bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure analysis of the noncrystalline material in poly(ethylene terephthalate) fibers
Authors: Fu Yigang , Busing William R. , Jin Yimin , Affholter Kathleen A. , Wunderlich Bernhard 
Published: April 2003

AbstractThe structures of the noncrystalline material of four poly(ethylene terephthalate) fiber samples have been studied by analyzing the X‐ray scattering patterns. The noncrystalline scattering patterns of the three semicrystalline fibers are revealed by removal of the crystalline contribution from the diffraction patterns. The crystalline phase diffraction is calculated from a structure model determined by a full‐pattern X‐ray fiber diffraction analysis. The noncrystalline materials is further divided into an amorphous and an oriented, intermediate phase. The azimuthal scattering pattern of the former is isotropic, the latter anisotropic. The intermediate phase does not only show parallel chains along the fiber direction, but a crystal‐like correlation is also possible, primarily in the materials between the oriented, fibrillar crystallites. The growth of the crystalline phase in fibers is intimately coupled to this intermediate phase. Both amount and detailed structure of the intermediate phase depend on the thermal and mechanical history of the fiber. A first discussion is given of the correlation between the three phases derived by X‐ray diffraction and three phases identified earlier by thermal analysis (crystalline, mobile amorphous and rigid amorphous). The mechanical properties of the fibers are seemingly more dependent on the intermediate phase than on the crystalline or amorphous phases.
On the kinetics and initiation mechanism of acrylamide polymerization using the ceric ion/acetoacetanilide system as initiator
Authors: Dong Jian Hua , Qiu Kun Yuan , De Feng Xin 
Published: April 2003

AbstractIt is found that acetoacetanilide (system. name: N‐phenyl‐3‐oxobutanamide) possesses a very high reactivity towards ceric ions, Ce4+, in initiating the polymerization of vinyl monomers. In the presence of acetoacetanilide, the rate of the acrylamide polymerization is larger by a factor of 30 than the rate of initiating by ceric ions alone. The reaction orders were 0,58, 0,75 and 1,2 with respect to acetoacetanilide, ceric ion and acrylamide concentration, respectively. The activation energy of the acrylamide polymerization initiated by ceric ion/acetoacetanilide is only 12,9 kJ/mol. According to the IR spectrum, fragments of acetoacetanilide are present in the polymer produced by the ceric ion redox initiator comprising acetoacetanilide. The C‐centered and N‐centered primary radicals generated via redox reaction of ceric ion and acetoacetanilide were detected by spin trapping and electron paramagnetic resonance. An initiation mechanism of the ceric ion/acetoacetanilide initiated polymerization is proposed on the basis of experimental results.
Mesogen conformation changes in thermotropic polyesters at phase transitions
Authors: Shilov Sergei , Volchek Boris , Zuev Vyacheslav , Skorokhodov Sergei 
Published: April 2003

AbstractMesogen conformations in thermotropic polyesters with alternating mesogens and poly(methylene) spacers were investigated by IR spectroscopy with polarized and unpolarized light. The selective deuteration of terephthaloyl‐bis(p‐oxybenzoate) mesogens gave a possibility of assigning part of the IR bands to terephthalic or to oxybenzoic fragments. It is shown that in the liquid crystalline melt the mesogen conformation is planar, but in the semicrystalline state it is mainly nonplanar. Differences in mesogen conformations of polymers containing an even or an odd number of methylene units in the spacer are detected. Thus, LC ordering seems to affect not only the conformation of the spacer but also the conformation of the mesogen.
The homogeneous photopolymerization of methyl methacrylate by colloidal cadmium sulfide
Authors: Popović Ivanka G. , Katsikas Lynne , Müller Udo , Veličković Jovan S. , Weller Horst 
Published: April 2003

AbstractA completely new method of initiating the homogeneous radical polymerization of methyl methacrylate in bulk or in solution via the photogeneration of an electron hole pair in colloidal cadmium sulfide is presented. A polymerization mechanism involving an excited cadmium sulfide particle in both the initiation and termination steps is proposed. In the initiation a methyl methacrylate molecule is oxidized by a positive hole photogenerated in a CdS particle, which results in a novel chain‐end structure of the poly(methyl methacrylate) (PMMA). Degradative chain transfer to reduced excited cadmium sulfide particles is responsible for chain termination. Thus, for the first time, a detailed polymerization mechanism in which all states of the polymerization, i.e., initiation, propagation, chain transfer and termination, is presented for the polymerization of vinyl monomers initiated by semiconductors. Thermogravimetry (TG) showed that the newly synthesized PMMA has greatly enhanced thermal stability when compared to normal radically prepared PMMA. In fact, the thermal stability approaches that of anionically prepared PMMA but is experimentally much easier to prepare. This technique enables the homogeneous embedding of CdS particles in a polymer matrix.
Zur kinetik der copolymerisation von methacrylaten mit entkoppelter seitengruppe
Authors: Rübner Joachim , Geßner Uwe , Rodekirch Gerhard , Ruhmann Ralf 
Published: April 2003

AbstractThe copolymerization behavior of methacrylate monomers with several decoupled side groups was studied depending on the structure of the linked mesogen. Some units (NN, CONH) in the mesogen influence the copolymerization reaction in spite of the strong decoupling by a C6‐spacer group and lead to retarding effects and to the preferred insertion of monomers with weaker mesogenic interactions. The liquid‐crystalline behaviour of the copolymers was not affected due to the relatively small differences in the copolymerization parameters.
A mechanistic study of the radical copolymerisation of p‐chlorostyrene with citraconic anhydride via 13C NMR spectroscopy
Authors: Brown Paul G. , Fujimori Kiyohisa 
Published: April 2003

AbstractThe composition and monomer unit sequence distribution of copolymers of p‐chlorostyrene (p‐CST) with citraconic (α‐methylmaleic) anhydride (CA) prepared in methyl ethyl ketone (MEK) at 50,0 ± 0,1°C were determined over a range of comonomer feed mole fractions using 13C NMR spectroscopy. The monomeric units in these copolymers were found to display a mild tendency to alternate, which increased as the mole fraction of CA in the feed increased. The existence of a 1:1 charge‐transfer complex formed between p‐CST and CA in the feed was confirmed via UV spectroscopy and the equilibrium constant for complex formation determined to be 0,10 ± 0,04 L/mol in MEK at ambient temperature. The terminal, penultimate, complex‐participation and complex‐dissociation models were each tested for applicability to the mechanism of copolymerisation for this comonomer system. On the basis of copolymer composition data, the penultimate, complex‐participation and complex‐dissociation models were each found to provide an adequate description of the mechanism of copolymerisation in the comonomer system via non‐linear least squares methods. An analysis of the comonomer unit sequence distributions for these semi‐alternating copolymers and the application of reactivity ratio related test functions to this data allowed applicability of the four models under investigation to be separated more explicitly, with the complex‐dissociation model providing the best fit to the data.
Polyanhydrides, 6. Thermotropic poly(ester anhydride)s derived from 2,5‐bis(alkylthio)terephthalic acids
Authors: Kricheldorf Hans R. , Domschke Angelika 
Published: April 2003

Abstract2,5‐Bis(alkylthio)terephthalic acids (and their acyl chlorides) were prepared by nucleophilic substitution of diethyl 2,5‐dibromoterephthalate with octane‐, dodecane‐ and hexadecanethiol. The poly(ester anhydrides) were obtained by thermal polycondensation of disubstituted terephthaloyl chlorides with silylated 4‐hydroxybenzoic acid and silylated hydroquinone. The resulting polymers were characterized by elemental analyses, inherent viscosities, differential scanning calorimetry (DSC) and wide‐angle X‐ray scattering (WAXS) measurements, optical microscopy and 13C NMR cross polarization/magic angle spinning (CP/MAS) spectroscopy. These measurements suggest that the disubstituted poly(ester anhydrides) form a sanidic type of layer structure in the solid state. Increasing length of the alkyl substituents favours the formation of ordered paraffin domains between the stacks of the main chains. The stability of these quasicrystalline paraffin domains decreases with increasing mole fraction of the anhydride groups. In contrast to their monosubstituted analogues the disubstituted poly(ester anhydrides) do not form normal nematic melts.
Electron transfer catalyzed by manganese tetratolyl‐prophyrinate across poly(γ‐methyl L‐glutamate) membrane
Authors: Dewa Takehisa , Satoh Mitsuru , Komiyama Jiro , Nango Mamoru , Tsuda Kazuichi 
Published: April 2003

AbstractA poly(γ‐methyl L‐glutamate) (PMLG) membrane containing manganese tetratolylporphyrinate (MnTTP) was prepared in order to examine the transmembrane electron transfer in a redox system constructed as S2O42−/membrane/Fe(CN)63−. Electron transfer was observed in 0,1 M pH 7,0 imidazole (Im) buffer but not in 0,1 M pH 7,0 phosphate buffer. The apparent transfer rate increased with MnTTP content and also with the Im concentration in the buffer, indicating that electron is transferred by MnTTP, which is coupled with proton transport by Im distributed in the membrane. The transfer catalyzed by MnTTP was more effectively accelerated with Im than with 2‐methylimidazole (2‐Melm) but not at all with 1‐methylimidazole (1‐Melm). This implies that the 1‐N site on the imidazoles as the axial ligand of MnTTP is a crucial position for the mediation of electron transfer between MnTTP's. In the pH range 6,0–8,5 of Im buffer, the electron transfer rate showed a maximum at pH 7,0. This pH dependence is discussed in terms of the concentration and mobility of proton in the membrane.
DSC and 13C NMR studies of ethylene‐propene copolymers prepared by a highly active and stereospecific catalyst
Authors: Zhang Xuequan , Chen Hui , Zhou Zinan , Huang Baotong , Wang Zhanwang , Jiang Ming , Yang Yongran 
Published: April 2003

AbstractEthylene‐propene copolymers (EPR) were synthesized at different feed compositions using a highly active and isospecific MgCl2‐supported Ti‐based catalyst. The thermal behavior of EPR was studied by differential scanning calorimetry, the heterogeneity by fractionation, and the chain structure by 13C NMR using the method of substituent chemical shift. The results show that EPR of very low crystallinity (1,0 wt.‐%) can be obtained at high propene content in the feed with a heptane‐insoluble fraction of only 0,9 wt.‐%. Thus, a high isotacticity in propylene sequences and a high randomness in EPR can be achieved at the same time, and producing high‐impact poly(propylene) in a reactor is possible with this catalyst. Sequence distribution and length distribution of ethylene sequences indicate that EPR is produced at multiple active sites, and each site is dominated not only by a first‐order Markovian model but also by unsteady diffusion factors.
Emulsion polymerization of butyl acrylate, 2. Effect of the initiator type and concentration
Authors: Capek Ignác 
Published: April 2003

AbstractThe free radical emulsion polymerization of butyl acrylate initiated by a water‐soluble initiator (ammonium peroxodisulfate, AP) at 60°C in the presence of a blend of anionic and non‐ionic emulsifiers was investigated. The effect of a blend of water‐ and oil‐soluble initiators (AP + 2,2′‐azoisobutyronitrile (AIBN)) is analyzed. Over the interval 2 the rate of polymerization is proportional to the 0,43rd or 0,25th power of the initiator (AP) concentration for runs without or with AIBN. The molecular weights of polymer were found to increase over the low and medium conversion ranges, and the increase is more pronounced at low conversions. Besides, the molecular weight slightly decreases with increasing AP concentration. The addition of AIBN was found to decrease the molecular weight and the rate of polymerization.
Ring opening metathesis polymerization of cyclic alkenes containing heteroatoms
Authors: Watkins Neil , Quigley Paul , Orton Michael 
Published: April 2003

AbstractThe Ring Opening Metathesis Polymerization (ROMP) of a series of cyclic alkenes bearing heteroatom functionality has been performed using a classical WCl6‐based catalyst system. All of the alkenes studied exhibited significantly slower polymerization rates compared with the hydrocarbon monomer dicyclopentadiene (DCPD), this being most pronounced for monomers containing a tertiary nitrogen atom substituted at the 2 position of the norbornene skeleton. Cyclic alkene anhydrides, prepared by the Diels‐Alder addition of cyclopentadiene to maleic and itaconic anhdrides, were found to be polymerizable with high yields giving cross‐linked polymers which exhibited very high glass transition temperatures. Monofunctional cyclic imide derivatives of the cyclopentadiene‐itaconic anhydride adduct were found to be polymerizable to moderate molecular weight thermoplastic materials with high glass transition temperatures, whilst difunctional cyclic imide derivatives led to cross‐linked thermoset polymers. The solution copolymerizations of the cyclopentadiene‐maleic anhydride adduct with DCPD, and of a cyclic imide derivative of the cyclopentadiene‐itaconic anhydride adduct with DCPD, were carried out to form copolymers in high yields having glass transition temperatures intermediate between those of the respective homopolymers.
Ring‐opening metathesis polymerization of endo‐ and exo‐5‐methoxymethylbicyclo[2.2.1]hept‐2‐ene; microstructure of the polymers
Authors: Ivin Kenneth J. , Lam Luk‐Mui , Rooney John J. 
Published: April 2003

AbstractThe title monomers 1 and 2 were polymerized by Ru‐, Ir‐, Mo‐, W‐ and Re‐based metathesis catalysts to yield polymers with cis contents ranging from 10% to at least 90% for 1 and 23–60% for 2. Assignments of the 13C NMR spectra were made. No significant head‐tail bias was observed in either polymer. A high‐trans polymer made from the optically active endo monomer ((−)‐1) was atactic, while high‐cis polymers could be either atactic or biased towards syndiotactic, depending on the catalyst.
Synthesis and characterization of crystalline poly(ethyleneimine)s with mesogenic side chains forming liquid crystals on quaternization
Authors: Masson Patrick , Heinrich Benoit , Frègre Yves , Gramain Philippe 
Published: April 2003

AbstractThe synthesis and thermal properties of a new type of side‐chain liquid‐crystalline polysalts are described. The polymers are first obtained by partial or complete alkylation of a linear poly(ethyleneimine) with 6‐(4‐methoxy‐4′‐biphenylyloxy)hexyl bromide or 12‐(4‐methoxy‐4′‐biphenylyloxy)dodecyl bromide. In a second step, polysalts are prepared by partial or complete quaternization with acyl bromide or dimethyl sulfate. Differential scanning calorimetry, polarizing optical microscopy and X‐ray diffraction experiments show that the polymers and copolymers alkylated with the mesogenic groups are all crystalline. When quaternized, they exhibit thermotropic smectic A phases. This behaviour confirms the smectogenic function of the ammonium units located in the backbone, as already observed with poly(4‐vinylpyridinium) salts.
Primary thermal degradation processes of poly(ether‐sulfone) and poly(phenylene oxide) investigated by direct pyrolysis‐mass spectrometry
Authors: Montaudo Giorgio , Puglisi Concetto , Rapisardi R. , Samperi Filippo 
Published: April 2003

AbstractThe thermal degradation processes which occur in poly(ether‐sulfone) (PES) and poly(phenylene oxide) (PPO) have been studied by Direct Pyrolysis‐Mass Spectrometry (DPMS). The pyrolysis mass spectra of PES and PPO contain molecular ions up to m/z 700, corresponding to pyrolysis compounds of sufficient size to allow the characterization of the primary processes which occur in the thermal cleavage of these polymers. The results obtained indicate that the thermal degradation of PES and PPO proceeds by thermal cleavage of the groups located at the bridges. In the case of PPO the bridges are all homogeneous, and therefore both an intramolecular thermal rearrangement or a radical cleavage process can account for the formation of the primary pyrolysis products. Formation of dibenzofuran units along the PPO chain is a parallel thermal process. In the case PES the simultaneous thermal cleavage of two different bridged units, diphenyl sulfone and diphenyl ether occurs. Extrusion of SO2, with consequent formation of compounds containing biphenyl units, is observed in the thermal degradation of PES. This process is accompanied by formation of dibenzofuran units along the polymer chain, as expected from the thermal cleavage of diphenyl ether units, and by another rearrangement of the polymer backbone, yielding structures containing more oxygen atoms with respect to that of PES.
Primary thermal degradation processes of poly(ether/ketone) and poly(ether ketone)/poly(ether‐sulfone) copolymers investigated by direct pyrolysis‐mass spectrometry
Authors: Montaudo Giorgio , Puglisi Concetto , Samperi Filippo 
Published: April 2003

AbstractThe mechanisms of thermal degradation of poly(ether‐ketone) (PEK) and four poly(ether‐ketone)/poly(ether‐sulfone) copolymers (PEK/PES) have been investigated by direct pyrolysis‐mass spectrometry (DPMS). Several families of pyrolysis compounds with H, OH and CHO end‐groups have been identified in the pyrolysis mass spectra of PEK. All these pyrolysis compounds can arise from degradation mechanisms involving cleavages of the bridged groups (diphenyl ether and dibenzophenone units). Our data show that the main degradation products of PEK are aldehydes, most likely formed by an intramolecular thermal cleavage of benzophenone units. Compounds containing dibenzofuran units have also been observed in the DCI mass spectrum of PEK. The thermal decomposition of a low molecular weight PEK sample occurs in two stages with the maxima of decomposition at 390°C and 490°C, respectively. This fact indicates the occurrence of an end‐group initiated thermal decomposition in the early degradation stage which is not present in the case of the high molecular weight PEK sample. The pyrolysis of PEK does not produce compounds containing biphenyl units, indicating that extrusion of carbonyls or recominbation processes are not involved. The thermal degradation compounds of the PEK/PES copolymers originate from the thermal cleavage of the bridge groups (diphenyl ether, benzophenone and diphenyl sulfone). The pyrolysis mass spectra of 1:1 (alt.), 1:1 (random), 3:1 and 1:3 PEK/PES copolymers appear essentially identical (apart for obvious differences in peak intensities), indicating that the molecular rearrangements (SO2 extrusion, transesterification, cleavage of bridges) which occur at higher temperatures and/or in the pyrolysis processes are able to randomize the distribution of comonomer units originally present in the copolymers. Differences in peak intensities have been found to reflect almost quantitatively the molar composition of the copolymers.
Aqueous ring‐opening metathesis polymerisation of 7‐oxanorbornene derivatives with oxygen‐containing functionalities
Authors: Lu Shui‐Yu , Amass Judith M. , Majid Nazia , Glennon Dermott , Byerley Andrew , Heatley Frank , Quayle Peter , Booth Colin , Yeates Stephen G. , Padget John C. 
Published: April 2003

AbstractA number of 7‐oxanorbornene derivatives with hydroxymethyl, methoxymethyl and acetoxymethyl functionalities were synthesised and investigated as monomers in ring‐opening metathesis polymerisation (ROMP) catalysed by commercial ruthenium trichloride in aqueous ethanolic solvents. Comparison was made with related polymerisations of 7‐oxanorbornene derivatives with anhydride, methoxymethyl and carboxylic acid functionalities. The structures of the polymers were investigated by 1H and 13C NMR and their molar masses and molar mass distributions by gel‐permeation chromatography.
Synthesis of vinyl‐terminated isotactic poly(propylene) using the coupling reaction between Zn‐terminated polymer and allyl halides
Authors: Kurosawa Hiroki , Shiono Takeshi , Soga Kazuo 
Published: April 2003

AbstractPropene was polymerized with the TiCl3/Al(C2H5)2Cl catalyst system using Zn(C2H5)2 as a chain transfer reagent. The resulting Zn‐terminated poly(propylene) (PP) was then brought into contact with allyl halides (chloride, bromide and iodide) in the presence of N‐methylimidazole to obtain vinyl‐terminated PP. Allyl bromide gave the highest conversion among these allyl halides. When the coupling reaction was conducted with allyl bromide at 40°C for 24 h, the conversion to the terminal vinyl groups was over 90% for atactic PP and approximately 60% for isotactic PP. The Zn‐polymer bonds of both atactic and isotactic PP were almost quantitatively converted into terminal vinyl groups at 130°C for 3 h.
The influence of regio‐ and stereoirregularities on the crystallization behaviour of isotactic poly(propylene)s prepared with homogeneous group IVa metallocene/methylaluminoxane Ziegler‐Natta catalysts
Authors: Fischer David , Mülhaupt Rolf 
Published: April 2003

AbstractPoly(propylene)s with narrow molecular weight distributions were prepared with various methylaluminoxane‐activated metallocene‐based Ziegler‐Natta catalysts to study the influence of randomly incorporated regio‐ and stereoirregularities on the crystallization behavior. As a function of the metallocene type and the polymerization temperature, the molecular weights varied between 11500 < Mn < 63 000, melting temperatures of annealed samples between 125 to 158°C, and the corresponding degrees of crystallinity, as measured by wide‐angle X‐ray scattering, between 49 and 67%. While the virgin poly(propylene)s exhibited exclusively the α‐modification, annealing and melt crystallization favored the development of the γ‐modification. The microstructure analysis by 13C NMR spectroscopy revealed a linear correlation between the content of the γ‐modification and the average length of the isotactic segments.