bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic mechanical behavior of poly(ether ether ketone)/poly(ether sulfone) block copolymers
Authors: Cao Junkui , Su Wencheng , Ma Rongtang , Wu Zhongwen , Shibata Mitsuhiro , Takeishi Hiroyuku , Yosomiya Ryutoku 
Published: April 2003

AbstractPoly(ether ether ketone) (PEEK)/poly(ether sulfone) (PES) block copolymers were synthesized via condensation reaction between fluorine‐terminated PEEK oligomers and hydroxyl‐terminated PES oligomers. The dynamic mechanical behavior of a composite sample prepared by compression molding of a glass fibre cloth and the copolymer was investigated by means of a dynamic viscoelastometer. The β relaxation peak and the α′ relaxation peak were observed in the logarithmic decrement curve of the amorphous block copolymer of PEEK/PES. The glass transition temperature (β relaxation peak) is shifted to higher temperature and approaches a constant value as annealing time and degree of crystallinity increase. The glass transition temperature of the copolymer rises more slowly upon annealing with increasing PES content. The α′ relaxation peak becomes smaller upon annealing, and eventually disappears. The α′ relaxation peaks are related to the motion of molecules upon transition from the non‐crystalline to the crystalline state. The α′ relaxation occurs for the copolymer with a degree of crystallinity of 0 to 3%.
Studies on sequence distribution of aliphatic/aromatic copolyesters by high‐resolution 13C nuclear magnetic resonance spectroscopy for evaluation of biodegradability
Authors: Witt Uwe , Müller Rolf‐Joachim , Deckwer Wolf‐Dieter 
Published: April 2003

AbstractCopolyesters with different stoichiometric compositions, obtained from 1,4‐butanediol, adipic acid, and terephthalic acid by molten‐state polycondensation, are studied by means of high resolution 13C NMR spectroscopy with respect to copolymer composition and block length distribution. The ratio of aliphatic and aromatic dicarboxylic acids in the polymer, which sensitively influences the biodegradability of the polymers, reflects the initial monomer composition during polycondensation. This indicates that under the conditions applied for polycondensation no loss for example of terephthalic acid due to sublimation occurs. It was found that the aliphatic and aromatic repeating units are randomly distributed within the polymer chain. The experimentally determined average sequence length distribution dependence on stoichiometric copolymer compositions are in accord with ideal polycondensation statistics. In combination with the results of the degradability of aromatic oligomers, predictions about the degradation characteristics of the aliphatic/aromatic copolymers can be made.
Thermodynamics of depolymerization of biotechnological poly[(R)‐3‐hydroxybutyrate] with formation of (R,R,R)‐4,8,12‐trimethyl‐1,5,9‐trioxadodeca‐2,6,10‐trione and of its polymerization with ring‐opening to highly isotactic poly[(R)‐3‐hydroxybutyrate] from 0 to 500 K at standard pressure
Authors: Lebedev Boris V. , Bykova Tat'yana A. , Kiparisova Elena G. , Vasil'yev Valery G. 
Published: April 2003

AbstractIn adiabatic vacuum and dynamic calorimeters the temperature dependence of the heat capacity C of (R,R,R‐4,8,12‐trimethyl‐1,5,9‐trioxadodeca‐2,6,10‐trione a twelve‐membered cyclic trilactone), biotechnological poly[(R)‐3‐hydroxybutyrate] and highly isotactic poly[(R)‐3‐hydroxybutyrate] was studied between 5 K and 500 K; temperatures and enthalpies of melting of the above mentioned substances were measured. In a calorimeter with a static bomb and an isothermal shield the energy of combustion of the same substances was measured. From the results the thermodynamic functions C (T), H0(T) − H0 (0), S0 (T), G0 (T) − H0 (0) were calculated in the range of 0 K to 500 K and thermochemical parameters ΔH, ΔH, ΔS, ΔG were estimated at T = 298,15 K and standard pressure. The thermodynamic parameters of depolymerization of the biotechnological polymer to the 12‐membered trilactone ΔH, ΔS ΔG and of the polymerization of the monomer formed in the highly isotactic poly[(R)‐3‐hydroxybutyrate] ΔH, ΔS, ΔG were calculated for 0 K to 500 K.
Kinetic and structural studies of the copolymerization of the cleavable bismaleimide p‐maleimidobenzoic anhydride and styrene
Authors: Winter Herman , Vegte Erik v. d. , Sijben Hans , Dušek Karel 
Published: April 2003

AbstractThe polymerization of a bismaleimide‐styrene system was studied by using a model compound, p‐maleimidobenzoic anhydride, that can be split by simple hydrolysis. Compared to known divinyl systems, a decreased reactivity of the pendant double bonds is observed, probably as a result of cyclization and the steric excluded volume effect. The use of a solvent causes an additional shift of the gel point towards higher conversion. Hydrolysis of gelled material affords soluble p‐maleimidobenzoic acid‐alt‐styrene copolymers. Compared to a linear system, methyl p‐maleimidobenzoate and styrene, the primary chains obtained by hydrolysis show an increased polydispersity, probably due to retardation of bimolecular termination of the free radicals that are attached to the polymer network (gel effect).
Investigation of the kinetics of ethylene polymerization with supported titanium‐magnesium catalysts of various composition
Authors: Skomorokhov Vladimir B. , Zakharov Vladimir A. , Kirillov Valerii A. 
Published: April 2003

AbstractA mathematical model of the polymerization process is suggested on the basis of kinetic data, obtained for the polymerization of ethylene with supported titanium‐magnesium catalysts of various compositions differing in particle size, content of electron donor modifier, oxidation state of titanium in the initial catalyst and combination with different cocatalysts. The model includes stages of the formation and deactivation of active sites and takes into account monomer diffusion into the polymer particle. The analysis of experimental data by means of the mathematical model allowed to obtain the rate constants for single stages of the polymerization process. The suggested model and the obtained set of parameters allow to make a satisfactory description of a wide spectrum of experimental data, corresponding to different shapes of kinetic curves. The kinetic parameters were found to depend on the oxidation state of titanium in the catalyst and on the nature of the cocatalyst.
Improvement of the synthesis of poly(L‐cystyl‐L‐cystine): a new biodegradable polymer
Authors: Bechaouch Soufiane , Coutin Bernard , Sekiguchi Hikaru 
Published: April 2003

AbstractA new synthesis of poly(L‐cystyl‐L‐cystine) by using N,N′‐bis(trimethylsilyl)cystine dibenzyl ester is described. The polycondensation of the latter with N,N′‐bis(benzyloxycarbonyl)cystine bis(pentafluorophenyl) ester allowed us to obtain polymers having higher molar masses (28 700 instead of 14000 g/mol) and improved properties compared with earlier methods. The partial as well as complete deprotection of the polymer using a new method, generally used in peptide chemistry, is also described.
All‐aromatic homo‐and copolyesters derived from 3,4′‐disubstituted diphenyl sulfides
Authors: Carpaneto Luca , Costa Giovanna , Peluffo Cristiana , Vezzani Sonia , Valenti Barbara 
Published: April 2003

AbstractThe synthesis of two new isomeric asymmetrically disubstituted disulfide monomers, [4‐(3‐hydroxyphenylthio)benzoic acid and 3‐(4‐hydroxyphenylthio)benzoic acid], with potential applications as all‐aromatic polymer chain flexibilizers and flame‐retardant additives, is here reported. The preparation and characterization of their homo‐ and copolymers obtained with 4‐hydroxybenzoic acid, terephthalic acid and hydroquinone or its phenyl and methyl derivatives is also described. The purity of the monomers has been determined by gas chromatography, elemental analysis and NMR spectroscopy. Both monomers and polymers have been characterized by several techniques. DSC analysis and optical microscopy in polarized light have been used to determine the phase behaviour of the polymers. The remarkable differences in crystallinity and mesogenicity of the polymers derived from the two isomeric monomers are compared to the behaviour of copolymers containing the analogous oxygen‐bridged compounds.
Hydrogenated butadiene/ethene/1‐olefin terpolymers as model substances for short‐chain branched polyethylene
Authors: Gerum Werner , Höhne Günther W. H. , Wilke Wolfgang , Arnold Manfred , Wegner Tino 
Published: April 2003

AbstractPoly[(butadiene‐alt‐ethene)‐co‐(butadiene‐alt‐1‐olefin)] terpolymers were synthesized by Ziegler‐Natta polymerization using VO(O‐neopentyl)2Cl/Al(i‐Bu)3 catalyst system in toluene. Variation of the 1‐olefin/ethene ratio in the monomer feed produces terpolymers with mixed units of butadiene‐alt‐ethene and butadiene‐alt‐1‐olefin. After hydrogenation one obtains model substances for LLDPE with a special distribution of methylene sequences between branching points. Differential scanning calorimetry (DSC) was used to determine the degree of crystallinity and the melting behavior. From the melting temperature region, the thickness distribution of the crystal lamellac, and thus the average number of C‐atoms between the alkyl branches, can be determined. From detailed X‐ray diffractometry, the mean crystallite size, the lattice distortions and the degree of crystallinity was determined for those products which show distinct reflections. The crystallization behavior can only be described by a three‐phase model.
Doped non‐conjugated polymers with enhanced electrical conductivity, 2
Authors: Sinigersky Vesselin , Kossmehl Gerhard , Mladenova Lyudmila , Schopov Ivan 
Published: April 2003

AbstractOur previous investigations showed that polymers built up of short aromatic blocks and methylene chains became conductive upon doping with iodine. Now we prepared similar polymers with conjugated blocks consisting of different types and numbers of rings (benzene, thiophene, 1,3,4‐oxadiazole) and methylene chains of different length. Despite being non‐conjugated these polymers can be doped with iodine, resulting in an increase in electrical conductivity by up to six orders of magnitude. The colour turns black and a new absorption maximum, characteristic of I3−, appears in the UV spectrum at 370 nm. These results confirm our previous assumption that in such a type of polymers, some ordering of the aromatic blocks takes place. This evokes enhanced interaction equivalent to an extension of the conjugation, thus allowing doping, leading to conductivity increase.
Chromatographic investigations of polyacetals in the critical range of liquid chromatography, 2. Determination of functionality and molecular weight distributions in α,ω‐bis(9‐anthrylmethylpoly(1,3,6‐trioxacyclooctane))s obtained by “active chain‐end mechanism”
Authors: Gancheva Valeria B. , Vladimirov Nikolai G. , Velichkova Rumiana S. 
Published: April 2003

AbstractThe fractions obtained by cationic active chain‐end polymerization of 1,3,6‐trioxacylooctane initiated with (CF3SO2)2O (I), CF3SOOCC6H4CO⊕⊖O3SCF3( II) and (C6H5)3C⊕PF (III) were investigated using high‐performance liquid chromatography (HPLC) at the “critical point” of adsorption. The propagating species were converted into 9‐anthrylmethyl groups by suitable reactions of termination of transformation. Their incorporation made the chain ends detectable in the ultraviolet spectrum. The samples were separated at conditions specified for poly(1,3,6‐trioxacyclooctane)s (polyTOCs) obtained with (CF3SO2)2O as initiator. The functionality and molecular weight distribution of polyTOCs obtained with mono‐ and bifunctional initiators and with different counterions were compared and discussed. In the reaction mixtures oligomers of undesired functionality were detected irrespective of the usage of mono‐ or even bifunctional initiators. A correct method was used to determine the completeness of the separation and to calculate the percentages of the individual fractions. The order of initiators depending on the amount of the undesired end‐functionality fractions in the products obtained has been established. Attempts were made to elucidate the reactions complicating the cationic chain‐end polymerization of cyclic acetals and leading to a mixture of cyclic, dead, monofunctional and bifunctional oligomers and polymers. The results were summarized and compared with functionality and molecular weight distributions of oligo(1,3,6‐trioxacyclooctane)s obtained by “activated monomer mechanism” which have been discussed in the first paper of this series.
Single site polymerization of ethylene and 1‐olefins initiated by rare earth metal complexes
Authors: Ihara Eiji , Nodono Mitsufumi , Yasuda Hajime , Kanehisa Nobuko , Kai Yasushi 
Published: April 2003

AbstractEthylene polymerization was explored by using the racemic SiMe2(2‐SiMe3‐4‐tBuC5H2)2Sm(THF)2 complex (1), meso type Me2Si(Me2SiOSiMe2)(3‐tBuC5H2)2Sm‐(THF)2 complex (2), and C1‐symmetric SiMe2[2,4‐(SiMe3)2C5H2][3,4‐(SiMe3)2C5H2]‐Sm(THF)2 complex (3) in the absence of methylaluminoxane. As a result, the meso isomer exhibits highest initiating activity, but the number‐average molecular weight is relatively low (Mn = 50000). In contrast to these complexes, the C1‐symmetric complex provides the highest molecular weight of polyethylene, Mn > 1000000, with relatively narrow molecular weight distribution (Mw/Mn = 1.60). Only the racemic complex exhibits good activity for the polymerization of propylene, 1‐pentene and 1‐hexene.
Synthesis, characterization and photoreaction of side‐chain liquid‐crystalline polymers comprising cinnamoyl biphenyl mesogen
Authors: Kawatsuki Nobuhiro , Sakashita Sin‐ichi , Takatani Ken , Yamamoto Tohei , Sangen Osamu 
Published: April 2003

AbstractLiquid‐crystalline (meth)acrylate monomers and polymers having mesogenic groups based on 4‐alkyloxy‐4′‐cinnamoylbiphenyl (m = 2, 6) were synthesized. The methacrylate monomers 4c, d were polymerized by free radical polymerization. Under the same conditions, the acrylate monomers 4a, b gave unidentified polymers in very low yield. To synthesize the acrylate polymer, the acrylate monomer having 4‐alkyloxy‐4′‐hydroxybiphenyl (m = 2, 6) was polymerized followed by the esterification of the hydroxy group using cinnamoyl chloride. All synthesized polymers having mesogenic moieties showed liquid‐crystalline phases in the high temperature range between 140°C and 245°C. The difference of aggregation of the cinnamoyl biphenyl mesogen among the polymers was studied by UV‐VIS spectroscopy at various temperatures. The photoreaction was performed in both solution and thin film. The [2+2] cycloaddition reaction preferentially occurred in the thin film although both [2+2] cycloaddition and photo‐Fries reactions could occur in the solution.
Micronecking in thin films of isotactic polypropylene
Authors: Plummer Christopher John George , Kausch Hans‐Henning 
Published: April 2003

AbstractThin melt crystallized spherulitic films of isotactic polypropylene have been deformed in uniaxial tension at different temperatures and examined by transmission electron microscopy. As the temperature was increased above approximately −80°C, a transition from high aspect ratio craze‐like features to highly voided shear deformation zones was observed, these latter initiating both at spherulite boundaries and along the spherulite diameters perpendicular to the tensile axis. In rapidly crystallized films, the draw ratio in the deformation zones was estimated to be close to the natural draw ratio of the melt entanglement network, and was independent of test temperature in the range investigated. However, for crystallization temperatures above approximately 125°C, the mean draw ratio within the deformation zones was found to increase with crystallization temperature. It was also observed that, although the draw ratios in deformation zones in ß spherulites were similar to those in α spherulites in films containing both modifications, the former showed more homogeneous textures. This suggests that the particularly pronounced textures associated with α spherulites in polypropylene thin films are linked to their crosshatched lath‐like lamellar morphology.
A 40‐membered cyclic arylene ether sulfone from bisphenol‐A: improved synthesis and properties
Authors: Xie Donghang , Gibson Harry W. 
Published: April 2003

AbstractBy the use of pseudo‐high dilution techniques a 40‐membered cyclic arylene sulfone 4, n = 1 was produced in 67% yield by “1 + 1 cyclization” of 4,4′‐dichlorodiphenyl sulfone with 4,4′‐bis(p‐hydroxyphenylisopropylidene phenoxy)diphenyl sulfone, derived in turn from bisphenol‐A and the dihalosulfone. This is a significant improvement over our previously reported yield of 11%. However, the use of cesium carbonate did not result in a yield improvement, i.e., no “cesium effect” was observed. The purity of macrocycle 4, n = 1 was established by high‐performance liquid chromatography (HPLC), NMR spectroscopy and fast atom bombardment mass spectrosccopy (FAB MS). Macrocycle 4, n = 1 has poor solubility due to its crystallinity (Tm = ca. 500°C), but does have high thermal stability (5% weight loss at 507°C in air). HPLC and FAB MS demonstrated that other homologous macrocyclic products resulted from “2 + 2 cyclization” (4, n = 3), “3 + 3 cyclization” (4, n = 5) and backbiting ether exchange reactions (4, n = 2). The high melting point of 4, n = 1 precludes its use as a monomer for melt ring opening polymerization, but this study provides a methodology for the synthesis of other cyclic monomers designed to have lower melting points and be useful in melt ring opening polymerizations.
Morphological observations of single‐chain glassy polystyrene by means of tapping mode atomic force microscopy
Authors: Qian Renyuan , Shen Jingshu , Bei Nianjiong , Bai Chunli , Zhu Chuanfeng , Wang Xinwen 
Published: April 2003

AbstractTapping mode atomic force microscopy has been used to observe single‐chain polystyrene (SCPS) particles sprayed with an atomizer onto freshly cleaved mica surfaces from very dilute solutions of a polydisperse polystyrene sample in good solvents, methylene cloride and benzene, and in poor solvents, CH2Cl2/MeOH 3/1.2 v/v and CH2Cl2/MeOH 3/1.3 v/v. The SCPS particles possess a definite morphology irrespective of the molecular weight but depending on the solvent. The morphology was found to change with time during drying after spraying and to be very sensitive to solvent environment and external forces exerted by the tip of the scanning probe. The particles became oriented due to probe‐tip‐particle interaction during probe scanning. Only qualitative comparison were made for the sizes of the observed images owing to the polydispersity and irregular shape of the particles and uncertainties about the tip convolution effects on the lateral dimensions. Only in the case of spraying the solution in poor solvents particles close to the shape of spheres were observed. In other cases the heights of the particles sprayed were an order of magnitude smaller than the lateral dimensions. AFM imaging has been applied to observe changes in morphology of SCPS particles sprayed from solutions after freeze thaw cycling. The results do not support the idea of cryogenic degradation of PS but the morphology of PS in solution changed to a smaller coil size during cryogenic freezing which persisted after being brought back to room temperature. When the freeze thaw cycled solution was heated to 100°C and then cooled to room temperature the coil size increased with a resulting morphology similar to the morphology observed before freeze thaw cycling.
Effect of bimodality on tear properties of silicone networks
Authors: Shah Gul Bali , Winter Ray Wlliam 
Published: April 2003

AbstractThe effect of blending a short and a long chain prepolymer, i.e. the effect of biomodality, and that of concentration of the crosslinker on mechanical properties has been investigated. The content of short chain prepolymer was varied from 0 to 80 wt.‐%. Different concentrations of crosslinker, 3.9, 9.1 and 12.3 wt.‐%, were used for the bimodal mixtures. It was found that the enhancement of tear properties was dependent upon both the bimodality and the amount of crosslinker used for curing. It has been shown that the enhancement cannot be explained in terms of the existing theoretical equations for tear properties.
On the chain stiffness of poly(lactide)s
Authors: Joziasse Cornelis A. P. , Veenstra Harm , Grijpma Dirk W. , Pennings Albert J. 
Published: April 2003

AbstractPoly(lactide)s (PLAs) are well known hydrolytically degradable polymers, that are widely used for biomedical applications. However, the intrinsic brittle nature of poly(lactide)s is still poorly understood. The stiffness of a polymer chain, expressed as the characteristic ratio C∞ plays an important role in the deformation mechanism of amorphous polymers. In order to investigate the effect of tacticity, high molecular weight poly(lactide) stereo‐copolymers with D‐lactide contents in the range 0–50 mol‐% were synthesised. These polymers were used in light scattering and differential scanning calorimetry (DSC) experiments for the determination of the characteristic ratio C∞ and glass transition temperature Tg. The results of the light scattering experiments in acetonitrile indicate that the characteristic ratio C∞ for poly(lactide)s depends on the L/D‐lactide ratio and increases with the tacticity of the polymer from 9.5 for racemic PDLLA to an estimated 11.8 for isotactic PLLA. These results are consistent with the observed brittle behaviour of poly(lactide) stereo‐copolymers and agree well with predictions obtained from group contribution methods. The choice of the relevant bond length used for the calculation of the characteristic ratio from the scattering data is not as obvious as it may seem and remains a point of discussion. The tacticity of poly(lactide)s also influences the glass transition temperature, which varies from 54°C for racemic to 63°C for isotactic poly‐(lactide).
Synthesis and polymerization behavior of 2,3‐dihydro‐1,4‐dioxin‐2‐one and its 3‐methyl derivative
Authors: Wulff Günter , Jakoby Kai 
Published: April 2003

AbstractThe hitherto unknown 2,3‐dihydro‐1,4‐dioxin‐2‐one (7) and its 3‐methyl derivative 8 have been synthesized for the first time. The olefinic double bond is inserted into the saturated 1,4‐dioxanone precursors 3 and 6a/b by a retro‐Diels‐Alder reaction in the last step of the synthesis. The 1,4‐dioxanone systems of 3 and 6 are prepared by reacting a vicinal dialkoxide with α‐halogenated acyl halides, thus forming the ester and the ether bond in a one‐pot reaction. Monomers 7 and 8 are polymerized by cationic initiation. The resulting products undergo fragmentation to form oligomers in the presence of protic solvents, indicting that ring‐opening polymerization of the δ‐lactone apparently leads to polyester chain segments.
Synthesis and properties of aromatic polyimides derived from 2,7‐triptycenediamine
Authors: Akutsu Fumihiko , Saito Go , Miyamoto Masahiro , Kasashima Yoshio , Inoki Mari , Naruchi Kiyoshi 
Published: April 2003

AbstractNovel aromatic polyimides were synthesized from 9,10‐dihydro‐9,10‐o‐benzenoanthracene‐1,5‐diamine (2,7‐triptycenediamine) and aromatic tetracarboxylic dianhydrides. The polymerization was carried out in a two‐step procedure including ring‐opening poly‐addition giving polyamic acids, followed by thermal cyclodehydration. The polyamic acids have high inherent viscosities (0.97–1.95 dL/g in 1‐methyl‐2‐pyrrolidone). The polyimides show high glass transition temperatures (392–409°C), high decomposition temperatures at 5% weight loss (516–566°C), and high weight residues (64–69% at 800°C). All polyimides are amorphous. The polyimide from the diamine with 3,3′,4,4′‐diphenylsulfonetetracarboxylic dianhydride (4,4′‐sulfonyldiphthalic anhydride) is soluble in pyridine, N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethyl sulfoxide and conc. sulfuric acid at 60°C, and shows high thermal stability. The introduction of 2,7‐triptycenediyl structure into the polyimide backbone has the effect of improving the solubility and maintaining the high thermal stability.