bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physical ageing of heterogeneous polymers
Authors: Maurer Frans H.J. 
Published: March 2011

AbstractPhysical ageing has a pronounced effect on the short term and long term viscoelastic behaviour of polymers. The Kohlrausch‐Williams‐Watts (KWW) equation has been used extensively to describe the relaxation behaviour of thermorheologically simple amorphous polymers. The description is not completely satisfying because of improper limiting values at very short and very long times. Adequate corrections can be made to account for these differences at very short times [1]. Probing physical ageing by probing free volume hole sites by Positron Annihilation Lifetime Spectroscopy has revealed a small reduction of the average size of the holes as a function of ageing time and a strong dependence on the ortho‐Positronium intensity. It has been shown that the decrease of the intensity as a function of ageing time in several polymers is not a physical ageing effect, but a radiation effect of the positron source [2]. The stress relaxation and physical ageing behaviour of heterogeneous blends and crystalline polymers is, however, much more complicated than in homogeneous amorphous polymers. Both breakdown of the time temperature superposition as well as the time ageing time superposition has been observed [3]. There exists a remarkable correspondence between these thermorheologically complex polymer systems, allowing description and prediction of the relaxation long term behaviour after taking into account the structure of these systems.
Synthesis of new telechelic oligomers and macro‐monomers by “constructive degradation”
Authors: Ebdon John R. 
Published: March 2011

AbstractTelechelic acrylic oligomers possessing terminal carboxylic acid, ketone, aldehyde or hydroxy groups can be synthesised in good yields by the ozonolysis of free radical copolymers of the appropriate acrylic monomer with a small amount of a 1,3‐diene, such as butadiene, 2,3‐dimethyl‐butadiene or 2,3‐diphenyl‐butadiene. The oligomers so‐prepared have high end‐functionalities (>98%), controllable average molecular weights, relatively narrow molecular weight distributions, and can be chain extended by a variety of means to give back high molecular weight polymers. Oligomers with perfect α‐phenyl ketone‐ω‐carboxylic acid functionality can be prepared by ozonolysing copolymers containing low concentrations of units derived from phenyl acetylene. Photolysis of copolymers of an alkyl vinyl ketone with monomers such as styrene yield, directly, oligomers with polymerisable unsaturated end‐groups, i.e. macromonomers.
Diacetylene‐containing polymers IV. Novel diacetylene‐containing polyamides and copolyamides
Authors: Fomin Sergei , Marin Margarita , Ogawa Takeshi 
Published: March 2011

AbstractNew monomers, bis(3‐ethynyl)dianilides, were synthesized from 3‐ethynylaniline and different diacid dichlorides and were polymerized by oxidative polycoupling to give soluble high molecular weight film forming diacetylene‐containing polyamides. UV‐induced and thermal cross‐linking of the polymer were studied. A correlation was found between the chain flexibility and the absoprtion peaks of visible spectra of cross‐linked polymer films. Third order nonlinear optical susceptibility (χ(3)) of the polymer films was in the range of 10−10‐10−9 esu.
Hydrogen bonding and the phase behavior of rod/coil mixtures
Authors: Tang Wei‐Long , Coleman Michael M. , Painter Paul C. 
Published: March 2011

AbstractOn the basis of a Flory lattice model it has been calculated that single phase rod/coil mixtures can be obtained and this is supported by some recent experimental results. However, in the absence of flexible side chains attached to the rigid rods, single phase mixtures are only obtained if the interactions between the rod and coil functional groups are very strong (e.g. phenol/pyridine) and the polymers are chemically similar (i.e. χ, describing non‐specific interactions, is small). If both flexible side chains and hydrogen bonding functional groups are attached to the rig rod, however, a much broader range of allowed χ values is obtained, so that with careful chemical design it should be possible to obtain a number of miscible rod/coil mixtures.
Liquid transport process in polymeric materials. Application with plasticized PVC with low matter transfer
Authors: Vergnaud J. M. 
Published: March 2011

AbstractWhen a plasticized poly(vinyl chloride), (PVC), is in contact with a liquid, some matter transfer may take place, the liquid entering the polymer while the plasticizer leaves the polymer. These two mass transfers are controlled by transient diffusion and are connected with each other. No mathematical treatment can be made and numerical models taking all the facts into account are built and tested. New methods are studied, in order to prepare plasticized PVC with low matter transfer. The principle of the method consists of creating a steep profile of the plasticizer within the polymer with a low concentration on the surface. Other improvement is obtained by depositing on the polymer surface a thin layer of a liquid poorly soluble in the liquid stored in the PVC packaging.
The nature of the growing species in living cationic polymerization: Principles, stereochemistry, and in‐situ NMR analysis
Authors: Sawamoto Mitsuo 
Published: March 2011

AbstractThe objective of this paper is to discuss:(i) the general approaches to living cationic polymerizations;(ii) the nature of the growing species thus generated.For the first, it is concluded that three general methods are currently available which involve the nucleophilic stabilization of the growing carbocations by (a) a suitable counteranion, (b) an added Lewis base, or (c) an added neutral salt. According to this view, a variety of initiating systems are classified. For the second, findings are presented for the recently developed living cationic polymerization of vinyl ethers by the HCl/SnCl4 initiating system in the presence of an added salt (nBu4N+Cl−). The nature of the growing species therein is discussed on the basis of the steric structure of the living polymers, relative to nonliving counterparts, and the in‐situ 13C NMR spectroscopic analysis of model reactions where the interaction of the growing end model [CH3CH(OR)Cl] with SnCl4 and the added salt is analyzed.
Some aspects of anionic butadiene copolymerization
Authors: Ying Shengkang 
Published: March 2011

AbstractThe relationship between ideal copolymerization behavior and the nature of reactive species in butyllithium (n‐BuLi) initiated anionic copolymerization of styrene (St)‐ butadiene (Bd) in nonpolar solvent has been discussed.The monomer reactivity ratios (m.r.r.) for various reactive species were evaluated by kinetic study and statistical approach (using 13C NMR data) in St‐Bd anionic copolymerization system with THF as polar additive. The Markovian mechanisms for different propagating reactions in this complex copolymerizing system have been postulated.Furthermore, “pseudo” zero order Markovian mechnism could be sophisticatedly established in the n‐BuLi/tertiary amyloxy potassium (t‐AmOK)/THF initiated St‐Bd copolymerization system, provided that the apparent rate constants of both monomers are equal. Thus, by adjusting the ratio of K/Li and THF/Li, copolymers with composition almost identical to the ratio of initial monomer feed composition at different stages of conversion could be obtained.
Anionic synthesis of in‐chain 3° amine‐functionalized polybutadienes
Authors: Quirk Roderic P. , Kuang Jianxin 
Published: March 2011

AbstractAnionic copolymerizations of butadiene (M1) with excess 1‐(4‐dimethylaminophenyl)‐1‐phenylethylene (M2) were conducted in benzene at room temperature for 24–48h using sec‐butyllithium as initiator. Anisole, triethylamine and t‐butyl methyl ether were added in ratios of [B]/[RLi] = 60, 20, 30, respectively, to promote copolymerization. Narrow molecular weight distribution copolymers with M̄n = 14 × 103 to 32 × 103 g/mol (M̄w/M̄n =1.02–1.03) and 8,12 and 30 amine groups per chain for anisole, triethylamine and t‐butyl methyl ether, respectively, were obtained. The butadiene monomer reactivity ratios (r1) were 42, 33 and 14 for anisole, triethylamine and t‐butyl methyl ether, respectively.
Structure and reactivity of propagating centers in the anionic polymerization of 2‐vinylpyridine initiated by lithium derivative/triethylaluminium
Authors: Hubert Philippe , Soum Alain , Fontanille Michel , Hogen‐Esch Thieo E. , Dimov Dimo 
Published: March 2011

AbstractThe polymerization of 2‐vinylpyridine initiated by an organolithium derivative in the presence of Et3Al in toluene solution gives a polymer with enhanced syndiotactic content. This paper is devoted to the study of the structure and reactivity of this system. Model anions were studied by UV‐visible and 13C NMR spectroscopy. Propagation kinetics are followed by a calorimetric technique allowing the determination of the corresponding rate constants and thermodynamic parameters. These values are discussed in terms of the reaction mechanism of this polymerization.
NMR Studies of polymeric materials ‐ an overview
Authors: Cheng H. N. , Early Thomas A. 
Published: March 2011

AbstractNMR has been used extensively in studies of synthetic polymers. The approaches employed may require solution NMR, solid state NMR, or NMR imaging. In each case, different techniques and analytical methodologies have been devised to facilitate experimentation or to maximize information output. These techniques are not mutually exclusive and often provide complementary information. A selective review is made herewith of polymer/NMR studies, with emphasis on the contributions made at NMR symposia held in Detroit in October, 1993 as part of the 20th FACSS meeting.
Applications of triple resonance NMR techniques to the study of polymer structure and reactivity
Authors: Rinaldi Peter L. , Li Lan , Hensley Darlene R. , Ray Dale G. , Harwood H. James 
Published: March 2011

AbstractThe utility of isotopic labeling combined with triple resonance nuclear magnetic resonance (NMR) techniques for polymer structure and reactivity investigations will be demonstrated. One dimensional (1D) and two dimensional (2D) 1H/19F/13C triple resonance NMR experiments have been used to study the structure of fluoropolymers; and 1H/2H/13C triple resonance techniques have been used to study the reactivity of poly[(styrene‐alt‐(methyl methacrylate)] and the structure of deuterated polybutadiene. These methods provide a unique ability to selectively detect resonances of structural features that are present in minute amounts in polymers, without interference from the much larger signals of the rest of the polymer.
Sequential identification of polymer microstructures by heteronuclear NMR correlations
Authors: Beshah Kebede 
Published: March 2011

AbstractA description of a systematic NMR methodology for the characterization of polymers in solution is presented. The method utilizes a set of two dimensional (2D) heteronuclear NMR correlation experiments. It is especially optimized for polymers that have characteristic short spin‐spin relaxation times. Microstructures of homopolymers and copolymers are determined objectively since the analysis is based only on near neighbor correlations of all carbon and hydrogen atoms. Applications to poly(acrylic acid) and ethylene/vinyl acetate copolymer are presented.
The analysis of heterogenous polymer systems using solid‐state NMR techniques
Authors: Sullivan Mark J. 
Published: March 2011

AbstractTwo different types of high resolution solid‐state 13C‐1H cross depolarization experiments were applied to a rubber toughened thermoset polymer. A polypropylene blend was examined using a solid‐echo 1H wide line pulse sequence over the temperature range from 27 to 197°C. The frequency domain spectra were curve fitted to obtain the relative abundances of the three distinct 1H T2 components as a function of temperature.
Dynamics of the interface in a model composite system
Authors: Blum Frank D. 
Published: March 2011

AbstractA review of recent experiments from the authors laboratory on the dynamics of aminofunctional silane coupling agents is given. Of special emphasis are two coupling agents, aminopropylsilane (APS) and aminobutylsilane (ABS) which were deuterated in the γ‐position. These two coupling agents have similar chemical behavior, but different dynamics. Deuterium NMR studies reveal that the APS moves slower on the silica surface than ABS. The mobility of the interfacial ABS was also found to be significantly slowed when it was overcoated with a polymerized layer of bismaleimide to form a composite. When the composite was treated with water, the interfacial mobility of the ABS increased. The flexural strength of the APS treated composite was the highest compared to ABS‐treated and bulk glass in an epoxy‐glass composite.
NMR measurement of the surface dynamics of poly(dimethylsiloxane) adsorbed on silica gel
Authors: Rethwisch David G. , van Alsten John , Dybowski Cecil R. 
Published: March 2011

AbstractCPMAS‐DD 13C NMR spectroscopy was used to examine the mobility of poly(dimethylsiloxane) adsorbed on silica gel (PDMS/SiO2) at submonolayer coverages. The spin‐lattice relaxation time in the rotating frame (T1ρH) decreased linearly with increasing loading. This is consistent with a decrease in the mobility of the polymer segments as the loading is increased. The decrease in mobility results from interpolymer interference. We propose a model that explains these results in terms of a surface intrinsic viscosity that incorporates the polymer‐polymer interactions on the surface.
Intermolecular interactions in polymer blends: 1D and 2D NMR studies
Authors: Mirau Peter A. , White Jeffery L. , Heffner Sharon A. 
Published: March 2011

AbstractMost mixtures of high molecular weight polymers are not miscible in the absence of specific intermolecular interactions. We have used two dimensional NMR in solutions and in the solid state to probe these interactions and to gain a molecular level understanding of the forces that control polymer blend formation. The results show that weak, but specific intermolecular interactions often control the phase structure of polymer blends.
NMR imaging as a new tool for rheology
Authors: Sinton Steve W. , Chow Andrea W. , Iwamiya Joseph H. 
Published: March 2011

AbstractExamples of NMR imaging used to study the evolution of microstructure and flow velocities in sheared, highly filled suspensions are described. Fast NMR imaging methods were used to freeze the motion in a falling‐ball experiment, allowing us to monitor the local concentrations of suspended particles and ball position during the course of the experiment The migration of particles induced by shear and concentration gradients was followed in a Couette cell. Flow imaging methods were developed and applied to a Newtonian fluid and a non‐Newtonian suspension flowing in an axisymmetric pipe contraction.
Some unusual features of the configuration of polymer loops in a melt
Authors: Brereton Michael , Vilgis Thomas A. 
Published: March 2011

AbstractA diversity of structural features can be imposed on a melt of polymer loops by controlling the linking number between each pair of loops. For the simple case of unlinked loops, considered in this paper, new statistical weighting factors have been found which depend on the global configurational properties of writhe and self inductance. The separate effect of these terms is extreme: the writhe term favours rod‐like statistics, whereas the inductance favours globular configurations. Together the two terms tend to cancel each other in a way which is reminiscent of the screened potential in polymer chain melts. The result is that the exponent which describes the size of an unlinked loop in a melt of unlinked loops is perturbed from the gaussian result of 0.5 to 0.45.
Forty years of industrial developments in the field of isotactic polyolefins
Authors: Galli P. 
Published: March 2011

AbstractThe interest for the stereospecific polymerization of olefins discovered by prof. Natta in 1954 was so high that only a few years elapsed between the discovery and the commercialization of polypropylene. The polypropylene discovery generated a tremendous scientific and technological effort for the development of the catalyst, the process, the products. The fundamental achievements in the polypropylene technology had a significant impact over the polyolefin technology in general. Thanks to it, polyolefinic polymers, copolymers and rubbers, polyefinic based materials and alloys via heterogeneous Ziegler‐Natta catalyst polymerization are today largerly the most important family of plastic materials.The ability to vary melt flow and the broad properties range of these materials, the excellent thermal and physical‐mechanical properties of isotactic polyolefins together with the favorable economics and their full and easy recyclability widen the concept of monomaterial application fuelling their dynamic expansion since the early sixties.
Ionization of MgCl2 during the formation of α‐olefin polymeryzation catalyst
Authors: Sobota Piotr 
Published: March 2011

AbstractThe examination of the reaction between [MgCl2(THF)2], TiCl4(3), AlCl3, AlEt3, AlEt2Cl and the synthesis and isolation of compounds as crystals and resolution of their structure by the X‐ray method were the subject of our study. It was expected that these investigations would help to understand the behaviour of MgCl2 towards the transition metal and furnish useful relationships to the structure of catalyst active center and to the polymerization mechanism in TiCl4(3)/MgCl2/AlEt3 system. Our studies have revealed that the main difference between the first and higher generations of Ziegler‐Natta catalysts is only the number of active centers.
Steric equivalence between internal and external donors as polymerization stereoregulators: A molecular mechanics study
Authors: Barino Luisa , Scordamaglia Raimondo 
Published: March 2011

AbstractNew models for steric environment of Ti isospecific polymerization sites on MgCl2 microcrystals are presented. They directly involve the presence of a donor molecule in order to obtain chiral activable Ti atoms otherwise belonging to isolated adsorbed TiCl4 molecules or Ti2Cl8 dimers which are lacking the required symmetry. The most important steric features of donor molecules have been obtained through structure‐activity relationships and molecular comparisons, while their adsorption on MgCl2 faces lateral to (001) has been studied through a conformational analysis approach.
Kinetics of olefin copolymerization with heterogeneous Ziegler‐Natta catalysts
Authors: Kissin Yury V. 
Published: March 2011

AbstractThe kinetics of the ethylene/1‐hexene copolymerization reaction with a Ti‐based Ziegler‐Natta catalyst has been studied. Kinetic analysis established the existence of several populations of active centers in the catalyst. The centers differ in two aspects: their ability to incorporate α‐olefin units into copolymer chains (i.e., their reactivity ratios) and the average molecular weights of the polymer chains they produce. The centers of different populations are formed at different rates and have different kinetic stabilities. As a consequence, both the molecular weight distributions of the copolymers and their compositional distributions are relatively broad and change with in time. Two kinds of catalyst poisons were found. The poisons of the first type, arylalkoxysilanes, preferentially deactivate the centers which have the highest ability to copolymerize α‐olefins with ethylene. These poisons decrease the average α‐olefin content in the copolymers and the fraction of their olefin‐rich components. The poisons of the second type, conjugated dienes, preferentially deactivate the centers which have the lowest ability to copolymerize α‐olefins with ethylene. These poisons significantly increase the content of the olefin‐rich components in the copolymers.
Comparative kinetic and active centre studies on magnesium chloride supported catalysts in propylene polymerization
Authors: Tait Peter J. T. , Zohuri G. Hossein , Kells Andrew M. 
Published: March 2011

AbstractThree different types of high activity magnesium chloride catalysts were prepared and used for propylene polymerization both in the absence and in the presence of external donors. The rates of polymerization were studied as functions of polymerization time, and the effects of methyl paratoluate and diphenyldimethoxysilane as external donors were investigated. Active centre concentrations (C*) were determined using tritiated methanol quenching and 14CO radio‐labelling in order to assess their applicability. A relatively good agreement between values of C* evaluated by the use of these two methods was obtained. The morphologies of the supports, catalysts and polymers produced were studied using scanning electron microscopy. A model involving expanding microreactors is proposed for polymer growth.
Some peculiar aspects of a new catalyst for propene polymerization
Authors: Luciani Luciano , Milani Federico , Zannetti Roberto 
Published: March 2011

AbstractAn investigation was carried out on the preparation of highly disordered samples of MgCl2 (in delta ‐form), starting from different Mg‐alkyls and chlorinating agents.Successively we studied which kind of silica carrier had to be preferred and which treatment was strictly' necessary to achieve a qualified catalyst precursor showing outstanding performance. Different routes were investigated to support the active, disordered MgCl2 on the silica carrier and then some following ways to complete the catalyst. The final result of this investigation was the synthesis of a catalyst showing the best performance with reference to the parameters of use in every polymerization process.It has to be e.g. mentioned:— high yield, referred to the residual content of Mg, Ti and Cl;— no activity decrease when operating at a very high hydrogen concentration;— possibility to polymerize also at elevated temperatures;— very high isotactic index and stereoregular structure, as measured by the NMR technique;— possibility to reach high MFR (Melt Flow Rate) (up to 400 g IPP/10 min at 230°C, 2,16 kg, ASTM D 1238L);— outstanding morphology and flowability.
Stereospecific oligo‐ and polymerization with metallocene catalysts
Authors: Kaminsky Walter 
Published: March 2011

AbstractThe regio‐ and stereo‐selectivity of metallocene/methylaluminoxane catalysts was shown to be significantly and rapidly enhanced by substitution of the indenyl ligands and by heterogenization of the zirconocenes. By oligomerization of 1‐butene with optically active metallocenes, it could be shown that there is a small influence from the growing polymer chain on the isotacticity, the overriding factor in every case being the existence of a chiral active centre. Each insertion step increased the stereospecificity, until the maximum value was achieved.
Stereospecific metallocene catalysts: Scope and limits of rational catalyst design
Authors: Spaleck Walter , Aulbach Michael , Bachmann Bernd , Küber Frank , Winter Andreas 
Published: March 2011

AbstractStructure‐performance relationships in the propene polymerization behaviour of a number of silicon bridged bisindenyl zirconocenes show a rational pattern. Prognosis of the polymerization behaviour of different type structures, however, often fails, which is demonstrated by three examples of new zirconocenes. These include two bisindenyl complexes with two‐membered silicon bridges and one isospecific bridged fluorenyl cyclopentadienyl species. It is thus demonstrated that the scope of a “rational catalyst design” in the field of metallocene catalysts is still limited.