bluuebunny/crossref_metadata_2025_split huggingface dataset:
X‐ray structure analysis of poly[di‐(3,4‐dimethylphenoxy)phosphazene]
Authors: Burkhart Craig W. , Gillette Paul C. , Lando Jerome B. , Beres John J. 
Published: April 2003

AbstractThe crystal structure of oriented poly[di‐(3,4‐dimethylphenoxy) phosphazene] (PDMP) was determined by x‐ray diffraction. Unit‐cell parameters were found to be a = 15.85, b = 19.43, and c = 9.85 Å. The unit cell is metrically orthorhombic with monoclinic space group P21. There were 48 refinable diffraction spots in the observed reciprocal lattice region, of which 28 were observed and 20 were unobserved. A refined model yielded the following residuals: R(obs) = 0.162 and 0.138. It was shown that a two‐chain unit cell with a [T3C]2 (trans, trans, trans, cis, trans, trans, trans, cis) backbone conformation was the correct structure. The dimethylphenoxy side groups were arranged in nearly parallel planes, slightly off‐normal to the fiber c axis. The polymer chains are extremely tightly packed and contain close but reasonable steric contacts.
Modeling the structure of chain‐molecule liquids: A computer simulation of the n‐alkanes C8–C30
Authors: Avitabile G. , Tuzi A. 
Published: April 2003

AbstractComputer models of a series of liquid n‐alkanes were generated, allowing for continuous variation of torsion angles and of atomic positions. Torsional and intramolecular and intermolecular non‐bonded potentials were introduced. Calculated fractions of gauche bonds are slightly higher than those calculated from a rotational isomeric state model. Calculated radial distribution functions exhibit peaks in good agreement with experimental data. No directional correlation between chains is found, except at very short distances. Calculated end‐to‐end distances and radii of gyration indicate random coil conformations. These results are unaffected by extension of the range of interaction to the attractive region and by variations of temperature and density.
Particle morphology of self‐hydrolyzed acrylate polymer colloids: A 13C NMR and DSC study
Authors: Tarcha P. J. , Fitch R. M. , Dumais J. J. , Jelinski L. W. 
Published: April 2003

AbstractMethyl acrylate polymer colloids can be hydrolyzed self‐catalytically by bound strong acid surface groups derived from the polymerization initiator. The kinetics of hydrolysis were earlier shown to be apparently pseudo‐zeroth‐order for any given latex, and first order with respect to surface strong acid concentration. A surface reaction zone model was proposed to explain the kinetics. This model leads to the prediction that the polymer particles will possess a core‐shell morphology after some hydrolysis has occurred. This study employs 13C NMR spectroscopy to investigate the particle morphology in the wet latex, a new application for this method. The temperature dependence of the 13C NMR integrated intensities at various levels of hydrolysis provides strong evidence that the particles do possess core‐shell morphology, and that the shell is composed of PAA/PMA copolymer. This shell is swollen and plasticized by water, resulting in greatly enhanced segmental mobility of the polymer chains as evidenced by marked narrowing of the NMR lines. Thermal measurements alone cannot distinguish particle morphology because PMA appears to be somewhat compatible with its partially hydrolyzed analog at the temperatures of measurement.
Tube relaxation: A necessary concept in the dynamics of strained polymers
Authors: Viovy J. L. , Monnerie L. , Tassin J. F. 
Published: April 2003

AbstractA theory for the relaxation of large strains in polymer melts is outlined. It is based on the Doi–Edwards slip‐link model and the new concept of tube relaxation. Self‐consistency makes this concept necessary when polymer melts are concerned. The discrepancy with previous non‐self‐consistent theories is not negligible and should be easy to observe experimentally. Special attention is given to the overall size and to the mean orientation of a labeled N‐chain in a step‐strained melt of P‐chains. Using semiquantitative arguments, we predict different regimes depending on the respective values of N and P, and propose approximate evolution equations for each case. These equations may be used to design and interpret a variety of fluorescence, infrared, or NMR polarization measurements, as well as small‐angle neutron scattering experiments.
Dynamic relaxation behavior of copolymers of n‐butyl methacrylate with n‐butyl acrylate and of 2‐hydroxyethyl methacrylate with ethyl acrylate, n‐butyl acrylate, and dodecyl methacrylate
Authors: Kolařík Jan 
Published: April 2003

AbstractThe effect of the α‐methyl group on the mobility of the main and side chains of methacrylateacrylate copolymers has been investigated. Poly(ethyl acrylate) shows a small secondary loss maximum (attributed to the rotation of COOR side chains) at 145 K, while in the case of poly(n‐butyl acrylate) this relaxation process is smeared out or possibly absent. On the contrary, poly(n‐butyl methacrylate) and poly(2‐hydroxyethyl methacrylate) exhibit secondary relaxations at about 278 and 301 K, respectively. From the dynamic mechanical response spectra of methacrylate‐acrylate copolymers one can see that the removal of the α‐methyl group causes a qualitative change in the molecular mechanism of the secondary relaxation, presumably as a consequence of the different participation of the main chains. The existing data, however, are insufficient to quantify these differences. The low‐temperature relaxation attributed to internal motion within the side groups is not distinctly affected by the presence of α‐methyl groups. If both components of the copolymer display the low‐temperature relaxation (above 77 K), the loss maxima preserve their identity to a large extent. The effect of copolymer composition on the main (glass) transition temperature has been described by means of a one‐parameter equation.
Study of light‐scattering changes induced in tRNA solutions by a strong optical field of picosecond pulses
Authors: Dobek A. , Deprez J. 
Published: April 2003

AbstractChanges in the light‐scattering components (λ = 0.53 μm) induced by a strong picosecond optical field (λ = 1.06 μm) applied to macromolecular transfer ribonucleic acid (tRNA) solutions were studied. Two beams were polarized vertically, and the intensity of the vertical and horizontal components of the light (λ = 0.53 μm) scattered at an angle of 90° were measured. The electric field of the strong 30‐ps laser pulse was 5.0 × 103 esu cgs. The experimentally determined changes allowed for calculation of the mean third‐order optical polarizability c, and its anisotropy δc. The measurements were performed in three different solutions: salt free, with magnesium ions, and without magnesium ions. Changes in tRNA structure reflected in changes of nonlinear light scattering, third‐order optical polarizability, and its anisotropy were observed.
The solid‐state polymerization and physical properties of bis(ethyl urethane) of 2,4‐hexadiyne‐1,6‐diol. II. Resonance Raman spectroscopy
Authors: Galiotis C. , Young R. J. , Batchelder D. N. 
Published: April 2003

AbstractResonance Raman spectroscopy has been used to measure the frequencies of the vibrational modes of the polymer backbone of fully and partially polymerized crystals of an ethyl urethane diacetylene. The data have assisted in the assignment of crystallographic structures to the different modifications of the crystals. Effective interatomic force constants have been derived and used to estimate the Young's modulus. For fully polymerized crystals a value of approximately 76 GPa was found. The dependence of the frequencies on elastic tensile strain parallel to the polymer chain direction was determined. By comparing the strain dependence of frequencies of partially polymerized singlecrystal fibers with those expected for model composites, it was concluded that the polymer chains in thermally polymerized crystals are considerably longer than in those polymerized using γ rays.
Flow characteristics of poly(ethylene terephthalate) deduced from pressure drop measurements
Authors: Crater Davis H. , Cuculo John A. 
Published: April 2003

AbstractA unique capillary die was designed which made possible the measurement of extrusion pressure at various locations along the capillary length. Entrance pressure drops, exit pressures, and other rheological characteristics were determined for the flow of poly(ethylene terephthalate) through this extrusion apparatus. The effect of die entrance angle, extrusion temperature, throughput rate and polymer molecular weight were considered. Two samples differing in molecular weight exhibited power‐law behavior at shear rates below 1000s−1. The entrance pressure drops and exit pressures were observed to increase with increasing molecular weight; furthermore, at a specific temperature, both‐increased with increasing shear rate. The values for entrance pressure drop obtained using Bagley analysis were consistently higher than those obtained from direct measurements.
Thermal effects on liquid‐crystalline order in polymers with mesogenic side groups
Authors: Shilov V. V. , Tsukruk V. V. , Lipatov Yu. S. 
Published: April 2003

AbstractX‐ray studies on polymers with phenyl benzoate side groups separated from the main chain by spacer groups of various lengths have been performed. It was found that the dimensions of liquid‐crystalline regions are 15–20 nm, and they contain four to six close‐packed layers. Thermal changes in x‐ray scattering are associated with the variation of sizes and concentration of liquid‐crystalline regions determined by the mobility of the main chain.
Morphological and structural changes in a copolymer of glycolide and lactide occurring as a result of hydrolysis
Authors: Fredericks Robert J. , Melveger Alvin J. , Dolegiewitz Lawrence J. 
Published: April 2003

AbstractThe changes in the structure and morphology of a random copolymer containing 92 mol % glycolide units and 8 mol % lactide units as a function of in vitro hydrolysis have been studied. A number of techniques, such as wide‐angle x‐ray diffraction, small‐angle x‐ray scattering, density measurements, infrared spectroscopy, and viscometry were employed in this study. The results showed that the hydrolytic attack was initiated in the amorphous areas of the polymer. After 28 days in the in vitro medium most of the amorphous areas had been chemically converted to lower‐molecular‐weight species such as oligomers of poly(glycolide‐co‐lactide). These low‐molecular‐weight species become water solble and are removed rapidly after day 28. Thus the fiber takes on a Swiss cheese character as the amorphous matter is hydrolyzed and eventually dissolved. As hydrolysis proceeds further, the crystalline areas of the polymer are attacked and eventually removed from the fiber by solubilization. The resulting voids in the fiber are eventually filled by a “collapse” of the structure. The role of the amorphous areas of the polymer in controlling the tensile strength of the suture is discussed.
A far‐infrared study of ionic interactions in poly(styrene sulfonic acid) ionomers
Authors: Mattera Vincent D. , Risen William M. 
Published: April 2003

AbstractThe far‐infrared spectra of poly(styrene sulfonic acid) (PSSA) ionomer films containing alkaline and alkaline earth ions have been studied, and strong, broad bands, whose frequencies are cation dependent, have been observed and assigned to cation motion. The force field elements for cations vibrating at sulfonate‐containing sites have been obtained for different models of the cation‐motion vibration. The effects of hydration, dehydration, and thermal annealing are discussed in light of ion clustering in these materials.
Studies on molecular motion of polysaccharides in the solid state by broad‐line nuclear magnetic resonance
Authors: Nishinari Katsuyoshi , Tsutsumi Akihiro 
Published: April 2003

AbstractBroad‐line NMR measurements have been carried out on solid amylose, pullulan, and dextran in order to shed light upon the relations between different modes of linkage of glucose residues and physical properties. Rotation of the methylol group attached to the C5 atom around the C5C6 linkage and the libration of glucose residues around the α‐1,6 linkage are suggested as the origins of the observed decrease of the second moment with increasing temperature.
Blends of poly(ethylene terephthalate) and cellulose
Authors: Field Nathan D. , Song Sang Sub 
Published: April 2003

AbstractPoly(ethylene terephthalate) (PET) (intrinsic viscosity 0.59) and cellulose (Whatman) are compatible in up to 7.5% (w/v) solutions in trifluoroacetic acid and in mixtures of trifluoroacetic acid and methylene chloride. Evaporation of the solutions yielded films that did not contain cellulose per se, but rather partial esters of cellulose and trifluoroacetic acid. Clear films were cast from these solutions with compositions of 100/0, 75/25, 50/50, 25/75, and 0/100 PET. cellulose (w/w). Infrared spectra and DSC measurements indicate specific polymer‐polymer interaction although two Tg were observed. Hydrolysis of the trifluoroacetate films to blends of PET and regenerated cellulose was accomplished by suspending the films in water at the boil. Infrared spectra indicate no interaction between the two polymers, although the films of the 50/50 and 25/75 PET. cellulose compositions were clear. The 25/75 composition, from its Tg and melting‐point behavior appears to be a dispersion of very small‐particle PET in a cellulose matrix. The 75/25 composition became opalescent during the hydrolysis and may be a dispersion of large‐particle cellulose in a PET matrix. The regenerated cellulose appears to be a mixture of cellulose II and IV polymorphs.
Crystallization of polymers under high tension: A dendrite model
Authors: Tiller William A. , Schultz J. M. 
Published: April 2003

AbstractThe crystallization of highly oriented homopolymer melts (or glasses) is modeled. It is shown that in such cases heat flow controls the kinetics and microstructure of the transforming material. The situation is modeled similarly to the growth of a thermal dendrite, with the inclusion of large and variable concentrations of defects in the fibrillar crystals. Expressions relating the undercooling, growth velocity, filament tip radius, and defect concentration to a normalized tensile force are derived. Example predictions for the case of isotactic polystyrene are given.
On the structure of polyurethane hard segments based on MDI and butanediol‐1,4: X‐ray diffraction analysis of oriented elastomers and of single crystals of a model compound
Authors: Born L. , Crone J. , Hespe H. , Müller E. H. , Wolf K. H. 
Published: April 2003

AbstractSingle‐crystal x‐ray diffraction analysis is performed on a model compound (bisurethane of diphenylmethane‐4–monoisocyanate and butanediol‐1,4) for the thermoplastic polyurethane (TPU) hard segment formed from diphenylmethane‐4,4′‐diisocyanate and butanediol‐1,4. The resulting structure is compared to structure models of corresponding TPU hard segments, especially to the structure proposed by Blackwell and Ross. Our results confirm this structure model showing a planar zigzag of the (CH2)4 group and planar hydrogen bonding between the urethane groups of adjacent molecules. X‐ray diffraction analyses of polymeric TPU hard segments and of TPU elastomers with noncrystallizing soft segments lead to a revision of the dimensions of the proposed lattice cell, resulting in a more plausible value of 1.3226g/cm3 for the crystal density.
The dependence of yield behavior on temperature, pressure, and strain rate for linear polyethylenes of different molecular weight and morphology
Authors: Truss R. W. , Clarke P. L. , Duckett R. A. , Ward I. M. 
Published: April 2003

AbstractThe temperature, strain‐rate, and pressure dependences of the yield stress have been determined for two polyethylene homopolymers of differing molecular weights and for a polyethylene copolymer. Samples were prepared by slowly cooling from the melt, and also by quenching in order to assess the effects of morphology on the yield behavior. The data have been analyzed on the basis of two Eyring processes acting in parallel. Comparison of all data sets reveals the existence in general of three distinct activated processes each with its own temperature, strain‐rate, and pressure dependences. The relative contribution of each process is dependent on the molecular weight, morphology, etc. Also discussed is the relation of these three yield processes to the well‐known loss processes of linear viscoelasticity.
Solution annealing of poly(TMPS) crystal mats
Authors: Narayanan M. J. Shanker , Magill J. H. 
Published: April 2003

AbstractPoly(tetramethyl‐p‐silphenylene siloxane) crystal mats initially prepared from benzene/methanol (2:1 v/v), when annealed in small amounts of solvent undergo considerable thickening in the chain direction. When the crystals are annealed above their formation temperature, their physical properties change rapidly at first before reaching an asymptotic limit commensurate with annealing time and type of solvent. Changes in melting temperature, heat of fusion, small‐angle x‐ray spacing, and wide‐angle x‐ray scattering patterns have been monitored for three solvents of varying solvent power, ranging from very good to extremely poor. Upon solution annealing, the original crystals mats equilibrate to more stable dimensions compatible with their environment. The activation energy of crystal thickening in contact with a liquid is estimated to be about an order of magnitude lower than that deduced from dry annealing data. It appears that the crystal surface and the crystalline core of the crystals comprising the mats must participate in the measured severalfold increase in long period noted after annealing. The lower surface (or interfacial) energy of the liquid annealed mats compared to isothermally melt‐crystallized polymer of similar molecular weight has a direct bearing on the polymer morphology and crystallinity.
Piezoelectricity and viscoelastic crystalline dispersion in highly oriented poly(vinylidene fluoride)
Authors: Yamada K. , Oie M. , Takayanagi M. 
Published: April 2003

AbstractThe effects of poling temperature on piezoelectricity and its thermal stability were investigated on the basis of the thermal molecular motion associated with the crystalline region. This was done by using a film of highly oriented poly(vinylidene fluoride) containing form‐I crystals. The film was prepared by a zone‐drawing apparatus of the forced‐quenching type. The piezoelectric stress constant e31 is a monotonically increasing function of the poling temperature which becomes steeper above ca. 320 K and again at ca. 400 K. The degree of orientation of the crystal b axis generated by poling also increases more steeply with poling temperature above ca. 320 K and again at 400 K. These temperatures correspond, respectively, to the crystalline dispersion temperature at 11 Hz, designated as αc, and the initiation temperature Tpm of large‐scale molecular motion corresponding to premelting of form‐I crystals. Thus the effect of poling temperature on piezoelectricity closely reflects the moleculer motion in form‐I crystals. The annealing temperature T'a at which e31 decreases to 70% of that of unannealed sample by annealing a poled sample increases with the poling temperature and again this increase is steeper above poling temperatures of ca. 320 K and ca. 400 K. Thus the decay of piezoelectricity depends on both the αc temperature and Tpm.
Distribution of polymer chain lengths inside a spherical volume: Solution in terms of a diffusion problem
Authors: Hermans J. J. , Hermans Jan 
Published: April 2003

AbstractThe probability W(t) that a given number t of segments of an infinite chain lie within a given sphere can be expressed in terms of the single‐pass length probability and the probability of reentrance into the sphere. The problem of calculating these two probabilities is equivalent to that of a diffusing particle exiting or entering the sphere after a given time, when the surface of the sphere is an absorbing wall. It is shown that the boundary condition, c = 0, usually applied to an absorbing surface cannot be used for the present purpose. The boundary condition used instead is the so‐called radiation condition ∂c/∂z = kc; it is shown that when k approaches infinity the final answer for W(t), which is given in the form of an infinite series, approaches the correct limit. In this same limit the ratio 〈t〉2/〈t〉2 has the value 2.4
Morphological and structural features of heat‐treated drawn polypropylene/high‐density polyethylene blends
Authors: Kojima M. , Satake H. 
Published: April 2003

AbstractThe ion etching technique has been applied to a morphological study of mechanically blended polypropylene (PP) with high‐density polyethylene (HDPE). Samples blended to PP/HDPE compositions of 65/35 and 85/15 by weight were highly drawn and then heat treated for 30 min at selected temperatures up to 163°C. When these samples are carefully ion‐etched several features are observed in electron micrographs, namely (i) crosshatched, and (ii) twisted or layered textured inclusions of HDPE crystals within arrays of lamellalike PP crystals situated perpendicular to the direction of drawing. X‐ray diffraction measurements of the drawn samples heat treated in the range 145–163°C for 30 min shows that oriented HDPE crystallizes with b‐axis orientation along the drawing direction. Supporting evidence is obtained from electron diffraction measurements. The molecular weight of the HDPE component is a major factor in the b‐axis‐oriented growth of HDPE crystals in PP/HDPE blends.
Copolymers of 1,1‐difluoroethene with tetrafluoroethene, chlorotrifluoroethene, and bromotrifluoroethene
Authors: Moggi Giovanni , Bonardelli Piergiorgio , Bart Jan C. J. 
Published: April 2003

AbstractCopolymers of 1,1‐difluoroethene with tetrafluoroethene, chlorotrifluoroethene, and bromotrifluoroethene have been prepared by emulsion polymerization, and their crystallinity has been investigated by means of x‐ray diffraction. The results are discussed in relation to copolymer composition and structure.
Real time small‐angle x‐ray scattering during annealing of polymer single crystals
Authors: Grubb David T. , Liu Jay J.‐H. , Caffrey Martin , Bilderback Donald H. 
Published: April 2003

AbstractExperiments at the Cornell high energy synchrotron source (CHESS) have shown that it is possible to obtain 2‐D small‐angle x‐ray scattering patterns from single crystal mats of high density polyethylene with a time resolution of 0.3 s. However, it took up to 5 s to heat the 0.1‐mm‐thick specimen to the annealing temperature. A logarithmic increase of long spacing was quickly established, after an induction time of <2 s at the higher annealing temperatures. At lower temperatures the original reflection remains, weakening, while a continuous scatter to smaller angles builds up. At 10–20 s annealing time a new maximum becomes clear, and then the logarithmic increase of long spacing begins. The intensity of this reflection is intially low and increases with annealing time. On cooling it decreases again. It seems that here we can directly observe two mechanisms of lamellar thickening, melting then recrystallization at short times and diffusional thickening at long times.
A new method for estimation of viscosity‐average molecular weight of polymers from GPC
Authors: Mahabadi H. Kh. 
Published: April 2003

AbstractA novel approach for the determination of the viscosity‐average molecular weight of polymers for which Mark–Houwink constants are not known is presented. This method can be applied to narrow as well as broad‐molecular‐weight‐distribution polymer samples and requires only the GPC chromatogram and viscosity data. The proposed method was tested using polystyrene and poly(methyl methacrylate) in toluene and THF. Molecular weights computed by the proposed approach are in good agreement with those obtained using conventional techniques.