bluuebunny/crossref_metadata_2025 huggingface dataset:
Blends of poly(ethylene terephthalate) and cellulose
Authors: Field Nathan D. , Song Sang Sub
Published: April 2003

Poly(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

The 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

Single‐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

The 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

Poly(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

The 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

The 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

The 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

Copolymers 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

Experiments 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

A 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.
Birefringence of high‐pressure injection‐molded high‐density polyethylene at 70.5 μm wavelength
Authors: Jacobsson Stellan , Hård Sverker , Boldizar Antal
Published: April 2003

A newly constructed far‐infrared laser interferometer was used to measure the birefringence of 1‐mm‐thick injection‐molded high‐density polyethylene test bars, manufactured at unusually high molding pressures. The long wavelength used, 70.5 μm, allowed nondestructive tests to be made, demonstrating the usefulness of far‐infrared techniques for probing crystalline polymers. The birefringence was shown to increase with increasing molding pressure, supporting the belief that molecular orientation increases with increasing molding pressure. The tensile modulus was also measured and was found to increase linearly with molding pressure.
The drawing behavior of polyethylene copolymers
Authors: Capaccio G. , Ward I. M.
Published: April 2003

The tensile drawing behavior of a range of selected polyethylene copolymers has been studied. Sheets were prepared by quenching molten polymer into cold water. Two‐centimeter‐gauge‐length samples were then drawn in air at 75 or 115°C in an Instron tensile testing machine at a crosshead speed of 10 cm/min. It was found that even at the very low concentration of one side branch per 1000 carbon atoms there was a very marked effect on the strain hardening behavior and the maximum draw ratio that could be achieved. The reduction in draw ratio increased with increasing branch concentration, and long branches were more effective than short branches in limiting the draw ratios achieved. The similarity between these effects and the effects of increasing M̄w or radiation crosslinking is noteworthy. This suggests that even a very small concentration of branches can significantly reduces the moleculer motions required for the process of plastic deformation. The Young's modulus/draw ratio relationship follows a pattern virtually identical to that observed in the case of homopolymers.
Changes in superstructure of drawn isotactic polypropylene with annealing: A two‐dimensional small‐angle x‐ray analysis
Authors: Rognoni A. Ferrero , Ferracini E. , Čačkovic̀ J. Loboda , Čačkovic̀ H.
Published: April 2003

Two‐dimensional small‐angle x‐ray (SAXS) analysis is extended and applied to isotactic polypropylene cold‐drawn and annealed near the melting point. The SAXS intensity down to very small angles is detected by a high‐resolution point‐collimation camera. The SAXS fiber pattern, exhibiting only one meridional reflection and continuous scattering on the equator, shows that the microparacrystallites (“bricks” of the macrolattice) are densely packed together laterally into finite extended layers. The drawing process increases the ultrafibrillar characteristics of the samples and annealing increases their lamellar character. Annealing is carried out at a temperature near the melting point with the ends of the samples fixed so that recrystallization under strain takes place. The volume crystallinity increases on annealing from 32 to 57%. The SAXS results are in good agreement with NMR results; nevertheless the ideal paracrystal model assumption is, in the present case, not quite consistent with the results.
Model calculations of the distribution function of molecular weight and chemical composition of binary statistical copolymers
Authors: Procházka Ondřej , Kratochvíl Pavel
Published: April 2003

Model calculations based on the kinetics of free‐radical copolymerization were carried out for the distribution functions of molecular weight and chemical composition, and for heterogeneity parameters of statistical copolymers. The calculations were conducted so as to depict the dependence of the heterogeneity parameters on the degree of conversion and to make possible an estimate of the maximal heterogeneity of statistical copolymers at given monomer reactivity ratios and rate constants. A comparison of the results obtained with a critical analysis of the feasibility of the determination of heterogeneity parameters by light scattering has revealed that, for statistical co polymers, this method can in principle be used with satisfactory accuracy only with samples of high degree of conversion and high molecular weight. The frequently used approximation P = 0 cannot be applied with out careful verification.
Crazing in polyethylene
Authors: Kamei Eiichi , Brown Norman
Published: April 2003

The tensile stress—strain curves of various types of polyethylene were compared from 77 to 298 K in nitrogen, isopentane, and the inert environment of helium at various strain rates. It was found that in general polyethylene crazes in a gas such as nitrogen at a temperature below 1.6 times its boiling point and in isopentane. Although the behavior of polyethylenes is similar to that of other polymers with regard to crazing in gases at low temperatures, they are in general less sensitive to the gas. The decrease in tensile strength of polyethylene in an environmental gas increases with crystallinity. The differences in the intrinsic low‐temperature brittle fracture stress are attributed to differences in the density of tie molecules. The intrinsic yield point at room temperature showed the usual increase with increasing crystallinity, but all the polyethylenes have the same yield point below the γ transition temperature.
Creep behavior of ultrahigh‐modulus polyethylene: Influence of draw ratio and polymer composition
Authors: Ward I. M. , Wilding M. A.
Published: April 2003

The creep behavior of ultrahigh‐modulus polyethylene monofilaments has been studied over the temperature range 20–70°C. A wide range of samples was examined in an attempt to determine the influence of draw ratio, molecular weight, copolymerization, and crosslinking by γ irradiation Prior to drawing. Results are also presented for a solution‐spun fiber. It is proposed that the permanent flow creep arises from a combination of two creep processes, one of which is associated with the crystalline regions of the oriented structure and the other with a molecular network.
NMR study of polyethylene crystallization kinetics under high pressure
Authors: Brown D. R. , Jonas J.
Published: April 2003

Crystallization of polyethylene under hydrostatic pressures of 1–4.5 kbar is directly observed using pulsed proton NMR. The rate of growth of extended‐chain polyethylene crystals is measured over this pressure range and to a maximum temperature of 227°C. The observed crystallization isotherms are superimposable on a log time scale; this implies a consistent mechanism for extended‐chain growth over this pressure range. Avrami coefficients for high‐pressure extended‐chain crystallization are determined to be 1.3–1.7. A decrease of crystal nucleus surface free energies with increasing pressure is indicated. Findings are consistent with Wunderlich's model of initial folded‐chain crystallization followed immediately by chain extension. Future applications of this NMR technique are briefly considered.
High‐temperature phases of poly(p‐xylylene)
Authors: Isoda Seiji , Kawaguchi Akiyoshi , Katayama Ken‐Ichi
Published: April 2003

The crystal structure of poly(p‐xylylene), as polymerized, is the α form. This transforms irreversibly to the β from by annealing or drawing. To clarify the mechanism of this transition, structural changes of the α and β crystals were examined with a high‐temperature stage in the electron microscope. Two high‐temperature phases, β1 and β2, were found and their structures were analyzed. In these structures lattice distortions due to rotational and translational motions of chains are in troduced, especially in the β2 form. The α → β transition is induced through such a disordered phase. The statistical arrangement of a molecule in the β‐form unit cell results from freezing the disorder in the high‐temperature phases.
Structural relaxation in amorphous polymers
Authors: Chow T. S.
Published: April 2003

A theoretical calculation based on the general solution of a multi‐ordering‐parameter model is found to be in good agreement with the measured volume relaxation of poly(vinyl acetate). This suggests that a limiting equilibrium state is eventually reached, which may resolve the disagreement between the behavior of the model and experiments discussed in the literature. In addition, the asymmetric character of the isothermal response and memory effect is satisfactorily calculated from the same basic equation. The distribution function and the temperature‐structure dependence of relaxation times are discussed.
Sorption and diffusion of toluene in highly oriented polypropylene
Authors: Choy C. L. , Leung W. P. , Ma T. L.
Published: April 2003

The sorption and diffusion of toluene vapor at 30°C in polypropylene with draw ratios from 1 to 18 have been studied. Drawing leads to the transformation of the initially spherulitic material into the fibrous structure, with many taut tie molecules lying mainly on the outer boundary of the microfibrils. The free volume and hence the sorption sites are thereby reduced, and the microfibrils become less and permeable as the draw ratio increases. As a result, the equilibrium concentration and the zero‐concentration diffusion coefficient drop by factors of 4 and 30, respectively. The diffusion coefficient increases exponentially with toluene concentration but the concentration dependence becomes weaker with increasing draw ratio, indicating that the severely constrained chain segments in the drawn samples have much less freedom to mix with penetrant molecules. Annealing relaxes the tie molecules and thus restores the sorption and diffusion properties to values corresponding to completely relaxed amorphous component, i.e., to values even higher than those of the undrawn but quenched material.
Crazing and shear deformation in crosslinked polystyrene
Authors: Henkee Chris S. , Kramer Edward J.
Published: April 2003

Thin films of polystyrene (PS) are bonded to copper grids and crosslinked with electron irradiation. When the films are strained in tension regions of local plastic deformation, either crazed or plane stress deformation zones (DZs), nucleate and grow from dust particles. the nature of the local deformation, as well as the local extension ration λ, is determined by transmission electron microscopy. The behavior of the PS glass is consistent with its being a network of molecular strands of total density v = vE + vX, where vE is the entangled strand density inferred from melt elasticity measurements of uncrosslinked PS and vX is the density of crosslinked strands determined from the ratio of the applied electron dose to the electron dose for gelation. when v is less than 4 × 1025 m−3 (<1.3vE), only crazes are observed whose microstructure is similar to those in uncrosslinked PS. As v increases from 4 × 1025 to 8 × 1025 m−3 (from 1.3vE to 2.5vE) shear deformation begins to compete with crazing. As v increases above 8 × 1025 m−3, only shear DZs are observed, the strain in which becomes progressively more diffuse as v increases. The λ in the crazes and DZs correlate well with λmax, the maximum extension ratio of a strand in a network of density v computed using the Porod×Kratky model. For crazes ln(λ) ≃ 0.9 ln(λmax) and for DZs ln(λ) ≃ 0.55 ln(λmax). The strain at which crack nucleation is first observed increases as v increases from <5% in uncrosslinked PS with v = 3.3 × 1025 m−3 to >20% in PS with v = 33 × 1025 m−3 (v = 10vE); crosslinking to still higher crosslink densities, e.g., v = 14vE, results in cracks which propagate in a catastrophic manner at low applied strains. An optimum v thus exists, one not too high to suppress local shear ductility but high enough to suppress crazes which can act as crack nucleation sites. these results are compared with previous results on a variety of linear homopolymers, copolymers, and polymer blends that are characterized by a wide range of v (v = vE). The transitions from crazing to crazing plus shear and from crazing plus shear to shear only take place at almost identical values of v. In addition the correlation between λ in the crazes and DZs and λmax for a single network strand is the same for both classes of polymers. This agreement implies that chain scission is the major mechanism by which strands in the entanglement network are removed in forming fibril surfaces. Craze suppression, by either increasing v in the crosslinked polymer or vE in the uncrosslinked ones, is due to the extra energy required to break more main‐chain bonds to form these surfaces.
Polymer fibers drawn to the limit
Authors: Slutsker Leonid I. , Utevskii Lev E.
Published: April 2003

The orientational drawing of polymers is known to be terminated because of sample rupture. The limiting draw ratio λlim reached may be different (either large or small) depending on the polymer and the actual drawing conditions. The purpose of the present work is to identify the change of supermolecular structure of polymer fibers which results in the termination of orientational drawing. Small‐and wide‐angle x‐ray diffraction were used to study the variation of geometrical parameters of this structure with increasing draw ratio λ. The geometrical parameters discussed are the dispersions (fluctuation) of long periods and of longitudinal sizes of crystalline as well as amorphous regions. In this study we used fibers of poly(vinyl alcohol), poly(ε‐caprolactam), polyoxymethylene, and poly(4,4′‐diphenyloxide) pyromellitimide. It is found that the long period dispersion of these polymers, drawn under different conditions, increases to approximately the same value for different samples drawn to the limit, this relative standard deviation δL of long periods being 0.30‐0.40. It is also found that the crystallite size dispersion does not increase with increasing λ; the increase of λL is due to increasing dispersion of the amorphous region lengths. For poly(vinyl alcohol) fibers drawn to the limit under different conditions and which have different λlim, the relative standard deviation of the sizes of amorphous regions δA turned out to be about the same (ca. 0.60). The latter evidence gives grounds to suggest that the rupture of polymers under drawing is associated with reaching a high degree of amorphous region size dispersion. In those regions which are considerably below the average size there probably will appear local overstress and molecular ruptures because the relative deformation of these regions is much larger than that of the adjacent regions in the cross section of the sample.
A spectroscopic study to interpret the increased piezoelectric effect at high temperature in poly(vinylidene fluoride)
Authors: Jei Lu Fei , Waldman David Allen , Hsu Shaw Ling
Published: April 2003

Spectroscopic experiments were carried out to directly measure the electric‐field‐induced microstructural changes in PVF2 at high temperature (65°C). We found, in comparison with roomtemperature measurements, that the reduction of the coercive field is directly related to faster dipolar orientation at this temperature. Furthermore, the α to β or δ phase transformation can take place at a much faster rate and lower field strength than has been previously reported either theoretically experimentally.
Concentration dependence of the first cumulant for partially labeled chains in dilute solutions
Authors: Hammouda B. , Akcasu A. Z. , Benmouna M.
Published: April 2003

We use Zimm's single‐contact approximation to investigate the concentration dependence of the first cumulant for partially labeled chains in dilute solutions. This approximation allows us to express interchain properties (such as the interference part of the generalized mobility) in terms of static structure factors, which are then modeled using a Gaussian chain model. We present numerical results for three specific labeling sequences.
Effects of polymer chain disentanglement on NMR properties. I. Proton magnetic relaxation in polyisobutylene
Authors: Cohen‐Addad J. P. , Guillermo A.
Published: April 2003

The transition of NMR properties from a solidlike spin system response to a liquidlike one observed on molten polymers or on concentrated solutions is analyzed to characterize the slow diffusion process of long linear polyisobutylene (PIB) chains. It is first shown that the relaxation function of the transverse magnetic component of protons linked to PIB chains obeys a superposition property when the polymer concentration is varied from 0.5 to 1.0g/cm3; this is interpreted as reflecting the applicability of the viscoelastic submolecule concept to the description of NMR properties. The transition in NMR properties is then analyzed numerically, using a model of polymer chain relaxation based on a multiple‐relaxation‐mode process analogous to the Rouse model. The terminal relaxation time τv1 is shown to depend upon the chain molecular weight M as M3; it is found to be equal to 8.3 × 10−2 s for molecular weight M = 2.25 × 105 and concentration c = 0.47 g/cm3 in carbon disulfide at room temperature.
Temperature dependence of the thermal expansivity of polymer crystals: Linear chain model
Authors: Choy C. L. , Wong S. P. , Young K.
Published: April 2003

A linear chain model is used to calculate the thermal expansivities of polymer crystals from room temperature down to liquid‐helium temperature. Because of restraint by strong covalent forces, vibrations along the chains give a negligible contribution. Vibrations transverse to the chains cause the length projected along the chain direction to decrease. The expansivity along the chain direction, αc∥is therefore negative, and has temperature dependence characterized by the low Debye temperature of transverse vibrations. These vibrations, through a cubic term in the interchain van der Waals potential, also cause a positive expansivity, αc⟂perpendicular to the chain direction. The theoretical predictions for αc∥and αc⟂agree quite well with experimental data over the wide temperature range under consideration.
Theoretical models for diffusion in glassy polymers. II
Authors: Cohen Donald S.
Published: April 2003

The author refines and generalizes a model for diffusion in glassy polymers which he previously introduced. The model unifies many diverse observations by explicity formulating the common property of a glassy polymer in all its various modes, namely the finite relaxation time due to its slow response to changing conditions. An integral approximation method is used to study the motion of the penetrant front and the glass‐gel interface and a useful polynomial approximation method is introduced for use in special simple situations.
The volume structural relaxation theory for amorphous polymers
Authors: Rostiashvilli V. G. , Nekhoda A. R. , Irzhak V. I. , Rozenberg B. A.
Published: April 2003

An interpolation model of density fluctuations in amorphous bulk polymers is suggested for the explanation of some peculiarities of structural relaxation of amorphous polymers volume. The main peculiarities of the model are (i) its account of the influence of fluctuations in the region where the WLF theory is true (the region of large fluctuations); (ii) its account of small fluctuations in the region where the dissipation mechanism appears to be considerably different from that in the region of large fluctuations; and (iii) its joining of the solutions of the resulting kinetic equations in the crossover region. On the basis of the suggested model we have obtained an equation of the Fokker‐Plank type for the distribution function for density fluctuations with nontrivial boundary conditions for large fluctuations, and a quasistatic solution for small ones. These equations are analyzed and numerically solved in the isothermal regime. The results show that the theory corresponds to the WLF theory at temperatures much higher than Tg and that memory effects are found in the Tg region. In addition, preliminary estimates show that near Tg an extreme form of temperature dependence on activation energy is observed. All these facts agree qualitatively with experiment.
Studies on polyethylene crystallized at unusually high supercoolings: Fold length, habit, growth rate, epitaxy
Authors: Martinez‐Salazar J. , Barham P. J. , Keller A.
Published: April 2003

The newly arisen possibility of crystallizing polyethylene at supercoolings much higher than were achievable previously has enabled the study of crystallization to be extended in several directions. Thus, fold length can be followed down to previously inaccessibly low crystallization temperatures, in the present case with sharp fractions, demonstrating the essential independence of the fold length of molecular weight. In this context the thinnest isolated crystal reported so far was obtained (ca. 6 nm). The faceted nature of crystals grown at such low temperatures and high rates has been noted, and is in line with new conceptions of polymer crystal growth. A previous observation of exceptionally high crystal growth rate (ca. 2 m/s) has been supplemented by measurements over a range of crystallization temperatures and the results found to be in good agreement with the predicated regime III behavior in the least theory of Hoffman. Observations of epitaxy on mica, while broadly in line with those by Lovinger, were revealing in several respects. Among these the observation that the substrate can influence the fold length when the chains are parallel to the substrate plane remains unexplained and puzzling.
Strain criterion in nonlinear creep and recovery in concentrated polymer solutions
Authors: Nakamura K. , Wong C.‐P. , Berry G. C.
Published: April 2003

Transient and steady‐state rheological data are reported for several anionic polystyrene solutions in tritolylphosphate (1. 6 < cM/ρMc < 7). Here c is the concentration of the solution, M is the molecular weight, ρ the density of the undiluted polymer, and Mc the molecular weight between entanglements as determined from zero‐shear viscosity. The polystyrene used had Mw = 410,000 and Mw/Mn < 1.06. Data are also given for solutions of polyisobutylene and poly(vinyl acetate) with larger Mw/Mn. The results give a critical strain γ′ ∝ c−1 such that linear viscoelastic behavior was obtained in a simple shear deformation with shear less than γ′. A simplified version of the constitutive equation of Bernstein, Kearsley, and Zapas is used with an empirical strain function F (γ) which contains γ′ as a parameter to discuss transient and steady‐state behavior in terms of the distribution of relaxation (or retardation) times determined for linear viscoelastic responce. Features of the dependence of the steady‐state viscosity ηk, recoverable compliance Rk, the first‐normal stress function Nk(1) on shear rate k are discussed in terms of F (γ) and the distribution of relaxation times to conclude that the latter plays a dominant role in the behavior observed in the range of k usually studied. The results predict that the reduced functions ηk/η0, Rk/R0, and Nk(1)/N0(1) should depend on η0R0k, and that the functional form depends markedly on the distribution of relaxation times, at least in the range η0R0k < 102. Comparison with the mechanistic model of Doi and Edwards shows a similar F (γ) but substantial differences in the reduced functions caused by a very narrow distribution of relaxation times in the model.
Mechanical relaxations and moduli of oriented nylon 66 and nylon 6
Authors: Leung W. P. , Ho K. H. , Choy C. L.
Published: April 2003

The mechanical relaxations of dry and wet nylon 66 and nylon 6 with draw ratios λ = 1–3 have been studied from −180 to 160°C and in the frequency range of 1 Hz to 10 MHz. The five independent elastic moduli C11, C12, C13, C33, and C44 have also been determined by an ultrasonic method at 10 MHz. Wide‐angle x‐ray diffraction and birefringence measurements reveal that the crystalline orientation rises sharply at low λ and becomes saturated near λ = 3; the amorphous orientation function increases continuously, reaching values of 0.3–0.5 at λ = 3. The alignment of molecular chains and the presence of taut tie molecules in the amorphous regions lead to a lowering of segmental mobility, thereby reducing the magnitude and increasing the peak temperature and activation energy of the α relaxation. Water absorption weakens the interchain bonding and so gives rise to effects opposite to those of drawing. At low temperature, the development of mechanical anisotropy is largely determined by the overall chain orientation, with the c‐shear mechanism contributing a small additional effect. However, above the α relaxation, where the amorphous region is rubbery, the stiffening effect of taut tie molecules becomes dominant and leads to increases in all moduli.
On the ordered structure of poly(butylene terephthalate) in polyester blends
Authors: Desper C. Richard , Kimura M. , Porter Roger S.
Published: April 2003

Some unusual x‐ray diffraction results have been obtained corresponding to an ordered structure in binary blends of a poly(butylene terephthalate) (PBT) with a polyarylate. The polyarylate is a noncrystallizable copolyester of bisphenol‐A with a 50–50 mix of terephthaloylisophthaloyl units. The two polyesters have been previously found by us to be compatible in their mutual amorphous phase. The x‐ray data are shown to be consistent with a nematic order for the PBT in the blends.
Crystallization in stretched and unstretched EPDM elastomers
Authors: Scholtens B. J. R. , Riande E. , Mark J. E.
Published: April 2003

Elastomeric networks were prepared from ethylene‐propylene‐diene (DPDM) terpolymers containing 5‐ethylidene‐2‐norbornene as the diene monomer incorporated to facilitate crosslinking. Such materials, although highly elastomeric, show some crystallinity over much of the compositional range and thus an understanding of their mechanical properties requires characterization of this crystallinity in both the stretched and unstretched states. The properties and techniques used in the present investigation for this purpose were differential scanning calorimetry, stress‐strain isotherms (at various extension rates), stress‐temperature coefficients, birefringence and stress‐optical coefficients, polarized light microscopy, small‐angle light scattering, and wide‐angle x‐ray scattering. Correlations of the various types of results obtained are used to elucidate the dependence of EPDM network crystallization on composition, strain, and temperature. It was found to be particularly important to use a wide variety of techniques to provide a reliable characterization of the poorly developed crystallinity present in typical EPDM elastomers.
Surface orientation of polypropylene. II. Determination for uniaxially and biaxially oriented films using internal reflection spectroscopy
Authors: Mirabella Francis M.
Published: April 2003

The major objective of this work was to develop a simple and rapid technique to quantitatively measure the macromolecular chain orientation in polypropylene surfaces. A previously described experimental design employing attenuated total reflection spectroscopy near the critical angle was applied. The infrared dichroism of the 841‐ and 809‐cm−1 bands of polypropylene was used to quantitatively determine a fractional orientation function of the macromolecular chains along the three major film axes (machine direction, transverse direction, and thickness or normal direction). The surface orientation of a set of polypropylene films uniaxially extended from 0 to 500% was determined using this technique. The variation of surface orientation, bulk crystallinity, and thickness with extension of these uniaxially extended films were compared. The surface orientation of an unoriented and several biaxially oriented polypropylene films was compared to the bulk orientation determined by a similar transmission infrared dichroism method. It was found that surface and bulk orientation were generally similar. It was shown that rather small orientations could be measured by the surface orientation method and that it was applicable to multilayer films and very thick samples, where the transmission method fails.
Thermodynamic and conformational properties of partially butyralized poly(vinyl alcohol) in aqueous solution
Authors: Shiomi Tomoo , Imai Kiyokazu , Watanabe Chiyoji , Miya Masamitsu
Published: April 2003

Phase separation behavior has been studied in aqueous solutions of partially butyralized poly(vinyl alcohol) (BuPVA) with various degrees of butyralization xBu and various molecular weights. It is found that these systems exhibit both upper and lower critical solution temperatures. The theta temperatures θLCST, evaluated by means of Shultz–Flory plots, are found to be 25.1, 23.3, and 14.4°C for BuPVAs with xBu of 7.5, 9.9, and 12.7 mol %, respectively. The unperturbed dimension 〈R2〉0/M is evaluated as ca. 1.2 × 10−16 Å2 in the above range of xBu from viscosity measurement at θLCST. Properties of the BuPVA solutions are compared with those of other PVA copolymers.
Configurational studies on amylose. I. Scattering functions
Authors: Yamaguchi Saburo , Hayashi Hisao , Hamada Fumiyuki , Nakajima Akio
Published: April 2003

Scattering functions for amylose chains have been calculated as a statistical mechanical average over eligible configurations based on the rotational isomeric state approximation. Main emphasis has been placed on an intermediate‐angle range (0.1 < h = (4π/γ)sinθ < 1.0 Å−1) where the scattering function is sensitive to local chain configurations. In order to avoid overestimation of the regularity of chain configurations, the rotational isomeric states for each glycosidic bond have been defined by a set of discrete torsion angles at intervals of 5°. Pair correlation functions for atoms separated by sequences shorter than 31 glucose units are evaluated by the Monte Carlo method, while the interference for longer sequences is calculated by a series expansion in the even moments of the chain. All carbons and all skeletal oxygens are treated as point scatterers in order to incorporate all the interferences between atoms in unit pairs in the calculations. The calculated scattering function shows appreciable oscillation at intermediate angles, reflecting the characteristic helical tendency of the configurations. The Debye function is found to be inadequate in the intermediate‐angle region owing to the non‐Gaussian character of the distribution function and to breakdown of the assumption that the mean‐square distance between a pair of atoms is proportional to the number of bonds between them, because of the bulkiness of the glucose unit.
Optical absorption of perdeuterated PMMA and influence of water
Authors: Avakian P. , Hsu W. Y. , Meakin P. , Snyder H. L.
Published: April 2003

The optical absorption coefficient of perdeuterated poly(methyl methacrylate) has been obtained by laser calorimetry at 568.2, 647.1, 676.4, and 752.5 nm. The lowest value of 18 dB/km is obtained at 647.1 nm. The dramatic effect of water uptake by the polymer on the total optical attenuation spectrum in the wavelength range 500–1000 nm has been investigated.
Isobaric thermal behavior of glasses during uniform cooling and heating. III. Predictions from the multiparameter KAHR model
Authors: Ramos A. R. , Hutchinson J. M. , Kovacs A. J.
Published: April 2003

The behavior of the multiparameter KAHR model (put forward by Kovacs, Aklonis, Hutchinson, and Ramos) has been investigated using a single‐box retardation spectrum to describe the kinetics of volume and enthalpy recovery of glasses in three‐step thermal cycles involving colling, isothermal annealing, and subsequent reheating. It has been shown that during the heating stage, the system may display up to three peaks in the expansion coefficient and the specific heat. The shifts of the peak temperatures Tp with respect to each of the four experimental variables Yi defining the thermal history are analyzed systematically in terms of a set of reduced variables, scaled by two of the material constants of the system. These shifts, from which the various partial derivatives (∂Tp/∂Yi)j≠i are estimated, are determined for five values of another material parameter x, which characterizes the relative contributions (O ≤ x ≤ 1) of temperature and structure to the retardation times. the results show that the upper peak is always small and is insensitive to the characteristics of the spectrum and to the value of x, while the relevant peak temperature depens only slightly on the cooling and heating rates. On the Other hand, the magnitude and the shifts of the main peak depend on all the experimental variables and the material constants in a rather complex manner. It is shown, however, that in limiting situations, involving fast heating of well‐stabilized glasses, the shifts of the relevant peak temperature T̂all reduce to a linear function of x−1. since this relationship is rather insensitive to the shape of the spectrum, the experimental determination of any one of the nonzero partial derivatives of T̂ provides a simple means for an independent estimate of the value of the important material constant x. Finally, the shifts of the upper and main peaks relative to each other will be analyzed in terms of the pertinent experimental variables and compared with actual data reported in the literature for polymer glasses.
The effect of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water
Authors: Jin X. , Ellis T. S. , Karasz F. E.
Published: April 2003

The influence of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water has been investigated by dynamic mechanical methods. Radiation crosslinking by high‐energy electrons was effective in preventing morphological changes during the measurement of the incremental change in heat capacity (ΔCp) at Tg, which was performed by differential scanning calorimetry. The experimentally determined value of ΔCp, when normalized to account for the crystalline phase, was found to deviate from a linear two‐phase relation and was reduced further than would be expected based on this model. It is proposed that nylon 6 is best described by a three‐phase model which consists of a crystalline domain, a wholly amorphous domain, and an “intercrystalline” region. The importance of this in explaining the relatively large depression of Tg by small quantities of water is illustrated by applying equations derived to account for the compositional dependence of Tg in polymerdiluent mixtures, based on a classical thermodynamic interpretation of the glass transition phenomenon.
The influence of strain deformation on the solubility of ethyl acetate vapor in poly(vinylidene fluoride)
Authors: Phillips J. C. , Peterlin A. , Waters P. F.
Published: April 2003

The degree to which a polymer film develops plastic flow depends largely on the total strain ϵ and the elongation time th. The magnitude and the time dependence of the elastic component ϵe of the total deformation are controlling factors, respectively, in the solubility and diffusion processes. The plastic deformation ϵpl seems not to contribute to the transport properties. The nonlinearity in solubility due to ϵ may be conveniently handled. In this study, the solubility of ethyl acetate vapor in poly(vinylidene fluoride) was determined as a function of pressure and total elongation at 30°C. These results suggest that the strain magnitude and time de pendence of the component deformations play important roles in transport behavior.
High‐temperature fourier transform infrared study of polystyrene/poly(vinyl methyl ether) blends
Authors: Garcia Dana
Published: April 2003

Fourier transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) miscible blends as a function of temperature are presented. Below the lower critical solution temperature (LCST) little change is observed in the interaction spectrum obtained via digital subtraction techniques. Once above the LCST, the magnitude of the interaction spectrum decreases as a result of the phase separation process. Comparison of the behavior of the ether CO stretching band in the reference PVME and in the blends has yielded a lower limit estimate for the interaction energy of about 0.15 kcal/mol.
Regression rates of polymers during burning of their volatile degradation products
Authors: Jellinek H. H. G. , Juznic K.
Published: April 2003

Regression rates as functions of air flow rates and oxygen content of the oxidant gas as well as the distance of the polymer surface from the top of the reaction vessel have been investigated for poly(methyl methacrylate), poly(α‐methyl‐styrene), a polymide, and isotactic polypropylene. The results are discussed from the standpoint of reaction kinetics, considering regression rates and energies of activation for diffusion and degradation.