bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cold crystallization and polymorphism in an oligo(aryl ether ketone)
Authors: Rueda Daniel R. , Zolotukhin Mikhail G. 
Published: April 2003

Abstract1,3‐Bis(4‐phenoxybenzoyl)benzene(1)was crystallized from the glassy state at different temperatures,Tc, above the glass transition temperature (Tg= 24°C). Analysis of X‐ray diffractograms and DSC thermograms revealed a new polymorphism: a one‐dimensional order phase (G1) and a new crystal phase (G2). In both cases the molecules adopt a linear extended conformation. G1 appears for 30°C <Tc< 35°C and its structure is like that of a smectic phase A with the molecular axis normal to the layer planes. Upon thermal treatment above 35°C G1 converts into the crystal phase G2 which shows an inproving lateral packing of the molecules upon heating. G1 and G2 show melting temperatures around 88 and 98°C, respectively. Provided that the thermal treatment of the cold crystallizing sample is done under ambient conditions, G2 converts into the most stable crystal phase 2 (Tm= 130°C). Similar thermal treatments carried out inside a DSC calorimeter under dry N2‐flow are not capable of provoking the change in the molecular conformation (from a linear extended to a V‐conformation) involved in the crystal phase transition of G2 to phase 2.
Silica supported zirconocenes and Al‐based cocatalysts: surface metal loading and catalytic activity
Authors: dos Santos João Henrique Zimnoch , Dorneles Silvio , Stedile Fernanda Chiarello , Dupont Jairton , de Camargo Forte Maria Madalena , Baumvol Israel Jacob Rabin 
Published: April 2003

AbstractThe Zr surface loading from Cp2ZrCl2 toluene solutions on different kinds of commercial silicas (Grace 948, 952 and 956) was determined by Rutherford backscattering spectrometry. In all silicas, a saturation trend was observed with increasing amount of metal in the initial solution, the largest Zr loading value (1 wt.‐%) being observed for silica Grace 948. Solid surface areas were determined by the BET method before and after metallocene immobilization, revealing that the values do not change after zirconocene impregnation. Two different kinds of cocatalyst were used, methylaluminoxane and trimethylaluminium. The aluminium loading on silica Grace 948 was determined using the 27Al(p,γ)28Si nuclear reaction and titrometry, both showing that methylaluminoxane leads to an “Al grafting” four times more efficient than does trimethylaluminium. Finally, the catalytic activity of these systems was tested in the polymerization of ethylene. The supported catalysts were shown to be active, specially using the low cost trimethylaluminium as a cocatalyst. The polymers obtained with the supported systems exhibited a higher molecular weight than those obtained with the homogeneous system.
A convenient route to poly(methylphenylsilane)‐graft‐polystyrene copolymers
Authors: Jones Richard G. , Holder Simon J. 
Published: April 2003

AbstractA graft copolymer of polystyrene on poly(methylphenylsilylene) was conveniently synthesised by using the bromomethyl groups of bromomethylated poly(methylphenylsilylene) as initiating sites for the bulk polymerisation of styrene by an atom transfer radical mechanism.
Temperature‐influenced ordering of mesogens in comb‐like liquid‐crystalline poly(methylsiloxane) macromolecules with side groups consisting of “phenyl benzoate” moieties in solution
Authors: Lavrenko Peter , Yevlampieva Natalia , Okatova Olga , Kolbina Galina , Olbrich Michael 
Published: April 2003

AbstractComb‐like poly(methylsiloxane) macromolecules P4, P6, and P11, with side groups consisting of “phenyl benzoate” moieties and different alkyl spacers (from 4 to 11 C‐atoms) between the backbone and the mesogenic side groups have been synthesized and investigated as well as low‐molar‐mass compounds M4, M6, and M11, as model molecules analogous to side chains of the macromolecule. The liquid‐crystalline phase transition temperatures have been determined. Mobility of the mesogens and the macromolecule as a whole in dilute solution was studied in external fields (electric and mechanical shear field). In dilute solution under the influence of a sinusoidal electric field, the polymer behaviour is typical of flexible‐chain polymer molecules where each mesogenic unit is oriented independently of the other ones. This is in contrast to the effect observed in a mechanical shear flow field. The Maxwell constant in positive for the solutions of compounds M4, M6, M11 and negative in polymers P4, P6, P11. This indicates the orientation of the macromolecule as a whole in the shear flow field, the mesogenic group main axis being oriented in the direction preferably normal to the macromolecular axis of primary polarizability. Temperature effects are also discussed.
Mesogenic azomethine based diepoxides – monomers for the synthesis of “liquid crystal” thermoset networks
Authors: Mormann Werner , Bröcher Markus , Schwarz Petra 
Published: April 2003

AbstractA series of azomethine linked di‐ and triaromatic (diad and triad) mesogenic diepoxides was synthesized. The easy accessibility of the corresponding bisphenols from suitable aminophenols, hydroxybenzaldehydes, terephthalaldehyde, and p‐phenylenediamine allows to investigate the influence of substituents and of the arrangement of aromatic rings in the mesogenic core on the thermal and phase behaviour. The unsubstituted triad terephthaldialdehyde based diepoxide forms a smectic mesophase while all the others exert nematic mesophases. Melting points of the unsubstituted triad diepoxides are around 200°C being lowered by the introduction of methyl substituents. The greatest decrease (m.p. about 130°C) is caused by a methyl or a chloro substituent in the central ring, while the clearing point decreases from 260°C for the unsubstituted compounds to app. 230°C.
Bis(cyclopentadienyl)zirconium dichloride supported on zeolites for ethylene polymerization
Authors: Marques Maria De Fátima V. , Henriques Cristiane A. , Monteiro José Luiz F. , Menezes Sonia M. C. , Coutinho Fernanda M. B. 
Published: April 2003

AbstractY zeolites with different sodium contents and a sodium mordenite were evaluated as support for bis(cyclopentadienyl)zirconium dichloride as catalyst for ethylene polymerization. The results showed that, although the activities of the supported catalysts were lower than that of the homogeneous system, the average molecular weight of the polyethylene produced from the former was in general much higher than that of the polymer produced in solution. Contrary to the expected trend if the specific area was the dominant factor for catalyst activity, the best catalyst was the one supported on NaM zeolite. Thus, our results indicate that the concentration of framework aluminium atoms is the dominant factor, but that the contribution of the external surface is also important.
Liquid crystalline main chain polymers containing the ferrocene unit as a side group, 2. Variation of the spacer length
Authors: Wilbert Götz , Traud Simone , Zentel Rudolf 
Published: April 2003

AbstractFour new ω‐ferrocenylalkyl diethyl malonates with varying length of the alkyl group from 4 to 10 methylene units were incorporated via Ti(OiPr)4‐catalyzed copolymerization into smectic liquid crystalline main‐chain polymers in contents of about 10 mol‐%. As mesogenic unit 4,4′‐bis(6‐hydroxyhexyloxy)azoxybenzene was used as diol component and diethyl phenyl malonate as diester component. Polymer analogous oxidation of the ferrocene units leads to liquid crystalline ionomers, which also form smectic phases. The ferrocene containing polymers were investigated in the oxidized and non‐oxidized state of the ferrocene unit. Differential scanning calorimetry (DSC) data show a shift towards higher phase transition temperatures after oxidation, which is in agreement with the behaviour of classical ionomers. Small angle X‐ray scattering (SAXS) experiments show an excess scattering to small angles, which is a hint for dispersed particles in the polymer matrix (ionic clusters). In one polymer series the ferrocene content was varied. Increasing the ferrocene content changes the type of the LC phase from smectic A to nematic presumably because of the bulkiness of the neutral ferrocene group. It is, however, possible to restore the smectic A phase by an oxidation of the ferrocene units to ferrocenium ions. This is a result of microphase separation in ionic domains and non‐ionic domains, which supports the formation of layered structures.
Studies of lyotropic liquid crystalline mesophases of some novel regioselective substituted cellulose derivatives, 2. Structural and optical properties
Authors: Derleth Christina , Zugenmaier Peter 
Published: April 2003

AbstractRegioselective substituted cellulose phenyl urethanes form lyotropic liquid crystalline mesophases in highly concentrated solutions with certain solvents. The structural and optical properties strongly depend on the site of substitution, e.g., 2‐, 3‐, 6‐position of the glucose residues as well as on the specific substitution of the phenyl ring of the carbamate group by fluorine, chlorine or methyl as compared to hydrogen and on the external parameters as concentration and temperature. By variation of the carbamate side groups a change of the helicoidal twist sense of the cholesteric structure is achieved leading to a compensation of left‐ and right‐handed twists that is to a quasi‐nematic structure. The experimental optical rotatory power can be described following theoretical considerations of de Vries by introducing a dispersion and a damping term.
Investigation of the initiation reaction of isoprene polymerization with 2‐ethylhexylsodium in heptane
Authors: Pakuro Natalia I. , Arest‐Yakubovich Alexander A. , Shcheglova Larisa V. 
Published: April 2003

AbstractThe kinetics of the initiation of isoprene polymerization in heptane with the hydrocarbon‐soluble alkylsodium compound 2‐ethylhexylsodium was studied. Initiation rates were estimated from the induction period and by measuring UV spectra of polyisoprenyl‐sodium (λmax = 304 nm) during the course of polymerization. The initiation reaction is first order in initiator both in the course of the reaction and with respect to the starting concentration of the initiator. The same result is obtained when 2‐ethylhexyllithium is used. The initiation rate constants are: ki = 1,6 · 10−3 and 5,5 · 10−4 L/(mol · s) for sodium and lithium compounds at 26°C, respectively. Aggregated forms of organoalkali compounds are suggested to take part in the initiation reaction of isoprene polymerization.
Free radical polymerisation studies of 4‐substituted styrenes, 2. Termination and chain transfer in the polymerisation of styrene, 4‐methoxystyrene and 4‐methylstyrene
Authors: Berry Robert William Huxley , Ludlow Andrew John , Mazza Robert John 
Published: April 2003

AbstractThe bulk polymerisation of styrene, 4‐methoxystyrene and 4‐methylstyrene was investigated at 60°C using 2,2′‐azoisobutyronitrile (AIBN) as the initiator. Initial rates (Ri0) and efficiencies (f) of initiation were calculated from the radioactive content of the polymer obtained by labelling the initiator as either [methyl‐14C4]AIBN or [cyano‐14C2]AIBN. Rates of polymerisation determined gravimetrically are in good agreement with rates determined by the dilatometer technique. An empirical linear relationship between the number of initiator fragments and the degree of monomer conversion was noted. Factors affecting the termination of polymer radicals are discussed and compared with other published work. The polymerisation reaction is terminated predominantly by combination in the case of all three monomers, and chain transfer constants to initiator and to monomer are of the order of 10−3 and 10−5, respectively.
New comblike copolymers of controlled structure and dimensions obtained by grafting by polystyryllithium onto poly(chloroethyl vinyl ether) chains
Authors: Schappacher Michel , Deffieux Alain 
Published: April 2003

AbstractThe grafting reaction of polystyrene branches onto poly(chloroethyl vinyl ether) (PCEVE) chains, based on the deactivation of polystyryl (PS) carbanionic ends onto chloroethyl ether functions has been investigated. The selectivity of the coupling is very high and allows the almost complete substitution of the chloride group of the CEVE units by PS chains with molar masses up to 15 000. The main side reaction observed is the deactivation of some PS chains, at the very beginning of the reaction. It is attributed mainly to impurities present in the PCEVE solution. Since the PCEVE polymer backbone and the PS grafts can be prepared by both living cationic and anionic polymerization, it is possible to synthesize poly(CEVE‐g‐styrene) copolymers possessing both a backbone with controlled dimensions and an adjustable number of branches having precise length and narrow molar mass distribution. The synthesis and the characteristics of comblike poly[(chloroethyl vinyl ether)‐g‐styrene]s are described.
Photochemical reactions of polystyrenes ring‐substituted with thiocyanato groups
Authors: Kern Wolfgang , Hobisch Josefine , Hummel Klaus 
Published: April 2003

AbstractThe photochemistry of poly(2‐vinylphenyl thiocyanate) (P(2‐VPT)), poly(3‐vinylphenyl thiocyanate) (P(3‐VPT)) and poly(4‐vinylphenyl thiocyanate) (P(4‐VPT)) is investigated under 254 nm UV light. Poly(4‐bromostyrene) (P(4‐BrSt)) is used as reference material. Experiments with phenyl thiocyanate show that the main photoreaction is a cleavage into cyano and phenylthio radicals which also occurs in the polymers. Photo‐crosslinking data for the polymers P(2‐VPT), P(3‐VPT) and P(4‐VPT) are evaluated with the Charlesby‐Pinner relation. For P(2‐VPT), P(3‐VPT) and P(4‐VPT) the qunatum efficiencies ΦCL of crosslinking are 0.018, 0.029 and 0.021, the quantum efficiencies ΦCL of chain scission are 9 · 10−4, 37 · 10−4 and 6 · 10−4. P(2‐VPT), P(3‐VPT) and P(4‐VPT) rank among the most sensitive negative resists in the polystyrene series. Hammett's σ constants for SCN substituents are determined (3‐SCN: σ = 0.50, 4‐SCN: σ = 0.45). However, a general correlation between the ΦCL or ΦCS values of ring‐substituted polystyrenes and Hammett's σ constants of the substituents is not found.
Enantioselective isotactic alternating copolymerization of styrene and 4‐methylstyrene with carbon monoxide catalyzed by a cationic bioxazoline pd(II) complex
Authors: Bartolini Stefano , Carfagna Carla , Musco Alfredo 
Published: April 2003

AbstractThe cationic bioxazoline Pd(II) complex 2 catalyzes the alternating copolymerization of carbon monoxide with styrene and 4‐methylstyrene, respectively, to yield a highly isotactic optically active polymer at room temperature and low carbon monoxide pressure (1–4 atm).
Length of chain segment motion needed for crystallization
Authors: Qian Renyuan , Wu Zhicai , Xue Zhaohong , Yan Ruifang 
Published: April 2003

AbstractThe length of chain segment motion needed for the crystallization of guttapercha from rubbery state was found to be around 180 CC bonds of the backbone chain. Thus, the crystallization process from the rubbery state or from the melt is not through chain folding, and the solidification model is a more appropriate physical picture of the process.
Polymerization of acetylenes carrying precursors of aminyl radicals
Authors: Dulog Lothar , Bognar Peter 
Published: April 2003

AbstractIn the search for organic ferromagnets polymers with a conjugated backbone and pendant persistent radicals are one route of interest. The synthesis of poly[4‐(4‐ethynylphenyl)‐2′,4′,6′‐trinitro‐2,6‐diphenyldiphenylamine] (p‐3) and poly[4‐(3‐ethynylphenyl)‐2′,4′,6′‐trinitro‐2,6‐diphenyldiphenylamine] (m‐3) as precursors of polyradicals are described. A dinuclear rhodium cyclooctadiene chloride complex as polymerization catalyst was used to yield polymers with molecular weights (gel‐permeation chromatography) of 100 000 for m‐3 and 210 000 for p‐3.
Miscibility of poly(vinyl chloride) with chitin derivatives having poly(2‐methyl‐2‐oxazoline) side chains
Authors: Aoi Keigo , Takasu Akinori , Okada Masahiko 
Published: April 2003

AbstractBinary blends of poly(vinyl chloride) (PVC) and chitin‐graft‐poly(2‐methyl‐2‐oxazoline) showed miscibility in the blend fraction range of the latter lower than ca. 10 wt.‐%. The glass transition temperature of PVC, which was determined by differential scanning calorimetry, changed to lower temperatures with increasing modified chitin contents up to 10 wt.‐%. Segmental interaction between PVC and the graft copolymer was confirmed by the carbonyl stretching band shift in the FT‐IR analysis.
Synthesis of novel functional poly[(R,S)‐ß‐hydroxybutyrate] containing phosphonoacetate end groups
Authors: Jedliński Zbigniew , Adamus Grazyna , Kowalczuk Marek 
Published: April 2003

AbstractAmorphous poly[(R,S)‐ß‐hydroxybutyrate], containing both phosphonoacetate and carboxylate functional end groups, was synthesized via anionic polymerization of racemic ß‐butyro‐lactone initiated by supramolecular complexes of potassium P,P‐dimethylphosphonoacetate. The living homopolymers, with alkali metal counter ions complexed with a crown ether, were utilized for the synthesis of block copolymers via condensation reaction with alkylene dihalides. As a result of this approach, coupled block copolymers containing phosphonoacetate functional end groups were obtained.
Reaction behaviour of monomeric β‐ketoesters, 4. Polymer network formation by Michael reaction of multifunctional acetoacetates with multifunctional acrylates
Authors: Moszner Norbert , Rheinberger Volker 
Published: April 2003

AbstractBased on the Michael reaction of multifunctional acetoacetates with multiacrylates, in the presence or absence of dimethacrylates, tailor made matrix materials can be prepared. This can be achieved in a one‐ or two‐step process. The Michael addition (first step) can be followed by radiation curing of excessive acrylate (second step).
Solution‐grown crystal of poly[bis(4‐isopropylphenoxy)phosphazene]
Authors: Nakamura Hitoshi , Miyata Tadakazu , Yonetake Koichiro , Masuko Toru , Kojima Morio 
Published: April 2003

AbstractThe structural features of poly[bis(4‐isopropylphenoxy)phosphazene] (PB(4‐ip)PP) have been studied by electron microscopy, X‐ray diffraction and differential scanning calorimetry techniques. Its orthorhombic lattice constants are determined as follows: a = 3,14 nm, b = 1,14 nm, c = 0,992 nm. The space group of this polymer is suggested to be P 212121–D, and the molecular conformation of the chains possibly to be (trans3cis)2. This polymer exhibits a crystal/crystal transition at 86°C below its T(1) transition (120°C). The thermal behavior is similar to the characteristics of poly[bis(p‐methoxyphenoxy)phosphazene].
Olefin polymerization with titanium tetrachloride catalysts supported on surface‐modified silica
Authors: Lee Dong‐ho , Yoon Keun‐byoung , Kang Kyung‐seok 
Published: April 2003

AbstractAfter modification of silica with benzoyl chloride (BC) to obtain BC‐modified SiO2 (BC‐SiO2), BC‐SiO2/TiCl4 and BC‐SiO2/BEM/TiCl4 catalysts were prepared by treating the BC‐SiO2 with TiCl4 directly or with butylethylmagnesium (BEM) followed by TiCl4, respectively. During the modification, BC reacts with hydroxyl groups of silica. In this way the corresponding ester is anchored on the silica surface and the CO group is coordinated with Ti and/or Mg. In addition, BEM is converted to MgCl2 in the reaction with TiCl4. These catalysts have reasonable activities for ethylene or propene polymerization.
Synthesis and characterization of polyurethanes containing cholesterol and phosphatidylcholine analogous moieties
Authors: Li Yujun , Shibata Yoshitomo , Nakaya Tadao 
Published: April 2003

AbstractSeveral new polyurethanes containing cholesterol and phosphatidylcholine analogous moieties were synthesized by addition polymerization of 2‐[bis(2‐hydroxyethyl)methylammonio]ethyl 5‐cholesten‐3β‐yl phosphate (2) with diisocyanates such as hexamethylene diisocyanate (HDI), 2,4‐tolylene diisocyanate (TDI), 4,4′‐methylenediphenyl diisocyanate (MDI) and m‐xylylene diisocyanate (XDI), respectively. They were characterized by their IR and 1H NMR spectral data and elemental analyses. Preliminary studies suggest that these polyurethanes show the viscosity behavior of common polyelectrolytes.
Enzymes in polymer chemistry, 8 Chemoenzymatic synthesis of polymerizable 11‐methacryloyl‐aminoundecanoic ester of 1‐ and 3‐O‐methyl‐α‐D‐glucose in 6‐O‐position
Authors: Geyer Ulrike , Klemm Dieter , Pavel Konstantin , Ritter Helmut 
Published: April 2003

AbstractThe paper describes the regioselective esterification of a glucopyranoside and glucose derivative with 11‐methacryloylaminoundecanoic acid in the presence of a lipase from Candida antarctica. The obtained modified sugar derivatives 6‐O‐(11‐methacryloylaminoundecanoyl)‐1‐O‐methyl‐α‐D‐glucopyranoside (3 a) and 6‐O‐(11‐methacryloylaminoundecanoyl)‐3‐O‐methyl‐α‐D‐glucopyranose (3 b) were polymerized radically with AIBN as initiator.
Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls, 2. Kinetic investigations with methyl methacrylate in toluene
Authors: Schlaad Helmut , Müller Axel H. E. 
Published: April 2003

AbstractThe kinetics of the polymerization of methyl methacrylate initiated by lithium alkyls (tert‐butyllithium or ethyl α‐lithiobutyrate) was investigated in the presence of aluminium alkyls (triethylaluminium or triisobutylaluminium) in toluene at −78°C. The rate of polymerization decreases considerably once the living dimer is formed. This suggests that the aluminate end‐group coordinates with the penultimate ester group of the polymer chain, thus decreasing reactivity. The results are at variance with an activated monomer mechanism.
Effect of photoinitiator on the molar mass distribution obtained from a pulsed laser polymerization
Authors: Bergert Ute , Beuermann Sabine , Buback Michael , Kurz Caroline H. , Russell Gregory T. , Schmaltz Claudia 
Published: April 2003

AbstractThe choice of the photoinitiator is not usually regarded as being as important consideration in attempting to determine the value of the propagation rate coefficient kp from a pulsed laser‐initiated polymerization (PLP). It is shown that in fact the choice of the photoinitiator can profoundly influence the success of such experiments. Specially, for a number of monomers it was found that the successful determination of kp is essentially impossible when 1,1‐azodicyclohexanecarbonitrile is employed as a photoinitiator. The likely reason for this phenomenon is discussed from which it would seem appropriate to be wary in using any azo compound as a PLP photoinitiator. From PLP experiments with a non‐azo photoinitiator, ambient pressure kp has been determined for bulk polymerization of methyl methacrylate over an extended temperature range.
On the explanation of the biphotonic processes in polyesters containing azobenzene moieties in the side chain
Authors: Ramanujam P. S. , Hvilsted Søren , Zebger Ingo , Siesler Heinz W. 
Published: April 2003

AbstractAn explanation for the recently observed biphotonic transitions in side‐chain polyesters with azobenzene moieties is given on the basis of experimental observations from optical and Fourier‐Transform infrared absorption spectra. We present for the first time experimental evidence that a red laser beam at 633 nm causes cis‐trans (Z—E) transitions in azobenzene.
Synthesis and properties of poly(arylene ether sulfone)s and poly(arylene ether ketones) derived from 4,4″‐dihydroxy‐o‐terphenyl
Authors: Akutsu Fumihiko , Takahashi Kenichi , Kasashima Yoshio , Inoki Mari , Naruchi Kiyoshi 
Published: April 2003

AbstractNovel poly(arylene ether)s with a rigid and zigzag 4,4″‐o‐terphenyldiyl structure, introduced into the polymer backbone were synthesized by nucleophilic displacement reaction of 4,4″‐dihydroxy‐o‐terphenyl with several activated aromatic dihalides in virtually quantitative yields. The poly(arylene ether)s having high molecular weight show both good solubility in common organic solvents and high thermal stability up to 545°C. They are amorphous with glass transition temperatures of 160–200°C.