bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal and molecular structure of 1,4‐bis(chloroacetyl)‐trans‐2,5‐dimethylpiperazine, a model compound of poly(trans‐2,5‐dimethyl‐1,4‐piperazinediylfumaroyl)
Authors: Bassi Ivano W. , Scordamaglia Raimondo 
Published: April 2003

AbstractThe molecular and crystal structure of 1,4‐bis(chloroacetyl)‐trans‐2,5‐dimethylpiperazine synthesized by us, was determined from X‐ray diffractometer data. The structure was solved by Patterson and Fourier methods and refined by least‐squares techniques to R 0,065 for 1081 independent reflections. The crystals are monoclinic, space group P21/n, with Z = 2 in a unit cell of dimensions: a = 9,486 (6), b = 9,139 (6), c = 7,036 (5) Å, β = 95,73 (10)°, the numbers in parentheses being the estimated standard deviations refering to the last significant digit. The trans‐2,5‐dimethylpiperazine ring is in a flattened‐chair conformation with the side methyl groups in axial position. The atoms of the amide are nearly coplanar. It seems to be proved that the structure of the trans‐2,5‐dimethylpiperazine ring in poly(trans‐2,5‐dimethyl‐1,4‐piperazinediylfumaroyl) is similar to that found for 1,4‐bis(chloroacetyl)‐trans‐2,5‐dimethylpiperazine.
Monomeric and polymeric azoinitiators
Authors: Walz R. , Bömer B. , Heitz W. 
Published: April 2003

AbstractThe reaction of ethylene glycol, 1,4‐butanediol, 1,6‐hexanediol, 3,6‐dioxaoctane‐1,8‐diol (triethylene glycol), poly(ethylene oxide)s with M̄n = 300,1000 and 3000, or with poly(propylene oxide)s with M̄n = 425 and 2000 in excess with AIBN leads to the corresponding bis(hydroxyalkyl) 2,2′‐azodiisobutyrates (1a–i). These initiators are suited to synthesize telechelics. With equimolar amounts of AIBN and 3‐oxapentane‐1,5‐diol (diethylene glycol), poly(ethylene oxide)s with M̄n = 300, 1000 and 12000, poly(propylene oxide) with M̄n = 425, or with poly(tetrahydrofuran) with M̄n = 1000 and 2000 polymeric azoinitiators of structure 2 are formed. Blockcopolymers may be synthesized by means of these polymeric azocompounds.
Cyclic oligomers formed during the polymerization of 1,3,6,9‐tetraoxacycloundecane
Authors: Rentsch Christoph , Schulz Rolf C. 
Published: April 2003

AbstractThe cationic polymerization of 1,3,6,9‐tetraoxacycloundecane (3) in CH2Cl2 at 0°C gives polymers with a regular OCH2(OC2H4)3 sequence. High polymers are obtained only after the formation of a considerable amount of oligomers. The oligomers up to the octamer ((C7H14O4)x; x=2–8) have been isolated individually and indentified by means of HP‐GPC and NMR as homologues of the cyclic monomer. The equilibrium concentrations of monomer and dimer are the same when the monomer and the dimer are polymerized and when the high polymer is depolymerized.
Untersuchung des abbaus hochmolekularer polyäthylenoxide im festzustand
Authors: Bortel E. , Lamot R. 
Published: April 2003

AbstractWith thermogravimetric analysis, IR and ESR measurements it could be shown that the low stability of high molecular poly(ethylene oxide) is due to a statistical degradation following a radical mechanism which leads to the formation of aldehyde groups at the end positions of the fragments. Mass spectroscopical investigations of degraded (aged) as well as of freshly prepared poly(ethylene oxide) revealed a consistent and easily comprehensible picture. Always 3 series of peaks could be found and the difference between two successive peaks amounts to 44 mass units in each series, corresponding to the oxyethylene unit. The mass spectra of degraded poly(ethylene oxide) were found to be always more rich in fragmentations than those of non degraded ones. The mechanism of poly(ethylene oxide) degradation caused by the action of electrons could be explained with the help of the obtained mass spectra. The degradation of high molecular poly(ethylene oxide), which even takes place at room temperature in the dark and in the absence of air, could be restricted considerably by adding a suitable stabilizer to the polymerization mixture.
Enzyme‐analogue built polymers, 5. On the specificity distribution of chiral cavities prepared in synthetic polymers
Authors: Wulff G. , Grobe‐Einsler R. , Vesper W. , Sarhan A. 
Published: April 2003

AbstractBy copolymerization of 4‐nitrophenyl α‐D‐mannopyranoside‐2,3;4,6‐di‐O‐(4‐vinylphenylboronate) (1) with ethylene dimethacrylate and methyl methacrylate macroporous polymers were obtained, in which after cleavage of the template, 4‐nitrophenyl α‐D‐mannopyranoside (2), chiral cavities with two boronic acid groups are present. From the dependence of the specificity for the resolution of racemates on the covering percentage of the cavities the frequency distribution of the specificity of the cavities could be deduced. With the distribution curve at hand the factors are discussed, which govern the conservation and the loss of specificity.
Photopolymer design: Photocrosslinkable styrylpyridinium substituted vinyl polymers with absorption maxima from 270 nm to 540 nm
Authors: Borden Douglas G. , Williams Jack L. R. 
Published: April 2003

AbstractStyrylpyridinium substituted vinyl polymers (6), which are in effect polymeric dyes, may easily be prepared by condensing poly[1‐(1,6‐dimethylpyridinium‐3‐yl)ethylene methyl sulfate] (3) with various aromatic aldehydes (5) using piperidine as catalyst. The preparation of 40 of these polymers prepared from 39 different aldehydes or combinations of them is reported. The spectral data show that they may be designed for maximum absorption almost anywhere from 270–540 nm and with a great variation in photosensitivity and solubility. It is possible to prepare the vinyl substituted styrylpyridinium salts and then polymerize them, or to prepare the styrylpyridine substituted vinyl polymer and then quaternize it, but the preferred method is to prepare the quaternized polymer 3 and then condense it with an aromatic aldehyde 5 to form the styrylpyridinium substituted vinyl polymer 6. These polymers do not require spectral sensitization and, in fact, we found no compounds that act as sensitizers.
13C NMR‐sequenzanalyse, 9. 1HNMR‐ und 13C NMR‐spektroskopische Untersuchungen zur cis/trans‐Isomerie bei niedermolekularen und polymeren Derivaten des Sarkosins
Authors: Kricheldorf Hans R. , Schilling Gerhard 
Published: April 2003

AbstractThe cis/trans‐isomerism of N‐formylsarcosine (1), its trimethylsilyl ester (3) and of N‐acetyl‐, N‐propionyl‐ as well as N‐pivaloyl sarcosine methyl ester (2a–c) was investigated by 1H and 13C NMR spectroscopy in various solvents. It was found that bulky N‐acyl groups favour the trans form, so that in the case of the pivaloyl group no cis form is detectable. The nuclear Overhauser effect of the formyl proton in 1 and 3 was determined in various solvents and the signals of cis and trans form could be assigned thereby unambiguously. The position of cis and trans signals relative to each other was found to be dependent on solvent and molecular structure. 1H and 13C NMR signals of polysarcosine (10) show in dimethyl sulfoxide more than four splittings, so that the influence of three peptide bonds on one signal is detectable. In water, formic acid and trifluoroacetic acid 1H NMR signals of 10 show only simple cis/trans splittings which demonstrate that trans bonds are preferred in these solvents. Sequence polypeptides like (‐β‐Ala‐Sar‐Gly‐)n (5a), (‐β‐Ala‐Sar‐D,L‐Ala‐)n (5b), or (‐β‐Ala‐Sar‐β‐Ala‐)n (5c) can be characterized by 13C NMR but not by 1H NMR spectroscopy. Only 13C NMR signals of the β‐Ala residue attached to the sarcosyl nitrogen show cis/trans splitting, whereas amino acids attached to the sarcosyl CO group do not. The free energy of activation (ΔG) for the rotation round the CO‐Sar bond was determined for some monomeric sarcosine derivatives as well as for 10 and its sequence polypeptides. Nearly identical values were found (ΔG = 75,3–76,2 kJ/mol (18,0–18,2 kcal/mol)) for all products.
Self polycondensation of oxalohydrazide, 2. Studies on the synthesis of poly(hydrazooxalyl)
Authors: Lehtinen Arja 
Published: April 2003

AbstractA series of poly(hydrazooxalyl)s (2) is prepared by self polycondensation of oxalohydrazide (1a) and by polycondensation of various derivatives of oxalic acid with 1a or hydrazine hydrate under a variety of reaction conditions. The molecular weights of the polymers were found to remain low. IR spectroscopy, X‐ray diffraction, and thermogravimetry were used to study the structure and thermal properties of the prepared polymers. The structure and properties of the polymers were found to depend largely on the monomers and the reaction conditions used in the synthesis, most polymers being partially cyclodehydrated and semicrystalline. 2 seems to possess an extended planar zigzag chain conformation similar to that of polyamides of aliphatic acids, although several crystalline modifications were observed for this polymer. It could also be enolized with strong bases and behaves like a polyelectrolyte in aqueous base solutions.
Studies on aqueous polymerization of acrylamide. Potassium persulfate/2‐mercaptoethylamine hydrochloride redox system
Authors: Husain Md. Mukhtar , Misra Sada Nand 
Published: April 2003

AbstractThe kinetics of aqueous polymerization of acrylamide, initiated by the potassium persulfate(K2S2O8)/2‐mercaptoethylamine hydrochloride (MEAH) redox pair was studied under nitrogen atmosphere at 30 ± 0,1 °C. The initial rates of polymerization were found to be proportional to [K2S2O8]1,5 (in the range of 0,8 to 1,2 mmol−1), to [acrylamide]1 (in the range of 0,8.10−1 to 1,2.10−1 mol 1−1), and to [MEAH]1 (in the range of 1,0 to 7,0mmol 1−1), respectively. The overall energy of activation was found to be 9,8 kcal mol−1 (40kJ mol−1). Water miscible alcohols and common salts (NaF, NaCl, (CH3)4NI) appeared to depress both the polymerization rate and the maximum conversion. With MnSO4.4H2O the reverse influence was found.
Cationic polymerization of N‐vinylcarbazole by tropylium salts at low temperatures
Authors: Rooney John M. 
Published: April 2003

AbstractCationic polymerizations of N‐vinylcarbazole (NVC) in methylene dichloride containing approximately 1% nitromethane were studied by adiabatic calorimetry at temperatures between −40 and −70°C. Tropylium salts containing AsF, SbF and SbCl counterions were used as initiators. Reaction halflives ranged from 2 to 80 seconds and first‐order plots displayed induction periods. Evidence indicated that the majority of the initiator was consumed, permitting estimation of propagation rate constants. For polymerizations involving the SbF counterion, these rate constants were found to be relatively insensitive to the concentration of initiator or excess anion and the conclusion is drawn that paired and unpaired PNVC+ SbF ions have similar reactivities at low temperatures. Correlation of the present results with those from previous work at 20 and 0°C yielded an Arrhenius exponential factor for propagation by unpaired ions of 30±9 kJ mol−1. The degree of polymerization approached the ratio [M]0/[1]0 at −70°C. At higher temperatures, molecular weights appeared to be governed by transfer reactions. The absence of significant chlorine content in polymer samples precluded the possibility of chain transfer to solvent.
Determination of the elastic modulus of polyamide crystals along the chain axis by x‐ray diffraction, 1. The α‐form of nylon‐6
Authors: Kaji Keisuke , Sakurada Ichiro 
Published: April 2003

AbstractStudies were carried out to determine the crystalline elastic modulus E1 along the chain axis for the α‐form of nylon‐6 [poly(ε‐caprolactam)] by X‐ray diffraction. To obtain an inherent E1 value of this polymer the problem was solved that different orders of meridional reflections give different E1 values. Thus the disagreement was found to be due to the increase of the crystallite size by the applied stress. When corrected for this effect, the values from the 040 and 0.14.0 reflections agreed well with each other. The resulting modulus was 183 GN/m2 at 23°C, which was much lower than a theoretically calculated value of 262,8 GN/m2 for the fully extended structure model by Manley and Martin. This seems to be due to the slight shortening at the amide group of the molecular chain because it was confirmed from the intensity changes of the 040 and 0.14.0 reflections of this polymer by the applied stress that the amide part is more extensible than the polymethylene section.Judging from similar considerations the previously reported E1 values for nylon‐66 and nylon‐6,10 are valid.
NMR spectra of some model compounds of polyisoprene
Authors: Dolinskaya Eleonora R. , Khatchaturov Aleksander S. , Poletayeva Irina A. , Kormer Vitali A. 
Published: April 2003

Abstract1H, 2D, and 13C NMR spectra of five compounds modelling various types of monomer units addition in linear polyisoprene were investigated: 1,8‐hexadeuterio‐6‐methyl‐2‐trideuteriomethyl‐2,6‐octadiene (1), squalene (2), 4,7methyl‐3,7‐decadiene (3), 2,15‐bis(trideuteriomethyl)‐1,16‐hexadeuterio‐6,11‐dimethyl‐2,6,10,14‐hexadecatetraene (4), and 4,8‐dimethyl‐4,8‐dodecadiene (5). Compounds 1 and 3 were prepared for the first time. Analysis of the whole complex of spectral characteristics obtained made it possible to accomplish the assignment of lines in the carbon spectra of the compounds. It could be shown, that for linear bonding of isoprene units in case of the head‐to‐head type of addition sequence the methylene carbons in cis‐ and trans‐units absorb at 31,5 and 38,6ppm, respectively, and in case of tail‐to‐tail type of addition sequence the absorption is observed in the region of 28,4–28,8 ppm for both isomeric units.
Solution fractionation of polystyrene by different methods
Authors: Klein Joachim , Werner Michael 
Published: April 2003

AbstractSystematic investigations of the solution fractionation of polystyrene were made in the system butyl acetate (solvent) and 1‐propanol (nonsolvent). For the method of “complete elution” it was possible to show, that (a) the amount of a dissolved fraction increases proportional to the loading of the support material with polymer, (b) the average molecular weight of a fraction is independent of the elution velocity. Subfractions from complete elution show an approach to a limiting value of the average molecular weight and a common high molecular range in gel permeation chromatograms. The existence of a critical limiting molecular weight M+ of polymer solubility, which is a necessary theoretical assumption of the complete elution method, could thus be verified experimentally. Comparison of fractions from complete elution with corresponding fractions from discontinuous solution fractionation demonstrates a better separation efficiency—more uniform fractions and less mutual overlapping of consecutive fractions—for the method of complete elution.
Polymorphie, kristallinität und schmelzwärme von poly(ε‐caprolactam), 2. Kalorimetrische untersuchungen
Authors: Illers Karl‐Heinz 
Published: April 2003

AbstractThe transition between the amorphous state and 3 crystalline modifications of poly(ε‐caprolactam) (polyamide‐6) has been investigated in Part 1 by IR spectroscopy. With these results as background the relation between heat of fusion ΔH* and specific volume v is now investigated as a function of crystallization temperature and time, using isothermal crystallization conditions from the melt as well as cold crystallization. The changes of ΔH* and v, which occur in the course of isothermal crystallization, allow qualitative statements on crystallinity changes and transitions between different crystalline modifications as a function of crystallization temperature. Quantitative results are obtained only in rare special cases, if either only one of the 3 crystalline modifications (α, γ, γ*) is formed or if the amount of one further modification is independent of crystallization time. Additionally, the situation is complicated by the fact, that for constant molecular weight and identical crystallization conditions the results strongly depend on (a) the origin of the polyamide‐6 pellets and (b) the mechanical prehistory of the melt. The reasons for these difficulties are differences in the number of (a) heterogeneous and (b) orientation‐induced homogeneous nuclei. This results in strongly varying crystallization rates, which has a considerable influence upon the relation between ΔH* and v.
Conformational changes of poly(oxymethylene) induced by pressure and mechanical treatment
Authors: Terlemezyan Levon , Mihailov Marin , Schmidt Pavel , Schneider Bohdan 
Published: April 2003

AbstractIR spectra of hexagonal poly(oxymethylene) samples prepared by various polymerization procedures have been studied. The samples were further modified by pressure and by milling in liquid nitrogen. It was found that the considerable differences observed in IR spectra in the range 900–1250 cm−1 are caused by irregularities of the G conformation of the polymer chain. The regularity of the G conformational structure increases by pressing and milling.
Cationic polymerization of methyl substituted 1,3‐dioxepanes
Authors: Okada Masahiko , Hisada Takako , Sumitomo Hiroshi 
Published: April 2003

AbstractThe polymerization of 4‐methyl‐1,3‐dioxepane (1a), 2,4‐dimethyl‐1,3‐dioxepane (1b), and 4,4‐dimethyl‐1,3‐dioxepane (1c) was investigated in 1,2‐dichloroethane at different temperatures ranging from −60 to 0°C by using boron trifluoride etherate as initiator. The polymerization of 1a involves an equilibrium between monomer and polymer, and gives a viscous polymer along with some cyclic oligomers of different sizes. 1H NMR and 13C NMR analysis of the polymer revealed that the bond cleavage of the unsymmetrical 1,3‐dioxepane ring in the polymerization occurred nearly randomly at the two acetal CO bonds. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentrations: ΔH=−9,3±1,3 kJ · mol−1 and ΔS=−38,8±7,8J · mol−1 · K−1. Dimethyl substituted 1,3‐dioxepanes were found to be very reluctant to polymerize: Only a liquid oligomer was formed in very low yield from 1b, and even oligomer was not obtained from 1c. The effect of methyl substituents on the cationic polymerizability of 1,3‐dioxepanes is discussed from the thermodynamic point of view.
Some remarks to the kinetics of anionic polymerization of ethylene oxide in dimethyl sulfoxide
Authors: Kazanskii Konstantin S. , Solovyanov Alexander A. , Dubrovsky Sergej A. 
Published: April 2003

AbstractThe kinetics of ethylene oxide (EO) polymerization in dimethyl sulfoxide with potassium tert‐butoxide as initiator at 323, 333, and 343 K has been studied. The process follows the first order with respect to initiator in the concentration range 1,5–5,9 · 10−3 mol · dm−3 and the rates are the same as in the polymerization of EO with dimsylpotassium (potassium methylsulfinylmethanide). It is supposed that the tert‐butoxide and dimsyl anions are equally effective as initiators and their ionization equilibrium does not affect the polymerization rate. The above conclusion agrees well with the very slow chain transfer to dimethyl sulfoxide in the anionic polymerization of EO.
Mechanism of the oxidative coupling of phenols: Influence of pH upon the electrochemical oxidation of xylenol in methanol
Authors: Roubaty Jean‐Louis , Bréant Mylène , Lavergne Madeleine , Revillon André 
Published: April 2003

AbstractIn acidic methanol, xylenol undergoes a bielectronic one step oxidation leading to the phenoxonium cation. Above pH 5,2 the reaction takes place in two monoelectronic steps, the first of which leading to a free radical. CC coupling, leading to quinones, occurs with the cation, whereas the free monomeric radical undergoes polymerization by CO coupling. The influence of the pyridine concentration upon the orientation of the coupling may be explained by the coincidence between the pKA of pyridine in methanol and the pH which favours disproportionation of the monomer radical.
Model compounds and 13C NMR investigation of isolated ethylene units in ethylene/propene copolymers
Authors: Zambelli Adolfo , Bajo Giuseppe , Rigamonti Ennio 
Published: April 2003

AbstractThe stereochemical environment of the isolated ethylene units, and the arrangement of the neighbouring propylene units, in ethylene/propene copolymers, prepared in the presence of syndiotactic‐specific and isotactic‐specific catalysts are investigated by comparing 13C NMR spectra of selectively 13C‐enriched copolymers and suitable model compounds. The implications of copolymer structure on polymerization mechanism are considered. In the presence of homogeneous syndiotactic specific catalyst systems both the regiospecificity and the stereospecificity are controlled by the last unit of the growing chain end. Regiospecificity and stereospecificity are unaffected by the ethylene units in the isotactic polymerization.
Studies on the polymerization of vinyl compounds in the presence of metal salts, 13. Polymerization of methyl methacrylate initiated by diaminomaleonitrile (DAMN)/copper ion/carbon tetrachloride
Authors: Narita Hiroshi , Hoshii Yasuhiro , Araki Mikio , Machida Seishi 
Published: April 2003

AbstractThe polymerization of methyl methacrylate initiated by the system diaminomaleonitrile (DAMN)/copper ion/carbon tetrachloride was investigated. The polymerization requires the presence of these three components, and both the cupric and the cuprous ion are suitable. The initial rate of polymerization with the cuprous ion is greater than that with the cupric ion. The cuprous ion was detected in both systems. It is considered that the cupric ion is reduced to the cuprous ion by DAMN, and the cuprous ion takes part in the initiation of the polymerization.
Kinetics and mechanism of the aniline‐formaldehyde reaction in acid medium
Authors: Nayar Mazhuvadyil R. Gopinathan , Francis Joseph D. 
Published: April 2003

AbstractThe kinetics and mechanism of the condensation of aniline and formaldehyde in acid medium were studied under various experimental conditions using a thin layer chromatographic method developed for this purpose. The reaction was found to be kinetically of first‐order with respect to formaldehyde. 4‐Aminobenzyl alcohol (1), N‐(4‐aminobenzyl)aniline (4), 4‐(4‐aminobenzyl)aniline (2), and a basic compound of unknown structure were found to be the initial products. By a judicious choice of concentrations and reaction conditions the individual reactions leading to the formation of the above products were isolated and their kinetics and energetic parameter were studied. A probable mechanism of the reactions is suggested.
Haupt‐ und seitenkettenkristallinität bei isotaktischen poly(1‐alkylethylen)en, 2. Röntgenographische, kalorimetrische und ramanspektroskopische untersuchungen am it‐poly(1‐eicosylethylen)
Authors: Trafara Gundolf , Koch Reimer , Sausen Eckhard 
Published: April 2003

AbstractIsotactic poly(1‐eicosylethylene) shows three polymorphic modifications. The orthorhombic modification I is formed during melt crystallization at a cooling rate ϕ<2,5K.s−1. The dimensions of the unit cell are calculated to be a=0,75 nm, b=8,8 nm and c=0,67 nm. The heat of fusion is 145J.g−1, the melting point is 363K. The monoclinic modification II is crystallized from the polymer solution (a=0,53 nm, b=10,8 nm, c=0,77 nm, β=94°). The heat of fusion amounts to 120J.g−1, the melting point is 356K. Modification III is formed during rapid quenching of the melt. The side‐chains crystallized closely packed in layers. Modification III shows no main‐chain crystallinity. The heat of fusion is 40J.g−1, the melting point is 348 K. The crystal field splitting in the Raman spectrum of modification +1418/1440cm−1 indicates an arrangement of the side‐chains as in orthorhombic polyethylene with two chains in the subcell. The subcells of both modifications II and III contain only one chain each.