bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transport of water vapour and gases in modified cellulose acetate matrices. Influence of the nature of the penetrant on diffusion and relaxation kinetics
Authors: Nguyen Xuan Quang , Šípek Milan , Nguyen Quang Trong , Hynek Vladimir 
Published: April 2003

AbstractMembranes developed by modification of a cellulose acetate (CA) matrix were studied by means of the flow method CA matrix is modified by poly(4‐vinylpyridine) (PVP), or an interpenetrating network (IPN) agent. The obtained diffusion coefficients, permeability coefficients and relaxation kinetic parameters for oxygen, carbon dioxide and water vapour enabled us to consider not only the transport properties of the membranes but also the influence of the relaxation processes on the membrane permeability and stability. The results show that the interactions between water molecules and polar groups on the polymer chains cause the membrane material to swell. This swelling process provokes an increase in the permeation flux of ca. 20–30%. Oxygen causes a consolidation of unstable membranes of the cellulose acetate matrix modified by IPN but not of blends with PVP. The consolidation process reduces the membrane permeability by ca. 38%, while carbon dioxide has no effects on the membrane properties. Membranes based on a modified cellulose acetate matrix have higher permeability than pure CA membranes.
Polymerization of 1,4‐butadiene over MgCl2‐supported cobalt catalysts combined with trimethylaluminium
Authors: Takeuchi Masaki , Shiono Takeshi , Soga Kazuo 
Published: April 2003

AbstractMgCl2‐supported Co catalysts with different loading amounts were prepared from the reaction of CoBr2[P(C6H5)3]2 or CoBr2(C5H5N)2 and MgCl2 in toluene solution. Polymerization of 1,3‐butadiene was conducted with them using Al(CH3)3 as cocatalyst, which gave polybutadiene composed of 1,2 and cis‐1,4 units. The content of 1,2 units could easily be regulated from approximately 0% up to 90% by controlling the loading amount of Co as well as by changing the amount of suitable Lewis base added. The sequence distribution of each unit was determined by means of 13C NMR using hydrogenated polybutadiene. Addition of ethylene to the polymerization system caused a marked decrease in the molecular weight of polybutadiene, but ethylene was incorporated neither in the main chain nor at the chain ends. The chain end analysis of very low‐molecular‐weight polybutadiene by 13C NMR suggested that 1,2 and 2,1 insertion reactions predominantly proceed at the initiation and propagation steps, respectively.
Polyimides with cyclohexyl‐substituted indan groups in the main chain
Authors: Maier Gerhard , Wolf Martin 
Published: April 2003

AbstractA diamine monomer containing the 1,3‐biscyclohexyl‐1‐methylindan group was prepared, starting from cyclohexyl phenyl ketone in four steps. This monomer was reacted with six different dianhydrides (pyromellitic dianhydride, 3,4:3′,4′‐biphenyltetracarboxylic dianhydride, 3,4:3′,4′‐benzophenonetetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, 4,4′‐sulfonyldiphthalic anhydride, 4,4′‐perfluoroisopropylidenediphthalic anhydride) to give the corresponding polyimides via the poly(amic acid) precursors and thermal imidization. All of these polyimides were soluble at least in N‐methyl‐2‐pyrrolidone (NMP) at elevated temperatures, some were soluble in NMP and chlorinated hydrocarbons even at room temperature. The polymers were characterized by nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and dynamic thermogravimetry. All polyimides proved to be amorphous with glass transition temperatures in the range between 261°C and 295°C depending on the nature of the dianhydride moiety. Their decomposition proceeds in two steps, starting at 400°C probably with loss of the cyclohexyl substituents.
Photocrosslinkable comb‐like polymers for membranes: polyamides from modified 5‐aminoisophthalic acid and aromatic diamines
Authors: Ommer Harald J. , Ritter Helmut 
Published: April 2003

AbstractA series of new comb‐like aromatic polyamides containing cinnamoyl groups in the side chains were synthesized by acylation of 5‐aminoisophthalic acid with 4‐alkoxycinnamoyl chlorides or N‐cinnamoyl‐6‐aminocaproyl chloride in DMAc solution and then polycondensated directly with various aromatic diamines. The preparation of homogeneous photocrosslinkable membranes from NMR solution was performed. The products were characterized by IR and NMR spectroscopy and thermal analysis. An amorphous structure was proved in all cases. A strong influence of the side‐chain structure on the photoreactivity has been observed.
Phenolic copolymer/polyelectrolyte/non‐ionic homopolymer interactions: thermodynamic and electrochemical studies in dimethylformamide/water mixtures
Authors: Chatterjee Saroj K. , Nigam Shalini , Chhabra Mamta , Kapoor Vandana 
Published: April 2003

Abstractp‐Aminobenzoic acid/p‐hydroxybenzoic acid/formaldehyde copolymer (I) was prepared and characterized. An interpolymer complex of copolymer (I) was prepared by adding stoichiometric amounts of a polyelectrolyte [poly(methacrylic acid)] and non‐ionic homopolymers [poly(N‐vinyl‐2‐pyrrolidone) and poly(ethylene oxide)]. The stability constant and related thermodynamic parameters (ΔH0 and ΔS0) were determined in DMF‐H2O mixtures of different compositions using Osada's method. The stepwise degradation of the complex is explained on the basis of the relative stability of various interacting forces, particularly in media of varying dielectric constant. Electrochemical studies in the media substantiate the observations from thermodynamic studies.
Free‐radical polymerization of acrylates and vinyl acetates initiated by transition metal/hydrosilane two‐component initiation systems
Authors: Imann Ralf , Bandermann Friedhelm , Korth Hans‐Gert 
Published: April 2003

AbstractThe polymerization of vinyl acetate (VA), methyl methacrylate (MMA), and methyl acrylate (MA) in ethyl acetate and tetrahydrofuran solution was initiated by the two‐component initiating systems Fe(III) 2‐ethylhexanoate or Co(II) acetylacetonate and pentamethyldisiloxane as co‐initiator. Whereas Fe(III) 2‐ethylhexanoate initiated the polymerization of all three monomers also in the absence of the siloxane, with an activity increasing from VA to MA, Co(II) acetylacetonate was completely inactive under these conditions. Addition of the siloxane co‐initiator raised the monomer conversions with both transition metal initiators, particularly pronounced for MMA and MA. Number‐average degrees of polymerization for poly(vinyl acetate) and poly(methyl acrylate) amounted to some hundred or less, but increased to several thousand for poly(methyl methacrylate). Electron spin resonance (ESR) spin trap experiments with N‐tert‐butyl‐α‐phenylnitrone (PBN) revealed that the transition metal compounds and the siloxane undergo a reaction in which free radicals are produced by oxidative cleavage of the co‐initiator to generate hydrogen atoms which initiate the polymerization. With Fe(III) 2‐ethylhexanoate PBN adducts of carbon‐centered radicals are observed in the absence and in the presence of the monomers. By way of contrast, with Co(II) acetylacetonate only the hydrogen atom adduct to PBN is observed in the absence of the monomers. Co(acac)2 is likely to form a new complex with the co‐initiator and the spin‐trap molecules. The co‐ordinated PBN competes with the two parent ligands of the complex for the liberated hydrogen atoms, however, due to favorable reaction rate the PBN‐H adduct is formed preferably. The PBN adducts of carbon‐centered radicals replace the PBN‐H adduct when the monomers are added to the initiator solution, i.e. the H atoms are now preferably trapped by the monomer molecules.
Grafting of maleic anhydride onto poly(tetrahydrofuran)
Authors: Rische Thomas , Zschoche Stefan , Komber Hartmut 
Published: April 2003

AbstractA well‐defined modification of poly(tetrahydrofuran)s was realized by grafting with maleic anhydride. The grafted products were investigated by Fourier‐transform infrared (FTIR) spectroscopy and 13C nuclear magnetic resonance (NMR) spectroscopy. FTIR spectroscopy evidenced a characteristic shift of the carbonyl valence vibrations of cyclic anhydrides to higher wave numbers due to grafting. The grafting of maleic anhydride, which occurred mainly onto poly(tetrahydrofuran) carbons in α‐position, was proved by means of 13C NMR spectroscopy. Furthermore, it was found that approximately 10% of all graftings took place onto poly(tetrahydrofuran) carbons in β‐position. All the grafted units were monosubstituted succinic anhydride units. Indications for the formation of poly(maleic anhydride) graft units were not found. The quantitative determination of grafted anhydride units was carried out by titration after hydrolysis to the acid form. Remarkably high values of percentage grafting up to 20 wt.‐% of maleic anhydride were obtained using an initiator concentration of only 2.5 mol‐% related to maleic anhydride. The high values of percentage grafting at an initail maleic anhydride concentration of 20 wt.‐% were due to a nearly complete conversion of the maleic anhydride. If the initial amount of maleic anhydride was higher than 20 wt.‐% phase separation took place during the reaction. This phase separation prevented complete conversion of the maleic anhydride.
Polymers of carbonic acid, 12. Spontaneous and hematin‐initiated polymerizations of trimethylene carbonate and neopentylene carbonate
Authors: Kricheldorf Hans R. , Lee Soo‐Ran , Weegen‐Schulz Bettina 
Published: April 2003

AbstractThe purity and reactivity of trimethylene carbonate (TMC, 1,3‐dioxan‐2‐one) depends largely on the purification procedure. Vacuum distillation and recrystallization from CCl4 are less efficient than recrystallization from tetrahydrofuran (THF) or ethyl acetate (EtAc). TMC recrystallized from CCl4 contains between 5 and 8 mol‐% of CCl4 which inhibits the spontaneous polymerization at temperatures ≥ 100°C as do other alkylating agents. The spontaneous polymerization of pure TMC may give high yields (up to 90%) and high molecular weights (weight‐average molecular weights up to 200 000). The polymerization mechanism is discussed. It seems to be anionic in nature. Neopentylene carbonate (NPC, 5,5‐dimethyl‐1,3‐dioxan‐2‐one) is rather insensitive to the purification procedure and does not undergo spontaneous polymerization at temperatures ⩽ 125°C. Hematin initiates the polymerizations of TMC and NPC in bulk, but high yields and high molecular weights were only obtained in the case of TMC.
Influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N‐tert‐butyl)TiCl2/methylaluminoxane Ziegler‐Natta catalysts
Authors: Sernetz Friedrich G. , Mülhaupt Rolf , Waymouth Robert M. 
Published: April 2003

AbstractStyrene was copolymerized with ethylene using Me2Si(Me4Cp)(N‐tert‐butyl)TiCl2/methylaluminoxane (Me = methyl, Cp = cyclopentadienyl) varying monomer concentration, styrene/ethylene molar ratio and polymerization temperature. Increasing styrene or decreasing ethylene concentration, respectively, in the monomer feed lowered both activity of the catalyst system and molecular weight of the copolymer. Only at low styrene content, a linear correlation of styrene concentration in the monomer feed and styrene incorporation in the copolymer was found. From copolymerizations at various temperatures the activation energy of the insertion step was calculated to be 56 kJ/mol. According to Fineman‐Ross plot, the copolymerization parameters are rE = 23,4 for ethylene and rS = 0,015 for styrene. Investigation of the thermal properties by means of differential scanning calorimetry and dynamic mechanical analysis revealed pronounced decrease of melting temperature and increase of glass transition temperature with increasing styrene content.
Inverse microemulsion polymerization of acrylamide in the presence of hexamethylenetetramine
Authors: Bartoň Jaroslav , Stillhammerová Martina 
Published: April 2003

AbstractThe inverse microemulsion polymerization of acrylamide is retarded in the presence of hexamethylenetetramine. The retardation effect of a given hexamethylenetetramine concentration on the kinetics of the polymerization of acrylamide depends on the pH of compartmentalized water droplets. For non‐crosslinked polymer particles the polymer particle diameter for a given composition of the inverse microemulsion increases in the presence of hexamethylenetetramine, while the relative molecular mass (molecular weight) of the polymer decreases. Depending on the pH value of the compartmentalized water droplets polymer particles with different crosslinking degree (of different swelling index) were obtained. The kinetics of polymerization and the polymer particle characteristics are discussed with respect to the hexamethylenetetramine effect on the stability of dispersed particles in an inverse microemulsion prior to and during the polymerization and in terms of the effect of “in situ” formed hexamethylenetetramine decomposition products and of their reactions with acrylamide and/or acrylamide structural units in the polymer.
Synthesis of polyesters with pendant chloromethyl group by polyaddition of bis(oxetane)s with diacyl chlorides catalyzed by quaternary onium salts
Authors: Kameyama Atsushi , Yamanoto Yuko , Nishikubo Tadatomi 
Published: April 2003

AbstractA new polyaddition of bis(oxetare)s with diacyl chlorides catalyzed by quaternary onium salts is described. The reactions of the new bifunctional monomer, bis(3‐methyl‐3‐oxetanylmethyl) terephthalate, with terephthaloyl chloride using quaternary ammonium halides proceed smoothly under mild conditions to give the corresponding polyester with chloromethyl group in the side chain. It was proved that quaternary onium halides such as tetraethylammonium bromide and tetrabutylammonium chloride and bromide (TBAB) had high catalytic activity in the polymerization in low polar solvents such as anisole and toluene to produce the polyester with high molecular weight. The polyaddition of various bis(oxetane)s with diacyl chlorides using TBAB as the catalyst also proceeded to give the targeted polyesters with pendant chloromethyl group, which is introduced simultaneously with the formation of the polymer backbone during the reaction.
Synthesis of SBC, SC and BC block copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(ε‐caprolactone) (C) block
Authors: Balsamo Vittoria , von Gyldenfeldt Friederike , Stadler Reimund 
Published: April 2003

AbstractThe sequential anionic polymerization of polystyrene‐block‐polybutadiene‐block‐poly(ε‐caprolactone) (SBC) triblock copolymers as well as polystyrene‐block‐poly(ε‐caprolactone) (SC) and polybutadiene‐block‐poly(ε‐caprolactone) (BC) diblock copolymers was achieved in benzene. To initiate the polymerization of the highly reactive ε‐caprolactone, the nucleophilicity of the carbanion has to be reduced. For this purpose 1,1‐diphenylethylene (DPE) was used. To avoid inter‐ and intramolecular transesterification reactions of the growing caprolactone block, the reaction time of this monomer in the block copolymers was strictly controlled. The reaction between polybutadienyl anions and DPE is too slow, and an incomplete reaction results in side reactions when ε‐caprolactone is added. An alternative method was developed, which consisted in the addition of a small quantity of styrene, after the polymerization of butadiene, to diminish the total reaction time and reduce the probability of chain transfer.
Low‐molecular‐weight poly(imide‐amide)s obtained by copolycondensation of 4,4′‐methylenedi(phenyl isocyanate), trimellitic anhydride and benzoic acid in N‐methyl‐2‐pyrrolidone, 2. Structural defects observed by 1H and 13C NMR
Authors: Sintès‐Zydowicz Nathalie , Pham Quang Tho , Michaud Philippe 
Published: April 2003

AbstractThe in depth examination (by 1H and 13C NMR, DSC, SEC and TGA) of the low‐molecular‐weight poly(imide‐amide)s synthesized with the mixture [4,4′‐methylenedi(phenyl isocyanate) (M) + trimellitic acid anhydride (T) + benzoic acid (B)] in N‐methyl‐2‐pyrrolidone (NMP) at temperatures lower than 180°C allowed the identification and quantitative determinations of all the unexpected and relatively stable structures. While amide functions are readily synthesized, the formation of imide from anhydride and isocyanate functions passes through 4‐amido‐1,2‐benzenedicarboxylic acid (Ti), 1,4‐di‐amido‐2‐benzenecarboxylic acid (T″) and disubstituted urea (u). At 180°C Ti completely disappears but traces of T″ and u remain; thus, the formation of imide can never reach its theoretical quantity. Traces of moisture in NMP may play the role of catalyst in the formation of imide, and reaction mechanisms are proposed.
Influence of the tacticity dependent microstructure on the space charge distribution of poly(vinyl chloride)
Authors: Vella Nathalie , Toureille Alain , Guarrotxena Nekane , Millan José‐Luis 
Published: April 2003

AbstractThe space charge distribution of three samples of poly(vinyl chloride) of different isotactic content has been studied by the thermal step technique, with a view to investigating the influence of some defined microstructural features on that important behaviour. It has been observed that the space charge increases substantially as the content of the local tetrad configuration, mmr, at the end of isotactic sequences increases. A first tentative interpretation is given.
Functionalized poly(ε‐caprolactone) and copolymers with ethylene oxide through heterogeneous anionic coordinated polymerization. NMR characterization and crystallinity
Authors: Jacquier Véronique , Miola Christelle , Llauro Marie‐France , Monnet Christiane , Hamaide Thierry 
Published: April 2003

AbstractFunctionalized poly(ε‐caprolactone)s have been easily prepared by using a new heterogeneous catalytic system consisting of aluminium alcoholate supported on porous silica and the corresponding alcohol in excess. The polymers have been fully characterized by 1H and 13C NMR spectroscopy. Oligo(caprolactone‐co‐ethylene oxide)s have been synthesized by the same catalytic system. The diad comonomer distribution as obtained by 1H NMR suggests a blocky structure. In addition, low degrees of crystallization have been determined by means of DSC.
Influence of chirality on the phase behaviour of copolymers containing cholesterol as mesogenic moiety
Authors: Weidner Steffen , Wolff Dietmar , Springer Jürgen 
Published: April 2003

AbstractLiquid‐crystalline side‐group copolymers containing cholesterol and chiral nonmesogenic chloropropionate acid groups were synthesized and investigated by means of size‐exclusion chromatography, proton nuclear magnetic resonance (1H NMR), polarization microscopy, X‐ray diffraction and differential scanning calorimetry. In addition the spacers of the cholesterol‐containing side groups were modified by substitution of two of the methylene groups by oxygen ether groups. The cholesterol‐containing homopolymer displays only an SA‐mesophase. Amounts of more than 50 mol‐% of the non‐mesogenic chiral co‐compounds led to the total disappearance of liquid‐crystalline phases. For less than 50 mol‐% a different phase behaviour was observed for the copolymers with unsubstituted and ether‐substituted spacers. Phase transition temperatures depend also on the chirality of the non‐mesogenic groups. Similar results were obtained by investigating a copolymer system, which contains chiral camphor‐10‐sulfonic acid moieties and which was synthesized to check this observation.
Low‐temperature 1H and 13C NMR investigation of trimethylaluminium contained in methylaluminoxane cocatalyst for metallocene‐based catalysts in olefin polymerization
Authors: Tritto Incoronata , Sacchi Maria Carmela , Locatelli Paolo , Li San Xi 
Published: April 2003

AbstractToluene‐d8 solutions of methylaluminoxane (MAO) after the addition of different amounts of trimethylaluminium (TMA) have been studied by means of 1H and 13C NMR at a temperature as low as −78°C to freeze out some of the fluxional equilibria of the molecule. A comparison of the half height width of the NMR signal W1/2 and of the mole ratio of the methyl signals before and after addition of known amounts of TMA allowed us to reach the following conclusions about the TMA contained in MAO solutions: (a) TMA is mainly bound to MAO; (b) TMA participates in disproportionation reactions.
Morphological studies on a novel poly(aryl ether ketone)
Authors: Wang Shanger , Wang Junzuo , Zhang Hongfang , Wu Zhongwen , Mo Zhishen 
Published: April 2003

AbstractThe morphology of a novel poly(aryl ether ketone) [PEDEKmK] was investigated via polarizing optical microscopy (POM), TEM, DSC, SAXS and electron diffraction (ED). A distinct change in lamellar thickness, orientation, and spherulitic morphology was observed due to crystal melting and recrystallization. However, the crystal packing mode is found to be identical before and after the recrystallization process.
Mécanisme de photoréticulation de polymères contenant le motif dicyclopentadiène en présence et en absence de benzophénone
Authors: Eisele Gilles , Fouassier Jean‐Pierre , Reeb Roland 
Published: April 2003

AbstractThe study of the mechanism of the processes taking place in photocrosslinking of the homopolymer of dicyclopentenyl acrylate (DCPA), was realized using ultraviolet and Fourier transform infrared (FTIR) measurements. Different kinetics of crosslinking in the presence and absence of benzophenone prove the efficiency of this photosensitive system. The particular structure of the acrylic matrix of poly(DCPA), i.e., the presence of a residual unsaturated bond and a cyclic structure, reveals its high photooxidation potential (hydroperoxyde formation as detected by FTIR between 3 300 and 3 600 cm−1).
Manipulation of the ferroelectricity in LC polymers via photomechanical isomerization of azobenzene moieties
Authors: Öge Tanja , Zentel Rudolf 
Published: April 2003

AbstractWe report the synthesis and characterization of a new ferroelectric liquid crystalline side chain copolymer containing photoisomerizable chromophores and non‐photoisomerizable mesogenic units. On illumination with UV‐light a suppression of the polar order is obtained as indicated by a substantial drop of the spontaneous polarization (PS) compared to the dark state. We interpret this as the phase order being disrupted by the cis‐isomer of the chromophore. After illumination with VIS‐light only the major part of Ps is restored. The photochemical cis‐trans back‐isomerization (restoration of the phase) leads to a different stationary state than the dark state of the material. The thermal reisomerization (cis‐trans) in the liquid‐crystalline phase was observed to be faster than in solution by one order of magnitude.
Ligand effects on olefin polymerizations with multinuclear zirconocene catalysts having dimethylsilylferrocene as a cyclopentadienyl substituent
Authors: Mitani Makoto , Oouchi Kunihiro , Hayakawa Michiya , Yamada Tohru , Mukaiyama Teruaki 
Published: April 2003

AbstractOlefin polymerizations were conducted with novel multimetallic zirconocene catalyst systems: RCpCpZrCl2 (1) (R = dimethylsilylferrocene; Cp = cyclopentadienyl) and (RCp)2ZrCl2 (2) in combination with methylaluminoxane or tetrakis(pentafluorophenyl) borates. In ethylene polymerization, the maximum catalyst activity was observed at a lower temperature (30–45°C) when using complex 1 or 2, compared with Cp2ZrCl2. It was also revealed that complex 1 is a more effective catalyst than Cp2ZrCl2 for copolymerization of ethylene and propene.