bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular motions, the α relaxation, and chain transport in polyethylene crystals
Authors: Mansfield Marc , Boyd Richard H. 
Published: April 2003

AbstractConformational energy calculations are used to investigate molecular motions in polyethylene crystals. From these a model is derived for the motion that accomplishes the net rotation translation that is believed to underlie the nuclear magnetic resonance (NMR) and dielectric α processes in polyethylenes and paraffins (and their dipole decorated derivatives). The resulting model is found to incorporate features of a number of previous models but differs significantly from all of them. The rotation is accomplished by means of a twisted (by 180°) region that propagates smoothly along the chain across the crystal. It differs from previous rotational models in that the twisted region is found to be rather localized (to ∼12 CH2 units). A dependence of activation energy on chain length (paraffins) or crystal thickness (polyethylenes), with the activation energy becoming independent of thickness in thick crystals, results not from the rotational lattice mismatch of the twisted region per se but from the translational lattice mismatch induced by the 180° rotation of one stem relative to the other. The twist differs from a stable point‐defect twist previously proposed (Reneker defect) in that the chain torsion is relatively uniform through the twist and there is no shortening of the chain accompanying it. Further, the twist propagates smoothly without local barriers to its advance. Thus the propagating twist is to be through of as a transition state rather than a hopping defect. Detailed atomistic conformational energy calculations on C22H46 crystals were combined with a simplified elastic theory for translational stem mismatch in longer chains. From the combined calculations the activation parameters for twist propagation as a function of chain length or crystal thickness could be calculated. The results were compared with experiment for the dielectric α relaxation in paraffins containing dissolved ketones and polyethylenes containing carbonyl groups. The agreement is quite good, especially considering the paucity of adjustable parameters in the model. There is only some slight uncertainty in the calculated entropy of activation and a scattering correction was made a posteriori to account for a slow continued drop‐off in relaxation rate in very thick crystals.
Specific volume of polysulfone as a function of temperature and pressure
Authors: Zoller Paul 
Published: April 2003

AbstractThe pressure–volume–temperature (PVT) properties of a commercial polysulfone derived from bisphenol A and 4,4′‐dichlorodiphenylsulfone are studied experimentally and theoretically in the temperature range 30–370°C and for pressures to 2000 kg/cm2. PVT surfaces are determined for an annealed glass, formed under zero pressure, and for the melt. Two glass‐transition lines must be distinguished: T(P) which is the intersection of the glass and melt PVT surfaces, and Tg(P), which is obtained by pressurizing the melt isothermally. The application of Ehrenfest‐type equations to these transitions are discussed. The Prigogine–Defay ratio r = ΔkΔCp/TV(Δα)2 at P = 0 is found to be equal to 0.95 (±20%), using ΔCp data determined on identical samples. The melt data is compared with the Simha–Somcynski hole theory, using the reducing parameters V* = 0.788 cm3/g, T* = 12,560°K, P* = 10,875 bar. The hole fraction appearing in the theory is found to be constant along T(P), but the glass PVT relationship cannot be reproduced by using the Simha–Somcynsky theory together with the assumption that the hole fraction remains constant in the glass. At P = 0 the hole fraction must be allowed to decrease with decreasing temperature, but at a slower rate than in the melt.
The thermoelastic effect in glassy polymers
Authors: Gilmour I. W. , Trainor A. , Haward R. N. 
Published: April 2003

AbstractThe thermoelastic effect has been measured in compression on four glassy polymers; namely, polystyrene, poly(methyl methacrylate), polycarbonate, and epoxy resin. Quantitative results have been obtained for the first time on three of these polymers. It has been shown that by paying attention to specimen geometry and instrumentation results can be obtained to a high degree of accuracy (better than ±1.5% on a given set of measurements). The polymers are shown to obey the classical Thompson equation for thermoelasticity in solids over the temperature range studied (ca. 220–350°K). By inference such materials can be expected to behave classically in general. The results have been used, as first suggested by Trainor and Haward, to obtain values for the linear thermal expansion coefficient and the values so obtained are shown to be in excellent agreement, in general, with literature values obtained by more conventional methods. Results are given for a range of stress from 5 MN m−2 to between 25 and 50 MN m−2 according to ambient temperature. The method affords a measurement of parameters, in particular, linear thermal expansion coefficient. Values of specific heat for the four plastics have been measured by differential scanning calorimetry and the results compared with published data.
Calculation of the Grüneisen constant of glassy polymers from thermoelastic data
Authors: Gilmour I. , Trainor A. , Haward R. N. 
Published: April 2003

AbstractThermoelastic measurements on a glassy polymer make it possible to measure directly the quantity αV/Cp where α is the coefficient of linear expansion, V the specific volume, and Cp the specific heat at constant pressure. By further measuring the bulk modulus (BT) it is possible to derive a relatively accurate value of the thermodynamic Gruneisen constant (γT) where γT = 3BTαV/Cv. The values obtained decrease only slightly with temperature.
A differential scanning calorimeter study of the crystal forms and polymerization kinetics of 2,4‐hexadiynyl‐1,6‐bis(p‐toluenesulfonate)
Authors: Barrall Edward M. , Clarke T. C. , Gregges A. R. 
Published: April 2003

AbstractThe thermal properties of 2,4‐hexadiynyl‐1,6‐bis(p‐toluenesulfonate) have been explored by program temperature and isothermal differential calorimetry. The heat of fusion for the rapidly heated pure solid was 8254 cal/mole (34,540 J/mole) at 367.1°K (93.8°C). This amounts to an entropy change of 22.5 cal/mole °K (94.1 J/mole °K). The energy of activation for the thermal polymerizations was 18.97 kcal/mole (79.37 kJ/mole). The thermal polymerization appears to follow a solid–solid phase transition which proceeds by random homogeneous nucleation throughout the process. The kinetics were simple first order over 70% of the reaction. Programmed temperature studies indicate that during the first 10% of the polymerization a new high temperature (mp 375.4°K) solid phase is formed which acts as the monomer form during the bulk of the reaction.
Assessment of branching in polymers from small‐angle x‐ray scattering (SAXS)
Authors: Garg Sunil K. , Stivala S. S. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering from solutions was applied in assessing branching using well‐characterized dextran hydrolyzates. It was found that the longitudinal and cross‐sectional properties of the polysaccharides vary in a manner predictable by the molecular topology of the chains. A hydrodynamically equivalent linear model for dextran is proposed and it has been shown that this model correctly predicts values of Φ and K, Flory's universal hydrodynamic constant and the Flory–Fox–Schaefgen parameter, respectively.
The relationship between chemical structure and viscoelastic properties of linear aliphatic polyesters
Authors: Ito M. , Kubo M. , Tsuruta A. , Tanaka K. 
Published: April 2003

AbstractThe effects of Chemical structure on the molecular motions in linear aliphatic polyesters have been investigated with a free‐oscillation torsion pendulum. Broad‐line NMR provided supplementary information. In the γ relaxation which corresponds to the local‐mode motions of main chains in the noncrystalline region, the polyesters which are composed of two methylene units in the diol part of the chemical repeat unit showed an extremely asymmetric loss curve with a relatively high‐loss peak temperature compared with that of the other polyesters. In addition to the two relaxations (β,γ) which have been observed in earlier dielectric measurements, a new relaxation (α) was found on the high‐temperature side of the glass transition of the polyesters. The α relaxation was assigned to molecular motions of methylene segments in the crystalline region. The α and β relaxations of the two‐dimensional series are situated close to the temperatures found for other polyesters with rather long methylene sequence in the chemical repeat unit. The results were explained in terms of a difference on the chain mobility in the noncrystalline regions which may be related to the difference of chemical structure of the polyesters.
Statistical thermodynamics of polymer crystal and melt
Authors: Simha Robert , Jain R. K. 
Published: April 2003

AbstractA crystalline‐state theory recently developed by Midha and Nanda is commented on and applied to the isobars of polyethylene, poly(vinylidene fluoride), and poly(chlorotrifluoroethylene) at atmospheric pressure, and to an isotherm of polyethylene. Satisfactory agreement with experiment results. This includes the volume change at the melting point Tm and the volume difference ΔV between crystal and melt below Tm, when crystal and the earlier liquid‐state theory are combined. A similar agreement is noted with respect to the results at high pressure. The scaling parameters obtained indicate the approximate role of melt temperature and volume as reducing quantities. An inverse proportionality between Tm and αl, the expansivity of the melt at Tm, derived much earlier for low‐molecular‐weight solids, is recovered with an identical numerical coefficient. The thermodynamic functions of polyethylene are investigated in both phases. For this purpose contributions of internal harmonic modes are considered within the framework of the equivalent s‐mer model. One or, at most, two average frequencies are adequate to represent the temperature dependence of the excess free energy and entropy over the value at absolute zero, when the external contributions are included for the crystal. A similar representation of the hard modes can be adopted for the melt. However, the free energy of segmental disorientation computed either from a constant entropy for the s‐mer or a rotational isomeric state model for the isolated chain does not appear to be an adequate representation over a sufficient temperature range. An additional temperature‐dependent term in the entropy and free energy is introduced and tentatively attributed to a volume‐ and temperature‐dependent short‐range ordering. Good agreement with experiment, including the entropy and temperature of fusion, ensues.
A new technique for studying gelation in polyesters
Authors: Martinelli F. J. 
Published: April 2003

AbstractA new method for studying polymer network formation has been devised. Crosslinking reactions are carried out in a recording viscometer, which provides accurate determination of incipient gel points and also serves as a high‐speed stirrer. The molten, nonstoichiometric mixtures are reacted to completion to eliminate the inaccuracies inherent in the determination of reaction extent and this, together with the use of esterification reactions with minimal side reactions, reduces many of the problems of previous methods. The experimental results for the reactions of simple model compounds are in very close agreement with Flory's network theory. A system containing crosslinking reagents with unequally reactive groups has also been considered and the accuracy of the method enables the reactivity ratios of the different groups to be calculated.
Steady‐state and dynamic rheology of poly(1‐olefin) melts
Authors: Wang Jeou‐Shyong , Knox Jack R. , Porter Roger S. 
Published: April 2003

AbstractThe steady‐state and dynamic melt rheology for a series of poly(1‐olefins) has been investigated. The series includes poly(1‐butene), poly(1‐hexene), poly(1‐heptene), poly(1‐octene), Poly(1‐undecene), poly(1‐tridecene), poly(1‐hexadecene), and poly(1‐octadecene). The flow behavior was investigated by use of a Weissenberg rheogoniometer. Measurements on poly(1‐butene) were also made using an Instron capillary rheometer. The empirical relationship developed by Cox and Merz was obeyed for the entire series of poly(1‐olefins) at all temperatures investigated. Graessley's theory was used to calculate the flow curves for the poly(1‐olefins) from the measured molecular weight distributions. The purpose was to investigate the effect of polymer composition on the shear rate dependence of viscosity. It was found that all experimental flow curves except those for poly(1‐hexene) can be fitted with the calculated curves from the individual molecular weight distributions. The conclusion is made that flow curves of poly(1‐olefins) depend predominately on molecular weight distribution and are essentially independent of side‐chain length even for poly(1‐olefins) with pendant groups as long as 16 carbon atoms. The low‐shear limiting Newtonian viscosity η0 for all poly(1‐olefins) was expressed by, η0 = KM̄ or by η0 = K′P̄ where M̄w is the weight‐average molecular weight and P̄w is the weight‐average degree of polymerization. The K and K′ values obtained decrease systematically as the side chain is increased.
Influence of extrusion ratio on the thermal properties and morphology of ultradrawn high‐density polyethylene
Authors: Kojima Shunji , Desper C. Richard , Porter Roger S. 
Published: April 2003

AbstractSolid‐state extrusion of high‐density polyethylene (HDPE) has received considerable attention. It has been shown that extrudate may have high values of optical clarity, tensile modulus (∼70 GPa = 7 × 1011 dyn/cm2), and c‐axis orientation. The effects of extrusion conditions on the properties of the resultant fibers have, however, not yet been clarified. A systematic study has thus been made here to evaluate extrusion pressure, temperature, and extrusion (draw) ratio, and the molecular weight of extruded HDPE. The effects of extrusion ratio on the degree of crystallinity, melting behavior, crystal orientation, and dimensional change along the extrusion direction are reported.
Influence of extrusion ratio on the tensile properties of ultradrawn polyethylene
Authors: Kojima Shunji , Porter Roger S. 
Published: April 2003

AbstractThe tensile properties have been evaluated for high‐density solid‐state polyethylene extruded to different extrusion (draw) ratios. The results are compared with measured and theoretical values on this and other polymers. An extrusion (draw) ratio and a deformation gradient are defined and discussed. The content of extended tie molecules in extruded high‐density polyethylene was calculated from a model and modulus data.
Low‐temperature dielectric spectrum of thermally oxidized polyethylene
Authors: Gilchrist John Le G. 
Published: April 2003

AbstractThree loss peaks in the dielectric spectra of thermally oxidized polyethylene at temperatures below 50°K are each apparently associated with specific species of nonvolatile oxidation products involving hydrogen atoms. We report how each is influenced by room‐temperature rolling, heat treatment, isotopic substitution, and chemical attack. One, the Vincett‐Phillips peak, is susceptible to attack by Cu2+, Fe3+, and HI, and is attributed to a hydroperoxide species. Its rapid and easy determination has promise in the study of polyethylene oxidation. Carson's (higher‐frequency) peak is tentatively attributed to an alcohol species and a new (lower‐frequency higher‐temperature) peak is described but not yet attributed. A few additional observations are made on the loss peaks associated with antioxidants of the substituted phenol type, as reported by Thomas and King.
Fracture surface morphology and phase relationships of polystyrene/poly(methyl methacrylate) systems. I. Low‐molecular‐weight polystyrene in poly(methyl methacrylate)
Authors: Parent Raymond R. , Thompson Edward V. 
Published: April 2003

AbstractSamples of low‐molecular‐weight polystyrene (PS) in poly(methyl methacrylate) (PMMA) were prepared by first dissolving PS in methyl methacrylate monomer and then polymerizing the monomer. Forty‐three specimens of varying number‐average molecular weight (2100–49,000) and composition (5–40 wt %) of PS were prepared, and the surface morphology and phase relationships studied by scanning electron microscopy. Four distinct types of phase relationships were observed: (i) a single phase consisting of PS dissolved in PMMA; (ii) PS dispersed in PMMA; (iii) PMMA dispersed in PS; and (iv) regions of PS dispersed in PMMA coexisting with regions of PMMA dispersed in PS. Values of the size and population density of the dispersed particles are reported. Finally, the size and distribution of the dispersed particles and the various types of phase relationships are discussed in terms of the ternary polystyrene/poly(methyl methacrylate)/methyl methacrylate phase diagram.
Selective chemical etching of poly(ethylene terephthalate) using primary amines
Authors: Sweet G. E. , Bell J. P. 
Published: April 2003

AbstractSeveral primary amines have been examined as selective degradative etchants for the investigation of poly(ethylene terephthalate) (PET) morphology. The objective is to remove less ordered regions, leaving crystals intact. The amines include 40% and 20% aqueous methylamine, 70%–40% aqueous ethylamine and pure and 40% aqueous n‐propylamine. Weight‐loss and x‐ray diffraction data show that certain concentration of aqueous amine solution simultaneously degrade and crystallize PET. This observation indicates the hazard of using some of these amine reagents to characterize PET morphology since the crystalline structure found after etching is likely to be a result of solvent‐induced crystallization during degradation. Data for 40% aqueous methylamine used at room temperature shows that crystallization does not occur during etching, and in light of earlier research indicates the favorable nature of this reagent as a selective degradative medium for PET. Application of this reagent disclosed that in oriented PET fibers chemical stress cracking occurs, causing the degradative reagent to lose its selectivity.
An ESR study of PMMA mechanoradicals and of their interaction with oxygen
Authors: Pilař J. , Ulbert K. 
Published: April 2003

AbstractAnalysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicalsCH2C(CH3)(COOCH3) (I) and CH2C(CH3)(COOCH3)CH2 (II) produced by the breaking of the polymer chain, and secondary radicals CH2C(CH3)(COOCH3)CHC(CH3)(COOCH3)CH2 (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).
Hydrostatic extrusion of linear polyethylene: Effects of molecular weight and product diameter
Authors: Gibson A. G. , Ward I. M. 
Published: April 2003

AbstractOriented rods of linear polyethylene have been prepared by hydrostatic extrusion at 100°C. Materials having a range of different molecular weights were investigated and their behavior was found to correlate well with the melt flow index. The differences in extrusion process characteristics for large‐ and small‐diameter products are discussed. In this context the effect of deformational heating is important and criteria are suggested for determining its significance and also for determining the stability of the process in terms of a critical extrusion pressure.
Chemical degradative stress cracking of poly(ethylene terephthalate) fibers
Authors: Sweet G. E. , Bell J. P. 
Published: April 2003

AbstractPoly(ethylene terephthalate) (PET), after certain thermal and mechanical histories, exhibits stress cracking when exposed to 40% aqueous methylamine. This reagent has also been used for selective degradation of PET films. Stress cracking is shown to occur during degradation only when a specimen supports an internal or externally applied stress, above a critical level. The cracking density in a filament is shown by the present work to increase as the draw ratio is increased or when the fiber is highly annealed. This increased cracking is associated with an increase in the magnitude of the internal residual stress resulting from molecular orientation developed during these processes. Because of this, crack density and fiber birefringence were found to correlate well. In addition, the geometry of the stress‐cracking pattern along a filament is affected by internal residual stress since the propagation of spiral and helical cracks results from the effect of a biaxial stress field remaining at the filament surface after processing.
Separation of dextrans by gel permeation chromatography
Authors: Soeteman A. A. , Roels J. P. M. , Van Dijk J. A. P. P. , Smit J. A. M. 
Published: April 2003

AbstractThe role of the intrinsic viscosity [η] as separation parameter in gel permeation chromatography (GPC) was studied for dextrans (from Leuconostoc mesenteroids B512) dissolved in water with deactivated silicagel (Porasil) as the column‐filling material. For that purpose specific viscosities of dextran fractions eluted by GPC were measured as a function of the elution volume v. Provided that the elution volumes are corrected for zonal spreading, they are related to the intrinsic viscosities in an unambiguous way, probably reflecting a unique relationship between degree of branching and molecular weights. This was further investigated by developing an iteration method to prepare two calibration curves γ(v) and g(v), respectively, relating ln[\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] and InM (M is the molecular weight) to v. It required that the weight‐average molecular weight Mw, the number‐average molecular weight Mn, and the average intrinsic viscosity [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] for a number of dextran samples (broad distributions) be previously known. The calibration curves found lead to consistent values of the above‐mentioned averages. Moreover, they allow‐establishment of the [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}]‐M relationship over the range 5000 < M < 500,000.
A simple model illustrative of some features of polymer dynamics
Authors: Jones D. A. , De Haro M. Lopez , Pugh D. 
Published: April 2003

AbstractA quasi‐one‐dimensional model for the dynamics of a polymer in dilute solution is described. The diffusion equation in the presence of energy barriers to conformational change is solved approximately for the case of high barriers, by a method closely analogous to the method of configuration interaction in molecular quantum mechanics. The dynamic shear viscosity is calculated in terms of the model and the ultrasonic absorption is discussed.