bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unusual instability effects observed in ionic and non‐ionic water soluble polymers
Authors: Kulicke W.‐M. 
Published: March 2011

AbstractThe solution instability of anionic, cationic and non‐ionic water soluble polymers was observed and examined. This instability can be easily observed by measuring the change in the solution viscosity.A viscosity increase with storage time was observed in the case of aqueous polyvinylalcohol solutions. A viscosity decrease with storage time was observed in the case of aqueous polyacrylamide solutions and derivates of polyacrylamide, also in the case of aqueous solutions of polystyrene sulfonate, starch‐acrylamide graft copolymers, amylose and poly(L‐glutamic) acid. This unusual solution instability was observed when the solutions were stored in the dark, at room temperature, and without mechanical influence.This instability effect is of scientific (molecular origin) and of technical (application) interest. The intention of this paper is to present an overall view of polymers which show this unusual instability effect, to report on the experiments done so far and to discuss possible reasons for this.
Photobehaviour of benzyl containing itaconate polymers
Authors: Abuin Elsa , Lissi Eduardo , Gargallo Ligia , Radić Deodato 
Published: March 2011

AbstractThe emission spectra of benzyl containing itaconate polymers were investigated in dilute tetrahydrofuran solutions. The polymers studied were poly(dibenzyl itaconate), poly(monobenzyl itaconate) and a (dibenzyl itaconate‐co‐dicyclohexylmethyl itaconate) copolymer. The photobehaviour of small compounds bearing the same chromophores was also investigated. The results obtained allow a discussion of the effect introduced by the polymer backbone upon the process of excimer formation.
Molecular weight determination of acrylonitrile polymers by gel permeation chromatography in N,N‐dimethylformamide
Authors: Azuma Chiaki , Dias Marcos L. , Mano Eloisa B. 
Published: March 2011

AbstractPeculiar elution behavior of the GPC of acrylonitrile polymers was investigated. The peculiarity was considered to be due to some substances which form a supermolecular structure with acrylonitrile polymers to cause a large UV absorption, detectable at 280 nm. The Mark‐Houwink‐Sakurada parameters of acrylonitrile polymers in 0.01M LiBr‐DMF at 60°C, needed for GPC universal calibration, were determined to be K=2.12 × 10−4 and a=0.75. The parameters obtained by us were different from the ones by other investigators, however, these values were reasonable for random coil polymers. The addition of inorganic salt, such as LiBr, in DMF removed the peculiar elution behavior of the GPC. The universal calibration using monodisperse poly(ethylene oxide) standards and the Mark‐Houwink‐Sakurada parameters could be applied for the determination of the molecular weights. The invalidity of the universal calibration for acrylonitrile polymers in DMF containing LiBr, seems to be caused by the difficulty in the determination of the molecular weight of polyacrylonitrile standards by absolute methods, such as light scattering and osmometry.
Theoretical investigations on the cationic propagation of vinyl monomers
Authors: Hallpap P. , Bölke M. , Heublein G. , Weiss C. 
Published: March 2011

AbstractExperimental investigations for elucidation and description of the complex mechanism of cationic polymerization can be confirmed, completed and deepened by quantum chemical model calculations. This is shown by means of calculations with CNDO/2– and MINDO/3–method considering solvent influence. The problems dealt with here are stability of counterions and cationic chain ends, potential energy surface of a cationic propagation step in the gas phase and in solution, the solvent effect on both reactions in competition with cationic propagation and on cationic copolymerization.
Verification of transfer‐suppressed cationic polymerization of vinyl monomers
Authors: Heublein O. , Spange S. 
Published: March 2011

AbstractA general approach to a transfer‐suppressed proceeding of cationic vinyl polymerization is put forward. The fundamental principle of the method consists in stabilization of the counter‐ion by interaction with acceptors. This results in an orbital controlled cation‐anion interaction and by this, suppression of side reactions, for example chain transfer due to lowering the ß‐hydrogen acidity of the growing cation and the specific monomer solvation of the propagation transition state.It is shown that picric acid, initiated polymerization of p‐methoxyatyrene and vinyl ethers, runs free of transfer in contrast to LEWIS‐acid initiated systems. Cationic polymerization, initiated by iodine based systems, are in the same category as demonstrated by molecular weight distributions, monomer addition experiments, thermokinetical data and UV‐spectroscopical measurements. The results are discussed in the framework of a general energetic scheme of propagation via cation‐anion orbital controlled interactions with propagating ion pairs.
Cationic polymerization by cyclic halonium ions I. The 2,5‐dimethylhexane/Bcl3/isobutylene system
Authors: Biswas Mukul , Kennedy Joseph P. 
Published: March 2011

AbstractAged 2,5‐dichloro‐2,5‐dimethylhexane (DDH)/BCl3 mixtures readily initiate the polymerization of isobutylene in CH2Cl2 at −35°C and yield asymmetric telechelic polyisobutylenes in the liquid range with narrow molecular weight distributions (Mw/Mn < 2.0). Kinetic studies indicate that chain transfer monomer is absent and DDH is not a chain transfer agent (i.e., inifer). According to results of model experiments, 1H and 13C NMR spectroscopy, chlorine‐content, dehydrochlorination, and IR studies, the structure of the head group of the polyisobutylene product is Cl(CH3) 2CH2CH2C(CH3)2‐and that of the tail group is ‐CH2C(CH3)2Cl. In line with the results of kinetic investigations and structure characterization studies it is postulated that the initiating cation is a cyclic chloronium ion formed from the DDH during aging in the presence of BCl3: magnified image
Activated monomer propagation in cationic polymerizations
Authors: Penczek Stanislaw , Kubisa Przemyslaw , Szymański Ryszard 
Published: March 2011

AbstractNew mechanism of cationic polymerization of cyclic ethers and acetals consisting in the activated (e.g. protonated) monomer addition to the electrically neutral macromolecule e.g.: magnified imageis discussed. It is shown, that when the ‐OH in the tail‐group is more nucleophilic than monomer itself this mechanism has chances to dominate over the traditional mechanism of propagation, involving tertiary oxonium ion.Kinetics of the polymerization process, elementary reactions, competition with the tertiary oxonium ion growth are discussed. Examples are given, based on the work on ethylene oxide and epichlorohydrin polymerization, showing how to apply the theory of the activated monomer in order to avoid side reactions, namely cyclization and disproportionation of the chains.
Polymerization of N‐substituted lactams
Authors: Puffr Rudolf , Sebenda Jan 
Published: March 2011

AbstractThis study deals with a comparison of the rates and activation parameters of the polymerizations of N‐methyl and N‐benzoyl derivatives of lactams containing 4, 9 or 13 ring atoms initiated by carboxylic acids, amino acids, strong protonic acids or Lewis acids. The respective polymerization mechanisms of substituted and unsubstituted lactams are discussed. The initiators mentioned above lead to the polymerization mechanisms with activated monomer in most cases. The use of stable carbenium cations results in a new type of polymerization of N‐benzoyl lactams with a cationic propagation centre on the chain.
Sterically controlled propagation in the cationic ring‐opening polymerization of bicyclic acetals
Authors: Sumitomo Hiroshi , Okada Masahiko 
Published: March 2011

AbstractThis paper deals with sterically controlled propagation in the cationic ring‐opening polymerization of bicyclic acetals in relation to the chemical synthesis of structurally regulated polysaccharides, particularly focusing on the following two topics:1) Chemical synthesis of (1→6)‐β‐linked polysaccharides by the ring‐opening polymerization of 1,6‐anhydrosugar derivatives. 2) Asymmetric selective copolymerization of racemic bicyclic acetal with optically active monomer.
Polymerization of ethylene with supported zirconium organic compounds
Authors: Ulbricht Joachim , Giesemann Jürgen 
Published: March 2011

AbstractThe polymerization of ethylene was studied with supported catalysts prepared by the reaction of Zr(benzyl)4 and Al2O3. The influence of the preparation of the catalysts and the reaction conditions on the overall rate of the polymerization was established. The rate exhibits a maximum which depends on the thermal pretreatment of the support and the quantity of the fixed Zr(benzyl)4. The concentration of the active centres of the catalysts was determined by quenching the polymerization with labelled butanol. The catalysts possess active centres which have different rates of propagation for ethylene. The decrease of the polymerization rate is caused by chemical reaction. The higher the concentration of free hydroxyl groups on the catalyst, the higher the rate of deactivation. Hydrogen in the monomer feed produces a decrease or an increase of the polymerization rate depending on the preparation of the catalysts.
Elastomers by atactic linkage of α‐olefins using soluble Ziegler catalysts
Authors: Kaminsky W. , Schlobohm M. 
Published: March 2011

AbstractWith bis (cyclopentadienyl) zirconiumIV‐compounds and methylalumoxane as soluble Ziegler catalyst propylene can be polymerized to pure atactic polypropylene with molecular weights up to 600 000. The copolymerization of ethylene and propylene or butene gives elastomers with different properties. The butene units are distributed at random in the polyethylene chain as carried out by 13C NMR measurements. The regiospecifity of the catalyst leads exclusively to the formation of head‐to‐tail enchainments. Using ethylene together with propylene and diolefins, EPDM rubber is formed. Glass transition temperatures of ‐60 to ‐50 °C could be observed.
Vinyl polymers with pending fluoranthene groups and their charge transfer behavior
Authors: Pfänder Rudolf , Höcker Hartwig 
Published: March 2011

AbstractIn the present paper the preparation of vinyl monomers with pending fluoranthene groups and different spacer length, their radical polymerization and their electron donor acceptor (EDA) complex formation with tetracyanoquinodimethane, tetracyanoethylene and SbCl5are studied. EDA complexes with a spacer length of 3 methylene groups are particularly favored. The electrical conductivity of the complexes as well as of radical cation salts of the polymers generated by anodic oxidation (formation of dark foils) is low (10−5S/cm) and the ESR signal is very broad ‐ indicating trapped electrons ‐ in contrast to highly crystalline low molecular weight fluoranthene radical cation salts.
The influence of matrix structure on the activity and selectivity of polymer supported catalysts
Authors: Widdecke H. , Klein J. , Haupt U. 
Published: March 2011

AbstractThe influence of the pore structure, surface area, crosslinking density and the distribution of catalytic groups on the activity / selectivity of polymer supported catalysts was investigated. As model catalysts a variety of styrene‐divinylbenzene‐copolymers functionalized with sulfonic acid groups were used. The isomerization of 1‐butene and the cleavage of methyl tert ‐ butyl ether (MTBE) were studied as gas phase reactions in the presence of the acid resins. The activity and selectivity was controlled by the acidity and accessibility of the polymer supported catalyst.
States of molecular assembly and physical properties of crystalline long‐chain compounds studied by vibrational spectroscopy
Authors: Kobayashi Masamichi , Kobayashi Tohru , Cho Yonghae , Kaneko Fumitoshi 
Published: March 2011

AbstractVarious types of molecular assembly of long‐chain compounds in solid states were investigated by means of infrared absorption, Raman and Brillouin spectroscopic methods. As for the polymorphism in even‐numbered n‐fatty acids, three monoclinic modifications, B, C, and E, all consisting of the orthorhombic polyethylene sublattice, give rise to their characteristic infrared and Raman spectra. A dynamical equilibrium between cis and trans conformations of the hydrogen‐bonded carboxyl groups in modification C, which is related to the high‐temperature stable character of this phase, is reflected to a dramatic change with temperature in the low‐frequency Raman spectra. A new type of reversible solid state phase transition was found between two A‐type (triclinic) modifications of myristic, palmitic, and stearic acids. The γ→α phase transition of oleic acid was found to be caused by a conformational disordering of polymethylene chains at the lamellar interfacial region.Two basic polytype structures, Mon and Orth II, of stearic acid B were investigated, and it was found that the low‐frequency phonon frequencies (below 50 cm−1) were strongly influenced by the polytype structure. Based on the spectroscopic considerations, Orth II was predicted as the thermodynamically stable phase around room temperature compared with Mon, and the stability is responsible for the vibrational free energy term. Some experimental findings which support this prediction were obtained. The values of the stiffness tensor elements of Mon and Orth II, measured by Brillouin scattering, indicate that the mechanical behavior of bulk crystals is very dependent on the polytype structure.The relationship between the mobility of chain molecules and the width of the spectral bands was investigated in a quantitative manner for the case of n‐alkane molecules entrapped in the urea inclusion adducts. The changes in the half‐width for the polarization components of various Raman bands on the transition from the orthorhombic to the hexagonal phase are interpreted in terms of the correlation functions of the Raman tensor related to the rotational motion of the alkane molecules around the chain axes.
Hydrogen bonding in polymers: III further infrared temperature studies of polyamides
Authors: Coleman Michael M. , Skrovanek Daniel J. , Painter Paul C. 
Published: March 2011

AbstractFourier transform infrared temperature studies of two semi‐crystalline polyamides, nylon 12 and a terpolymer of nylon 6/66/610 are presented. The results obtained are consistent with those recently published from similar studies of an amorphous polyamide and nylon 11 and further bolster our general interpretation of the infrared spectra of polyamides.
Characterization of Kevlar fiber surfaces using a newly developed infrared photoacoustic technique
Authors: Chatzi E. G. , Urban M. W. , Koenig J. L. 
Published: March 2011

AbstractA newly developed infrared photoacoustic technique has been used to obtain information about the orientation of the surface functional groups of Kevlar‐49R fibers. This method involves the use of a highly polarizable gas in the photoacoustic cell and comparison of the spectra with a non‐polarizable coupling gas. A highly polarizable inert gas, xenon, enhances the surface modes oriented parallel to the surface and suppresses the intensity of the perpendicular modes. This method shows differences in the structure of the skin and the core of the fibers. The polymer chains in the skin are oriented parallel to the surface, and in the core they are almost radially oriented.
Computer‐supported infrared spectrometry of polyethylene, ethene copolymers, and amorphous poly(alkyl ethylene)s
Authors: Solti Agnes , Hummel Dieter O. , Simak Peter 
Published: March 2011

AbstractThe advent of computer‐supported IR spectrometers, especially Fourier‐transform IR interferometers, made possible considerable progress in the fine‐structure elucidation of the seemingly well‐known polyethylene and ethene copolymers. This paper gives a review on the results obtained in several laboratories in the following fields: identification of side‐groups and olefinic structures, characterization of ethene homo‐ and copolymers made with different catalysts, by spectral enhancement, difference and derivative spectroscopy, and measurements of the dichroism of oriented samples. In one chapter, recent results with amorphous poly(alkyl ethylene)s obtained with a modified Phillips catalyst are reported.
Electronic spectra of dilute solutions of cationic and radicalic poly (n‐vinylcarbazole)
Authors: Klöpffer Walter , Rippen Gerd , Kowal Joanna 
Published: March 2011

AbstractFluorescence spectra of liquid solutions of PVCA are dominated by two kinds of excimer emission which are characteristic for the mode of preparation of the polymer. Luminescence spectra of solid solutions are more monomer‐like, indicating shallow exciton traps. Substantial hypochromic effects are reported for the two lowest energy singlet transitions of PVCA. No significant difference could be observed for PVCA samples of cationic and radicalic origin.Note a ‐ Presented in part at the EUROANALYSIS V European Conference on Analytical Chemistry, Kraków, August 1984
Ordnungszustände im system polyamid‐6 und polyamid‐6, 6
Authors: Keil Wolfgang , Trafara Gundolf 
Published: March 2011

AbstractBlends of PA‐6 and PA‐6,6 were studied by DSC for different conditions of crystallization. All samples were characterized by x‐ray diffraction. From dilute solution the components crystallize in separate modifications. In the melt both components are compatible. PA‐6‐ and PA‐6,6‐segments are linked together. During rapid quenching of the melt in the samples of about equal composition of PA‐6 and PA‐6,6 a modification is formed possibly built by a three‐dimensional network of hydrogen bonds between PA‐6‐ and PA‐6,6‐segments. If the samples of the same composition are annealed at 25 K below the melting temperatures of PA‐6 and PA‐6,6 for 3 hours in each case a modification appears as in quenched samples in addition to only partially ordered crystallites of PA‐6 and PA‐6,6. Despite optimal annealing there is no complete separation of the components.
Sterically controlled cationic propagation in the ring‐opening polymerization of bicyclic acetals and bicyclic oxalactones
Authors: Sumitomo Hiroshi , Okada Masahiko 
Published: March 2011

AbstractSterically controlled cationic propagation in the ring‐opening polymerization of bicyclic acetals, which is important and attractive in relation to the chemical synthesis of structurally defined polysaccharides, involves a selective cleavage of acetal bonds, configurational changes of the asymmetrical acetal carbons, and the enantiomer selection at the chiral growing chain end.Also in the polymerization of a bicyclic oxalactone having bicyclo[3.2.1]octane skeleton resulting peculiarly in the selective formation of macrolides of specific ring sizes, the exclusive bond scission accompanied by the inversion of the configuration of the acetal carbon takes place, and, as a result, sequences of four or five consecutive monomer units of the same chirality form at a growing chain end. Optically pure cyclic tetramer and cyclic pentamer (20‐ and 25‐membered macrolides, respectively) were prepared by the oligomerization of a monomer mixture of 36 % optical purity under the reaction conditions where racemic monomer gave racemic cyclic dimer highly selectively, whereas optically active monomer afforded cyclic tetramer and cyclic pentamer, respectively.Ring‐opening polymerization of another two kinds of newly synthesized bicyclic lactones having bicyclo[2.2.2]octane skeleton was conducted by the use of cationic, anionic, and coordinated initiators. From 1H and 13C NMR analysis of the resulting polyesters and comparison of the spectra with those of model compounds, the mechanism of polymerization, together with the polymerization reactivity of the monomers, is discussed.
Ring opening polymerization of cycloolefins by means of metathesis catalyst: Kinetic and thermodynamic effects on the product distribution
Authors: Höcker Hartwig 
Published: March 2011

AbstractThe metathesis reaction of cycloolefins is a ring‐opening polymerization with a metallacyclobutane system as the key intermediate. A kinetically and a thermodynamically controlled regime of the reaction clearly can be distinguished, the latter being characterized by a ring‐chain equilibrium.
Telechelic polymers by cationic ring‐opening polymerization
Authors: Goethals Eric J. 
Published: March 2011

AbstractBy means of cationic ring‐opening polymerization a wide variety of telechelic polymers can be prepared. After a general description of the chemistry of this kind of polymerization, the introduction of functional end groups by initiation, by end capping and by transfer reactions is described. The following monomers, which have successfully been used to produce telechelics by cationic mechanisms, are discussed: tetrahydrofuran, various epoxides, cyclic acetals and cyclic amines, cyclosiloxanes.
Polymerization of phosphorus containing cyclic monomers: Synthesis of polymers related to biopolymers
Authors: Penczek Stanislaw , Biela Tadeusz , Klosinski Pawel , Lapienis Grzegorz 
Published: March 2011

AbstractThe mechanism of polymerization is discussed, in which cyclic esters of phosphoric acid, and related compounds are converted into linear macromolecules, modelling nucleic and teichoic acid backbones. Structures like deoxyribose polyphosphate and glycerol polyphosphate were prepared from the corresponding cyclic compounds.These polymerizations involve heterolytic breaking of the P‐O bond in the cyclic monomer and proceed by ionic mechanism. Both 5‐ and 6‐membered monomers have been polymerized. The thermodynamic parameters of the ring‐chain interconversion were determined; the 5‐membered rings polymerization is driven by the exothermicity of the ring‐opening, whereas polymerization of several 6‐membered rings is endothermic and allowed because of the positive change of entropy.Anionic polymerization, and particularly the pseudo(coordinate)anionic polymerization provides, in contrast to the cationic process, high‐molecular‐weight polymers with more uniform structure. Anionic polymerization proceeds mostly (at the applied conditions) on the macroion – ‐pairs. The elementary reactions consist of the nucleophilic attack of the paired macroanions on the phosphorus atom in the cyclic monomer molecule. Rate constants of the elementary reactions for the model monomers will be presented.Stereochemistry of the propagation steps is shown to be governed by the statistical ring‐opening, leading to the three kinds of polymer units (head‐to‐tail and two symmetrical units).Apart from the ring‐opening, the polyaddition of diepoxides to phosphorous and phosphoric acids is described.Finally, a few examples of preparation of models of biopolymers are given, namely poly(deoxyribose phosphate) and poly(glycerol phosphate).
Physical properties of polyesters prepared from β‐lactones
Authors: Prud'Homme Robert E. 
Published: March 2011

AbstractPolyesters derived from substituted β‐propiolactones exhibit a wide variety of physical properties depending upon the number, nature and position of their substituents. Their properties can be changed even more by preparing atactic and isotactic polyesters, and polyesters with intermediate degrees of isotacticity. Moreover, the isotactic polyesters with opposite configurations form stereocomplexes with unique properties.