bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid‐crystalline polyethers and copolyethers of 4‐hydroxy‐acetophenone azine with a homologous series of flexible methylene spacers
Authors: Cimecioglu A. Levent , Weiss R. A. 
Published: April 2003

AbstractThe synthesis of high‐molecular‐weight polyethers and copolyethers based on 4‐hydroxyacetophenone azine and α,ω‐dibromoalkanes was carried out in N‐methyl‐2‐pyrrolidone via Williamson etherification using the caesium salt of the diol. Polyethers were composed of a homologous series of flexible methylene spacers with m = 5−12, while the copolyethers contained a 1:1 mole ratio of two different spacers with m = 5/7, 6/8, 7/9, 8/10, 9/11 and 10/12. Polymers with relatively short spacers (m = 5−8 methylene groups) exhibit enantiotropic mesomorphism, whereas those having m = 8−11 are tentatively identified to be monotropic. The polyether with m = 12 is crystalline. Copolyethers are enantiotropic and their mesophase ranges are considerably wider than those of the homopolyethers. The mesophases were identified to be nematic by polarised light microscopy. The transition temperatures of both the homopolymers and copolymers show classical even‐odd variations as a function of the spacer length.
Studies on the polymerization of ethylene using a high‐yield MgCl2‐supported titanium catalyst, 1. Effects of synthesis parameters on catalyst activity and polymer properties
Authors: Fuhrmann Hans , Bredereck Hartmut , Pracht Heinz 
Published: April 2003

AbstractThe preparation of a highly active Ti‐Mg catalyst in two steps is reported. the first step is a Grignard reaction conducted in hexane with an under‐stoichiometric amount of tetrahydrofuran. In the second step the Grignard suspension is treated with a TiCl4/CCl4 mixture. Owing to optimized synthesis conditions after a thermal activation the catalyst suspension is ready for use in combination with an alkylaluminium cocatalyst without further separation and drying operations. Because of its high response to H2 the catalyst may preferably be used for the production of polyethylene (PE) for injection moulding. Depending on the Ti content the catalyst shows an activity of between 184 and 250 kg PE per g Ti per h and per bar for a PE with melt flow index between 20 and 30 g/10 min. The content of Ti4+ in the catalyst is high (up to 72 wt.‐%). The catalyst suspension shows a marked resistance against reduction by the cocatalyst. The catalytic activity not only depends on the mole ratio of the individual catalyst components but even more on their actual concentration in the reaction medium.
Polymeric phthalocyanines and their precursors, 17. Structure and photoelectrochemical properties of thin films of polymeric phthalocyanines from bridged diphthalonitriles
Authors: Yanagi Hisao , Wada Minoru , Ueda Yasukiyo , Ashida Micho , Wöhrle Dieter 
Published: April 2003

AbstractThin films of polymeric phthalocyanines 4a–c were prepared by in‐situ syntheses from oxy‐and phenoxy‐bridged diphthalonitriles 3a–c with copper layers deposited on Ti plates and KCI crystals. The structure of the polymers was characterized by VIS, IR and photoelectron spectra, and scanning electron microscopy. The most uniform structure was obtained for polymer 4c, in which phthalocyanine rings were linked two‐dimensionally by flexible bridges of phenoxy groups. Polymers 4a and 4b are structurally not uniform, and formation of phthalocyanine rings was incomplete especially in polymer 4a. Photoelectrochemical properties of polymeric phthalocyanine electrodes were investigated in Ti/4a–c/Fe(CN)63−/4−/Pt cells. The electrode of 4a shows n‐type semiconducting behavior under illumination. The current‐voltage curve for the electrode of 4b did not show remarkable rectification or photocurrents. On the other hand, cathodic photocurrents were obtained for the electrode of 4c, indicating a p‐type semiconducting behavior under illumination. The photoelectrochemical properties were related to the structural uniformity of the polymers.
Polymerization of monomers containing functional silyl groups, 12. Free‐radical polymerization of 2‐silyl‐substituted 1,3‐butadienes
Authors: Takenaka Katsuhiko , Hirao Akira , Nakahama Seiichi 
Published: April 2003

AbstractFree‐radical polymerizations of five 2‐silyl‐substituted 1,3‐butadienes, 2‐trimethoxysilyl‐1,3‐butadiene (1), 2‐triisopropoxysilyl‐1,3‐butadiene (2a), 2‐[diisopropoxy(methyl)silyl]‐1,3‐buta‐diene (2b), 2‐[isopropoxy(dimethyl)silyl]‐1,3‐butadiene (2c), and 2‐trimethylsilyl‐1,3‐butadiene (3), were carried out in bulk. Considerable amounts of Diels‐Alder dimers as well as polymers were obtained at 80°C with AIBN as an initiator. Formation of the dimer was suppressed completely at 15°C with a redox type initiator, a combination of benzoyl peroxide and N,N‐dimethylaniline. In these cases, the polymerization rates were extremely low, resulting in low polymer yield, at most 50%. The microstructures of the resulting polymers were predominantly E‐1,4, regardless of the polymerization conditions and the substituents at the silicon atom. The results of copolymerizations of silyl‐butadienes (M1) and styrene (M2) show that the former monomers have higher reactivity than the latter (r1 = 4,1 − 2,2;r2 = 0,4 − 0,5). The r1 values decrease with an increase in the number of methyl groups at the silicon atom.
Synthesis of polystyrene‐poly(tert‐butyl acrylate) diblock copolymers bearing fluorescent groups at the junctions
Authors: Hruska Zdenek , Vuillemin Bruno , Riess Gérard , Katz Aviva , Winnik Mitchell A. 
Published: April 2003

AbstractAB‐type diblock copolymers composed of polystyrene as the A block and poly(tert‐butyl acrylate) as the B block were synthesized by sequential anionic polymerization. 1‐(2‐Anthryl)‐1‐phenylethylene, a new fluorescent monomer, and 1‐(9‐phenanthryl)‐1‐phenylethylene were used to introduce fluorescent moieties at the block junctions. Ultraviolet (UV) spectroscopy and gelpermeation chromatography (GPC) analyses were used to characterize the prepared copolymers.
Synthèse de polyquinazolones à chaîne latérale fluorée
Authors: Boutevin Bernard , Ranjalahy‐Rasoloarijao Laurent , Rousseau Alain , Garapon Jacques , Sillion Bernard 
Published: April 2003

AbstractBis(4H‐3,1‐benzoxazin‐4‐one) substituted in 2‐ and 2′‐position with CH2CH2RF, where RF is a perfluorinated alkyl group, have been prepared. Polycondensation with 4,4′‐oxydianiline and with 4,4′‐methylenedianiline led to polyquinazolones which have different inherent viscosities according to the solvent of polycondensation and to the proportions of reactants used. The thermal behavior of these polymers characterized by differential scanning calorimetry or thermogravimetry was studied. The polyquinazolones are thermostable and exhibit a fluorine content of 50 mass‐%.
Tri‐armed star polymers by living cationic polymerization, 3. Synthesis of tri‐armed star poly(p‐methoxystyrene)
Authors: Shohi Hajime , Sawamoto Mitsuo , Higashimura Toshinobu 
Published: April 2003

AbstractTri‐armed star polymers of p‐methoxystyrene (pMOS) were synthesized by living cationic polymerization with a trifunctional initiator CH3C[(p‐)C6H4OCH2CH2OCH(CH3)I]3 (6) or C6H3(1,3,5‐)[COOCH2CH2OCH(CH3)I]3 (9) with zinc iodide as activator in toluene at −15°C. The number‐average molecular weight (Mn) of the polymers increased proportionally to the monomer conversion and further increased upon addition of fresh feed of pMOS to completely polymerized reaction mixtures; the polymers invariably exhibited very narrow molecular‐weight distributions (MWD) (Mw/Mn < 1,1). The living polymers were terminated with 2‐hydroxyethyl methacrylate to give a tri‐armed macromonomer where each arm is capped with a methacrylate group, and the quantitative end‐capping, in turn, showed the existence of three living ends per molecule. When the ester‐type initiator residue (core) of the poly(pMOS), obtained with the 9/ZnI2 system, was hydrolyzed under alkaline conditions, Mn was reduced to one third of the original value, with the narrow MWD being unchanged, thus indicating that the polymer possesses three arms with uniform and controlled length.
Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert‐butyl chloride catalyst system, 1. Effect of norbornadiene/styrene feed ratio
Authors: Sagane Toshihiro , Minami Shuuji 
Published: April 2003

AbstractThe cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl2/tert‐butyl chloride catalyst system in CH2Cl2 at −50°C, and the effect of NBD/St feed ratio on the solubility, the glass trtansition temperature (Tg) and the molecular weight of the copolymers was investigated. A soluble copolymer was prepared at 40 mol‐% (or above) of St in the feed, although the NBD homopolymer comprised an insoluble fraction which might have been formed by a crosslinking reaction between the double bonds in the NBD units of the polymer. The copolymer has a statistically random sequence distribution of the two monomeric units not only in the polymer chain but also over the whole molecular weight range (from 103 to 106). The Tg of the amorphous copolymer is controlled by the NBD/St composition in the range from 100°C through 290°C. A soluble copolymer with highest Tg (ca. 170°C) could be prepared at a NBD/St feed ratio of 60/40 mol‐%.
Ring‐opening metathesis polymerization of syn‐ and anti‐7‐methylbicyclo[2.2.1]hept‐2‐ene initiated by Mo(CHCMe3)(NC6H3‐2,6‐i‐Pr2)(OCMe3)2
Authors: Feast W. James , Gibson Vernon C. , Ivin Kenneth J. , Khosravi Ezat , Kenwright Alan M. , Marshall Edward L. , Mitchell Jonathan P. 
Published: April 2003

AbstractThe ring‐opening metathesis polymerization of syn‐ and anti‐7‐methylbicyclo[2.2.1]hept‐2‐ene (Ms and Ma) by Mo(CHCMe3)(NC6H3‐2,6‐i‐Pr2)(OCMe3)2 has been followed by 1H and 13C NMR spectroscopy in C6D6 and CD2Cl2 as solvents. The anti monomer Ma polymerizes first, followed much more slowly by the syn monomer Ms, leading to a block copolymer. The reaction is considerably faster in CD2Cl2, where it proceeds to completion, than in C6D6. In C6D6kpa/kia = 9, as determined from the proportion of residual initiator. The double bonds formed are mainly trans (80–90%) in both blocks and the diads embracing the trans double bonds in the Ma blocks have an isotactic bias: (σm)t = 0,69 in C6D6, independent of monomer concentration; the diads in the Ms bloks have a slight tactic bias, probably isotactic. The tacticity is interpreted in terms of control of addition of monomer by the configuration of the chiral carbons in the C5 ring nearest to the molybdenum centre in the propagating metal‐carbene complex.
Ceric ion consumption in graft copolymerization of methacrylonitrile/methacrylate mixtures onto amylomaize
Authors: Vázquez Blanca , Goñi Isabel , Gurruchaga Marilo , Areízaga Javier , Valero Miguel , Guzmán Gonzalo M. 
Published: April 2003

AbstractA study on the Ce(IV) consumption in the graft copolymerization of methacrylonitrile/n‐alkyl methacrylate mixtures methyl, ethyl and butyl methacrylate/methacrylonitrile (MMA/MAN, EMA/MAN and BMA/MAN) was carried out. Ce(IV) consumption increased with increasing mole fraction of the methacrylate in the monomer feed and with increasing the n‐alkyl group length of the methacrylate, but in no case the consumption was total. The molecular weight distribution of the copolymers was obtained through gel‐permeation chromatography. For all systems investigated, both number‐average molecular weight (Mn) and weight‐average molecular weight (Mw) increased with increasing methacrylate concentration in the monomer feed. The ratios Mw/Mn increased in the following order: MMA/MAN < EMA/MAN < BMA/MAN. For the MAN/MMA system, the number of grafted chains (in mmol) increased as the methyl methacrylate content increased in the monomer feed, and for the MAN/EMA and MAN/BMA systems, this parameter presented a maximum value. The number of D‐anhydroglucose units per grafted chain (frequency) decreased with increasing methacrylate concentration in monomer feed for the MAN/MMA system, and this parameter reached a minimum value at a methacrylate mole fraction of 0,5 for the other two systems.
Emulsion copolymerization of styrene and butyl acrylate with itaconic acid
Authors: Václavová Eva , Hrivík Alexander , Chrástová Viera 
Published: April 2003

AbstractThe emulsion copolymerization of styrene with itaconic acid and butyl acrylate with itaconic acid (methylenesuccinic acid), initiated by a redox system in the presence of a nonionic emulsifier, was studied at 40°C. Examination of the influence of itaconic acid on the copolymerization with both monomers showed that the presence of itaconic acid had a negative influence on copolymerization conversion and on the rate of copolymerization. the reaction order with respect to itaconic acid is −0,34 for the copolymerization of itaconic acid with styrene and −1,40 for its copolymerization with butyl acrylate. In the case of the copolymerization with styrene, itaconic acid has no effect on particle number concentration and particle size. Itaconic acid participates in particle nucleation during its copolymerization with butyl acrylate. Formation of oligomeric radicals in the water phase led to a decreasing number of particles and to increasing particle size.
Solid‐solid‐liquid phase transfer reactions catalyzed by polymer‐supported ureas
Authors: Kondo Shuji , Okamura Takeshiro , Takesue Masakazu , Kunisada Hideo , Yuki Yasuo 
Published: April 2003

AbstractPolymer‐supported ureas were prepared by copolymerization of the corresponding vinyl monomers and divinylbenzene with 2,2′‐azoisobutyronitrile. These polymers show catalytic activity in the reaction of 1‐bromooctane with solid potassium thiocyanate, although the corresponding monomeric ureas are inactive. The catalytic activity is enhanced remarkably by replacing the amino hydrogen for a methyl group. Further, the catalytic activity is affected by some experimental parameters such as stirring, particle size of the catalyst, degree of crosslinking, and solvent. On the basis of the above results, a plausible catalytic reaction mechanism consiting of collisional contact between the solid catalyst and the reagent is proposed.
Solution copolymerization of monomethyl itaconate and methyl methacrylate
Authors: Kelemen Peter , Hrivík Alexander 
Published: April 2003

AbstractThe copolymerization of monomethyl itaconate (M1) (4‐methyl 1‐hydrogen 2‐methylene‐succinate) with methyl methacrylate (M2) was studied in bulk and in ethyl acetate solution. The reactivity ratios were determined to be r1 = 0,56 ± 0,02 and r2 = 1,56 ± 0,05. The dependences of copolymerization rate and degree of polymerization on initiator concentration, total monomer concentration and composition of monomer feed were measured. The reaction order with respect to the initiator concentration was near to the theoretical one (0,5), while that with respect to the total monomer concentration was considerably higher than predicted by theory (1,0). It could be explained by the influence of transfer reactions and diffusion control of termination reactions. Transfer reactions contribute to the reaction order mainly at low monomer concentration, while the influence of the medium viscosity becomes predominant at high monomer concentration.
Is 1,2‐bis(2,4‐octadecadienoyl)‐sn‐glycero‐3‐phosphorylcholine (DODPC) an efficient chiral probe to study conformational changes in lipid membranes?
Authors: Faupel Peter , Buβ Volker 
Published: April 2003

AbstractIn order to study its possible use as a chiral membrane probe, small unilamellar vesicles of 1,2‐bis(2,4‐octadecadienoyl)‐sn‐glycero‐3‐phosphorylcholine (DODPC, 1), a doubly unsaturated phospholipid molecule, and vesicles of 1,2‐dipalmitoyl‐ or 1,2‐dimyristoyl‐sn‐glycero‐3‐phos‐phorylcholine or egg‐lecithin, containing DODPC, were prepared and investigated by UV and circular dichroism (CD) spectroscopy. The phase transitions that are clearly manifest in the UV effect reproducible but only small changes in the CD. This indicates that at least in the area of unsaturation the molecule is rather stiff and insensitive to its micro‐environment. A non‐membrane‐forming short‐chain model compound, 1,2‐bis(2,4‐hexadienoyl)‐sn‐glycero‐3‐phos‐phorylcholine, 2, was used to study the chiroptic properties of the isolated molecule; the results are in agreement with calculations and support the contention that bis‐unsaturated lipid molecules should in principle be able to function as chiral labels.
2H NMR study of solvent and solute mobility in polymer solution, gel and glass states
Authors: Sentosa Petrus , Fujara Franz , Sillescu Hans 
Published: April 2003

Abstract2H spin relaxation times, T1 and T2 and solid echo line shapes were investigated in 2‐propanol (2‐POH) solutions of poly(butyl methacrylate) (PBMA) in a wide concentration and temperature range, covering the solution, gel and glass states. From the results in deuterated 2‐POH‐d6 we found that the polymer influence upon solvent mobility is largely suppressed in the gel and glass states in contrast to normal polymer solutions where below the glass transition an increasing amount of solvent slows down with decreasing temperature. From 2H NMR of deuterated butyl side groups in the PBMA‐d9/2‐POH system we found that the side group motion is anisotropic and largely independent of solvent concentration in the gel and glass states which confirms that polymer‐polymer interaction via side group interpenetration should be considered as the main cause for gel formation in this system.
Synthesis of high‐molecular‐weight poly(dimethylsiloxane) of uniform size by anionic polymerization, 1. Initiation by a monofunctional lithium siloxanolate
Authors: Maschke Ulrich , Wagner Thomas , Coqueret Xavier 
Published: April 2003

AbstractAn improved procedure for the anionic polymerization of hexamethylcyclotrisiloxane (D3) initiated by a monofunctional lithium derivative is reported. The initiator seeding solution is preferably prepared in benzene, and tetrahydrofuran is used as a cosolvent which makes the presence of additional promoters useless. The main advantage of this procedure is that it delays the appearance of bimodality which is believed to result from a sudden change in aggregate molecularity during the course of the reaction. Applying this method, poly(dimethylsiloxane) samples having a single functional endgroup and possessing high molecular weights and narrow molecular weight distributions (1,03 ≤ M̄w/M̄n ≤ 1,06) were prepared on the 100 g scale.
Synthesis and thermal properties of poly(arylene‐1,2,4‐oxadiazole)s with flexible, linear alkoxymethyl side branches
Authors: Park Sang‐Bong , Jung Jin Chul 
Published: April 2003

AbstractPoly(arylene‐1,2,4‐oxadiazole)s (PAOs) bearing flexible, linear side chains, 3a‐c, were prepared by solution cyclodehydration of their precursors, poly(arylene acyloylamide oxime)s (PAAs), 2a‐c, which were synthesized by solution polycondensation of 2,5‐bis(n‐alkoxymethyl)‐terephthaldiamide oximes (DIS‐TADO), 1a‐c, with terephthaloyl dichloride (TPC). The length of the n‐alkoxy group was varied from methoxy via butoxy to octyloxy. The reduction of the phase transition temperatures and the enhancement of the solubilities of 3a‐c were greatly affected by the length of the side chains. PAOs with longer side chains, 3b and 3c, are nematic type liquid‐crystalline polymers.
Basic studies on the inifer mechanism, 1. Interaction of 1,4‐bis(1‐chloro‐1‐methylethyl)benzene with BCl3
Authors: Dittmer Thomas , Pask Stephen D. , Nuyken Oskar 
Published: April 2003

AbstractA mixture of 1,4‐bis(1‐chloro‐1‐methylethyl)benzene (1) and BCl3 at −80°C in CH2Cl2 yields a red colour, which is explained as a result of the formation of a charge transfer (CT) complex between the carbenium ion formed after Cl− abstraction from 1 and the aromatic π‐system of 1. This view is supported by UV/VIS and conductivity measurements. These measurements and their consequences for the cationic polymerization are discussed in detail.
Basic studies on the inifer mechanism, 2. Interaction of 1,4‐bis(1‐methoxy‐1‐methylethyl)benzene with BCl3 in CH2Cl2
Authors: Dittmer Thomas , Pask Stephen D. , Nuyken Oskar 
Published: April 2003

Abstract1,4‐Bis(1‐methoxy‐1‐methylethyl)benzene is a representative of a novel generation of inifers, initiator/transfer agents for cationic polymerizations. In contrast to the classical initiator 1,4‐bis(1‐chloro‐1‐methylethyl)benzene its activation needs an excess of BCl3. This behavior is closely related to a complex formation between the ether and BCl3. On the basis of combined UV/VIS and conductivity measurements a mechanism for the ion formation is suggested.
Liquid‐crystalline side‐group polyesters with definite lengths of the main‐chain spacers
Authors: Böhme Axel , Lindau Jürgen , Rötz Uwe , Hoffmann Frank , Fischer Hartmut , Diele Siegmar , Kuschel Frank 
Published: April 2003

AbstractNew liquid‐crystalline polyesters 1 with 4‐(phenylazo)azobenzene moities as mesogenic side groups and a polyester backbone structure characterized by a systematic variation of the length of the flexible non‐mesogenic main‐chain segments were synthesized. The polyesters were investigated by differential scanning calorimetry, polarizing microscopy, miscibility studies and X‐ray diffraction. With increasing number of methylene groups in the backbone spacer, the thermal stability of the nematic and/or smectic phases first decreases and then increases.
Determination of surface morphology of diblock copolymers of styrene and butadiene by atomic force microscopy
Authors: Annis Brian K. , Schwark Dwight W. , Reffner John R. , Thomas Edwin L. , Wunderlich Bernhard 
Published: April 2003

AbstractA detailed study by atomic force microscopy of the surfaces of diblock copolymers which exhibit lamellar and spherical microphase domains in the bulk is presented. The surface morphology of the lamellar samples consists of corrugations. Transmission electron microscopy of cross sections which include the surface and near surface demonstrate the connection between the corrugations and the bulk lamellae. The surface of a sample with spherical bulk domains was found to consist of a series of pits that can be linked with centers on the faces of the cubic cell arrangement of the bulk. Disclinations and intersections of lamellae could be found. The latter result in lamellar break‐up in the contact area of the two lamellar orientations. Lamellar tilt can lead to variation in periodicity and depth of the surface morphology. Damage due to scanning was observed, but only for the sample with spherical morphology.
Cleavage of oligopeptide p‐nitroanilides attached to N‐(2‐hydroxypropyl)methacrylamide copolymers by guinea pig intestinal enzymes
Authors: Kopečková Pavla , Ikesue Koichi , Kopeček Jindřich 
Published: April 2003

AbstractN‐(2‐Hydroxypropyl)methacrylamide copolymers containing oligopeptide side chains terminated with p‐nitroaniline, and low‐molecular‐weight oligopeptide p‐nitroanilides, were synthesized. They were used as substrates to evaluate the enzymatic activity in the gastrointestinal tract of guinea pigs. Brush border membrane enzymes and luminal enzymes (supernatant and pellet) were isolated from guinea pig small intestine and colon, and the cleavage of the substrates was studied in vitro. The results indicate the presence of endopeptidase activity in both small intestine and colon brush border. Phosphoramidon, a potent inhibitor of endopeptidase‐24.11, was effective in the cleavage of low‐molecular‐weight substrates, but ineffective in the cleavage of polymeric substrates, indicating the participation of a different endopeptidase in the cleavage of the latter. Luminal enzymes were more active in the cleavage of polymeric substrates (when compared to low‐molecular‐weight ones) in accordance with the physiological function of the gastrointestinal tract. The enzymatic activity, both luminal and brush border, was considerably lower in the colon than in the small intestine. This suggests that the colon might be a suitable site for the oral delivery of peptides and proteins.