bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR characterization of biodegradable polyesters
Authors: Chûjô Riichirô 
Published: March 2011

AbstractBiodegradable polyesters obtained by fermentation of Alcaligenes eutrophus are characterized with the aid of H, D, C NMR spectroscopy. Copolymers of 3‐hydroxybutyrate and 3‐hydroxyvalerate are Bernoullian or mixture of two Bernoullian copolymers depending on fermentation conditions. The reverse reaction was found in the reaction catalyzed by beta‐ketothiolase during biosynthetic pathway. The fractional population of gauche and trans conformers around the skeletal CH‐CH2 bond is 0.6:0.4 for both poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) in chloroform. This result suggests the possibility of formation of isomorphic crystals between copolymers with different composition ratios.
Chain segment ordering in uniaxially strained networks: A deuterium NMR investigation
Authors: Deloche Bertrand 
Published: March 2011

AbstractThe deuterium NMR (2H‐NMR) is used for probing the chain segment orientation in polymer networks under uniaxial stress. The method is based on the observation of an incomplete time averaging of quadrupolar interactions affixed to deuterated segments. The samples are end‐linked polydimethylsiloxane networks. The 2H‐NMR experiments are performed either on labelled network chains or an labelled probe polymer chains dissolved in the network. The basic results are the following:— The induced uniaxial order is related to a uniaxial dynamics of chain segments around the direction of the applied constraint.— A permanent orientation is observed on free polymer chains dissolved in the deformed networks.— The mean degrees of orientational order induced along short and long chains in bimodal networks are the same.These experimental facts appear as evidences for cooperative orientational couplings between chain segments in the deformed networks.
ESR studies on polymers with particular electronic and magnetic properties
Authors: Roth Hans‐Klaus , Krinichnyi Viktor I. 
Published: March 2011

AbstractMeasurements on insulating and conducting polymers from the polyaniline (PANI) family and investigations on semiconducting poly(tetrathiafulvalenes) (PTTF) have been used for illustration and discussion of some methodical questions of electron spin resonance (ESR). This concerns especially the new possibilities of the recently developed high‐resolution ESR in the 2 mm wave band. It was applied for the study of the nature and dynamics of paramagnetic centres (PC) and charge carriers in PANI and PTTF. The rate of the quasi‐one‐dimensional (1D) intrachain electron motion and of the three‐dimensional (3D) interchain electron hopping has been estimated separately. In iodine ‐ doped PTTF the maximum electrical conductivity is 10−4 S ·cm−1. It is almost identical with the 3D‐conductivity estimated by ESR and shows the typical temperature dependence of a semiconductor. The quasi‐1D‐conductivity is several orders of magnitude higher and shows in its dependence on temperature similarities with a metal. The PANI samples show in the highly doped form a maximum conductivity of about 10 S ·cm−1 and relativly small differences between the 1D‐ and 3D‐conductivity, supporting the model of metallic islands.
Synthesis of polysiloxanes with electron‐donating groups by anionic ring‐opening polymerization
Authors: Chojnowski Julian , Rózga Krystyna , Fortuniak Witold , Kowalewska Anna 
Published: March 2011

AbstractAnionic kinetically controlled ring opening polymerization of cyclotrisiloxane is explored as a method of synthesis of copolymers having the chain composed of dimethylsiloxane units and siloxane units bearing an uncharged nucleophilic (electron‐donating, ED) group. Model monomers for these studies are derived from hexamethylcyclotrisiloxane (D3) in which one methyl group is replaced by the organophosphorus group of general formula ‐ (CH2) nP(X)Ph2 where X is lone pair, O or S. This method is shown to give significant advantages over the thermodynamically controlled homopolymerization and copolymerization of nucleophile‐substituted cyclosiloxanes which have so far been used for synthesis of ED substituted siloxane copolymers. The yield of the copolymers is much higher and the molecular weight distribution is narrow. The arrangement of the ED substituents along the chain, although not purely uniform, is much more regular as compared with the statistical distribution. The content of cyclic oligomers was higher than in the polymerization of unsubstituted D3, which is rationalized on the basis of intramolecular interaction of the counter‐ion with the ED groups.
Possibilities offered by plasma modification and polymerization to enhance the bio‐ and hemocompatibility of polyester membranes
Authors: Schué F. , Clarotti G. , Sledz J. , Mas A. , Geckeler K.E. , Göpel W. , Orsetti A. 
Published: March 2011

AbstractThe deposition of films from an argon plasma containing a mixture of ethylene oxide or hydrogen and perfluorohexane was tried to obtain very hydrophobic, less hydrophobic and intermediate coatings. This paper studies more extensively the deposition of a thin coating from a perfluorohexane and hydrogen plasma on polysulfone and polyhydroxybutyrate membranes to optimize their surface properties without affecting their filtering properties. The plasma deposition of smooth and very hydrophobic fluorocarbon coatings seems to increase the bio‐ and hemocompatibility of poorly biocompatible membranes. The treated substrates were characterized by measuring the mass variations, surface profilometry and contact angle measurements, as well as scanning electron microscopy and electron spectroscopy for chemical analysis.
Particle morphology effects on the performance of PMMA filled with aluminium hydroxide in a variety of fire tests
Authors: Hughes P. , V. Jackson G. , N. Rothon R. 
Published: March 2011

AbstractThe effect of aluminium hydroxide particle size and shape has been investigated on the performance of (polymethyl methacrylate) composites in a number of flammability tests. As a subsidiary exercise correlation between the tests has been investigated. The work has shown the expected effect of particle size on performance, with surface area giving the best measure of particle size if non‐spherical particles are involved. While the smallest particles always give the best results, the effect varies markedly according to the test and is most pronounced in the ISO ignitability test. Some possible explanations for these effects are proposed but more experiments are needed to choose between them. Correlation between the various tests is generally poor and reliance on any one of them for product development would be unwise.
Pyrolysis of flame retardants and fire protected polymers
Authors: Kettrup A. , Matuschek G. , Cyrys J. , Ohrbach K. H. 
Published: March 2011

AbstractThe simultaneously working combination of thermal analysis and mass spectrometry (TA/MS) is a very useful method for studying the degradation process of polymeric materials during thermal treatment [1–7]. Beside the thermal effects, as recorded from thermogravimetry (TG) or differential thermal analysis (DTA) the evolved degradation products can be determined and identified by the on ‐ line coupled mass spectrometer. Additional their temperature depending abundance can be registrated.Combustion of polymers in horizontal (BIS) or vertical (VCI) furnaces and subsequent off line high resolution GC/MS analysis of pyrolysis products is suitable for the simulation of burning processes
Characterization of fire retardant polymer blends by temperature resolved in‐source pyrolysis mass spectrometry
Authors: Luijk R. , Pureveen J. , Commandeur J. M. , Boon J. J. 
Published: March 2011

AbstractThe characterization of fire retardant polymer blends by temperature resolved in‐source pyrolysis mass spectrometry (PYMS) is demonstrated with a few examples. Electron impact (EI) and electron capture negative ionization (ECNI) were used to identify the thermal degradation products of polymer blends containing brominated fire retardants.PYMS (EI mode) offers an analytical instrument for a fast analysis of unknown mixtures of polymers and for the presence of fire retardant additives. Under electron impact conditions, in vacuo, low‐molecular weight additives like fire retardants mainly evaporate from the polymer matrix. PYMS (EI mode) has been used for the characterization of addition polymers like polystyrene and acrylonitrile‐butadiene‐styrene copolymer, and for condensation polymers like the polyester poly(butylene terephthalate).Applying electron capture negative ionization, at low argon pressure in the ionization chamber, a more realistic pyrolysis situation is created because the premature loss of volatile additives is suppressed. The selectivity of ECNI for electron accepting groups like bromine makes it possible to study the influence of brominated compounds on the degradation processes in the melt. This is demonstrated by our studies on polystyrene and acrylonitrile‐butadiene‐styrene copolymer. High‐molecular weight pyrolysis products in the m/z range of 1000 ‐ 2000 are detected for p‐bromopolystyrene and for a blend of high impact polystyrene with the fire retardant system decabromodiphenyl ether/antimony(III) oxide. In addition to the formation of antimony bromides shown in earlier studies, the emission of the synergist antimony(III) oxide as a dimeric cluster (Sb4O6) or as a reduced Sb4 cluster is observed under PYMS conditions.
Chemical and physical properties of foamed cokes and their effect on inflammability
Authors: V. Gnedin E. , Novikov S. N. , A. Khalturinskij N. 
Published: March 2011

AbstractBy means of IR and Raman spectroscopy chemical and physical properties of foamed cokes, formed during combustion and pyrolysis of PP based compositions, containing intumescent fire retardants (IFR) were investigated. It was established that thermal conductivity coefficients of coke material lie in the range of 0.12–0.32 W/m/K and are weakly dependent on the initial composition of IFR. It was shown that the effectiveness of IFR is mainly determined by the internal microstructure of the foamed cokes and the kinetic parameters of their formation.
Chances and limitations of high‐performance polymers
Authors: Wartusch Johann 
Published: March 2011

AbstractHigh Performance Polymers, especially when inherently flame retardant, are of potential interest for electrotechnical and electronic applications and are systematically investigated. In the course of R&D work on these materials ‐ in spite of a number of properties of high interest ‐ some deficiencies were found as, for example, predominantly poor metal adhesion. Further, in individual cases they possess poor stress cracking resistance, limited thermal stability and/or only medium hydrolytic stability. Moreover the industrial application of HPP is hindered by higher prices and nonavailability in larger quantities. In case of no success in current efforts (tailor made blends, surface modification) these deficiencies might contribute to a certain decline of HP polymers as already observed in a few cases.
Exchange and free radical grafting reactions in reactive extrusion
Authors: Hu Guo‐Hua , Flat Jean‐Jacques , Lambla Morand 
Published: March 2011

AbstractThe potential of two types of reactions for reactive extrusion was evaluated in our laboratory: exchange reactions of copolyesters and free radical grafting of monomers onto polyolefins. Specifically, the alcoholysis of ethylene and vinyl acetate copolymers, the transesterification of ethylene and alkyl acrylate copolymers (EAA) and the aminolysis of alkyl acrylate copolymers were investigated as the exchange reactions while the grafting of maleic anhydride (MA) onto polypropylene (PP) as the free radical reactions. The exchange reactions are very slow without catalysts. Tin derivatives, such as dibutyl tin dilaurate (DBTDL) and dibutyl tin oxide (DBTO), are good catalysts for the alcoholysis and the transesterification, but not for the aminolysis. For the latter, tautomeric compounds, such as 2‐pyridone and 2‐mercaptopyridone, are efficient. Comparative kinetic studies showed that, for all the three exchange reactions, the reacting medium (solution or the homogeneous melt) does not affect their reaction mechanisms nor their intrinsic rate constants. Additionally, mechanical mixing does not contribute to the overall reactions. As for the free radical grafting of MA, the presence of electron‐donating monomers and styrene (ST) in particular was shown to be very effective in improving the grafting yield while minimising the degradation of PP. This was proven to be due to the formation of a charge transfer complex between MA and such a monomer.
Poly(arylether oxazole)s and poly(arylether thiazole)s with pendent trifluoromethyl groups
Authors: Maier Gerhard , Nuyken Oskar , Hecht Reinhold 
Published: March 2011

AbstractBis(oxazolyl)benzenes and bis(thiazolyl)benzenes containing fluorine atoms and trifluoromethyl groups in the heteroaromatic moieties have been synthesized. These compounds can be used as monomers for the preparation of poly(arylether oxazole)s and poly(arylether thiazole)s with pendent trifluoromethyl groups. The high reactivity of the new oxazole monomers is demonstrated by the synthesis of the corresponding poly(arylene ethers) under extremely mild reaction conditions. The polymers have been characterized by spectroscopical methods, DSC, and dynamic thermogravimetry.
Reaction between polyesters and phosphorus compounds in the molten state
Authors: Jacques B. , Legras R. , Devaux J. , Nield E. 
Published: March 2011

AbstractThe reactions occurring between polyesters and phosphorus compounds in the molten state are investigated. A large molecular weight increase is observed in blends of Poly(ethylene terephtalate) and Poly(butylene terephtalate) after triphenyl phosphite addition. The formation of links containing phosphorus atoms between the polyester chain ends has been established. The weakness of this bond makes the observations difficult. An effect of phosphite on promoting the direct esterification between chain ends is suggested but not definitely proved yet.
Dependence of the moduli of random bimodal networks on chain‐length distribution
Authors: Sharaf M. A. , Mark J. E. 
Published: March 2011

AbstractThere have now been a number of experimental studies on the preparation and elastomeric properties of random bimodal networks of polydimethylsiloxane. The mole per cent of the short chains and their molecular masses covered a wide range, thus resulting in various polydisperse chain‐length distributions. The networks were studied with regard to their stress‐strain isotherms in elongation, and values of their moduli in the large‐deformation (phantom) limit were found to depend on the chain‐length distribution. This Important result is in disagreement with phantom network theory, which assumes the elastic modulus is dependent only on the mean value of chain lengths such that the cycle rank of the network is preserved. The effective functionality of the long chains was found to depend on the number of short chains present. Better agreement with experiment was obtained when account was taken of the connectivity of the very short chains, in what is essentially a bimodal distribution of both network chain lengths and cross‐link functionalities. Relevant here is the fact that as the degree of chemical cross‐linking Increases, the shear modulus G moves away from the affine limit, toward the phantom limit. This increase toward phantom behavior is presumably due to the fact that the mutual interspersion of chains is less when the chains are shorter, even in the small‐strain region.
Characterization and gel point of randomly linked high cis‐polybutadiene networks
Authors: Pyckhout‐Hintzen W. , Müller B. , Springer T. 
Published: March 2011

AbstractCis—Polybutadiene networks (98% cis), crosslinked in the bulk state by gamma irradiation were characterized in terms of their mechanical properties. Data from stress‐strain analyses, swelling degrees, stress relaxation and random—linking theory are in accordance and the estimated gel points practically coincide. Trapped entanglements contributed up to 30% to the network modulus, from which also the plateau modulus was determined. The tensile data were obtained from Mooney—Rivlin representations. It was concluded that the assumption of additive contributions from chemical and entanglement crosslink densities in the Langley theory works well in the range of doses investigated here. A comparison with a tube—like approach of these networks is made.
Influence of the dispersed phase upon the behaviour of nylon/rubber blends; crosslinking effect
Authors: Seo Yongsok 
Published: March 2011

AbstractNylon 6 and crosslinked SBS rubber blends were prepared. Their impact strength tests demonstrated the possibility of the existence of a maximum in impact strength at a moderate degree of crosslinking level. However, its peak value was not so much eminent as that happened in tensile test or brittle polymer's impact test. This seems due to complex mechanism occurred in dispersed phase. Based on our experimental data, we believe cavitation is important in nylon toughening. Interpretation of nylon toughening mechanism by cavitation and particle deformation is suggested for the reason of low peak value. Even though delamination is also possible, tensile strength data support cavitation in the rubber particle which seems to be more plausible for toughened nylon 6.
Critical behavior of trifunctional randomly branched polycyanurates
Authors: Bauer Jörg , Burchard Walther 
Published: March 2011

AbstractThe behavior near the gelation threshold of trifunctional randomly branched polycyanurates is studied by static and dynamic light scattering. By static measurements the critical exponents γ, σ and η were obtained, which describe the divergence of the weight average (Mw) and the cutoff (M*) molecular weights and the radius of gyration (Rg) respectively. All these independently measured exponents together with τ, characterizing the power law behavior of the molecular weight distribution and measured by size exclusion chromatography coupled with light scattering, confirm the predictions of the three‐dimensional percolation theory. With the help of size exclusion chromatography coupled with a light scattering and a viscosity detector, a fractal dimension D = 2.24 is obtained. On the other side, from the corresponding exponent for the whole unfractionated samples a fractal dimension D = 2.21 results, using a theory of Daoud. This suggests that the fractal dimension of the polycyanurates in dilute solution lies between the theoretical predictions D = 2.5 for the unswollen and D = 2.0 for the completely swollen state. Furthermore, it is shown by dynamic light scattering that the power law behavior over some decades in time of the time autocorrelation function and the divergence of the mean relaxation time are characteristics of the gelpoint. The development with increasing reaction time of the time correlation function of the gelling system from the pregel through the gelpoint into the gel state is analyzed quantitatively by a hybrid of a stretched exponential and a power law function.
Randomly branched polycyanurates ‐ modification of the network structure
Authors: Bauer Monika , Bauer Jörg 
Published: March 2011

AbstractPolycyanurates (poly(2,4,6‐trisaroxy‐1,3,5‐triazines)) are built up through a step‐growth polycyclotrimerization of difunctional aromatic cyanic acid esters and form an ideally trifunctional randomly branched network, where all initial cyanato groups are linked with the triazine branching units at full conversion. Results on modifications of the high network density of pure polycyanurates are reported for three types of comonomers: monofunctional cyanic acid esters, difunctional phenols and difunctional aromatic glycidyl ethers. Using the coreaction of mono‐ and difunctional aromatic cyanic acid esters, additional chain segments, dangling ends and low molecular weight compounds are built, the fractions of which are dependent on the initial admixture of the monofunctional compound and its relative reactivity. Therefore, the critical conversion at the gel point is shifted to higher values and the network density at full conversion decreases. The abstraction of phenols from intermediately formed iminocarbonic ester structures is utilized for the modification of the polycyanurate network through the coreaction of difunctional aromatic cyanic acid esters with phenols. It was found that the critical conversion and the network structure are dependent on all the initial amount of phenols, their reactivity and functionality. The modification with the help of glycidyl ethers is characterized by an insertion of the oxirane ring into the cyanurate and the succeeding reactions into isocyanurates and oxazolidinones. Depending on the initial mixture and the reaction conditions, a large spectrum of chemical and topological network structures can be obtained, what is demonstrated by both experimental and theoretical investigations.
Novel macromolecular architectures: Globular block copolymers containing dendritic components
Authors: Hawker Craig J. , Wooley Karen L. , Fréchet Jean M. J. 
Published: March 2011

AbstractThe synthesis of three different macromolecular architectures, dendritic segment‐block, layer‐block, and surface‐block copolymers, all of which can be regarded as new types of block copolymers, is discussed. The factors determining the physical properties of each of these unusual materials are studied and related to the dendritic structure.
Preparation of crystalline and solvent resistant polycarbonates via ring‐opening polymerization of cyclic oligomers
Authors: Brunelle Daniel J. , Krabbenhoft Herman O. , Bonauto David K. 
Published: March 2011

AbstractA route to solvent‐resistant polycarbonates which may also be crystalline has been achieved through the intermediacy of cyclic oligomeric carbonates. Mixed oligomeric cyclics of a variety of bisphenols were prepared via the carefully controlled hydrolysis‐condensation of their bischloroformates. Following ring‐opening polymerization, the polymers were evaluated for potential solvent resistance. Copolymers of hydroquinone and bisphenol A containing ratios of hydroquinone to BPA between 50/50 and 70/30 were found to be insoluble in CH2Cl2, tetrahydrofuran, and CHCl3, as well as other organic solvents. Polymers containing ratios of hydroquinone/BPA greater than 60/40 show a crystalline melting point by DSC at about 310°C and a glass transition temperature at 154°C.
Structurally perfect ladder polymers: Shape and conversion
Authors: Löffler M. , Schlüter A.‐D. 
Published: March 2011

AbstractThe influence of the symmetry and rigidity of Diels‐Alder (DA) ladder polymers on their shape in solution is discussed. Theoretical evidence is presented, which shows that certain representatives of this class of polymers attain the unprecedented shape of two‐dimensional coils. The second half of this article describes how one can unfold these polymers with chemical transformations and possibly even obtain fully aromatic ribbons.