bluuebunny/crossref_metadata_2025 huggingface dataset:
Steric effects on excimer formation in isotactic and atactic polystyrene and poly(ar‐methylstyrene)s in solution
Authors: Ishii Tadahiro , Handa Takashi , Matsunaga Satoru
Published: April 2003

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Coisotactic shift contributions caused by sterically crowded isotactic side‐chain alkyl groups are proposed for peak assignments of isotactic propylene/butene‐1 copolymers. Previously disputed analyses of methine triads and PB tetrads of backbone methylene carbons (α,α′‐CH2) have been verified using first‐order Markovian distribution theory. Coisotactic shift contributions also account for the reverse order of the propylene‐centered triads from that predicted by the Grant‐Paul equation.
Studies of orientation and structure of crazed matter in polystyrene. I. Optical measurements
Authors: Brown H. R.
Published: April 2003

The optical birefringence and refractive index have been measured for crazes grown in specimens of varying thickness. The birefringence was found to consist of the sum of a small negative orientation term and a large positive form term. The latter term could be altered by filling the craze with liquids of various different refractive indexes. Two crazes, which showed a relatively constant width as the specimen thickness changed, could be described by a model with craze having a constant refractive index and birefringence but with impervious dense skins on either side. The numerical value of the form birefringence was approximately 0.6 of that predicted from a model of parallel rods which is not surprising as crazes have a networklike structure. The values of craze refractive index were in good agreement with other measurements. The existence of skins, of thickness approximately 300 nm, places some doubt on the relevance of thin‐film electron microscope observations to the situation in the bulk. Other crazes which tapered in width were found to show both varying skin thickness and refractive index along their length.
Effects of extension on the gas permeability of hard elastic polypropylene film
Authors: Shimizu Y. , Akabane H. , Tanioka A. , Miyasaka K. , Ishikawa K.
Published: April 2003

Permeabilities of He, N2, O2, Ar, and CO2 in stretched hard‐elastic polypropylene film exhibiting extraordinarily high elasticity were measured as functions of temperature, pressure, and extension ratio. The permeability decreases slightly for strains of 10% or less, increases abruptly for strains from 15% to 30%, and then increases gradually for strains up to 100%. In recovery from extension, changes in permeability are similar to those in extension. The gas permeation mechanism is of the solution‐diffusion type for extensions less than 15%. Above 15% extension, the mechanism involves permeation through voids created during deformation. The apparent mean pore size, estimated from the gas permeation, is very large at comparatively small extensions, and decreases with increasing extension. The change in specific volume accompanying extension of the sample indicates that only a very small fraction of the voids are interconnected to form channels that traverse the thickness of the film.
Determination of crystallinity of swollen poly(vinyl alcohol) by laser Raman spectroscopy
Authors: Iwamoto Reikichi , Miya Masaru , Mima Seiichi
Published: April 2003

Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm−1, while a crystalline Raman band is found at 1147 cm−1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water‐swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.
Thermal properties of polyamides containing 1,3–cyclohexane rings
Authors: Inoue Kazuo , Hoshino Sadao
Published: April 2003

The effect of the 1,3–cyclohexane rings in the chain backbone on thermal properties of polyamides, especially the glass‐transition temperature, has been studied using polyamides based on 1,3–cyclohexanebis(methylamine). The increase in glass‐transition temperature was far greater than that obtained with the analogous polymers containing m–benzene rings. However, the effects of 1,4–cyclohexane and p‐benzene rings are nearly equal. Several possible causes for this difference are examined. It is concluded that restricted chain mobility due to steric hindrance of the cis‐1,3–cyclohexane ring, the predominant isomer, is the most likely cause of the difference.
Optical rotatory dispersion and vacuum ultraviolet circular dichroism of poly[(R)‐oxypropylene]
Authors: Hirano Tsuneo , Sato Akira , Tsuruta Teiji , Johnson W. Curtis
Published: April 2003

The circular dichroism (CD) spectrum of poly[(R)‐oxypropylene] in a number of solvents has been measured in the vacuum ultraviolet region. Two CD bands were measured for cyclohexane, acetonitrile, and trifluoroethanol solutions. The CD spectrum was extended to 140 nm and three bands were measured in a 1,1,1,3,3,3‐hexafluoro‐2‐propanol solution. The similarity of these four CD spectra in sign, shape, and intensity confirm that poly[(R)‐oxypropylene] has similar conformations in all solvents studied, even though the optical rotatory dispersion (ORD) in the visible region is positive for the cyclohexane solution but negative for the alcohol solutions. A Kronig–Kramers transform of the two CD bands observed for the cyclohexane solution accounts for the observed positive ORD spectrum. In contrast, a third large and negative CD band centered below 160 nm is necessary to account for the negative ORD spectra observed for the alcohol solutions. Apparently the anomalous sign variation of the ORD curves observed in the visible region is due to subtle changes in the interplay of a large number of CD bands. Solvent interaction, observed as a blue shift of the first two CD bands for the alcohol solutions, could produce the subtle changes necessary to change the sign of the ORD curve in the visible region. The first two CD bands of poly[(R)‐oxypropylene] are tentatively assigned as nσ* and the third as an n3s.
Dielectric evidence for thermal creation of defects in polyethylene crystals
Authors: Boyd Richard H. , Sayre John A.
Published: April 2003

A recent study of the effect of pressure on the dielectric α process in slightly oxidized linear polyethylene showed that the intensity of the process decreases with increasing temperature. This phenomenon was attributed to thermal generation of conformational defects. In the present work a quantitative interpretation of that data is carried out to arrive at defect creation energy parameters. It is found that the creation energy lies in the range of 3–6 kcal/mole and that it has a high degeneracy or statistical weight (in the range 40–800). The statistical weight is interpreted as largely arising from the number of sites in a given crystalline chain for a defect to occur, that is, the number of CH2 units spanning the crystal. It is speculated that kinks are the likely conformational defect.
Oriented polymers from solution. I. A novel method for producing polyethylene films
Authors: Coombes A. , Keller A.
Published: April 2003

A novel method for the production of uniaxially oriented polyethylene film is demonstrated, it being an extension of the “surface growth” method for obtaining polyethylene fibers from solution using a Couette apparatus. The film growth is found to be affected by temperature, rotor speed, rotor material, and surface roughness. Together with its possible practical importance, film growth is presented as a useful means of sample preparation and as a way to increased linear fiber growth rates. In addition, its use for studies on solution grown polypropylene fibers is indicated as well as its implications for “surface growth” of polymer crystals in general.
Total integrated light‐scattering intensity from polymeric solids
Authors: Koberstein J. , Russell T. P. , Stein R. S.
Published: April 2003

Presently existing theories of small‐angle light scattering by polymeric materials are extended by consideration of the total integrated scattering intensity. It is shown how this quantity, known as the total integral or Porod invariant in small‐angle x‐ray scattering, may be used to calculate the average square of the fluctuations in refractive index and orientation. Calculations are presented using both statistical and model approaches.
Molecular architecture and physicochemical properties of some vinyl alcohol‐vinyl acetate copolymers
Authors: Scholtens B. J. R. , Bijsterbosch B. H.
Published: April 2003

Two series of vinyl alcohol‐vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer‐solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1‐butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1‐butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.
Viscosity of poly(vinyl acetate) and its concentrated solutions
Authors: Berry G. C. , Nakayasu H. , Fox T. G.
Published: April 2003

Data on the viscosity of poly(vinyl acetate) (PVOAc) and its concentrated solutions in diethyl phthalate (DEP) and cetyl alcohol (CeOH) are examined over the molecular weight range 8 × 103 < M < 1.3 × 106, the range 0.15 < φ < 1.0 of the volume fraction φ of polymer, the temperature range 308 to 430°K for PVOAc and its solutions in DEP, and at 396°K in CeOH. The latter is the θ temperature for dilute solutions of PVOAc in CeOH. The data are analyzed with the relation η = KXc(αφM/Mc)a exp[1/β(T – T0)], where a is 1 or 3.4 for αφM less than or greater than a constant Mc, respectively, and XC, is a constant. The expansion factor αφ of the chain dimension is found to be essentially unity for φ > ca. 0.25, increasing with decreasing φ for smaller φ. Both β and T0 depend on φ, and T0 also depends on M at low M.
Relationship of stress to uniaxial strain in crosslinked poly(dimethylsiloxane) over the full range from large compressions to high elongations
Authors: Pak Hyungsuk , Flory Paul J.
Published: April 2003

Experiments on inflated sheets of crosslinked poly(dimethylsiloxane) covering a sixfold range of compression are combined with measurements in elongation conducted on specimens from the same sample to obtain the relationship of stress to strain over a 24‐fold range in the extension ratio λ1. With increase in λ the reduced force [f] ≡ f(λ1 – λ)−1 rises to a maximum near λ = 1.2–1.4, then decreases very slowly with further increase in λ. The form of the relationship of [f] to λ confirms recent theory.
Entanglement networks of 1,2‐polybutadiene crosslinked in states of strain. VII. Stress‐birefringence relations
Authors: Carpenter Rick L. , Ferry John D.
Published: April 2003

Crosslinks are introduced by γ irradiation into 1,2‐polybutadiene while strained in uniaxial extension near Tg with stretch ratio λ0, thereby trapping a proportion of the entanglements originally present. The stress at any subsequent strain λ is accurately given by the sum σN + σx, where σN is the stress contributed by a trapped entanglement network with λ = 1 as reference and a Mooney–Rivlin stress‐strain relation, and σx is that contributed by a crosslink network with λ = λ0 as reference and neo‐Hookean stress‐strain relation. The birefringence is accurately given as δn = ℯNσN + ℯxσx, where the ℯ's are the respective stress‐optical coefficients. From measurements at λ = λ0 where σx = 0, ℯN can be determined separately. For polymer with 88% 1,2 microstructure, ℯN and ℯx are nearly equal and independent of irradiation dose, though strongly dependent on temperature. For polymer with (95–96)% 1,2, ℯN and ℯx are different (even opposite in sign) and dependent on dose. This behavior is associated with a side reaction of cyclization by the γ irradiation, which is inhibited by the 1,4 moiety in the polymer with lesser 1,2 content. It is responsible for residual birefringence in the state of ease (λ = λs) where σN = –σx and the stress is zero.
Bulk properties of synthetic polymer‐inorganic salt systems. V. Mechanical properties of oriented poly(caproamide)
Authors: Acierno D. , La Mantia F. P. , Polizzotti G. , Ciferri A.
Published: April 2003

Single filaments of nylon‐6 and of its mixtures with KCl, LiCl, and LiBr (salt content up to 5% w/w) were prepared by extrusion at 265°C. As‐spun filaments with a varying degree of orientation were obtained by altering the take‐up velocity a t constant outflow velocity. These as‐spun filaments were further subjected to controlled thermal and mechanical treatments. Determinations of the elastic modulus, of birefringence, of wide‐angle x‐ray scattering, and of shrinkage were carried out for the as‐spun and for the treated filaments. While KCl caused no detectable alteration of the properties of nylon‐6, lithium halides caused a considerable increase of the elastic modulus of the polymer. Under the conditions adopted, moduli up to 14 GPa were obtained. The birefringence of as‐spun fibers was, however, lower when lithium salt was present. Greater shrinkage a t 170°C was exhibited by the salted than by the pure polymer. The body of results has been interpreted in terms of a more efficient orientation of the extruded polymer when lithium salt is present. The latter effect is associated with the role of these salts in reducing the crystallization rate and in increasing the melt viscosity of the polyamide as characterized in preceding papers of this series. Lithium salts also favor the α → γ transformation between the two crystalline forms of nylon‐6. The transformation was, however, reversed under sufficiently high applied stress.
Oriented polymers from solution. II. Fibers and films of polyethylene/polypropylene blends
Authors: Coombes A. , Cannon C. G. , Keller A.
Published: April 2003

A version of the surface growth method by Zwijnenburg and Pennings is being used to produce blended fibers of polyethylene and polypropylene under conditions where polypropylene does not yield to this fiber growth technique but would grow films. The blended fiber contains intimately mixed crystalline regions of each pure component and combines thermal and mechanical properties of both. The growth method itself underlines the part played by adsorbed surface layers and entanglements within such layers which can involve the entanglement of chemically different species. This feature suggests a potentially new method for blend production.
Molecular characterization and glassy‐state properties of poly(spiro[2,4]hepta‐4,6‐diene)
Authors: Hayashi Seiji , Ikuma Sadao , Okuyama Kenji , Kajiyama Tisato , Takayanagi Motowo
Published: April 2003

Poly(spiro[2,4]hepta‐4,6‐diene) (PSHD) is a random copolymer composed of 1,2 and 1,4 units. Although PSHD has been reported to have a very large Sakurada–Mark–Houwink exponent (a = 1.71) characteristic of rigid rods, a new determination of the intrinsic viscosity–molecular‐weight relation for fractionated samples with known copolymer composition gives a smaller value (0.81). The rigidity of the PSHD molecule was also investigated by calculations of the conformational energy associated with the main chain and the dynamic viscoelasticity associated with the molecular motion in a solid state. A sharp potential energy minimum occurs at a dihedral angle χ1 = 260° in polymer composed of all trans 1,4 units. The dynamic loss tangent for the primary absorption decreases with increasing fraction of the 1,4 unit. These properties result from the characteristics of the stiff 1,4 unit sequences in the molecular chain. The density of PSHD decreases with increasing content of 1,4 units and was found to be considerably smaller than values for typical polymers, in relation to the occupied volume of the repeat unit. This fact can be explained by the peculiar aggregation state of molecular chains composed of rigid and flexible units.
Second virial coefficients of homopolymers and copolymers of butadiene and styrene in tetrahydrofuran
Authors: Stacy C. J. , Kraus Gerard
Published: April 2003

Second virial coefficients have been measured in tetrahydrofuran for a series of anionically polymerized narrow distribution homopolymers and copolymers of butadiene and styrene. The results fit the general empirical equation A2 = M−1/4(0.0216wB + 0.00995wS + CwBwS), where M is the polymer molecular weight, wB and ws are the weight fractions of butadiene and styrene, and C is a constant which is zero for block polymers and equal to 7.9 × 10—3 for random copolymers. The equation is independent of the degree of 1,2 addition of butadiene and fits data on both linear and tetrachain star‐branched polymers within experimental error.
Cellulose acetate butyrate in solution. I. Hydrodynamic behavior
Authors: Vyas N. G. , Shashikant S. , Patel C. K. , Patel R. D.
Published: April 2003

Cellulose acetate butyrate has been studied in regard to its hydrodynamic properties in several solvents. The polymer was fractionated by precipitation, and the molecular weight distribution of the polymer fractions was determined by gel permeation chromatography. The number‐average molecular weight was estimated by osmometry. The Mark–Houwink–Kuhn–Sakurada relations between viscosity and molecular weights were established, and the unperturbed dimensions of the polymer chains were evaluated. In light of these data, current theories of polymer solutions are discussed. A new method of estimating unperturbed dimensions is proposed for semiflexible linear polymers.
A calorimetric study of acrylate photopolymerization
Authors: Tryson G. R. , Shultz A. R.
Published: April 2003

The kinetics of the photoinitiated polymerization of lauryl acrylate (LA), 1,6‐hexanedioldiacrylate (HDDA) and pentaerythritol tetraacrylate (PET4A) have been investigated using differential scanning calorimetry (DSC). An autoacceleration phenomenon is observed with the multifunctional acrylates, but not with lauryl acrylate. The empirical dependences of reaction rate on such parameters as incident light intensity, initiator concentration, and temperature have been established and are in general found to vary with monomer conversion. Apparent activation energies for the photopolymerizations have been determined from rate versus temperature data. The multifunctional acrylates show an increasing activation energy with monomer conversion, whereas the apparent activation energy for lauryl acrylate not only decreases with conversion, but becomes negative at conversions greater than about 30%. The ratio kp/k is calculated from rate versus conversion data under constant illumination and the (independently determined) initiation rate. Analysis of rate versus time data under nonsteady‐state conditions (light turned off) yields the ratio kt/kp. With these two ratios the rate constants for propagation (kp) and termination (kt) may be separated and their respective values calculated. Both kp and kt are found to decrease substantially with monomer conversion, indicating a significant change in the rates of both the propagation and termination steps as the polymerization advances. These observations are explained in terms of a radical isolation phenomenon and diffusion control of the propagation step.
Light scattering study of an aromatic polyamide‐hydrazide polymer
Authors: Bianchi E. , Ciferri A. , Tealdi A. , Krigbaum W. R.
Published: April 2003

The aromatic Polyamide‐hydrazide, Monsanto X‐500, has been studied by light scattering in dimethyl sulfoxide, a thermodynamically good solvent. The unperturbed dimensions, (〈r〉av/M)1/2 = 1.93 × 10−8 at 25°C., indicate a rather highly extended chain. The persistence length falls in the range 35–63 Å, which corresponds to a length of between two and four formula units. This is considerably smaller than the values which have been reported for the aromatic polyamides, poly(p‐benzamide) and poly(p‐phenylene terephthalamide). X‐500 appears to approximate coil‐like behavior at a molecular weight of 45,000. Theoretical predictions, based upon the 〈r〉av/bL ratio, are compared with the observation that no evidence for an anisotropic phase has been found in X‐500 solutions in dimethyl sulfoxide at polymer volume ranging from 0.12 to 0.19 (depending upon the concentration of added LiCl).
Intrinsic viscosity of polystyrene
Authors: Einaga Y. , Miyaki Y. , Fujita H.
Published: April 2003

Zero‐shear‐rate intrinsic viscosities [η]0 in benzene at 25°C and in cyclohexane at 34.5°C were measured for two series of polystyrene samples: six fractions ranging in Mw(weight‐average molecular weight) from 8.8 × 106 to 5.7 × 107 and 11 “monodisperse” samples ranging in Mw from 4 × 103 to 4.8 × 106. The results, combined with typical literature data, yielded

These relations cover the broadest range of molecular weights reported so far in the literature on synthetic polymers. In contrast to Slagowski et al., we observe no “anomaly” in the molecular weight dependence of [η]0 for benzene solutions of very high molecular weight samples (>107).
Melting and crystallization of a polyphosphate
Authors: Benkhoucha Rachid , Wunderlich Caryn C. , Wunderlich Bernhard
Published: April 2003

Lithium polyphosphate crystals produced by crystallization during polymerization and crystallization from the polymer melt were analyzed by thermal analysis. The glass‐transition and melting temperature, heat of fusion, and entropy of fusion were found to be 336°C, 651.5°C, 21 kJ/mole, and 23 J/deg mole, respectively. Crystallization from the macromolecular melt was followed by thermal analysis, x‐ray diffraction, and electron and optical microscopy. It could be shown that chain folding may be the first step to crystallization from the macromolecular melt. Oligomers could not effectively nucleate crystallization. Lithium polyphosphate is shown to present a prime example of the processes involved in crystallization during polymerization and macromolecular melt crystallization.
Theory of the instability and failure of viscoelastic materials in tension
Authors: Coleman Bernard D. , Zapas Louis J.
Published: April 2003

In a tensile test of a bar or fiber formed from a transversely isotropic viscoelastic material, the initial motion in regions away from the clamps is a homogeneous uniaxial extension. If the applied tensile load is “tame” in the sense that it is given by a piecewise smooth function of time, then during the early stages of loading, the homogeneous extension of the specimen is also tame. It is, however, often the case that at a time tc, previous to the instant of fracture, the motion departs from a tame homogeneous extension. The critical time tc is the “failure time” of the specimen, i.e., the time at which the motion first changes character; tc precedes, often by a constant factor, the time at which neck‐down is easily visible. The problem of calculating tc for a given loading program is here treated within the framework of the general theory of nonlinear simple materials with fading memory. For such materials the instantaneous tensile modulus, i.e., the derivative of the immediate change in tensile stress with respect to a sudden change in tensile strain, depends upon the previous history of the strain. Reasons are presented here for identifying tc with the earliest time t0 at which the instantaneous tensile modulus becomes zero. It is shown that at a time at which the instantaneous modulus vanishes one cannot arbitrarily assign the rate of change of tensile stress and have the motion remain in the class of tame homogeneous extensions.
Some phenomenological consequences of the Doi–Edwards theory of viscoelasticity
Authors: Graessley William W.
Published: April 2003

Doi and Edwards have recently proposed a molecular theory for the dynamics of entangled polymer liquids based on a tube model to represent the mutual constraints on configurational rearrangement of the chains. Expressions for diffusion coefficient, plateau modulus, zero‐shear viscosity, steady‐state recoverable compliance, and terminal relaxation time can be devloped, and relations among these properties that depend only upon observable quantities can be obtained. Several such relations are derived and are compared with experimental observations.
Particle structure of suspension poly(vinyl chloride) and its origin in the polymerization process
Authors: Davidson J. A. , Witenhafer D. E.
Published: April 2003

The initial stage of the suspension polymerization of poly(vinyl chloride) (PVC) is characterized by the formation of colloidally stable micron‐sized grains of PVC inside the polymerizing ca. 150 μm vinyl chloride droplets. The fate of these micron‐sized PVC grains depends upon the agitation conditions. If no agitation is employed, they serve as growth centers for further polymerization to give a final particle possessing a uniform internal bead morphology. In agitated systems, these grains coagulate early in the conversion to give a more irregular structure in the interior of the PVC particle. The formation of these stable growth centers appears to be unique to PVC. The polymerization of acrylonitrile, also insoluble in its monomer, is characterized by rapid agglomeration of the precipitated polymer throughout the polymerization. In PVC, the colloidal stability of the polymerizing grains is demonstrated to be electrical in nature. A pericellular membrane or skin formed by polymerization in both the water and vinyl phase completely surrounds the polymerizing droplet after about (1–2)% conversion. This skin is responsible for the charge retention of the PVC grains inside the polymerizing monomer droplets.
Conformation of polystyrene with special emphasis to the near all‐trans extended‐chain model relevant in polystyrene gels
Authors: Atkins E. D. T. , Isaac D. H. , Keller A.
Published: April 2003

In light of novel and problematic diffraction patterns arising through the thermoreversible gelation of isotactic polystyrene, the conformational possibilities were examined with particular reference to other conformational works published recently on this polymer. The specific objective was to ascertain whether highly extended, helical backbone geometries such as are required by the new x‐ray patterns are possible or not with a purely isotactic arrangement of side groups. The first realization was that the recently announced low‐energy, near‐trans conformations are not relevant to the present issue as they do not provide the required extended geometry. Further, specific sampling of the conformational energy map revealed that the required high chain extension may be energetically feasible, contrary to traditional conceptions and to recent conformational calculations elsewhere. The divergences as regards the latter were traced to the specific choice of nonbonded atomic radii—all within generally accepted limits—which accordingly has a crucial effect even to the extent whether specific conformation types are forbidden or energetically stable. The implications this has for conformational analysis in general are being pointed out. While the novel crystal structure has not been solved, the present study at least eliminates the previously believed categoric objections to it being associated with isotactic chains and, beyond this, opens up new perspectives as regards conformational possibilities in polyolefins. The more general problems concerning the nature and origin of the gelation phenomenon nevertheless remain.
Small‐angle light scattering from thin polymer films: Multiple scattering from Debye–Bueche scatterers
Authors: Koberstein Jeffrey T. , Stein Richard S.
Published: April 2003

An extension of Hartel's theory for multiple scattering has been applied to the case of small‐angle light scattering from polymer films with random two‐phase morphology. The scattering is treated in terms of Debye–Bueche theory from which values of the correlation length, an average phase size, and mean‐square fluctuation in polarizability are determined. It is shown that multiple scattering leads to a reduction in the angular dependence of scattering due to an enhancement of scattering at high angles. This leads to an underestimate of the correlation length and an overestimate of the magnitude of the mean‐square polarizability fluctuation.
Small‐angle x‐ray scattering studies of melting
Authors: Schultz J. M. , Fischer E. W. , Schaumburg O. , Zachmann H. A.
Published: April 2003

The course of melting of melt‐crystallized polyethylene fractions and of a poly(ethylene oxide)‐polystyrene‐poly(ethylene oxide) triblock copolymer has been followed by small‐angle x‐ray scattering (SAXS). Changes in the intensity and shape of the SAXS curves indicated that both surface melting and melting over the full crystallite thickness (full‐strand melting) take place. Full strand melting is the final, irreversible process. Comparison with an analytical model indicates that in the earlier stages of the irreversible, full‐strand process the crystallites melt out randomly throughout the bulk. Later stages may occur by the simultaneous melting of a larger stack of crystallites.