bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical mechanical model for diffusion of simple penetrants in polymers. II. Applications—nonvinyl polymers
Authors: Pace R. J. , Datyner A. 
Published: April 2003

AbstractThe theory developed in Part I of this series is applied to a number of nonvinyl “smooth” chained homopolymers. The agreement between predicted and observed activation energies of diffusion for simple penetrants is generally good, particularly for polyethylene. Discrepancies observed for the smallest penetrants, He and H2, in some polymers may be rationalized in terms of atomic scale irregularities on the polymer chain surface. It is shown that in favorable cases the theory may permit diffusion data to be used as an additional check on the accuracy of conformational energy maps for polymers.
Characterization of the ladder polymerization of a crystalline cyclotetradiyne monomer
Authors: Banerjie A. , Lando J. B. , Yee K. C. , Baughman R. H. 
Published: April 2003

AbstractThe polymerization of the cyclic tetradiyne monomer, [(CH2) 2CCCC(CH2)2]4, containing interstitial chloroform has been investigated using Raman and Fourier‐transform infrared spectroscopy and x‐ray diffraction techniques. A loss of crystallographic register between chains occurs during the polymerization reaction, although crystalline order in the chain‐axis projection is retained. These studies indicate that 50 Mrad of 60Co γ‐ray irradiation produces 1,4‐addition polymerization at most of the diacetylene functionalities. Unreacted diacetylene groups are present primarily, although not completely, in soluble oligomeric material. Infrared spectroscopy indicates that this low molecular weight material has a butatriene (cumulene) backbone structure rather than the acetylenic structure of the insoluble polymer.
Environmental stress cracking of polyethylene: Criteria for liquid efficiency
Authors: Shanahan M. E. R. , Schultz J. 
Published: April 2003

AbstractThe environmental stress cracking (ESC) of polyethylene in nonreacting, nonswelling liquids has been studied using uniaxial creep tests. For active liquids, three types of behavior have been recognized. At low stresses, “pure” ESC occurs; at intermediate stresses, time to failure is largely controlled by the ability of the liquid to flow into a growing crack; and at high stresses, ESC is in competition with failure by necking, and the latter prevails. The liquid does not therefore play a significant role in this last case. Nonactive liquids produce results similar to those observed in air. It is believed that this is because these liquids are unable to flow into growing cracks sufficiently quickly even at low stresses and thus the liquid does not influence failure behavior. This criterion for activity of the liquid is largely determined by the viscosity of the liquid and by the spreading coefficient of the liquid on the solid—a parameter defining the ability of the liquid to wet the solid.
Effect of crystallization time on the properties of melt‐crystallized linear polyethylene
Authors: McCready M. J. , Schultz J. M. , Lin J. S. , Hendricks R. W. 
Published: April 2003

AbstractLinear polyethylene was crystallized isothermally from the melt. Specimens were removed at different crystallization times and quenched to room temperature. The density, static mechanical properties, and small‐angle x‐ray scattering (SAXS) behavior of these specimens were measured at room temperature. The density and Young's modulus increased with crystallization time, whereas the upper yield point decreased with crystallization time. SAXS data showed that a zero‐angle peak gradually disappeared as crystallization time increased. Concurrently, the breadth of the SAXS peaks, the Bragg angle, and the integrated intensity decreased. Changes in the ratio of second‐ and first‐order peak intensities were also noted. On the basis of the SAXS and density data, it was concluded that a competition exists between the thickening of existing crystals and the creation of new crystallites between the older ones. At relatively low crystallization times, numerous new crystals can form during quenching to room temperature, whereas quenching after prolonged crystallization primarily results in the additional thickening of existing crystals. No change in the density of the amorphous material is found. A model is given whereby the upper yield stress is coupled to these morphological changes through a stress concentration effect caused by a decreased population of chains connecting adjacent crystallites. The tie‐chain population change occurs by their elimination as crystallites disappear.
Kinetics of craze initiation in polystyrene in N‐alcohols
Authors: Iisaka K. , Nishimoto Y. , Shibayama K. 
Published: April 2003

AbstractThe kinetics of craze initiation has been investigated for unmodified and rubber‐modified polystyrenes in n‐alcohols. The dependence on time and temperature of the critical strain at which crazes could be detected visually was determined with a Bergen elliptical strain device. Sorption studies were also conducted at room temperature on films exposed to the saturated vapor of n‐alcohol. The analysis of crazing data in terms of the Eyring model gave activation energies from 9.4 to 17.4 kcal/mole, increasing with increasing chain length of n‐alcohol and increasing rubber content. The activation volume multiplied by a stress concentration factor decreased with increasing rubber content and was nearly independent of the chain length of the n‐alcohol. The larger the diffusion coefficient, which we measured by sorption experiments, the smaller was the activation energy for craze initiation. The values of diffusion coefficients, estimated from the experimental data on craze initiation, were found to be comparable with those from the sorption experiments. It was concluded that the rate of craze initiation on exposure to liquids is controlled by the diffusion of the molecules of liquid into polymer.
Steric effects on excimer formation in isotactic and atactic polystyrene and poly(ar‐methylstyrene)s in solution
Authors: Ishii Tadahiro , Handa Takashi , Matsunaga Satoru 
Published: April 2003

AbstractEffects of tacticity and steric hindrance on excimer formation were investigated in isotactic and atactic polystyrene, poly(o‐methylstyrene), poly(m‐methylstyrene), and poly(p‐methylstyrene) in the presence and absence of a quencher (CCl4). The calculated rate constants for excimer formation in the isotactic polymers except for poly(o‐methylstyrene) were almost the same and larger than those in the corresponding atactic polymers. These results indicate that excimer formation was due to not only rotational sampling but also energy migration to trapping sites. It was found that steric hindrance on excimer formation was intimately related to the excition diffusion length in the polymer chain.
Light scattering characterization of thermodynamic interaction of polymers in dilute solution. Effect of solvent and molecular weight
Authors: Kratochvíl Pavel , Straková Dagmar , Podešva Jiří 
Published: April 2003

AbstractInteraction of nonidentical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by A24, the second virial coefficient for interaction of unlike species. This parameter is related to the compatibility of the two polymers in solution and is obtainable experimentally, e.g., by light scattering. With chemically markedly different polymers, A24 depends neither on the molecular weight of the polymers nor on the solvent and becomes characteristic of the polymer pair. For a mixture of two copolymers or of a homopolymer and a copolymer with similar compositions, A24 depends both on the solvent and on the molecular weight of polymers. Under such circumstances A24 ceases to be a quantity given only by the chemical structure of the two polymers; however, under suitable conditions it remains a sensitive function of the difference between the chemical nature of polymer components.
Chain dynamics of end‐group modified polystyrenes as studied by fluorescence depolarization
Authors: Chapoy L. L. , Kops J. , Vayla N. B. 
Published: April 2003

AbstractPolystyrenes, both linear and crosslinked with various crosslink densities, having modified end‐group structures, were synthesized with the objective of studying chain‐end mobility in the glassy state. One end of each polymer chain of these polystyrenes was modified with a fluorescent molecule. These polymers containing fluorescent probes in specific environments have been used in studies of segmental motion using fluorescence depolarization. The mobility has been studied below the glass‐transition temperature as a function of temperature and crosslink density. The experimental data show that chain‐end mobility is not of major importance in connection with the β‐transition.
Fourier analysis of polymer x‐ray diffraction patterns
Authors: Crist B. , Cohen J. B. 
Published: April 2003

AbstractIn analyzing the shapes of diffraction peaks from polymers, it has been mistakenly assumed that it is possible to distinguish between models based on “microstrains” and on paracrystallinity. It is shown that either paracrystallinity or distortions due to dislocations give rise to disorder of the second kind and cannot be distinguished by current diffraction methods. Fourier analysis of shapes of peaks from polymers gives quite satisfactory results, despite comments in the literature to the contrary. The analysis can now be carried out with single peaks; multiple orders are not required.
Shish‐kebab structures of nylon‐6 obtained from quiescent solutions by application of self‐seeding
Authors: Stamhuis J. E. , Pennings A. J. , Chanzy H. D. 
Published: April 2003

AbstractA study has been made of the morphology and structure of nylon‐6 crystals grown from diluted 1,4‐butanediol solution. Isothermal crystallization from homogeneous solution resulted in smooth ribbons or lath‐shaped crystals aggregated into sheaves. Shish‐kebab structures of nylon‐6 could be grown from the quiescent solution by self‐seeding techniques. Electron microscopic investigations and small‐angle x‐ray measurements showed that the molecules in the lath‐shaped backbones of the shish kebab are folded and oriented perpendicular to the long axis of the crystals. The polyamide laths have the α‐monoclinic crystal structure with the hydrogen bonds parallel to the long axis. It is suggested that due to the anisotropic type of bonding in the crystal lattice the crystals fragment laterally during the heating stage in the self‐seeding technique. Structural defects, e.g., twinning sites introduced during the dissolution and subsequent crystallization may cause the growth of shish‐kebab structures from quiescent solution.
X‐ray investigation of the structure of poly(tetramethylene terephthalate)
Authors: Stambaugh B. , Koenig J. L. , Lando J. B. 
Published: April 2003

AbstractPoly(tetramethylene terephthalate) (PTMT) undergoes a reversible stress‐induced crystal‐crystal phase transition. X‐ray fiber‐diffraction photographs were obtained from the oriented, unstressed (α) phase. Relative intensities were measured from these photographs. These were used to help check the reported structures of the α phase. Structures and observed intensity data from other authors were also utilized. Results show the α phase contains a non‐trans, non‐gauche bond rotation in the tetramethylene chain and a nonplanar terephthalic acid residue. A tilt of 3.5° between the fiber axis and the c axis was determined in a direction 210° counterclockwise from the b* axis.
Diffusion of large penetrant molecules in amorphous polymers
Authors: Vrentas J. S. , Duda J. L. 
Published: April 2003

AbstractA new version of the free‐volume theory of diffusion is modified to describe self‐diffusion phenomena in polymer + solvent systems for solvents which do not move as single units. The free‐volume equations are used to interpret data which appear to illustrate that some large solvent molecules do indeed move in a segmentwise manner. The dependence of the effective activation energy for diffusion on solvent size is examined, and the importance of energy effects on the diffusion process is considered.
Extra meridional reflections of drawn polyoxymethylene
Authors: Saruyama Yasuo , Miyaji Hideki , Asai Kenjiro 
Published: April 2003

AbstractExtra meridional reflections (00l: l = 3, 5, 13, 15, 21) were observed in drawn polyoxymethylene (POM). The 003, 0015, and 0021 x‐ray diffraction intensities increase on annealing, while the 005 and 0013 intensities decrease. It is concluded that crystalline regions are of two kinds: in the first, which generates the 003, 0015, and 0021 reflections, the molecular conformation is slightly distorted from the uniform helix by intermolecular steric hindrance between the CH2 groups; and in the second, which generates 005 and 0013 reflections, the molecular conformation is distorted in another way. The second form is converted into the first by annealing. The displacements in the c direction of the CH2 groups and the oxygen atoms from the uniform helix in the first form are about 1.0% and 0.75% of the interval between a CH2 group and an oxygen atom along helix axis of the POM crystal; thus the correct conformation in the stable state is known. The nature of distortion in the second region is not clarified but several characteristics are offered.
Crystallization of bisphenol‐A polycarbonate. III. Spherulitic growth rate of the plasticized polymer
Authors: Legras R. , Mercier J. P. 
Published: April 2003

AbstractMeasurements of the spherulitic growth rates of bisphenol‐A Polycarbonate plasticized with pentaerythritol tetranonanoate (PETN), trimellitic acid tri(n‐octyl‐n‐decyl)ester (TMDO), and tritolyl phosphate (TTP) are reported. The incorporation of a plasticizer enlarges the crystallization range, decreases the temperature of maximum growth rate and accelerates the kinetics to a considerable extent. The growth‐rate parameters are calculated from a least‐squares analysis of the experimental data according to the kinetic theory of Hoffman and Lauritzen. From the growth‐rate data given here and the overall crystallization kinetics reported previously, concentrations of seeds inducing the crystallization were determined.
Properties of amorphous and crystallizable hydrocarbon polymers. IV. Melt rheology of linear and star‐branched hydrogenated polybutadiene
Authors: Raju V. R. , Rachapudy H. , Graessley W. W. 
Published: April 2003

AbstractSome results on the melt rheology of hydrogenated polybutadiene (HPB) with narrow‐molecular‐weight distribution are reported and compared with the corresponding properties of the precursor polybutadienes (PBD) and fractions of linear polyethylene (PE). In linear samples the dynamic moduli obeyed frequency‐temperature superposition. The relationship between melt viscosity and intrinsic viscosity at 190°C for HPB was indistinguishable from that for PE, but their flow activation energies were slightly different (Ea = 7.2 kcal for HPB and 6.4 kcal for PE). Like PE, but unlike the PBD precursors, the dynamic storage modulus at low frequencies was anomalous. Otherwise, the dynamic moduli of HPB and its PBD precursor were essentially superposable. Plateau moduli from different samples were somewhat variable around an average of G = 2.31 × 107 dyn/cm2. The dynamic moduli for the HPB stars, unlike their PBD precursors, did not obey temperature‐frequency superposition. At high frequencies the temperature coefficient approached that for linear HPB, but it increased with decreasing frequency, reaching limiting values which depended on the arm length. The flow activation energy ranged from 9 kcal to more than 15 kcal as arm length increased.
Thermoelasticity of networks in swelling equilibrium with single component diluents: Specific polymer‐diluent interactions
Authors: Britton A. T. , Sullivan J. L. , Smith K. J. 
Published: April 2003

AbstractUsing thermoelastic measurements, specific polymer‐diluent interactions have been demonstrated for atactic poly(vinyl alcohol) networks swollen in water. This was done by following a thermodynamic parameter as a function of network swelling, which was controlled by varying the extent of network crosslinking. At low crosslinking (high swelling) the ratio of the energy component fe of the force to the total force f was found to be perhaps a little less than −0.38 for poly(vinyl alcohol) swollen in water to less than 0.36 volume fraction of polymer. The method of evaluation is new and should be applicable to other polymer single component diluent systems.
Characterization of the crystallization behavior of the eutectic‐forming binary system polyoxyethylene and glutaric acid. I. melting and crystallization behavior
Authors: Gryte Carl C. , Berghmans H. , Smets G. 
Published: April 2003

AbstractThe crystallization characteristics of the binary system polyoxyethylene (PEO)‐glutaric acid were determined. From the extrapolated melting point depression data the heat of fusion for PEO is 2506 ± 200 cal/mole of repeat unit while the heat of solution for the glutaric acid amounts to 6.7 ± 1.2 cal/cm3. A melting point of 348 K is found for the high‐molecular‐weight PEO. A calorimetric glass‐transition temperature for mixtures of the two components is relatively independent of the melt composition and appears at 217 K. A eutectic is observed whose composition and melting temperature depend on the nature of the PEO crystal phase.
Intrinsic birefringence of poly(ethylene terephthalate)
Authors: Gupta V. B. , Kumar Satish 
Published: April 2003

AbstractIn the existing literature various values are given for the intrinsic birefringence of the crystalline and the amorphous phases in poly(ethylene terephthalate) (PET). These values have either been calculated theoretically or obtained from experimental data on the basis of certain models. In this investigation, using the Samuels two‐phase model which correlates sonic modulus with structural parameters, intrinsic birefringence values for the crystalline (Δnc) and amorphous (Δna) phases have been determined by studying 30 PET samples prepared by heat setting to have a wide range of structures; the results are Δnc = 0.29 and Δna = 0.20. These values are discussed along with others in the literature and it is concluded that in the light of the present work, the values used by many authors need reexamination.
Twinning in macroscopic polymer single crystals
Authors: Young R. J. , Dulniak R. , Batchelder D. N. , Bloor D. 
Published: April 2003

AbstractTwinning in macroscopic single crystals of poly(TSHD) has been investigated using scanning electron microscopy. Two particular chain‐axis rotation twins have been identified unambiguously. They have K1 twinning planes of (012) and (212). It is also thought that twins with K1 planes of (212) and (202) may possibly occur. The possible mechanisms of twinning in polymer crystals have been discussed and chain‐axis rotation twinning in poly(TSHD) has been compared with a similar type of deformation that has been suggested to take place in polyethylene crystals.
Polymer crystallization from the melt at large undercoolings
Authors: Calvert Paul 
Published: April 2003

AbstractConsideration of crystallization kinetics in high‐molecular‐weight polymers shows that adjacent reentry is unlikely in melt crystallization and that sections of individual chains will crystallize concurrently at several sites. Hence the characteristic crystallization process will be that of a loop of chain with both ends attached to different sites on the crystal surface. Analysis of this process leads to predictions of crystallinity values for various conditions of chain mobility in the crystal and of entanglements in the amorphous regions. Observations on polymers crystallized at high undercoolings where a crystallinity of about 30% is usually observed suggest that the common case is that of a highly entangled amorphous layer and rapid, local annealing of the chains but with no long‐range motion in the crystal. This model of loop crystallization is shown to agree with available small‐angle neutron scattering data. The overall crystallization kinetics are in accord with surface nucleation controlled growth which also arises out of the Lauritzen‐Hoffman adjacent reentry model and has been shown to fit experimental results on growth rates.
Raman spectroscopic studies of the solid‐state polymerization of diacetylenes. I. Thermal polymerization of 1,6‐di‐p‐toluenesulfonyloxy‐2,4‐hexadiyne
Authors: Bloor D. , Kennedy R. J. , Batchelder D. N. 
Published: April 2003

AbstractThe resonance Raman spectra of polymer chains in partially polymerized crystals of 1,6‐di‐p‐toluenesulfonyloxy‐2,4‐hexadiyne are reported. The polymer chain distortion is deduced using the results obtained previously for fully polymerized samples under tensile strain. Changes in crystal lattice dimensions both parallel and lateral to the polymer chains are found to be important in interpreting the variations in frequency of the Raman‐active vibrational modes. Further evidence is found for the resonant interaction of backbone and side‐group vibrations reported previously. This interaction is affected by the lateral dimensional changes and is also sensitive to residual strain fields in the monomer crystals. It is not necessary in the interpretation of the Raman spectra to take any account of changes in polymer chain length during polymerization.
Factors affecting stress transmission in crystalline polymers
Authors: Gibson A. G. , Holt J. S. , Hope P. S. 
Published: April 2003

AbstractThe paper is concerned with stress transmission in and around the molecular ties which connect lamellae in many semicrystalline polymers. Assuming a continuum model, finite element calculations have been performed to investigate stresses and displacements for a cylindrical tie embedded in a sheath of lamellar crystal. Two specific cases were studied: the single‐ended case where the tie enters the lamella from one side only, and the double‐ended case where it passes right through the lamellar crystal. Elastic constants for crystalline polyethylene were assumed, and a variety of different geometries were investigated, corresponding to single‐chain or multichain ties with sheaths of various diameters. The finite element study confirmed that the distance for stress diffusion from the tie into the lamellar sheath can be quite large, and that there are significant displacements due to tensile deformation of the tie within the crystal and shear deformation of the lamellar sheath. An interesting feature in the case of multichain ties is that tensile stress is concentrated around the outer surface of the tie. An analytical model is proposed, based upon shear lag theory. This model considers only the tensile stresses in the tie and the shear stresses in the sheath, and gives results which are fairly similar to those of the finite element calculations. Finally, the results of this study are applied to the problem of stress transmission in an oriented polymer having a lamellar structure. The main factors influencing stress transmission are: (i) the ratio G/E of the crystalline phase; (ii) the ratio of tie radius to lamellar crystal thickness; and (iii) the proportion of ties in the interface. By examining the range of values which (ii) and (iii) may take, it is concluded that the effective stiffness of intercrystalline ties can only be about 0.25 to 0.7 of the theoretical chain stiffness in most cases.
Coisotactic shift contributions in 13C NMR spectra of propylene/butene‐1 copolymers
Authors: Usami Takao , Kosugi Yoshio , Takeuchi Tsugio 
Published: April 2003

AbstractCoisotactic shift contributions caused by sterically crowded isotactic side‐chain alkyl groups are proposed for peak assignments of isotactic propylene/butene‐1 copolymers. Previously disputed analyses of methine triads and PB tetrads of backbone methylene carbons (α,α′‐CH2) have been verified using first‐order Markovian distribution theory. Coisotactic shift contributions also account for the reverse order of the propylene‐centered triads from that predicted by the Grant‐Paul equation.