bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of γ‐irradiation in the molten state on the dynamic mechanical β relaxation and on the thermally stimulated depolarization currents of polyethylene
Authors: Pineri M. , Berticat P. , Marchal E.
Published: April 2003

Dynamic mechanical and thermally stimulated depolarization current data have been obtained on polyethylene, γ‐irradiated in the molten state, as a function of irradiation dose. The β peak which appears in mechanical experiments has been attributed to motions of the chain backbone. The branches, like the crosslinks coming from γ‐irradiation, are fixed tie points for the chains.
Persistence vectors and higher moment tensors of polyoxyalkanes
Authors: Abe Akihiro , Kennedy J. W. , Flory P. J.
Published: April 2003

Statistical mechanical averages of vectors and tensors characterizing the spatial configurations of polyoxymethylene (POM) and polyoxyethylene (POE) chains, i.e., the chain vector r connecting the ends of the chain and the tensors formed from this vector, are evaluated in internal reference frames attached to the first two bonds of each chain as functions of its length. Convergences of the persistence vectors a ≡ 〈r〉 with chain length to their limits a∞ are delineated. For POE, the orientation of a∞ with respect to the X1 axes (the direction of the first bond) depends markedly on the choice of the initial bond and hence also on the internal frame of reference. Cartesian tensors up to fourth rank formed from the displacement vector ρ = r − a are evaluated for n = 4–1922 bonds for POM and n = 3–300 bonds for POE. The second moment tensor 〈ρρT〉 calculated for POM is nearly cylindrically symmetric about the axis perpendicular to the plane of the first two bonds. Corresponding symmetry is absent in POE. Correlation with the freely jointed chain is investigated for the components of the tensors of fourth rank formed from the reduced vector
\documentclass{article}\pagestyle{empty}\begin{document} $\tilde \rho = \left\langle {\rho \rho ^{\rm T} } \right\rangle ^{ - 1/2} \rho $\end{document}. Use of the equivalent chain model for this purpose is validated for POE but not for POM, even at n = 2000 bonds. At the limit 1/n = 0, the parameter m, representing the number of bonds of the real chain equivalent to one of the model, is estimated to be ca. 31 for POM. For POE a value of m = 10.3 ± 1.3 holds for n > 20 for all components. Results are compared with those calculated previously for polymethylene, poly(dimethylsiloxane) and polypeptides. The fact that values of m derived by analysis of moments are larger than those obtained in the usual manner by fitting the model chain to 〈r2〉0 and rmax for the real chain demonstrates the inadequacy of artificial models for the representation of the real chain.
Structure–chain length correlations in poly(N‐vinylcarbazole)
Authors: Griffiths C. H. , Van Laeken A.
Published: April 2003

Narrow molecular weight distribution samples of PVK have been prepared over the molecular weight (Mn) range of 3.7 × 103 to 2.7 × 106. No evidence of influence of the synthetic procedure on polymer tacticity has been observed. The glass‐transition temperature Tg was linearly dependent on 1/Mn (Tg∞ = 227°C) as predicted by the Fox‐Flory chain‐end free‐volume model but no measurable change in free volume was detected. Crystallizability decreased with Mn and was zero in fractions below Mn = 46,000. This behavior coincides with that predicted by the nucleation theory outlined by Hoffman.21 This indicates that the chain‐end free energy controls the stability of PVK folded‐chain nuclei. The critical molecular weight for nucleation at 305°C was found to be some where in the range Mn = 1 ± 0.5 × 105. No change in the structure of the folded‐chain lamellae with Mn was observed but evidence was obtained to support adjacent reentry of chains and a resulting localized crystal distortion.
The determination of the molecular weight distribution of amylose by gel permeation chromatography
Authors: Van Dijk J. A. P. P. , Henkens W. C. M. , Smit J. A. M.
Published: April 2003

The universal calibration for gel permeation chromatography (GPC) has been applied to amylose and dextrans. The molecular weight distribution of amylose has been measured starting from known data on dextrans. The agreement found between the molecular weight averages resulting from GPC and those obtained by other methods justifies the procedure followed. The GPC measurements were performed with dimethylsulfoxide as the elution solvent and deactivated silica gel (Porasil) as the column‐filling material.
The mechanical degradation of polystyrene
Authors: Grayson Michael A. , Wolf Clarence J. , Levy Ram L. , Miller Daniel B.
Published: April 2003

The catastrophic failure of a polymeric material is preceded by a number of complex, partially understood events occurring on the molecular level. These events range from the flow of ordered regions to the cleavage of primary bonds in the chain. In recent years, stress‐induced bond cleavage in polymers has received increased attention, many authors nothing the presence of free radicals and/or volatile products released upon fracture; a free‐radical decomposition mechanism involving up to 103 molecules per chain rupture also has been postulated. A special tensile stress–strain and shear apparatus was developed and located inside the ion‐source housing of a time‐of‐flight mass spectrometer to characterize the volatile products released during mechanical degradation of polystyrene. Volatile compounds evolved during stress and fracture of polystyrene were monitored either continuously or by z‐axis modulated oscilloscopic display. The polystyrene was purified by two methods: vacuum outgassing and fractional reprecipitation. Large amounts of styrene evolved from both the as‐received and outgassed samples; however, essentially none was observed from the reprecipitated samples. Previous reports on monomer evolution during mechanical stress of polystyrene may be the result of residual monomer and not mechanical degradation products. The product of the surface density of primary radicals and the chain length for unzipping is less than 3 × 1010 radicals/mm2 indicating a maximum radical concentration of approximately 1010 radicals/mm2.
The effects of combined pressure–temperature on mechanical behavior of polypropylene
Authors: Yoon H. N. , Pae K. D. , Sauer J. A.
Published: April 2003

The effects of combined pressure and temperature on the mechanical behavior of polypropylene have been studied. Tests were conducted in tension and compression superimposed on various hydrostatic pressures up to 7 kbar at temperatures of 20, 50, and 75°C. The experimental data have been analyzed in view of molecular and continuum approaches.

It has been observed that the Young's modulus and the yield strength in both tension and compression increased significantly with increasing pressure at all temperatures studied. However, the rate of increase of the Young's modulus undergoes abrupt change about the glass‐transition pressure (Pg). The Pg is linearly dependent on the test temperature and the pressure coefficient of the Tg is estimated, from Pg versus temperature relations, to be about 18°C/kbar for the polypropylene samples of this study. Pressure dependence of the yield stress is described by a generalized Eyring theory incorporating pressure effects and two flow mechanisms, the α‐ and the β‐relaxation processes. The theory predicts a bilinear dependence of the yield stress of polypropylene on hydrostatic pressure as observed in the tests.

The paper also described a method of healing stress whitening in polypropylene by a combination of shear stress and hydrostatic pressure.
Monte Carlo study of defect fluctuations and reptation in polymer melts
Authors: Kimmich R. , Doster W.
Published: April 2003

Defect fluctuations in highly distorted polymer chains were simulated by Monte Carlo calculation. The NMR autocorrelation function was derived and described by the superposition of three exponential functions with time constants spread over two orders of magnitude. As a consequence of defect diffusion, longitudinal chain diffusion (reptation) can be expected in polymer melts. By simulating the mean‐square displacement of a segment, it was found that after sufficiently long times, compared with defect density correlation times, a linear relationship holds fairly well. As a rule of thumb, it can be stated that the linear Einstein equation is valid for times much greater than 103 mean step times in practical cases (chain length: several thousand segments, defect concentration: 10–20%), or, in other words, for mean‐square displacements greater than a few diffusion step lengths. A long‐time chain‐diffusion coefficient depending on the molecular weight and on the defect concentration could be derived. Effects on the low‐field NMR relaxation behavior are derived and discussed.
Carbon‐13 NMR spin‐lattice relaxation times of isotactic and syndiotactic sequences in amorphous polypropylene
Authors: Randall James C.
Published: April 2003

Spin‐lattice relaxation times (T1) for methyl, methylene, and methine carbons in an amorphous polypropylene have been measured as a function of temperature from 46 to 138°C. The carbons from isotactic sequences characteristically exhibited the longest T1's of those observed. The T1 differences increased with temperature with the largest difference occuring for methine carbons where a 32% difference was observed. Activation energies were determined for the motional processes affecting T1's for isotactic and syndiotactic sequences with essentially no dependence upon configuration noted.
Nonlinear viscoelasticity of polystyrene solutions. III. Stress development at the start of steady shear flow and an experimental check of some constitutive models
Authors: Osaki Kunihiro , Ohta Shinichi , Fukuda Mitsutoshi , Kurata Michio
Published: April 2003

The development of the shear stress at the start of shear flow at constant rate of shear κ was measured for polystyrene solutions in diethyl phthalate with a cone‐and‐plate rheometer. Ranges of molecular weight M and concentration c were 3.10 × 106−7.62 × 106 and 0.112−0.329 g/cm3, respectively. The shear stress as a function of time t exhibited a marked maximum at large κ when either M or c was relatively low. When M and c were high, the maximum was broad and low. In a few extreme cases no maximum was observed in the range of κ studied. The constitutive model of Bernstein, Kearsley, and Zapas could describe approximately the shear stresses at a sudden start and on cessation of steady shear flow with a memory function evaluated from the strain‐dependent relaxation modulus. The strain dependence of the memory function for solutions of low M or c was approximately expressed as exp{−α|s|} where α is a constant (ca. 0.37) and |s| is the absolute value of shear strain. When M and c were high, the strain dependence was found to be more diffuse and to require several terms if approximated by exponential functions of |s|. The Lodge model based on a strain‐rate dependent relaxation spectrum was not able to describe the strain‐dependent relaxation modulus as well as the interrelation between shear stresses at a sudden start and a cessation of steady shear flow.
Application of fourier transform infrared spectroscopy to the study of semicrystalline polymers: Poly(ethylene terephthalate)
Authors: D'esposito L. , Koenig J. L.
Published: April 2003

An infrared absorbance subtraction technique has been used to “isolate” bands in the composite spectrum of semicrystalline polymers according to their crystalline or amorphous character. Amorphous and crystalline spectra for annealed, melt‐quenched, and solution‐cast poly(ethylene terephthalate) have been separated. The spectra of the amorphous component show an increased intensity of bands associated with the trans configuration of oxygen about the CC bond when the polymer is annealed. This increased “trans” band intensity reflects the increased proportion of trans structures as a result of annealing. The amorphous trans bands are shifted approximately 1–3 cm−1 from their positions in the crystalline “trans” spectrum. The frequency shift of these bands can be attributed to the differences in chain interactions that exist in the amorphous phase and the crystalline lattice. We have also found that under identical anealing conditions the amorphous phase of the melt‐quenched polymer contains an increased intensity of conformational trans bands compared to the sample cast from solution.
Reduction of dielectric loss in radiation‐polymerized polyethylene
Authors: Nakagawa Koichi , Tsuru Shinji
Published: April 2003

Low dielectric loss polyethylenes have been produced by γ‐radiation polymerization of oxygen‐free ethylene monomers. Dielectric measurements were made at 500 MHz and 20°C. The lowest dielectric loss tangent of the polyethylene was 3.3 × 10−5. Polar groups contributing to the dielectric loss have been found to be carbonyl groups, terminal vinyl groups, methyl groups, and hydroxyl groups contained in the polyethylene. The contribution of each group to the loss tangent has been calculated from a comparison of the variation of the loss tangent with the content of each group as determined by infrared analysis. It has been found that the reduction of the loss tangent is mainly due to the decrease in the concentrations of the carbonyl groups and the terminal vinyl groups and that the presence of a considerable amount of the hydroxyl groups prevents a further reduction of the loss in the polyethylenes. The results obtained from the analysis of the radiation‐polymerized polyethylenes were applied to commercially available polyethylenes.
Piezoelectric relaxation in poly(γ‐benzyl‐glutamate)
Authors: Furukawa Takeo , Fukada Eiichi
Published: April 2003

The piezoelectric d‐ and e‐constants, together with the elastic constant and the dielectric constant, were measured for oriented poly(γ‐benzyl‐glutamate) (PBG) films with various elongation ratios as a function of frequency and temperature, using an apparatus developed by us. The results are discussed in terms of a general theory of piezoelectricity for inhomogeneous systems, in particular for a disperse two‐phase system. The piezoelectricity of PBG film is proved to originate from the piezoelectric and optically active symmetry of PBG crystallities and their orientation distribution by three findings: (1) the d14 component of the piezoelectric matrix, which is the only component for a uniaxially or uniplanarly oriented system, is observed; (2) d14 > 0 for PBDG and d14 < 0 for PBLG; (3) d14 is proportional to the degree of orientation Fc of PBG crystallites, as determined by x‐ray diffraction. By extrapolating to perfect orientation, d14 is determined to be 5 × 10−8 cgs esu, if the side chains of PBG are rigid. The piezoelectric relaxation of PBG due to thermal motion of the side chains has a dual character: it is relaxational at lower frequencies and retardational at higher frequencies. On the assumption that the α‐helical main chains surrounded by the bulky side chains are responsible for the origin of the piezoelectricity, such relaxation phenomena are interpreted in terms of the relaxation of the local elastic field in the main chains. An equivalent model having the same frequency characteristics is proposed to include the higher order structure of the PBG film.
Comments on the optical properties of fully conjugated polymers: Analogy between polyenes and polydiacetylenes
Authors: Baughman R. H. , Chance R. R.
Published: April 2003

The similarity of the π‐electron backbones of the polyenes and the polydiacetylenes suggests an analogy between these two fully conjugated, linear polymers. The extent of the analogy is discussed through the examination of a series of model compounds: the polyenes and the polyenynes. The optical band gaps and the polarizabilities of polyenynes are compared to those of the polyenes and to the predictions of a modified free‐electron model. It is concluded that the chain‐dependent electronic properties of the polyenes may be extrapolated with some confidence to the polydiacetylenes.
Carbon‐13 nuclear magnetic resonance quantitative measurements of average sequence lengths of like stereochemical additions in polypropylene and polystyrene
Authors: Randall James C.
Published: April 2003

Sequence lengths of stereochemical additions in vinyl polymers are described in terms of the number average lengths of like configurational placements. Under these circumstances, a pure syndiotactic polymer has a number average sequence length of 1.0; a polymer with 50:50 meso, racemic additions has a number average sequence length of 2.0 and polymers with more meso than racemic additions have number average sequence lengths greater than 2. Amorphous and crystalline polypropylenes and an amorphous polystyrene are examined using 13C NMR as examples of the applicability of the average sequence length method. The results appear to be accurate for amorphous and semicrystalline polymers but limitations are present when this method is applied to highly stereoregular vinyl polymers containing predominantly isotactic sequences.
Birefringence and stress relaxation in polyisobutylene
Authors: Berglund Charles A. , Taylor Carl R.
Published: April 2003

Relaxation of birefringence and stress in simple extension has been studied for polyisobutylene at ‐26.0°C and 25.0°C for extension ratios ranging from about 1.2 to 2.0. The dependence of both the stress and birefringence on the extension ratio, for a given time, is well described by equations of the Mooney–Rivlin form. The Mooney–Rivlin treatment of the birefringence experiments was found to reinforce but not add to information available from the stress‐relaxation experiments alone. At 25.0°C, the stress‐optical coefficient is found to be stress dependent. Possible explanations of this behavior are discussed. An experiment is also reported in which the birefringence is observed under zero stress immediately after cutting a strained sample. The zero stress birefringence is believed to be due to regions of stress‐induced crystallization taking a finite time to melt after the stress is removed.
Effects of inorganic salts on the properties of aqueous poly(ethylene oxide) solutions
Authors: Boucher E. A. , Hines P. M.
Published: April 2003

Cloud‐point curves have been determined for aqueous solutions of poly(ethylene oxide) (PEO) at several concentrations for a variety of inorganic salts (sulfates, carbonates, nitrates, and chlorides). From these, theta conditions have been determined. The resulting dependences of the critical temperature θ (mostly between 300 and 360°K) on the molar concentrations (or ionic strengths) of the salts in solution cannot wholly be summarized in sequences of ion effects. The major findings are that sulfates and carbonates are much more effective in reducing θ than the chlorides and nitrates at the same concentrations. The trends found depend on salt concentration, i.e., certain plots of the data cross over, but they broadly agree with those found for comparable systems by other workers. Exceptional are the chlorides of Group II and LiCl which show minima when θ is plotted against molar salt concentration. While interpretations based on solvent structure‐breaking are not adequate, there are similarities in behavior with the structure‐breaking attributes of the ions based on independent studies (infrared). The results are briefly discussed in terms of current postulates: a more detailed discussion will accompany further experimental studies on these systems.
The theory of phase transition kinetics with growth site impingement. II. Heterogeneous nucleation
Authors: Tobin Marvin C.
Published: April 2003

The kinetics of phase transformation are treated for heterogeneous nucleation, where all nuclei are simultaneously initiated, and where initiation follows first‐order kinetcs. The phase transformation curves are sigmoid. For simultaneous initiation in two dimensions, a(t)/(1 − a(t)) ∝ t2. For first‐order initiation, we have, approximately, a(t)/(1 − a(t)) ∝ t2.85, and v(t)/(1 − v(t)) ∝ t3.74.
Interpenetration of polystyrene chains in bulk polymer
Authors: Worsfold D. J.
Published: April 2003

Polystyrenes lightly substituted with either tertiary amine groups or nitrophenol groups have been allowed to interact in concentrated t‐butylbenzene solution and in bulk polymer. Above the glass transition temperature a temperature dependent equilibrium is achieved in the bulk polymer between the two substituents and the amine salt of the phenol. The degree of association found is considerably greater in the bulk polymer than in solution. The results show that much interpenetration of the polymer occurs, and the results are discussed in terms of models of the bulk amorphous state of the polymer.
Relation between preferential solvation and intrinsic viscosity of polymers in solvent mixtures
Authors: Dondos A. , Benoît H.
Published: April 2003

Preferential solvation and intrinsic viscosity measurements are reported for three systems: polystyrene + benzene + methanol, polystyrene + carbon tetrachloride + methanol, and poly(2‐vinylpyridine) + ethanol + cyclohexane. Plots of the coefficient of preferential solvation λ′ as a function of variation of the segment density Δρ for a given ternary system, give a single curve for a large range of molecular weight and solvent mixture composition. This correlation between λ′ and Δρ is verified in previously published data.
Phase‐separation phenomena in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide). I. Thermodynamic parameters of solutions in toluene
Authors: Koenhen D. M. , Smolders C. A.
Published: April 2003

New experimental data have been collected on thermodynamic properties of solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) in toluene. The Flory–Huggins interaction parameters g have been determined from light scattering measurements. These values are in agreement with values obtained by osmotic measurements at low concentrations and they allow the calculation of a melting point curve which fits the experimental melting points. No liquid–liquid phase separation can be calculated, as was concluded in a preceding paper. Spinodals could not be detected by light scattering or DSC‐measurements. This also indicates that liquid–liquid phase separation does not occur. The phase separation on cooling of a PPO‐toluene solution is thus believed to be a crystallization phenomenon.
Broad‐line NMR and dynamic mechanical behavior of some aromatic polyesters
Authors: Frosini V. , Levita G. , Landis J. , Woodward A. E.
Published: April 2003

The dynamic mechanical properties of four aromatic polyesters were measured at temperatures in the 78–540°K region at 103–104 cps. The polymers studied were: poly(1,3 phenylene isophthalate), poly(1,4 phenylene terephthalate), poly(4,4′ diphenylene isophthalate), and poly(4,4′ diphenylene terephthalate). All four polymers had β loss peaks at about 280°K. Distinct β* mechanical processes were found for the two terephthalate esters. Broad‐line nuclear magnetic resonance measurements were carried out in the 150–440°K temperature range on the four polyesters mentioned above in addition to poly(4,4′ diphenylene 4,4′ biphenyl dicarboxylate). A change in NMR second moment takes place in the 190–330°K region, the magnitude of which is dependent on the polymer structure. The results are compared with those found for a series of aromatic polyamides and are discussed in terms of possible motional processes.
Crystallization during polymerization of diphenylsilylene by a chemical transport reaction
Authors: Lee Chung Jen , Wunderlich Bernhard
Published: April 2003

Crystallization during polymerization of polydiphenylsilylene has been accomplished. Best results are obtained by initial thermal polymerization to the amorphous macromolecule. The macromolecules are then decomposed and repolymerized by sublimation. Macroscopic extended‐chain single crystals are produced. The polymer crystals, once molten, will not recrystallize. Their initial characterization is described using infrared, Raman, ultraviolet, and nuclear magnetic resonance spectroscopy. X‐ray and thermal analysis data are also given.
Self‐hardening of highly oriented polyethylene
Authors: Arridge R. G. C. , Barham P. J. , Keller A.
Published: April 2003

Ultra‐oriented polyethylene fibers obtained by drawing to approximately 30 times their original length have a Young's modulus of approximately 800 kbar. Such fibers, if unconstrained, contract on heating to a length near the original. We have studied the forces causing this contractile behavior by monitoring the stress in the fiber while maintaining it at constant length. In the course of this we observed a complex sequence of both reversible and irreversible behavior. In the reversible case we observed first energy and then entropy elastic behavior. The most significant feature observed is that at sufficiently high temperature the fiber stress relaxes to an unmeasurably low value. A fiber allowed to relax in this way possesses a much lower room temperature tensile modulus (ca. 80 kbar) immediately after relaxation but, remarkably, this modulus increases to approach the initial high value over a period of a few hours when the fiber is stored either clamped or unclamped at room temperature. High x‐ray orientation is preserved throughout the storage period but the density which dropped during the stress decay rose again in the course of the spontaneous stiffening. None of the stress relaxed fibers displays large‐scale contractile behavior on subsequent heating.

A phenomenological composite model is proposed which involves stiff microfibrils of short length—surrounded by a matrix present as a minority component. The softening of this matrix on heating and its subsequent stiffening on storage, involving a certain amount of melting and recrystallization, respectively, could then be responsible for the observed variations in the macroscopic tensile properties using simple fiber composite theories. The fibers are likely to be of extended‐chain type produced by the initial drawing while the matrix may consist of a combination of oriented amorphous material (tie chains), randomly oriented chains, and transverse lamellar overgrowth present in varying proportions in the different stages of sample treatment. The wider implications, fundamental and practical, of this remarkable self‐hardening process are indicated.
Diffusion in polymer–solvent systems. II. A predictive theory for the dependence of diffusion coefficients on temperature, concentration, and molecular weight
Authors: Vrentas J. S. , Duda J. L.
Published: April 2003

A new free‐volume theory is combined with the thermodynamic theory of Flory and the entanglement theory of Bueche to provide a means of predicting the temperature, concentration, and molecular weight dependence of mutual‐diffusion coefficients in amorphous polymer–solvent systems. The predictions of the theory are compared with actual data for the ethylbenzene–polystyrene system.
Brillouin scattering and hypersonic relaxation in amorphous polymers
Authors: Patterson G. D.
Published: April 2003

Mechanical relaxation at hypersonic frequencies is measured using Brillouin spectroscopy for polyisobutylene, atactic polypropylene, polydimethyl siloxane, and polyvinyl acetate. The temperatures of maximum loss determined in the gigahertz range are compared to the published transitions maps for the above polymers. It is found that the hypersonic relaxation data fall on an extrapolation of the secondary main chain glass–rubber relaxation line above the region where the primary and secondary lines merge.
Polyelectrolytes near the rod limit
Authors: Odijk Theo
Published: April 2003

The problem of a polyelectrolyte near the rod limit is formulated incorporating both the short‐range stiffness of the backbone (the “wormlike chain”) and the electrostatic interaction between segments taken as a Debye–Húckel potential. By the use of a physically valid approximation an expression is derived for the mean‐square extension length of a short polyelectrolyte chain. Some remarks are made on the relationship between the electrostatic interaction and the usual excluded‐volume problem for polymer solutions.
Chemical origin of thermally stimulated discharge currents in polyacrylonitrile
Authors: Stupp S. I. , Carr S. H.
Published: April 2003

Thermally stimulated discharge has been used in the past to diagnose and estimate the magnitude of electrical polarization in polymers. Nevertheless, molecular characterization of operative phenomena by this technique alone is often a difficult task. In the present work, infrared attenuated total reflection spectroscopy has been used to investigate the origin of thermally stimulated discharge currents near 200°C in externally unpolarized films of polyacrylonitrile (PAN). Spectroscopic analysis of thermally degraded films reveals some unsaturation of the PAN backbone and possibly the generation of cyanide ions. Opposite surfaces in a solvent‐cast film give different spectra, indicating a gradient in chemical degradation products across the film thickness. Data suggest that nonuniform generation of charged species and unsaturated bonds gives rise to internal potentials in PAN. The origin of thermally stimulated currents in PAN near 200°C is thus believed to be associated with the onset of chemical degradation.
Eutectic solidification of the quasi binary system of isotactic polypropylene and pentaerythrityl tetrabromide
Authors: Smith P. , Pennings A. J.
Published: April 2003

This paper reports of a study on eutectic solidification of the quasi binary system of unfractionated isotactic polypropylene and the dentritic growing diluent pentacrythrityl tetrabromide. This system was characterized by a eutectic‐type experimental phase diagram with a eutectic composition of 68% (w/w) of polypropylene. The eutectic temperature was found to depend on kinetics, and was established by differential scanning calorimetry to be 122 and 102°C at a cooling rate of 0.5 and 32°C/min, respectively. A remarkeable nucleating effect of the primary diluent crystals was observed in the solidification of diluted polypropylene solutions. Here the eutectic horizontal was located at a temperature which was 15°C higher than in the eutectic solutions exceeding the temperature at which the pure polymer crystallized from the melt by 8°C. The eutectic microstructures produced were found to depend on the rate of solidification, which was varied by pulling the polypropylene solutions through a fixed temperature gradient of 3°C/mm at different speeds ranging from 0.2 to 80 mm/hr. At rates lower than 3 mm/hr the polymer and the diluent crystallized simultaneously from the eutectic solution in a uncoupled mode of growth, forming a coarse structure of diluent crystals and isotactic polypropylene spherulites with dimensions of about 0.1 mm. At higher speeds the simultaneous crystallization of the macromolecules and solvent molecules proceeded in a co‐operative manner with a nonplanar growth front. A rodlike eutectic microstructure was produced, in which diluent rods, lined up in the growth direction, were dispersed in a polypropylene matrix. The lateral dimension λ1 of these rods were found to depend on the growth rate R in the following way: λ12 R = 10−9 mm3/sec, and ranged from 0.3 to 1.0 μm. This was in accord with values calculated by using the current theory of rod eutectic growth of Jackson and Hunt.
Electrical conductivity of crystallizable polyphenylacetylene
Authors: Holob G. M. , Ehrlich P.
Published: April 2003

The dc conductivity of crystallizable poly(phenylacetylene), made in the presence of ferric acetylacetonate and triethylaluminum, and its dependence on time, temperature, pressure, and crystallinity was determined. A decrease in conductivity upon annealing is probably attributable to an irreversible conformational transformation of the polymer. There is also a reversible decrease in conductivity upon compression which, under some conditions, corresponds to a volume of activation as high as 70 cm3/mole. Upon complexing with iodine the conductivity is increased by several orders of magnitude and activation energies and volumes are greatly reduced, even at iodine concentrations as low as 1.6 mole % iodine per monomer unit. Although an identification of unpaired spins with the charge carriers is probably not justified, defect states, whose presence is demonstrated by electron spin resonance, may play a major role in the charge transport process. The strong reversible decrease of the conductivity with an increase in pressure is plausible, if intermolecular charge transport is the rate‐controlling step, an interpretation consistent with the large increase in conductivity upon complexing with small amounts of iodine.
D2‐m‐carborane siloxanes. V. Structure–property relationships
Authors: Peters E. N. , Kawakami J. H. , Kwiatkowski G. T. , Hedaya E. , Joesten B. L. , McNeil D. W. , Owens D. A.
Published: April 2003

D2‐m‐decacarborane dimethylsiloxane has unusual thermal stability and resistance towards reversion, however, this material exhibits a crystalline phase, Tm at 68°C. To obtain an elastomeric material, this crystallinity is disrupted by replacing 30 to 50% of the m‐carborane with p‐carborane moieties or by the incorporation of phenyl moieties on the polymer backbone. The latter approach is preferred since improved thermo‐oxidative stability accompanies this modification. Correlation of the glass transition temperature and thermo‐oxidative stability with the polymer structure are presented.
Conformational transition of the copolymer of maleic acid and styrene in aqueous solution. II
Authors: Okuda Toshihiko , Ohno Nobumichi , Nitta Katsutoshi , Sugai Shintaro
Published: April 2003

The temperature dependence of the conformational transition from a compact to expanded‐coil form of the alternating copolymer of maleic acid with styrene in aqueous 0.03M NaCl solution was studied at 15 to 40°C by pH titration, optical titration, and calorimetric measurements. The pH titration curve scarcely changed with temperature. The degree of dissociation of primary carboxyl groups in the copolymer at the midpoint of the conformational transition, determined by the optical titration, was almost independent of temperature. The standard enthalpy change of the transition at 25°C estimated from the calorimetric data was 0.363 kcal/mole, which may mean that the difference between the standard free energy changes of the transition at 20°C and 40°C does not exceed experimental error. The enthalpy change agrees well with the heat of transfer of benzene from the hydrophobic to the aqueous medium, and thus the compact form of the copolymer is considered to be stabilized by the hydrophobic interaction between the phenyl residues in the interior of the molecule.
The solubility of nitrogen in polyethylene above the crystalline melting point at high pressure
Authors: Atkinson E. B.
Published: April 2003

A simple method of measuring the solubility of gases in polymers at elevated temperatures and high gas pressures is described by direct weighing of the sample after cooling to ambient temperatures. Changes in gas content during cooling which would cause errors are largely prevented by nucleating bubbles throughout the samples immediately prior to cooling, with the effect of making the internal partial pressure of gas equal to the external pressure while the polymer is soft and thus preventing gas flux to or from the sample. Results are given for the solubility of nitrogen in branched polyethylene in the temperature range 130–190°C at gas pressures up to 1,030 bar. A kink in the solubility isotherm at temperatures just above the normal crystalline melting point is believed to be caused by a pressure shift of the melting point. Comparison of the results with previous work by Lundberg et al. suggests a systematic error in the latter which reduced the apparent solubility at higher pressures.
Photoconduction in poly(ethylene terephthalate). I. Mechanisms of carrier generation
Authors: Takai Yoshiaki , Osawa Toshifumi , Mizutani Teruyoshi , Ieda Masayuki
Published: April 2003

Mechanisms of photocarrier generation in poly(ethylene terephthalate) (PET) have been investigated. In the wavelength range of λ ≦320 nm, the photocurrent spectra correspond closely with the optical absorption spectra of PET and the assignment of the absorption peaks revealed that photocarriers are generated through ππ* excitations. In the wavelength range from 320 to 400 nm, photocarriers are injected from metal electrodes. The threshold energies for Al and Cu electrodes are 2.87 and 2.94 eV, respectively, indicating the presence of surface states. The simplified model gives the density of the surface states as 1.7 × 1014 cm−2 eV−1.
Domain size dependence of glass transition temperature
Authors: Couchman P. R. , Karasz F. E.
Published: April 2003

The effect of particle size on glass transition temperatures is discussed. The phenomenon is treated in terms of Ehrenfest second‐order thermodynamics and in addition related to free volume concepts. Consistent formulas are obtained and the order of magnitude of the effect is estimated.
X‐ray diffraction and infrared studies on annealed highly syndiotactic poly(vinyl chloride)
Authors: Baker C. , Maddams W. F. , Preedy J. E.
Published: April 2003

X‐ray diffraction scans and infrared absorption spectra for the C‐CI stretching region were obtained for a highly syndiotactic poly(vinyl chloride) (PVC) sample made by the urea clathrate method. When the polymer was annealed at a series of increasing temperatures up to 180°C, x‐ray diffraction measurements showed that the crystallinity increases steadily with annealing temperature. Even at 50°C an increase above the original value of 63% was detectable and by 180°C it had reached 70% with a further increase to 78% after cooling to ambient temperature. There is a concurrent significant increase in the lateral crystallite dimensions. However, the infrared spectrum did not change, in agreement with the recent prediction of Moore and Krimm that there is no observable band splitting from interchain interaction in crystalline regions, thus indicating that these C‐CI bands cannot be used as a measure of crystallinity. The results from computer curve fitting of the spectra suggest that at least 85% of the polymer consists of long planar syndiotactic sequences and there is therefore substantial order along the chain direction. A mechanism for the increase in crystallinity on annealing, involving the lateral ordering of these regular chains, is discussed. Furthermore, as the temperature is raised some amorphous material is converted to a nematic phase, and this may crystallize during the subsequent cooling.
Origin of double melting peaks in drawn nylon 6 yarns
Authors: Todoki Minoru , Kawaguchi Tatsuro
Published: April 2003

The differential scanning calorimetry (DSC) melting curves of drawn nylon 6 were studied from the standpoint of reorganization of the crystals during the heating process. A new method was presented to obtain the DSC curve associated with the growth and melting of the original crystals, and that with the recrystallization and final melting process, separately. The results obtained show that, in the case of a heating rate of 10°C/min, the original crystals in the sample start perfecting themselves at temperatures far below their initial melting temperature and melt out below 222°C, recrystallization starts at about 210°C, and the newly emerged crystals melt out at 228°C. The superposition of two such constructed DSC curves reproduces the observed DSC curve well. Therefore, the double melting peaks of the sample are considered to be the result of superposition of three processes which occur successively during heating; perfection of the original crystals, melting of the perfected crystals concurrently with recrystallization, and melting of the recrystallized crystals.
The effect of density on the properties of high molecular weight polyethylenes
Authors: Trainor A. , Haward R. N. , Hay J. N.
Published: April 2003

Ultrahigh molecular weight polyethylene has been crystallized at various pressures (0–330 MN m−2) to material of a wide range of specific gravities (0.928–0.967). Tensile measurements illustrate that the properties of these materials are dependent on specific gravity (sg), in that the yield stress increases linearly with sg. Low sg (0.928–0.944) materials exhibit higher yields stress than low molecular weight materials of the same sg but the opposite is true for higher sg material. Low sg material also extends uniformly after yielding while above a sg of 0.944 necking becomes more marked. Orientation hardening is observed with all these materials above 200% extension and is more marked than with low molecular weight polymers. Differential scanning calorimetry (DSC) analysis of the pressure crystallized materials indicate that in the range 200–400 MN m−2 two phases are present, i.e., chain‐folded and chain‐extended lamellas. Increasing or decreasing the pressure changes the crystalline component to chain‐extended or chain‐folded morphologies, respectively. The reorganization of the crystalline components on drawing is discussed.
Polymer–monomer binary mixtures. I. Eutectic and epitaxial crystallization in poly(ϵ‐caprolactone)–trioxane mixtures
Authors: Wittamann J. C. , Manley R. St. John
Published: April 2003

Binary mixtures of a linear polyester (poly(ϵ‐caprolactone)) and a crystallizable monomer (trioxane) have been investigated by means of differential scanning calorimetry and optical and electron microscopy. The phase diagram indicates the existence of a eutectic at a temperature TmE = 314°K and for a polymer volume fraction ϕ2E = 0.70, values close to those predicated by the Flory–Huggins theory (using χ = 0.3). Microscopic studies reveal unusual morphologies: (1) In hypoeutectic mixtures, at room temperature, the solvent crystallizes as highly ramified or branched needles. When the remaining melt reaches the eutectic composition, transcrystallization of the polymer is induced by the epitaxial deposition (as established by electron diffraction) of polycaprolactone on the existing trioxane crystals, and leads to highly ordered structures. (2) In hypereutectic mixtures a predominantly spherulitic texture is observed. Blends of trioxane and several other linear polyesters are found to exhibit similar behavior.
A study of thermodynamic behavior of polystyrene solutions in benzene at moderate concentrations by sedimentation equilibrium
Authors: Chu Sung Gun , Munk Petr
Published: April 2003

The method of sedimentation equilibrium was used to obtain values of the thermodynamic interaction coefficient χ as a function of concentration. Five samples of polystyrene with molecular weights ranging from 36,000 to 1,750,000 were studied in benzene over the concentration range up to the volume fraction equal to 0.03. The experimental data were used to test the theory of Koningsveld et al. (Macromolecules, 7, 73, 1974). This theory predicts that the interaction term in the free enthalpy of mixing may be split into one term common for all molecular weights and another term, which depends on molecular weight and vanishes exponentially at high concentrations. It is concluded that the functional form proposed by the theory gives a fair description of experimental data. However, the phenomenological coefficients obtained from the experiment differ significantly from the values predicted by the theory.
Influence of pressure and chemical structure on the thermal conductivity of vitreous poly(alkyl methacrylates). I
Authors: Barker R. E. , Chen R. Y. S. , Frost R. S.
Published: April 2003

The influence of pressure on the thermal conductivity K of four vitreous poly(alkly methacrylate) polymers has been measured by steady state techniques. The measurements were made under pressures up to 2 kbar and over a temperature range between 173 and 300°K. For each member of the homologous series, K was found to increase with applied pressure. Shifts in thermal conductivity transition temperatures (attributed to glass transition phenomena) of 25, 26, and 16°C per kbar of applied pressure were observed for poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n‐isobutyl methacrylate).
Flow‐induced crystallization of poly(ethylene terephthalate) melts in a capillary die: Formation and properties of the crystalline toroid
Authors: Griswold Phillip D. , Cuculo John A.
Published: April 2003

An unusual crystalline aggregate, which is toroidal in shape, has been formed at the entrance region to capillary dies during the high‐pressure extrusion of poly(ethylene terephthalate) melts in an Instron capillary rheometer. The toroidal remnant was discovered in capillary dies removed from the rheometer after the occurrence of oscillating flow. Detailed observations of the rheological factors involved in the formation of the crystalline toroid were made. Examination of recovered entrance plugs disclosed that the crystalline toroid was a hard, stagnant zone which throttled the bulk flow of polymer melt into the capillary during the extrusion experiments. Hot‐stage optical microscopy, differential scanning calorimetry, and wide‐angle x‐ray techniques were used to initiate a structural study of the crystalline toroid. The toroid contained clusters of fibrous crystals which persisted to high temperatures. The fibrous clusters were randomly oriented in a matrix polymer which melted normally. Based upon the rheological and structural evidence, a mechanism of crystalline toroid formation is proposed.
Solid‐state relaxations in poly(ethylene oxide). II. Study using the spin‐labeling technique
Authors: Lang M. C. , Noël C. , Legrand A. P.
Published: April 2003

Poly(ethylene oxide) (PEO) was spin‐labeled with 3‐chlorocarbonyl‐2,2,5,5‐tetramethylpyrroline‐1‐oxyl. Correlation times were calculated from 173 to 375°K. For estimating slow‐motion rotational correlation times three models were used: Brownian diffusion, “moderate jump” diffusion, and “large jump” diffusion. Analysis of the changes in the extrema separation and spectra shape with temperature strongly suggests the presence of β and γ processes in solid poly(ethylene oxide). The Brownian diffusion model gives, for the γ relaxation, an activation energy of 8 kcal mole−1 which is in good agreement with that found using dielectric relaxation measurements.
Polarized Raman scattering of concentrated solutions of poly(dimethyl siloxane) in benzene
Authors: Thornley P. W. , Shepherd I. W.
Published: April 2003

Raman depolarization (ρ) measurements have been made over the temperature range 20 > T > 60°C for solutions of poly(dimethyl siloxane) (mol wt 7.7 × 104 and 2.0 × 104) for several concentrations up to 100%. The band studied was the highly polarized methyl stretch at 2907 cm−1. Computer calculations of the probability pt of a rotational isomer being trans allow the ρ values to be related to ΔG, the free energy of mixing. ΔG is plotted as a function of concentration and minima are observed at 60 ± 3% (mol wt = 7.7 × 104) and 70 ± 3% (mol wt = 2 × 104).