bluuebunny/crossref_metadata_2025_split huggingface dataset:
Specific volume studies of γ‐irradiated polytetrafluoroethylene from 40 to 150°C
Authors: Licht W. R. , Kline D. E. 
Published: April 2003

AbstractThe effect of γ‐irradiation and post‐irradiation heat treatment on the specific volume versus temperature relationships of polytetrafluoroethylene (PTFE) samples (1/2‐in. diameter rods) have been studied over the 40–150°C. temperature range for radiation doses up to 8.9 X 108 rad. At low doses the specific volume at any temperature decreased with dose, but above about 108 rad it increased with dose. Similarly, the rate of volumetric expansion initially decreased with dose, while, at very high doses (8.9 X 108 rad) the rate of expansion at temperatures above 100°C. exceeded that of the unirradiated PTFE. Heating at 150°C. for 100 hr. produced a substantial decrease in the specific volume and a decrease in the rate of expansion for the irradiated samples. Irradiation effects in PTFE are considered to be a result of such factors as radiation‐induced chain scission, increased crystallinity, and increased void content. Changes resulting from post‐irradiation heat treatment can be attributed to increased crystallinity, decreased void content, and weight loss.
Internal motion in some aromatic polyesters and linear aromatic chains
Authors: Mattes Rainer , Rochow Eugene G. 
Published: April 2003

AbstractLow‐temperature internal motions of the following polyesters have been investigated by broad line nuclear magnetic resonance: poly(methylene terephthalates) (2–6 methylene groups), poly[1,4‐(dimethylene)cyclohexylene terephthalate], poly(diethyleneglycol terephthalate), poly(1,2‐propylene terephthalate), poly(1,4‐phenylene terephthalate), poly(2,2,3,3,4,4‐hexafluoropentamethylene terephthalate), poly[1,4‐phenylenebis(dimethyl) siloxane], and poly(2,6‐dimethylphenylene oxide). No complex line structure was found for any of the samples. Molecular motions in the polyesters appear to be restricted by polar forces arising from the ester groups. Above—196°C. the line width decreases smoothly with increasing temperatures for all polymers except poly[1,4‐(dimethylene)cyclohexylene terephthalate] and poly[1,4‐phenylenebis(dimethyl)siloxane]. These two show a definite transition in line width at −20°C. and +12°C., respectively, caused by the onset of considerable internal motion. At −196°C. the lattices are rigid except for polymers containing methyl groups: poly(1,2‐propylene terephthalate), poly[1,4‐phenylenebis(dimethyl) siloxane], and poly(2,6‐dimethylphenylene oxide). Internal motion that can be ascribed to be a reorientation of the methyl groups is present at −196°C. for these three polymers, as is demonstrated by comparison of experimental second moments and those calculated on the basis of various models.
Sizes and interfacial free energies of crystallites formed from fractionated linear polyethylene
Authors: Mandelkern L. , Price J. Michael , Gopalan M. , Fatou J. G. 
Published: April 2003

AbstractReplicas of fracture surfaces of fractions of linear polyethylene, which were crystallized at elevated temperatures for extended time periods, were examined by electron microscopy. Striated. lamella‐type crystallites were observed for all molecular weights over the range 3.2 × 103−5.7 × 105. In agreement with Anderson's previous report, for molecular weights of 12,000 or less, the crystallite thicknesses were comparable to the extended chain length. As the molecular weight increased above this level, however, the crystallite sizes increased only slightly and hence at high molecular weights were very much smaller than the extended chain length. From the measured melting temperatures, crystallite interfacial free energies were calculated from the theory for the melting of finite size crystals comprised of chains of finite length. The crystallite interfacial free energy was found to increase with molecular weight. Based on these results, a crystallization process is outlined which allows for the formation of either extended chain crystallites, or crystallites whose size is much smaller than the extended chain length without any change in nucleation mechanism or arbitrary adjustment in growth mechanism with molecular weight.
Free volumes in simple and polymeric liquids
Authors: Miller A. A. 
Published: April 2003

AbstractValues of ε0ν0 the vaporization energy and volume in the hypothetical liquid state at 0°K., are derived for some simple polar and nonpolar molecules used as models for vinyl polymers. The following empirical relationship between the free volume fraction, f = (v − v0)/v, and the liquid compressibility coefficient β is demonstrated: −f2 ∝︁ This is applied to several vinyl polymer liquids near their glass transition temperatures, Tg, giving. fg ≃ 0.17, if the “hard‐core” volume v* is considered to be independent of pressure and temperature, (i.e., v* = v0); or, fg ≃0.12, if the P,T dependence of v* is considered to be the same as that of the glass. These agree with fg values derived by Simha and Boyer from thermal expansion coefficients for the two analogous cases. An empirical viscosity‐free volume equation of the Doolittle form: η = ATneb/f is applied to the glass transition, on assuming that this is an isoviscosity state and with the use of reported values for the expansion and compressibility coefficients and dTg/dP for three polymers: polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). Reasonable values of b/n are thus obtained. This viscosity equation is critically examined in the light of molecular theories of liquid viscosity.
Effect of strain on the thermodynamic melting temperature of polymers
Authors: Krigbaum W. R. , Dawkins J. V. , Via G. H. , Balta Y. I. 
Published: April 2003

AbstractX‐ray diffraction, sonic velocity, and birefringence measurements were used to study the variation of the apparent melting point of strained natural rubber and polychloroprene vulcanizates with elongation ratio and crystallization temperature. The procedure of Hoffman and Weeks was employed to obtain the thermodynamic melting point, tm, for each elongation ratio α. The parameter β relating to the distribution of fold lengths is unusually large for low elongation ratios and decreases into the usual range only at higher elongations. The observed variations of tm with α for these two polymers are compared with the theoretical predictions of Flory and Roe and Krigbaum. Although the predictions of the Flory theory depend somewhat upon the value assigned for the number of repeating units per statistical link, and this parameter is not well known for polychloroprene, we nevertheless conclude that his treatment offers a better representation of the melting point elevation for high elongations. Due to the approximations introduced, the treatment of Flory is not valid for lower elongations. Any attempt to improve this treatment must begin by specifying the free energy of the semicrystalline system, which implies a knowledge of the distribution of crystallite orientations and how this distribution varies with strain and with the crystallization conditions.
Dynamic mechanical properties of crystalline, linear polyethylene
Authors: Penn Robert W. 
Published: April 2003

AbstractTwo sets of dynamic mechanical property data and some stress relaxation data for semicrystalline, linear polyethylene are treated by data reduction methods previously described. These data can be represented by a master plot of reduced modulus versus reduced frequency and two sets of temperature‐dependent shift factors. The first of these factors reflects the change of viscoelastic relaxation times with temperature. The second represents a separable change of modulus with temperature which applies over the entire time or frequency range of the experiments. This change is larger and in the opposite direction to that found applicable in the behavior of noncrystalline plastics and rubbers. The two sets of dynamic data show the same frequency–temperature dependence which can be represented by an activation energy of 22 kcal./mole. Small differences in the modulus–temperature dependence are attributed to differences in molecular weight or annealing conditions. The stress relaxation data superposes to a curve in good agreement with the dynamic data but with a factor of 20 difference in time scale. This difference is attributed to the finite strains used in the stress relaxation measurements. Such strains might be expected to increase free volume in simple extension deformations and so accelerate the relaxation.
NMR observations of drawn polymers. V. Sorption into drawn and undrawn polyethylene
Authors: Peterlin A. , Olf H. G. 
Published: April 2003

AbstractNMR measurements on undrawn polyethylene (PE) samples in contact with a solvent such as C2Cl4 indicate an increase in the mobility of the mobile chain segments as compared to dry samples. Highly drawn PE shows no such effect. This is because Sa, the sorption per unit mass of noncrystalline material present, decreases from 20.9 wt.‐% (dry basis), found for undrawn quenched PE, to 0.63 wt.‐% after drawing (Sa determined at 25°C. and 0.80 vapor activity). Drawing also reduces the segment mobility according to the NMR spectrum. It is shown that these effects are caused by considerable structural changes occurring in the noncrystalline regions of PE upon drawing. Annealing of drawn PE samples at successively higher temperatures leads to a gradual relaxation of the noncrystalline regions towards the state characteristic of undrawn PE. With increasing annealing temperature Sa as well as the mobility approach values found with undrawn PE.
Narrow molecular weight distribution poly(styrenesulfonic acid). Part I. Preparation, solution properties, and phase separation
Authors: Carroll William R. , Eisenberg Henryk 
Published: April 2003

AbstractA method is described for the conversion of polystyrene to poly(styrenesulfonic acid) without change in the molecular weight distribution; the reaction is performed at room temperature in 100% H2SO4 and uses Ag+ catalyst. The resulting polyelectrolyte has solubility and other characteristics significantly different from those of previously investigated poly(vinylsulfonic acid). This permits a study of the influence of the aromatic group on the local and long range interactions in solution. The barium salt of poly(styrenesulfonic acid) is unusual in showing both upper and lower consolute temperatures in solution.
Epitaxial crystallization of homopolymers on single crystals of alkali halides
Authors: Koutsky J. A. , Walton A. G. , Baer Eric 
Published: April 2003

AbstractEpitaxial deposition of homopolymers from solution [polyethylene, isotactic polystyrene, poly‐3,3‐bischloromethyloxacyclobutane (Penton) and polypropylene] was found on the (001) faces of cleaved alkali halide single crystals. Electron and optical microscopy studies have shown that the polymer usually grew from small, rodlike crystallites which were oriented in (110) directions of the halide crystal. Large oriented, four‐leaved, “rose” structures also were observed for polyethylene. Electron diffraction studies indicate that the polymer chain axes for polyethylene, isotactic polystyrene, and Penton generally lie parallel to the (001) faces of the halide crystal and are also oriented in the 〈110〉 directions of the crystal face. Investigations on the effect of various halide substrates upon the epitaxial crystallization habit of polyethylene inferes that lattice matching does not play the major role in orientation. Two possible explanations are offered for this epitaxial behavior.
Wideline NMR studies of oriented nylon 66
Authors: McMahon P. E. 
Published: April 2003

AbstractWideline NMR techniques have been applied to both singly and doubly oriented specimens of nylon 66. Variations in the spectra obtained are observed for different orientations of the specimens relative to the applied field. These variations demonstrate that the zigzag chain axis is essentially parallel to the draw direction and that motion occurs in all of the sample. The motion is of two types: random in the mobile regions and rotation of segments about the chain axis in the rigid regions.
Persistent polarization in polymers. II. Depolarization currents
Authors: Miller M. L. , Murray J. R. 
Published: April 2003

AbstractDepolarization currents were used to study the persistent polarization induced in polystyrene and poly(methyl methacrylate) by cooling with flow under pressure. These studies showed that the charge on electrets made by flow under pressure consists in part of a surface charge which leaks off rapidly in moist air and in part of a charge due to volume polarization which decays more slowly. The volume polymerization produced in poly(methyl methacrylate) by flow under pressure is of the same order as that produced by cooling under a voltage drop, but flow under pressure produces a larger surface charge.
Effect of stereosequence length on crystallization kinetics of propylene oxide polymers
Authors: Aggarwal S. L. , Marker Leon , Kollar W. L. , Geroch R. 
Published: April 2003

AbstractCrystallization kinetics of crystalline fractions of propylene oxide polymers made with different catalysts have been studied by isothermal dilatometric and microscopical measurements. Isothermal microscopical measurements indicate that spherulite growth in these polymers proceeds from predetermined nuclei. The half time for spherulitic appearance is less than, but of the same order as, the half time for complete crystallization. Only by taking this factor into account can the dilatometric data be represented by the Avrami equation. The deviation of the crystallization isotherm from that predicted from the microscopical data using the Avrami theory is attributed to a secondary crystallization process taking place within the spherulite. Crystallization continues long after spherulites completely occupy the available volume in the polymer. By assuming that the secondary crystallization proceeds as a first‐order process in the uncrystallized, but crystallizable, portions of the melt, it is shown that the crystallization isotherms can be completely described in terms of four parameters. These are: (1) the time constant for the primary crystallization process; (2) the time constant for nucleation; (3) the time constant for the secondary crystallization process, and (4) the extent of secondary crystallization. The important conclusions of these studies are: the rates of nucleation and of spherulitic growth are far more dependent on temperature than on stereoregularity; the ratio of the rate of the secondary crystallization process to that of the primary crystallization process is almost independent of temperature, but increases with increasing stereoregularity of the polymer.
Orientation behavior of stereoregular poly(vinyl alcohols)
Authors: Nomura Shunji , Kawai Hiromichi 
Published: April 2003

AbstractThe orientation behavior of stereoregular poly(vinyl alcohols) was investigated during stretching and after releasing the stress on the bulk polymers at relatively high humidity (80% R. H.) A structural model, differing from polyethylene, was proposed in which the crystallites were embedded in a considerably swollen amorphous matrix without any definite physical interaction so as to form an aggregation of crystallites, a superstructure. The crystal orientation followed, in principle, “the first borderline case” of Kratky, but with some difference from theory in orientation, while the noncrystalline orientation was represented by the freely jointed equivalent chain model of Kuhn and Grün with a value of N/γ as small as around 5. The difference between crystal orientation found and the theorietical orientation is discussed and some factors which prevented the crystal orientation are considered.
Molecular weight determination of polyamides by vapor pressure osmometry
Authors: Ohama Mariko , Ozawa Takeo 
Published: April 2003

AbstractThe vapor pressure osmometry method for determining the molecular weight of polyamides has been studied by use of the newly developed solvents. Polymers used were polycaprolactams, polyenanthamides, and polypelargonamides. The measurements were carried out with 2,2,3,3‐tetrafluoro‐1‐propanol and 2,2,3,3,4,4,5,5,6,6,7,7‐dodecafluoro‐1‐heptanol as solvents at 50 and 130°C., respectively. Endgroup determinations on samples were also done in m‐cresol by 0.1 N‐hydrochloric acid. Reduced resistance differences (ΔR/C)0 obtained by vapor pressure osmometry at 50°C. were found to be in linear relation with the reciprocal of the number‐average molecular weight determined by endgroup titrations; but anomalous results were obtained when dodecafluoroheptanol was used as the solvent at 130°C.
Configurational entropy of polyethylene and other linear polymers
Authors: Smith Richard P. 
Published: April 2003

AbstractThe configurational entropy of the polyethylene chain at the melting points calculated in two ways. In both calculations, tetrahedral angles and discrete trans and gauche arrangements of all bonds are assumed, and trans bonds are assumed more stable than gauche by energy U1. First, calculations are made on chains of up to N = 18 bonds, disallowing all configurations having overlapping atoms, and the result is extrapolated to large N. Second, a calculation is made directly for long chains, with overlaps excluded only over every short chain segment. The results are in almost exact agreement, suggesting that the second method can be safely used with other molecules. The calculated configurational entropy is in line with that suggested by the entropy of fusion, assuming the chains to acquire a configurational freedom in the melt which approaches that of independent chains.
Crystallographic studies of nylon 4. I. Determination of the crystal structure of the α polymorph of nylon 4
Authors: Fredericks Robert J. , Doyne Thomas H. , Sprague Robert S. 
Published: April 2003

AbstractThe crystal structure of the α polymorph of nylon 4 has been determined from the x‐ray diffraction patterns of uniaxially oriented monofilaments. In general the crystal structure of α nylon 4 is similar to that of α nylon 6. The unit cell is monoclinic with the following dimensions: a = 9.29 ± 0.05 A., b = 12.24 ± 0.05 A., c = 7.97 ± 0.05 A., and β = 114.5 ± 1.0°. There are eight monomeric units in the unit cell. The theoretical density is 1.37 g./cc. and the observed density 1.25 g./cc. The space group is P21. The nylon 4 chains are of the extended planar zigzag type, with the plane of the zigzag approximately parallel to the a axis of the unit cell. Along the a axis, every other chain is inverted—an antiparallel arrangement of chains—thus permitting complete hydrogen bonding and the formation of sheets of nylon 4 chains. Along the c axis of the unit cell, the second sheet is displaced by3/10 of the b axis, thus leading to a staggered arrangement of sheets. The sheets are held in place by van der Waals forces.
Crystallographic studies of nylon 4. II. On the β and δ polymorphs of nylon 4
Authors: Fredericks Robert J. , Doyne Thomas H. , Sprague Robert S. 
Published: April 2003

AbstractIn addition to the α polymorph, two crystalline forms of nylon 4, the β and δ polymorphs, have been observed and studied.The β polymorph of nylon 4, which has not been found in a pure condition, appears to be similar to the β polymorph of nylon 6. The extended planar zigzag conformation of chains, found in the α polymorph, is present also in the β polymorph. Three models have been proposed to explain the observed data. In model 1, the staggered shear of van der Waals bonded sheets found in the α polymorph is abandoned; in model 2, the sheets are displaced by 1/2 the b axis, and in model 3 the chains are arranged in a parallel array. The β polymorph is converted to the α form in air upon heating for 11 min. at 227°C. and upon immersion in water for 2 hr. Models 1 and 2 would be converted to the α polymorph by a slippage of the van der Waals bonded sheets while the conversion from model 3 would involve a rupture of hydrogen bonds, a rotation of the chains through 90°, and the reformation of hydrogen bonds. The δ polymorph is formed by rapidly quenching extruded nylon 4 against chilled rolls. It is a metastable form which has only been observed in an unoriented condition. Upon orientation it is completely converted to the α polymorph. In addition to this, its conversion to the α form occurs under conditions similar to the β–α transition. The observed diffraction pattern can be indexed on the basis of a hexagonal packing of chains. High‐temperature x‐ray diffraction studies of the α polymorph suggest that the δ form, or a structure similar to it, is the high‐temperature form of nylon 4.
Mechanical properties and transition temperatures for copolymers of N‐n‐alkylacrylamides and acrylonitrile
Authors: Jordan Edmund F. , Riser George R. , Parker Winfred E. , Wrigley A. N. 
Published: April 2003

AbstractRandom copolymers of N‐n‐butyl‐, N‐n‐octyl‐, or N‐n‐octadecylacrylamide with acrylonitrile were prepared in tert‐butanol at 60°C. to test the effect of amide homologs as internal plasticizers. At room temperature under high deformations all samples showed brittle failure; at 100°C. flexible and resilient copolymers were obtained. At low deformations, torsional stiffness values Tf followed the equations of Wood, Fox, and Dimarzio and Gibbs, the latter two modified by use of mole fraction instead of weight fraction. Mole fraction appeared to function better than weight fraction for these special cases where wi > 2mi and where modulus‐temperature curves were broad. Because literature values for the glass (or brittle) temperatures of homologs of poly‐n‐alkyl acrylates, methacrylates, n‐alkyl styrenes and alkenes, and estimated values for poly‐N‐n‐alkylacrylamides, plotted as a function of the logarithm of the number of single bonds in repeat units, extrapolate to an average value of −111°C. at a chain length of eighteen carbon atoms, and because side‐chain melting points of linear eighteen carbon side‐chain homologs appear to have a common value of 48–50°C. regardless of structure, it was concluded that similar glass and melting transitions are obtained when the side chain reaches eighteen carbon atoms in any series of homologs. Transitions for longer side‐chain lengths then approach the limit of a polyethylene graft, where Tg is −81°C. and Tm is 137°C.
Crosslinking of gelatin by aqueous peroxydisulfate
Authors: Needles H. L. 
Published: April 2003

AbstractAqueous gelatin (5%) is crosslinked in the presence of 0.040–0.020M peroxydisulfate at 70°C., but in 0.40M peroxydisulfate, gelatin initially is crosslinked and then redissolves to give a solution of reduced viscosity. The rate of crosslinking depends on the concentration of peroxydisulfate, the nature of peroxydisulfate's cation, and the pH range of the solution during crosslinking. Addition of silver ion to gelatin–peroxydisulfate solutions increases the rate of crosslinking, whereas addition of hydroquinone inhibits crosslinking. Further, induced decomposition of peroxydisulfate is observed in the presence of gelatin. Acetylated and esterified gelatins are crosslinked by aqueous peroxydisulfate, but the ability of deaminated gelatin to crosslink is greatly reduced. Crosslinking is believed to proceed via sulfate and hydroxyl free‐radical attack of gelatin, with in situ generation of reactive intermediates that crosslink with other reactive sites in gelatin. Possible sites of crosslinking in gelatin have been suggested in light of viscosity data, chemical and amino acid analyses, and peroxydisulfate's known mode of decomposition.