bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical aspects of the radiation‐induced conductivity in polymers
Authors: Tyutnev A. P. , Sadovnichii D. N. , Boev S. G. 
Published: April 2003

AbstractIt has been demonstrated that radiation‐induced conductivity (RIC) is strongly dependent on the chemical structure of the macromolecules, this dependence being influenced by the position of the active molecular group acting as a hopping center for charge carriers: main chain vs pendant case. Both RIC magnitude and its nature (free ion vs geminate) are affected. Annealing of the radiation‐induced conductivity (RIC) in four common polymers (PS, PET, LDPE and PTFE) continuously irradiated in vacuum to doses of about 5 × 104 Gy has been studied. While substantial recovery (up to 75%) has been observed in PS and PET, only steady degradation of RIC has been encountered in LDPE and especially in PTFE (annealing at elevated temperatures has been fulfilled only in air). Unlike other polymers tested, PS shows recovery that depends critically on the surrounding atmosphere (air or vacuum). To describe these results one relies heavily on the radiation‐induced oxidation as a chain radical process with degenerate branching (a case of LDPE and PTFE) and catalytic recombination of macroradicals (as in PS).
FTIR spectroscopic studies on the interfacial reactions of oxazoline‐functionalized polymers
Authors: Schäfer R. , Kressler J. , Mülhaupt R. 
Published: April 2003

AbstractThe interfacial reaction of immiscible polymeric systems containing oxazoline and carboxylic acid groups, respectively, has been studied by FTIR spectroscopy and FTIR microscopy. A poly(butadiene‐co‐acrylonitrile) rubber, where the nitrile groups are partially converted to oxazoline groups, is thermally annealed in a two‐layer specimen with poly(ethene‐co‐methacrylic acid). The formation of the esteramide in the interface is measured quantitatively by FTIR difference spectroscopy. Evaluating the formation of the amide I band leads to reaction rate constants ranging from 0.0125 to 0.022 s−1 in the temperature range from 170 to 230°C. It can be shown by FTIR microscopy that this system is immiscible because there is no interdiffusion across the interface. Also the formation of an esteramide in the interfacial reaction of the system poly(ethene‐co‐methacrylic acid)/bis(1,3‐oxazoline‐2‐yl)‐terminated poly(dimethylsiloxane) is monitored qualitatively by FTIR spectroscopy.
Graft copolymerization onto wood fibers. Ozone‐activated hydrophobization of pretreated wood pulp
Authors: Daneault C. , Sain M. M. , Lavoie C. 
Published: April 2003

AbstractDespite the fact that graft copolymerization is a favored reaction for cellulose xanthate, a significant part of the cellulose and lignin component is subject to undesired degradation reaction. Exposure of thermomechanical pulp to ozone followed by grafting by the xanthation method further degrades the cellulose and decreases graft yield. Graft yield can be improved by introducing chemical crosslinks to the cellulose backbone before or after ozone exposure. It is suggested that crosslinking with formaldeyde recombines some of the degraded chains of hydroxylated cellulose after ozone exposure and also helps to prevent degradation of cellulose chain during grafting of cellulose xanthate. Sizing of pulp with dispersed and saponified rosin—Al complexes slows down the grafting reaction and decreases the polymer add‐on percentage significantly. An exposure to ozone before or after the sizing process improves grafting efficiency and graft yield and the copolymer formation is the preferred reaction. The surface morphology of sized pulp has practically no influence on the grafting parameters. Unlike the sizing mechanism, the chemical nature of the sizing agent influences the grafting process. Sizing of pulp with an alkyl ketene dimer significantly decreased the copolymer formation by preventing reactive cellulose hydroxyl group from reacting.
The sorption of N‐cetylpyridinium chloride on leacril fibers. Electrokinetic properties
Authors: Espinosa‐Jiménez M. , Giménez‐Martín E. 
Published: April 2003

AbstractAn experimental investigation on the streaming potential and sorption of N‐cetylpyridinium chloride on Leacril fibers has been carried out. The results reveal that the uptake of N‐cetylpyridinium chloride on Leacril fibers takes place by means of electrostatic attraction between the cation of the surface‐active agent used and both the sulphonate and the sulfate end‐groups of the Leacril.Given the hydrophobic character of Leacril and the amphiphilic nature of the N‐cetylpyridinium chloride molecules, hydrophobic attractions between the fiber and the hydrophobic part of the surfactant might account for the interaction, explaining the sorption of N‐cetylpyridinium chloride even when it is hindered by electrostatic repulsion.The electrical characterization of Leacril fibers has been carried out and the methods employed for the determination of zeta potentials of Leacril fibers are discussed, on the basis of streaming potential technique. In our case for this hydrophobic fiber, the linear model of Goring and Mason of a bundle of capillaries gives the most precise values of zeta potential. Also discussed is the behavior of the surface conductance of the system in the above process of sorption.
Investigation of the structure of low molecular weight polybutadienes and epoxides made therefrom
Authors: Maenz K. , Möllhoff M. , Stadermann D. 
Published: April 2003

AbstractModel calculations on low molecular weight polybutadienes (PCILO, MM2) lead to statements about preferred conformations and, therefore, about the secondary structure of these polymers. The results of the calculations enable a better interpretation of experimental results obtained in epoxidation reactions of the polybutadienes.
Search for conducting doped polymers with great chemical stability: Regiospecific poly(3,3″‐dihexyl‐2,2′:5′,2″‐terthiophene)
Authors: Magnoni M. C. , Gallazzi M. C. , Zerbi G. 
Published: April 2003

AbstractPrevious calculations have suggested that the formation and the stability of charge transfer bonds in doped polyconjugated systems may be maximized by a favored topology of the dopant molecule. The preferred site of attack is found where the steric hindrance is minimized. Following these principles, regiospecific poly(3,3″‐dihexyl‐2,2′:5′,2″‐terthiophene) was synthesized and doped with FeCl3. The time and temperature dependence of the dedoping process has been studied by the analysis of the doping induced infrared spectrum. This material in the doped state shows an extremely great stability (in air, even at relatively high temperatures) never previously reported for any other doped system.
Surface enrichment in thin films of PVC and PMMA
Authors: Kunze K. , Stamm M. , Hartshorne M. , Affrossman S. 
Published: April 2003

AbstractThe surface enrichment in thin bilayer films of poly(vinyl chloride) (PVC) and deuterated poly(methyl methacrylate) (PMMAd) was studied by neutron reflectometry, X‐ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). In a layer system, where the PVC film is placed on top of a thin PMMA film, the PMMA chains migrate to the surface, although annealing of the films is performed below the glass transition temperature of PMMA. In addition, the surface segregation in blends of these materials was studied by XPS and SSIMS. In all cases PMMA is enriched at the surface. Results from the different techniques, probing different, sample depths, are consistent, if an exponential concentration profile of PMMAd at the surface is assumed. Concentration profiles at the surface are discussed with respect to theoretical models and diffusion coefficients are estimated.
Crystal structure and morphology of bromo‐substituted fully aromatic liquid crystal polyesters
Authors: Liu J. , Geil P. H. , Huh S.‐M. , Lin J.‐I. 
Published: April 2003

AbstractThe bromo‐substituted main chain liquid crystal polyesters poly(3‐bromo‐4‐oxybiphenylene‐4′‐carbonyl) (PBOBC) and poly(5‐bromo‐6‐oxy‐2‐naphthoyl) (PBONY) have been polymerized as lamellar single crystals using the confined thin film melt polymerization (CTFMP) technique. Electron diffraction indicates a triclinic (pseudo‐orthorhombic) unit cell with a12.71, b3.85, c10.50 Å, αβγ90° for PBOBC and a monoclinic unit cell with a13.02, b4.06, c17.15 Å, β101° for PBONY. The crystal structures of the two polymers have been simulated by the Cerius2 program and are suggested to have space group P for PBOBC and space group P121/c1 for PBONY. DSC measurements indicate that these two bromo‐substituted fully aromatic polyesters have crystal‐mesophase transition temperatures (Tk‐m389°C for PBOBC and 429°C for PBONY) with TGA indicating the onset of degradation at similar temperatures (400 and 420°C). The Tk‐m are between those of the corresponding non‐substituted and phenyl‐substituted aromatic polyesters. Possible reasons for the Tk‐m differences are considered in detail.
Novel aspects of the microstructure of poly(ethylene oxide) as revealed by microhardness: Influence of chain ends
Authors: Calleja F. J. Baltá , Cruz C. Santa 
Published: April 2003

AbstractThe microhardness (H) of a series of melt crystallized samples of poly(ethylene oxide) (PEO) was investigated as a function of molecular weight and crystallization temperature (Tc). It is shown that for a given molecular weight, H and the crystal hardness (Hc) increase with Tc, following a thermodynamic approach which takes into account the dependence of Hc upon crystal thickness (ℓc). A combined analysis of H‐data and DSC results reveals that, both the surface free energy (σe) and the hardness‐derived parameter b of the samples of unaffected by Tc. The microhardness of the PEO samples was markedly affected by molecular weight. Furthermore, it is shown that the molecular weight variations produce changes in the surface free energy due to variations in the number of chain ends on the crystal surface, giving rise to a parallel variation in the b parameter. As a consequence, the melting temperature and the crystal hardness exhibit a similar dependence on crystal thickness.
Synthesis in microemulsion and characterization of low charge density ampholytic terpolymers
Authors: Neyret S. , Candau F. , Selb J. 
Published: April 2003

AbstractHigh molecular weight and low charge density ampholytic terpolymers based on acrylamide (AM), as a neutral monomer, and sodium 2‐(acrylamido)‐2‐methylpropanesulfonate (NaAMPS) and [2‐(methacryloyloxy)ethyl]trimethylammonium chloride (MADQUAT) as charged monomers have been prepared by a microemulsion polymerization technique. An optimization of the process for the selection of the different components of the microemulsion has been achieved by applying criteria based on the hydrophile‐lipophile balance (HLB) and cohesive energy ratio concepts. Composition‐conversion curves were determined for samples containing different monomer feeds. The drifts observed in the terpolymer compositions with conversion were compared to those calculated from the reactivity ratios determined in binary copolymerizations performed in solution and in microemulsion. The results show that the reactivity of the monomers in ternary systems depends on the ionic strength, i.e. on the monomer feed composition.
Seeded emulsion polymerization of butylacrylate: “Zero‐one or pseudo‐bulk?”
Authors: Zirkzee H. F. , Van den Enden M. J. W. A. , Van Kilsdonk W. T. , Van Herk A. M. , German A. L. 
Published: April 2003

AbstractThe kinetics of the emulsion polymerization of butyl acrylate at 20°C in Smith‐Ewart interval III were investigated using a redox initiator system peroxodisulfate–bisulfite–copper. The aim of this work was to obtain more basic knowledge about the kinetic behavior of the butyl acrylate system. Monomer conversion into polymer was based on gravimetrically calibrated online densitometry. The experimentally obtained conversion versus time curves for these seeded reactions were fitted by a linear regression procedure (slope and intercept) as well as by a nonlinear regression procedure based upon zero‐one kinetics. The conclussion is that the emulsion polymerization of butyl acrylate may reflect zero‐one kinetics up to a particle size of approximately 130 nm. The rate coefficients for entry and exit can be obtained fairly accurately with the slope and intercept procedure and with the nonlinear regression method if the propagation rate coefficient is accurately known. However, this is not the case. Therefore the development of universal procedures for obtaining the propagation rate coefficients is essential, since this parameter is of paramount importance in all further model calculations concerning emulsion polymerization.
Polymerization of styrenes and acrylates carrying dendrons of the first and second generation
Authors: Neubert I. , Klopsch R. , Claussen W. , Schlüter A.‐D. 
Published: April 2003

AbstractThe synthesis of dendronized acrylate and styrene monomers with Fréchet‐type as well as urethane‐based dendrons of the first and second generation and their radically initiated polymerization to the high molecular weight dendrimers 6(G‐1,2) and 8a(G‐2) is reported. The latter polymer carries four THP‐protected hydroxy functions per repeat unit whose quantitative deprotection is also described.
Trends in polymer chemistry 1996
Authors: Frey H. , Kressler J. , Richtering W. , Mülhaupt R. 
Published: April 2003

AbstractImportant advances have been made in controlled radical polymerization, particularly in the application of the new technique for the preparation of novel block copolymers. CO‐copolymers are becoming increasingly popular. Increasing research efforts are also being devoted to discrete supermolecular structures as well as the preparation of nanometer‐size noble metal clusters in polymer matrices. MALDI‐TOF continues its triumph in synthetic polymer chemistry.
NMR imaging of the competitive vulcanization of natural rubber and polybutadiene blends
Authors: Klei B. , Koenig J. L. 
Published: April 2003

AbstractNMR imaging was used to study the spatial heterogeneity of the molecular mobility of the competitive vulcanization of natural rubber and high‐cis polybutadiene blends. The NMR images showed the presence of domains of widely different molecular mobilities. This heterogeneous mobility reflects differences in the crosslink density internal to each component of the blend. The differences in the internal crosslink density probably arise from differences in diffusion and solubility of the curatives. Additionally, overall, the poor dispersion of sulfur and accelerator due to inadequate mixing also contributes to the heterogeneity.
Anthracenol[2,3‐C:6,7‐c′]difuran, a new monomer for diels—alder polyaddition reactions
Authors: Kintzel O. , Schlüter A.‐D. 
Published: April 2003

AbstractThe anthracenedifuran precursor 7 was obtained in a short sequence from its lower homologue 1. On thermal treatment, 7 generates the highly Diels‐Alder (DA)‐active anthracenodifuran “8”. Its bisdiene character is proved by trapping with diquinone 9, which gives the [9]cyclacene derivative 10 and oligomeric material.
New approaches to advanced polymers by selective cellulose functionalization
Authors: Klemm D. , Heinze T. , Philipp B. , Wagenknecht W. 
Published: April 2003

AbstractThe uniform structure of cellulose, combined with its hydrophilicity, biocompatibility, chirality, and structure‐forming capacity, as well as its broad synthetic potential, make the design of cellulose‐based advanced materials a challenge for polysac‐charide research. The synthesis of new cellulose products with regiocontrolled pattern of functionalization and of well defined supramolecular nanoscale architectures is a highlight in recent cellulose chemistry.The present feature will discuss regioselective functionalization of cellulose and cellulose derivatives with respect to reactivity of the polymer depending on molecular and supramolecular structure. Experimental examples of functionalization via ester intermediates of controlled stability as well as via protecting or activating ether groups are described and the efficiency of the reaction routes and procedures is evaluated.Moreover, problems and progress in techniques of product analysis and structure–property relationships as well as potential applications of regioselectively functionalized cellulosics are presented together with a discussion of possible future developments in cellulose chemistry.
Polyesters with 1,4,7‐trioxanonyl segments in their main chain. Novel ion‐conducting matrices
Authors: Mertens J. J. A. , Jenneskens L. W. , Wentzel B. B. , Wübbenhorst M. , Van Turnhout J. , Van de Leur R. H. M. 
Published: April 2003

AbstractThe amorphous polyester 1a prepared by melt condensation of 1,5‐bis‐(9‐hydroxy‐1,4,7‐trioxanonyl)naphthalene (2a) and adipoylchloride (3a), which contains bis‐1,4,7‐trioxanonyl (triethyleneglycol) segments in its main chain, represents a matrix for ion‐conducting materials. Despite the fact that only triethyleneglycol segments are present, which are shorter than the minimum required for full solvation of Li+ cations, ion‐conductivities of σ = 3.3 times; 10—5 S cm—1 at 368 K are found for Li+/1a 0.25 (cations per polymer repeat unit). Hence, more than one bis‐1,4,7‐trioxanonyl segment (either intra‐ or interchain) has to be involved in Li+ complexation. The σ value compares favorably with previous data for more complex polymer matrices.
Poly(norbornene carboxylic acid ester)s: Synthesis and properties
Authors: Heinz B. S. , Heitz W. , Krügel S. A. , Raubacher F. , Wendorff J. H. 
Published: April 2003

AbstractThe vinylic polymerization of 5‐norbornene‐2‐carboxylic esters with different palladium catalysts to polymers of high molecular weights is reported. Computer simulations based on a force field approach show that these polymers display a rigid statistical chain conformation and are thus a further example of rotationally strongly constrained polymers. The polymers are soluble in a variety of solvents despite their rigidity, they are amorphous, possess glass transition temperatures well above 250°C, and have a high packing density. The dipoles located in the lateral groups perform a secondary relaxation process similar to the case of flexible or rigid rod‐like polymers containing ester groups.
Photochemical and photopolymerization study of 2,6‐dihalogen derivatives of p‐nitroaniline in the presence of N,N‐dimethylaniline as a bimolecular photoinitiator system
Authors: Costela A. , Garcia‐Moreno I. , Diaz F. , Dabrio J. , Sastre R. 
Published: April 2003

AbstractSteady‐state photolysis at 365 nm has been employed to carry out a structure—reactivity investigation of the 2,6‐dihalogen derivatives of p‐nitroaniline (pNA). Detailed studies of the spectroscopy of these molecules were accomplished. Photoreduction behavior of the 2,6‐dihalogen derivatives of p‐nitroaniline in the presence of N,N‐dimethylaniline (DMA) has been analyzed. The efficiency of these compounds as photoinitiators was studied by following the polymerization kinetics of the lauryl acrylate (LA) monomer by differential scanning photo‐calorimetry (Photo‐DSC) under aerobic and anaerobic conditions. Using size exclusion chromatography (SEC) analysis of the polymers their number‐average molecular weights, the number‐average degree of polymerization, and the length of the kinetic chain were determined and information on the nature of the end‐chain groups and the chain‐transfer behavior of these photoinitiators systems were obtained. The polymerization activity of the 2,6‐dihalogen derivatives of pNA proved to be higher than those obtained with conventional aromatic ketone photoinitiators.
In situ conductivity of a low band‐gap conducting polymer: Measurement of intrinsic conductivity
Authors: Huang H. , Pickup P. G. 
Published: April 2003

AbstractIn situ conductivity measurements on the low band‐gap polymer, poly‐4‐dicyanomethylene‐4H‐cyclopenta[2,1‐b;3,4,b′]dithiophene have provided both p‐ and n‐type conductivities as a function of the potential. A minimum in the conductivity, at a potential between the formal potentials for p‐ and n‐doping, yields an intrinsic conductivity of 1.0 × 10−8 S cm−1, consistent with the optical band‐gap of ∼0.8 eV.
Impact of degradation mechanisms on poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) during composting
Authors: Eldsäter C. , Albertsson A.‐C. , Karlsson S. 
Published: April 2003

AbstractThe individual impact of different degradation mechanisms occurring during composting on the degradation of poly(3‐hydroxybutyrate‐co‐6%‐3‐hydroxyvalerate) [poly(3HB‐co‐6%‐3HV)] have been assessed in simulated tests. Biotic hydrolysis with Aspergillus fumigatus had the largest impact on the breakdown of poly(3HB‐co‐6%‐3HV) during composting conditions, with small changes in molecular weight and large weight loss. The major degradation products in the biotic environment were 3‐hydroxy butyric acid and 3‐hydroxy valeric acid. Abiotic hydrolysis during composting conditions (sterile water pH 7 at 60°C) has minor or no effect during such short times as 21 days. During abiotic hydrolysis both monomers and dimers were idientified while the abiotic thermo‐oxidation of poly(3HB‐co‐6%‐3HV) showed no degradation at all. The quantitation of degradation products and copolymer composition analysis by 1H NMR indicate that the abiotic hydrolysis is not random. Crotonic and 2‐pentenoic acid which is produced at 100°C in air was not produced at 60°C during 298 days. We propose that this temperature is too low to promote the well‐known six‐member transition that produces crotonic acid, 2‐pentenoic acid and oligomers with crotonyl or pentenoyl end groups.
Stabilization of aqueous α‐Al2O3 suspensions with block copolymers
Authors: Orth J. , Meyer W. H. , Bellmann C. , Wegner G. 
Published: April 2003

AbstractWater‐soluble diblock copolymers (DBCPs) with a polyelectrolyte block are accessible by sequential anionic polymerization of tert‐butylmethacrylate (TBMA) and ethylene oxide (EO), followed by polymer analogous conversion of the PTBMA into poly(methyacrylic acid) (PMAA) blocks. These materials are highly efficient dispersants for oxide ceramic powders in aqueous media. A series of block copolymer samples with Mn ranging from 1300 to 38 900, and (EO:MAA) block length ratios from 0.5 to 11.7 were prepared with polydispersities close to 1.2. The influence of overall molecular weight and block length ratio, pH and ionic strength on the stability of aqueous α‐Al2O3 suspensions was investigated by sedimentation and adsorption experiments, surface plasmon resonance (SPR) and electrokinetic measurements. The copolymers are capable of stabilizing alumina suspensions by a combination of specific adsorption of one block on the particle surface and a shielding effect provided by the nonadsorbing block. In addition, the adsorption of the negatively charged PMAA block on the oppositely charged alumina surface reverses the electrophoretic potential of the oxide particles, a process which is strongly pH dependent. With respect to the powder dispersing efficiency, an optimum was found when the DBCP consisted of a short PMAA anchoring and an approximately tenfold longer PEO stabilizer block with an overall molecular weight of about 5000. Alumina suspensions with the DBCP added were highly dispersed and rather stable against salt addition in a much wider pH window than block‐copolymer‐free suspensions.
Highly conjugated alternated poly(3‐octylthiophene‐co‐thiophene)
Authors: Bolognesi A. , Bertini F. , Consonni R. , Mendichi R. , Schieroni A. Giacometti , Provasoli A. 
Published: April 2003

AbstractA soluble copolymer formed by thiophene and 3‐octylthiophene has been obtained by using nickel catalyst polymerization. The nearly alternated structure allows the formation of a highly conjugated system although the copolymer microstructure is not regioregular. 1H‐NMR, GPC characterization and pyrolysis experiments support the alternated structure of the copolymer. Moreover, theoretical calculations indicate that the average angle between adjacent monomeric units has been reduced, in agreement with the observed shift towards lower energy of the electronic spectra of this alternated structure.