bluuebunny/crossref_metadata_2025 huggingface dataset:
Adsorption of polymers at the solution–solid interface. X. Reinforcement studies of nitrile rubbers by silicas
Authors: Clark P. J. , Howard G. J.
Published: April 2003

Vulcanizates of three acrylonitrile–butadiene copolymers were prepared by γ‐ray irradiation. Two pyrogenic silicas of differing surface areas and with surface modifications were incorporated as fillers. Measurements of initial modulus, stress–strain hysteresis, tear energy, and swelling show little differences between the reinforcement effects of the various fillers, although the extent of filler reinforcement is related to the acrylonitrile content of the rubber. The considerable range of interaction energies implied by solution adsorption studies are not reflected in the reinforcement phenomena.
Kinetics of grafting acrylonitrile onto starch
Authors: Gugliemelli L. A. , Swanson C. L. , Doane W. M.
Published: April 2003

Acrylonitrile (AN) was graft copolymerized onto gelatinized and granular wheat starch in aqueous media in the presence of ceric ammonium nitrate initiator at 91‐364 anhydroglucose units (AGU) per cerium (IV) and at 1.08‐4.33 AN to AGU ratios. Molecular weights and dispersities of polyacrylonitrile side chains were determined by gel‐permeation chromatography. Conversion‐time plots of AN polymerizations in both gelatinized and granular starch systems show characteristics common to heterogeneous polymerizations that could be explained on the basis of buried polymer radicals. The rates of polymerizations were directly related to the square root of the corrected cerium(IV) concentration and to the 1.3 power of the AN concentration. Graft copolymerization of AN onto starch, at least during initial stages, is not suitably explained by a kinetic scheme involving termination by polymer radical with cerium(IV) ion.
2‐alkyl‐1,3‐butadiene polymerization under the influence of π‐allylic complexes of transition metals
Authors: Vasiliev V. A. , Kalinicheva N. A. , Kormer V. A. , Lobach M. I. , Klepikova V. I.
Published: April 2003

Stereoregulation in the polymerization of 2‐alkyl‐1,3‐butadienes with transition metal π‐allylic complexes has been studied. The direction of isoprene polymerization is shown to be a function of the nature of the metal and ligands in the allylic compound. The presence of acidic ligands in π‐allylic complexes of Zr, Cr, Mo, and Co contributes to 1,4‐addition and increases the selectivity of π‐allylic nickel complexes, favoring cis‐1,4‐structure formation. Investigation of the model reaction of 2‐alkyl‐1,3‐butadienes with bis(π‐perdeuterocrotyl nickel iodide) revealed that active sites have an π‐allylic type structure. The mechanism of formation of π‐allylic adducts and the main factors which determine the dependence of direction and rate of polymerization on the nature of a monomer in the diene series: 2‐methyl‐1,3‐butadiene(isoprene), 2‐ethyl‐1,3‐butadiene, 2‐isopropyl‐1,3‐butadiene, and 2‐tert‐butyl‐1,3‐butadiene, are discussed.
Synthesis of polyesters from active diesters
Authors: Ogata Naoya , Okamoto Shinji
Published: April 2003

Ester‐exchange and polycondensation reactions of active diesters such as diphenyl, dithiophenyl, or dipyridinyl esters of adipic or terephthalic acids with glycols were carried out in order to investigate the reactivity of these active diesters toward nucleophilic replacement. Catalysts such as potassium carbonate were required for the esterexchange of these active diesters. Comparison of the reactivity of these active diesters with that of ordinary diesters in the presence of potassium carbonate as a catalyst indicates the rates or the equilibrium constants of the exchange reactions of these active diesters were much larger than those of ordinary diesters, indicating that polyesterification reactions favorably occur. Polyesters were obtained in good yield either by solution or bulk methods in mild conditions.
Kinetics of radiation‐induced grafting reactions. II. Cellulose acetate–styrene systems
Authors: Yasukawa T. , Sasaki Y. , Murakami K.
Published: April 2003

Kinetics of grafting reactions of styrene to preirradiated cellulose acetate have been studied by labeling the active sites with bromine atoms. The dilution of styrene monomer with methanol affected grafting reactions remarkedly: e.g., as the concentration of methanol in monomer solutions increased, the growth rates of individual graft radicals decreased while the average lifetimes increased. The integrated amounts of active sites which participated in grafting reactions were also affected by the constitution of monomer solutions and varied roughly in proportion to the extents of swelling of cellulose acetate. Grafting yields for styrene/methanol = 1/1 were higher than for 3/1 and 1/3 throughout the duration of grafting reactions, which is due not only to the high molecular weight of graft chains but also to the large number of graft chains for the 1/1 system compared to the other systems.
Anionic polymerization and copolymerization in heterogeneous systems on surfaces with aromatic structure
Authors: Panayotov Ivan M. , Rashkov Ilya B.
Published: April 2003

Methacrylaldehyde, methyl methacrylate, methacrylonitrile, styrene and isoprene readily polymerize on potassium–graphite inclusion compounds in ethereal and hydrocarbon solvents. The structure of polymethacrylaldehyde, poly(methyl methacrylate), and polyisoprene as well as the composition of styrene–acrylonitrile and styrene–isoprene copolymers have been investigated. The copolymers have a high content of styrene units which is interpreted in terms of selective adsorption of styrene on the initiator surface.
Conformational properties of structurally rigid polyamides. I. Conformation of polyamides and model diamides derived from optically active cyclic 1,2‐dicarboxylic acids
Authors: Montaudo G. , Finocchiaro P. , Overberger C. G.
Published: April 2003

The conformational equilibria of piperidine diamides derived from five cyclic 1,2‐dicarboxylic acids (I–V) have been investigated by dipole moment measurements and a priori conformational energy estimates. Since these diamides represent the building blocks of the polyamides derived from the above cyclic diacids and piperazine or trans‐2,5‐dimethylpiperazine, the results obtained in the study of the models have been used to investigate the conformation of the polymers. The overall evidence suggests that cyclopentane, cyclohexane, and bicyclooctane piperazine polymers behave as rigid rods in which the structural units possess approximately the same conformational preference exhibited by the respective model diamides.
Conformational properties of structurally rigid polyamides. II. Effect of strong acids on the circular dichroism spectra of asymmetric polyamides with varying degree of structural rigidity
Authors: Montaudo G. , Overberger C. G.
Published: April 2003

We have investigated the effect of methanesulfonic acid (MSA) on the circular dichroism (CD) spectra of some stereoregular polyamides derived from three cyclic 1,2‐dicarboxylic acids (I–III) and piperazine (PIP), trans‐2,5‐dimethylpiperazine (DMPIP), or N,N′‐dimethylethylenediamine (DMED). On the basis of a detailed knowledge of the conformational properties of these polymers, we have attempted an essentially empirical interpretation of the CD spectra and of their relative changes. A striking dependence of the optical properties from the conformational properties and/or transitions in the polymers has been found. Although far from suggesting a 1:1 correspondence between CD spectra and conformational changes, we wish to stress their general correspondence.
Anionic polymerization initiated by diethylamide in organic solvents. I. The use of lithium diethylamide as a polymerization catalyst and the effect of solvent type on the polymerization of isoprene and styrene
Authors: Angood A. C. , Hurley S. A. , Tait P. J. T.
Published: April 2003

Lithium diethylamide has been found to be an active initiator for the polymerization of isoprene both in hydrocarbon media and in a variety of polar solvents, such as diethyl ether and tetrahydrofuran. The successful initiation of styrene polymerization is, however, strongly dependent upon the type of solvent employed. Thus no polymerization is observed in hydrocarbon media or in diethyl ether solution, but polymerization occurs rapidly in either tetrahydrofuran or 1,2‐dimethoxyethane solution. These polymerization processes are anionic in nature and are characterized by sigmoidal conversion–time plots, indicating that the initiation reactions are relatively slow compared to chain propagation.
Crystallization‐induced reactions of copolymers. III. Ester interchange reorganization of poly(cis/trans‐1,4‐cyclohexylenedimethylene terephthalate)
Authors: Lenz R. W. , Go S.
Published: April 2003

Random copolymers of cis‐ and trans‐1,4‐cyclohexylenedimethylene terephthalate were permitted to undergo ester‐interchange reorganization at temperatures just below the melting point. As predicted from the principles of crystallization‐induced reactions of semicrystalline copolymers proposed in the first two papers of this series, the copolymers were observed to undergo changes in physical properties which are associated with the conversion of a random to a block copolymer. The driving force for this antiequilibrium ordering process is believed to be the irreversible expansion of the crystalline regions following replacement of cis by trans glycol units. Solubility, crystallinity, and crystallization properties were monitored to determine the effects of copolymer composition, temperature, catalyst, and molecular weight on the reorganization rate. This type of process is also believed to be responsible for the direct preparation of block copolymers by a solid‐state polycondensation reaction used in this study.
Cyanopolyesters
Authors: Banucci Eugene G.
Published: April 2003

The reaction of alkyl acyl cyanides with electron‐rich aromatic substrates in highly acidic media was found to give high yields of bisadducts. Reactions with phenol produced two new eyanobisphenols which readily underwent polycondensation with acid chlorides. The resultant polyesters can be directly compared to the polyesters of bisphenol‐A (BPA) strictly on the basis of polar effects since steric differences are nominal. Thermal, mechanical, electrical and solubility characteristics are reported for the cyanopolycarbonates, which show higher thermal transitions and thermal stability than BPA polycarbonate.
Infrared spectra of three crystalline forms of cationically synthesized poly‐3‐methyl‐1‐butene
Authors: Elliott J. J. , Kennedy J. P.
Published: April 2003

Poly‐3‐methyl‐1‐butene has been synthesized by Et2AlCl/tBuCl initiator at −130°C. A cast film of this material gave three well defined crystalline phases, α, β, and γ, characterized by infrared spectroscopy. The γ polymorph could not be obtained independently of the other two. Synthesis and/or manipulative procedures that would consistently give only one of the polymorphs are still unavailable. Evidently, the three crystalline phases have very similar lattice energies, and the subtle factors that determine the ultimate nature of the crystal lattice are not yet understood.
Time dependence of shear and normal stresses of polystyrene and poly(ethylene oxide) solutions
Authors: Laufer Z. , Jalink H. L. , Staverman A. J.
Published: April 2003

The time dependence of shear and normal stresses during constant shearing of some polystyrene and poly(ethylene oxide) solutions in Aroclor 1248 was measured by means of a Weissenberg rheogoniometer. The stresses of the poly(ethylene oxide) solutions first increase rapidly with the increase of strain, then decrease to a value lower than the value in the stationary state, pass another maximum smaller than the first one, and finally reach a steady value. At the end of the shearing of these solutions at high shear rates, the formation of aggregates was clearly evident. The polystyrene solutions became time‐dependent only after a certain shear rate and then showed a rheopectic behavior. The difference in behavior is explained qualitatively by the differing tendencies of these polymer chains to form a network.
Thermodynamic aspects of the partitioning of a solute in a gel–solvent system
Authors: De Ruvo A.
Published: April 2003

An expression is derived for the partitioning of a solute molecule in a two‐phase system: swollen gel and free solvent. The approach is thermodynamic, and no specific mechanism for the accessibility of the solute to the gel is assumed. Instead, general interaction terms between the components, i.e., polymer–solvent–solute, are introduced.
Copolymerization of acrylamide and styrene. II. Reactivity ratios with unperturbed acrylamide
Authors: Minsk L. M. , Kotlarchik C. , Meyer G. N.
Published: April 2003

It 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

The 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

The 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

The 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

A 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

The 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

Block 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

A 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

Analytical 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

Nylon 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

The 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

One 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

The 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

The 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

An 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

An 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

A 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

The 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

Permeability, 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

Dynamic 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

The 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.
Solid‐state polymerization of oxetanes. II. Investigation of the growth of the polymer phase as related to the mechanism of polymerization
Authors: Keggenhoff B. , Wegner G.
Published: April 2003

The radiation‐induced solid‐state polymerization of 3,3‐bischloromethyloxetane (BCMO) was investigated by direct observation of the development of the morphology of the growing polymer phase in single crystals of the monomer. Electron microscopy shows that the polymerization gives rise to amorphous polymer in the first step. The polymer forms irregular platelets which aggregate into larger units without reflecting the crystalline order of the monomer. Subsequent to polymerization, the amorphous polymer crystallizes to the β‐modification of poly‐BCMO. If the partially polymerized crystals are extracted by solvents of the monomer, crystallization of the polymer is enhanced, and morphological artifacts arise which were previously mistaken for the true morphology of the “as polymerized” polymer. The copolymerization behavior of solid solutions of 3‐ethyl‐3‐chloromethyloxetane (ECMO) and BCMO does not differ from the liquid bulk copolymerization with respect to copolymer composition, which is different from the composition of the monomer mixture. It is concluded that the polymer chains grow in noncrystalline zones as in a polymerization in the liquid state by which amorphous polymer is formed. No lattice control was observable in this solid‐state polymerization.
Generation and decay of peroxy radicals in deformed polyethylene
Authors: Davis L. A. , Pampillo C. A. , Chiang T. C.
Published: April 2003

The rate of peroxy radical accumulation as a function of strain at various temperatures in AC1220 high molecular weight polyethylene has been determined by EPR spectroscopy. The results of isothermal radical decay experiments are used, where appropriate, to correct the apparent accumulation rate to the actual rate. An exponential dependence of radical concentration [R], on true strain is observed at all temperatures investigated in the range from 160 to 294°K. For constant effective strain, measured from the approximate strain at which radical accumulation initiates, it is found that d[R]/de exhibits two sharp transitions as a function of temperature. One of these, at low temperature, is believed to be associated with the glass transition of the amorphous phase of the material; the other, at higher temperature, is believed to occur as a result of a change in the rate‐controlling mechanism of deformation.
Macrolattice based on a lamellar morphology in an SBS copolymer
Authors: Dlugosz J. , Folkes M. J. , Keller A.
Published: April 2003

By means of an extrusion technique, a uniformly oriented macrolattice based on an alternating sequence of polystyrene and polybutadiene lamellae has been obtained. This is confirmed by the techniques of low‐angle x‐ray diffraction, electron microscopy, and electron diffraction. Layer thicknesses and spacings have been derived, and good quantitative agreement exists between the values obtained by the different methods. In addition, the electron micrographs exhibit many singular features which are of potential importance both in their own right and for the macroscopic properties.
Polyethylene single crystals: Melting and morphology
Authors: Harrison Ian R.
Published: April 2003

Determination of important thermodynamic and physical properties of polymers has often been frustrated by the tendency of these materials to reorganize when heated. A novel technique has been developed which permits a more careful examination of the relationships existing between melting and morphology of single crystals. This has lead to the observation that high molecular weight polymers possess much narrower melting ranges than had been previously reported. By using this technique it has been possible to identify distinct transition temperatures for {100} and {110} fold sectors. DTA and DSC data have been previously reported for dried down single crystals. The applicability of this data to single crystals as they exist in suspension is questioned.
Environmental aspects of adhesion and adhesive joint strength
Authors: Schonhorn Harold , Frisch H. L.
Published: April 2003

We have outlined a theory which considers the durability of adhesive joints in the presence of a hostile environment. The approach is basically the Griffith theory modified for the presence of liquids. Two main conditions for spontaneous delamination of a composite appear to be immiscibility of the liquid in the environment with the members of the composite and complete interaction of the liquid (in a surface‐chemical sense) with one or more members of the composite. In the absence of chemisorption and interdiffusion in an A‐B composite, we find that (σfL/σf)2 = WABL/WAB, where σf is the critical stress to failure, WAB is the work of adhesion, and the superscript L refers to the presence of a liquid phase. When the liquid (L) interacts, in a surface‐chemical sense, with the composite, we have WAB > WABL, and σfL < σf. To illustrate the main features of the theory, composites are prepared whose interfacial tensions have been modified by the presence of an adsorbed monolayer of a fatty acid. In this instance, the interfacial tensions are changed so that WAB ≈ WABL and σfL ≈ σf. The composite then becomes more stable under an applied stress in the presence of an environment of high relative humidity.
Scattering of light from spherulitic polymers: Effect of internal structure
Authors: Prud'homme R. E. , Yoon D. , Stein R. S.
Published: April 2003

The scattering from a two‐dimensional spherulite is calculated on the basis of an assembly of anisotropic rods imbedded in an isotropic matrix and arranged in a spherulitic distribution. Provided the dimensions of the rods are small compared with the wavelength of the light, the scattering from such an assembly is shown to be identical with that from an internally uniform spherulite. The effective polarizabilities of this uniform spherulite in the radial and tangential directions are equal to the average polarizabilities in these directions of the constituent rods together with their surroundings.
Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as‐spun polyolefin fibers
Authors: Kitao Toshio , Ohya Seigo , Furukawa Junji , Yamashita Shinzo
Published: April 2003

Three different polyolefins, a linear polyethylene, an isotactic polypropylene, and an isotactic polybutene‐1, were melt‐spun into filaments. The degree of orientation of the filaments was measured by polarized‐light microscopy, x‐ray diffraction, and a retraction technique, and the results were then related to the melt‐draw ratio. The increase in the elastic deformation ratio of polymer chains by spin‐stretching, estimated by thermal retraction at a temperature above Tm, was monotonic with respect to the melt‐draw ratio. On the other hand, as‐spun filaments of polyethylene and polypropylene were characterized by a plateau in birefringence over the range of melt‐draw ratios from 8 to 80. The change in orientation functions for crystals in these filaments was similar to the change of birefringence. On the other hand, the birefringence and the crystalline orientation functions for polybutene‐1 increased smoothly with increasing melt‐draw ratio. The most highly melt‐drawn filaments of these polymers had a strongly oriented structure, corresponding to that in highly cold‐drawn specimens.
Elastic interaction between linear polymeric chains and periodic potentials
Authors: Kausch H. H. , Langbein D.
Published: April 2003

The elastic displacement of an axially stressed chain within crystalline surroundings, which was first treated by Chevychelov, is reexamined. We compare the results obtained for homogeneously distributed masses with that for discrete atoms, considering the nonuniformity of the potential of a crystal containing hydrogen bonds. In polyethylene and polyamide the maximum mechanical excitation of a chain penetrates into the crystal a distance of 15 to 20 chain atoms. The effect of the relative position of the crystal boundary on the stress‐strain field was studied and the energy of defects calculated.
Calculation of composition heterogeneity of block and graft copolymers
Authors: Vorlíček Jiří , Kratochvíl Pavel
Published: April 2003

The composition heterogeneity has been calculated for some block and graft copolymers. General relationships have been derived for a model of the poly(A‐g‐B) or poly‐(A‐b‐B) type fulfilling the assumption of random grafting. Numerical results have been calculated for special cases of particular interest. These include a copolymer having independent molecular weight contributions from units of species A and B (a special case of which is a block copolymer) and a graft copolymer where the grafting is not accompanied by crosslinking or degradation side reactions and no homopolymer B is formed. Two other model systems represent the effects of the presence or absence of both homopolymers. For the above models, the dependence of the composition heterogeneity on the structure‐determining parameters (average number of grafts in the molecule, polydispersity index of the molecular weight of the backbone and graft) is discussed. The heterogenities thus calculated are in many cases comparatively low. The composition heterogeneity of the system is in most cases increased by the presence of homopolymers.
Cryogenic tensile stress–strain properties of cis‐ and trans‐polybutadienes, polyisoprenes, and related copolymers
Authors: Morgan Roger J.
Published: April 2003

The low‐strain‐rate tensile stress–strain properties of cis‐ and trans‐polybutadienes and ‐polyisoprenes, polybutadiene (cis/trans/vinyl), butyl rubber, and two SBR copolymers have been investigated from 77°K to up to 25°K below the glass transition temperature Tg. The energy Ep dissipated in a stress–strain test in the region of previously reported secondary glass transitions is found to be a function of both the free volume f̄ at the Tg and the damping A from 4°K to Tg −25°K. The complex relationship between the impact strength, the free volume and the damping is briefly discussed. The effect of quenching through the Tg with liquid nitrogen was found to increase the value of Ep for all materials. In a number of cases this increase was associated with the presence of internal crazes. The surface‐craze initiation stress is increased by the presence of surface residual compressive stresses caused by quenching. The internal tensile stresses balancing the surface compressive stresses together with the applied tensile stress cause internal dilatation and hence preferential initiation of internal crazing.