bluuebunny/crossref_metadata_2025 huggingface dataset:
Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). IV. Influence of solvent type
Authors: Buter R. , Tan Y. Y. , Challa G.
Published: April 2003

Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C or 35°C in various solvents in the presence of stereoregular poly(methyl methacrylate) (PMMA). The occurrence of stereospecific replica polymerization appeared to be related to the capability of stereoassociation of isotactic and syndiotactic PMMA. The solvents can be roughly divided into three types. Type A solvents are polar solvents, which promote stereoassociation resulting in gelation and precipitation. Examples are dimethylformamide, dimethyl sulfoxide, and acetone. Type B solvents are nonpolar aromatic solvents like benzene and toluene, wherein stereoassociation is weaker but still leads to gelation. Type C solvents are very good solvents, in which stereoassociation does not occur. Chloroform and dichloromethane belong to this class. In solvents of type A as well as type B, polymerization in the presence of i‐PMMA as a polymer matrix was syndiospecific. However, in the presence of s‐PMMA as a polymer matrix the polymerization was isospecific only in type A solvents. The syndiotactic or isotactic triad contents of the polymer formed could be as high as ca. 90% at low conversions. In solvents of type C, polymerization in the presence of stereoregular PMMA proceeds according to a normal radical mechanism. Syndiotacticity was always less than 70%. Stereocomplexes formed in situ during replica polymerization were partly crystalline as detected by x‐ray diffraction. The highest crystallinity was detected in those formed in type A solvents.
γ‐Radiolysis of ketone polymers. I. Studies of symmetrical aliphatic ketones as model compounds
Authors: Slivinskas J. A. , Guillet J. E.
Published: April 2003

γ‐Radiolysis of model ketones of the general structure R(CO)R, neat and in hydrocarbon solution, show that the radio‐chemical degradation of these aliphatic ketones can be explained by mechanisms analogous to those generally accepted for the photochemical decompositions of the same compounds. The G (type I) and G (type II) yields are found to decrease with increasing total chain length of the ketone as monitored by the products (RH) and (CH3COR), respectively. Differences in the relative yields of type I and II products are attributed to the higher incident energies involved in γ‐radiolysis as compared to ultraviolet photolysis. Evidence is presented for energy transfer from paraffinic solvents to aliphatic ketonic solutes. Solid‐ and condensed‐phase studies show the importance of rotational and diffusional mobility to the yields of the type II and I processes, respectively.
Organoaluminum–cyclic ether‐cyclic imide catalysts for the polymerization of epoxides
Authors: Masuda Yasushi , Hani Hiroshi
Published: April 2003

A catalyst for the polymerization of epoxides consisting of trialkylaluminums, cyclic ethers, and cyclic imides has been investigated. Various catalyst components were examined to reveal that the combination of triisobutylaluminum, dioxane, and succinimide gives the most active catalyst. The catalytic activity is greatly enhanced with aging in which the change in color from pale yellow to dark red takes place. The polymerization data show that the dioxane provides a pathway for the catalyst components to form an active species. The dioxane‐containing catalyst is likely to be different in structure from that of the dioxane‐free catalyst. It was shown that the catalyst solution is electrically conductive. A parallel correlation seems to exist between the electrical conductivity and the catalytic activity, suggesting that the catalytic species may be of an ionic character.
NMR analysis of Ti(NEt2)4–AlMe3 catalyst system and its polymerization activity
Authors: Koide Naoyuki , Iimura Kazuyoshi , Takeda Masatami
Published: April 2003

Studies have been made by NMR and ESR spectroscopy to elucidate the reaction mechanism in which the Ti(NEt2)4–AlMe3 catalyst system is involved. The two reaction products of Ti(NEt2)3Me and Al(NEt2)Me2 have been confirmed by NMR spectroscopy when Ti(NEt2)4 is reacted with AlMe3, and two kinds of paramagnetic species have been noted by ESR spectroscopy. It has been found that Ti(NEt2)3Me plays an important role as an active species for the polymerization of styrene.
Radiation‐induced grafting in the polyethylene–styrene system and differential thermal analysis of the grafted samples
Authors: Imai Masahiko , Shimizu Harumichi
Published: April 2003

The graft polymerization of styrene onto high‐density polyethylene films was carried out by γ‐irradiation in the vapor phase. Two methods were used for grafting in these experiments: a preirradiation method and a simultaneous irradiation method. The effects of these grafting methods on the reaction mechanism of grafting and on the properties of the grafted samples were investigated. The amounts of styrene homopolymer in the grafted samples is under 2% in the case of the preirradiation method and above 10% in the case of the simultaneous irradiation method. The activation energies were calculated to be 18 kcal/mole for grafting in the preirradiation method and 15 kcal/mole for weight increase of polyethylene films in styrene vapor. The difference in the dimensional expansion between in the direction of stretching and the direction prependicular to it is smaller with preirradiation grafting than with grafting by the simultaneous irradiation method. Differential thermal analysis of the grafted films shows an endothermic peak due thermal decomposition which decreases gradually from 450°C to 415°C with increase in degree of grafting from 30 to 60%. The lowering of this peak temperature appears at a lower degree of grafting when the preirradiation method is used. On the basis of these results, it is concluded that the reaction rate of radiation‐induced grafting in the vapor phase depends closely upon the processes of adsorption, dissolution, and diffusion of styrene monomer in polyethylene films; in the case of simultaneous irradiation method, the reaction proceeds comparatively uniformly in the amorphous region, while in the case of the preirradiation method, the reaction proceeds mainly at the boundary of the crystalline and amorphous regions.
Analyses of synthetic resins by application of 13C NMR
Authors: Mukoyama Y. , Tanno T. , Yokokawa H. , Fleming J.
Published: April 2003

In a study of synthetic resin analysis, 13C NMR spectra of phenol resins were measured, and the chemical shifts of the various carbon sites compared with the resins' reactivity with formaldehyde. Measurements were made with phenol, para‐substituted phenols, chlorophenols, hydroxytoluenes, dimethyl(hydroxy)benzenes, dihydroxybenzenes, and dihydroxytoluenes. The chemical shifts of these phenols were compared with calculated shifts obtained by using a simple summing rule. These chemical shifts are closely related in magnitude to the reactivity of the phenols with formaldehyde. For example, resorcin has the greatest reactivity with formaldehyde of the above‐mentioned phenols and this experimental result agrees well with the measured large 13C chemical shifts for resorcin.
Electron spin resonance studies of propagating radicals in polymerization. I. Methacrylate propagating radicals
Authors: Harris James A. , Hinojosa Oscar , Arthur Jett C.
Published: April 2003

Ferric chloride‐photosensitized free‐radical initiation was used to generate propagating radicals in polymerization of methacrylic acid (MAA), allyl methacrylate (AMA), methyl methacrylate (MMA), 1,3‐butylene dimethacrylate (1,3‐BDMA), hydroxypropyl methacrylate (HPMA), lauryl methacrylate (LMA), hexyl methacrylate (HMA), and methacrylamide (MA) in rigid glasses of methanol or acetone at near liquid nitrogen temperatures. The formation and conformational changes of these propagating radicals at different temperatures were studied by electron spin resonance (ESR) spectroscopy. When methanol was the rigid glass, ·CH2OH radicals were formed initially and were stable below −160°C. As the temperature of the rigid glass was increased, the ·CH2OH radicals reacted with monomer to yield propagating radicals. With the exception of the propagating radical for methacrylamide, the propagating radicals of the methacrylates examined initially generated five‐line ESR spectra which gradually changed to nine‐line spectra, as temperature of the rigid glass was increased. It was concluded that one type of propagating radical was formed in all cases. However, when the temperature of the rigid glass was increased, the single structural conformation that initially allowed one of the methylene hydrogens and methyl group to interact with the unpaired electron to generate only a five‐line spectrum was changed to yield a second conformation that allowed interaction to generate an additional four‐line spectrum. Finally, a mixture of the propagating radical for methacrylate monomer in two structural conformations was obtained, and an ESR spectrum consisting of nine lines (5 + 4 lines) was generated. In the case of the propagating radical for methacrylamide this change to yield two structural conformations evidently was hindered, so that only an ESR spectrum consisting of five lines was generated.
Solution properties and unperturbed dimensions of poly‐p‐fluorostyrene and poly‐m‐fluorostyrene
Authors: Matsuo K. , Stockmayer W. H.
Published: April 2003

Molecular weights and solution viscosities are reported for unfractionated free‐radical polymers of m‐fluorostyrene and p‐fluorostyrene in several solvents. The estimated unperturbed dimensions lead to characteristic ratios C∞ at 25°C of 12.2 ± 0.5 and 11.6 ± 0.4 for the meta and para polymers, respectively. These are similar in magnitude to those of other polystyrenes.
Cyclization equilibrium constants and the conformations of polydimethylsiloxane chains
Authors: Wright P. V.
Published: April 2003

Experimental molar cyclization equilibrium constants for dimethylsiloxane cyclics having from 8 to ca 400 skeletal bonds are presented. The results for an undiluted equilibrate, an equilibrate in toluene solution, and an equilibrate in diglyme solution are compared. The increases in the equilibrium concentrations of cyclic oligomers, previously found to be large in good solvents (e.g., toluene) are found to be small in the poor solvent (diglyme). For macrocyclics, the cyclization equilibrium constants in the undiluted equilibrate and in diglyme (theta conditions) are found to be in good agreement with calculations which were carried out by assuming that chains are unperturbed and by using the rotational isomeric state model of Flory, Cresenzi, and Mark for polydimethylsiloxane. However, with chain polymer in dilute solution in a good solvent (toluene), the macrocyclization equilibrium constants are found to be lower than in the other two equilibrates. This result confirms the work of other authors who suggested that in this case the chains were expanded by excluded‐volume effects.
Light scattering from tilted two‐dimensional spherulites
Authors: Hashimoto Takeji , Todo Akira , Kawai Hiromichi
Published: April 2003

The theory of small‐angle light scattering was developed for oblique incidence of the light beam on the surface of a two‐dimensional spherulite. Results of the theory were compared with previously reported results of light scattering from two‐dimensional and three‐dimensional spherulites for normal incidence, and with some experimental patterns. The comparisons suggest that the scattering intensity distributions of two‐dimensional spherulites deviate from those of three‐dimensional spherulites when the sample surface is tilted with respect to the propagation direction of the incident beam, although they are almost identical when the sample surface is normal to the incident beam. Observation of the change of scattered intensity distributions upon tilting the samples thus provides a method of distinguishing between two‐dimensional and three‐dimensional spherulites. Moreover, this observation makes it possible to determine the degree of planar orientation of the optic axes of optically anisotropic scattering elements within two‐dimensional spherulites. The calculations were carried out for special cases of two‐dimensional spherulites with the optic axis orientation confined to the two‐dimensional plane and randomly or helicoidally rotated around the spherulite radii.
Dielectric relaxation in styrene‐related polymers at low temperatures
Authors: Irvine J. D. , Work R. N.
Published: April 2003

The complex dielectric constants ϵ* = ϵ′ − jϵ″ of each of several members of a system of copolymers of 4‐chlorostyrene and 4‐methylstyrene have been measured from 1.6°K to 300°K and from 0.1 kHz to 20 kHz. The principal experimental findings are: the strength of the relaxation process which occurs near 50°K at 1 kHz varies linearly with changing copolymer composition; both the apparent activation energy (H = 2.7 ± 0.7 kcal/mole) and the shape of the relaxation curve are independent of the composition variable and of the temperature (or frequency) within the ranges studied; and the ratio of the relaxation strength of poly‐4‐methylstyrene to that of poly‐4‐chlorostyrene in the 50°K process is about 25 times the corresponding ratio for the primary relaxation process that occurs in the neighborhood of the glass‐transition temperature. These findings suggest that in the 50°K process the phenyl groups relax independently of one another; that the apparent activation energy and the shape of the relaxation spectrum are determined primarily by the nature of the intrachain forces; and that the strength of the relaxation process depends primarily on effects of intermolecular forces that are governed by the molar “free volume” of the copolymers.
Invariance of the long spacing–crystallization temperature dependence of polyamides precipitated from solution
Authors: Dreyfuss P. , Keller A.
Published: April 2003

Previously it was found that the lamellar thickness of solution‐grown polyamide crystals as assessed by low‐angle x‐ray diffraction appeared to be unaffected by crystallization conditions. This point has now been re‐examined in detail on nylon 6.6 with crystallization temperature Tc as the main variable. Over a very wide range of Tc the lamellar thickness was invariant; a notable increase could be produced only at the highest Tc. The “invariant” lamellar thickness occurs at larger supercoolings than can be realized in the much‐studied polyethylene, which may explain why it has not yet been reported for polyethylene. The existence of this minimum invariant value raises important questions concerning the applicability of the current kinetic theories over such a wide range of supercoolings. Several other polyamides also revealed invariant long spacings after crystallization from solution. This provides the justification sought for comparing, in the paper which follows, the long periods observed for a large number of polyamides.
Survey of the long spacing of polyamides crystallized from solution
Authors: Dreyfuss P.
Published: April 2003

A series of linear, aliphatic polyamides in which the number of carbon atoms in the repeat unit ranged from three to twenty‐four was crystallized from solution. All gave lath‐shaped crystallization products (usually aggregated in the form of sheaves) that were unmistakable lamellar. Sedimented mats of the crystals were examined by lowangle and wide‐angle x‐ray diffraction. Each polyamide had a characteristic layer thickness (fold length) which was determined by the length of the repeat unit and the number of hydrogen bonds in the lamella. The thickness was independent of other variables examined including crystallization conditions. The polyamides studied cover a wide range: they border on polypeptides at the one extreme and approach polyethylene at the other. For all these materials there emerged a unifying pattern which relates chemical structure directly to chain folding.
Kinetics of craze formation in glassy polymers
Authors: Narisawa I. , Kondo T.
Published: April 2003

Craze initiation and propagation near a Griffith crack were studied in poly(methyl methacrylate) and polycarbonate. Craze propagation results either in eventual catastrophic failure or in termination of propagation. Photoelastic observations indicate that high stress concentration at the initial crack tip is relieved immediately after craze initiation and craze propagation introduces no new stress concentration at the craze front. These results lead to the conclusion that the criteria for craze initiation and propagation are described fairly well by the stress intensity factor. A fracture mechanics model proposed by Marshall et al. can explain the kinetics of craze propagation in poly(methyl methacrylate). However the growth rates are lower in polycarbonate than in poly(methyl methacrylate). This is attributed to the difference in a penetrant activity.
Relation between hydraulic permeability and diffusion in homogeneous swollen membranes
Authors: Paul D. R.
Published: April 2003

The question of viscous flow versus molecular diffusion mechanisms for pressure‐induced liquid transport through membranes is critically examined for the specific case of homogeneous swollen membranes. It is shown that previous attempts to compute diffusion coefficients from hydraulic permeabilities for such systems have used an equation which is grossly in error. It estimates diffusion coefficients which are orders of magnitude too high and often exceed self‐diffusion coefficients. This has frequently led to the conclusion that viscous flow predominates. The origins of the errors in this equation are indicated, and a substitute equation is developed which gives diffusion coefficients well below that for self‐diffusion when applied to literature data. As a result it is concluded that molecular diffusion is the dominant mechanism in homogeneous systems.
Stress–strain behavior in extension of elastomer networks with crosslinks of different lenghts
Authors: Hasa J. , Van Der Hoff B. M. E.
Published: April 2003

Stress–strain behavior in extension and the swelling of polymer networks with different lenghts of crosslinks is reported. These networks were prepared by copolymerization of butyl acrylate with different amounts of various difunctional comonomers which yield crosslinks of 4, 7, 10, and 16 bonds in length. The efficiency of the comonomers in crosslinking is low, improving with increasing length of the chain between their unsaturated endgroups. Analysis of a large number of stress–strain data obtained at elongations between 2 and 8% elongation showed that in this deformation range the stress–strain relation based on the statistical theory of elasticity represents the data better than does Hooke's law or the Mooney‐Rivlin relation. It was found that the relation between the modulus at small deformations and the swelling ratio of the various samples inindependent of the length of the crosslinks. Also the shapes of the Mooney‐Rivlin curves are the same for all networks. Furthermore, the creep behavior of various networks with different crosslink lengths is the same for networks compared at the same elastically effective chain concentration. It is concluded that the lenght of the crosslinks, at least up to 16 bonds, does not affect the elastic response of polymer networks.
Internal motions in an alternating copolymer of ethylene and tetrafluoroethylene
Authors: Starkweather Howard W.
Published: April 2003

Internal motions in an alternating copolymer of ethylene and tetrafluoroethylene were investigated by dynamic mechanical and dielectric measurements and by nuclear magnetic resonance. At 1 Hz the α, β, and γ relaxations were observed at 110, −25, and −120°C in a quenched sample. The activation energy was 76 kcal/mole for the α relaxation and 10.6 kcal/mole for the γ relaxation. These relaxations are attributed to the motion of long and short segments in the amorphous regions, respectively. The β relaxation, which was observed only in the dynamic mechanical experiments, appears to occur in the crystalline regions. The copolymer is isomeric with poly(vinylidene fluoride), but it has a higher melting point and a much lower dielectric loss.
Small‐angle scattering of circularly polarized light from an anisotropic sphere
Authors: Holoubek J.
Published: April 2003

A theory of the small‐angle scattering of circularly polarized light from an anisotropic sphere has been derived. The validity of the theory has been verified, and a relationship between the structural information thus obtained and the structural information obtained with linearly polarized light has been demonstrated.
Hydrogen bonding effects in the glassy state of random copolyamides
Authors: Hatakeyama Tatsuko , Kanetsuna Hisaaki
Published: April 2003

The thermal behavior of random copolyamides which are used as model polymers with hydrogen bonds has been investigated by differential scanning calorimetry (DSC), x‐ray diffraction, and infrared spectroscopy. The quenched copolyamides have only halo patterns in their x‐ray diffraction photographs. A random copolymer of nylons 6, 66, and 610 (in a composition ratio of 3: 4: 3) was found to have 20% of unbonded amide groups immediately after quenching. When the sample was kept at the glass transition temperature (20°C), no change in x‐ray diffraction was observed after the treatment. The free amide band in the infrared spectrum at 3450 cm‐1, however, was decreased in intensity by keeping the sample at the glass transition temperature. The transition peak height observed in a DSC curve also increased in the same experiment. Large glass transition peaks were found in DSC curves after annealing of the random copolyamides in the vicinity of the glass transition temperature. It is probable that the free amide groups in the amorphous chains were rearranged and formed new hydrogen bonds during the heat treatment at the glass transition temperature. Packing and restriction of the amorphous chains due to the increase in hydrogen bonding seemed to increase the height of the transition peak in a DSC curve. It is inferred from the above results that in the case of the random copolyamide, structures corresponding to a given enthalpy of the glassy state can be related to the number of hydrogen bonds.
Conformational and packing stability of crystalline polymers. II. Several isotactic helical polymers
Authors: Tadokoro Hiroyuki , Tai Kazuo , Yokoyama Masaaki , Kobayashi Masamichi
Published: April 2003

The most stable conformations of typical isotactic helical polymers, polypropylene (PP), poly‐4‐methyl‐1‐pentene (P4MP), poly‐3‐methyl‐1‐butene (P3MB), polyacetaldehyde (PAA), and poly(methyl methacrylate) (PMMA), were analyzed without fixing the fiber identity period by taking into account the intramolecular potential energy due to the internal rotation barriers, and van der Waals and electrostatic interactions. According to the results of the calculations, the number of chemical units per turn N in the stable conformations is 2.91 for PP (value determined by x‐ray diffraction: 3.0), 3.52 for P4MP (3.5), 4.17 for P3MB (4.0), and 3.94 for PAA (4.0). This indicates that the molecular conformations of these four polymers are governed primarily by intramolecular interactions, i.e., steric hindrance of side chains, and are additionally modified by the intermolecular interactions in the crystal. For PMMA, the lowest minimum in the potential map corresponds to N = 12, but the energy difference between the minima of N = 12 and N = 5 (corresponding to the actual one) is only 3 kcal/mole of monomer unit. The (5/1) helix of PMMA may be reasonably interpreted in terms of the intermolecular interactions mainly due to the polar and bulky side groups. The intermolecular interaction energy of isotactic PAA in the crystal lattice is also calculated and discussed.
Feasibility of determination of heterogeneity in copolymer composition by light scattering
Authors: Vorlíc̆ek Jir̆í , Kratochvíl Pavel
Published: April 2003

The sensitivity of the light‐scattering method for the determination of the composition heterogeneity of copolymers is discussed in terms of the accuracy of measurements of the intensity of scattered light. When the composition is independent of molecular weight, a nomographic solution has advantages. The nomograph is used to investigate the feasibility (a) of the determination of heterogeneity by a single measurement at zero refractive index increment of the copolymer and (b) of the determination of the heterogeneity from two measurements. The results show that in the case of low heterogeneities the light‐scattering method can be used only at higher molecular weights. By using the heterogeneities calculated elsewhere, the possibility of determining them for the individual types of copolymers is discussed. It appears that reported discrepancies between measured and calculated heterogeneities are mostly found in cases where the sensitivity of the light‐scattering method for the determination of the composition heterogeneity is low.
Effect of polymerization conditions on the morphology of as‐polymerized poly(vinylidene chloride)
Authors: Wessling R. A. , Oswald J. H. , Harrison I. R.
Published: April 2003

Poly(vinylidene chloride) (PVDC) separates from the reaction mixture during the free‐radical polymerization of vinylidene chloride. The morphology of the “as‐polymerized” powder is determined by the degree of undercooling existing in the reaction medium at the time of crystallization. Crystallization occurs simultaneously in the process of polymerization and subsequently by the precipitation of polymer which formed in solution. As the medium becomes more favorable, an increasing portion of the polymer forms in solution and then crystallizes. The morphology developed by polymerization in borderline solvents such as dioxane can be nearly duplicated by recrystallization under similar conditions. The simultaneous occurrence of solution and solid phase polymerization leads to a double DTA endotherm. The upper peak at ca. 200°C represents the melting point of PVDC. The size and temperature of the lower peak vary with polymerization conditions. The results can be correlated with the degree of under‐cooling as estimated by the difference between the polymerization temperature and the temperature at which the crystalline polymer dissolves in the reaction mixture.
Crystal structure of an alternating copolymer of ethylene and tetrafluoroethylene
Authors: Wilson F. C. , Starkweather H. W.
Published: April 2003

The unit cell of an alternating copolymer of ethylene and tetrafluoroethylene was determined by x‐ray diffraction. In spite of uncertainties due to irregularities in the chain structure and a low level of crystallinity, a reasonable unit cell and structure was derived which gives a calculated crystalline density of 1.9 g/cm3. The unit cell is believed to be either orthorhombic or monoclinic with the following parameters: a = 9.6 Å, b = 9.25 Å, c = 5.0 Å, (γ = 96°). The molecular conformation is that of the extended zigzag, and the molecular packing appears to be orthorhombic, each molecule having four nearest neighbors with the CH2 groups of one chain adjacent to the CF2 groups of the next.
Effect of N‐substitution on the crystallinity of polylaurolactam
Authors: Shalaby S. W. , Fredericks Robert J. , Pearce Eli M.
Published: April 2003

Poly(N‐ethyl laurolactam) and poly(N‐benzyl laurolactam) were prepared from the corresponding monomers by hydrolyic polymerization. Unlike the partially crystalline poly(N‐methyl laurolactam), these two homopolymers were completely amorphous by x‐ray diffraction. Diffraction patterns of copolymers of N‐ethyl laurolactam or N‐benzyl laurolactam with laurolactam were shown to be composition‐dependent. For N‐ethyl laurolactam copolymers, crystallinity developed with 20% laurolactam as a comonomer and increased steadily with a subsequent change in the x‐ray pattern, up to 50% laurolactam. Higher laurolactam percentages resulted in copolymers having a nylon 12 x‐ray pattern. N‐Benzyl laurolactam copolymers with 30% laurolactam showed only 6% crystallinity. The x‐ray patterns of N‐benzylated nylon 12 made with more than 50% laurolactam showed patterns similar to that of nylon 12. Differential scanning calorimetry data of all these polymers substantiate the x‐ray findings. The effect of type and concentration of the N‐substituent on the glass transition, melting, and crystallization temperatures of the polymers is discussed.
Texture of injection‐molded polypropylene
Authors: Mencik Z. , Fitchmun D. R.
Published: April 2003

Injection‐molded specimens of polypropylene were examined by x‐ray diffraction for texture and orientation patterns as a function of the distance from the surface and of molding conditions. At least three distinct layers in the surface region whose texture patterns differ and an isotropic core of the moldings have been identified. These layers show preferred orientations; the axes of symmetry of the oriented textures lie in a plane passing through the direction of flow and perpendicular to the mold surface, but are inclined to the mold surface at a small angle. Some of these layers may be missing in conditions of either very high or very low shear during the injection‐molding flow. A tentative explanation of the formation of the texture patterns is proposed.
Small‐angle x‐ray scattering of semicrystalline polymers. II. Analysis of experimental scattering curves
Authors: Crist B. , Morosoff N.
Published: April 2003

The small‐angle x‐ray scattering (SAXS) patterns of a number of linear polyethylene (PE) and polyoxymethylene (POM) samples have been measured and compared to the intensity functions of one‐dimensional paracrystalline lattices. It was found that the ratio of the angular positions of the second and first scattering maxima (θ2/θ1) is generally less than or equal to 2.0, implying that the paracrystalline lattice statistics are symmetric or moderately skewed to larger periods. The Bragg spacing (“long period”) of such samples is within 3% of the identity period of the macrolattice. With quenched POM the ratio θ2/θ1 is substantially larger than 2.0, which indicates either extremely asymmetric lattice statistics or coexisting structures within the material. From consideration of the reduced widths of the first scattering maxima, it was found that some broadening is present in addition to that from the paracrystallinity. This excess broadening could result from a finite lattice length of ∼1000 Å. The need for careful experimental technique for obtaining the actual position of the scattering maximum is emphasized. In addition, it is demonstrated that the scattering curve and the correlation function of the system yield essentially the same apparent structural periods.
Crystallization during polymerization of poly‐p‐xylylene. II. Polymerization at low temperature
Authors: Treiber Gert , Boehlke Klaus , Weitz Alexander , Wunderlich Bernhard
Published: April 2003

The polymerization of p‐xylylene was followed with a newly designed differential thermal analysis system at temperatures between −196°C and −20°C. It was found that at the lower temperatures the monomer condenses first to the crystalline monomer before simultaneous polymerization and crystallization. At the higher temperatures, polymerization and crystallization are successive. The data are in agreement with the morphology and crystal structure data derived in Part I of this series of papers on crystallization during polymerization of poly‐p‐xylylene.
Relation between dielectric behavior and structure in some solid polypeptides
Authors: Tanaka Akira , Ishida Yōichi
Published: April 2003

An attempt to interpret the prominent dielectric relaxations of poly(γ‐benzyl L‐glutamate) and poly(γ‐methyl L‐glutamate) in terms of their structures was made by applying the barrier theory of Hoffman. Potential energy maps for the rotation of the polar side group, which are required in this application, were calculated by taking account of molecular environment of the polar side group. The dichroic ratios from infrared measurements were satisfactorily calculated, based on the maps. This provides evidence that the maps are reliable. In applying the barrier theory, it was modified by the assumption that the conformations of the side groups are distributed according to the Boltzmann law. On the basis of the maps, the magnitude of the dielectric absorption and the mean relaxation time were calculated in terms of the modified barrier theory; these were in fairly good agreement with the experimental data.
Molecular weight determinations by gel‐permeation chromatography and viscometry
Authors: Spatorico A. L. , Coulter B.
Published: April 2003

The hydrodynamic volume concept can be used effectively with gel‐permeation chromatographic (GPC) and viscosity data to estimate the molecular weight of a variety of polymers. Agreement is within ±5–10% of the absolute values and thus is satisfactory for many purposes. An iterative computer technique and a method developed by Funt and Hornof for analyzing GPC–viscosity data were found to be equivalent with respect to estimating the molecular weights for the five cases studied. The latter is easily employed but restricted to the case where the sample of interest and the GPC calibration standards have approximately equal Mark‐Houwink parameters. Since GPC measurements are commonly performed in thermodynamically good solvents, the general applicability of the method is not impaired. Using the unperturbed dimensions of the polymer chain to estimate the molecular weight of a variety of polymers was not as satisfactory as the above techniques. This approach generally gave biased molecular weight values (consistently low or consistently high). Agreement with the absolute values ranged from 10 to 30%. We therefore believe that either of the techniques based on the hydrodynamic volume concept can be used more effectively to estimate the molecular weight of a series of polymers than the treatment based on the unperturbed dimension.
Electron spin resonance studies of spin‐labeled polymers. IV. Slow‐motional effects in solid polystyrene
Authors: Bullock A. T. , Cameron G. G. , Smith P. M.
Published: April 2003

Shape changes in the electron spin resonance spectrum of spin‐labeled polystyrene have been studied as a function of temperature in the range 77–340°K. Rotational correlation times have been calculated by using recent theories of slow‐motional effects on ESR spectra. Three models were used, namely, Brownian, moderate jump diffusion, and large jump diffusion. The moderate jump model gave correlation times in good accord with those found by other techniques for the δ relaxation in polystyrene. The relaxation was found to be independent of molecular weight.
Calculations of the strength of the polyethylene molecule
Authors: Boudreaux D. S.
Published: April 2003

A theoretical determination of the elastic modulus, the breaking strength, and breaking strain is made for a single infinitely long molecule of polyethylene (CH2)∞. These results are compared with those of a similar calculation on a molecule of polyethylene with a side chain attached. It is found that the presence of a side chain weakens the molecule by approximately 17%.
Relation between refractive index and density of polymer solutions
Authors: Looyenga H.
Published: April 2003

The relation between the fractive index n and the density ρ of a liquid mixture is formulated as

where wi and Rsi are the weight fraction and the specific refraction, respectively, of component i. The calculation of the specific refraction of straight‐chain polyethylene and polystyrene from data for pure compounds of low molecular weight is discussed. The result is applied to dilute solutions of polystyrene in toluene. The calculated values of (dp/dw)0 and (d2ρ/dw2)0 at three different temperatures are compared with measured values. The agreement is satisfactory.
Low‐temperature specific heat of polystyrene and related polymers (1.6° to 4°K)
Authors: Zoller P. , Fehl D. L. , Dillinger J. R.
Published: April 2003

The specific heat of polystyrenes of different origin and molecular weight, of α‐substituted and ortho‐substituted polystyrenes, and of polystyrenes crosslinked with different amounts of divinylbenzene have been measured between 1.6 and 4°K. The specific heat of all samples shows a temperature dependence that can not be explained by assuming a Debye frequency spectrum for the vibrational modes in these polymers. Good agreement is obtained by fitting the data to a superposition of a Debye T3 term and an Einstein specific heat with a characteristic temperature of 15–18°K. This localized frequency mode may have its origin in the one‐dimensional nature of the polymer chain. A simple calculation of the length of a polystyrene chain necessary to obtain these characteristic temperatures shows reasonable agreement with the number of Einstein oscillators observed in the samples.
Nascent polypropylene morphology: Polymer fiber
Authors: Wristers J.
Published: April 2003

A new morphological structure has been shown to be a general feature of polyolefin powders. This feature is a fiber approximately 0.5 μ in diameter and is common to a large number of samples of polyethylene, ethylene‐propylene copolymer, polypropylene, polybutene‐1, and poly‐4‐methylpentene‐1 samples. Polymer particles prepared with different catalysts under different conditions are composed of these fibers. The fibers grow from globules formed during the initial phase of polymerization, and their formation at high catalyst efficiency suggests that not all primary catalyst particles have equivalent activities.

The fiber structure is one of at least six levels of order prevailing in the polypropylene particle. While the catalyst particle is responsible for some of the distinctive morphological arrangements, polymer morphology is the primary cause for the other structures. The primary catalyst particle is thought to be the determinant for the fiber.
Direct examination of polymerization catalyst by electron scanning microscopy
Authors: Wristers J.
Published: April 2003

Direct examination of different polymerization catalysts with an electron scanning microscope is made possible by modification of the inlet port. This represents the first time that polymerization catalysts are thus directly observed at high magnification. The procedure differs from the more tedious and restricted examinations usually performed with electron transmission microscopes. Distinct differences between various catalysts are observed depending on their mode of preparation. These differences account for diverse physical properties of polymers produced with these catalysts.
Fold length of single crystals of polystyrene: A conflict with crystallization theories at high supercoolings
Authors: Jones D. H. , Latham A. J. , Keller A. , Girolamo M.
Published: April 2003

The purpose of the work was to test existing theories of chain folded polymer crystallization over a supercooling range which is much is excess to what could be hitherto realized. This was made possible by the recognition that crystallization of isotactic polystyrene in solution could be conducted over an exceptionally wide range of temperatures in an isothermally controlled manner. The results revealed that the familiar inverse dependence of the fold length on supercooling (the behavior observed and studied in polyethylene) was only displayed at the lowest supercooling; at high supercoolings the fold length reached a constant lowest value unaffected by further lowering of the crystallization temperature. This is in conflict with present theories, which predict a catastrophic upswing in fold length at high supercoolings. It is demonstrated that the observations cannot be made compatible with this prediction by any conceivable adjustment of the numerical parameters. The implications of these findings are discussed.
Diffusion and sorption of gases in poly(ethylene terephthalate)
Authors: Toi Keio
Published: April 2003

The sorption and diffusion of gases in poly(ethylene terephthalate) (PET) films have been measured by using a newly devised apparatus which gives the sorption rate curves from the initial to the equilibrium state. By analysis of sorption data for carbon dioxide in PET film, it was shown that the diffusion rate, as well as the equilibrium solubilities, could be explained by the dual‐mode sorption mechanism proposed by Vieth et al. Constants of their equation were used in the analysis of our experimental results, in which the apparent diffusion coefficients were dependent on pressure. The result showed that the dual‐mode sorption mechanism indeed applies to diffusion. The value of the real diffusivity obtained in amorphous PET was 5.7 × 10−9 (± 8%) cm2/sec in the range of pressure from 0 to 1 atm. It is believed that this apparatus has wide applicability, not only to diffusion of gases in polymers, but also to the measurement of surface properties, and can be used to study the morphology of a variety of polymers.
Structural studies of polyethers. IX. Planar zigzag modification of poly(ethylene oxide)
Authors: Takahashi Yasuhiro , Sumita Isao , Tadokoro Hiroyuki
Published: April 2003

A new crystal modification was found in poly(ethylene oxide) stretched about two‐fold after necking at room temperature. An x‐ray diffraction analysis indicated that the planar zigzag molecule passes through a triclinic unit cell with parameters α = 4.71 Å, b = 4.44 Å, c (fiber axis) = 7.12 Å, α = 62.8°, β = 93.2°, and γ = 111.4°. The space group is P1−Ci1. Packing of the molecule is very similar to that of monoclinic polyethylene.
Moiré patterns in the electron image of solution‐grown polymer crystals
Authors: White J. R.
Published: April 2003

Relative tilt between two similar thin crystals may result in the formation of a moiré pattern in the electron image. Patterns hitherto interpreted as being parallel moirés or rotation moiré obtained from overlapping solution‐grown polymer crystals are reconsidered, and it is shown that in some cases a tilt model is more acceptable. The general features of tilt moiré patterns predicted for crystals of this kind are discussed and compared with micrographs appearing in the literature. Methods of distinguishing tilt moiré patterns are indicated, though it is admitted that such experiments would be difficult to complete in the time limited by destruction of the crystal structure under the action of the electron beam. Extinction contours may also sometimes be confused with long‐period tilt moiré patterns, and again careful experimentation is required for accurate identification. The model of the structure of solution‐grown polyethylene crystals inferred from a tilt moiré interpretation of many of the electron image fringe patterns found in the literature is consistent with that derived from other sources.
Transient permeation of organic vapors through elastomeric membranes
Authors: Curry J. E. , McKinley M. D.
Published: April 2003

The permeation of benzene and acetone vapors through sulfur‐cured natural rubber was studied by the time‐lag method. The experimental results were analyzed by a method suggested by Meares. The zero concentration diffusion coefficient D0 was obtained by the early‐time method. The Frisch time‐lag equation was utilized to estimate both the solubility coefficient s and the additional parameter b required to define the concentration dependence of the diffusion coefficient: D(c) = D0 exp {bc}. This form of concentration dependence was manifested by the corresponding permeability coefficient values. At low entering penetrant pressure, where the transport coefficients are constant, indirect evidence was obtained that D0 is the mechanistically correct diffusion coefficient. The solubility coefficient values calculated for benzene vapor in natural rubber are in reasonable agreement with published equilibrium sorption data for a similar rubber compound. At higher entering penetrant pressures, average diffusion coefficients obtained at steady state tended to be larger than the corresponding average diffusion coefficients derived from the time lags. This same effect has been detected by other experimental approaches. Permeation experiments designed for this rapid method of analysis appear capable of yielding information consistent with that obtained by more time‐consuming traditional methods.
Cloud‐point curves for polystyrenes of low polydispersity in cyclohexane solution
Authors: Krause Sonja , Stroud Dale E.
Published: April 2003

Cloud‐point curves and relative volumes of the coexisting phases just below the cloud‐point temperatures were observed for a commercial sample of “monodisperse” polystyrene and one of its fractions. As expected from theoretical considerations, the cloud‐point curve for the more monodisperse sample was flatter near the peak over a greater concentration range than that of the parent sample. Furthermore, the critical point for the fraction appeared to be closer to the peak of the cloud‐point curve than was that of the unfractionated polymer. In addition, it was learned that one type of impurity could be detected with extraordinary sensitivity by means of the cloud‐point curve.
Ultrasonic absorption and dielectric loss in heterophase block copolymers
Authors: Shen M. , Kaniskin V. A. , Biliyar K. , Boyd R. H.
Published: April 2003

A styrene–butadiene–styrene block copolymer (SBS) and a plasticized SBS were studied as a function of temperature by an ultrasonic wave propagation technique at 9 MHz. Two absorption maxima were found for each of these polymers, one being attributable to the primary glass transition of the polybutadiene blocks and the other to that of the polystyrene blocks. The SBS was cast from two different solvents, namely benzene and tetrahydrofuran–methyl ethyl ketone. Parallel dielectric loss measurements were also made of the SBS in the frequency range of 50–105Hz. Relaxation temperatures determined from the ultrasonic and dielectric loss maxima over a range of measurement frequencies can be correlated by an Arrhenius‐type equation. The polystyrene loss peak in the ultrasonic data was found to be much weaker than the polybutadiene loss peak. However, these two peaks were of comparable magnitude in dielectric data. This observation was interpreted as being due to the onset of structured–unstructured (heterophase to homogeneous) transitions at sufficiently high temperatures. Ultrasonic data were also compared with low‐frequency dynamic mechanical data (11 Hz) and stress relaxation data (102–105sec) through the use of simple time–temperature superposition principle. Considerable discrepancies were found by using this principle, indicating that the heterophase SBS block copolymer was thermorheologically complex.
Steady‐shear viscosity of polydimethylsiloxanes over the range from the lower to the upper Newtonian region
Authors: Ito Yoshio , Shishido Shunsuke
Published: April 2003

The mechanism of non‐Newtonian behavior for flow from the lower to the upper Newtonian region is explained by a modification of Graessley's theory. In the theory proposed here, a viscosity ηfric, which is based on friction between polymer segments and is almost shear‐independent, is introduced in addition to Graessley's entanglement viscosity ηent, which decreases with increasing shear rate. The theory is applied to previously obtained data on steady flow of polydimethylsiloxanes of different molecular weights. The agreement between calculated and experimental results is good. In polymers with the molecular weight above the critical molecular weight for entanglement Mc, the major contribution to viscosity near zero shear rate is ηent. As the shear rate increases, the flow curve has an inflection where ηfric cannot be disregarded in comparison with ηent. In the upper Newtonian region, ηfric has more influence on the viscosity than ηent. The theory can also explain the experimental results on flow of polymers with molecular weight below Mc, which were shown to be slightly non‐Newtonian in the previous paper.