bluuebunny/crossref_metadata_2025 huggingface dataset:
An isochronous decoration method for measuring linear growth rates in polymer crystals
Authors: Dosiere M. , Colet M.‐Ch. , Point J. J.
Published: April 2003

The long spacing l of lamellar crystals of linear polyethylene increases with the crystallization temperature Tc. For low degrees of supercooling, the ratio Δl/ΔT is around 0.5 nm K−1 for PE single crystals obtained from solution in xylene. In the restricted situation where only conduction in the crystallization vessel is involved, a heat transfer analysis shows that about 20 s is needed to change by 5 K the crystallization temperature Tc in a cylindrical vessel of 1.5 mm radius. Such rapid change of the crystallization temperature induces a sharp increase or decrease of the thickness of the single crystals. After conventional shadowing with palladium–gold alloy, the steps on the crystals are observed by conventional bright‐field electron microscopy. A pioneering work was performed in this way by Bassett and Keller in 1962. Our technique allows one to determine both the shape and the dimensions of single crystals or twinned crystals of polyethylene as a function of the time of crystallization, and therefore give the quasi‐instantaneous growth rates at various times.
Gas sorption in poly(vinyl benzoate)
Authors: Kamiya Yoshinori , Mizoguchi Keishin , Naito Yasutoshi , Hirose Takuji
Published: April 2003

High‐pressure sorption (up to 50 atm) for CO2, N2, and Ar in poly(vinyl benzoate) (PVB) was studied at temperatures from 25 to 70°C by a gravimetric method utilizing an electromicrobalance. The results are described by Henry's law above the glass transition temperature Tg for all gases. The dual‐mode sorption model, Henry's law plus a Langmuir isotherm, applies to the sorption isotherms of N2 and Ar in the glassy state, and the dual‐mode parameters are given. For CO2, a new type of sorption isotherm is observed below Tg. The isotherm is concave to the pressure axis in the low‐pressure region and turns into a straight line with increasing CO2 pressure which can be extrapolated back to the coordinate origin. The linear part of the isotherm is characteristic of the rubbery state, while the nonlinear part stems from glassystate behavior. The “glass transition solubility” of CO2, at which PVB film changes from the glassy to the rubbery state, decrease as the temperature increases. The disappearance of microvoids, that is, the decrease of the Langmuir capacity, may be due to a large plasticizing effect of sorbed CO2. The difference between the N2 and Ar isotherms and the CO2 isotherm is discussed from this standpoint.
A quantitative explanation of the difference in the temperature dependences of the viscoelastic softening and terminal dispersions of linear amorphous polymers
Authors: Ngai K. L. , Plazek D. J.
Published: April 2003

A coupling model of relaxation that can account for viscoelastic properties in both the softening and terminal dispersions is found to explain quantitatively also their different temperature dependences.
Dynamic mechanical properties of plasticized polystyrene‐based ionomers. II. Melt rheology
Authors: Bazuin C. G. , Eisenberg A. , Kamal M.
Published: April 2003

A high molecular weight styrene ionomer containing 5 mol% sodium methacrylate was blended with a styrene oligomer (MW 800) and investigated by dynamic mechanical techniques. The focus of the study is on the dynamic melt rheology of these materials, whose ratios by weight of ionomer to oligomer are 60/40, 40/60, and 25/75. The glass‐transition temperature and ionic transition are first characterized by torsion pendulum measurements as a function of temperature. It appears that a maximum level of plasticization is achieved for the ionic regions, the extent depending on sample history. Time–temperature superposition is obeyed by the blend of 60 wt% ionomer, but not by the other two blends. Relaxations due to the ionic regions are clearly evident in the relaxation spectra of all three blends. Above a particular temperature, the 25 wt% blend indicates an Arrhenius type of dependence.
A MNDO study of the structural and electronic properties of polysilane model compounds
Authors: Bigelow Richard W. , McGrane Kathleen M.
Published: April 2003

The results of MNDO geometry optimizations on selected H(SiH2)nH polysilane model compounds are presented. Near energetic degeneracy is indicated for all‐trans(T), alternating gauche–trans (GT), and all‐gauche (G+G+) models (n = 10). The most stable (T) and least stable (G+G+) conformations are separated by only ca. 0.11 eV. The existence of low‐energy barriers to moderate structural distortion is also suggested. Orbital localizations and charge density distributions along the “polymer” backbone are found to be sensitive functions of such distortion. The ground‐state electronic distribution of the saturated all‐trans silane chains are calculated to be considerably more polarizable than the fully conjugated H(CH)nH π‐electron framework of comparable length. The one‐electron HOMO → LUMO excitation can be viewed essentially as an in‐plane Si 3p → Si3s + H1s intramolecular charge transfer transition. The qualitatively different atomic orbital character of the HOMO and LUMO levels yields transition moment components for the separate repeat units which are relatively small. In the case of the rigidly trans conformation, the phase relationships of the transition moment terms are such as to constructively sum to a large net value reflecting strong optical absorption, as is observed experimentally.
Model MDI/butanediol polyurethanes: Molecular structure, morphology, physical and mechanical properties
Authors: Christenson C. P. , Harthcock M. A. , Meadows M. D. , Spell H. L. , Howard W. L. , Creswick M. W. , Guerra R. E. , Turner R. B.
Published: April 2003

Model butanediol–MDI–polypropylene oxide polymers have been synthesized to explore the structure–property relationships in urethane/polyether polymers. The results of mechanical, thermal, and spectroscopic analyses agree remarkably well. The phase mixing in these polymers decreases with increasing hard‐segment length, while the hard‐segment stability increases with increasing hard‐segment length. This is demonstrated clearly by dynamic mechanical, differential scanning calorimetry, infrared, and NMR studies. The importance of hydrogen bonding to the stability of the hard segment is strongly supported by the variable‐temperature infrared experiments. The critical hard‐segment size for phase segregation was shown to be two butanediols per hard segment. The temperature limit of the flatness of the storage modulus was tied to the thermal stability of the hard‐segment hydrogen bonding which is controlled largely by the length of the hard segment and the extent of the hydrogen bonding.
Molecular orientation in biaxially oriented sheets of poly(ethylene terephthalate). I. Characterization of orientation and comparison with models
Authors: Bower D. I. , Jarvis D. A. , Ward I. M.
Published: April 2003

A study of molecular orientation in a series of five one‐way‐drawn sheets of poly(ethylene terephthalate) is reported. Five orientation averages P which characterize the benzene‐ring orientation were determined directly by Raman spectroscopy. Two further averages P and P were determined from a combination of Raman spectroscopy and refractive index measurements on the basis of two different conformational models. As in a previous publication, the seven averages P were used to estimate all the P up to fourth order for the benzene rings on the assumption that in each case the actual distribution of orientations is close to the most probable distribution. The seven orientation averages P for each drawn sheet were also compared with those calculated on the basis of two simple models for the development of molecular orientation during drawing, the pseudoaffine deformation scheme and the rubber network model. It was shown that the orientation of the chain axes is closer to that predicted by the rubber network model, the pseudoaffine deformation scheme greatly overestimating the degree of chain biaxiality. The results also show that the benzene ring planes are preferentially oriented toward the planes of the sheets. The chain axis orientation is, however, nearly uniaxial and similar to that observed for uniaxially drawn samples, suggesting that there is no direct connection between the processes of chain axis orientation and preferential orientation of the benzene‐ring planes.
Refractometry of lyotropic mesophase systems: Ethyl cellulose/m‐cresol and ethyl cellulose/acetic acid
Authors: Suto Shinichi , Ise Hirotada , Karasawa Mikio
Published: April 2003

An Abbé refractometer with a rotatable polarizer mounted on the eyepiece is used for determining the two principal refractive indices of birefringent concentrated solutions of ethyl cellulose in m‐cresol and in acetic acid. At a certain concentration, birefringence appears for both systems, and the concentration agrees with that for the onset of iridescence (here defined as the critical concentration Ca for formation of the liquid‐crystalline phase). The birefringence of concentrated solutions depends strongly on concentration and temperature and can be generalized by a master curve. The refractive index increments for both systems are almost independent of temperature at high concentrations.
Crystallization in oriented poly(ethylene terephthalate) fibers. II. Consequences in subsequent deformation
Authors: Yoon K. J. , Desai P. , Abhiraman A. S.
Published: April 2003

When a melt‐spun poly(ethylene terephthalate) (PET) fiber is heat treated at a temperature above its glass transition temperature, the relative rates at which the crystallization and major orientational relaxation processes occur have been shown to have a pronounced effect on the structure of the fiber and its deformability. The present study describes the consequences of this aspect, with examples from drawing of melt‐spun PET fibers subsequent to their crystallization by thermal annealing. Additional features of the highly ordered PET fibers which can be produced through a combination of oriented crystallization and drawing at high temperatures are also given.
Fiber spinning from the nematic melt. I. Copolyester of poly(ethylene terephthalate) and p‐oxybenzoate
Authors: Muramatsu Hiromochi , Krigbaum W. R.
Published: April 2003

The Tennessee Eastman copolyester of poly(ethylene terephthalate) with 60 mol % p‐oxybenzoate units was spun with various capillaries using a constant shear rate at the wall. Variables examined were the length‐to‐diameter ratio L/D of the capillary, the spin draw ratio Vf/V0, and the spinning temperature. Fibers spun at 260°C showed improved homogeneity of orientation through the cross section, better crystallite orientation, and higher initial moduli as L/D was increased. The spin draw ratio required to optimize these fiber properties decreases as L/D is increased. For example, when L/D = 49.44, the initial modulus has nearly reached its plateau value at a spin draw ratio of 10. However, in contrast to the results of Sugiyama, Lewis, White, and Fellers, we find that some spin draw is always required to optimize fiber properties. Fibers spun with a spin draw ratio of approximately unity showed very poor crystallite orientation and initial moduli. It is suggested that loss of orientation under these conditions may be due to the different velocity profiles in the spinneret and in the solidifed fiber. Fibers were also spun at five temperatures using a capillary having L/D = 49.44. Shear in the capillary is more effective in introducing orientation when the spinning temperature is 260°C or above. At spinning temperatures of 240 and 250°C, the initial modulus increases more slowly with spin draw ratio, and appears to have a lower plateau value. Acierno, La Mantia, Polizzotti, Ciferri, and Valenti spun the same polymer under conditions in which essentially all the orientation was introduced by spin draw. They used a very low extrusion velocity at the spinneret, a small L/D, and spin draw ratios up to 3000. They reported that the initial modulus increased with decreasing spinning temperature, in contrast to our results. Thus the optimum spinning conditions may depend upon whether most of the orientation is introduced by shear in the capillary, or by a high spin draw ratio.
Electron trapping in low‐density polyethylene
Authors: Markiewicz A. , Fleming R. J.
Published: April 2003

Thermoluminescence (TL) emission from low‐density polyethylene has been investigated. The glow curves of gas‐free samples x‐irradiated at −190°C and heated to room temperature were found to contain three peaks numbered I, II, and III in order of increasing temperature, in agreement with earlier results. The sites of all traps are accessible to absorbed gases; in the presence of air, O2, N2 or Ar, “gas” traps are formed, resulting in the appearance of an additional peak IV in the glow curve at a temperature between peaks I and II, large reductions in the intensities of peaks II and III, and various changes in peak I. The peak I, II, and III traps are formed from particular chain configurations occurring in the chain‐fold regions of the samples, these configurations being broken up by different forms of molecular motion within the chains. It is unlikely that the peak IV traps are just the gas molecules themselves; they are probably formed from new chain configurations occurring in the amorphous regions of the samples in the presence of the gas, the properties of the gas influencing the associated TL intensity and emission temperature. These traps are also broken up by molecular motion. The samples can be divided into two main types, differing mainly in the height of peak I relative to peak II, which is of nearly constant intensity in all samples. We suggest that two types of trap which are not interconvertible are associated with peak I, and that the dominant type in a given sample depends on the fine details of the sample fabrication process.
Conformational reorganization viewed by the raman spectrum of aromatic polyesters
Authors: Kim Jong S. , Lewin Menachem , Bulkin Bernard J.
Published: April 2003

Analysis is made of the asymmetry of the carbonyl stretching vibration of poly(ethylene terephthalate) and poly(propylene terephthalate) as a function of annealing frrom amorphous to crystalline polymer. An apparently anomalous behavior of carbonyl band half‐width as a function of density for PPT is shown to be due to this asymmetry. The results are interpreted in terms of the conformational redistribution which occurs upon annealing.
Field‐induced dipole reorientation and piezoelectricity in heavily plasticized nylon 11 films
Authors: Scheinbeim J. I. , Mathur S. C. , Newman B. A.
Published: April 2003

Nylon 11 films with very low initial crystallinity were made by dissolving the nylon 11 in 2‐ethyl‐1,3‐hexanediol at 150°C. Films were cast from the solution and excessive plasticizer was removed in a vacuum oven. Films were then melt pressed and quenched to yield heavily plasticized nylon 11 films containing ca. 30% by weight of the plasticizer. These films were poled under vacuum to allow the plasticizer to evaporate in the presence of an electric field. A high piezoelectric response (d31 = 7.1 pC/N) was observed for the films subjected to the maximum electric field (Ep = 350 kV/cm) while the sample contained a large fraction of plasticizer. Significant development of crystallinity was observed without apparent indication of orientation of the crystallites. These studies suggest that the observed piezoelectric response originates primarily from oriented hydrogen bonds in the amorphous regions of nylon 11.
Light scattering by optically heterogeneous materials: Structural aspects of dichromatic laser speckle patterns
Authors: Holoubek Jaroslav , Lednický Frantis̆ek , Sedlàc̆ek Blahoslav , Mikeš Josef
Published: April 2003

An analysis is given of dichromatic speckle patterns formed by small‐angle scattered light in the illumination of optically heterogeneous systems with light of two nearby wavelengths. The existence of the radial‐fibrillar appearance of the speckle patterns is explained; it is shown that the occurrence of the radial‐fibrillar “structure” corresponds to the measurable correlation of dichromatic speckle patterns as specified by the spectral spatial cross‐correlation function of intensity fluctuations. A measurement of speckle‐pattern correlation to determine σz (the standard deviation of optical path fluctuations due to the passage of coherent light through a layer of heterogeneous material) is described, and the relations between σz and the structural parameters for two simple types of heterogeneous materials are discussed. Experimental results obtained with a series of samples of polyethylene filled with CaCO3 are in comparatively good agreement with theoretical values.
Temperature and time dependence of diffusion of PCL into PVC
Authors: Parker M. A. , Vesely D.
Published: April 2003

The phenomenon of diffusion between two joined polymers [poly(vinyl chloride) and poly(ε‐caprolactone)] has been investigated by light microscopy and electron microscopy of thin sections taken perpendicular to the interface. It has been established that the diffusion is unidirectional, i.e., PCL into PVC, and that the solubility is limited and increases with temperature. Chlorine x‐ray analysis has shown that the concentration profile consists of a sharp change at the PCL boundary and a gradual change at the diffusion front. The diffusion region morphology has been found to be inhomogeneous and reveals density fluctuations within the PVC matrix. The diffusion behavior is therefore different from the classical Fickian diffusion previously noted and can be well described by a sorption mechanism.
Tests of a “free‐volume” model of gas permeation through polymer membranes. II. Pure Ar, SF6, CF4, and C2H2F2 in polyethylene
Authors: Stern S. A. , Sampat S. R. , Kulkarni S. S.
Published: April 2003

Permeability coefficients for Ar, SF6, CF4, and C2H2F2 (1,1‐difluoroethylene) in polyethylene membranes were determined from steady‐state permeation rates at temperatures from 5 to 50°C, and at applied gas pressures of up to 15 atm. The temperature and pressure dependence of the permeability coefficients was represented satisfactorily by an extension of Fujita's free volume model of diffusion of small molecules in polymers. The parameters required by this model were determined from independent absorption (diffusivity) measurements with the above gases in polyethylene rods. The present work confirms the results of previous studies with CO2, CH4 C2H4 and C3H8 in polyethylene.
Theoretical study of sequence distributions in polydienes. IV. Experimental test
Authors: Wang Zhiyu , Yan Deyue , Wang Fusong
Published: April 2003

The effects of reaction time t, monomer conversion Y, and initial molar ratio of monomer to initiator M0/I0 on the microstructure of polybutadiene and polyisoprene generated by sec‐BuLi or sodium naphthalene were examined. The structural parameters determined by IR and NMR vary with t(Y) or M0/I0 monotropically and nonlinearly during the initial stage of the polymerization of dienes (or in the case of small monomer to initiator molar ratio), and then reach fixed values. The experimental data measured confirm the theoretical predictions for the unsteady stage after the beginning of the polymerization given in parts II and III of this series.
The temperature dependence of radiation sensitivity of large molecules
Authors: Kempner E. S. , Wood Robert , Salovey Ronald
Published: April 2003

The change in radiation sensitivity with temperature is quantitatively the same for biological macromolecules and synthetic polymers. The mechanism(s) for this effect is (are) due to secondary processes occurring after the primary ionization and are associated with the presence of free radicals.
The effect of surface treatment on the alignment and phase transition of a polypeptide liquid crystal
Authors: Hakemi H.
Published: April 2003

Poly(γ‐benzyl‐L‐glutamate) (PBLG), was utilized as a surface coating agent in order to obtain parallel molecular orientation in thin layers of PBLG liquid‐crystalline solutions confined between coated surfaces. It was found that in a thickness range much larger than the cholesteric pitch value, the texture was predominantly planar cholesteric. At film thickness comparable or smaller than the pitch, isotropic spherulites developed from a homeotropic nematic phase. Because of the coupling between the solution concentration and nematic director, as well as large differences in the elastic moduli of PBLG liquid‐crystalline solutions, the long‐range intermolecular interaction was unfavorable. Competition between parallel orientation induced by the surface coating of PBLG and inherent perpendicular orientation induced by PBLG molecules in the bulk would favor a short‐range helix‐coil transition mechanism, which results into a reentrant isotropic phase.
Analysis of trichroic infrared absorption in solids. II. One‐way drawn poly(ethylene terephthalate)
Authors: Fina L. J. , Koenig J. L.
Published: April 2003

The techniques of polarized infrared spectroscopy and sample tilting are applied to one‐way drawn poly(ethylene terephthalate) (PET) films to calculate the trichroic absorption as a function of frequency. Of specific interest in this study is the distribution of vibrational modes in the plane transverse to the draw direction. The rotational isomeric content of the films is found by the method of least squares and compared with a density‐method prediction of crystallinity. A two‐phase model to describe PET morphology in the oriented state is examined and found to be inadequate. The segmental orientation as a function of strain is followed with five conformationally sensitive infrared modes. High segmental orientation is found in the trans conformers of both amorphous and crystalline phases. Little net segmental orientation in the gauche conformers of the amorphous phase occurs.
Kinetics of fiber heat treatment. II. Poly(ethylene terephthalate) fibers
Authors: Peszkin Perla N. , Schultz J. M. , Lin J. S.
Published: April 2003

Microstructural changes occurring during the process of crystallization in as‐spun poly(ethylene terephthalate) (PET) have been monitored using wide‐ and small‐angle X‐ray scattering, optical birefringence, shrinkage measurements, and specific gravity.

Shrinkage and birefringence results show a competition between two processes: chain re‐coiling on the one hand and crystallization on the other hand. A consistent correlation among WAXS, SAXS, shrinkage, and birefringence results is demonstrated. SAXS data show a fibrillar morphology. On the basis of WAXS results, the crystallization is envisioned as a two stage process: first, the formation of defective fibrils, and then the formation of more perfect crystals. WAXS results also demonstrate a remelting phenomenon in samples which have experienced positive shrinking.
Dynamic light scattering of polystyrene single chains in a semidilute solution of poly(methyl methacrylate) and benzene
Authors: Numasawa N. , Hamada T. , Nose T.
Published: April 2003

Translational diffusion and internal motion have been observed by dynamic light scattering of optically labeled single chains of polystyrene (PS) in a semidilute solution of poly(methyl methacrylate) and benzene for the case in which the dimension Rg of the PS chain is comparable to the correlation length of the matrix solution. The molecular weight Mw dependence of the hydrodynamic radius Rh is expressed as Rh ∼ M, while Rh ∼ M in pure benzene. The average linewidth Γ for internal motions (KRg > 1) appears to depend on the magnitude K of the scattering vector approximately as Γ ∝ K4 at higher KRg ( > 1), in contrast with the fact that Γ ∝ K3 approximately for KRg > 1 in pure benzene. The scaling law for the K dependence of Γ does not hold in low‐molecular‐weight PS owing to the K dependence of Γ/K2 for KRg < 1.
Rheological behavior of thermotropic flexible main‐chain polyesters based on 4,4′‐dioxy‐2,2′‐dimethyl azoxybenzene mesogens. I. Oscillatory shear behavior
Authors: Blumstein A. , Thomas O. , Kumar S.
Published: April 2003

The rheological properties of fractionated thermotropic nematic polyesters 4,4′‐dioxy‐2,2′‐dimethyl azoxybenzenenonanediyl (n = 7) (AZA‐9) and dodecanediyl (n = 10) (DDA‐9)
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have been determined under oscillatory shear in the nematic and isotropic phase. A markedly more pronounced shear thinning characterizes the polydisperse DDA‐9 polymer as compared to the fractionated polymer in the nematic state. This difference becomes less pronounced in the isotropic phase. In all cases, the elastic compliance J′ in the isotropic state is much lower than in the nematic state. The values of relaxation time λ, although lower in the isotropic state, are not very different in the nematic state. The loss tangent tan δ is significantly higher in the isotropic phase for lower molecular weights. For molecular weights of 13,000 and above, this difference becomes smaller and shifts to lower angular frequencies. For AZA‐9 and DDA‐9, η→0 the limit of the dynamic viscosity can be represented by η* = M with a value of α similar for both phases and approximately equal to 4.
Drawing of ultrahigh‐molecular‐weight polyethylene single‐crystal mats: The crystallinity
Authors: Furuhata Kenichi , Yokokawa Takuya , Seoul Chang , Miyasaka Keizo
Published: April 2003

Single‐crystal mats of ultrahigh‐molecular‐weight polyethylene can be drawn uniformly to high draw ratios, more than 20χ at the highest, after the necking process is completed. The dynamic mechanical modulus of the drawn mats increases markedly during the uniform drawing stage. The structural changes induced by the uniform drawing at 100°C have been followed by wide‐angle and small‐angle x‐ray scattering, infrared absorption, differential scanning calorimetry, and birefringence. The crystallinity is estimated from the x‐ray amorphous scattering intensity, the IR absorbance of gauche bands, the heat of fusion from DSC, and the density. The estimated crystallinities of the drawn mats are all very high and increase slightly and monotonically with increased drawing after necking, though the values of the crystallinity depend on the method of estimation. IR gauche bands and the SAXS peak due to the long period disappear at a draw ratio of about 80χ. All the results suggest that the uniform drawing after necking destroys the two‐phase structure made up of alternately stacked crystalline and amorphous regions and then reorganizes it into a single‐phase crystalline structure.
Electron diffraction structure analysis of epitaxially crystallized n‐paraffins
Authors: Dorset Douglas L.
Published: April 2003

Electron diffraction data from a series of paraffins epitaxially crystallized on benzoic acid are used to determine their crystal structures. Even‐chain paraffins from n‐C32H66 to n‐C60H122 are shown to crystallize isostructurally as the orthorhombic polymorph described for n‐C36H74. Like the even‐chain compounds, odd‐chain paraffins do not crystallize in their lowest‐energy form. A quantitative zonal crystal structure analysis for n‐C33H74 suggests that the molecular packing is in the B‐polymorphic form proposed earlier by other workers.
Environmental stress cracking of low‐density polyethylene in normal alcohols
Authors: Ogata Nobuo , Yanagwa Teruaki , Yoshida Koukichi
Published: April 2003

Fracture mechanics was used to investigate the environmental stress cracking of low‐density polyethylene with 4.0 melt flow index. Annealed samples were prepared; a single edge notch was made and then the samples were fractured under constant load in four different liquid alcohols. The relation between the stress intensity factor K and the crack speed a˙ has been investigated. The log a˙ vs. logK curves are influenced not only by temperature but also by the alcohol used as the environment. This influence has been studied in detail. The conclusions are as follows: the crack speed at high K is determined by the diffusion mechanism, and this mechanism cannot be explained in terms of hydrodynamics but can be explained in terms of thermally activated molecular motion. On the other hand, the crack speed at low K is strongly related to the plasticization and the stress relaxation of the crack tip material.
Sorption of CO2, C2H4, N2O and their binary mixtures in poly(methyl methacrylate)
Authors: Sanders E. S. , Koros W. J.
Published: April 2003

Sorption of carbon dioxide, ethylene, and nitrous oxide in poly(methyl methacrylate) (PMMA) at 35°C has been characterized for each gas as a pure component and for mixtures of carbon dioxide/ethylene and carbon dioxide/nitrous oxide. Pressures up to 20 atm were examined. Pure‐component sorption isotherms are concave to the pressure axis for each of the gases. This behavior is accurately described by the dual‐mode sorption model. Using only the purecomponent dual‐mode parameters and the generalization of the model for gas mixtures, one can predict the total concentration of gas sorbed in the polymer to within an average deviation of ±2.01% for the CO2/C2H4/PMMA system and ±0.98% for the CO2/N2O/PMMA system. In both systems, for each component of the mixture, sorption levels were lower than corresponding pure‐component sorption levels at pressures equal to the partial pressure of the respective components in the mixture. Depression of the sorbed concentration in mixture situations appears to be a general feature of the above systems and can be substantial in some situations. For the CO2/C2H4/PMMA system, use of pure‐component sorption data to estimate the total sorbed concentration in the mixture would be in error by as much as 40% if one failed to account for competition phenomena responsible for depression in mixed‐gas situations. Mixture pressures as high as 20 atm were studied for both systems and in the CO2/N2O/PMMA system sorbed concentrations reach 33.90 [cm3(STP)/cm3 polymer] without any significant deviation from model predictions.
Mesogenic random copolymers. II. Copolymers with one flexible and two rigid segments
Authors: Watanabe Junji , Ikeda Kenichi , Krigbaum W. R.
Published: April 2003

We have investigated copolyesters based on a single aliphatic dibasic acid flexible segment and two rigid segments arising from 4,4′‐dihydroxybiphenyl (PB) and 2,6‐dihydroxynaphthalene (PN). Homopolyesters based on the latter rigid segment exhibit no enantiotropic mesophase for 5 ≤ n ≤ 8. The copolymers are designated PBN‐n where n is the number of methylene units in the dibasic acid. From the temperature–composition phase diagram, the odd‐membered PBN‐5 and PBN‐7 exhibit only a nematic phase. The temperature range of the nematic phase decreases progressively with increasing mole fraction of naphthalene units. The even‐membered PBN‐6 and PBN‐8 exhibit a smectic SH mesophase and a newly induced nematic phase. Comparison with a previous study of copolymers involving a single rigid segment and two flexible segments reveals that the smectic SH phase is more easily disrupted, and converted to a less ordered nematic phase, by different rigid segments than by different flexible segments. The isotropization entropy of a series of nematogenic equimolar copolymers exhibits a marked odd–even effect, with the observed ΔSNI values being quite large for the even‐membered copolymers.
Characterization and properties of polyethylene blends I. Linear low‐density polyethylene with high‐density polyethylene
Authors: Hu Shi‐Ru , Kyu Thein , Stein Richard S.
Published: April 2003

A blend system of linear low‐density polyethylene (LLDPE) (ethylene butene‐1 copolymer) with high‐density (linear) polyethylene (HDPE) is investigated by differential scanning calorimetry (DSC), wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), Raman longitudinal‐acoustic‐mode spectroscopy (LAM), and light scattering (LS). For slowly cooled or quenched samples, one single endotherm is evident in the DSC curve which depends on the composition. No separate peaks are observed in the WAXD, SAXS, Raman‐LAM, and LS studies on the LLDPE/HDPE blends. This observation along with the fact that no peak broadening is observed suggests that these peaks are associated with the presence of a single component. In no case did we see double peaks or a broadened peak that might be associated with two closely spaced unresolved peaks. This suggests that segregation has not taken place at the structural levels of crystalline, lamellar, and spherulitic textures. A single‐step drop in the scattered intensity (IHv) as a function of temperature is seen in the LS studies. It is therefore concluded that cocrystallization between the LLDPE and HDPE components occurs. The mechanical and optical α, β, and γ relaxations of these blends are explored by dynamic birefringence. The 50/50 blend displays the intermediate relaxation behavior between those of the components in all α, β, and γ regions. This observation is reminiscent of the characteristic of the typical miscible blends.
Characterization and properties of polyethylene blends II. Linear low‐density with conventional low‐density polyethylene
Authors: Kyu Thein , Hu Shi‐Ru , Stein Richard S.
Published: April 2003

Melting and crystallization phenomena in blends of a linear low‐density polyethylene (LLDPE) (ethylene butene‐1 copolymer) with a conventional low‐density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light‐scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.
Quantitative small‐angle light‐scattering studies of the melting and crystallization of LLDPE/LDPE blends
Authors: Ree Moonhor , Kyu Thein , Stein Richard S.
Published: April 2003

Small‐angle light‐scattering (SALS) patterns were obtained during melting and crystallization of blends of linear low‐density polyethylene (LLDPE) with conventional low‐density polyethylene (LDPE). Quantitative measurements of these SALS patterns using a two‐dimensional optical multichannel analyzer apparatus (OMA2) indicate that the LLDPE which is miscible with the LDPE component in the molten state crystallizes first, forming volume‐filling spherulites. The LDPE then crystallizes within the preformed spherulites. These findings are supported by optical microscopy studies showing that the blend samples were volume filled with one kind of the spherulites having a radius comparable to that of the pure LLDPE. The SALS intensity curve changes with composition of the blends in a manner that may be interpreted by considering the orientation of crystals within spherulites. It has been observed that the spherulites in the blend have more diffuse boundaries as the LDPE content increases. The lattice spacing and long spacings in blends were obtained by wide‐angle and small‐angle x‐ray scattering, respectively. The SALS technique along with differential scanning calorimetry (DSC) is shown to be useful for determining the crystallization behavior of a crystallizable polymer blend system.
Photophysical investigations of interpolymer interactions in solutions of a pyrene substituted poly(acrylic acid), poly(vinyl amine), poly(1‐aminoacrylic acid), and poly(1‐acetylaminoacrylic acid)
Authors: Arora Kartar S. , Turro Nicholas J.
Published: April 2003

Photophysical properties of the pyrene chromophore covalently bound to poly(acrylic acid) were used to investigate the interactions of a pyrene substituted poly(acrylic acid) (1) with poly(vinyl amine hydrochloride) (PVAm), poly(1‐aminoacrylic acid) (PDA), and poly(1‐acetylaminoacrylic acid) (PADA) in aqueous solutions. A number of photophysical parameters were obtained from fluorescence emission and excitation spectra, the deconvolution of decay curves for pyrene monomer, and excited state complex fluorescence and the quenching of pyrene monomer fluorescence by nitromethane in polymer solutions. These photophysical parameters were considered to reflect the inter‐ and intrapolymer interactions in solutions of 1, PVAm, PDA, and PADA. The formation of interpolymer complexes between 1 and PVAm was noticed at low (< 4) as well as high (> 8) values, whereas PDA and 1 formed interpolymer complexes at low pH only. No interpolymer complex formation was detected in solutions of 1 and PADA under low or high pH conditions. The structures of interpolymer complexes formed between 1 and PVAm under low and high pH conditions were found to be determined by the conformation of 1. There were significant differences in the interpolymer interactions of 1 and PDA in comparison to those of 1 and PVAm; in particular, the fluorescence from the excited state complex was enhanced in solutions of 1 and PVAm but quenched in solutions of 1 and PDA. The investigations of terpolymer solutions of 1, PVAm, and PADA indicated that the nature of interpolymer complexes formed in terpolymer solutions was determined by Coulombic interactions of the amino and carboxylic group containing polymers.
Synthesis and electrical and optoelectronic properties of poly[(N‐benzyldiphenylamino)methane]
Authors: Akhter Md. Aquil , Pramanik Panchanan , Biswas Mukul
Published: April 2003

Poly[(N‐benzyldiphenylamino)methane] was synthesized by the condensation polymerization of benzyldiphenylamine and formalin (30% HCOH in water) and examined for electrical and optoelectronic properties. Dark conductivity and photoconductivity of the polymer film were investigated by steady‐state measurements. Current‐voltage characteristics and intrinsic photoconduction of the polymer in the visible wavelength range were studied. A superlinear current increase is tentatively explained in the light of the Poole‐Frenkel effect. Dielectric constant and dielectric loss parameters of the polymer are independent of frequency (50 Hz–10 kHz) and temperature (273–323 K), respectively. The growth and decay rates of the photocurrent depend on the applied voltage, and the photocurrent varies directly with the light intensity. The activation energies for dark conductivity and photoconductivity are 1.16 eV and 1.05 eV, respectively, and the optical energy band gap as evaluated from absorption coefficient spectra is 2.86 eV.
A scaling analysis of the fracture mechanisms in glassy polymers
Authors: Evans K. E.
Published: April 2003

Recent experimental work on craze growth in polymers has shown that the reptation model for polymer motion may be successfully applied, in certain cases, to the behavior of glassy polymers in the solid phase. In this paper, a simple scaling analysis is presented to show how the primitive path model for reptation may be applied to the behavior of glassy polymers before and during slow crack growth. Different dynamic regimes are identified and related to the relaxation times of the polymer chain. The dependence on polymer chain length for each mechanism is described. Estimates for the fracture energy of each process are presented.
Miscibility and volume changes of mixing in the polystyrene/poly(2‐chlorostyrene) blend system
Authors: Tsujita Yoshiharu , Iwakiri Keiko , Kinoshita Takatoshi , Takizawa Akira , MacKnight William J.
Published: April 2003

The specific volume‐temperature relationships of polystyrene, poly(2‐chlorostyrene), and their polymer blends as well as the volume change of mixing Δvm of the blends were obtained in the liquid state by dilatometry. The equation of state parameter and the molecular parameter of each homopolymer and blends were determined according to the lattice fluid theory of Sanchez and Lacombe. The experimental Δvm obtained agreed quite well with that predicted from theory, and the enthalpy of mixing ΔHm was also predicted using the pair molecular parameter. These two values were negative, indicative of miscibility of polystyrene and poly(2‐chlorostyrene) in the liquid state. The absolute values of Δvm and ΔHm were about twice those for polystyrene and poly(phenylene oxide) blend, suggesting a specific interaction between the two polymers.
Small‐angle neutron scattering of a model crystallizable polymer: Crystallization and size‐mismatch effects
Authors: Crist B. , Tanzer J. D. , Graessley W. W.
Published: April 2003

Small‐angle neutron scattering (SANS) experiments have been conducted on mixtures of nearly monodisperse hydrogenated polybutadiene (HPB) and its deuterated counterpart (DPB) in molten and semicrystalline states. A direct comparison of scattering patterns from molten and quench‐crystallized samples shows unambiguously that chain conformation is unchanged by crystallization over large and intermediate size scales. The HPB's are shown to have slightly larger coil dimensions than linear polyethylenes of the same molecular weight. The scattering law for mixtures of different chain lengths was also investigated. Mismatched mixtures of monodisperse components give rise to scattering with an angle dependence well described by the Debye function for a Gaussian chain, even in the 50/50 composition range. This permits evaluation of SANS parameters [apparent radius gyration (Rg)e and apparent degree of polymerization Ne] by analysis of the full scattering curve, removing the restrictions that the Guinier condition (qRg < 1) be satisfied. The values of (Rg)e and Ne obtained from experiment are in good agreement with predictions of the scattering law for ideal mixtures.
Macromolecular order in spin‐oriented nylon 6 (polycaproamide) fibers
Authors: Salem D. R. , Moore R. A. F. , Weigmann H.‐D.
Published: April 2003

Wide‐angle x‐ray scattering (WAXS) has been used to characterize the ordered phases of spin‐oriented nylon 6 fibers wound at speeds ranging from 5000 to 8000 m/min. Quantitative analysis of the radial diffractometer scans by a computerized curve‐fitting procedure reveals that the unit‐cell geometry of both the α and γ crystalline morphologies are highly dependent on winding speed and on annealing conditions. At 800° m/min, there is a particularly large reduction in the intermolecular distance along the van der Waals forces of the α unit cell, which is accompanied by substantial crystal growth in the hydrogen‐bond direction. Similar increases in the width and perfection of the α crystals result from water annealing and steam treatment. The perfection of the γ crystals increases with winding speed and after annealing in water, but steam treatment increases the intermolecular distance along the hydrogen bonds while reducing it along the van der Waals forces. Using bulk density measurements and the experimentally determined crystalline density pc for each sample, the volume‐fraction crystallinity (VFC) is shown to pass through a maximum at ca. 6500 m/min. This maximum arises from a decrease in α crystallinity with increasing winding speed together with an increase in γ crystallinity, which levels off above ca. 7000 m/min. It is demonstrated that the determination of VFC assuming constants pc would lead to large errors. The orientation of the α crystals is found to be much less than that of the γ crystals, but it increases quite rapidly with winding speed. Water and steam treatments cause increases in α orientation and decreases in γ orientation.
Temperature and pressure dependence of the viscosities of perfluoropolyether fluids
Authors: Cantow M. J. R. , Barrall E. M. , Wolf B. A. , Geerissen H.
Published: April 2003

The viscosities of two structurally different perfluoropolyether fluids were determined at a series of temperatures and pressures, from 25 to 100°C and from 1 to 1000 bars. Flow activation energies and volumes as well as their temperature and pressure coefficients were derived. An attempt was made to relate measured and derived quantities to the compound structures.
Observation of single‐chain scattering from homopolymer blended with a triblock copolymer
Authors: Quan X. , Gancarz I. , Koberstein J. T. , Wignall G. D.
Published: April 2003

A small‐angle neutron scattering method has been developed to determine the chain conformation of homopolymer chains dispersed in a block copolymer matrix. Two contrast matching techniques are used to achieve this result and are demonstrated for a system based on a styrene‐hydrogenated butadiene‐styrene triblock copolymer and a hydrogenated butadiene homo‐polymer. Composition matching uses a blend of labeled and unlabeled molecules to match the scattering density of another component. Phase matching requires a block copolymer which has been synthesized such that the scattering densities of the blocks are equal. This polymer provides a transparent matrix in which a composition‐matched blend of homopolymer can be dispersed to isolate the single‐chain scattering function of the homopolymer chains.
Small‐ and intermediate‐angle neutron scattering from amorphous and semicrystalline polyethylene terephthalate
Authors: McAlea K. P. , Schultz J. M. , Gardner K. H. , Wignall G. D.
Published: April 2003

Small‐ and intermediate‐angle (0.006 < Q < 0.25 Å) neutron scattering experiments have been performed on polyethylene terephthalate (PET). Amorphous and semicrystalline samples with deuterated PET molecular weights of 24,200 and 40,500 were prepared. The average value of R/M determined in the small‐angle region for the amorphous samples is 0.406, in close agreement with the experimental θ‐solvent (0.398–0.420) and theoretical (0.394) values for unperturbed dimensions. The intermediate‐angle results for the amorphous sample are consistent with the random coil prediction to Q = 0.08 Å, but beyond this Q value there is some deviation from Gaussian behavior. The semicrystalline samples show a decrease in the radius of gyration as measured in the small‐angle region and an increase in intensity (when compared to the amorphous data) in the intermediate‐angle region, especially for the low‐molecular‐weight material. These results suggest that crystallization in PET is accompanied by greater molecular reorganization than has previously been observed in most bulk polymers.
Determination of the thermodynamic polymer‐polymer interaction parameter of miscible blends prepared from two crystalline polymers
Authors: Zhang Huanzhi , Prud'Homme Robert E.
Published: April 2003

The melting points of miscible blends prepared from two crystalline polymers, poly(caprolactone) (PCL), and Saran a random copolymer of vinylidene chloride with vinyl chloride [P(VCl2‐VC)], vinyl acetate [P(VCl2‐VA)], or acrylonitrile [P(VCl2‐AN)], have been measured by differential scanning calorimetry as a function of the crystallization temperature. The equilibrium melting points of these blends have been determined by Hoffman‐Weeks plots. From two series of data, one of which was obtained by measuring the melting points of PCL crystals and the other by measuring the melting points of Saran crystals, the thermodynamic polymer‐polymer interaction parameters of PCL/Saran blends have been calculated over the full range of composition. The two series of data merge into a smooth curve, which is composition dependent, despite the fact that the melting points of PCL and P(VCl2‐VC) or P(VCl2‐VA) are very different at 58.1, 183.5, and 184.2°C, respectively. Calculations using the “equation of state” Prigogine‐Flory thermodynamic theory indicate that the temperature dependence of the thermodynamic interaction parameter in typical polymer blends is small, which agrees with the experimental results.