bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical activity as a tool in the investigation of the conformational equilibria of poly‐α‐olefins in solution
Authors: Pino P. , Neuenschwander P. 
Published: June 2010

AbstractAn attempt has been made to evaluate the contribution derived from the investigation of optically active poly‐α‐olefins to our knowledge of the conformational equilibria of isotactic vinyl polymers in solution. The data obtained from the measurement of optical rotation and its temperature coefficent, as well as of optical rotatory dispersion, in solution, leaves little doubt about the existence, for the most stereoregular poly‐α‐olefin, in solution, of main chain sections spiralized in both screw senses with one of the two screw senses prevailing. For a given degree of stereoregularity the length and the prevalence of the chain sections spiralized in the more favored screw sense depend on the structure of the lateral chains; the type of screw sense prevailing depends on the absolute configuration of the asymmetric carbon atoms contained in the monomers. This qualitative model has been confirmed by a series of experiments, including measurements of chiroptical properties in the solid state and determination of the end‐to‐end distance and copolymerization of chiral with nonchiral monomers. The possibility of extending the above model to include polymers containing functional groups for which no suitable method exists to relate optical activity to conformation and the consequences of ordered conformations for the isotactic vinyl polymers in solution are briefly discussed.
Polyisoprene and polybutadiene derivatives of potential biomedical interest. Part II
Authors: Pinazzi C. P. , Menil A. , Rabadeux J. C. , Pleurdeau A. 
Published: June 2010

AbstractSome polyalkadienes (polyisoprenes and polybutadienes) have been modified along the macromolecular backbone by hydroboration‐hydroxylation followed by reaction with phosgene. These polyalcohols and new polychloroformates in reaction with pharmaceuticals such as quinine, cholesterol, and testosterone, lead to new polycarbonates of potential biomedical interest.
Substitutions Electrophiles Sur Le Polyphenylsiloxane
Authors: Conan Jean , Llauro Marie‐France , Bartholin Michel , Guyot Alain 
Published: June 2010

AbstractOn étudie le comportement du polyphenylsiloxane, polymère en échelle de formule brute (Ø ‐ SiO3/2)n, vis à vis des réactions de substitution des noyaux phényles pendants: nitration et chlorométhylation. Le caractère hautement électroattracteur du groupement SiO3/2 désactive le noyau aromatique, mais confère au polymère sa remarquable tenue en milieu acide. La réaction de dégradation qui accompagne le chloromethylation et forme des structures cycliques, a des conséquences limitées du fait de la structure en échelle du polyphenylsiloxane; le polymère ainsi modifié perd sa rigidité.
Synthèse D'Alcools Terpéniques par Oligomerisation Anionique en Phase Hétérogene
Authors: Rupprecht Robert , Brossas Jean 
Published: June 2010

AbstractTerpenic alcohols have been synthetized by anionic dimerization of isoprene in the heterogeneous phase and oxidation of carbanions. Metallic lithium is used as initiator. A small number of isomers have been obtained and characterized.
Kinetic study of the anionic polymerization of propylene sulfide. VI. Influence of the solvent and of several cryptating agents
Authors: Hemery P. , Boileau S. , Sigwalt P. 
Published: June 2010

AbstractSolvent effect upon the reactivity of ion pairs has been examined for the cesium salt of polypropylene sulfide. k± increases with the dielectric constant of solutions. The size effect of the counterion upon the propagation rate constants has been studied in tetrahydrofuran (THF) at −30°C. Values of the dissociation constant KD and of the interionic distance parameter a have been deduced from conductivity measurements made on seeds of living polypropylene sulfide with the cryptate Na+∥222∥ as counterion. k± and k− were determined for several cryptated counterions. Cryptated ion pairs are more reactive than free ions.
Ion‐dipole interactions and chiroptical property changes of an optically active nylon‐type polyamide in CaCl2‐methanol solutions
Authors: Bris Joel Le , Vert Michel , Selegny Eric 
Published: June 2010

AbstractThe chiroptical properties of poly(‐) 1,2‐diaminopropane sebacamide) (I) and of its model molecule: the N, N'‐didecanoyl (‐) 1,2‐diaminopropane (II) in CaCl2‐methanol solutions have been investigated by ORD (optical rotatory dispersion) and CD (circular dichroism) over a wide range of salt/monomeric units or salt/model molar ratios τ. The origin of the observed CD bands is discussed on the basis of the electronic transitions of isolated amide chromophores. The polymer behaves exactly as if the monomeric units were completely independent. The optical activities of (I) and (II) in CaCl2‐methanol solutions are found to depend on two overlapping phenomena: an ion‐dipole complex which prevails at low τ; a solvent‐like effect of the excess salt on the complexed species. A method for calculating the ion‐dipole association constant Kc from the optical rotatory power changes as a function of τ, is described. It is not necessary to know [ϕms] and [mms], the molar specific rotatory powers of the model and polymeric complexed species, which are subsequently deduced using Kc. The structure of the ion‐dipole complex and the nature of the solvent‐like effect are discussed.
Analysis of conformational changes in polystyrene and its derivatives in dilute solution by using the ultraviolet absorption behavior of model compounds
Authors: Van Nguyen‐Luong Bach , Noël Claudine , Monnerie Lucien 
Published: June 2010

AbstractStudy of the variation as a function of temperature of the molar extinction coefficients of dilute solutions of various alkylbenzenes, the configurational isomers of 2, 4‐diphenylpentane and 2, 4, 6‐triphenylheptane, and polystyrene and certain of its halogenated and methylated derivatives, has revealed behavioral anomalies. These have been attributed to changes in the position of the benzene rings whether accompanied or not by rotations of the backbone bonds leading to an overall conformational change.
Polyurethane networks
Authors: Rutkowska M. , Kwiatkowski A. 
Published: June 2010

AbstractThermoplastic urethane elastomers are interesting materials, to work with when physical and mechanical properties of plastics are being studied. This is due to the frequently large or sometimes, exclusive participation of the secondary bonding. Measurements were taken in order to establish the size and extent of reaction of the primary and secondary bonds in thermoplastic urethane elastomers obtained from polyethylene adipate, 4,4 diphenylmethane diisocyanate, and the following chain extenders: ethylene glycol, propylene glycol 1,3; propylene glycol 1,2; butylene glycol 1,4. Through a series of simple stress‐strain measurements at different temperatures, and by using the swelling equilibrium method in different solvents, the crosslinking density with primary and secondary bonds was determined; in addition, we have also found the activation energy of secondary bonds in thermoplastic urethane elastomers.
Photoelastic behavior of poly(n‐alkyl acrylate) networks in the rubbery state
Authors: Ilavský M. , Hasa J. , Dušek K. 
Published: June 2010

AbstractThe photoelastic behavior of poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate), and poly (octyl acrylate) networks was investigated in the temperature range 15–95°C. The temperature dependence of unperturbed chain dimensions dIn (r20/dT, and the temperature dependence of the optical anisotropy of the statistical segment, dIn δα /dT, were determined. For all polymers, low positive values of dIn (r20)/dT were found, while the absolute values of dIn δα /dT were high and decreased with the increasing length of the side chain. These results led to the suggestion that correlations exist between side chains of poly(alkyl acrylate) networks, and that the extent of these correlations increases with the increasing length of the side chain. The stress‐optical coefficient of poly(alkyl acrylates) is independent of both time and deformation, but decreases markedly with increasing content of the crosslinking agent, which is explained by disturbances of the local order due to cross‐linking rather than to non‐Gaussian behavior. The experimental values of δα, which were negative in all cases and decreased with increasing length of the side group, were compared with the calculated values of the optical anisotropies of monomeric units for various models of the latter.
Mechanical behavior of lightly cross‐linked polyurethanes
Authors: Dzierźa W. , Janáček J. 
Published: June 2010

AbstractStress‐strain and stress‐relaxation behavior, ultimate properties and equilibrium swelling of polyurethane elastomers based on poly (ethylene adipate), poly (ethylene maleate), propylene glycol, and 4,4‐diphenyl methane diisocyanate (MDI) have been studied. The elastomers were crosslinked by an excess of MDI and by tetramethylthiuram disulfide (TMTD); the latter was supposed to form additional crosslinks on the unsaturated bonds. Although no true equilibrium was found during the stress relaxation experiments, samples crosslinked by MDI measured at 25, 50, and 80°C, and samples crosslinked with additional TMTD measured at 50°C gave very good Mooney‐Rivlin plots, from which the elastic parameters C1 and C2 could be determined. The E (10 sec) and E (100 sec) moduli from the stress‐relaxation experiments, the relaxation speed, C1 values, and equilibrium swelling degree v2 were used to estimate the effect of MDI and of additional crosslinks due to TMTD. It was found that if TMTD was added as a second crosslinking agent to MDI systems, the moduli first passed through a minimum. On the other hand, TMTD was found to have a negative effect on the tensile strength σb and strain‐at‐break εb values throughout the whole concentration range used. The results obtained were clarified on the basis of mutually influencing crosslinking reactions in the formation of the resulting networks.
Trends in polymer characterization
Authors: Billmeyer Fred. W. 
Published: June 2010

AbstractThe unique properties of polymers derive chiefly from their long‐chain nature, their high molecular weights, and their molecular weight distribution. The characterization of these properties has developed in steps, each followed by a period of consolidation and application. The most recent of these steps of advancement were the introduction of gel‐permeation or liquid‐exclusion chromatography (GPC), solving the problem of determining molecular weight distributions, and the calculation of the unperturbed dimensions of polymer chains. In the current period of consolidation following these advances, disturbing trends are evident. More use is being made of empirical but rapid techniques such as GPC, but less regard is being paid to the need for the calibration samples required to give them meaning. Absolute methods for molecular weight measurement, providing such samples, are practiced far less than a decade ago, and much special apparatus developed for these techniques is no longer commercially available. These methods are vital, and their continuing development and practice must be encouraged.
Monte carlo simulation of a random‐flight chain in a restricted environment: The polymer‐in‐a‐box problem
Authors: Smitham James B. , Napper Donald H. 
Published: June 2010

AbstractComputer simulations of polymer chains in restricted environments were carried out by the Monte Carlo technique. The model investigated was that of a random‐flight chain that commenced at an impenetrable barrier. The effect of close packing of contiguous polymer chains and the likely effects of the self‐excluded volume of the segments on the thickness of the adsorbed layer were studied.The results obtained suggest that the extension normal to the interface of a random‐flight chain with no volume exclusion was seemingly hardly affected by the presence of lateral compressive boundaries, at least at the usual surface coverages studied experimentally. When the effects of volume exclusion were simulated, the extension normal to an impenetrable barrier increased. This implies that the effects of excluded volume are likely to be responsible for the experimentally observed expansion of polymers normal to the interface.
Comparison of different methods of determining the functionality of polyisocyanates
Authors: Guise G. B. , Zoch C. G. 
Published: June 2010

AbstractGel‐point methods for the determination of the functionality of some of the most widely used types of industrial polyisocyanate and polyisocyanate derivatives have been investigated. No single method was applicable to all types, and the most suitable method for each type was determined.With aliphatic polyisocyanates such as N,N′,N‐tris(6‐isocyanatohexyl)biuret I and II b or c (derived from trimethylolpropane and diisocyanates), the most satisfactory method was gel‐point titration with amino‐terminated polyethers. This method was unsuitable for the more reactive aromatic polyisocyanates IIa (from trimethylolpropane and tolylene diisocyanate) or III (poly(methylene phenylene) polyisocyanate), but these could be gelled by reaction with water. Gel‐point condensations with polyamines could be used for the less reactive phenol‐ and ketoxime‐blocked polyisocyanates.Poly(carbamoyl sulfonate) (VI) could be gelled either by hydrolysis to a polyurea in the presence of excess tertiary amine or by reaction with a diamine in the presence of a slight excess of tertiary amine to neutralize the bisulfite released. In all the gelations studied, the functionalities depended on concentration as a result of intramolecular reactions; this is a possible source of error in functionality determinations, particularly in the titration method.
Hydration of biopolymers
Authors: Watt I. C. , D'Arcy R. L. 
Published: June 2010

AbstractWater‐vapor sorption by a range of biopolymers is reviewed to demonstrate the general similarities in sorption characteristics. The interaction of water and the protein wool keratin is considered in more detail and further analyzed in terms of a three‐component isotherm equation. Similar analyses have been applied to the water‐vapor absorption isotherms of chemically modified wools and nylon 66. Changes in the secondary structure of wool affect the water content only at high humidities and have little effect below 80% R.H., where specific site absorption is the predominant mechanism. The analyses confirm that both the polar side chains and the peptide groups of the main polypetide chains provide specific sites for association of water molecules. Sorption hysteresis is shown to be dependent on the experimental procedure for determining “equilibrium” water content. By adopting an experimental technique which minimizes conformational changes during desorption of water from wool, sorption hysteresis is reduced and may be eliminated at low humidities. It is apparent that hysteresis water, when present, is not associated with specific sites but results from conformational changes in the substrate.
Persulfate‐initiated reactions of N‐vinylpyrrolidone
Authors: Senogles E. , Thomas R. 
Published: June 2010

AbstractIn the presence of excess water and potassium persulfate, N‐vinylpyrrolidone reacts to form 1,1‐bis(1′‐pyrrolidonyl)ethane. At lower water concentrations, potassium persulfate initiates the cationic polymerization of vinylpyrrolidone.
Pulse radiolysis of N‐vinylpyrrolidone
Authors: Davison A. , Sangster D. F. , Lynn J. E. , Senogles E. 
Published: June 2010

AbstractThe pulse radiolysis of N‐vinylpyrrolidone and poly(vinylpyrrolidone) in aqueous solution has been studied. The absorption spectra of the intermediates produced have been measured and the kinetics of their disappearance studied. Further study is necessary before the precise structure of the intermediates can be described.
Grafting of methyl methacrylate to polypropylene
Authors: Burchill P. J. , Pinkerton D. M. , Stacewicz R. H. 
Published: June 2010

AbstractThe mutual γ‐irradiation method has been employed to graft methyl methacrylate (MMA) to polypropylene (PP) film in solutions open to the air. It was observed that grafting occurs only when the monomer solutions contain water. This effect of water has been related to a reduction in the oxygen solubility in aqueous solutions. There is some evidence that water affects the kinetics of the graft polymerization.
Stopped‐flow studies of cationic polymerizations
Authors: Pepper D. C. 
Published: June 2010

AbstractThis paper summarizes results and conclusions from an extensive study by stopped‐flow methods of the rapid nonstationary phase of the polymerization by HClO4 in CH2Cl2 of styrene and some styrene derivatives. With styrene, this precursor reaction is detectable but unimportant at 0°C, becomes longer‐lasting as the reaction temperature falls, and at –97°C is the only contributor to the polymerization.Detailed studies at −60 and −80°C, identifying a transient absorption (λmax‐340 nm) as that of the (poly)styryl carbenium ion, lead to the conclusion that the reaction is a composite, with nonionic as well as ionic components. The rates of the polymerization by the two mechanisms can be distinguished only in favorable circumstances (presence of perchlorate salts) but can be interpreted to yield approximate rate constants for propagation by polystyryl carbenium ion‐perchlorate ion‐pairs, viz., kp± ∼ 2000 M−1S−1 at −80°C; 4000–5000 at −60°C. The rate constants of propagation by free ions are estimated as 10–20 times greater.
Kinetics of isobutyl vinyl ether polymerization initiated by trityl salts: A critical reexamination
Authors: Subira F. , Sauvet G. , Vairon J. P. , Sigwalt P. 
Published: June 2010

AbstractKinetics of isobutyl vinyl ether polymerization initiated by Ph3C+SbCl6− in CH2Cl2 were reexamined by using adiabatic calorimetry and spectrophotometry as previously applied to p‐methoxystyrene polymerization. Consumptions of monomer and trityl hexachloroantimonate were followed simultaneously in the temperature range −40° to +25°C. Initiation appeared to be slow (incomplete initiator consumption at temperature equal to or lower than 0°C), and significant transfer and termination processes prevent the system to be considered as “living” (active‐centers concentration goes through a maximum during the polymerization). The initiation step was found to be first‐order with respect to monomer and to initiator, and an overall second‐order with respect to monomer was found for the polymerization. Initiation parameters were separately determined, whereas propagation, transfer to monomer, and termination parameters were computed on the basis of a unimolecular termination process, this leads, for example, to the following rate constants at 0°C and to the activation energies of corresponding reactions:

.
Study of thermal oxidation of polyolefins. VI. Change of molecular weight distribution in the thermal oxidation of polyethylene and polypropylene
Authors: Iring M. , László‐Hedvig S. , Kelen T. , Tüdós F. , Füzes L. , Samay G. , Bodor G. 
Published: June 2010

AbstractIn the thermal oxidation of low density polyethylene (PE) in the melt phase and isotactic polypropylene (PP) in the solid phase, the changes in molecular weight distribution (MWD), weight average molecular weights (Mω), and average number of chain scissions have been studied by gel permeation chromatography (GPC).It has been established that in the case of PP degradation, there is an increase in molecular weight during the induction period both at 80 and 760 torr with simultaneous scission of the macromolecules. In contrast, a similar tendency can be observed in the degradation of PE only at very low (20 torr) pressures, i.e., the degree of molecular weight increases proportional to the length of induction period.For both polymers at the temperature of investigations, considerable molecular weight decrease can be detected both at reduced and atmospheric pressures at the onset of measurable oxygen absorption.In the maximum rate oxidation of PE and PP, the increase of temperature, oxygen pressure, and degradation time each causes a shift of the MWD curves towards lower molecular weights.The average number of chain scissions against the amount of absorbed oxygen was also studied. It has been found that the average number of chain scissions per 1 mole absorbed oxygen is considerably higher for PE than for PP.Molecular weight studies performed in the kinetic range of thermal oxidation show that under given conditions, Intermolecular combination reactions and chain scissions may occur simultaneously.
A “heterogeneous” model for oscillations of chemiluminescence in nonstationary oxidation of hydrocarbons
Authors: Rychlý J. , Matisová‐Rychlá L. , Lazár M. 
Published: June 2010

AbstractThe oscillations of the chemiluminescence intensity observed after oxygen drop in the system ethylbenzene‐benzene‐Co (naphthenate)2 are interpreted by the formation and decay of dissipative structures in the oxygen solution induced by the change in the direction of the temperature gradient between the sample and thermostatting equipment.
The influence of sample holders on oven aging of polypropylene
Authors: Drake W. O. 
Published: June 2010

AbstractThe effect of various types of glass specimen holders on the observed degradation time of polypropylene samples was investigated. Depending upon the type of holder used, different results could be obtained with the same antioxidants.In partially enclosed holders, degradation products from samples drastically reduced the long‐term stability of other samples contained in the same holders. No evidence was found to indicate that this influence extended to adjacent sample holders, nor was any evidence found to suggest a positive influence of one sample upon another.Furthermore, under routine testing conditions, no such adverse effects were found. However, in ovens not having sufficient circulation of air or without adequate exchange of fresh air, such adverse effects are believed possible.
Supermolecular structure and mechanical stress distribution among the chemical bonds in polymers
Authors: Friedland K. J. , Marikhin V. A. , Myasnikova L. P. , Vettegren V. I. 
Published: June 2010

AbstractStress distribution among the polymer chain segments and parameters of the supermolecular structure of oriented polypropylene, polyethylene terephthalate and polycaproamide films have been compared. The stresses have been determined by infrared spectroscopy, and the structure has been studied by electron microscopy and small‐angle and wide‐angle X‐ray scattering. The polymers studied are shown to have a microfibrillar structure. The sizes of long periods, the lengths of crystallites and amorphous regions are found. Stress distribution among the polymer chain segments is extremely nonuniform. Most of the segments, i.e., 90–95%, are subjected to stresses close to the applied stress, the rest of the segments, i.e., 5–10%, experience stresses which are at least an order of magnitude higher. Highly overstressed segments lie in the amorphous regions of microfibrils. They bear the major part of the applied load (not less than 80–90%). A model for the amorphous regions' structure of microfibrils in oriented polymers is discussed.
Chain orientation distribution and elastic properties of poly (p‐phenylene terephthalamide), a “rigid rod” polymer
Authors: Northolt M. G. , van Aartsen J. J. 
Published: June 2010

AbstractOn the basis of a single‐phase structural model a theory has been developed, which yields a relation between the fiber compliance and the chain axis distribution. It is shown that this relation, viz.

Is quantitatively fulfilled for poly(p‐phenylene terephthalamide) fibers studied in this investigation.