bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combined liquid‐crystalline polymers: Rigid‐rod type main‐chain polyester with lateral mesogenic groups
Authors: Reck Bernd , Ringsdorf Helmut , Gardner Kenncorwin , Starkweather Howard 
Published: April 2003

AbstractA series of combined main‐chain side‐group liquid‐crystalline polymers was synthesized by melt polycondensation from trans‐1,4‐cyclohexanedicarboxylic acid, chloro‐1,4‐phenylene diacetate and 6‐(4‐methoxy‐4′‐biphenylyloxy)hexyl‐1,4‐phenylene diacetate. These polyesters combine the features of rigid‐rod main‐chain LC‐polymers and of side‐group LC‐polymers. Polymers with small fractions of mesogenic side‐groups (5 and 10 mol‐%) have lower melting points than the parent polymer poly(chloro‐1,4‐phenylene 1,4‐cyclohexanedicarboxylate) but are still liquid crystalline up to their decomposition at T ≥ 400°C. In polymers with larger fractions of mesogenic side‐groups (50 and 100 mol‐%) partial isomerization of the trans‐1,4‐cyclohexanedicarboxylate units to the cis‐form occurs. The cis units represent kinks which disrupt the rigid‐rod main‐chain structure, leading to non‐crystalline polymers with clearing temperatures below 350°C. The clearing temperatures of a series of polyesters with 100 mol‐% mesogenic side‐groups and trans contents ranging from 23 to 97% suggest that some interaction between mesogenic side‐groups and residual mesogenic segments in the main chain is required for the formation of a liquid‐crystalline phase. X‐ray diffraction patterns obtained from melt‐spun fibers show that the polymers with 5 and 10 mol‐% mesogenic side‐groups are highly crystalline and have a triclinic unit cell. The mechanical properties of the combined polymers were studied by means of dynamic mechanical thermal analysis (DMTA). Three different mechanical loss processes were observed. The glass relaxation was found to be more pronounced in the polymers with larger fractions of mesogenic side‐groups, suggesting that the latter have a plasticizing effect.
Effect of the structure of external alkoxysilane donors on the polymerization of propene with high activity Ziegler‐Natta catalysts
Authors: Seppälä Jukka V. , Härkönen Mika , Luciani Luciano 
Published: April 2003

AbstractPropene was polymerized in bulk in the presence of high activity heterogeneous Ziegler‐Natta catalyst with the purpose of finding correlations between the structure of an external alkoxysilane donor and the polymer. Nineteen silane compounds (1–8) of the structure RnSi(OR′)4‐n, where n = 1–4, R°C6H5, alkyl or H; R′ = C1–3‐alkyl, were used as external donors. The effect of Si/Al mole ratio was studied. The effect of the external alkoxysilane donor on the polymerization strongly depends on the number and size of alkoxy groups and the size of hydrocarbon groups attached to the silicon atom. Two major effects were observed: selective deactivation of atactic active centers and the increased production of high‐molecular‐weight isotactic polypropylene. Evidently, at least one free non‐hindered alkoxy group in the complex between alkoxysilane and AlEt3 is required for the selective deactivation. Also, the size of the hydrocarbon group of the donor strongly influences the selectivity of the deactivation.
Low‐molecular‐weight copolymers composed of L‐lactic acid and various DL‐hydroxy acids as biodegradable carriers
Authors: Fukuzaki Hironobu , Aiba Yoshikazu , Yoshida Masaru , Asano Masaharu , Kumakura Minoru 
Published: April 2003

AbstractBiodegradable copolymers of L‐lactic acid (L‐LA) and DL‐α‐hydroxy acids with relatively low molecular weights, for example L‐LA/DL‐lactic acid (DL‐LA), L‐LA/DL‐α‐hydroxybutyric acid (DL‐HBA), L‐LA/DL‐α‐hydroxyisovaleric acid (DL‐HIVA), and L‐LA/DL‐α‐hydroxyisocaproic acid (DL‐HICA), were synthesized by quantitative direct copolycondensation without catalysts at 200°C. The in vitro degradation, which was evaluated by measuring the weight loss of these copolymers in M/15 phosphate buffer solution (pH 7,2) without enzymes at 37°C, is strongly dependent on the kind and molecular weight of these copolymers, resulting in the formation of different degradation patterns such as parabola type (L‐LA/DL‐HBA system), linear type (L‐LA/DL‐LA system), and S type (L‐LA/DL‐HIVA and L‐LA/DL‐HICA systems).
Stable free radical paramagnetic monomers containing aminoxylamine oxide moieties. An intermediate step toward organic ferromagnetic polyradicals
Authors: Dulog Lothar , Kim Jeong Soo 
Published: April 2003

AbstractCondensation reactions of 2,3‐dimethyl‐2,3‐butanediyldihydroxylamine (2) with three monomeric aldehydes, 4‐vinylbenzaldehyde, 4‐ethynylbenzaldehyde and 2‐propynal (1a–1c) were performed to give the 1,3‐dihydroxy‐4,4,5,5‐tetramethylimidazolidine derivatives 3a–3c, which were oxidized to the corresponding stable free radical aminoxylamine oxides 4a–4b and the unstable radical 4c. The monoradical 4b was coupled to the diradical 4d. The measured molar paramagnetic susceptibilities of the aminoxylamine oxides 4a, 4b, 4d approached the theoretical value, according to the Curie‐Weiss law. All electronic absorption spectra showed the strong characteristic absorption maxima of aminoxylamine oxide stable free radicals. ESR spectra in diluted solution showed a 2nI + 1 pattern for the monoradicals 4a–4c and 4nI + 1 pattern for the diradical 4d.
Physical properties of biaxially oriented poly(ethylene terephthalate) film as affected by dimethyl sulfoxide
Authors: Hsieh You‐Lo , Timm Debra A. , Göritz Dietmar , Reichert Werner 
Published: April 2003

AbstractThe effects of a strongly interacting solvent, i.e., dimethyl sulfoxide (DMSO), on several physical properties of biaxially oriented and annealed (210°C) poly(ethylene terephthalate) (PETP) films were investigated. Physical properties which reflect changes in bulk morphology such as density, thermal behavior, tensile properties, and deformation dilatometric measurements were found to be dependent upon the temperatures of solvent treatment in the range between 60 and 160°C. The densities of PETP films were lowered to a minimum at solvent temperatures of 100 and 120°C with a slight recovery at higher temperatures. A similar dependence on solvent temperature was also observed on the heat of fusion and yield stress data. The pressure decrease in dilatometric measurements during step‐wise deformation of untreated PETP were explained by gas adsorption. Gas adsorption may be due to decreased molecular order in PETP during deformation. Higher gas adsorption on PETP treated with DMSO at temperatures at and above 80°C further substantiated that internal spaces were induced by DMSO at elevated temperatures. These solvent‐induced spaces were deformed under stress, thus creating surfaces and spaces for additional gas adsorption. The results show that the energy from a strongly interacting chemical, such as DMSO, can induce microstructural changes in PETP below the previous processing (drawing and annealing) temperatures.
Rheo‐optical fourier‐transform infrared spectroscopy of polymers, 15. Orientational and modificational changes during uniaxial elongation of high‐, low‐ and linear low‐density polyethylenes
Authors: Siesler Heinz Wilhelm 
Published: April 2003

AbstractThe transient structural changes of high‐, low‐ and linear low‐density polyethylenes were studied by simultaneous mechanical and Fourier‐transform infrared (FTIR) spectroscopic measurements. The rheo‐optical FTIR data provide a detailed picture of the progress and extent of crystal‐axis orientation and orthorhombic‐to‐monoclinic phase transition during elongation up to 400% strain. Apart from a higher degree of orientation as a consequence of the mechanical treatment, high‐density polyethylene may be differentiated from the low‐density types by running through a maximum in the content of monoclinic phase upon neck formation. With reference to the investigated structural changes, the linear low‐density polyethylenes generally exhibit a behaviour intermediate to the high‐density and low‐density types.
Unvernetzte epoxid‐amin‐additionspolymere, 27. Hybridnetzwerke — Möglichkeiten der carbonsäureanhydridmodifizierung und nachvernetzung von epoxid‐amin‐prepolymeren
Authors: Klee Joachim 
Published: April 2003

AbstractThe reaction of cyclic dicarboxylic anhydrides (3) with prepolymers 2 (from aniline and 2,2‐bis[4‐(2,3‐epoxypropoxy)phenyl]propane (1)) results in new modified prepolymers 4–6 containing carboxylic groups and reactive glycidyl end groups. The structure of 4–6 was determined by IR, 1H NMR, 13C NMR spectroscopy, elemental analyses and M̄n (by v. p.o.) values. By simple heating to 100–140°C prepolymers 4–6 were crosslinked to hybrid networks (7). Their structure was studied by IR and solid‐state 13C NMR spectroscopy.
Molecular imprinting by noncovalent interactions. Enantioselectivity and binding capacity of polymers prepared under conditions favoring the formation of template complexes
Authors: Sellergren Börje 
Published: April 2003

AbstractA molecular imprinting procedure based on electrostatic and hydrogen bonding interactions was developed, resulting in polymers of high selectivity for complexing of L‐phenylalanine anilide. The polymerization conditions were chosen in such a way that the formation of solution complexes between methacrylic acid (MAA) and the template (L‐phenylalanine anilide) prior to polymerization would be favored. Thus, by increasing the ratio of MAA to the crosslinker (ethylene dimethacrylate, EDMA), polymers of a higher enantioselectivity and binding capacity were obtained. In the chromatographic mode, a high chiral separation factor (a = 3,4) was observed even for polymers prepared in presence of nearly 50 mol‐% MAA in the monomer mixture. However, the use of polymers prepared by initiating at a lower temperature (40 instead of 60°C) and polymers prepared using porogens of lower polarity (benzene instead of acetonitrile) only resulted in higher capacity factors (K'). The association constant for the binding of L‐phenylalanine anilide to the sites of an imprinted polymer as well as the number of accessible sites of the latter were estimated from a binding study using a batch and a chromatographic procedure.
Group transfer polymerization of methyl methacrylate in tetrahydrofuran with tetrabutylammonium cyanide as catalyst
Authors: Schmalbrock Urban , Sitz Hans‐Dieter , Bandermann Friedhelm 
Published: April 2003

AbstractGroup transfer polymerization of methyl methacrylate (MMA) in tetrahydrofuran with (1‐methoxy‐2‐methyl‐1‐propenyloxy)trimethylsilane (1) as initiator and tetrabutylammonium cyanide as catalyst was investigated. Beside a fast isomerization, only very slow dimerization reactions of the initiator in the presence of the catalyst were observed. Therefore, the system was found to behave like a living one. Values of M̄wM̄n approached 1,3 at low catalyst concentrations. Tacticity measurements yielded about 60% syndiotactic, 36% heterotactic and 3% isotactic triads. Induction periods in time‐conversion curves obtained with 1 as initiator and intercepts in the plots of the number‐average molecular weight (M̄n) vs. monomer conversion vanished, when the reaction was initiated with the first addition product of 1 and MMA. This is assumed to be a strong indication, that in the investigated system a slow initiation step between 1 and the first MMA unit precedes the propagation reaction.
Asymmetrically substituted liquid‐crystalline phthalocyanines and side‐chain polymers derived from them
Authors: Van der Pol Johan F. , Neeleman Ernst , Nolte Roeland J. M. , Zwikker Jan W. , Drenth Wiendelt 
Published: April 2003

AbstractAsymmetrically substituted, liquid‐crystalline phthalocyanines were synthesized. They contain one methoxy, six dodecyloxy and one acryloyloxy‐ or methacryloyloxydodecyloxy groups. The latter functions were polymerized under free radical conditions to give polymers with molecular weights between 9000 and 47000. The aggregation behaviour of the phthalocyanines in the polymer side chains was studied in solution by absorption and fluorescence spectroscopy. An enhanced intramolecular interaction between the phthalocyanines was observed. In the solid state this interaction is reflected in the spontaneous formation of a columnar structure. The polymers, however, do not display liquid‐crystalline behaviour. Temperature‐dependent luminescence measurements (at 4,2 – 300 K) were performed and the results are explained by the presence of an efficient energy migration process through the stacked phthalocyanine units.
Synthèse de polystyrènes chlorométhylés renfermant des radicaux tétrathiafulvalénylphénoxyméthyles
Authors: Bonfils Frédéric , Fabre Jean‐Marc , Giral Louis , Montginoul Claude , Mungroo Aumduth , Sagnes René , Schué François 
Published: April 2003

AbstractIn order to study the influence of the nature of the moiety bearing a tetrathiafulvalenyl group in the polymers upon the microlithographic properties of resists, poly(p‐chloromethylstyrene)s and poly(styrene‐co‐p‐chloromethylstyrene)s containing the 4‐tetrathiafulvalenylphenoxymethyl group with a variety of controlled molecular weights and molecular weight distributions were studied. The copolymers were all prepared by reaction of poly(4‐vinylbenzyl chloride) with potassium 4‐tetrathiafulvalenylphenolate (3). Without exception, the resulting poly[p‐chloromethylstyrene‐co‐p‐(tetrathiafulvalenylphenoxymethyl)styrene]s are highly insoluble. However, by reaction of potassium 4‐tetrathiafulvalenylphenolate with poly(styrene‐co‐p‐chloromethylstyrene) soluble copolymers could be prepared.
Cationic η3‐allylmetal complexes, 12. Oligomerization of styrene with cationic allylnickel compounds: Catalysts, products and the influence of phosphines
Authors: Ascenso José , Dias Alberto R. , Gomes Pedro T. , Romão Carlos C. , Neibecker Denis , Tkatchenko Igor , Revillon André 
Published: April 2003

AbstractThe complex [η3‐methylallyl(η4‐cycloocta‐1,5‐diene)nickel] hexafluorophosphate (2) was found to be an efficient catalyst for the oligomerization of styrene without using a Lewis acid. Oligomers and polymers with low degree of polymerization were obtained and characterized by GPC and NMR spectroscopy. Solvents and ligands have a strong effect on the catalyst activity, the molecular weight distributions and the polymer microstructure. The end groups were characterized in the case of the ligand‐free and the tributylphosphine and tricyclohexylphosphine‐modified systems. A terminal benzylidene group was observed except for the latter basic and bulky phosphine which led to a methylene terminal group. A mechanism involving a hydridonickel species is proposed.
Synthesis of polysulfone‐block‐polysiloxane copolymers, 5. A model study on the hydrosilylation side‐reactions
Authors: Torrès Ghislaine , Madec Pierre‐Jean , Maréchal Ernest 
Published: April 2003

AbstractAll the side‐reactions of a hydrosilylating model system (1‐allyloxy‐3‐phenoxy‐2‐propanol/. . .‐Si(CH3)2H in the presence of hexachloroplatinic acid (CPA); R = [CPA]/[SiH] > 10−4) are identified by 13C and 1H NMR. In such conditions the vinyl ether isomers and the residual silanes, formed when R < 10−4, are changed into several new species. The most important side‐reaction consists in a silane‐alcohol condensation (secondary alcohol of the model and, to a much lower extent, tertiary alcohol(tert‐butyl alcohol) used as solvent of CPA), which leads to silyloxygrafted moieities. Hydrogen formed in this condensation can partially saturate the vinyl ether isomers the remaining fraction of which is cyclized into a 2‐ethyl‐1,3‐dioxolane derivative. All the side‐reactions observed in the case of the model system take place when α,β‐diallyloligosulfones are polycondensated with α‐dimethylsilyl‐ω‐hydrooligosiloxanes.
Solution behavior of a graft copolymer in selective solvents for its backbone or grafts
Authors: Tuzar Zdeněk , Kratochvil Pavel , Procházka Karel , Contractor Kiran , Hadjichristidis Nicos 
Published: April 2003

AbstractAssociation of a graft copolymer polyisoprene‐graft‐polystyrene in solvent mixtures selective either for polyisoprene backbone (THF/heptane) or for polystyrene grafts (THF/ethanol; 1,4‐dioxane/ethanol) was studied by static and dynamic light scattering and sedimentation velocity. Values of molar mass and dimensions of graft copolymer micelles were determined, and qualitative information on the dynamics of the unimer ⇌ micelles equilibrium was obtained.
Complexation of poly(monobenzyl itaconate) and poly(N‐vinyl‐2‐pyrrolidone) in dilute solution
Authors: Pérez‐Dorado Angel , Piérola Ines F. , Baselga Juan , Gargallo Ligia , Radic Deodato 
Published: April 2003

AbstractUpon mixing dilute solutions (10−4 – 10−2 mol/l) of poly(monobenzyl itaconate) (PMBI) and poly(N‐vinyl‐2‐pyrrolidone) (PVP) in methanol, soluble polycomplex particles are formed. Here we report on the spectrophotometric determination of the turbidity of different solutions of PVP and PMBI as a function of polymer concentration and PVP molecular weight. Viscosity measurements were also performed. The polycomplex is weak. Polycomplex particles are more compact and much larger than separated chains of polyacid and polybase. No definite stoichiometry is observed and a microgel‐like structure is proposed.
Autoxidation von dienen mit polyfulven‐strukturelementen
Authors: Schädeli Ulrich , Neuenschwander Markus 
Published: April 2003

AbstractThe reactivity of dienes 1–8, trienes 9, 10 and polymer 11 towards autoxidation in benzene solution was studied systematically. Incorporation of oxygen into 1–8 and 10 was found to be characterized by an induction period, a nearly linear oxygen uptake during several days and a limit of 1 mol oxygen per diene or triene unit. 9 takes up two mole of oxygen, and solutions of 11 show no linear oxygen uptake. The rates of oxygen uptake of olefins 1–11 were measured using standardized reaction conditions. The resulting autoxidation rates are strongly influenced by the number of methyl groups at the diene unit as well as by the ring size. 13C NMR and GPC measurements of the isolated oxydation products from 1,4,5,6,7 and 10 show that linear chains of oligomeric polyperoxides are formed, which can be considered to be alternating copolymers of oxygen and the olefin. O2‐incorporation predominantly takes place in 1,4‐position of dienes 1,4,5,6,7 and in 1,6‐position of triene 10. The formation of low‐molecular‐weight endoperoxides was not observed. A plausible reaction mechanism involves diradical intermediates of type 20 and 21–23.
Orientation during the conversion of precursor polymer films to poly(arylenevinylene) films
Authors: Stenger‐Smith John D. , Lenz Robert W. , Wegner Gerhard 
Published: April 2003

AbstractPreliminary, systematic measurements of the drawing process of sulfonium salt precursor polymer films were obtained using an Instron tensile tester equipped with an environmental chamber, both of which were interfaced with a computer to measure variables such as stress, temperature, and strain. Under the conditions in which highly oriented samples were obtained, at high strain rates and with high heating rates, orientation appeared to be dependent upon the rate of strain but not upon the total strain. Measurements of the storage and loss moduli at similar heating rates revealed that the loss modulus and the ratio of loss modulus to the storage modulus increased with increasing temperature. These results suggest that the solid sulfonium salt precursor polymer of poly(p‐phenylenevinylene), PPV, undergoes a phase transition to form an intermediate, liquid‐like state during the thermal elimination reaction. Experiments were also performed at a lower strain and heating rate, in which the orientation did depend upon the total strain. However, these polymer films were not as well oriented as were the films drawn at the higher strain and heating rates. Taken together, these results suggest that the transition to a liquid‐like phase may be necessary in obtaining highly oriented samples.
Thermo‐oxidative degradation of polyamide 6 and 6,6. Kinetics of the formation and inhibition of UV/VIS‐active chromophores
Authors: Karstens Ties , Rossbach Volker 
Published: April 2003

AbstractThe thermal oxidation of polyamide 6 and 6,6 gives rise to azomethine groups (Schiff's bases) as a result of the reaction of aldehyde and ketocarbonyl groups with amino end groups. During the course of degradation, these azomethine groups react with each other in an aldol‐type condensation to produce conjugated unsaturated oligoenimine structures that absorb in the UV/VIS range. During aldol condensation, the amino end groups are re‐formed, allowing them to react again with the carbonyl groups which are continuously supplied by thermal oxidation (auto‐oxidation) to form azomethine groups once more. The concentration and sequence length distribution of the oligoenimine structures can be correlated to the concentration profiles of the amino end groups, carboxyl end groups, and carbonyl groups, in a kinetic model. The concentrations of the individual oligo‐enimine species calculated with the aid of the model, are in agreement with the figures found experimentally with UV spectroscopy. Sterically hindered phenols inhibit the formation of carbonyl groups, and thus indirectly counteract the formation of oligoenimine structures (kinetic model for the autoxidation of polymers).
Unvernetzte Epoxid‐Amin‐Additionspolymere, 31. Polykationen auf Basis von Epoxid‐Amin‐Additionspolymeren. Herstellung und Eigenschaften
Authors: Klee Joachim , Hörhold Hans‐Heinrich , Kremer Friedrich 
Published: April 2003

AbstractNew cationic polymers (4 and 8) with‐defined separation of charges were obtained by N‐quaternization of epoxide‐amine addition polymers with benzyl chloride, butyl bromide and methyl iodide. The termal decomposition of 4 and 8 starts at temperatures between 320 and 370°C. Dielectric measurements in the frequency range 102 to 107 Hz show a dependence of the conductivity on the temperature. The cationic polymer 4d exhibits a conductivity of δ = 10−6 S/cm at 89°C and 106 Hz.
Anionic polymerization of butyl cyanoacrylate by tetrabutylammonium salts, 1. Initiation processes
Authors: Eromosele Ighodalo Clement , Pepper David Charles 
Published: April 2003

AbstractAnionic polymerizations of butyl cyanoacrylate by tetrabutylammonium salts (acetate, cyano‐ and chloroacetates, and bromide) in tetrahydrofuran and 1,2‐dimethoxyethane show definite ‘retardation periods’ in presence of strong acids. The back‐extrapolated ‘retardation times’ are proportional to [Acid] and inversely proportional to [Salt] and to [Monomer]1,5. The deduced rate of chain‐initiation increases with temperature, in contrast to the negative temperature dependence of initiation by covalent amines. A stationary‐state theory of the retardation is proposed, having a composite initiation process, involving a reversible precursor stage.
Anionic polymerization of butyl cyanoacrylate by tetrabutylammonium salts, 2. Propagation rate constants
Authors: Eromosele Ighodalo Clement , Pepper David Charles 
Published: April 2003

AbstractAnionic polymerizations of butyl cyanoacrylate were initiated in tetrahydrofuran (plus a few experiments in 1,2‐dimethoxyethane) by the salts tetrabutylammonium hydroxide, bromide, acetate and three substituted acetates. The hydroxide gives near‐ideal ‘living polymerization’ kinetics, with kp close to 106l·mol−1. s−1 at 20°C. The kinetics of the reactions initiated by the acetates and bromide are analysed by the slow‐initiation‐no‐termination theory, using values of the initiation rate constants evaluated in Part 1. The kp values derived are in the same range as those from the OH‐initiated reactions and those of the zwitterionic polymerizations initiated with covalent bases, i.e., tertiary phosphines and amines. A ca. 4‐fold variation of kp with concentration of active species is given a speculative analysis in terms of dissociation from paired to free ions, yielding tentative estimates for k ≈ 105 and k ≈ 107l·mol−1·s−1 in THF at 20°C. Molecular weights were all high Mn ≈ 106, with Mw/Mn ≈ 2.