bluuebunny/crossref_metadata_2025_split huggingface dataset:
The photochemistry of ring substituted polystyrenes, 5. Photolysis of poly(p‐amino) and poly(p‐nitrostyrenes)
Authors: Weir Neil A. , Milkie Terence H. 
Published: April 2003

AbstractThe short‐wave (λ = 254 nm) photochemistry of poly(p‐aminostyrene) (PPAS), and poly(p‐nitrostyrene) (PPNS) films was studied under high vacuum conditions (≈ 10−6 mbar) at 25°C. The principal reaction product in both cases was hydrogen, but both polymers also underwent coloration, crosslinking, and chain scission. Rates of chain scission and hydrogen formation were found to be considerably greater for PPAS, and these was attributed to the stabilizing effect of the p‐amino group (relative to that of the p‐nitro group) on the intermediate free radicals. The very high rate of crosslinking of PPAS would suggest the participation of the p‐amino group in crosslinking reactions.
Association of block copolymers in selective solvents 2. Viscosity, diffusion and light‐scattering measurements on hydrogenated poly(styrene‐isoprene) in trans‐decalin/decane mixtures
Authors: Mandema W. , Emeis C. A. , Zeldenrust H. 
Published: April 2003

AbstractThe association of a hydrogenated poly(styrene‐isoprene) block copolymer has been studied in mixtures of a selective (decane) and a non‐selective solvent (trans‐decalin). Viscosity, diffusion and light‐scattering studies were made within the temperature range of 25–100°C. Relatively small, compact micelles with a rather monodisperse distribution are found at low temperatures and high decane concentrations; very large, polydisperse associates are formed at intermediate decane concentrations and also at increasing temperature from the compact micelles prior to complete dissociation. These large particles have no particular effect on the inherent viscosity, which shows a gradual, continuous decrease as the polymer passes from the associated to the dissociated state. The association also gives rise to drastic changes in the UV absorption of the polystyrene part of the polymer. Kinetic experiments indicate a time scale of the order of ten seconds for the association‐dissociation transition.
Relationships between linear expansion factors of polymer coils from viscosity and light scattering
Authors: Chiantore Oscar , Guaita Marino 
Published: April 2003

AbstractThe validity of several relationships which have been explicitly or implicitly proposed to describe the dependence of the linear expansion factor αη, as obtained from viscosity data, on the linear expansion factor αs, as given by light scattering measurements, was tested by applying standard statistical procedures to 133 pairs of αη and αs values. The results so obtained show that the simple identity αη = αs does not disagree with the experimental data. In limited ranges of αη values, however, a better fit is given by two relationships obtained by combining a theoretical equation by Tanaka et al., relating αs and the excluded volume variable z, with the empirical dependence between αη and z, as observed by the same authors. Following a similar empirical approach, a new realtionship is derived which describes the dependence of αη on αs, in the whole range of αη values, better than the identity; nevertheless the αη values calculated from αs through such a new relationship are always very close to αs, the differences being most probably smaller than the errors affecting the experimental determination of the expansion factors.
Head‐to‐head polymers, 14. Thermal degradation of head‐to‐head and head‐to‐tail polystyrenes and poly(vinylcyclohexane)s
Authors: Lüderwald Ingo , Vogl Otto 
Published: April 2003

AbstractThe thermal degradation behavior of head‐to‐head (H‐H) and head‐to‐tail (H‐T) polystyrenes and poly(vinylcyclohexane)s has been investigated by direct pyrolysis in a mass spectrometer. Both H‐H and H‐T isomers show only small differences in their initial temperatures of decomposition but remarkably different degradation processes. Whereas H‐T polystyrene decomposes in accordance with earlier investigations mainly by a radicalic depolymerization into the monomer and yields only a small amount of dimer and trimer, the H‐H polystyrene shows no unzipping and only a statistic degradation into oligomeric styrenes. The formation of stilbene is a diagnostic reaction of H‐H polystyrene. The pyrolysis‐mass spectra of H‐H and H‐T poly(vinylcyclohexane)s are more similar than those of the polystyrenes but the favored thermal cleavage between the two tertiary carbon atoms or next to the tertiary carbon atoms of the polymer backbone chain leads to some characteristic fragments, e.g. 1,3‐dicyclohexylpropene from the H‐T and 1,2‐dicyclohexylethane from the H‐H polymer.
Effect of pressure on the sedimentation coefficient in dilute and semi‐dilute solutions of polyisobutylene in octane
Authors: Nyström Bo , Roots Jaan 
Published: April 2003

AbstractSedimentation measurements over the concentration interval 3–16 kg. m−3 and the pressure range 0,1–5 MPa are reported for the system polyisobutylene/octane. The pressure influence on the sedimentation process was found to be less pronounced at higher than at lower concentrations.
Gelchromatographische refraktionierung, molekulargewichtsabhängigkeit der axialen dispersionsfunktion
Authors: Berger Knud C. 
Published: April 2003

AbstractThe knowledge of axial dispersion is necessary for the determination of molecular weight distributions from gel permeation chromatograms. This work deals with the determination of the axial dispersion function and its dependence on the molecular weight using refractionation method. The results of a number of fractionated and unfractionated samples of polystyrene reveal that peak dispersion in GPC arises mainly from diffusion in the stationary phase on the basis of the theoretical expression proposed by Kubin.
Mechanismus der photopolymerisation des styrols, 3. Zur kinetik der photo‐elementarprozesse
Authors: Kauffmann Harald Friedrich 
Published: April 2003

AbstractThe photoinduced free radical bulk polymerization of styrene (M)—in the absence of any sensitizer or free radical initiator—was investigated at different intensities, Ja, and at different wavelengths, λe, of the exciting light (λe = 313 nm, 335 nm; 25°C). The polymer conversion was followed dilatometrically in optical cells and the photo‐oligomers which are built up simultaneously in the polymerizing system —cis‐1,2‐diphenylcyclobutane (c‐CB), trans‐1,2‐diphenylcyclobutane (tr‐CB), 1‐phenyl‐1,2,3,4‐tetrahydronaphthalene (1‐PhT), 2‐phenyl‐1,2,3,4‐tetrahydronaphthalene (2‐PhT), 1‐phenyl‐4‐(1‐phenylethyl)‐1,2,3,4‐tetrahydronaphthalene (T1) and 2‐phenyl‐4‐(1‐phenylethyl)‐1,2,3,4‐tetrahydronaphthalene (T2),—were quantitatively analyzed by GLC. The quantum yields were found to be φc‐CB = 0,10, φtr‐CB = 0,02, Φ1‐PhT = 0,0084, Φ2‐PhT = 3,7.10−3, ΦT = 5,0.10−4, respectively, and from the experimentally observed dependence of the rate of polymerization, VP, on the square root of the light intensity, Ja, the apparent quantum yield of the formation of radicals can be calculated to be ΦS = 5,6.10−4. On the basis on the proposed structure of the photointermediates, I, which had been previously confirmed by 1H NMR spectroscopy in enriched systems, the kinetic treatment of the photostationary state gives a complete data set of mean values of partial quantum yields, φ, concerning all the photo‐elementary processes of I under polymerizing conditions: φS = 2,56.10−3, φT = 2,3.10−3, φPhT = 5,5.10−2 and φ2M = 0,94 (retro‐Diels‐Alder decomposition).
Röntgenkleinwinkel‐untersuchungen zur struktur der crazes (fließzonen) in polycarbonat und polymethylmethacrylat
Authors: Paredes Edgar , Fischer Erhard W. 
Published: April 2003

AbstractSmall angle X‐ray scattering measurements were made on samples of polycarbonate (PC) and poly(methyl methacrylate) (PMMA) containing crazes. A sharp, well pronounced maximum in the scattering intensity was observed in the direction perpendicular to the draw direction. The distribution of scattered intensity around the draw direction and the effect of contraction of the craze fibrils on the scattering curve, support the suggestion that the observed maximum in intensity arises from interfibrillar interference. Calculated scattering curves for a system of parallel cylinders with a liquid like order are in good qualitative agreement with the observations. The average fibril's diameter a can be determined from the position of the scattering intensity maximum and from the asymptotic behavior of the scattering curve. Very good agreement was obtained between the two methods. No alteration of a with Mw was found for the PMMA samples. For PC it was found that a increased with increasing draw temperature and decreased with increasing draw rate. We can attribute this behavior to the dependence of the yield stress σy on the drawing conditions, because aσy was found to remain constant. This quantity is defined as the fibrillation energy. On the basis of this observation the results are discussed in terms of the “meniscus instability” model of Argon and Salama. A simple explanation of the results can be given by proposing an energy balance during craze growth.
Polyene sequence distribution in degraded poly(vinyl chloride) as a function of the tacticity
Authors: Martinez Gerardo , Mijangos Carmen , José‐Luis‐Millán  , Gerrard Donald L. , Maddams William F. 
Published: April 2003

AbstractFour fractions of poly(vinyl chloride) (PVC) having appreciably different tacticity distributions were prepared by selective extractions on samples polymerised at temperatures between +60 and −50°C. They were degraded thermally at 180°C in the solid state to conversions in the range 0,2 to 0,5% and in solution at 200°C to conversions in the range 1,6 to 5%. The polyene sequence distribution was investigated by ultra violet/visible (UV/VIS) and resonance Raman spectroscopy. The results show that the type of polyene sequence distribution depends markedly on the tacticity distribution of the polymer. Cross‐linking reactions occur more readily as the syndiotacticity increases. The results are discussed and interpreted with reference to previous work relating degradation processes and tacticity.
Polymerisation von fulvenen, 1. Synthese und eigenschaften kationischer polyfulvene
Authors: Rentsch Christoph , Slongo Mario , Schönholzer Stefan , Neuenschwander Markus 
Published: April 2003

AbstractThe cationic polymerization of a series of pentafulvenes with two exocyclic substituents yields highly reactive unsaturated polymers, which are soluble in nonpolar organic solvents. The preparative aspects as well as some properties of the polymers are discussed. Most polymers are very sensitive to oxygen. For instance poly(5‐isopropylidene‐3‐cyclopenten‐1,2‐ylene) (2a), which is obtained with molecular weights up to 350 000, consumes more than one mol‐equivalent of oxygen per repeating unit.
Poly(L‐lysine)/sulfated poly(vinyl alcohol)/acridine orange complex
Authors: Cho Chong‐Su , Kōmoto Tadashi , Kawai Tohru 
Published: April 2003

AbstractIn order to clarify the arrangement of sulfated poly(vinyl alcohol) (PVS) chains about the α‐helical poly(L‐lysine) (PLL) chain in the previously reported complexes of PLL/46 mole‐% sulfated poly(vinyl alcohol) (PVS‐46) and PLL/PVS‐95, induced circular dichroism was studied on PLL/PVS/acridine orange (AO) complexes in acidic aqueous solution. A positive ellipticity, [θ], of ca. 3 400 deg·cm2·dmol−1 at 465 am and small negative values of [θ] at 435 and 510 nm indicated a right‐handed super helical arrangement of AO molecules about the right‐handed α‐helix of PLL, where PVS chains were intercalated. The amount of AO molecules responsible for the induced CD was estimated as low as a few mole‐%. Taking into consideration the arrangement of ε‐amino groups of the right‐handed α‐helical PLL and the distance among the neighboring ε‐amino groups on the radial projection of the helix, the PVS chain segments could be arranged both in the right‐handed and in the left‐handed superhelices about the right‐handed α‐helix of PLL. In cases of the PLL/PVS‐25/AO and PLL/PVS‐30/AO complexes, no induced CD and a quite weak CD were obtained, resp., being consistent with random coil conformation of PLL in the PLL/PVS‐25 and PLL/PVS‐30 complexes mentioned previously.
Dependence of non‐Newtonian flow properties of polystyrene solutions on solvent viscosity
Authors: Ito Yoshio , Shishido Shunsuke 
Published: April 2003

AbstractSteady shear viscosities were measured over a range of shear rates from lower to upper‐Newtonian flow region for solutions of polystyrene in the high‐viscosity solvent tricresyl phosphate at three different temperatures. The influence of solvent viscosity on the non‐Newtonian flow property was studied and compared with the results obtained previously by use of a lowviscosity solvent with similar solvent power for polystyrene as tricresyl phosphate. For the moderately concentrated solutions, the non‐Newtonian viscosity could be explained by Graessley's entanglement viscosity theory modified by a frictional viscosity. The result shows that only the frictional viscosity is affected by variation of solvent viscosity. As the entanglement viscosity decreases with increasing shear rate and is practically masked by the shear independent frictional viscosity, the flow appears as to be upper‐Newtonian in spite of the difference in solvent viscosity. The lower critical concentration for entanglement was determined on the basis of a lower limit for the applicability of the modified Graessley theory. The values of the critical concentrations are independent of the magnitude of solvent viscosities.
Interpretation of rates of polymer‐polymer reactions in terms of statistical thermodynamics of dilute polymer solutions
Authors: Iwata Hiroo , Ikada Yoshito 
Published: April 2003

AbstractThe influence of long‐range polymer interactions on intermolecular polymer reactions is studied for those cases where the rate‐determining step is not diffusion‐controlled but chemical process controlled. Rate consants are derived for the reaction between a reactive group linked to the l1th segment of polymer 1 and a ractive group linked to the m2th segment of polymer 2 as well as for the reaction between polymers 1 and 2 carrying both randomly distributed reactive groups. The rate constant is closely related to the second virial coefficient in the latter case. After formation of the bond between polymers 1 and 2, the second reaction is assumed to take place between the remaining reactive groups A and B within the two linked chains. The apparent second‐order rate constant of this reaction is predicted to increase with decreasing concentration of the reactive groups.
Polymeric viologens as electron donors in hydrogen production by intact cells of Clostridium pasteurianum, Desulfovibrio desulfuricans, and Rhodospirillum rubrum
Authors: Chuaqui Claudio A. , Lynn Kenneth R. , Williams Ross E. , Martin Stanley M. 
Published: April 2003

AbstractThe behaviour of 5 polymeric viologens 2a – e as electron donors in the production of hydrogen by intact cells of Cl. pasteurianum, D. desulfuricans, and R. rubrum was studied. The hydrogen production was followed by gas chromatography and the results indicate that Cl. pasteurianum and D. desulfuricans are much more active than R. rubrum. Polymeric viologens 2a – e show lower initial rates than the low molecular weight viologens 1a and 1b. However, this is independent of the final amount of hydrogen produced, since the polymers are as efficient or more efficient than 1a and 1b. The results are briefly discussed in terms of redox potentials, substituent effects and conformational factors.
NMR investigation on oligo‐ and poly(galacturonic acid)s; gel formation in the presence of Ca2+ counterions
Authors: Rinaudo M. , Ravanat G. , Vincedon M. 
Published: April 2003

AbstractIn this paper, the assignment of the 1H and 13C NMR spectra of poly(galacturonic acid)s is proposed; the 4C1 chair conformation of the monomeric unit in poly(galacturonic acid) is confirmed and the composition of the anomeric mixture at the reducing end (α−D)/(β−D) = 35 : 65 mol/mol independent of the degree of polymerization DP (2 ⩽ DP ⩽ 5) is given. It is demonstrated on oligomers that both 13C and 1H chemical shifts and coupling constants are nearly unaffected by exchanging Na counterions with Ca; the osmotic coefficient of Ca depends on the DP just as predicted by an electrostatic mechanism. The intrinsic viscosity of the polymer increases and the intensity of 13C NMR signals decreases suddenly for 0,3 equivalents Ca2+ per carboxylic site. These results confirm a multichain association followed by a rigid gel formation; the crosslink is proposed to correspond to a cooperative “egg‐box” mechanism on chain segments randomly distributed in the gel.
Reaction mechanism of oxygen‐initiated ethylene polymerization at high pressure
Authors: Tatsukami Yoshiharu , Takahashi Tsutomu , Yoshioka Hiroshi 
Published: April 2003

AbstractThe kinetics of the oxygen‐initiated polymerization of ethylene at high pressure up to 2,220 kbar was systematically investigated in a constant volume system in a temperature range from 60 to 250°C. In the higher temperature range (above 190°C), where no induction period exists, rate equations for both the oxygen consumption and the polymerization were derived by considering a retardation reaction by oxygen. The numerical calculation of these equations by the Runge‐Kutta‐Gil method indicated an excellent agreement with experimental results.
Solution properties of poly(N‐1,1‐dimethyl‐3‐oxobutylacrylamide), 1. unperturbed chain dimensions
Authors: Chiantore Oscar , Trossarelli Luigi , Guaita Marino 
Published: April 2003

AbstractThe Mark‐Houwink relationship for poly(N‐1,1‐dimethyl‐3‐oxobutylacrylamide), (poly[1‐(1,1‐dimethyl‐3‐oxo‐butylaminocarbonyl)ethylene]), in 2‐butanone at 25°C and the unperturbed chain dimensions have been obtained following standard procedures. The characteristic ratio and the steric factor are quite large, indicating that the lateral substituents are effective in expanding the unperturbed dimensions owing either to their bulkiness or to the possibility of being involved in intramolecular hydrogen bonds.
The spinning of silk, 1. Molecular weight, subunit structure, and molecular shape of bombyx mori fibroin
Authors: Trefiletti Vincenzo , Conio Giuseppina , Pioli Franco , Cavazza Barbara , Perico Angelo , Patrone Eligio 
Published: April 2003

AbstractThe molecular structure of Bombyx mori fibroin is still subjected to much controversy; there are discordant reports in the literature on both the value of the molecular weight and the subunit structure of the molecule. The method reported in the present paper allows the molecular weight of Na2CO3 extracted fibroin samples to be unambiguously determined, and investigations on the composition and the molecular weight of the peptides arising from the degradation process succeeded in establishing some overall aspects of the structure of the subunits. The main results are: (1) the molecular weight of undegraded fibrion is 4 · 105; (2) two small subunits are disulfide linked to the main chain; (3) the subunits are located near the terminals of the main chain; (4) in agreement with previous partial literature data, the small subunits are rich in bulky and acid amino acids; our work further shows that they possess a three‐block structure, consisting of a central hydrophobic core bearing two strongly acid sequences at the terminals. The mechanism of degradation of the fiber appears to be directed by structural, rather than chemical, factors, and its detailed investigation may represent a valuable method to determine the molecular architecture of the fiber.
Redox polymerization, 3. Kinetics of acrylonitrile polymerization initiated by the redox systems cyanoacetic acid/Mn(III) and 2‐butanone/Mn(III) in aqueous sulfuric acid
Authors: Jayakrishnan Athipettah , Mahadevan Venkatanarayana 
Published: April 2003

AbstractThe kinetics of Polymerization of acrylonitrile initiated by the redox systems cyanoacetic acid/Mn(III) and 2‐butanone/Mn(III) were investigated in the temperature range of 30 – 50°C in aqueous sulfuric acid. The kinetics are consistent with the formation of a 1 : 1 complex between the reducing agent and Mn(III), its unimolecular decomposition yielding the initiating radical. Extensive oxidation of the primary radical with exclusively mutual termination of growing radicals accounts for the kinetics of the polymerization. Rate and equilibrium constants as well as thermodynamic parameters were evaluated and their significance is discussed.
On the kinetics of polymer degradation in solution, 9. Pulse radiolysis of poly(ethylene oxide)
Authors: Gröllmann Ulrich , Schnabel Wolfram 
Published: April 2003

AbstractPoly(ethylene oxide) was irradiated with pulses of 16 MeV electrons (pulse length up to 100 ns) in aqueous and acetonitrile solutions in the absence and presence of oxygen. The change of the light scattering intensity (LSI) after the pulse was monitored. In acetonitrile solution, at a concentration of 2,3 · 10−2base mol/1, main chain rupture occurred both in the presence and in the absence of O2. In aqueous solutions at [PEO] = 2,3 · 10−2base mol/1 the LSI increased after the pulse in the absence of O2(crosslinking) and decreased at [O2] = 1,4. 10−3mol/1 (main chain scission). The rate of LSI decrease was correlated with a diffusion process in the case of O2free acetonitrile solution and with a chemical reaction in the cases of O2saturated aqueous and acetonitrile solutions. In the latter two cases it was found that a bimolecular reaction precedes bond scission in the main chain. It is assumed that peroxyl macroradicals (PO) react with each other forming oxyl macroradicals (PO•) which decompose relatively rapidly by main chain scission.
Polyimidines, 7. Synthesis and the polymerization of 3‐(p‐Aminophenyl)‐3‐phenylphthalide
Authors: Lohr Raymond A. , Cassidy Patrick E. 
Published: April 2003

AbstractA new monomer for the preparation for polyimidines has been synthesized from 3,3‐diphenylphthalide. The starting material can be mononitrated on one of the pendant phenyl groups by the use of acetyl nitrate or nitronium tetrafluoroborate. The resulting nitrophthalide is then reduced to the amine with hydrogen over PtO2 or with ammonium sulfide with overall yields of 85–90%. 3‐(p‐Aminophenyl)‐3‐phenylphthalide then can undergo self‐condensation to provide a new polyimidine with a rigid backbone structure which may be a candidate for liquid crystal formation. The condensation can take place at temperatures of 180–350°C, either in polyphosphoric acid or nitrobenzene as solvents, or without solvent in a sealed tube. The yield from the polymerization is as high as 89% and inherent viscosities range up to 0,19 dl/g. Thermal stabilities in air and nitrogen are as high as 520 and 565°C, respectively; however a significant difference occurs in thermal stability for different methods of synthesis. All polymers were soluble in chloroform, dimethylformamide and other organic solvents.
Dynamic mechanical relaxations in poly(oxyoctamethylene)
Authors: Pereña José M. , Marco Carlos 
Published: April 2003

AbstractDynamic mechanical, calorimetric and X‐ray diffraction measurements of poly(oxyoctamethylene) are carried out, in order to determine its viscoelastic relaxations and to elucidate the influence of the crystalline form of this polyether on its degree of crystallinity. The dynamic mechanical measurements were performed using a dynamic viscoelastometer at four frequencies ranging from 3,5 to 110 Hz, in the temperature range from −150°C to 60°C. Two relaxations are observed. The one occurring at the lowest temperature (−139°C at 3,5 Hz) has an activation energy of 10 ± 1 kcal/mol (42 ± 4 kJ/mol) and is considered as the γ relaxation which takes place in all the polymers with three or more adjacent methylenic units. The other one appears at −24°C and its activation energy is higher than 100 kcal/mol. The assignment of other of the two relaxations as glass transition of the polymer is discussed in context of the relaxation maxima of other members of the polyether series.