bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid‐crystal behaviour of some laterally substituted stiffchain polyesters containing 2‐phenylbenzoxazole units
Authors: Centore Roberto , Roviello Antonio , Sirigu Augusto , Kricheldorf Hans R. 
Published: April 2003

AbstractThe synthesis and the phase behaviour of three laterally substituted stiff‐chain polymers containing 2‐phenylbenzoxazole units is reported. Polymers were obtained by reaction of 2‐(4‐acetoxyphenyl)‐6‐acetoxybenzoxazole with 2‐phenoxyterephthalic acid (polymer 2a), 2‐phenylthioterephthalic acid (polymer 2b) and 2‐hexadecylthioterephthalic acid (polymer 2c). Polymers 2a and 2b are virtually non‐crystalline. 2a is nematogenic, while for 2b a smectic‐like liquidcrystal phase is observed, whose structural periodicity is probably connected with the intercalated stacking of the lateral phenyl groups along the direction of the chain axes. The solid phase of 2c is of the sanidic type. On melting, a liquid‐crystal phase with equatorial periodicity is observed. This periodicity is probably related to the segregation of the stiff chains between the paraffinic layers.
Fluorination of polymers containing COOH/COOR groups with SF4/HF, 1. Model reactions with low molecular weight compounds
Authors: Nuyken Oskar , Dannhorn Wolfgang , Obrecht Werner 
Published: April 2003

AbstractModel studies with low molecular weight compounds are performed in order to evaluate the feasibility of synthesizing fluorine‐containing polymers by modification of commercially available products. The conversion of COOH and COOR into CF3 moieties by means of SF4/HF is checked with the following low molecular weight models for poly(acrylic acid) and poly(acrylic ester)s: hexanoic acid (1), ethyl hexanoate (2), 2,4‐dimethylglutaric acid (3), 4‐carboxypimelic acid (4) and 2,2‐diethylmalonic acid (5). For the model compounds, the reaction conditions have been optimized. The desired products are obtained in high yield and in high selectivity. Therefore, this type of reaction will be applied to the modification of polymers in the next step.
Free radical suspension polymerization kinetics of styrene up to high conversion
Authors: Tefera Nurelegne , Weickert Günter , Bloodworth Robert , Schweer Johannes 
Published: April 2003

AbstractStyrene was polymerized using different amounts of azoisobutyronitrile as initiator at temperatures of 70°C, 75°C and 80°C in suspension. The course of reaction up to almost complete conversion was modeled within a classical kinetic framework. Optimal simultaneous descriptions of both conversion and average degree of polymerization data were possible using two sets of values for the variation of the overall termination rate coefficient kt with conversion. One explanation for this is that kt is chain length dependent. Evidence for this necessity was derived by considering all kinetic parameters, except the termination rate coefficient, as reliable absolute values.
Polymerization of L‐lactide and ϵ‐caprolactone in the presence of methyl trifluoromethanesulfonate
Authors: Rangel Irma , Ricard Michèle , Ricard Alain 
Published: April 2003

AbstractThe cationic polymerization of L‐lactide and ϵ‐caprolactone initiated by methyl trifluoromethanesulfonate in nitrobenzene was studied. The monomer conversion and the average molecular weight decrease when the temperature increases. The kinetics constants for L‐lactide and ϵ‐caprolactone polymerizations are, respectively, equal to 1,7·10−3 min−1 and 1,60·10−3 min−1 at 50°C. The thermodynamic parameters were determined from the temperature dependence of the equilibrium monomer concentration. Thus for L‐lactide and ϵ‐caprolactone polymerization the enthalpy and entropy values are, respectively, equal to ΔH(L‐lactide) = −24,9 kJ/mol; ΔS(L‐lactide) = −25 J/(mol·K) and ΔH(ϵ‐caprolactone) = −15,35 kJ/mol; ΔS(ϵ‐caprolactone) = −35 J/(mol·K).
Electron paramagnetic resonance investigation of the nature of the propagating species in methyl methacrylate polymerization
Authors: Tonge Matthew P. , Pace Ronald J. , Gilbert Robert G. 
Published: April 2003

AbstractThe electron paramagnetic resonance (EPR) spectrum of methyl methacrylate polymerizing in a range of systems is simulated using a consistent set of parameters for two rotamers of a single free radical. The 9‐line spectrum observed in bulk and emulsion polymerization was fitted by a superposition of two spectra corresponding to two rotamers of a long‐chain species (each a somewhat hindered, non‐rotating macroradical), having anisotropic methylene proton hyperfine couplings which can be treated as isotropic to a good approximation. The 13‐line spectrum observed at low conversion with very high radical flux was simulated as a superposition of the spectra of two very similar rotamers, the EPR spectra of which are indistinguishable; either rotamer is part of a very short chain (primarily an initiator fragment which has propagated once) undergoing free rotation in a low‐viscosity medium. Thus the EPR spectra can be explained without having to invoke earlier suggestions that there are two types of free radicals (“trapped” and “untrapped”) in these systems, corresponding to the 9‐line and 13‐line spectra. The existence of an enormous proportion of very short free radicals under conditions of high radical flux is supported by quantitative calculations of the radical chain‐length distribution. It is suggested that the two rotamers have significantly different propagation rate coefficients because of differences in the hindered rotations in their transition states.
Protection and polymerization of functional monomers, 22. Synthesis of well‐defined poly(4‐vinylbenzoic acid) by means of anionic living polymerization of N‐(4‐vinylbenzoyl)‐N′‐methylpiperazine, followed by deprotection
Authors: Ishizone Takashi , Kurosawa Hiroki , Hirao Akira , Nakahama Seiichi 
Published: April 2003

AbstractAnionic polymerizations of N‐(4‐vinylbenzoyl)‐N′‐methylpiperazine (3a) and N‐(4‐vinylbenzoyl)morpholine (3b) were carried out in tetrahydrofuran at −78°C with oligo(α‐methylstyryl)‐dilithium, ‐disodium, and ‐dipotassium. The polymerizations of both 3a and 3b proceeded quantitatively to give stable living polymers having predicted molecular weights and narrow molecular weight distributions. Novel block copolymers, poly(3a)‐block‐polystyrene‐block‐poly(3a) and poly(3b)‐block‐polystyrene‐block‐poly(3b), were synthesized by using these living polymerization systems. Under acidic conditions (6 N HCl in 1,4‐dioxane‐water), quantitative hydrolysis of the amide linkage of the poly(3a) was achieved to give a well‐defined poly(4‐vinyl‐benzoic acid).
Protection and polymerization of functional monomers, 23. Synthesis of well‐defined poly(2‐hydroxyethyl methacrylate) by means of anionic living polymerization of protected monomers
Authors: Mori Hideharu , Wakisaka Osamu , Hirao Akira , Nakahama Seiichi 
Published: April 2003

AbstractAnionic polymerizations of 2‐[(trimethylsilyl)oxy]ethyl methacrylate (1), 2‐[(tert‐butyldimethylsilyl)oxy]ethyl methacrylate (2), and 2‐[(methoxymethyl)oxy]ethyl methacrylate (3), the protected forms of 2‐hydroxyethyl methacrylate (HEMA), were carried out in THF at −78°C with 1,1‐diphenylhexyllithium or 1,1‐diphenyl‐3‐methylpentyllithium in the presence of LiCl. The resulting poly(1–3)s were found to possess predictable molecular weights and very narrow molecular weight distributions. The sequential polymerizations of tert‐butyl methacrylate with the anionic propagating ends of poly(1–3) gave block copolymers in quantitative efficiency. Thus, the anionic polymerizations of 1–3 proceeded without transfer and termination reactions to afford stable living polymers. Complete hydrolysis of the protective groups of poly(1–3)s produced linear poly(HEMA) quantitatively. Novel well‐defined di‐ and triblock copolymers containing hydrophobic [polystyrene, poly(4‐octylstyrene), polyisoprene] and hydrophilic segments [poly(HEMA)] were also prepared by sequential polymerization of the corresponding hydrophobic comonomers with 1, followed by deprotection.
A modified synthesis of liquid‐crystalline poly(ethylene terephthalate‐co‐oxybenzoate)s with completely random chain structure
Authors: Böhme Frank , Komber Hartmut , Leistner Dirk , Rätzsch Manfred 
Published: April 2003

AbstractA new method for synthesis of liquid‐crystalline poly(ethylene terephthalate‐co‐oxybenzoate)s (PET/HBA) is proposed. In order to prevent formation of PET‐rich phases, complex monomers were used instead of PET. In comparison tc copolyesters synthesized conventionally, the new products proved to be much more homogeneous. 13C NMR measurements evidenced that the chain segment distribution is almost random. In contrast to literature data for a copolyester composition of PET/HBA (50/50 mol/mol) only a single glass transition was detected by dynamic mechanical analysis. The influence of transesterification reactions on the homogeneity is discussed.
Thermally induced relaxation and recovery of the macroscopic orientation in a side‐chain liquid crystalline polyacrylate
Authors: Yuan Guoxiong , Zhao Yue 
Published: April 2003

AbstractThermal relaxation behavior of a mechanically induced macroscopic orientation of the mesogenic groups in a side‐chain liquid crystalline polyacrylate was investigated using timedependent polarized infrared spectroscopy. It was found that a complete relaxation occurred only at temperatures in the nematic to isotropic transition region, and that, more interestingly, the completely relaxed macroscopic orientation was recoverable by cooling the sample to its nematic state. This thermally induced relaxation and recovery of the macroscopic orientation was reversible upon repeated temperature changing cycles over an aging time of more than five hours. Moreover, the level of the orientation recovery was found to be sensitive to the recovery and relaxation temperatures and to the annealing duration at the relaxation temperature before cooling. A tentative interpretation is proposed for this orientation recovery.
Polymeric surfactant systems in the asymmetric hydrogenation of amino acid precursors with a rhodium complex
Authors: Flach Herbert Niels , Grassert Ingrid , Oehme Günther 
Published: April 2003

AbstractThe synthesis of new types of soluble and insoluble amphiphilic systems is described, being polysoaps, crosslinked polysoaps, an amphiphilised ion exchanger, and ion exchangers loaded with ionic surfactants. It was possible to synthesise insoluble polymeric systems which nevertheless showed micellar properties. The polymers were tested as aids in the stereospecific hydrogenation of (Z)‐methyl α‐acetamidocinnamate to the methyl ester of N‐acetylphenylalanine (R) by means of an optically active rhodium complex in water. With linear polysoaps the effect on the reaction was dependent on the structure of the soap molecules. The enantioselectivity of the reaction with monomeric surfactants in water was almost attained. Crosslinked polysoaps showed the same effects on the hydrogenation as linear polysoaps with an analogous structure. Macromolecular ion exchangers loaded with amphiphilic counterions gave in hydrogenation almost the same effect as these counterions give when they are not bound to an insoluble carrier. Enantioselectivities and reaction rates were usually slightly lower than with monomeric surfactants. However, there is an advantage in the separation of catalyst and product after reaction. It was shown that the rhodium‐containing amphiphilic ion exchangers could be reused for up to 9 times.
Structure of the hard segments in non hydrogen bond forming polyurethane elastomers as derived from oligomeric model compounds
Authors: Eisenbach Claus D. , Nefzger Hartmut , Hayen Heidi , Enkelmann Volker 
Published: April 2003

AbstractSeveral molecularly uniform oligourethane model compounds for the hard segment of segmented polyurethane elastomers with piperazine (PIP) and tetramethylene bischloroformate based hard segments have been synthesized. X‐ray structure analysis was performed on single crystals with both compounds representing different parts of the piperazine‐1,4‐diylcarbonyloxy‐tetramethyleneoxycarbonyl repeating unit or containing at least one complete repeating unit and methylurethane end groups. A common feature of the model compounds investigated was that the PIP rings are in the chair conformation; the oxytetramethyleneoxy unit is in the g+ tg− conformation, which is also the conformation of the higher melting modification of the two hard segment model polymorphs. The conformation and packing model of the hard segment was derived from the crystal structure of the model compound containing one repeating unit by connecting the two methyl end groups of successive molecules by a CH2CH2 unit without shifting the molecules, i. e., by replacement of two opposing OCH3 groups by an oxytetramethyleneoxy chain in the g+ tg− conformation. The resulting cell for the polyurethane model structure is triclinic and contains two units of half a polymer repeat, and is in excellent agreement with the experimental X‐ray powder diffraction pattern of the hard segment polymer.
Synthesis and polymerization of N‐trimethylsilylacrylamide: A hydrophobic acrylamide
Authors: Dasgupta Arnab , Sivaram Swaminathan 
Published: April 2003

AbstractN‐Trimethylsilylacrylamide (TMSAm), a hydrophobic acrylamide, has been synthesized and characterized. The monomer could be polymerized in benzene by 2,2′‐azoisobutyronitrile or benzoyl peroxide to poly(TMSAm). The silylated polymer was characterized with 1H NMR. Poly(TMSAm) is stable in the absence of moisture. It could be quantitatively hydrolyzed to polyacrylamide under mild conditions. The monomer has been copolymerized with styrene in benzene by benzoyl peroxide to yield polymers which on hydrolysis give copolymers of acrylamide and styrene.
Extrapolation of solubility data of monomeric, oligomeric and polymeric hydrocarbons
Authors: Horacek Heinrich 
Published: April 2003

AbstractSolubility data of hydrocarbons in poly(propylene) were determined by means of inverse gas chromatography and vapour pressure measurements. For better extrapolation, these data were arranged in solubilities of monomers in monomers, in dimers, in oligomers and in polymers as well as in solubilities of monomers, dimers and oligomers in polymers. The results indicate that cyclic compounds are better solvents for polymers than linear ones, because both are more similar in terms of end‐groups. From a theoretical point of view, the extrapolation of solubilities of monomers in polymers to polymers in polymers leads from the Bunsen solubility to the ideal rubber elasticity. The extrapolation of solubilities of monomers in monomers to monomers in their polymers conduces from the ideal gas law or the solubility in itself to the Henry law. The knowledge of solubility is important for the physical foaming process where very fine cell structures are promoted by supercritical gases. Solubility data of propene in hydrocarbons and in poly(propylene) support the thermodynamics of poly(propylene) manufacturing: the heat of solution for propane in poly(propylene) was determined to be 14,7 kJ/mol.
Pop‐corn polymerization of 2‐hydroxyethyl methacrylate and the influence of a charged comonomer
Authors: Starodubtzev Sergei G. , Makhaeva E. E. , Golubev V. B. , Lachinov M. B. 
Published: April 2003

AbstractThe three‐dimensional copolymerization of 2‐hydroxyethyl methacrylate and ethylene dimethacrylate in the presence of water has been studied. An increasing concentration of ethylene dimethyacrylate results in the formation of a pop‐corn polymer. The flakes of the pop‐corn polymer initiate the polymerization of an added monomer which again results in a pop‐corn polymer. The addition of a small percentage of charged monomer into the copolymerization batch (potassium methyacrylate) prevents the formation of a pop‐corn polymer. An experimental investigation of the free‐radical polymerization kinetics was carried out.
Functional metallomacrocycles and their polymers, 27. Catalase‐like activity of water‐soluble polymer containing a phthalocyanine‐manganese complex
Authors: Kimura Mutsumi , Nishigaki Tadayoshi , Koyama Toshiki , Hanabusa Kenji , Shirai Hirofusa 
Published: April 2003

AbstractThe decomposition reaction of hydrogen peroxide by a water‐soluble polymer containing phthalocyanine‐Mn (1c, 1d) was studied in aqueous solution. The catalase‐like activity was varied by the kind of added nitrogen base and its concentration. The catalase‐like activity is also dependent upon the basicity of the nitrogen base and the equilibrium constant for the coordination of the nitrogen base to phthalocyanine‐Mn in lc or 1d. In this catalytic system, the deprotonation of hydrogen peroxide and the formation of a five‐coordinated manganese species are an important factor in the catalase‐like activity. Copolymers 1c and 1d have high activity as catalyst for the decomposition of hydrogen peroxide in the presence of dimethylaminopyridine (DMAPy). The catalytic system obeys Michaelis‐Menten kinetics with respect to the concentration of hydrogen peroxide. The reaction proceeds according to a mechanism similar to that of a reaction catalyzed by catalase.
Studies on the polymerization of ethylene using a high‐yield MgCl2‐supported titanium catalyst, 4. Structural investigation by X‐ray diffraction and electron spin resonance measurements on the state of titanium ions in the standard system and its modifications
Authors: Fuhrmann Hans , Herrmann Werner 
Published: April 2003

AbstractThe MgCl2‐supported titanium catalyst MTKST was characterized by X‐ray diffraction measurement and electron spin resonance (ESR) spectroscopy. To obtain a better understanding of the nature of active sites the process of catalyst formation was interrupted at several stages to obtain samples for ESR measurements. Likewise some systematic modifications of the standard system were performed and the results were studied by ESR technique. The structural data were correlated with the activity pattern in the polymerization of ethylene. It is suggested that the precursor of an active site is a clustered titanium species containing titanium ions of mixed valence state which is complexed and alkylated by AIR3 giving a polymerization active species of high efficiency. A comparison with the polymerization data suggests that the active species or its immediate precursor is characterized by an ESR signal with rhombic anisotropy with g1 = 1,94, g2 = 1,89, g3 = 1,76.
Chemoenzymatic synthesis of linear poly(sucrose acrylate): Optimization of enzyme activity and polymerization conditions
Authors: Chen Xiaomao , Johnson Amy , Dordick Jonathan S. , Rethwisch David G. 
Published: April 2003

AbstractWe have achieved significant improvements in the synthesis of poly(sucrose acrylate). A screen of 15 commercial enzymes was carried out and Alcalase 2T was selected as the best enzyme because of its high activity and selectivity for acylation of sucrose at only one site. The rate of the enzyme catalyzed acylation of sucrose to form sucrose 1'‐acrylate was increased by a factor of ca. 100 compared to previous reports. This rate was increased 10‐fold by treating the as received enzyme by adjusting the pH to the optimum value for the enzyme. An additional 10‐fold increase was achieved by adding a lyoprotectant such as sucrose or poly(ethylene glycol) prior to lyophilizing the enzyme. Significantly higher molecular weights were obtained in aqueous polymerization systems than when N,N‐dimethylformamide (DMF) was used as the solvent. Similarly, higher molecular weights were observed for oxidation/reduction than for azo‐type free radical initiators. We have demonstrated that copolymers of sucrose acrylate and acrylic acid are readily prepared. Finally, by optimization of the polymerization system, we have increased the number‐average molecular weight of the poly(sucrose acrylate) from M̄n = 54 000 to molecular weights M̄n as high as 2 400 000.
Differential scanning calorimetry and thermogravimetry studies of polyacrylamide prepared by free‐radical polymerization in inverse microemulsion and in solution
Authors: Janigová Ivica , Csomorová Katarína , Stillhammerová Martina , Bartoň Jaroslav 
Published: April 2003

AbstractIn spite of the free‐radical polymerization of acrylamide in different reaction environments (non‐percolating (A) and/or percolating (B) inverse microemulsions, water/isopropanol solution (C)) the polyacrylamides obtained did not differ in their Tg values (A: 468 K; B: 469 K; C: 468 K). Similarly, the course of thermogravimetry curves for all three samples A, B and C, was practically identical. The results confirmed that the spatially oriented array of acrylamide molecules at the water/oil interface of the inverse micellar system was destroyed already at early stages of polymerization. The formation of longer polymer chains due to the polymerization at water/oil interface was thus restricted or even eliminated in favor of the propagation of polyacrylamide growing chains in isotropic conditions of water pools of inverse micelles.
Doped polymers by oxidative polymerization, 3. Electrochemical synthesis of poly[trans‐1,2‐di(2‐furyl)ethylene]
Authors: Koßmehl Gerhard , Greczmiel Thomas , Plieth Waldfried 
Published: April 2003

AbstractRedoxable poly[trans‐1,2‐di(2‐furyl)ethylene] films (PDFE) were synthesized by electrochemical polymerization of trans‐1,2‐di(2‐furyl)ethylene (DFE). Acetonitrile, benzonitrile, nitromethane and propylene carbonate proved to be useful solvents for this polymerization reaction. Suitable supporting electrolytes are tetrabutylammonium perchlorate (TBAP), tetrabutylammonium tetrafluoroborate and lithium perchlorate. To avoid irreversible overoxidation of the polymer, the potential should not exceed 1,15 V (vs. Ag/AgCl). The maintenance of the furan rings in the polymer can be gathered from the reflection IR spectrum. The redoxability of the polymer can be proved by means of the UV/Vis spectrum, which shows a shift of maximum absorption from 310 nm in the reduced state to 345 nm in the oxidized state. PDFE shows an electrochromic behaviour. The potential of oxidation of DFE lies in the same range as the analogous thiophene derivative trans‐1,2‐di(2‐thienyl)ethylene (DTE). A comparison of the polymer PDFE and its corresponding thiophene derivative poly[trans‐1,2‐di(2‐thienyl)ethylene] (PDTE) shows that PDFE is more sensitive to overoxidation, and its electrical conductivity is several orders of magnitude lower.
The morphology of poly(ethylene oxide)‐barium perchlorate complexes
Authors: Maunu Sirkka L. , Rinne Hannu , Sundholm Franciska 
Published: April 2003

AbstractPoly(ethylene oxide) dissolves a wide variety of inorganic salts and forms solid complexes with multiphase structures. The interaction between polymer chains and ions directs the morphology of the sample. The structure is very sensitive to the preparation methods and the purity of the materials. In this work the morphology of poly(ethylene oxide)‐Ba(ClO4)2 complexes has been analysed. The effect of the salt concentration and the variations in the molar mass of the polymer was studied. The multiphase structures were investigated by infra‐red spectroscopy, differential scanning calorimetry, optical microscopy, 13C cross polarization and magic‐angle spinning NMR spectroscopy, and wide angle X‐ray scattering. Two different crystalline phases and changes in the amorphous phase were found for the complexes when the salt concentration was varied.