bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid crystal elastomers: Influence of the orientational distribution of the crosslinks on the phase behaviour and reorientation processes
Authors: Küupfer Jürgen , Finkelmann Heino 
Published: April 2003

AbstractThe influence of the crosslinking conditions on the phase behaviour and reorientation processes of nematic elastomers is investigated. Two series of elastomers with various network anisotropies crosslinked either in the nematic or in the isotropic state were investigated by means of IR‐dichroism and stress‐strain measurements. The experimental results clearly demonstrate that for nematic elastomers not only the coupling between the network anisotropy and the state of order has to be considered. It is shown that the influence of the crosslinks and their orientational distribution on the phase behaviour, the state of order as well as on director reorientation processes cannot be neglected.
Copolymerization of olefins with SiO2‐, Al2O3‐, and MgCl2‐supported metallocene catalysts activated by trialkylaluminiums
Authors: Soga Kazuo , Kaminaka Manabu 
Published: April 2003

AbstractCopolymerizations of ethylene with propene, of ethylene with 1‐hexene and of propene with 1‐hexene were carried out at 40°C under atmospheric pressure with SiO2‐, Al2O3‐ and MgCl2‐supported metallocene catalysts using common alkylaluminiums as cocatalyst. From a detailed analysis of copolymers by 13C NMR, all the copolymers obtained were found to be random (r1·r2 ≤ 1). When ethylene was used as a base monomer, the polymer yield markedly increased with increasing comonomer concentration. The molecular weight of the copolymers obtained in this study were found to be much higher than those obtained with homogeneous Kaminsky‐Sinn catalysts. Whereas, the polydispersity (Mw/Mn) of the copolymer is dependent on the combination of monomers as well as on the inorganic compounds used as carrier.
Phase separation in poly(methyl methacrylate)‐block‐poly(2,3‐dibromopropyl methacrylate) copolymers
Authors: Davy Kenneth W. M. 
Published: April 2003

AbstractAB block copolymers poly(methyl methacrylate)‐block‐poly(2,3‐dibromopropyl methacrylate) were prepared by a two‐stage process involving the sequential anionic polymerization of methyl methacrylate and allyl methacrylate followed by bromination of the pendant allylic groups. Transmission electron microscopy of thin sections of cast films revealed phase separation, the morphology depending upon composition of the block. In particulate form these copolymers gelled with methyl methacrylate to form doughs that could be moulded and heat cured to produce hard X‐ray opaque copolymers.
Production of poly(β‐hydroxyalkanoates) with β‐substituents containing terminal ester groups by Pseudomonas oleovorans
Authors: Scholz Carmen , Fuller R. Clinton , Lenz Robert W. 
Published: April 2003

AbstractPseudomonas oleovorans was grown separately on the methyl, ethyl and tert‐butyl esters of octanoic, nonanoic and decanoic acid in attempts to obtain poly(β‐hydroxyalkanoates), PHAs, with ester groups at the terminal position of the β‐substituent. The growth rate increased from methyl to tert‐butyl esters, but the rate for the slowest growing substrates, the methyl esters, could be accelerated by using special feeding techniques, either by prefeeding with sodium acetate or by cofeeding with a good growth and polymer producing substrate, sodium octanoate. For the ethyl esters the prefeeding technique had minimal success, but a considerable increase of the growth rate was achieved by starting the bacterial growth with a pre‐culture that was grown on the substrate under investigation. Tert‐butyl nonanoate as the substrate gave the most rapid growth, but the growth rate was not influenced by special feeding techniques. All of these substrates formed copolymers which contained up to eight different repeating units and some had terminal ester groups on alkane side chains of varying lengths. The use of methyl esters as substrates resulted in the incorporation of a reasonably high degree of pendant methyl ester groups in the polymer produced, and the amount of repeating units carrying pendant ester groups dependend directly on the oxygen supply available to the bacterial culture. The fermentation of substrates with ethyl ester groups resulted in the formation of copolymers containing either unsubstituted units or units containing either ethyl or methyl ester groups, or both. The reason for this unexpected behavior was not clarified. The large tert‐butyl ester group was not maintained as a substituent group in the polymer, but instead, growth on this substrate always resulted in producing polymers consisting of the unsubstituted repeating units expected from the corresponding carboxylic acid alone.
Structural analyses of poly(m‐xylene‐α,α′‐diyladipamide) and nylon 66 by 15N solid state NMR
Authors: Yeo Joo‐Hong , Asakura Tetsuo , Shimazaki Hisashi 
Published: April 2003

Abstract15N solid state NMR, viz. both 15N cross polarization (CP) NMR and 15N CP/magic angle spinning (MAS) NMR, is applied to the structural determination—including molecular orientation—of uniaxially oriented poly(m‐xylene‐α,α′‐diyladipamide) film and nylon 66 fiber on the basis of the chemical shift tensors. In the spectrum of a poly(m‐xylene‐α,α′‐diyladipamide) block sample whose fiber axis was set up parallel to the applied magnetic field, a single main peak with 20% powder pattern (non‐crystalline domains) was observed. The small difference in the structure of the main chain between these two uniaxially stretched polyamides was clarified from the chemical shift data of the parallel spectra which reflect the angle between the NH bond and the fiber axis. Determinations of the angles between various molecular‐fixed axes and the axis of polymer alignment were tried.
Modelling of size‐exclusion chromatograms from molecular weight distribution calculations. Application to the grafting of polymers onto functionalized silica
Authors: Guillot Jean , Leroux Denis 
Published: April 2003

AbstractThe objective of this paper is the modelling of the molecular weight distribution (MWD) and the polydispersity index (P. I.) of polystyrene grafted on porous silica beads prefunctionalized by a thiosilane molecule. Grafting occurs by a transfer reaction to the fixed mercapto groups. We have analysed the MWD of both grafted and ungrafted polymers by size‐exclusion chromatography (SEC). A good agreement between the experimental SEC diagrams and those calculated from the reaction rate constants is obtained with the following hypotheses: (1) the medium is a two‐phase system constituted of an interparticle phase and a porous intraparticle phase with a high local mercapto group concentration in the pores; (2) a higher transfer efficiency of the transfer agent in the pores (what could be attributed to a higher mobility of the very short chains inside the pores); (3) a lower termination rate in the pores, which results in a higher rate of polymerization than in the interparticle phase (probably due to an increase of the medium viscosity).
Nuclear magnetic resonance spectroscopic characterization of carboxymethylcellulose
Authors: Baar Andreas , Kulicke Werner‐Michael , Szablikowski Klaus , Kiesewetter René 
Published: April 2003

AbstractPrevious assignment of the signals in the spectra of carboxymethylcellulose, based on an incremental calculation and hence on low‐molar‐mass model substances, made determination of the partial degree of substitution fundamentally impossible because overlapping of the relevant signals was predicted. However, the methods of acid and enzymatic hydrolysis employed generate the monomer or a mixture of polymers, oligomers and monomers and hence a large number of end groups, which also influence the nuclear magnetic resonance (NMR) spectra. By using ultrasound, it was possible to degrade the molar mass (lower limit of molar mass approx. 100000 g/mol), without oligomers being generated and cleavage of side groups occuring. The viscosity of 10 wt.‐% polymer solutions was so low that the partial degree of substitution could be determined quantitatively for the first time. An additional 13C NMR spectroscopic examination of the acid hydrolysate enabled the composition of the eight monomers of sodium carboxymethylcellulose (NaCMC) to be determined in a degree of substitution (DS) range of 0,8–3,0. Knowledge of the monomer compositions is then used to reassign the signals of the polymer spectra, which are then evaluated. Comparison with titrimetric methods (polyelectrolyte titration and ASTM method) showed some wide discrepancies with the absolute method (NMR) in the case of samples with a DS greater than 1. The results of the 13C NMR spectroscopic examination of the acid hydrolysate were also used to determine the relative rate constants of the etherification reaction (k2:k3:k6 = 3,0:1,0:2,1), and these were then compared with published data.
Structure of polypropene and poly(ethylene‐co‐propene) produced with an alumina‐supported CpTiCl3/common alkylaluminium catalyst system
Authors: Soga Kazuo , Uozumi Toshiya , Saito Masayoshi , Shiono Takeshi 
Published: April 2003

AbstractBoth propene polymerization and ethylene/propene copolymerization were conducted with an Al2O3‐supported CpTiCl3 (Cp: cyclopentadienyl) catalyst using a common alkylaluminium as cocatalyst. The catalyst system gave atactic polypropene with frequently inverted propene units which are randomly distributed over the polymer chain. The structure of poly(ethylene‐co‐propene) produced with the catalyst system was found to be very different from that obtained with ordinary titanium based catalysts.
Fractionation of polypropylene according to molecular weight and tacticity
Authors: Lehtinen Arja , Paukkeri Ritva 
Published: April 2003

AbstractDifferent extraction techniques were applied to the fractionation of isotactic polypropylene. In solvent gradient extraction experiments two different solvent/non‐solvent systems were studied. Investigation of the fractions obtained by GPC, DSC and FTIR indicated that the fractionation proceeded according to molecular weight when ethylene glycol monobutyl ether/diethylene glycol monobutyl ether was used as a solvent/non‐solvent system at 159–161°C. The fractions covered a broad molecular weight range, had narrow molecular weight distribution and showed only small variations in their isotacticity. Xylene/ethylene glycol monoethyl ether combination at 121–128°C separated polypropylene in fractions mainly according to stereoregularity, the separation being less dependent on molecular weight. A large number of fractions with varying stereoregularity could be produced. Successive extraction with solvents of increasing boiling temperature gave fractions differing both in molecular weight and isotacticity, and was the only method to separate the stereoblock copolymer. Comparison of heptane extractables and xylene solubles methods showed differences in the structure and molecular weight of heptane and xylene soluble fractions and heptane and xylene insoluble fractions, respectively.
Liquid‐crystalline polysulfones, 4. Radiation‐induced degradation
Authors: Braun Dietrich , Arnold Norbert , Schmidtke Ingrid 
Published: April 2003

AbstractPolysulfones are degraded by high‐energy radiation with highly specific bond scission of the main chains. The effect of γ‐ and electron‐beams on selected liquid‐crystalline polysulfones was determined. The radiation‐induced degradation of polysulfones by elimination of the monomers can be used for electro‐optical displays.
(Co)polymers of L‐lactide, 2. Mechanical properties
Authors: Grijpma Dirk W. , Pennings Albert J. 
Published: April 2003

AbstractThe effect of copolymerization of L‐lactide with several lactones and cyclic carbonates and the processing variables in compression moulding of poly(L‐lactide) homopolymers on the mechanical properties was investigated. Sharp maxima in the impact strength versus comonomer composition and heat of fusion were obtained, reflecting the important role of the presence of a crystalline fraction in the material. Crystalline domains increase the interconnectivity of a physical polylactide network and decrease the molecular weight between these physical crosslinks. The brittle strength concomitantly increases, and as the yield stress remains more or less constant, an increase in impact strength is observed. Very high crystalline as‐polymerized poly(L‐lactide) prepared with less active catalysts on the other hand has an extremely low entanglement density and therefore a low brittle tensile strength.
Synthesis and characterization of ether‐type chitin derivatives
Authors: Kim Seon Jeong , Kim Seong Soo , Lee Young Moo 
Published: April 2003

AbstractNovel ether‐type chitin derivatives were synthesized by reacting alkali salts of chitin with 1‐chloropropane, propylene oxide and 3‐chloro‐1,2‐propanediol to prepare propylchitin (PPC), hydroxypropylchitin (HPC) and dihydroxypropylchitin (DHPC), respectively. The structures of these chitin derivatives were confirmed by FT‐IR and solid state CP/MAS 13C NMR spectrometry. The substituents are introduced primarily at the C6 position of the glucosamine unit in chitin, with a degree of substitution of approx. 30–50%. The three chitin derivatives are soluble in weakly acidic aqueous solutions, DHPC even in pure water.
Solvent effect on the methacrylic acid‐methyl methacrylate radical copolymerization. Analytical estimation by linear and nonlinear solvation energy relationships
Authors: Georgiev Georgi S. , Dakova Ivanka G. 
Published: April 2003

AbstractThe calculated methacrylic acid‐methyl methacrylate monomer reactivity ratios in toluene (rMA = 1,06 ± 0,02; rMMA = 0,10 ± 0,01), isopropyl alcohol (rMA = 0,33 ± 0,02; rMMA = 0,78 ± 0,03), acetone (rMA = 0,63 ± 0,02; rMMA = 0,31 ± 0,02) and acetonitrile (rMA = 0,46 ± 0,03; rMMA = 0,27 ± 0,03) depend strongly on the polarity, proton donor and proton acceptor ability of the solvent. It is proved that the solvent influence on the logarithm of the relative comonomer reactivities is expressed much better by the linear relationships of the solvatochromic polarity, proton donor and proton acceptor indexes than by the dependences reflecting these effects individually. The possibility of a statistically confident description of the complex solvent influence on the comonomer reactivities by quadratic solvatochromic relationships taking into account the interdependence of solvent effects is shown for the first time.
Chemical synthesis and complexing behaviour of branched cyclodextrins composed of an amylose and a β‐cyclodextrin residue
Authors: Kubik Stefan , Wulff Günter 
Published: April 2003

AbstractThe synthesis of a new class of branched cyclodextrins is presented. In these compounds an amylose residue with a degree of polymerization (DP) of 30 is attached to the C6 position of a β‐cyclodextrin molecule via an alkyl spacer. Hence, these hosts are composed of a combination of two different components linked covalently, both having individual properties. The complexing behaviour was investigated by circular dichroism (CD) spectroscopy. The CD spectra indicate that the inclusion geometry of some guest compounds into the β‐cyclodextrin cavity is influenced by the amylose side chain. However, an additional complexation of these guests inside the amylose helix was not observed.
Orientational distribution in stretched poly(methyl methacrylate) from 13C NMR spectroscopy
Authors: Kulik Andrzej S. , Spiess Hans Wolfgang 
Published: April 2003

AbstractThe orientational distribution in drawn amorphous poly(methyl methacrylate) extended to the ratio λ = 3 was measured with one‐ and two‐dimensional carbon‐13 NMR spectroscopy. In the analysis, signals from the carboxyl carbons were used as a probe of the orientational distribution. The angular‐dependent line shapes were analyzed to determine the orientational distribution function and the order parameter 〈P2〉. The analysis yielded 〈P2〉 = 0,21. A two‐dimensional rotor‐synchronized magic angle spinning experiment was also used to measure the order parameter. The obtained value 〈P2〉 = 0,22 is in excellent agreement with the 1D result. The experimental results obtained for 〈P2〉 are compared to those proposed by the pseudo‐affine model. 〈P2〉 predicted by theory is reduced due to conformational disorder present in the glassy state.
On the polymerization of N,N,N′,N′‐tetramethyl‐α,ω‐alkanediamines with dibromoalkanes—an in‐situ NMR study
Authors: Wang Jianguo , Meyer Wolfgang H. , Wegner Gerhard 
Published: April 2003

AbstractBased on the Menschutkin reaction, α,ω‐alkanediamines with α,ω‐dibromoalkanes were employed to synthesize cationic polyelectrolytes named ionenes. By means of in‐situ 13C NMR we have characterized the influence of ionic charges on the reactivity of the polymerizing species. The progress of aliphatic ionene polymerization has been found to be a complex reaction. At least four elementary building reactions and two side reactions (Hoffmann degradation and intramolecular cyclization) have been detected in the course of ionene polymerization. As a result, the broad molecular weight distribution which is usually found in ionenes can be explained in terms of the kinetics and by side reactions. Also, the difficulty of achieving high molecular weight ionenes can be understood on the basis of our NMR results.
Calorimetric study of 5‐trimethylsilyl‐2‐norbornene, of its polymerization process and of poly(5‐trimethylsilyl‐2‐norbornene) from 5 to 600 K at standard pressure
Authors: Lebedev Boris , Smirnova Natal'ya , Novosyolova Nina , Makovetskii Kiryll , Ostrovskaya Irina 
Published: April 2003

AbstractThermodynamic properties of 5‐trimethylsilyl‐2‐norbornene (TMSNB) and poly(5‐trimethyl‐silyl‐2‐norbornene) (PTMSNB), viz. the temperature dependence of the isobaric heat capacity Cop of the monomer between 10 and 330 K and of the polymer from 7 to 600 K, were studied by adiabatic vacuum and differential dynamic calorimetry. Temperature and enthalpy of monomer melting as well as parameters of glass transition and glassy state of the monomer and the polymer were determined. From the experimental data, the thermodynamic functions H°(T)‐H°(0), S°(T) and G°(T)‐H°(0) were calculated for TMSNB in the range of 0 to 330 K and for PTMSNB from 0 to 380 K. In a differential automatic calorimeter, the enthalpy of polymerization of TMSNB to PTMSNB in toluene solution was measured at T = 301 K and p = 101,325 kPa. Under similar physical conditions and in the same calorimeter, enthalpies of dissolution for the monomer and the polymer were estimated. The results were used to calculate the enthalpy, entropy and Gibbs function of bulk polymerization of TMSNB in the range of 0 to 380 K at standard pressure. The ceiling temperature of the polymerization process was also evaluated.
Iridescent coloration of a copolymer gel in an organic solvent
Authors: Gong Jianping , Okuzaki Hidenori , Osada Yoshihito 
Published: April 2003

AbstractA polymer gel formed from acrylic acid and methyl acrylate, moderately swollen in toluene or benzene, exhibits iridescent coloration. The color changes with temperature and composition of the gel. This phenomenon has been associated with specific scattering of light.
Preparation and characterization of fluorine‐containing aromatic condensation polymers, 4. Preparation and characterization of fluorine‐containing aromatic polyazomethines and copolyazomethines from perfluoroisopropylidene group‐containing aromatic diamines and/or isopropylidene group‐containing aromatic diamines and phthaladehydes
Authors: Saegusa Yasuo , Kuriki Minoru , Nakamura Shigeo 
Published: April 2003

AbstractA series of novel fluorine‐containing aromatic homopolyazomethines and copolyazomethines were synthesized by solution polycondensation of perfluoroisopropylidene (perfluoropropane‐2,2‐diyl) group‐containing aromatic diamines, 2,2‐bis[4‐(4‐aminophenoxy)phenyl]‐1,1,1,3,3,3‐hexafluoropropane (4,4′‐[1,1,1,3,3,3‐hexafluoropropane‐2,2‐diylbis(1,4‐phenyleneoxy)]dianiline (1a)) and 2,2‐bis(4‐aminophenyl)‐1,1,1,3,3,3‐hexafluoropropane (4,4′‐(1,1,1,3,3,3‐hexafluoropropane‐2,2‐diyl)dianiline (1b)), and/or the corresponding analogous isopropylidene group‐containing aromatic diamines, 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane (4,4′‐[isopropylidenebis(1,4‐phenyleneoxy)]dianiline (1c)) and 2,2‐bis(4‐aminophenyl)propane (4,4′‐isopropylidenedianiline (1d)), with terephthalaldehyde (2a) and isophthaladehyde (2b). The effect of fluorine substitution on the synthesis and properties of these polymers was investigated by comparison with those of the corresponding homopolyazomethines but without fluorine. Film‐forming fluorine‐containing polyazomethines with reduced viscosities up to ηred= 0,44 dL · g−1were obtained in high yields by usingm‐cresol as reaction medium. Incorporation of perfluoroisopropylidene groups in the polyazomethine backbone greatly enhanced the solubility of the polymers in various organic solvents including chloroform and tetrahydrofuran. Their thermal stability was also successfully improved by the introduction of fluorine, and both the temperatures of 5% and 10% weight loss in air increased monotonically with the increase of the fluorine content. The surface properties of the films or the contact angles formed by water and diiodomethane were, however, scarcely affected by fluorine substitution. The mechanical properties of the films, such as tensile strength and initial modulus, fairly decreased by the modification.
Ferroelectric liquid‐crystalline elastomers
Authors: Brehmer Martin , Zentel Rudolf , Wagenblast Gerhard , Siemensmeyer Karl 
Published: April 2003

AbstractOriented liquid‐crystalline (LC) elastomers (polar monodomains, concerning the direction of polarisation) have been prepared from polar monodomains of ferroelectric LC‐polysiloxanes by a radical photocrosslinking process. Attempts to perform ferroelectric switching lead in these soft elastomers to an elastic stress which prohibits—for low voltages—a complete reorientation of the polar axis (ferroelectric switching). A ferroelectric switching can, however, be observed for high voltages. The loop of hysteresis of this switching is asymmetric concerning the zero point of the driving voltage. Piezoelectric measurements show that these elastomers combine an elastic memory for one polar state with enough flexibility to allow a reorientation of the polar axis.
Soluble polyimides containing perylene units
Authors: Dotcheva Dobrinka , Klapper Markus , Müllen Klaus 
Published: April 2003

AbstractNovel soluble polyimides containing perylene units have been synthesized. The polymers were prepared in a one‐step polycondensation reaction from 1,6,7,12‐tetrakis(4‐tert‐butylphenoxy)‐3,4:9,10‐perylenedianhydride and aliphatic and aromatic diamines. The amorphous polyimides have a very good solubility in a wide range of organic solvents and exhibit thermal stability up to 350°C. The polymers consist of 10 to 30 monomer units and show a narrow molecular weight distribution. The dark red materials can be used as polymeric dyes (absorption wavelength: λmax = 590–610 nm) and exhibit fluorescence near 620 nm.