bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational study of sodium pectate from circular dichroism induced in dyes
Authors: Pal Medini Kanta , Mandal Nemai
Published: April 2003

Sodium pectate (1c) induces strong circular dichroism (CD) in 3,7‐bis(dimethylamino)‐1,9‐dimethylphenothiazinium chloride (2b) and weak CD in 1‐ethyl‐2‐[3‐(1‐ethyl‐2‐(1H)‐quinolylidene)propen‐2‐yl]quinolinium chloride (pinacyanol chloride) (4) and 2,8‐bis(dimethylamino)‐acridinium chloride (Acridine Orange) (3), and no CD in 3,7‐bis(dimethylamino)phenothiazinium chloride (Methylene Blue) (2a), besides inducing strong metachromasia in all these dyes. The signs of the CD spectra induced in the dyes 2b, 3 and 4 by pectate are opposite to those induced by hyaluronate (HYAT). Pectate is, thus, inferred to have a 31 helical conformation (like HYAT) with the sense of helicity opposite to that of HYAT. Such an inference is also in harmony with the reported 3‐fold screw axis of pectate fibre from X‐ray crystallography. Since left‐handed extended helical polyglutamate induces negative biphasic CD, 1c, depicting positive biphasic CD with the same dye, may be assigned by analogy to have a right‐handed helicity.
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

A 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

Propene 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

Biodegradable 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

Condensation 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

The 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

The 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

The 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

A 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

Group 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

Asymmetrically 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

In 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

The 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

All 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

Association 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

Upon 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

The 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

Preliminary, 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

The 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

New 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

Anionic 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

Anionic 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.
Structural analysis of poly(3‐alkylthiophene)s
Authors: Leclerc Mario , Diaz Francisco Martinez , Wegner Gerhard
Published: April 2003

Poly(3‐hexylthiophene) (PT6), poly(3‐octylthiophene) (PT8), poly(3‐decylthiophene) (PT10) and poly(3‐dodecylthiophene) (PT12) were synthesized by electrochemical and chemical polymerization. Investigation of these polymers by means of gel permeation chromatography indicates that the polymers prepared from the different monomers under similar conditions do not differ substantially considering molecular weight and molecular weight distribution. Bimodal distributions were found for electropolymerized polymers, and with increasing polymerization time, the high‐molecular‐weight and probably highly branched fraction increased relatively to the low‐molecular‐weight fraction. The microstructure of the polymers was investigated by nuclear magnetic resonance, and it has been found that the polymers exhibit more types of structural units than expected from a simple coupling of adjacent thiophene moieties in 2,5′‐positions. Chemical oxidation with iron trichloride in chloroform gave soluble, high‐molecular‐weight poly(3‐alkyl‐thiophene)s with a rather low amount of irregular couplings, and these more regular polymers exhibited a higher degree of crytallinity. Room temperature conductivities of the oxidized polymers were between 0,1 and 30 S/cm depending on the polymerization conditions, but these values were rather independent of the length of the alkyl substituent.
Graft polymerization onto a polystyrene resin containing thermolabile azo groups and the effect of the grafted resin on asymmetric reduction of oxime ethers
Authors: Inoue Kenzo , Takemoto Hidemi , Tanigaki Teiichi
Published: April 2003

Graft polymerization of various vinyl monomers onto a polystyrene resin (6) containing azo groups having the ability to initiate the radical polymerization was performed. The graft efficiency of vinyl monomers onto 6 increases with time of polymerization and achieves more than 85%. The swelling of 6 affects remarkably the graft efficiency. Scanning electron microscopy (SEM) shows that considerable amounts of graft copolymers are located at the surface of 6. The graft copolymer of chloromethylstyrene onto 6 was treated with (S)‐(−)‐2‐amino‐3‐(p‐hydroxyphenyl)‐1,1‐diphenyl‐1‐propanol to yield a resin (9) carrying chiral amino alcohol functions. Resin 9/borane was used for asymmetric reductions of acetophenone oxime O‐methyl and O‐benzyl ethers, leading to 1‐phenylethylamine with 43% and 46% enantiomeric excess (e.e.), respectively. These values are higher than those obtained with the generally used polystyrene resin, suggesting that the enantioselectivity can be improved by modification of the support resin.
Effect of hydrogen on propene polymerization with solvay‐type TiCl3/Cp2 TiMe2 catalyst
Authors: Sun Lixin , Soga Kazuo
Published: April 2003

Polymerization of propene with a highly isospecific Solvay‐type TiCl3/Cp2TiMe2 catalyst in the presence and absence of hydrogen was investigated. It was found that hydrogen exerts almost no effect on the molecular weight and the stereoregularity of the resulting polypropylene. Furthermore, the H2/D2 exchange reaction hardly proceeds over the catalyst. To discuss this unusual behavior, plausible mechanistic explanations on the basis of the structure of active species are proposed.
Stabilization of polystyrene/poly(methyl methacrylate) blends by in situ compatibilization with graft copolymers
Authors: van Ballegooie Peter , Rudin Alfred
Published: April 2003

Copolymers of styrene and ortho‐vinylbenzaldehyde (o‐VBA) are useful precursors to multicomponent polymer systems. Graft copolymers of poly(styrene‐stat‐o‐VBA) can be produced by free‐radical chain transfer to methyl methacrylate monomer to yield materials that display some potential as interfacial agents with binary blends of polystyrene and poly(methyl methacrylate). Significant improvements in ultimate tensile strengths and energy to rupture values have been witnessed for polystyrene/poly(methyl methacrylate) mixtures that contain various levels of the graft component. Scanning electron microscopy of representative fracture surfaces demonstrate a decrease in the particle size of the dispersed phase; it is suggested that this morphological factor contributes to the superior mechanical properties of these composites. In this regard, both the isolated and the crude graft copolymers are able to compatibilize, and thereby enhance, the material properties of polystyrene/poly(methyl methacrylate) blends.
Orientational behaviour of polymer blends containing a liquid‐crystalline component
Authors: Uzman Mehmet , Kühnpast Kurt , Springer Jürgen
Published: April 2003

This paper describes the orientational behaviour of polymer blends containing a side‐group liquid‐crystalline polymer (LCP). The macroscopic orientation of the LC phase in these blends, and the possibility to freeze in this state are of technical interest. The orientation of LCP‐containing blends through mechanical forces depends on a variety of structural, thermal, energetical and also morphological properties, which are strongly dependent on the kinetical and thermal history. This report describes the optical‐ and scanning electron microscopy (SEM), X‐ray diffraction and interfacial tension studies of the liquid‐crystalline polyacrylate 1a and the poly(methacrylate) 1b in poly(methyl methacrylate) (PMMA) and polycarbonate matrices. 1a droplets in thermoplastic matrices can be oriented macroscopically during fibre‐drawing, but, as a result of higher interfacial tension between the components, 1b‐containing blends can not.
Tacticity and dielectric relaxation around the glass transition of poly(vinyl chloride), a dynamic‐dielectric study
Authors: del Val Juan José , Alegría Angel , Colmenero Juan , Mijangos Carmen , Martínez Gerardo , LuisMillán José
Published: April 2003

Molecular motions of poly(vinyl chloride) (PVC) in the glass transition range were studied by means of dielectric spectroscopy. The measurements were carried out with three different PVC samples obtained at different polymerization temperatures (0, 60 and 90°C) showing strong variations in their contents of syndiotactic, heterotactic and isotactic triads. The results show that all parameters (relaxation strength, temperature of the maxima of loss curves, evolution of the shift factors, master curves) characterizing the dielectric α‐relaxation in the liquid state of PVC are strongly affected by the tacticity. These facts are interpreted in terms of the role of specific local conformations in the motion of chain segments in the polymer molecules. These conclusions are in agreement with those outlined from the results previously obtained on PVC for the molecular motions in the glassy state just below the glass transition temperature.
Nematic elastomers: The influence of external mechanical stress on the liquid‐crystalline phase behavior
Authors: Schätzle Joachim , Kaufhold Wolfgang , Finkelmann Heino
Published: April 2003

The influence of external mechanical stress on the nematic‐isotropic phase transformation of nematic elastomers was investigated. The experimental results of IR‐dichroism measurements in the nematic phase and stress‐optical measurements in the isotropic phase are in good agreement with the theoretical predicitions of the phenomenological Landau‐de Gennes theory. This is for the first time that a significant influence of an external field on the nematic‐isotropic phase transformation temperature and on the nematic order parameter S has been proved.
Rigid rods with flexible side chains — A route to molecular reinforcement?
Authors: Heitz Thomas , Rohrbach Peter , Höcker Hartwig
Published: April 2003

Liquid‐crystalline main‐chain polyesters with polystyrene side chains of different length and number per main chain were synthesized using aromatic hydroxyfunctional polystyrene (PS) macromonomers, terephthalic acid derivatives and tert‐butylhydroquinone as co‐diol. The molecular weight of the polystyrene side chain was varied in the range from 1000 to 20000. The influence of this novel type of substituent on the solubility, thermal behaviour and miscibility with PS as a flexible matrix polymer is discussed. The properties of the new compounds are compared to those of the respective homopolyester. The graft copolyesters are, depending on the characteristics of the polymeric substituent, soluble in common organic solvents and their thermal transition points are lowered compared to the homopolyester. Compared to blends of the homopolyester, the improvement of miscibility of the polymer‐substituted rigid rods with PS as an example for a flexible matrix polymer can be valued as a step to molecular reinforcement.
Cyclization versus polymerization in phase transfer catalyzed polytioetherification
Authors: Shaffer Timothy D. , Kramer Michael C.
Published: April 2003

Some unexpected results were observed in the phase transfer of catalyzed (PTC) (two phase, aqueous‐organic) polymerization of α,ω‐dibromoalkanes with sodium sulfide. Alkane dielectrophiles containing fewer than six methylene units give rise to large, and sometimes quantitative, amounts of cyclic thioethers. These cyclic sulfides are formed under “polymerization” conditions and can be minimized by using only the monomer as the organic phase. Alkane dielectrophiles containing more than six methylene units yield only polymer. When a comonomer system composed of a 1:1 mixture of 1,4‐dibromobutane (DBB) and 1,8‐dibromooctane (DBO) is employed, the resulting copolymer's molecular weight and polydispersity are vastly improved compared to the corresponding homopolymerizations. Microstructurally, this copolymer is formed by complete consumption of DBO and partial incorporation of DBB. The remaining DBB forms tetrahydrothiophene (THT). These two odd and seemingly conflicting results could not be explained by “normal” or “inverse” PTC extraction mechanisms. Support of this new mechanism is given in the PTC polymerization of DBO with sodium sulfide in the presence of a catalytic amount of THT. The resulting polymer is of very high molecular weight and narrow polydispersity; it also does not contain tetramethylene sequences. Using this new mechanism, all results suggest the participation of cyclic sulfides either facilitates cyclic formation or enhance polymer reactivity as controlled by the length of the alkane dielectrophile.
Effect of ethyl benzoate on the microstructure distributions of olefin homopolymers and copolymers prepared with supported titanium catalyst
Authors: Wu Qing , Yang Nan‐Loh , Lin Shangan
Published: April 2003

The microstructure distributions of ethylene‐propene(EP) copolymers and propene homopolymers prepared with supported titanium catalyst were analyzed by 13C NMR spectroscopy. A two‐site model with an isospecific site and a non‐stereospecific site was used to describe the stereospecific polymerization of propene. A second two‐site model with individual r1r2 = 1 was applied to the analysis of the ethylene‐propene copolymerization. The addition of an external base, ethyl benzoate (EB), alters the relative concentrations of catalytic sites. Based on the comparison of the results from the homopolymers and copolymers prepared under different EB concentrations, the correlations between the stereospecificity and the activity toward the monomers were established: the isospecific site produces the copolymer with lower ethylene content; the non‐stereospecific site gives the copolymer with higher ethylene content.
Kinetic study of the polymerization of N,N′‐methylenebis(acrylamide) in aqueous dispersion systems
Authors: Capek Ignác , Funke Werner
Published: April 2003

The aqueous‐phase polymerization of N,N′‐methylenebis(acrylamide) initiated by potassium peroxodisulfate in the absence and in the presence of the anionic emulsifier sodium dodecylsulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the 0,75 and 0,24 oder with respect to potassium peroxodisulfate and N,N′‐methylenebis(acrylamide) concentrations, respectively. On the other hand, it is independent of the concentration of sodium dodecylsulfate. This agrees with the polymerization of a monomer soluble in water. Therefore, the equations for a homogeneous polymerization were applied to evaluate the experimental results. The calculated ratio kp/kt0,5 of the rate constants of propagation kp and termination kt for the N,N′‐methylenebis(acrylamide) polymerization at zero conversion in the absence of emulsifier are scattered in the interval between 3,1 and 3,4 dm1,5 · mol−0,5 · s−0,5 and in the presence of emulsifier in the interval between 2,4 and 3,5 dm1,5 · mol−0,5 · s−0,5. They are close to those obtained for the homogeneous polymerization of acrylamide in the aqueous phase. The lower values of kp/kt0,5 ≈ 0,3–0,6 dm1,5 · mol−0,5 · s−0,5 determined for the polymerization of N,N′‐methylenebis(acrylamide) for conversions between 30 and 60% follow from the hindered termination reaction within the polymer particles. The polymer dispersions formed are unstable. The growth of the polymer particles proceeds predominantly by coalescence. This suggests a kinetics which does not follow the Smith‐Ewart theory but is characterized by a continuous particle nucleation and agglomeration. The interval 1 occurs at the beginning of the dispersion polymerization when polymer particles are being formed. Interval 2 follows, once the number of polymer particles has been fixed.
UV and IR studies of the photolysis of poly(alkylsilane)s
Authors: Devaux Jacques , Sledz Joseph , Schué François , Giral Louis , Naarmann Herbert
Published: April 2003

UV and IR spectroscopy were used to follow the photolysis of poly(syclohexylmethylsilane) (1) and poly(hexylmethylsilane) (2). Striking correspondences were found between wavelengths at maximum absorption and absorbance in UV region and particular IR bands which undergo bleaching in parallel. New IR band assignments are proposed. In addition, there is some evidence of a random scission of the chains with no significant contribution of an unzipping process.
The molecular weight effect on the mesomorphic behaviour of liquid‐crystalline poly(ester‐β‐sulfide)s
Authors: Laus Michele , Angeloni Annino S. , Galli Giancarlo , Chiellini Emo
Published: April 2003

A DSC study is reported on the dependence of thermal properties on molecular weight in two series of thermotropic liquid‐crystalline poly(ester‐β‐sulfide)s, 9S4 and 9S5. The molecular weights range from approximately 1 600 to 14 000. All of the polymers exhibit a nematic phase preceded, at lower temperature, by a smectic A phase which is monotropic in the majority of the cases. The nematic‐isotropic transition temperatures and relevant entropy changes were found to be practically insensitive to molecular weight variations. In contrast, the smectic A‐nematic transition temperatures and entropy changes increase with increasing molecular weight and reach a plateau value at an average chain length of 6–7 repeating units. It is suggested that in the nematic phase of these polymers the flexible segment plays a role of diluent of the rigid groups, whereas at the nematic‐smectic A transition a cooperative increase in chain stiffness takes place.
Hydrophobic water‐soluble polymers, 1. Dilute solution properties of poly(1‐vinyl‐2‐piperidone) and poly(N‐vinylcaprolactam)
Authors: Eisele Michael , Burchard Walther
Published: April 2003

Poly(vinyllactams) form a class of non‐ionic water‐soluble polymers from which only poly‐(1‐vinyl‐2‐pyrrolidone) (PVP) is well known and has been investigated extensively. The homologues poly(1‐vinyl‐2‐piperidone) (1, poly[1‐(2‐oxo‐1‐piperidyl)ethylene]) and poly(N‐vinylcaprolactam) (2, poly[1‐(2‐oxoperhydroazepin‐1‐yl)ethylene]) which are still soluble in water at room temperature have not yet been studied in aqueous solution. In this work the synthesis of these two polymers by radical polymerization in solution and the investigation of the dilute aqueous solution properties of these polymers by static and dynamic light scattering measurements are presented. Special attention is paid to the influence of the increasing hydrophobicity of these polymers on coil dimensions and structures in aqueous solution.
Effect of crosslinker on properties of copolymeric N‐vinyl‐2‐pyrrolidone/methyl methacrylate hydrogels and organogels
Authors: Davis Thomas P. , Huglin Malcolm B.
Published: April 2003

The γ‐ray initiated copolymerisation of N‐vinyl‐2‐pyrrolidone with methyl methacrylate in the presence of crosslinker has been effected to high conversion. At two fixed compositions of the principal monomers, the inclusion of different concentrations of the tetrafunctional crosslinkers ethylene dimethacrylate and a low molar mass poly(ethylene glycol) dimethacrylate produced crosslinked xerogels, which were subsequently swollen in water and 1,4‐dioxane to yield hydrogels and organogels, respectively. These gels were characterised by determinations of sol fraction, equilibrium solvent content and uniaxial compression stress/strain measurements. Differences among the swelling and mechanical properties according to the nature and concentration of crosslinking agent and according to the nature of the swelling medium are noted and discussed.
13C NMR studies of thermotropic liquid crystalline poly(γ‐alkylaryl L‐glutamate)s
Authors: Yamamoto Ryôta , Araki Kazuo , Imamura Yoshio , Asakura Tetsuo , Iizuka Eisaku , Iida Shûji
Published: April 2003

The molecular motions of three kinds of poly(γ‐alkylaryl L‐glutamate)s (1–3) having a phenylene or a biphenylylene group and alkyl groups with various length, containing 6 to 22 carbon atoms, were investigated by means of 13C NMR spectroscopy as a function of temperature. The observed range of temperature covers the “crystal‐to‐liquid‐crystal” phase transition temperature, Tm. It was found that these phase transitions are caused by an increase of the motions of aromatic or alkyl groups in the side chain, depending on the samples, and that the motion of main chains of polymers 1–3 with α‐helical conformation does not occur on the NMR time scale at least up to 160°C. The degree of the mobility of the alkyl chain in the side chain of 1–3 depends on their length above Tm.
Gradient high performance liquid chromatography of polymers, 1. Characterization of the products obtained by grafting methyl methacrylate onto ethylene‐propene‐diene rubber by SEC‐HPLC cross fractionation using evaporative light scattering detection
Authors: Augenstein Michael , Stickler Manfred
Published: April 2003

The products of the grafting reaction of methyl methacrylate (MMA) onto ethylenepropene‐diene rubber (EPDM) were characterized by size exclusion chromatography (SEC) and gradient HPLC to give detailed information about the grafting parameters. Evaporative light scattering detection (ELSD) was used for the quantitative evaluation of the HPLC runs. Gradient elution was shown to fractionate the grafting products according to chemical composition. By means of SEC‐HPLC cross fractionation the two‐dimensional distribution of chemical composition and molecular weight (CCMWD) was established qualitatively.
The use of low‐molecular‐weight model compounds in an investigation of polyelectrolytes, 2. Potentiometric properties of poly[(methacrylic acid)‐co‐(2‐dimethylaminoethyl methacrylate)] and its quaternary ammonium salt
Authors: Přádný Martin , Holata Jan , Ševčík Stanislav
Published: April 2003

The potentiometric behaviour of two polyampholytes, poly[(methacrylic acid)‐co‐(2‐dimethyl‐aminoethyl metharylate)] and poly{(methacrylic acid)‐co‐[2‐(methacryloyloxy)ethyltrimethyl‐ammonium iodide]} is described. The dissociation constants of low‐molecular‐weight compounds modelling the structural units and diads of polyampholytes are reported, and effects of adjacentgroups on the potentiometric behaviour of the copolymers are discussed.
Synthesis of polyorganosiloxanes with imidazolyl groups in the side chain
Authors: Nemoto Nobukatsu , Yotsuya Tadashi , Aoyagi Shigenobu , Ueno Yukihiko , Ikeda Koji , Takamiya Nobuo
Published: April 2003

An imidazolyl ring was introduced into the side chain of poly(3‐chlorocarbonylpropylmethyl‐siloxane) (4) by esterification with 4(5)‐hydroxymethylimidazole (1), the imino group being protected during esterification by the 2‐nitrobenzyl group which can be easily cleaved by UV light irradiation without attacking the main chain. The photolytic cleavage of the 2‐nitrobenzyl group was completed with a yield of ≈ 100% after 2 h without any remarkable side reaction. The polyorganosiloxanes (6), with a high content of imidazolyl groups in the side chain, are slightly soluble in hot DMSO and DMF. From this fact, in addition to the result of the measurement of Tg, it is suggested that very strong intermolecular hydrogen bonds are operating.
Liquid‐crystalline polyimides, 1. Thermotropic poly(ester‐imide)s derived from 4‐hydroxyphthalic acid, 4‐aminophenol and various aliphatic α,ω‐diacids
Authors: de Abajo Javier , de la Campa José , Kricheldorf Hans R. , Schwarz Gert
Published: April 2003

Poly(ester‐imide)s with a regular sequence of aliphatic spacers and aromatic imide mesogens were prepared in two ways. Either aliphatic α,ω‐diacids were condensed with an acetylated diphenol derived from 4‐hydroxyphthalic acid and 4‐aminophenol, or aliphatic α,ω‐diacid dichlorides were condensed with the silylated diphenol. The resulting poly(ester‐imide)s were characterized by elemental analyses, viscosity measurements, microscopy under polarized light, DSC‐ and WAXS measurements. All poly(ester‐imide)s are crystalline materials with a layered supermolecular structure in the solid state. Above the melting point a nematic mesophase exists over a broad temperature range. A pronounced odd‐even effect was found for the temperature of isotropization, but not for the melting points.
Studies on the kinetics and initiation mechanism of acrylamide polymerization using persulfate/aliphatic diamine systems as initiator
Authors: Guo Xin Qiu , Qiu Kun Yuan , De Feng Xin
Published: April 2003

The effects of various aliphatic diamines on vinyl polymerization using ammonium persulfate as initiator were studied. It was found that diamines with two amino groups separated by an ethylene unit possess higher promoting activities than those with two amino groups linked by other α,ω‐alkylene units such as methylene or propylene. The promoting activities of diamines on vinyl polymerization are in the order: tertiary diamine > secondary diamine > primary diamine. The methyl group is a preferred substituent at the amino groups of the diamine, being faster oxidized by persulfate (to produce the dialkylaminomethyl free radical) than the α‐methylene groups. The primary free radicals produced through redox‐reaction of persulfate and aliphatic diamines were studied using the spin trapping technique and ESR spectroscopy. An initiation mechanism of persulfate/aliphatic diamine systems is proposed.