bluuebunny/crossref_metadata_2025_split huggingface dataset:
Untersuchungen zur irreversibilität von Netzwerkentschlaufungen beim Fließen von Polymerschmelzen
Authors: Ehrecke Petra , Wagner Manfred H. 
Published: April 2003

AbstractExperimental and theoretical investigations of stress relaxation after “double‐step” shear experiments lead to a better understanding of the irreversibility assumption of polymer melts. Here we compare measurements of shear stress relaxation for a branched polyethylene and a (linear) polyisobutene melt to theoretical predictions of Wagner's first and second equation and to a molecular theory of Doi. None of these theories is able to describe all the results of the measurements. These investigations demonstrate, however, what types of “double‐step” shear experiments are most sensitive to the irreversible disentanglement of polymer melts.
Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 5. Nuclear magnetic resonance study of the model dimer in tetrahydrofuran
Authors: Kříž Jaroslav , Dybal Jiří , Lochmann Lubomír , Janata Miroslav , Vlček Petr 
Published: April 2003

AbstractDi‐tert‐butyl 2‐lithio‐2,4,4‐trimethylglutarate (1) as a model of the living dimer of tert‐butyl methacrylate was studied in deuterated tetrahydrofuran (THF‐d8) solution by 6Li, 7Li, 1H and 13C NMR. In agreement with earlier observations from infrared spectroscopy and with quantum chemical ab initio and semiempirical self‐consistent field calculations, 1 is shown to have a strong tendency to an intramolecular coordination of Li to the penultimate ester carbonyl group. The competing linear form of 1 (with uncoordinated penultimate ester group) is shown to exist due to its stabilization by self‐aggregation to form a dimer of 1. In contrast to the monomeric form of 1, the dimer does not bind THF into a specific solvate. Given the entropy‐driven solvation at low temperatures, the occurrence of the dimeric aggregate is enhanced by higher temperature and concentration of 1. Both the cyclic and linear form of 1 are shown to exist in at least two different conformers and various solvation states. Their mutual exchange is several orders of magnitude slower than the anionic propagation reaction of tert‐butyl methacrylate.
Synthesis and properties of polyamides and poly(amideimide)s based on 4,4′‐[1,4(or 1,3)‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline
Authors: Hsiao Sheng‐Huei , Yang Chin‐Ping , Fan Jr‐Chen 
Published: April 2003

AbstractThe diamines 4,4′‐[1,4(or 1,3)‐phenylenebis(isopropylidene‐1,4‐phenyleneoxy)]dianiline (p‐3 and m‐3) were synthesized in two steps from the condensation of 4,4′‐[1,4(or 1,3)‐phenylenediisopropylidene]diphenol (p‐1 and m‐1) and p‐chloronitrobenzene in the presence of K2CO3 in N,N‐dimethylformamide (DMF), giving the corresponding bis(4‐nitrophenoxy) compounds, followed by reduction with the hydrazine/Pd‐C system. A series of aromatic polyamides, aliphatic‐aromatic polyamides, and poly(amide‐imide)s were prepared by the direct polycondensation of the diamines with aromatic or aliphatic dicarboxylic acids and phthalimide unit‐bearing dicarboxylic acids in N‐methyl‐2‐pyrrolidone (NMP) using triphenyl phosphite and pyridine as condensing agents. In addition, two series of polyamides were prepared from terephthalic acid or isophthalic acid and aromatic diamines with isopropylidene and/or ether linking groups between the phenylene units, and the structure‐property relationships of these polyamides were studied. Almost all the resultant polymers were amorphous in nature and could be solution‐cast into transparent, tough, and flexible films. Most of the polymers exhibited moderately high thermal stability. Thus, they are considered as new candidates for processable high‐performance polymeric materials.
A study of the thermal degradation of poly(mono‐n‐alkyl itaconates)
Authors: Velada José L. , Cesteros Carlos , Madoz Ana , Katime Issa 
Published: April 2003

AbstractThe thermal degradation of the first six members of poly(mono‐n‐alkyl itaconates) by thermogravimetry (TG), differential scanning calorimetry (DSC), Fourier Transform infrared (FTIR) and FTIR evolved gas analysis (FTIR‐EGA) was studied. The degradation mechanism involves cyclic anhydride formation followed by crosslinking due to the linear anhydride formation. In both processes water and/or alcohol evolution was detected. Also, decarboxylation processes take place on all polymers at high temperatures ( > 180°C). A mechanism of the degradation process is proposed.
Synthesis and liquid crystalline properties of azobenzene‐containing poly(vinyl ether)s with narrow molar mass distribution
Authors: Chiellini Emo , Galli Giancarlo , Bignozzi Maria Chiara , Angeloni Sante A. , Fagnani Marco , Laus Michele 
Published: April 2003

AbstractA series of new liquid crystalline (LC) poly(vinyl ether)s with different molar masses was synthesized via a two‐step procedure involving the preparation of functional matrices by living cationic polymerization of an ω‐chloroalkyl vinyl ether monomer followed by a grafting reaction of an azobenzene mesogenic unit onto them. By appropriately adjusting the experimental conditions, it was possible to predetermine the molar mass characteristics of the LC polymers. Each of the parent and modified poly(vinyl ether)s had a narrow molar mass distribution. The LC polymers were semicrystalline and formed a nematic mesophase, enantiotropic or monotropic in character. The transition temperatures increased with increasing molar mass up to a limiting value and then remained nearly constant. Accordingly, poly(vinyl ether)s with predetermined molar mass and narrow molar mass distribution could be prepared.
Dipolar correlation and activation energies for the subglass relaxations of chains with asymmetric side groups
Authors: Díaz‐Calleja Ricardo , Riande Evaristo 
Published: April 2003

AbstractThe effect of the location of the halogen atom on the distribution of activation energies associated with the subglass relaxation of poly(o‐chlorophenyl acrylate) (POCPA) and poly(m‐chlorophenyl acrylate) (PMCPA) is studied. Poly(p‐chlorophenyl acrylate) (PPCPA) was also investigated, though not in depth due to its low dielectric activity. The high temperature and frequency dependence found for the activation energy on the high temperature side of the subglass relaxations may not correspond only to simple mechanisms associated with the ß‐process but also to more complex mechanisms associated with the glass‐rubber relaxation. Dielectric activity arising from motions about OCar bonds is responsible for the high dielectric strength exhibited by these polymers. Theoretical calculations based on the rotational isomeric state model are in fair agreement with the experimental relaxation strengths.
Synthesis of oligo[2]catenanes
Authors: Geerts Yves , Muscat Dirk , Müllen Klaus 
Published: April 2003

AbstractTwo new difunctionalised [2]catenanes 5 b, c have been synthesised. Oligomers 10 c, d containing interlocked rings in the main chain were prepared via Pd° coupling of 5 b with comonomers 9 c, d and degrees of polymerization of up to 8 have been reached. These materials were characterized by 1H NMR spectroscopy, fast atom bombardment‐mass spectroscopy, gel‐permeation chromatography and differential scanning calorimetry.
The curing reaction of poly(ether‐sulfone)‐modified epoxy resin
Authors: Chen Yung‐Sin , Lee Jun‐Shen , Yu Tzyy‐Lung , Chen John‐Chang , Chen Wen‐Yih , Cheng Min‐Chin 
Published: April 2003

AbstractOne of the useful methods to improve the toughness of epoxy resin is by mixing the resin with poly(ether‐sulfone) (PES). In the present work, two hydroxyl‐terminated PESs with molecular weights Mn = 28 600 and 4 200 were used for blending with epoxy resin. The curing reaction of diglycidyl ether/bisphenol‐A (DGEBA) with 4,4′‐diaminodiphenyl sulfone (DDS) in the presence of hydroxyl‐terminated PES was studied by means of differential scanning calorimetry (DSC) and gel‐permeation chromatography (GPC). For the DGEBA‐DDS‐PES system with a stoichiometric ratio of epoxy and amino groups the DSC experimental results showed that at a fixed molecular weight of PES the curing reaction rate decreases with increasing PES concentration. At a fixed PES concentration (in the range of between 0 and 20 wt.‐% of PES), the DGEBA‐DDS system modified with hydroxyl‐terminated PES with lower molecular weight had a faster curing reaction rate at low conversion and a slower curing reaction rate at high conversion. The GPC results showed the evidence of etherification between low‐molecular‐weight PES with epoxy resin. However, very little etherification of high‐molecular‐weight hydroxyl‐terminated PES with epoxy resin was found. Based on the experimental results, a curing reaction mechanism of DGEBA with DDS in the presence of hydroxyl‐terminated PES is proposed.
Thermodynamics of 2,2‐dimethyltrimethylene carbonate, of its bulk polymerization process and of poly(2,2‐dimethyltrimethylene carbonate) from 0 to 470 K at standard pressure
Authors: Lebedev Boris V. , Kulagina Tat'yana G. , Telnoy Vadim I. , Vasil'ev Valery G. 
Published: April 2003

AbstractIn the present work the thermodynamic properties of 2,2‐dimethyltrimethylene carbonate (DTC) and poly‐2,2‐dimethyltrimethylene carbonate (PDTC) were studied by precise calorimetry. In adiabatic and dynamic vacuum calorimeters the temperature dependence of the heat capacity of DTC and PDTC was studied between 5 and 470 K. Temperature and enthalpies of physical transitions were determined, and in an isothermal calorimeter energies of combustion of the above compounds were measured. From the results the thermodynamic functionsC(T),H°(T)–H°(0),S°(T),G°(T)–H°(0) were calculated for various physical states of the monomer and the polymer from 0 to 470 K. The standard enthalpies of combustion and thermochemical parameters of formation ΔH, ΔS, ΔGof the objects studied were estimated atT=298,15 K andp= 101,325 kPa. The zero entropyS(0) and configurational entropySof PDTC in the glassy state and the difference in zero enthalpies of the polymer in the glassy and crystalline statesH(0)–H(0) were estimated. The results were used to calculate the thermodynamic parameters of the bulk polymerization of DTC (ΔH, ΔS, ΔG) in the range of 0 to 420 K. It was established that for the process DTC → PDTC, ΔG< 0 if the polymer is crystalline and ΔG> 0 in the case of amorphous PDTC (glassy or liquid). The ceiling temperature isT= 500 K.
Side chain liquid crystal polymers of 2,3‐disubstituted norbornenes via ring‐opening metathesis polymerization, 1 influence of flexible spacer length m = 2 to 12 on the thermotropic behaviour
Authors: Ungerank Markus , Winkler Berthold , Eder Elisabeth , Stelzer Franz 
Published: April 2003

AbstractBis[(4′‐cyanobiphenyl‐4‐yl)oxy‐n‐alkyl]norborn‐5‐ene‐2,3‐dicarboxylates with alkyl chain lengths m = 2 – 12 were synthesized. Most of the monomers exhibit thermodynamically metastable liquid crystalline phases with respect to the crystalline phases. Polymers were prepared by ring‐opening metathesis polymerization (ROMP) using the molybdenum carbene initiator [Mo(CH‐t‐Bu) (NAr) (t‐BuO)2] (t‐Bu = tert‐butyl) with NAr = 2,6‐diisopropylaniline. All polymers show thermotropic liquid crystalline phases. Results on characteristic phases and the influence of the number of methylene units m in the flexible spacer on the thermal behaviour (glass transition temperature, isotropization temperature, odd‐even effect, enthalpy change) of these new side chain liquid crystal polymers (SCLCP's) are given. They are compared to monosubstituted polynorbornene derivatives and to SCLCP's with other backbones.
Syntheses and characterization of poly(aminophenazines)
Authors: Premasiri Ajith H. , Euler William B. 
Published: April 2003

AbstractThe oxidative polymerization of o‐phenylenediamine was studied under a variety of conditions. At room temperature the reaction of o‐phenylenediamine with ammonium persulfate in HCl acid medium gives a dimer, 2,3‐diaminophenazine. The same reaction at 70°C results in a trimer with an open structure, [3‐amino‐2(3,4‐diaminophenylamino)]‐phenazine hydrochloride. At 118°C, the oxidative polymerization in glacial acetic acid medium gives poly(aminophenazine) acetate, analogous to polyaniline. However, either because of the atactic nature of the polymer and the consequences of this on the stability of charge carriers or because protonation occurs at localized amines, no electrical conductivity was found.
Diacetylene‐containing polymers, 8. Synthesis and characterization of novel high molecular weight diacetylene‐containing poly(ester‐co‐urethanes)
Authors: Fomine Sergei , Posada Imelda , Ogawa Takeshi 
Published: April 2003

AbstractNovel high molecular weight diacetylene (DA) — containing polymers, poly{[bis(3‐butynyl) 3,5‐diynylene sebacate]‐co‐[bis(3‐butynyl) hexamethylenedicarbamate]}s, were synthesized and characterized. The copolymers were found to be semicrystalline and their degree of crystallinity went through a minimum due to a random composition of the copolymers. The copolymers containing less than 40 mol‐% of bis(3‐butynyl) hexamethylene‐dicarbamate (2) were found to be thermoplastic. The glass transition temperature of the copolymers tends to increase with increasing monomer 2 content. All the copolymers underwent topochemical cross‐polymerization on electron‐beam irradiation or heating in the solid state and the maximum of the visible absorption spectra of the cross‐polymerized copolymers showed a long wavelength shift with increasing monomer 2 content. Upon introduction of 10 mol‐% of the urethane monomer 2 the tensile strength of the copolymer increases from 250 MPa to 280 MPa.
New polyurethanes based on diphenylmethane diisocyanate and 1,4:3,6‐dianhydrosorbitol, 1. Model kinetic studies and characterization of the hard segment
Authors: Cognet‐Georjon Estelle , Méchin Françoise , Pascault Jean‐Pierre 
Published: April 2003

Abstract1,4:3,6‐Dianhydrosorbitol (DAS) seems to be an interesting reagent for the synthesis of polyurethanes. In the present work, the kinetics of the reaction of DAS with a monoisocyanate (p‐tolyl isocyanate, p‐TI) and with a diisocyanate (4,4′‐diphenylmethane diisocyanate, MDI) were studied with the help of a chromatographic method (size exclusion chromatography, SEC). When the condensation reaction is performed in tetrahydrofuran (THF) solution, with dibutyltin dilaurate (SnDBDL) as catalyst, DAS exhibits two equireactive hydroxyl groups. The reaction rate can be well described by a second‐order equation modified to include catalysis by the formed urethane functions. MDI and DAS were then condensed using two different experimental procedures (bulk and solution polycondensation in THF, in the presence of SnDBDL), and the characteristics of the resulting polyurethanes were compared. Bulk polycondensation led to an amorphous polymer, whereas the polyurethane prepared in solution was semi‐crystalline. In both cases, we obtained a very high glass transition temperature ( ≈ 186°C). The synthesis of samples with various polymerization degrees gave a better understanding of the molecular weight distribution of segmented polyurethanes based on MDI and DAS.
New ferrocene‐containing copolyesters
Authors: Wilbert Götz , Wiesemann Amadeus , Zentel Rudolf 
Published: April 2003

AbstractWe have synthesized four new ferrocene monomers (three diols and one diester). The redox potential of these ferrocene derivatives varies between 0 mV and 230 mV due to different degrees of ring alkylation. Amorphous and liquid crystalline copolyesters were prepared with these monomers in the polymer main chain. Cyclovoltammetric measurements show that the redox potential of the ferrocene units is increased by about 40 mV upon polymer formation (esterification). Since the ester group is 4 to 6 σ‐bonds away from the ferrocene unit this increase is probably caused by some charge‐transfer interaction through space. First rheological measurements show an unusual rubber‐like behaviour of the ferrocene‐containing copolyesters.
Light scattering peaks from aqueous solutions of acrylamideacrylic acid copolymers
Authors: Boudenne Nawel , François Jeanne 
Published: April 2003

AbstractAqueous solutions of acrylamide‐acrylic acid copolymers of high molecular weight have been investigated by light scattering. It was shown that a scattering peak can be obtained if the samples used have been prepared by alcaline hydrolysis of polyacrylamide and if the solutions are filtered and sonicated. In the range of the lower concentrations, the position of this peak, q*, is found to vary with the polymer concentration C, as C1/3, and to be independent of the charge density. The addition of very small amounts of salt provokes the disappearance of the peak. A phase diagram (charge density versus concentration of the polymer) has been established. It shows that these experiments were carried out in a concentration range intermediate between the dilute and the semidilute regimes (transition regime). The experimental scaling laws however correspond to the theoretical predictions for the dilute regime. Moreover, the q* values are much lower than those calculated by the random phase approximation theories.
Copolymerization of ethylene with 1‐hexene and 1‐octene: correlation between type of catalyst and comonomer incorporated
Authors: Quijada Raul , Dupont Jairton , Miranda Márcia S. Lacerda , Scipioni Rosângela B. , Galland Griselda B. 
Published: April 2003

AbstractThe behaviour of catalytic systems based on zirconium compounds for the copolymerization of ethylene with 1‐hexene and 1‐octene is reported. The metallocenes (CH3)2SiCp2ZrCl2, Cp2ZrCl2 (Cp = η5‐cyclopentadienyl), C2H4[Ind]2ZrCl2 and (Ind = η5‐indenyl) were chosen for this study. The bridged catalysts, (CH3)2SiCp2ZrCl2 and C2H4[Ind]2ZrCl2, and the metallocene Cp2ZrCl2 showed similar catalytic activities for home‐ and copolymerization of ethylene with 1‐hexene. 13C NMR analysis showed that the composition of copolymerization products depends on the catalytic system, in other words, on the ligand structure of the transition metal. Copolymers obtained using the bridged catalysts have greater incorporation of comonomer. Thermal analysis and viscosity measurements demonstrated that an increase of the comonomer concentration reduces the melting point, the crystallinity and the molecular weight of the copolymer. Results from infrared spectroscopy showed that β‐elimination is one of the possible termination reactions. The monomer reactivity ratios r were determined for all catalytic systems using Fineman‐Ross and 13C NMR methods. The values of r1 (M1 = ethylene) and r2 (M2 = α‐olefin) showed an effect of the type of metallocene and of α‐olefin on the structure of the copolymer obtained.
Stereospecific polymerization of methylthiirane in homogeneous phase, 5. Study of the interconversion between active sites
Authors: Boucard Valérie , Dumas Philippe , Sigwalt Pierre 
Published: April 2003

AbstractThe enantioasymmetry of polymerization reactions of racemic methylthiirane in bulk are studied, initiation being made using racemic or optically active seeds of molar weight equal to 40000, synthesized in bulk from bis(isopropyl‐S‐cysteinato)cadmium. In these conditions, active sites are enantiomers and the enantioasymmetric constant kR, measuring the preferential choice of the R antipode, is depending only on the relative number of the two types of active sites. We have observed an interconversion between the enantiomeric active sites CR* and CS*. The ratio [CR*]/[CS*] is only varying with conversion and reaches a limiting value that depends on cadmium concentration. For low cadmium concentrations, ([CR*]/[CS*])lim = 1.00, showing a complete racemization of the enantiomeric active sites, while for higher cadmium concentrations, ([CR*]/[CS*])lim = 1.07 ± 0.03. This value of 1.07 can be attributed to the presence of aggregation of dimeric species which create a chiral neighbourhood around cadmium atoms. Diastereoisomeric active sites present when active sites are born by chains of lower molar weights seem also to interconvert. The interconversion between active sites implies the presence of stereoblocks in the main chain.
Electrochemical synthesis of titanium‐based Ziegler‐Natta catalysts and their potential application in ethylene homo‐ and copolymerization
Authors: Brusson Jean‐Michel , Mortreux André , Petit Francis , Bujadoux Karel , Leprevost Benoit 
Published: April 2003

AbstractHighly active Ziegler‐Natta catalysts have been synthesized using an electrochemical process in their preparation, with the aim of producing selectively titanium(III) species from TiCl4. The use of an undivided cell, an aluminium anode and a halogenated solvent (dichloromethane or 1,2‐dichloroethane), has allowed the production in situ of chloroalkyl aluminium species, by cathodic reduction of TiCl4, thus giving rise to a new Ziegler‐Natta catalytic combination. The possibility of scale up for this lectrochemical synthesis has been clearly shown. The Ti/Al system was modified so as to enhance its activity, first by adding a soluble dialkylmagnesium compound and then a soluble vanadium compound such as VOCl3. This Ti/Al/Mg/V highly active system was used under different conditions: in a hydrocarbon medium at low (80°C) and high (200°C) temperature and also under supercritical conditions in a continuous high‐pressure autoclave reactor, to produce homoor copolymers of ethylene with α‐olefins. Compared to similar heterogeneous catalysts obtained by comilling, the observed activities are shown to be very much improved, especially under high pressure and high temperature conditions. This may be related to the very narrow granular distribution centered at 2,5‐3 μm, compared to a much broader distribution (centered at 6 μm) obtained with the comilled catalyst.
Thermal degradation of polymers in the melt, 1. Characterization of volatile oligomers formed by thermal degradation of polyisobutylene
Authors: Sawaguchi Takashi , Takesue Tomoyuki , Ikemura Tadashi , Seno Manabu 
Published: April 2003

AbstractChemical structures of a number of components of volatile oligomers including (n+2)‐mers (n ≧ 0) produced by thermal degradation of polyisobutylene were systematically determined by high‐resolution capillary gas chromatogaphy/mass spectrometry (GC/MS). The total ion current (TIC) chromatogram consists of about 100 peaks ranging from dimers (2‐mers, n = 0) to dodecamers (12‐mers, n = 10) and most of the main peaks are classified into four types of terminal monoolefins: a trisubstituted olefin with a tert‐butyl end, a vinylidene olefin with a tert‐butyl end, a trisubstituted olefin with an isopropyl end, and a vinylidene olefin with an isopropyl end. The formation of these monoolefins is reasonably interpreted by intramolecular hydrogen abstractions (back‐biting) of primary and tertiary terminal macroradicals and subsequent β; scissions at the inner position of the main chain. In all the chromatograms of each (n+2)‐mer (n ≧ 1), the retention times of terminal trisubstituted types of monoolefins were shorter than those of terminal vinylidene types of monoolefins, in contrast to the elution order of dimers. The relative intensities between the interesting peaks of each (n+2)‐mer (n ≧ 1) clearly represent that back‐biting more predominantly occurs at the methylene hydrogen rather than at the methyl group consistent with the difference in the bond dissociation energy of the HC bond of interest, as opposed to the steric hindrance mechanism5,7.