bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallization mechanisms for LLDPE and its fractions
Authors: Wilfong Debra L. , Knight G. W. 
Published: April 2003

AbstractThe crystallization behavior of two ethylene/octene copolymers, which differ in hexyl branch concentration, and their fractions were assessed. Fractionation of the crystalline linear low density polyethylenes (LLDPEs) was achieved by temperature rising elution fractionation. As the column temperature was raised, the eluted fractions exhibited a reduction in branch concentration and an increase in molecular weight. This was attributed to the difference in reactivity between ethylene and octene and the subsequent depletion of the ethylene monomer in the solution process. Spherulites formed during the crystallization of the whole polymers were well developed, banded, and displayed a wide distribution of sizes. However, spherulites of the LLDPE fractions were less well developed, more uniform in size, and tended to progressively deteriorate and become smaller as the concentration of branches increased. The ethylene and octene blocks of the copolymer crystallized independently, and it was proposed that the octene portion formed short, curved lamellae in the interfacial region of the lamellae formed from the linear ethylene portion of the molecule. Decreases in d spacing for fractions with increased short chain branching corresponded with similar drops in molecular weight.
Solution and thermal properties of poly(1,3‐dioxocane)
Authors: Alamo Rufina G. , Bello Antonio , Fatou José G. , Obrador Carmen 
Published: April 2003

AbstractPoly( 1,3‐dioxocane) was synthesized by cationic ring‐opening polymerization with triphenyl‐methane hexafluoroantimoniate as the initiator and was studied with regard to its solubility, unperturbed chain dimensions, and thermal transitions. The intrinsic viscosity and Flory‐Huggins interaction parameter were used to determine the solubility parameter, δp = 9.6 cal1/2cm−3/2, a value that agrees with that calculated empirically. Fractions were obtained from the solvent/non‐solvent system benzene/methanol at 25°C. The number‐average molecular weight Mn and intrinsic viscosity [η] were measured in toluene at 25°C. The relation [η] = 1.459. 10−4 Mn0.79 was found. A value of 5.3 was obtained for the characteristic ratio 〈r2〉0/nl2. Results are correlated with the main thermal transitions of this polyformal.
Intrinsic crazing and anisotropy of maximum recoverable extension in oriented glassy polycarbonate
Authors: Heymans Nicole 
Published: April 2003

AbstractThe critical draw ratio for initiation of intrinsic crazing in polycarbonate below the glass transition temperature has been determined after preorientation in the melt. Even when referred to the isotropic state, this ratio is found to depend not only on the extent of preorientation but also to be distinctly anisotropic. Under the assumption that intrinsic crazing occurs at the maximum extension of the entanglement network, these results are incompatible with a strain dependent but homogeneous breakdown of the entanglement network, but can be interpreted in terms of departure from affine transformation of the radius of gyration of an entangled length.
On the theory of the effective nuclear magnetic relaxation time T2e and its application to polymer melts
Authors: Schneider H. , Hiller W. 
Published: April 2003

AbstractA general expression for the magnetization decay of a multipulse group is derived. This formula is applied to a three‐component model of molecular motions in polymer melts. The influence of the several components on the magnetization decay is discussed. The relation of the effective nuclear magnetic relaxation time T2e to the Anderson‐Weiss formula is also shown, and an analytical expression for the transverse relaxation in melts is derived. Finally T2e is compared with the relaxation time in the rotating frame T1ρ in the melt. The theoretical results for T2e are tested with measurements of frequency dependence in polyethylene melts.
Influence of migration of plasticizer during melt mixing on the transitions and properties of PC/CAB blends
Authors: Jurado M. J. , Gaztelumendi M. , Nazabal J. , Mondragon I. 
Published: April 2003

AbstractStatic and dynamic mechanical properties, morphology, and thermal behavior of polycarbonate (PC)/plasticized cellulose acetobutyrate (CAB) blends were investigated to determine whether the plasticizer of the CAB modifies the miscibility of the blend and the mechanical properties of this essentially incompatible blend. In spite of the lack of transparency of the blends, both dynamic mechanical and thermal analysis results show the presence, at all blend compositions studied, of a single glass transition temperature which varies with the composition of the blend. Considering the ternary nature of the blends, we propose that plasticizer migration and the difficulty of discerning the presence of one or two peaks in a narrow temperature range may account for the observed behavior. Scanning electron microscopy confirms the immiscibility of the blends. The blends show large positive deviations of the tensile moduli from linearity and very low ductility. The reported tensile strength data are discussed in terms of several different equations for composites. This mechanical behavior is explained as a consequence of the migration of the plasticizer and of its subsequent antiplasticizing effect on the properties of the blend.
A temperature window of extrudability and reduced flow resistance in high‐molecular weight polyethylene; interpretation in terms of flow‐induced mobile hexagonal phase
Authors: Waddon A. J. , Keller A. 
Published: April 2003

AbstractAn unexpected feature of melt flow behavior has been identified in high‐molecular weight (≥ 4.105) polyethylenes such as are being considered unprocessable at conventional temperatures (> 160°C) and at practicable extrusion rates (> 1 cm/min). In addition to a lower temperature window of smooth extrudability, lying in the range of 138–155°C already observed in previous works, we now discovered within this window a narrow temperature interval (150–152°C) of minimum flow resistance (viscosity). The new effect has the attributes of being associated with a new phase of increased fluidity. This, in turn, we attribute to a transient mesophase arising through the chain‐orienting effect of the elongational flow within the extrusion orifice; from the experiments presented here, this mesophase depends critically on both molecular weight and strain rate. The hexagonal form of polyethylene, known to exist under other circumstances, is suggested as this mesophase. The relevance of the new findings for applications (extrusion, melt rheology) and for fundamentals (orientation‐induced phase transformations, liquid crystals from flexible chains in particular) should be obvious and are accordingly highlighted.
Local order in a globally deformed polymer network with nematiclike interactions
Authors: Walasek Janusz 
Published: April 2003

AbstractThe influence of nematiclike interactions, that is, preference for the alignment of neighboring chain segments, is considered for a globally deformed polymer network. The local order is characterized by an orientation factor which is the average of second Legendre polynomial, being a function of segment orientations, calculated with the actual distribution of chain segment orientations. For the description of interactions between segments, a molecular mean‐field approach is used. The orientation‐dependent potential is assumed proportional to cos2θ, where θ is the angle between the direction of the orienting field and the chain segment vector. The local orientation factor of deformed polymer network, is calculated for various values of interaction strength and network structural parameters (contraction coefficent, length of network chains). For some values of these parameters, the local order can be considerable.
Dilation of substituted polycarbonates caused by high‐pressure carbon dioxide sorption
Authors: Fleming G. K. , Koros W. J. 
Published: April 2003

AbstractMass sorption/desorption and volume dilation/consolidation measurements are reported for tetramethyl and hexafluoro polycarbonate samples in the presence of carbon dioxide pressures up to 900 psia at 35°C. These results are combined with previous results for bisphenol‐A‐polycarbonate. The combined sorption and volume dilation measurements are used to analyze the thermodynamics of the three gas‐polymer systems, and the partial specific volumes of carbon dioxide and the polymer are reported as functions of sorption level. Desorption and subsequent resorption measurements with the substituted polycarbonates show large and long‐lived hysteretic effects similar to those seen with standard bisphenol‐A‐polycarbonate. Finally, assumptions inherent in the dual‐mode model are shown to provide a satisfactory description of the volume dilation behavior for the substituted polymers.
Phase transformation and structure of n‐C50H102/n‐C60H122 solid solutions formed from the vapor phase
Authors: Zhang W. P. , Dorset D. L. 
Published: April 2003

AbstractBinary solid solutions of n‐paraffins (n‐C50H102/n‐C60H122) epitaxially prepared on potassium hydrogen phthalate substrate from the vapor phase have been studied by electron diffraction to characterize their phase transitions and structure. The continuity of solid solution in the n‐C50H102/n‐C60H122 system is demonstrated once lamellar ordering of the crystal packing is achieved. However, such ordering is achieved only by annealing and proceeds through a series of intermediate chain packings. At first, the electron diffraction patterns from all samples prepared at room temperature resemble those from polyethylene, in which no spots corresponding to the interlayer spacings appear. Longitudinal chain translations are induced by annealing to cause the lamellar reflections to appear, while the “polyethylene” subcell reflections remain unsplit until the crystal structure with well‐defined methyl end planes is reached.
High‐temperature, high‐resolution nuclear magnetic resonance of poly (p‐phenylene sulfide)
Authors: Wade Bruce , Abhiraman A. S. , Wharry Stephen , Sutherlin Dirk 
Published: April 2003

AbstractA high‐temperature, high‐resolution 13C nuclear magnetic resonance spectroscopy technique was developed for the analysis of poly (p‐phenylene sulfide) (HT/HR NMR of PPS). This technique can be applied to the identification and quantitative analysis of end groups and polymer structure in high‐temperature polymers where solution temperatures above 200°C are required for analysis. Verification of calculated 13C NMR shift values of chloro‐terminated and hydrogen‐terminated end groups was made by HT/HR NMR of two oligo (p‐phenylene sulfide) model compounds. Identification of the chlorine end group was made in high‐molecular weight PPS. On the high‐molecular weight PPS, identification and quantitative analysis of amino and N‐alkylamino end groups were possible only after derivatization of the polymer with 13C‐enriched benzoyl chloride.
Solid‐state phase behavior and molecular‐level mixing phenomena in a strongly interacting polymer blend
Authors: Belfiore Laurence A. , Lutz Thomas J. , Cheng Chihmin , Bronnimann Charles E. 
Published: April 2003

AbstractThis research contribution addresses mixing phenomena in a polymer blend that exhibits strong intermolecular association and bieutectic phase behavior. Molecular‐level observations of specific interactions between dissimilar blend components have been obtained from high‐resolution solid‐state proton and carbon‐13 nuclear magnetic resonance (NMR) experiments at ambient temperature. Results illustrate mixing effects on the isotropic chemical shifts of the critical component in a completely or partially phase‐mixed blend. Perturbations in the NMR spectra result from conformational changes, hydrogen bonding, molecular complexation, or altered packing geometries that occur concomitantly with the mixing process. More convincing evidence that two components of a strongly interacting blend reside in a near‐neighbor environment is obtained from the measurement of proton spin diffusion between dissimilar species. Proton spin diffusion is measured directly via the high‐resolution CRAMPS experiment (Combined Rotation and Multiple Pulse Spectroscopy) in a molecular complex of poly (ethylene oxide) and resorcinol. A primary objective of this research endeavor is to bridge the gap between macroscopic and molecular‐level probes of phase behavior and intermolecular association in mixtures that form molecular complexes. In this respect, the temperature ‐composition projection of the thermodynamic phase diagram is generated for binary mixtures of poly (ethylene oxide) and resorcinol, whose interaction sites are characterized via solid‐state NMR. Under fortuitous conditions that are related to the overall mixture composition, two morphologically and crystallographically inequivalent phenolic 13C NMR signals are identified for resorcinol when the blends exist in a two‐phase region below the eutectic solidification temperature. The success of this proposed structure–property relationship scheme, which bridges molecular‐level mixing phenomena (via NMR) with solid‐state phase behavior (via differential scanning calorimetry) depends on our ability to understand material properties at a level where continuum hypotheses are no longer valid.
Study of segmental orientation in poly (vinyl chloride)/poly (α‐methyl‐α‐n‐propyl‐β‐propiolactone) blends by fourier‐transform infrared spectroscopy
Authors: Chabot Paul , Prud'Homme Robert E. , Pézolet Michel 
Published: April 2003

AbstractFourier‐transform infrared (FTIR) spectroscopy has been used to investigate the segmental orientation of poly(vinyl chloride) (PVC)/poly (α‐methyl‐α‐n‐propyl‐β‐propiolactone) (PMPPL) blends in uniaxially stretched samples over a wide range of compositions and draw ratios. The results indicate that for pure PVC, syndiotactic segments reach a higher degree of orientation than isotactic segments and gauche conformations. Similarly, for pure PMPPL, crystalline segments orient more than amorphous segments at any given elongation. Thus, for both polymers, the higher orientation is obtained for the more rigid segments or those located in a more rigid (crystalline) phase. The addition of the macromolecular plasticizer PMPPL has no effect on the orientation of PVC syndiotactic segments, but it lowers the orientation of PVC gauche conformations, suggesting that the polyester is located in the amorphous regions of PVC. Finally, the PMPPL orientation function initially decreases with the addition of PVC and thereafter remains constant. The results are discussed in terms of interpenetrating networks and relaxation processes.
Mass transfer modeling of asymmetric membrane formation by phase inversion
Authors: Tsay C. S. , Mchugh A. J. 
Published: April 2003

AbstractA derivation is presented of a ternary diffusion model to describe the mass transfer processes associated with the quench bath period of the phase inversion process for membrane formation. The complete governing equations, initial conditions, and boundary conditions in the casting film and coagulation bath are presented. Equations for ternary chemical potentials and diffusion coefficients are consistently based on constant specific volume formulations. The model is applied to the analysis of mass transfer paths and their effects on membrane structure formation. Precipitation times are determined for given sets of conditions by superposing calculated mass transfer paths on the ternary phase diagram and observing when the miscibility gap is crossed. Comparisons are made with an earlier reported study on the membrane‐forming system: water‐acetone‐cellulose acetate (CA). Agreement between predicted and measured precipitation times is found to be excellent. The polymer film composition profile at the moment of precipitation is shown to be a useful indicator of both skin and sublayer structures, allowing distinctions to be made between conditions leading to spongelike and fingerlike morphologies. The influence of model parameters on the mass transfer paths and associated polymer profiles is also discussed.
Star polymer diffusion in concentrated solutions: Dependence on functionality via the coupling model
Authors: Ngai K. L. , Rajagopal A. K. , Lodge T. P. 
Published: April 2003

AbstractThe coupling model is formulated in terms of the dynamic constraint entropy, Sc(t), and subsequently compared with measured tracer diffusion coefficients D for linear, 3‐arm star, and 12arm star polystyrenes in solutions of poly (vinyl methyl ether) (PVME) /o‐fluorotoluene. Inequalities between the dynamic constraint entropies, Scf and Scf′(t), respectively, for f‐arm and f′‐arm stars, enable us to explain the experimental observation that at constant arm molecular weight, the ratio Dstar/Dlinear decreases substantially with increasing concentration above the entanglement concentration for the PVME. This work indicates that not only the reptation model, but also the coupling model, can account for the experimental observation that in entangled solutions the mechanism for diffusion depends on diffusant architecture.
Compatibility studies of blends of polycarbonate and poly(ethylene terephthalate)
Authors: Kim Woo Nyon , Burns Charles M. 
Published: April 2003

AbstractBlends of bisphenol‐A polyarbonate (PC) and poly(ethylene terephthalate) (PET) has been investigated by differential scanning calorimetry and scanning electron microscopy. Blends were prepared by screw extrusion and solution casting with weight fractions of PC in the blends varying from 0.90 to 0.10. From the measured glass transition temperature (Tg) and apparent weight fractions of PC and PET dissolved in each phase, it appears that PET dissolves more in the PC‐rich phase than does the PC in the PET‐rich phase. The composition‐dependent values of the Flory–Huggins polymer–polymer–interaction parameter were determined and found to be from 0.054 to 0.037 for extruded blends at 275°C and from 0.058 to 0.040 for solution casting at 25°C. The interaction parameter decreases with increasing PET concentration. This result is consistent with the values of the Tgs, the microscopy study, and the measured extrudate swell ratios which show that compatibility increases more in the PET‐rich compositions than in the PC‐rich compositions. The PC–PET blends are not microscopically miscible for all the blend compositions.
Influence of polymer composition on the thermal characteristics of sulfonated EPDM ionomers
Authors: Maurer J. J. , Harvey G. D. , Agarwal P. K. 
Published: April 2003

AbstractDetailed thermal characterization of sulfo‐EPDM ionomers was carried out. The endotherms observed via differential scanning calorimetry (DSC) and multiple inflections observed via thermal mechanical analysis (TMA) are speculated to be due to associated ionic species in the polymers. A large time dependence of the DSC endotherm was observed, suggesting substantial variations in the nature of the ionic species over this period. The influence of ionomer composition on thermal characteristics was probed with whole polymers and polymer fractions. In general, trends in the DSC and TMA data paralleled those expected on the basis of the anticipated effect of polymer sulfonation level, molecular weight, and counterion type on the strength of the physical crosslinking of these polymers. Both the DSC endotherms and the TMA inflection regions are rationalized in terms of a previously developed ionic‐bond exchange model.
Influence of initial polymer concentration in solution and weight‐average molecular weight on the drawing behavior of polyethylenes
Authors: Bastiaansen C. W. M. 
Published: April 2003

AbstractThe influence of initial polymer concentration in solution (c), weight‐average molecular weight (Mω), and drawing temperature on the solid‐state drawing behavior of linear polyethylenes was investigated. Optimum conditions, with respect to maximum attainable draw ratio, are observed in isothermal drawing experiments. Moreover, it is shown that high maximum attainable draw ratios can also be obtained upon multistage drawing of UHMW‐PE (ultrahigh‐molecular‐weight polyethylene, Mω > 106 g/mol) gel films cast from concentrated solutions. The high maximum attainable draw ratio in combination with the high molecular weight (Mω > 106 g/mol) and polymer concentration (c = 10% w/v) is of particular interest because it results in tapes or fibers with a high Young's modulus (100 GPa) and tensile strength (2.5–3.5 GPa). It is also shown that the maximum attainable draw ratio of polyethylenes scales with the Bueche parameter (c · Mω) to the −0.5 power. This experimental observation indicates that intermolecular interactions not only dominate the rheological properties of polyethylene melts and concentrated solutions, but also strongly influence the solid‐state drawing behavior of linear polyethylenes.
A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers
Authors: Stutz H. , Illers K.‐H. , Mertes J. 
Published: April 2003

AbstractA generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers has been developed, which takes into account the influences of end groups, branching, and crosslinking, and their functionality distribution. DiBenedetto's theory was found to correctly characterize the influence of crosslinks on the glass temperature. Normalized to constant crosslink functionality, the crosslink constant is a universal parameter suggesting that the entropic theory of glasses is applicable to crosslinked systems. Data on linear polymers and networks from the crosslinking of polymer chains, vinyl/divinyl‐copolymers and step‐growth polymers, such as polyurethanes, amine‐cured epoxies, or inorganic glasses, are presented.
Rheological and thermal properties of a commercial liquid‐crystalline polyesteramide
Authors: Gonzalez J. M. , Muñoz M. E. , Cortazar M. , Santamaría A. , Peña J. J. 
Published: April 2003

AbstractA commercial main‐chain liquid‐crystalline, naphthalene‐based polyesteramide, was studied by three experimental techniques: extrusion capillary rheometry, dynamic viscoelasticity, and differential scanning calorimetry (DSC). From capillary rheometry a maximum at 360°C was observed in viscosity temperature curve. This result is compared with literature data for other thermotropics, and the possibility of a transition from a nematic to an isotropic phase is considered. The results obtained from dynamic viscoelasticity and DSC agree, and reveal the existence of a glass transition at 128°C (by DSC) and 137–147°C (by viscoelastic measurements, depending on frequency) as well as melting at 282°C. Annealing below 230°C produces two types of crystals, whereas annealing above this temperature gives rise to only one type of crystal, the melting temperature of which can be, depending on annealing time, as high as 340°C. The results are compiled in a phase diagram with six regions, four of them corresponding to the solid state, one to a liquid mesophase, and one to an isotropic phase.
Optical anisotropy of a thermotropic liquid‐crystalline polymer in transient shear
Authors: Hsiao Benjamin S. , Stein Richard S. , Deutscher Klaus , Winter H. Henning 
Published: April 2003

AbstractA rheo‐optical apparatus, based on a linear shear rheometer, has been constructed to study the deformation of liquid–crystalline polymers. This apparatus uses optical techniques such as flow birefringence, small‐angle light scattering, and optical microscopic image analysis. The rheological responses were simultaneously measured under varying temperatures and deformation conditions. The modified Debye‐Bueche equation for scattering, in the nonspherically symmetrical form, was adapted to analyze small‐angle light‐scattering data. The orientation correlation lengths, determined by this method, reveal the deformation mechanism in nematic melts. Flow birefringence results are in agreement with the proposed mechanism.