bluuebunny/crossref_metadata_2025_split huggingface dataset:
Product design for productivity and innovation with engineering thermoplastics and their blends in the nineties
Authors: Bailly C. , Sederel W. L. 
Published: March 2011

AbstractCompanies must constantly improve their technologies to survive the competitive battle in the nineteen nineties and beyond. This now holds more than ever for producers of engineering thermoplastics, who traditionally have enjoyed significantly higher margins than the commodity plastic producers. In today's competitive environment it is vital to be the high quality, low cost producer. At the same time products and processes need to become “greener”. The drivers call for specific R&D approaches focused at cost and ecological improvements of processes and products. Examples are:(i) novel catalysis with fewer process steps, higher yields and selectivity for the production of monomers and polymers.(ii) solvent‐free polymerisation processes, resulting in lower investment cost, lower operating cost and the lack of solvent traces in the final product(iii) design of polymer modifications, e.g. higher flow and/or higher heat co‐polymers such that products can be produced in existing equipment resulting in acceptable Return‐on‐Investment (ROI).Higher flow products are specifically needed for thin‐wall designs to allow optimum use of the high mechanical properties of engineering thermoplastics, making shorter processing cycles possible during moulding and bringing less material in the environment.This paper reviews various routes to high flow technology, such as improving processing window, molecular engineering and blends. The pull for these technology developments come from optical data storage, thin wall bumper and super thin note bloc computer applications. The need for greener products is addressed through improved flame and fire retardant product design.
Interfaces in polymer matrix composites from micromechanical tests to macromechanical properties
Authors: Verpoest Ignaas , Desaeger Muriel , Ivens Jan , Wevers Martine 
Published: March 2011

AbstractThe properties of a composite material are gouverned by the fibre, the matrix and the interface properties. However, in a test, used to determine a composite property, the influence of the interface is often muffled by other influences (fibre volume fraction, inhomogeneity, voids, defects,). To understand the relation between the composite performance and the fibre‐matrix interface properties, it is necessary to work in several steps. In a first step, a thorough understanding of the fibre‐matrix interface behaviour is needed. This not only involves the determination of the interface properties using micromechanical test methods, but also the fundamental study of the stresses at the interface and of the failure events occuring during the test. In this paper, the fragmentation, the pull‐out and the micro‐indentation test will be elaborated. The former test is used to explain the importance of an accurate data reduction model. In a second step, the influence of these interface properties on the composite performance is investigated. It is well known that an improved interface quality is beneficial for the transverse tensile and the interlaminar shear strength. However, a strong fibre‐matrix interface is not favourable for all composite properties. This is illustrated by an overview of micromechanical models, developed to understand the macromechanical behaviour of composites. Three properties are addressed: the longitudinal tensile strength, the interlaminar fracture toughness, and the damage development in cross‐ply laminates.
Ultimate toughness of amorphous polymers
Authors: van Der Sanden M.C.M. , Meijer H.E.H. 
Published: March 2011

AbstractThe deformation and toughness of amorphous glassy polymers is discussed in terms of both the molecular network structure and the microscopic structure at length scales of 50–300 nm. Two model systems were used: polystyrene‐poly(2,6‐dimethyl‐1,4‐phenylene ether) blends (PS‐PPE; where PS possesses a low entanglement density and PPE a relatively high entanglement density) and epoxides based on diglycidyl ether of bisphenol A (DGEBA) with crosslink densities comparable with up to values much higher than the thermoplastic model system. The microscopic structure was controlled by the addition of different amounts of non‐adhering core‐shell‐rubber particles. Toughness is mainly determined by the maximum macroscopic draw ratio since the yield stress of most polymers approximately is identical (50–80 MPa). It is shown that the theoretical maximum draw ratio, derived from the maximum (entanglement or crosslink) network deformation, is obtained macroscopically when the characteristic length scale of the microstructure of the material is below a certain dimension; i.e. the critical matrix ligament thickness between added non‐adhering rubbery particles (‘holes’). The value of the critical matrix ligament thickness (IDc) uniquely depends on the molecular structure: at an increasing network density, IDc increases independent of the nature of the network structure (entanglements or crosslinks). A simple model is presented based on an energy criterion to account for the phenomenon of a critical ligament thickness and to describe its strain‐rate and temperature dependency.
From incompatible poly(aryl ether sulfone)/polyamide 4.6. blends to new impact resistant alloys by a synergistic combination of a block copolymer emulsifier and an impact modifier
Authors: Koning C. E. , Fayt R. , Bruls W. , Vondervoort L.v.D. , Rauch T. , Teyssié PH. 
Published: March 2011

AbstractThe compatibilization and impact modification of blends of a relatively new engineering plastic polyamide 4.6 (PA 4.6) and a poly(aryl ether sulfone) (PSU) are investigated. PSU‐b‐PA6 block copolymers, which can be easily synthesized by ring opening polymerization of ϵ‐caprolactam in the presence of a commercial PSU, were found to be very efficient emulsifiers for these incompatible blends. Small amounts (1–4%) of copolymer are sufficient to significantly reduce the particle size and to improve the tensile and impact properties. Combinations of the copolymer and an impact modifier (ethylene‐propylene rubber grafted with maleic anhydride) are synergistic and high impact PSU/PA 4.6 alloys are obtained in that way.
1,3‐Dipolar cycloaddition: A new approach to telechelics
Authors: Maier Gerhard , Nuyken Oskar , Losert Klaus 
Published: March 2011

AbstractThe ability of the cycloaddition reaction between aromatic aldazines and diisocyanates to form polymers was studied. Reaction conditions were found which allow the direct synthesis of telechelics by this reaction. These telechelics have two isocyanate end groups due to the nature of the cycloaddition reaction. Functionality of a telechelic oligomer was confirmed to be f = 1.95 by end goup titration. Chain extension experiments were successful with this material.
Reaction and diffusion on amberlyst‐15 ion‐exchange polymer
Authors: Velo E. , Recasens F. 
Published: March 2011

AbstractIn this work, the effects of liquid polarity on the intrapolymer diffusion rates of iso‐Butene, using the heterogeneously catalysed hydration of i‐Butene to tert‐Butyl alcohol, are studied. Values for the effective diffusivity are correlated as a function of tert‐Butanol concentration and temperature. The tortuosity factor of the solid polymer matrix is seen to decrease with temperature and increase with alcohol content. Tentative conclusions regarding the shrinkage of the macroporous matrix, are drawn.
A development of Ahmad‐Stepto gelation theory
Authors: Rolfes H. , Stepto R. F. T. 
Published: March 2011

AbstractThe Ahmad‐Stepto (A‐S) theory of gelation in RA2+ RBf polymerisations has been improved and developed to include general polymerisations of A‐ and B‐bearing reactants, namely, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\sum\limits_{\rm i}}{\rm RA}{_{{\rm fai}}} + {\sum\limits_{{\rm i}}}{\rm RB}{_{{\rm fbi}}} $$\end{document} polymerisations and \documentclass{article}\pagestyle{empty}\begin{document}$$ {\sum\limits_{\rm i}}{\rm RA}{_{{\rm fai}}} $$\end{document} self‐polymerisations. It is found that the values of the ring‐forming parameter needed to fit experimental data on polyester‐forming RA2+ RB3 polymerisations are much nearer to those expected from solution properties than the values required by A‐S theory. The present theory is proposed as a useful basis for the prediction of unknown gel points from reactant structures and reaction conditions.
Mechanistic discussion on deviation from ideal network formation in radical polymerization of multivinyl monomers
Authors: Matsumoto Akira 
Published: March 2011

AbstractThe network formation in the radical polymerization of multivinyl monomers, especially including diallyl esters and dimethacrylates, is dealt by focusing our attention on the mechanistic discussion on deviation from ideal network formation. Thus, in the bulk polymerization of diallyl phthalate, the actual gel point was obtained to be 6.9 times higher compared with the theoretical one. In common multivinyl polymerization systems, the discrepancy was more than 10 times and sometimes, more than 102. Moreover, the extent of deviation was enhanced with increasing primary chain length, the content of pendant vinyl groups in the prepolymer, and dilution. In order to interpret reasonably the greatly delayed gelation different structural factors were considered. The primary factor concerns the significance of the thermodynamic excluded volume effect on the intermolecular crosslinking reaction between growing radical and prepolymer, especially at high molecular weight. Beyond the theoretical gel point, a secondary factor is related to the intramolecular crosslinking which becomes progressively important with conversion. The latter leads to the restriction of segmental motion of prepolymer and, moreover, imposes the steric hindrance, inducing the significance of the reduced reactivity of prepolymer as a tertiary factor. Solvent effect was observed as much delayed gelation in a good solvent as opposed to Walling's results, although this is expected by considering the significance of excluded volume effect.
Gelation process of amylose‐DMSO‐water system
Authors: Takeyama Hidenobu , Kobayashi Masatoshi , Yajima Hirofumi , Endo Ryuichi , Kohyama Kaoru , Nishinari Katsuyoshi 
Published: March 2011

AbstractAmylose gel is obtained by cooling amylose aqueous solution at a certain cooling rate. In order to clarify the gelation process of amylose in the mixed solvent of water and DMSO, the characteristics of turbidity and dynamic viscoelasticity of the solution as a function of temperature have been studied by optical and rheological methods, respectively. Accordingly, cloud temperature (Tc) at which the aggregation of amylose occurs, and gelation temperature (Tgel) at which the elasticity began to appear were obtained. Tc and Tgel were strongly dependent on cooling rate, and these values shifted to higher temperatures with decreasing cooling rate. However, there was difference between Tc and Tgel, and Tc was higher than Tgel, indicating the gelation process occurs in two stages.
Dynamics of shearing in flocculating fine sediment suspensions
Authors: Aijaz Saima , Jenkins Scott A. 
Published: March 2011

AbstractThe variability of rheological properties in cohesive sediment suspensions are studied and related to the flocculation process. It was found that the steady state shear stress increases exponentially with increasing sediment concentration and increases logarithmically by increasing the salinity of the suspension. The salinity dependence of the shear stress was correlated with changes in the floc‐size. These results reflect the dominant influence of fluid‐sediment interactions on the flocculation behavior of the suspension. An analytic model predicting shear stress as a function of the physical and electrochemical properties of the fine sediment suspension is developed.
Swelling and scattering investigations on chemically cross‐linked poly(vinyl alcohol) hydrogels
Authors: Horkay Ferenc , Burchard Walther , Geissler Erik , Hecht Anne‐Marie , Zrinyi Miklós 
Published: March 2011

AbstractSwelling and scattering measurements are reported from chemically cross‐linked polyvinyl alcohol) hydrogels and the corresponding semi‐dilute polymer solutions. The mixing free energy in the swollen network is found to be significantly smaller than that of the corresponding polymer solution at identical concentration. Static light scattering and small‐angle neutron scattering measurements indicate the presence of large‐scale static structures in the solution. Reasonable agreement is found between the osmotic moduli obtained from light scattering measurements and macroscopic osmotic observations.
On the scattering by polymers and copolymers at high angles
Authors: Benoît H. 
Published: March 2011

AbstractIn this paper we discuss the interpretation of the large angle scattering for chains, either being rod like, rigid or presenting excluded volume effect. It is shown that on highly branched polymers one can obtain a parameter which depends on the functionality of the crosslinks and on the average length of the blocks in the chain. One shows also how this type of analysis allows the interpretation of neutron results during transesterification.
Dynamic and static light scattering by weakly ionized gels and solutions
Authors: Candau Sauveur J. , Moussaïd Abdellatif , Joosten Jacques G. H. 
Published: March 2011

AbstractDynamic light scattering (DLS) and static light scattering (SLS) experiments have been performed on partially neutralized poly(acrylic acid) and poly(methacrylic acid) solutions and gels. The gels exhibit a non‐ergodic behavior, much less marked however than that observed in neutral systems. By combining DLS and SLS, the fluctuating part of the light scattered from PAA gel was separated from the total scattered intensity and found to be almost equal to the intensity scattered by the solution. Also the diffusion coefficient associated with the dynamic fluctuation was found to be the same in the PAA gel and the PAA solution.
Dynamic viscoelastic comparison of chemical and physical gels
Authors: Yu Qun , Amis Eric J. 
Published: March 2011

AbstractThe dynamic viscoelastic behavior of TEOS (tetraethoxysilane) and gelatin during the sol‐gel transition is compared. Different profiles of dynamic storage modulus G″ and loss modulus G″ with time are seen. Gelation time tgel is determined from the frequency independent tan δ = G″/G' for both systems. During the period following the gelation point, a transition in the scaling exponent of G' with (t ‐ tgel) is seen. For TEOS, the exponent changes from 0.494 to 5.24; for gelatin, from 0.24 to 2.11. The percolation model is used to qualitatively explain the differences in different networks.
Computer simulation of the formation of polymer networks
Authors: Akgiray Omer 
Published: March 2011

AbstractComplex crosslinked polymer structures can be quite easily modeled with the aid of computers. BTOSYM's implementation of an algorithm that has been developed by Eichinger and his co‐workers over the last few years is described. This algorithm allows us to model both random (as in sulfur‐cured rubber) and site‐specific (as in end‐linked silicones) crosslinking reactions. The simulation method provides detailed information on gel points, cycle rank, modulus of elasticity and other characteristics of the networks as they are formed. Illustrative results obtained with the program are presented.
A nuclear magnetic resonance study of molecular anisotropy in strained networks and network blends
Authors: Brereton M. G. 
Published: March 2011

AbstractThe splitting of the nuclear magnetic resonance line, seen in strained networks, is shown to originate from the anisotropic screening of the excluded volume interaction by density fluctuations. In a blend concentration fluctuations also contribute to the screening and are greatly enhanced if the phase separation point is approached. The effect on the line shape has been calculated and is shown to be sensitive to the thermodynamics of the phase separation.
Inhomogeneous biopolymer gels
Authors: Stading Mats , Langton Maud , Hermansson Anne‐Marie 
Published: March 2011

AbstractThe microstructure and rheological behaviour of inhomogeneous biopolymer gels was studied using a model system of β‐lactoglobulin. It can form both fine‐stranded and particulate gels which can be homogeneous or inhomogeneous depending on pH and heating rate. The dense and loose regions of the fine‐stranded gels had different relaxation times which significantly influenced the mechanical spectrum. The particulate gels showed coarser inhomogeneities influencing the fracture properties of the gels.
Synthesis and properties of aramid dendrimers
Authors: Backson S. C. E. , Bayliff P. M. , Feast W. J. , Kenwright A. M. , Parker D. , Richards R. W. 
Published: March 2011

AbstractThe synthesis, characterisation and properties of simple low molecular weight aromatic amide dendrimers is described. The insights into the problems inherent in the synthesis of such systems provided by molecular modelling studies are discussed along with possible strategies for circumventing them. Preliminary results concerning blends of aramid dendrimers with poly(hexamethyleneadipamide) are presented.
Highly branched aromatic polymers prepared by single step syntheses
Authors: Kim Young H. 
Published: March 2011

AbstractHighly branched polyphenylenes, polyphenylene ethers, aromatic polyesters and polyamides synthesized from AB2 type monomers are reviewed. Polyphenylenes were obtained by aryl‐aryl coupling reactions of 3,5‐dihalo‐phenyl organometallic reagents. 13C NMR indicates about 70% branching efficiency. A Tgat 236°C was observed, but the polymer did not form films. Polyethers were prepared by oxidative coupling of 2,4,6‐tribromophenol and 2,4‐dibromophenol. The former monomer gave high molecular weight polymers but the latter monomer did not polymerize well. Condensation of 3,5‐diaminobenzoic acid (I) and 3‐aminoisophthalic acid derivatives in an amide solvent gave lyotropic hyperbranched aromatic polyamides. The GPC indicated a large degree of polymer aggregation in the amide solvent in the absence of a complexing salt.
Metallo‐ and metalloido‐micellane™derivatives: Incorporation of metals and nonmetals within unimolecular superstructures
Authors: Newkome George R. , Moorefield Charles N. 
Published: March 2011

AbstractCascade polymeric architecture possessing internal functionalities was employed for the preparation of metallo‐ and nonmetallo‐MicellaneTM derivatives. Specifically, tetra‐ and dodeca‐o‐carborane superclusters, were obtained via treatment of the corresponding 1st and 2nd generation tetra‐ and dodeca‐alkyne, hydrocarbon cascade (MicellaneTM) derivatives with decaborane. Reaction of the same polyalkyne dendritic precursors with Co2(CO)8 afforded the benzyl protected, CobaltomicellanesTM possessing 12 and 24 internal metal centers, respectively. Control of amide‐based, carboxylic acid terminated macromolecular hydrodynamic radius via changes in solution pH was demonstrated. Heterocascade syntheses employing amide and metalligand monomer connectivity were accomplished. The relation of interior cascade reactivity to macromolecular “void volume” was examined.
New comb‐like polymers: Synthesis, structures and reactivity
Authors: Ritter Helmut 
Published: March 2011

AbstractComb‐like polymers have been widely investigated mainly to correlate their structures with the thermal behaviour. Our interests are directed on the synthesis of new types of comb‐like polymers bearing reactive groups in the side chains, main chain or as end groups. One part of the investigations deals with the behaviour of photosensible polymers containing azobenzene, cinnamic acid and mesoionic moieties. The use of enzymes as catalysts for the synthesis of new methacrylic derivatives and for the modification of polymers illustrates a fascinating contribution to polymer chemistry. The classical Diels‐Alder addition was also used for the synthesis and modification of polymers. Finally, the construction of polymers containing rotaxanes in the side chains is presented.
Polysilanes with various architectures
Authors: Maxka Jim , Chrusciel Jerzy , Sasaki Manabu , Matyjaszewski Krzysztof 
Published: March 2011

AbstractCopolymers and homopolymers containing silicon atoms connected to three and four other silicon atoms have been prepared and characterized. We report the first evidence of dendritic polymers with silicon backbones. Copolymers made from RSiCl3 and R1R2SiCl2 resemble hybrid materials of polysilyne and polysilanes. Polymers, which contain tetrasilyl‐substituted Si atoms, [(SiMe2)4Si]n and (Si)m(Me2Si)n, have also been synthesized. These molecules appear to be the first hyperbranched polymers, which have applications based on their electronic properties. The properties of these molecules fit into the hierarchy of 1‐D to 3‐D topologies known for Si materials.
Synthesis and characterization of macrocyclic polystyrene block‐copolymers
Authors: Gan Yao‐Dong , Zöller Joachim , Yin Rui , Hogen‐Esch Thieo E. 
Published: March 2011

AbstractThe synthesis of macrocyclic polystyrene‐ block‐poly(2‐vinylpyridine) and macrocyclic polystyrene‐ block‐poly(dimethylsiloxane) was carried out by initiation of 2‐vinylpyridine (2VP) and hexamethyl‐cyclotrisiloxane (D3) by difunctional living polystyryllithium followed by coupling with 1,4‐bis(bromethyl)benzene (1,4‐DBX) and dichloro‐dimethylsilane (Cl2SiMe2), respectively. A small portion of the living ABA precursors were protonated to serve as isobaric linear precursors. The linear and macrocyclic block copolymers were characterized by size‐exclusion chromatography (SEC). The ratios of apparent cyclic/linear SEC molecular‐weight maxima versus degree of polymerization (DP) show increases with decreasing DP varying from 0.70 ± 0.03 at high DP ≤ 200 to 0.78 ± 0.044 at low DP (≥60) whereas that of the linear ABA block copolymers decreased. Increases in glass transition temperature (Tg) were also observed for the cyclic PS‐b‐PDMS copolymers with respect to the isobaric linear precursors. The macrocycles were characterized by 1H and 13C NMR and in the case of macrocyclic PS‐b‐PDMS by 29Si NMR as well. Broadening in the NMR absorptions of the macrocyclic block copolymers is general and is similar to that observed for the homopolymers. Differemtial scanning calorimetry (DSC) analysis of the PS‐b‐P2VP macrocycles shows increases in Tg at lower molecular weight as was observed for the PS and P2VP macrocycles.
Macro‐cyclic aramids (2n‐AZA[2n]paracyclophane‐2n‐ones):new intermediates for the synthesis of p‐aramids
Authors: Memeger Wesley , Lazar Joseph , Ovenall Derick , Arduengo Anthony J. , Leach Roger A. 
Published: March 2011

AbstractAn easy route to a new class of n‐azapara[2n] cyclophane‐n‐ones, N‐substituted p‐oriented cyclic aromatic amide (cycloaramid) oligomers, is described. The bulky diamine, N, N′‐di‐sec‐butyl‐p‐phenylenediamine is condensed with terephthaloyl dichloride at elevated temperature in o‐dichlorobenzene to provide a high yield of N, N′‐di‐sec‐butyl‐p‐phenyleneterephthalamide cyclic oligomers (from dimer to tridecamer). The cyclization is favored by the cis conformation of the N‐substituted amide bonds present in the growing chain. Ring opening polymerization of these new cycloaramids to high molecular weight linear polymers can be effected in the melt phase with highly nucleophilic catalysts, such as 1,3‐dialkylimidazole‐2‐thiones especially when an acid cocatalyst is employed. The N‐substituted polymers yield crystalline films and fibers with an axial repeat length which can only be explained by an unexpected trans conformation of the amide bonds. The facile synthesis of other macrocyclic amides by the steric control of macrocyclization by N‐substitution of the amide bond is also described.