bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of the metathesis polymerization and copolymerization of syn‐ and anti‐7‐methylnorbornene initiated by the tungsten‐carbene complex
Authors: Kress Jacky , Ivin Kenneth J. , Amir‐Ebrahimi Valia , Weber Patrick 
Published: April 2003

AbstractThe tungsten‐carbene complex was used to initiate the metathesis polymerization of syn‐and anti‐7‐methylbicyclo [2.2.1] hept‐2‐ene (Ms and Ma). Two kinds of experiment were performed:(i) the reactions were followed at low monomer/initiator ratios by 1H NMR spectroscopy at 220–250K; (ii) polymers and copolymers of Ms and Ma were prepared at room temperature and their microstructure analysed by 13C NMR spectroscopy. The propagating tungsten‐carbene species derived from both Ma could be detected. Some rate constants were evaluated for various steps in the mechanism. A polymer of Ms was prepared for the first time, containing 90% trans double bonds and probably isotactic. After hydrogenation this polymer exhibits two first‐order transitions, with DSC maxima at 179 and 230°C. Hydrogenated atactic polymers of Ma and of norbornene also exhibit first‐order transitions. Conditions are described for the preparation of block and tapered block copolymers of Ma and Ms.
Mechanisms and kinetics of the anionic polymerization of acrylates, 1. Oligomerization of tert‐butyl acrylate and characterization of products
Authors: Janata Miroslav , Lochmann Lubomír , Müller Axel H. E. 
Published: April 2003

AbstractThe anionic polymerization of tert‐butyl acylate (tBuA) initiated by tert‐butyl α‐lithioisobutyrate was investigated in THF at 25°C. The individual oligomers were isolated and characterized by UV, IR and NMR spectroscopy. The distribution of products was determined in the range of reaction times 0,02 s ≤ t ≤ 1800 s. The oligomerization is extremely fast. Even after 0,02 s at ‐30°C, no residual monomer could be detected. After short reaction times the reaction mixture almost exclusively consists of linear oligomers of tBuA. This indicates that there is no termination reaction by Claisen condensation during polymerization. Nevertheless, the molecular weight distribution is rather broad (M̄w/M̄n = 2,15). The very large amount of dimer observed is an indication of its low reactivity. A two‐state mechanism is proposed to account for the high polydispersity. Only after longer reaction times side products are formed by Claisen condensation (“back‐bitting”). The termination product of the trimer is an enolized cyclic β‐ketoester.
The correlation of rotational isomers in polyethylene‐like crystals
Authors: Xenopoulos Alexander , Noid Donald W. , Sumpter Bobby G. , Wunderlich Bernhard 
Published: April 2003

AbstractThe molecular dynamics technique to simulate the behavior of polyethylene crystals, described earlier, is used to study the creation and mobility of rotational isomers of a polyethylene‐like chain in a crystal environment. Both a “gross defect” (formed by perturbation of the cartesian coordinates) and a “kinetic defect” (formed by placing a specific amount of kinetic energy that excites a pure local torsion) are added to the central chain of a polyethylene crystal. The initial dynamic instability quickly forms a more stable, but more or less static defect that, subsequently, moves somewhat along and between neighboring chains, and finally, gets quenched on a time scale of a few picoseconds. Increasing the temperature leads from a highly correlated state to a state where defects are created and quenched statistically (condis state). Increasing the energy input for defect generation leads to the creation of different static defects. The onset of conformational disorder is independent of the initial perturbation. There is a correspondence of the observed defects to the defects proposed for polyethylene based on molecular mechanics calculations, but lifetimes are relatively short.
Synthesis of novel functional styrene monomers having trimethylsilyl and hydroxyalkyl groups by the reaction between 4‐vinylbenzyllithium derivatives and oxiranes
Authors: Nagasaki Yukio , Takahashi Seiji , Tsuruta Teiji 
Published: April 2003

AbstractNew synthetic routes for styrene derivatives having both trimethylsilyl and hydroxyalkyl groups were investigated. Reactions between oxirane (5a) and chemical species present in an equilibrium system resulting from 4‐(trimethylsilylmethyl)styrene (1s) and lithium diisopropylamide (2) in tetrahydrofuran give an addition product (8a) between 2 and 5a preferentially. By using alkyl‐substituted oxiranes such as ethyloxirane (5c) and tert‐butyloxirane (5e), a 1 : 1 addition reaction of 1s with the oxiranes takes place predominantly to form 1‐alkyl‐3‐trimethylsilyl‐3‐p‐vinyl‐phenyl‐1‐propanol (8) homologues. From results of studies on the reaction between 2 and several oxiranes, it was concluded that the selective formation of 8 homologues was attained by suppression of reactions between oxirane and 2 owing to steric hindrance between alkyl substituents of oxirane and isopropyl groups of 2. The reactivity of 8 in polymerization reaction was also estimated on the basis of spectroscopic measurements. 8 was found to have a reactivity similar to that of 4‐(trimethylsilylmethyl)styrene (1s).
Conformational transition of block copolymers in dilute solution and their morphology in the solid state
Authors: Tsitsilianis Constantinos , Staikos George , Dondos Anastasios , Lutz Pierre , Rempp Paul , Benoît Henri 
Published: April 2003

AbstractBlock copolymers poly(methyl methacrylate)‐block‐polystyrene‐block‐poly(methyl methacrylate) and polystyrene‐block‐poly(tert‐butyl methacrylate) were prepared by anionic polymerization and were studied in dilute solution as well as in the bulk state. The viscometric study revealed that the block copolymers exhibit a conformational “transition” occurring in a narrow temperature range. Films were obtained with the same copolymers by casting at different temperatures, chosen below and above the “transition”. From the investigation of these films by differential scanning calorimetry, using the entropy relaxation method, and by dynamic mechanical measurements, it was shown that the block copolymers exhibit a rather segregated structure if they are obtained below the “transition” temperature, and that they adopt a quasi‐Gaussian conformation (implying a better miscibility of the two kinds of blocks) if the solvent is evaporated above the “transition” temperature.
Synthesis and properties of a thermotropic copolyester based on 4‐hydroxyacetophenone azine
Authors: Cimecioglu A. Levent , Fruitwala Hitesh , Weiss R. A. 
Published: April 2003

AbstractThe synthesis of a thermotropic copolyester based on 4‐hydroxyacetophenone azine (1) and a 50 : 50 (mole ratio) mixture of sebacoyl/dodecanedioyl dichlorides was investigated in chloroform via a low‐temperature solution route. Polymers with an inherent viscosity ηinh between 0,27–1,56 dL · g−1 were characterised by 1H NMR, IR, thermal analyses, gel permeation chromatography and static light scattering techniques: Enantiotropic polymers exhibit a large mesophase range (≈100°C) and the values of both crystal‐nematic and nematic‐isotropic transitions are molecular‐weight dependent. Intrinsic viscosity was determined to relate to molecular weight by [η]/(dL · g−1) = 9,6 · 10−4 M̄ in chloroform at 25°C, and the persistence length was calculated to be of the order of 27 Å.
Energy calculations on chain conformation and mode of packing of crystalline syndiotactic cis‐1,4‐poly(1,3‐pentadiene)
Authors: Napolitano Roberto 
Published: April 2003

AbstractConformational and packing energy calculations were performed on crystalline syndiotactic cis‐1,4‐poly(1,3‐pentadiene). The lowest energy conformation of a single polymer chain — under the constraint of the experimental identify period along the chain axis (8,5 Å) — was found. The analysis of modes of packing shows that the lowest packing energy is obtained in the P21/c space group. A possible structure of the polymer is suggested.
Telechelics via addition of dithiols onto alkadienes, 2. Base and acid catalysis
Authors: Nuyken Oskar , Völkel Thomas 
Published: April 2003

AbstractThe base‐catalyzed Michael‐type addition of dithiols onto activated diacrylates and dimethacrylates proceeds quantitatively and leads to products with anti‐Markovnikov orientation of the addition. This reaction was used to prepare telechelics using non‐stoichiometric ratios of monomers. The acid‐catalyzed addition of dithiols onto divinyl ethers also yields polymers and telechelics, however, these products show Markovnikov orientation of the addition.
A study of band texture formation of nematic solutions of poly(1,4‐phenyleneterephthalamide) in sulfuric acid
Authors: Chen Shouxi , Qian Renyuan 
Published: April 2003

AbstractThe band texture formation of nematic poly(1,4‐phenyleneterephthalamide) (PPTA)/H2SO4 solutions after shearing between rotating plates was studied. For a thickness of the solution layer larger than 20 μm the band texture appears immediately after the cessation of shearing, but a critical shear rate is needed which was demonstrated directly using polarizing microscopy. When the solution‐layer thickness was less than 10 μm, an induction time tb needed for the development of the band texture after the cessation of shearing was observed, which was of the order of 10 to 102 s. It is thus shown without any ambiguity that the band texture is formed during relaxation of shear orientation. The effects of solution concentration, solution‐layer thickness, shear rate, and shearing time on tb were studied. Once the band texture is formed from a sheared solution, it will take hours to relax completely to a randomly oriented domain texture. The factors influencing this relaxation time were also studied.
The laser‐flash‐initiated polymerization as a tool of evaluating (individual) kinetic constants of free‐radical polymerization, 6. The influence of monomer consumption during sample preparation
Authors: Schnöll‐Bitai Irene , Olaj Oskar Friedrich 
Published: April 2003

AbstractThe instantaneous differential molecular weight distribution curves for a polymer prepared under the influence of periodic laser flashes of constant intensity were calculated as a function of conversion and accumulated up to final conversions in the range between 0 and 20%. If these cumulated distributions are subjected to the conventional analysis with respect to the position of the inflection points, which are an excellent measure of kp · [M]t0 (kp = rate constant of chain propagation, [M] = monomer amount concentration, t0 = pulse separation), it is seen that this relationship, the validity of which was originally established in the limit of vanishing conversion, becomes the more deficient the higher is the conversion. This is even so when the initial monomer concentration is replaced by the average monomer concentration over the conversion interval examined. In the latter case, however, the deviations are reasonably small and do not exceed the limits of experimental accuracy in determining the position of the inflection point. Thus the application of this method of calculating kp is justified also for conversions up to at least 20%. The determination of k/t from rate of polymerization and weight‐average degree of polymerization (kt representing the rate constant of mutual chain termination) on the other hand, is completely insensitive towards conversion.
Kinetic investigation of the dispersion polymerization of N,N′‐methylenebis(acrylamide) in the presence of various emulsifiers
Authors: Capek Ignác , Funke Werner 
Published: April 2003

AbstractThe aqueous‐phase dispersion polymerization of N,N′w‐methylenebis(acrylamide) (MBA) in the presence of various additives was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization is found to be proportional to the concentration of sodium 1,2‐bis(2‐ethylhexyloxycarbonyl)ethanesulfonate (AOT) raised to the power of 0,42 (conc. of emulsifier <10−2) and to the conc. of ethylene glycol monooctylphenyl ether (TR) raised to the power of 0,23. On the other hand, it is independent of the conc. of poly(ethylene glycol) (PEG) and Tween 80 (TW). The rate of polymerization is proportional to the conc. of potassium peroxodisulfate (K2S2O8) raised to the power of 0,54 or 0,8 for systems with AOT or TW, respectively, and to the conc. of MBA raised to the power of 0,47 or 0,28 for the two respective systems. The effect of pH on the polymerization of MBA is assigned to the change of the decomposition rate of K2S2O8. The stabilization effect of the emulsifiers used decreases in the following order: AOT > TR ≈ PEG ≈ TW.
Cyclic oligo[oxymethyleneoligo(oxyethylene)]s and linear poly[oxymethyleneoligo(oxyethylene)]s studied by differential scanning calorimetry
Authors: Nekoomanesh Mehdi H. , Nicholas Christian V. , Booth Colin 
Published: April 2003

AbstractCyclic oligo[oxymethyleneoligo(oxyethylene)]s and linear poly[oxymethyleneoligo(oxyethylene)]s have been prepared by condensation of tri‐, tetra‐, penta‐ and hexaethylene glycols, including a number of samples not reported previously. The linear and cyclic products were characterised using nuclear magnetic resonance and gel‐permeation chromatography, and then studied using differential scanning calorimetry. Even‐odd effects in the values of the melting points and enthalpies of fusion of the samples are demonstrated.
The ene reaction between N‐isobutylallylnadimide and N‐isobutylmaleimide as a model for the cross‐linking reaction in bis(allyl)nadimide polymerization
Authors: Vijayakumar Chinnaswamy Thangavel , Lederer Klaus , Kramer Andreas 
Published: April 2003

AbstractThe reaction between N‐isobutylallylnadimide (NIBANI) and N‐isobutylmaleimide (NIBMI) was taken as a model reaction to obtain insight into the curing mechanism of polymeric alloys and composites consisting of bis‐ or tris(allyl)nadimides and bismaleimides. The reaction between NIBANI and NIBMI is not catalyzed by boron trifluoride etherate, neither at room temperature nor in refluxing methylene chloride. The thermally induced reaction (200°C) between NIBANI and NIBMI in equimolar quantities gives an indirect proof for the occurrence of an ene reaction. The high reactivity of the ene reaction product to undergo further Diels‐Alder reaction was proved by GPC and direct inlet mass spectral studies.
Dielectric relaxation of poly(benzyl methacrylate)
Authors: Kihira Yasuharu , Ichidayama Kouji , Takagi Sadao 
Published: April 2003

AbstractThe relaxation processes in atactic poly(benzyl methacrylate) were studied by means of dielectric measurements. Beside the α‐ and β‐relaxation processes due to the segmental motions of the main chain and of the entire side chain, respectively, a process designated as γ was found to occur in the temperature range between −60°C and 0°C. For the γ‐relaxation, the time‐temperature superposition principle is applicable. A linear relationship between temperature and the relaxation frequency fm or shift factor aT was found. Apparent activation energies estimated from the temperature dependence of fm and aT are 50 and 53 kJ · mol−1, respectively. The γ‐process is considered to result from the movement of the benzyl group in the side chain.
Imidization of polypromellitamic acid based on 4,4′‐methylenedianiline
Authors: Marek Miroslav , Schmidt Pavel , Schneider Bohdan , Bednář Bohumil , Králíček Jaroslav 
Published: April 2003

AbstractImidization of polyamic acid prepared from pyromellitic dianhydride and 4,4′‐methylenedianiline was investigated at 373–493 K. At a certain degree of imidization, depending on the reaction temperature, the reaction is significantly slowed down. For this reason, imidization was divided into two phases, a fast and a slow one, and the rate constants were calculated from the kinetic equation of a first‐order reaction. At imidization temperature above 443 K the activation enthalpy of the reaction decreases, probably due to the thermal decomposition of complexes of o‐carboxybenzamide groups with residues of the solvent. At higher imidization temperatures also the activation entropy of imidization decreases; this is probably caused by the higher rigidity of the film because of evaporation of the solvent which acts as a plasticizer.
On the chemical modifications of poly(maleic anhydride‐co‐isobutene) by means of hydrolysis, ammoniation or aminations
Authors: Bortel Edgar , Stysło Maria 
Published: April 2003

AbstractRing‐opening reactions of maleic anhydride (1)/isobutene (2) copolymer (M̄w = 2,76 · 105 g/mol), carried out by the use of: NaOH solution (hydrolysis); NH3; NH(CH3)2; N(CH3)3; NH(C2H5)2 and H2N(CH2CH2NH)2CH2CH2NH2 (TETA), resp., yielded water‐soluble products, with the exception of the TETA‐modified copolymer. The degrees of conversion α were found to be in the range between 87 to 100%, with the exception of the N(CH3)3‐reacted copolymer where α = 41,6%. As a result of the conversion reactions, the weight‐average molecular weights M̄w dropped significantly, by 30% in the case of hydrolysis, and by 40% in the cases of ammoniation or amination, despite the mild conditions which were employed. Based on nitrogen contents found analytically, as well as on 13C NMR spectra, it was concluded that under the given conditions the reactions using ammonia or amines do not proceed beyond the half‐amidation step. 13C NMR investigations on products of both the ammoniation and amination reactions indicate a directing influence produced by the CH3 groups of the isobutene unit. As a result, only those carbonyl groups remote from the pendant substitutents are prone to an attack which causes amidation.
A solid‐state 13C NMR study on heterogeneous Ziegler‐Natta catalyst components
Authors: Sormunen Pekka , Hjertberg Thomas , Iiskola Eero 
Published: April 2003

AbstractZiegler‐Natta catalysts supported on MgCl2 have been studied by CP‐MAS (cross‐polarization, magic‐angle spinning) 13C NMR spectroscopy. The support was activated mechanically and chemically, and then treated with a monoester (ethyl benzoate) or a diester (diisobutyl phthalate). Catalytic species were obtained by a treatment with TiCl4. Complexation and crystal disordering phenomena are clearly observed as changes in the chemical shifts and line broadenings. Line splittings were observed, especially for the diester due to nonequivalent crystal coordination sites. The diester shows a different behaviour compared to the monoester thus reflecting its better ability as a stereoselectivity‐controlling agent. The titanation led to the formation of a new, estercontaining and ordered complex on the surface of the carrier. The mobility of the surface complexes is restricted, crystalline complexes being more constrained.
New liquid‐crystalline side‐chain polymers with large transversal polarizability
Authors: Leube Hartmann F. , Finkelmann Heino 
Published: April 2003

AbstractNew side‐on liquid‐crystalline side‐chain polymers (LCSCP's) are presented as having a systematic variation of the anisotropy of polarizability with respect to the mesogenic short axis. Starting from hydroquinone as core of the rod, the polarizability perpendicular to the mesogenic long axis is increased stepwise upon replacing hydroquinone by naphthalene and anthracene derivatives. Naphthalene derivatives with cyclohexane carboxylic acid derivatives as side parts show to be the first side‐on attached LCSCP's exhibiting a smectic phase.
Polysilanes fonctionnels, 2. Synthèse d'α,ω‐bis(triméthylsilyl)poly(méthylvinylsilane)s. Caractérisation des octaméthyl‐divinyl‐2,3 tétrasilane et nonaméthyl‐trivinyl‐2,3,4 pentasilane
Authors: Noireaux Patrick , Mérand Philippe , Reyx Danièle 
Published: April 2003

AbstractLow‐molecular‐weight organosilane polymers containing the methylvinylsilanediyl unit were prepared by sodium coupling of the corresponding organochlorosilanes. GPC, IR and 1H NMR analyses were performed. Principal objectives in this work were to isolate the first oligomers, tetra‐and pentasilane, to determine their spectroscopic characteristics and to compare the GPC characteristics with those of hydrocarbon polymers.
Kinetics of 1,3‐cyclohexadiene polymerization initiated by organolithium compounds in a non‐polar medium, 1. Pure propagation step
Authors: Zhong Xing Fu , François Bernard 
Published: April 2003

AbstractThe kinetics of propagation of the anionic polymerization of 1,3‐cyclohexadiene initiated by organolithium compounds in cyclohexane is reported. At low monomer concentrations secondary reactions are avoided. The propagation follows a half‐order kinetics with respect to living‐chain concentration, suggesting an association of two of these chains. The apparent rate constant is found to be 6,9 · 10−4 L1/2 · mol1/2 · s−1 at 20°C with an apparent activation energy of 16,6 kcal/mol (69,5 kJ/mol).
Conformational and packing energy calculations on the low‐temperature phase (phase II) of poly(tetrafluoroethylene)
Authors: Napolitano Roberto , Pucciariello Rachele , Villani Vincenzo 
Published: April 2003

AbstractConformational energy calculations were performed on phase II of poly(tetrafluoroethylene) under the constraint of three different experimentally proposed chain repeating distances. The corresponding conformations were used in packing energy calculations effected for the different unit cells reported in the literature. The results suggest the existence of both conformational and structural disorder in the crystalline state.
Morphology of ABA triblock copolymers consisting of poly(γ‐benzyl L‐glutamate) as the A component and polystyrene as the B component
Authors: Janssen Koen , van Beylen Marcel , Samyn Celeste , Scherrenberg Rolf , Reynaers Harry 
Published: April 2003

AbstractThe morphology in the solid state of ABA triblock copolymers consisting of poly(γ‐benzyl L‐glutamate) (A) and polystyrene (B) was investigated. Transmission electron microscopic measurements (TEM) revealed that the morphology varied with the length of the polypeptide block. Small‐angle X‐ray scattering (SAXS) data were in accordance with these TEM‐results. Wide‐angle X‐ray (WAXS) data showed that the distance between the α‐helices in the polypeptide lamellae changed with the composition of the block copolymers.
Chiral liquid‐crystalline poly(ester/β‐sulfoxide)s by asymmetric oxidation of prochiral nematic poly(ester/β‐sulfide)s
Authors: Angeloni Annino S. , Laus Michele , Caretti Daniele , Chiellini Emo , Galli Giancarlo 
Published: April 2003

AbstractA new class of prochiral liquid‐crystalline poly(ester/β‐sulfide)s 2 and 3 containing the SC6H4S group was prepared, which were then asymmetrically oxidized to chiral liquidcrystalline poly(ester/β‐sulfoxide)s 4 and 5 comprising the \documentclass{article}\pagestyle{empty}\begin{document}$\hbox{---} \mathop {\rm S}\limits^ * \left( {\rm O} \right)\hbox{---} {\rm C}_6 {\rm H}_4 \hbox{---} \mathop {\rm S}\limits^ * \left( {\rm O} \right)\hbox{---}$\end{document} group. A chiral 2‐sulfonyloxaziridine 6 was used as the asymmetric oxidant and the reaction is highly chemoselective with quantitative yield. A 13C NMR analysis of a model poly(ester/β‐sulfoxide) 8 is performed, which allows to evaluate the asymmetric induction and the enantiomeric excess for the asymmetric oxidation product. While the parent polymers 2 and 3 are nematic, the chiral modified polymers 4 and 5 are cholesteric.