bluuebunny/crossref_metadata_2025_split huggingface dataset:
Copolymerization of acrylamide and styrene. II. Reactivity ratios with unperturbed acrylamide
Authors: Minsk L. M. , Kotlarchik C. , Meyer G. N. 
Published: April 2003

AbstractIt was reported earlier that the copolymerization of acrylamide and styrene is strongly affected by the copolymerization medium. The effect was attributed to a change in the polarity of the ethylenic bond in the acrylamide monomer due to hydrogen bonding and/or dipole—dipole interaction, depending on the medium. In view of those findings, it was suggested that absolute values for the reactivity ratios for the copolymerization of these two monomers might be obtained only when the acrylamide monomer is unperturbed. Copolymerizations of these monomers at a number of ratios, therefore, were done in benzene, which does not undergo hydrogen bonding and has no dipole moment, at high dilution, when amide—amide interactions between acrylamide molecules should be essentially eliminated. The values of r1 and r2(M1 = acrylamide) were 9.14 ± 0.27 and 0.67 ± 0.08, respectively. There appears to be some indication in this system that high dilution adversely affects the reactivity of the acrylamide monomer while enhancing that of styrene. This aspect requires more study.
Photo‐induced radical formation in cellulose
Authors: Ogiwara Yoshitaka , Kubota Hitoshi 
Published: April 2003

AbstractThe characteristics of cellulose radicals produced by photo‐irradiation were studied from their ESR spectra. All spectra of the irradiated samples contained a singlet spectrum with a line width of 28 gauss. Spectra consisting mainly of a single absorption line were observed in the initial stage of irradiation. With the elapse of irradiation time, two absorption lines with a line width of 8 gauss were added to the original singlet spectrum, leading to the three absorption lines widths of 8, 28, and 8 gauss, respectively, of which the middle line with a line width of 28 gauss showed the maximum intensity. This three‐line spectrum was easily produced when hydrogen peroxide or metallic ions such as Fe3+, Ag+, Fe2+, and Ce4+ were used as sensitizers. The observed ESR spectra consisted of a singlet with a line width of 28 gauss and a triplet with a line width of 8 gauss and a splitting factor of 28 gauss. The triplet component was more unstable toward warming, as compared with the singlet component. Based on the experimental results, it was suggested that cellulose radicals due to the scissions of cellulose chains corresponding to the ESR spectra with a single line could be the most important factor for the initiation of graft copolymerization.
Free‐radical grafting of monomers to polydienes. I. Effect of reaction conditions on grafting of styrene to polybutadiene
Authors: Brydon A. , Burnett G. M. , Cameron G. G. 
Published: April 2003

AbstractThe radical‐induced grafting of styrene onto polybutadiene (PBD) in benzene solution at 60°C has been studied. Provided the PBD concentration is kept below about 1.0 monomermole/l. the polymerization of styrene shows normal kinetic behavior. The proportion of polystyrene incorporated as graft is independent of the initiator (benzoyl peroxide) concentration but increases as the ratio of PBD to styrene in the reaction medium increases. Azobisisobutyronitrile produces no graft copolymer in this system. It appears that the reaction leading to graft formation is direct attack of initiator radicals on the rubber, probably by a hydrogen‐abstraction reaction.
Grafting onto wool. V. Kinetics of graft copolymerization of methyl methacrylate in the viscous media of wool fibers
Authors: Arai Kozo , Shimizu Masamichi , Shimada Machiko 
Published: April 2003

AbstractThe graft copolymerization of methyl methacrylate in S‐carboxymethylated wool fibers was investigated in the aqueous LiBr‐K2S2O8 system. The rate of grafting, the degree of polymerization of graft polymer, and the number of grafting sites were determined on varying the thiol content at a constant concentration of monomer. Kinetic considerations lead to the following expression in agreement with the experimental results: Z/DP = {(ktd + ktc)/kp2[M]2} Rp, where Z is the number of DNP endgroups of polymer; DP is the average degree of polymerization; kp, ktd, and ktc are the rate constants of propagation, termination by disproportionation, and termination by recombination, respectively; [M] is the concentration of monomer in fibers, and Rp is the overall rate of grafting. For wool fibers in media sufficiently high viscosity, the rate constants ktd and ktc of diffusion‐controlled termination are approximately equal and not affected by the change in cross‐link density, provided that the thiol and disulfide interchange occurs. The possibility of occurrence of mechanical bond scission through a radical mechanism is involved in systems with extremely small amounts of thiol groups.
Structure and thermal stability of aliphatic polyoxamides
Authors: Shalaby S. W. , Pearce Eli M. , Fredericks Robert J. , Turi E. A. 
Published: April 2003

AbstractA homologous series of aliphatic polyoxamides, nylon 122, 102, 82, and 62, were prepared by the bulk polycondensation of dialkyl oxalates with diamines. Infrared spectroscopy, x‐ray diffraction, differential thermal analysis, thermogravimetric analysis, and gas chromatography were used to study the structure and thermal stability of these polyoxamides. From the fiber pattern of nylon 122, a structural repeat distance of 19.5 Å was measured. This was in close agreement with the expected value for an extended planar, zigzag chain conformation. With the exception of the expected decrease in the structural repeat distance along the chain axis resulting from the different number of methylene groups, nylons 122, 102, and 82 were isostructural. Nylon 62 appeared to pack in a similar manner to the other materials studied. However, there were differences in the diffraction pattern of this polymer; these may be indicative of a different chain conformation or of strain in the crystalline regions of the polymer. The infrared spectra indicate the presence of strong hydrogen bonding in all the polymers. Thermal analysis and pyrolysis data revealed catastrophic polymer degradation between 400 and 500°C in nitrogen, with appreciable homolytic cleavage of the oxamide group.
Tetrachlorobisphenol‐A adipate polymers. II. Spherulitic crystallization of poly(tetrachlorobisphenol‐A adipate)
Authors: Berghmans H. , Lanza E. , Smets G. 
Published: April 2003

AbstractThe spherulitic radical growth rate G of poly(tetrachlorobisphenol‐A adipate) was studied at different crystallization temperatures as a function of molecular weight using an optical polarizing microscope. By assuming a two‐dimensional growth mechanism, with a jump factor G0 depending on the molecular weight, and assuming surface energy terms σu and σe essentially constant, it is possible to correlate the growth‐rate data with the model of Hoffman.
Tetrachlorobisphenol‐A adipate polymers. III. Synthesis and crystalline properties of block copolymers of poly(tetrachlorobisphenol‐A adipate) and polystyrene
Authors: Lanza E. , Berghmans H. , Smets G. 
Published: April 2003

AbstractBlock copolymers having poly(tetrachlorobisphenol‐A adipate) (PTBA) and polystyrene (PS) sequences were synthesized were synthesized by photodegradation of an oxime‐containing polyester in the presence of styrene. Crystallinity, melting behavior, and spherulitic growth rates were studied as a function of block compositions and molecular weights. A model was proposed based on a complete phase separation between the two components. The influence of the polymer composition on the spherulitic growth rate is described by introducing a supplementary pre‐exponential factor into the equation for the growth rate. This parameter is a measure of the tortuosity of the actual path that has to be covered owing to the presence of the noncrystallizable blocks.
Kinetics of growth of developing spherulites
Authors: Stein R. S. , Misra A. 
Published: April 2003

AbstractA model containing two rate constants is presented for the development of spherulites from sheaves. One, GR, is a radial spherulite growth constant while the other, GS, describes the rate of increase of apex angle of the sheaf. On the basis of this model, Avrami kinetics are developed which predict a change in the Avrami constant n from 5 to 3 as the sheaf develops into a spherulite. HV light‐scattering patterns are calculated according to this model and are found to compare favorably with those found during the early stages of the crystallization of poly(ethylene terephthalate).
Multimerization: Association and aggregation. XIII. Concentration dependence of apparent average molecular weights of a poly‐disperse associating polymer in a theta solvent
Authors: S̆olc Karel , Elias Hans‐Georg 
Published: April 2003

AbstractAnalytical expressions are derived for the concentration dependences of different apparent average (n,w,z) molecular weights for two types (end‐to‐end and segment‐to‐segment) of open association of polymolecular unimers. The open association is defined as an association leading to an unlimited number of multimer species. The type of association depends upon the number of associogenic sites per unimer molecule: for the end‐to‐end type this number is constant, whereas for the segment‐to‐segment type it is proportional to the degree of polymerization of the unimer. For the end‐to‐end association, a simple relation exists between the polydispersity (M̄r)w/(M̄r)n of the mul‐timer and the association number r and the polymolecularity (M̄I)w/(M̄I)n of the unimers: (M̄r)w/(M̄r)n = 1 + r−1[(M̄I)w/(M̄I)n − 1]. The z‐average and higher averages of the r‐mers may be lower than the corresponding averages of the unimers. In the theta‐state, (M̄n)app,Θ and (M̄w)app,Θ are linear functions of c/(M̄n)app,Θ, whereas a more complicated relation exists for the apparent higher averages. For the segment‐to‐segment association, both (M̄w)app,Θ and (M̄z)app,Θ are linear function of the weight concentration c, whereas no closed expression could be found for (M̄n)app,Θ. For the polydispersities of multimers one finds (M̄I)z/(M̄r)w = 1 + r−1[(M̄I)z/(M̄I)w − 1], and, in the special case of a Schulz‐Zimm distribution of unimer molecular weights, (M̄r)n/(M̄r)w = 1 + r−1[(M̄I)n/(M̄I)w − 1].
Use of chloranil to trap free radicals in nylon 6
Authors: Ham Joe S. , Davis Michael K. , Song Jung‐Hyun 
Published: April 2003

AbstractNylon 6 in the form of bundles of fibers or rods was treated to contain traces of chloranil of other quinones. When stressed within an EPR cavity, the radicals produced were trapped in a relatively stable form containing the quinone. This method offers a quantitative measurement of the integrated number of free radicals produced during a stress history.
Drawing of fibers from irradiated polyethylene single crystals
Authors: Peterman J. , Gleiter H. 
Published: April 2003

AbstractThe relationship between the structural defects present in crystalline polymers and the molecular structure of the drawn material is studied by drawing fibers from irradiated polyethylene single crystals. Irradiation introduces a structural defect in the crystal lattice since it generates crosslinks preferentially, the density of which is controlled by the radiation dose. Observations by means of transmission electron microscopy and electron diffraction indicate that fiber drawing occurs by breaking off of single blocks of folded chains and by subsequent thermally activated rearrangement of the molecules in the drawn material. With increasing crosslink density the size of the blocks decreases, and the fibers become increasingly interconnected so that a network of fibers is formed. If the dose is about 10 Mrad, the crosslinks present in the crystals result in the formation of bundles of fibers. Above 35 Mrad the formation of fibers (single fibers as well as bundles) ceases, and the drawn material forms a thin (15 Å), continuous film. The observed change in morphology with increasing dose (crosslink density) is interpreted in terms of the additional bonding forces between adjacent chains due to crosslinks.
Crystal structure and radiation‐induced solid‐state polymerization of 1,3,5,7,9,11‐hexoxecane
Authors: Chatani Yozo , Ohno Takao , Yamauchi Tadafumi , Miyake Yasuhiko 
Published: April 2003

AbstractOne of the cyclic oligomers of formaldehyde, 1,3,5,7,9,11‐hexoxecane, was found to undergo polymerization in the solid state to form polyoxymethylene both during and subsequent to x‐ or γ‐irradiation. The polymer yield increases with polymerization temperature but decreases drastically near the melting point of the hexoxecane crystal. In order to clarify the specificity of the solid‐state polymerization, the crystal structure of hexoxecane was first analyzed; hexoxecane forms a trigonal crystal with cell dimensions of a = b = 7.917 Å, c = 11.345 Å, space group R3–C3i2, three molecules of 3 symmetry per unit cell. The polyoxymethylene as polymerized from a single crystal of hexoxecane is highly crystalline and the crystallites are definitely oriented with respect to the original crystal. There are three kinds of oriented trigonal polyoxymethylene: i.e., with the polymer chains oriented along the 〈100〉, 〈001〉, and 〈210〉 axes of the hexoxecane crystal. The relative yields of these crystallites depend upon the polymerization temperature. In addition to the ordinary trigonal polyoxymethylene, oriented orthorhombic polyoxymethylene was also found in the case of polymerization during treatment with x‐rays.
Gel‐permeation chromatographic studies of cellulose degradation. I. Treatment with hydrochloric acid
Authors: Chang M. , Pound T. C. , Manley R. St. John 
Published: April 2003

AbstractThe molecular weight distribution in various celluloses degraded with hydrochloric acid has been studied by gel‐permeation chromatography. Measurements were made on the residue after hydrolysis, on the degradation products solubilized by the acid, and on whole degraded samples comprising the product soluble in the acid plus the residue. It is shown that the total number of crystallites decreases during hydrolysis while the chain length distribution remains constant. The crystallites are gradually broken down into molecular fragments which show a size distribution centered on species with a degree of polymerization of about 8. Possible interpretations of these results are discussed.
Conformational transition of the copolymer of maleic acid and styrene in aqueous solution
Authors: Ohno Nobumichi , Nitta Katsutoshi , Makino Shio , Sugai Shintaro 
Published: April 2003

AbstractThe pH‐induced conformational transition of maleic acid–styrene copolymer in aqueous NaCl solutions has been investigated by potentiometric titration, viscosimetry, and dilatometry. The dependence of the intrinsic viscosity on the degree of neutralization of the primary carboxyl group indicates that the transition is from a compact to a loosely coiled form. From titration data, the standard free energy change ΔG° per monomole, for the transition from the uncharged compact from to the hypothetical uncharged loosely coiled one is estimated to be about 370–280 cal/monomole for concentrations ranging from 0.0092 to 0.2739N in NaCl. The value of ΔG° decreases slightly with increasing temperature in the temperature range from 15 to 30°C. The volume change associated with the transition was found to be −0.6 ml in 0.01N NaCl and −0.9 ml in 0.09N NaCl per monomole, respectively. From viscosity data, changes of molecular dimensions and the long‐range interaction parameter through the transition region have been discussed.
Surface stresses and crystal twisting in hippuric acid and in polymers
Authors: Calvert Paul D. , Uhlmann D. R. 
Published: April 2003

AbstractAn approximate model is developed which relates the twisting seen in the spherulitic crystallization of many materials to surface stresses. Expressions are presented for the twist period as a function of the surface stress. These are compared with previous experimental data on polyethylene and data on hippuric acid obtained in the present investigation. In both cases the experimental data are in accord with the predictions of the model.
Paracrystalline lattice disorder in cellulose. I. Reappraisal of the application of the two‐phase hypothesis to the analysis of powder x‐ray diffractograms of native and hydrolyzed cellulosic materials
Authors: Kulshreshtha A. K. , Dweltz N. E. 
Published: April 2003

AbstractAn examination of powder x‐ray diffractograms of native and hydrolyzed cellulosic materials obtained from widely different sources revealed the presence of materials having a higher degree of molecular order than ramie hydrolyzate, the conventional crystalline standard for cellulose. With the use of these materials as new crystalline standards, a critical reappraisal has been made of the validity of the application of the two‐phase (i.e., fringed‐micelle) hypothesis to the fine structure of cotton and related cellulosic materials. It is concluded that the lattice structure of cotton and related celluloses of plant or bacterial origin is liquid‐like or paracrystalline.
Low‐density polyethylene: Variation of branching frequency with molecular weight and its influence on molecular weight as determined by gel‐permeation chromatography
Authors: Westerman Lowell , Clark Jack C. 
Published: April 2003

AbstractA method for determining long‐chain branching frequency and molecular weight averages for unfractionated low‐density polyethylene (LDPE) by the combined use of gel‐permeation chromatography (GPC) and intrinsic viscosity data has been reported (GPC–IV method). The method assumes that the number of long branches λ per unit molecular weight is a constant independent of molecular weight. Recent data reported on λ as a function of molecular weight M in commercial LDPE indicate that this assumption is not generally valid, and concern has been expressed as to the size of the errors in molecular weights calculated using this assumption. The errors associated with assuming that λ is constant were evaluated in this study by first determining the way in which λ varies with M for two typical commerical LDPE resins by fractionation and application of the GPC–IV method to representative fractions. The experimentally determined relations between λ and M were then employed in the calculation of molecular weight and molecular size averages from GPC–IV data on the original unfractonated samples. Although it was found that λ increases with molecular weight for both samples, the results indicate that the error involved in assuming that λ is a constant is no greater than the precision with which molecular weight averages can be evaluated by GPC.
Small‐angle x‐ray scattering of semicrystalline polymers. I. Review of existing models
Authors: Crist Buckley 
Published: April 2003

AbstractThe effect of previously proposed distributions of particle size and interparticle “gap” lengths on the small‐angle x‐ray scattering of a paracrystalline one‐dimensional macrolattice has been examined. It was concluded that the general paracrystalline model, in which the fluctuations of crystalline and amorphous thickness both contribute to the destruction of long‐range order, best describes the structure of lamellar aggregates in semicrystalline polymers. By using this model, the influence of symmetric and asymmetric lattice statistics on the positions of the scattering maxima were investigated. It was found that positively skewed thickness distributions result in the second‐order maximum occurring at an angle greater than twice that of the first‐order maximum (sx̄2/sx̄1 > 2.0); the position of the first‐order maximum is generally greater than the Bragg angle of the structure. With negatively skewed distributions, the ratio of the scattering angles, sx̄2/sx̄1, is less than 2.0, and the first maximum is displaced below the Bragg angle. Qualitatively similar behavior is found with lattices characterized by symmetric lattice statistics, though these deviations from the Bragg conditions are smaller than in the case of negatively skewed distributions. The ratio of the scattering angles of the second and first maxima best reflects the general shape of the lattice statistics in a paracrystalline lattice. The effect of a transition zone, having properties intermediate between those of the crystalline and amorphous regions, was also considered. While the intensity of the higher‐order maxima is decreased, no significant shift of the scattering angles results from the incorporation of such a transition zone.
Transport of heavy organic vapors through silicone rubber
Authors: Suwandi M. S. , Stern S. A. 
Published: April 2003

AbstractPermeability, solubility, and diffusion coefficients have been determined for halothane (CF3CHClBr) and methoxyflurane (CHCl2CF2OCH3) in silicone rubber at temperatures from 17 to 60°C and at relative pressures from 0.05 to 0.96. The solubility of both penetrants in silicone rubber is a strong function of penetrant concentration (or relative pressure), and can be represented satisfactorily by the Flory‐Huggins relation with single values of the interaction parameter χ. The solubility coefficients decrease with increasing temperature at constant pressure. Mutual diffusion coefficients exhibit maxima when plotted against penetrant concentration; these maxima are attributed to the mass flow of polymer together with dissolved penetrant. Intrinsic diffusion coefficients increase linearly with increasing concentration. The energies of activation for diffusion are low, probably because of the ease of segmental motion about the SiO linkage. The diffusivity data are examined in terms of Fujita's “free volume” model and of transition‐state theory. Permeability coefficients for the two penetrants are large, of the order of 10−6–10−5 cm3(STP)‐cm/(sec‐cm2‐cm Hg), and increase markedly with increasing concentration or decreasing temperature. This behavior is regarded as a consequence of the low energies of activation for diffusion.
Dynamic light scattering of polyethylene. II. Results and interpretation
Authors: Hashimoto T. , Prud'homme R. E. , Stein R. S. 
Published: April 2003

AbstractDynamic light‐scattering measurements are reported for a medium‐density and a low‐density polyethylene. It is found that the scattering at small angles can be described in terms of the deformation of spherulites, whereas that at larger angles depends upon rearrangements of partially ordered crystals within the spherulites.
Solid‐state polymerization of oxetanes. I. Lattice parameters and packing properties of the monomers
Authors: Keggenhoff B. , Wegner G. 
Published: April 2003

AbstractThe crystallographic unit cells of melt‐crystallized 3,3‐bischloromethyloxetane and 3,3‐bisbromomethyloxetane were determined by the Weissenberg method. The two isomorphous lattices are triclinic with two molecules in the unit cell. 3,3‐Bisfluoromethyloxetane forms plastic crystals in the temperature range between −36°C and +22°C, as shown by differential calorimetry and NMR broad‐line spectroscopy. The Debye‐Scherrer diagram and the general physical properties indicate the formation of a face‐centered cubic lattice. No correlation between the lattice parameters of the monomer and polymer can be found On the basis of these results, the question is raised as to whether a topochemical polymerization of bishalomethloxetanes, i.e., a solid‐state polymerization without destruction of the crystal lattice, can take place at all. The halomethyl side groups of the oxetanes can be shown to possess different conformations in monomer and polymer crystals, so that a conformational change of the groups and rearrangement of the molecules must take place during polymerization. Therefore, a topochemical mechanism for the solid‐state polymerization of bishalomethyloxetanes seems to be impossible.