2Si(2‐Me‐4‐Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found—in most cases—able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)‐terminated PE and s‐PS polymers after an oxidative workup process, suggesting the formation of the B‐polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac‐Me2Si(2‐Me‐4‐Ph)2ZrCl2. Both TEB and Me‐B‐9‐BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO‐catalyzed ethylene polymerization; nevertheless, Me‐B‐9‐BBN failed in vain with rac‐Me2Si(2‐Me‐4‐Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as BH‐bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane‐terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534–3541, 2010