bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permeation of gases through modified polymer films. I. Polyethylene–styrene graft copolymers
Authors: Huang R. Y. M. , Kanitz P. J. F. 
Published: April 2003

AbstractThe permeabilities of nitrogen, oxygen, and carbon dioxide through polyethylene–styrene graft copolymer films were measured by means of a gas permeability apparatus based on a modification of Barrer's high vacuum technique. Polyethylene–styrene grafts were prepared by mutual γ‐ray irradiation of low‐density polyethylene films in styrene–methanol solution. Densities and thicknesses of the graft copolymer films were determined. It was observed that the gas permeability constants decreased with increasing grafting to minimum values at 20–30% styrene grafting and increased again above 30% grafting. These results are explained in terms of a decrease in the free volume of the amorphous regions of the polyethylene by a “filling in” effect of the grafted polystyrene chains. Above 30% grafting, disruption of the crystallites may occur resulting in increased gas permeation. Activation energies for gas permeation through polyethylene–styrene graft copolymer films were calculated and found to decrease with increasing per cent styrene grafting. For nitrogen permeation, the activation energy decreased from 11.7 kcal/mole for unirradiated polyethylene to 9.5 kcal/mole for a 50.5% graft. Corresponding values for oxygen and carbon dioxide were 10.2–8.2 kcal/mole for a 48.7% graft and 8.4–6.5 kcal/mole for a 50.5% graft.
Transport properties and their correlation with the morphology of thermally conditioned polypropylene
Authors: Vieth Wolf , Wuerth Walter F. 
Published: April 2003

AbstractTime‐lag and static sorption experiments were employed to measure permeability, diffusivity and solubility constants of He, A, and CF4 in polypropylene films cooled at various rates from the melt and subsequently annealed at varying temperatures near the melting point. While solubility constants in films annealed above 90°C showed the normal variation with the amorphous content of the polymer, solubility constants for all unannealed, quenched films were remarkably constant and independent of the rate of cooling. In fact, all quenched films appeared to have the same amorphous content (ca. 41%). The remaining material is believed to be a mixture of monoclinic and hexagonal crystallinity, the volume ratio of the two being a function of the rate of quenching, and changing on annealing, in favor of the more stable, monoclinic form; the transition occurring rather sharply at 90°C. X‐ray diffraction provided supporting evidence for the presence of the hexagonal crystals. The diffusion behavior in crystalline polypropylene is normal and Fickian but instead of the usual decline with increasing crystallinity, diffusivities showed definite enhancement in the case of the annealed films, i.e., the expected monotonic decline of D with increasing crystallinity is not observed. This behavior is attributed to a reduction in diffusional impedance through formation of defects in existing crystallites, as the lamellae thicken, in a manner similar to that observed on annealing of polyethylene single crystals. The apparent activation energies of diffusion were essentially constant and independent of thermal history. This suggests that in a highly crystalline polymer diffusion is not so much impeded by the restricted mobility of chain segments but rather by the extremely small dimensions of the available diffusive pathways. In support of the argument that the transport properties of polypropylene are controlled at a level of microstructure well below the characteristic dimensions of spherulities, it was observed that bulk‐crystallized polypropylene has a spherulitic structure whose size and texture do not change significantly on annealing.
Some rheological properties of water‐soluble hydroxypropylcellulose
Authors: Elliott John H. 
Published: April 2003

AbstractWater‐soluble hydroxypropylcellulose having a hydroxypropyl molecular substitution (MS) of approximately 4.0 is a thermoplastic which may be fabricated in conventional plastic‐forming equipment. Its high‐temperature rheological properties have been measured over a wide range of temperatures, shear rates, frequencies, and diluent concentrations, by using the Weissenberg rheogoniometer. The rheological behavior of such hydroxypropylcelluloses is quite different from that of a nonpolar thermoplastic. This behavior may be interpreted in terms of two types of supermolecular structure: a crystalline phase which persists up to at least 215°C (as established by x‐ray examination), which is dispersed in an amorphous but highly hydrogen bonded matrix of stiff molecules.
Polymer rheology: Influence of molecular weight and polydispersity
Authors: Cross Malcolm M. 
Published: April 2003

AbstractLiterature data on the non‐Newtonian flow of bulk polymer and of polymer solutions are correlated on the basis of a four‐parameter equation, η = η∞ + (η0 − η∞)/[1 + (τD)m], η being the viscosity at shear rate D, and η0 and η∞ limiting values at D = 0 and D = ∞, respectively. The parameters η0, η∞, and τ all show dependence on molecular weight, and in general there is good correlation between τ and η0. There is evidence that τ is related to a molecular weight higher than the weight‐average. The exponent m shows dependence on molecular weight distribution and approaches an upper limit of unity for a monodisperse linear polymer. For linear unblended polymers it may be expressed empirically by m = (M̄n/M̄w)1/5.
Effect of mastication on molecular weight and molecular weight distribution of EPDM polymer and SBR
Authors: Baranwal Krishna , Jacobs Howard L. 
Published: April 2003

AbstractEPDM and SBR were masticated on an open mill. The temperature range of mastication for EPDM was 68–480°F. SBR was milled at 170–200°F. The gel‐permeation chromatography analyses were made on the masticated samples. For EPDM at 68°F, molecular weight decreases and molecular weight distribution narrows with mastication time; the degradation process is nonrandom. At constant mastication time between 182 and 315°F, there is little change in molecular weight. Mastication for 18 min at 480°F broadens the molecular weight distribution; the degradation is random. For SBR at 170–200°F, molecular weight decreases and molecular weight distribution narrows with mastication time; the degradation process is also nonrandom. Nonrandom degradation for both EPDM and SBR results in a narrowing of the molecular weight distribution, without build‐up of low molecular weight molecules, and without a shift in the peak molecular weight. This is contrary to nonrandom degradation of natural rubber where a shift in the peak molecular weight occurs with mastication time.
Prediction of polymer densities
Authors: Van Krevelen D. W. , Hoftyzer P. J. 
Published: April 2003

AbstractA method is proposed for predicting the density of a linear, amorphous polymer. The method is based on the additivity of group increments for the molar volume of a polymer unit. It is analogous to the published methods for predicting the molar volume of organic liquids. The method may be improved as additional experimental values on polymer densities become available.
Autoxidation of poly(alkylene glycols) in solution
Authors: Reich Leo , Stivala S. S. 
Published: April 2003

AbstractData reported for the autoxidation of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) in solution at relatively long reaction times were analyzed. A relatively simple and a more general kinetic scheme with corresponding rate expressions were used. It was found that the more general scheme gave somewhat more satisfactory agreement between calculated and observed values of several reaction variables. Limitations in the applications of both schemes to PEG and PPG autoxidations are mentioned.
Investigation of creep phenomena in polyethylene and polypropylene
Authors: Sinclair James E. , Edgemond John W. 
Published: April 2003

AbstractAlthough creep in thermoplastics, especially for polyethylene, has been investigated throughly, not too much information exists to establish activation energies at different stress levels by the application of high stress‐level, short‐time creep tests. Extrapolation of data to zero stress gives a true material activation energy which is a measure of internal resistance to deformation. Descriptions of specific creep parameters and equipment with a relatively simple phototube recording device are offered along with a discussion of results and recommendations for future fields of investigation.
Effect of conjugated trienes on the oxidation of polyisoprenes
Authors: Campbell D. S. 
Published: April 2003

AbstractThe effect of low concentrations of conjugated triene on the rate of oxidation of polyisoprenes has been investigated. At concentrations similar to those expected to occur in sulfur vulcanizates of NR, conjugated trienes exert a significant accelerative effect on both the uninhibited and the inhibited oxidations of squalene. This accelerative effect is also present, but to a lesser extent, in the inhibited oxidation of carbon–carbon cross‐linked NR vulcanizates.
Aging and loss of flocculation activity of aqueous polyacrylamide solutions
Authors: Shyluk W. P. , Stow F. S. 
Published: April 2003

AbstractThere is a rapid and a slow stage in the decrease of reduced specific viscosity versus time (aging) for a solution of a high intrinsic viscosity polyacrylamide in water. The rapid stage is irreversible and has a fairly high temperature coefficient. Results of the latter type are usually associated with a weak‐link scission mechanism, but they can also be reconciled with a disaggregation mechanism. A disaggregation mechanism is also indicated for the rapid stage by an increase in the first‐order rate contant with a decrease in the polymer concentration or an increase in the shear rate and by the absence of the rapid stage during the aging of the same sample in formamide. Chemical changes in the polymer are suspected as being responsible for the RSV change during the slow stage in the aging of the high intrinsic viscosity polyacrylamide and also in the aging of a polyacrylamide of low intrinsic viscosity. The aging of the polyacrylamide of high intrinsic viscosity is paralleled by a decrease in the ability of the polymer to increase the subsidence of kaolin suspensions. This decrease in the flocculation activity is attributed to a weakening of the interparticle bridging by a change from a strong adsorption of the bridging polymer to two particles to a strong adsorption of the bridging polymer to one particle but weak adsorption of the bridging polymer to the other particle.
Reactivity of cotton after treatment in alkaline and acid swelling agents
Authors: Warwicker J. O. , Clayton J. W. 
Published: April 2003

AbstractThe reactivity of scoured Acala 4‐42 cotton before and after treatment with alkaline and acid swelling agents has been assessed by a number of methods. It is shown that the reactivity depends more on the type of swelling, whether it is interfibrillar or intrafibrillar, than on the degree of swelling achieved. Furthermore, the reactivity of the treated cotton depends on whether the reaction is carried out in a nonswelling or a swelling medium. Thus high intrafibrillar swelling can lead to a loss in reactivity of the treated cotton if the subsequent reaction takes place in a medium incapable of swelling the treated cotton, on the other hand, interfibrillar swelling can lead to an increase in reactivity in the same reaction mixture.
Influence of water on stress corrosion cracking of epoxy bonds
Authors: Mostovoy Sheldon , Ripling E. J. 
Published: April 2003

AbstractEnvironment assisted fracturing, or stress corrosion cracking of adhesive joints in liquid water or a humid atmosphere was shown to occur at values of applied crack extension force ςa considerably below those required for onset of opening‐mode rapid fracture ςc. The minimum value of ςa below which no cracking was observed, ςSSC, was dependent on the relative humidity and the particular adhesive used. For two adhesive systems, the one with the lower hardener content and post cure temperature showed both a lower absolute value of ςSSC and a lower ratio of ςSSC to ςc. The value of ςSSC for both adhesive systems decreased as the humidity was increased. As the relative humidity approached 100%, the value of ςSSC approached its value for liquid water. Values of ςc for the two adhesives differed by a ratio of approximately 2:1. When water was introduced to the crack tip, ςc for the less tough material increased while it was not significantly changed for the tougher material.
NMR analysis of chlorinated poly(vinyl chloride)
Authors: Svegliado G. , Grandi F. Zilio 
Published: April 2003

AbstractThe chlorination of poly(vinyl chloride) takes place preferentially at the methylenic carbon, leading to 1,2‐dichloroethylenic units, and to a lower extent at the methynic, leading to 1,1‐dichloroethylenic units. The ratio between 1,2‐ and 1,1‐dichloroethylenic units tends to decrease with increasing degree of chlorination, and it seems to depend also on the chlorination conditions. The number‐average sequence length of 1,2‐dichloroethylenic units does not differ significantly from 1 during a great part of the process, substantially in agreement with a random distribution of these units along the chain. The 1,1‐dichloroethylenic units can be found either between two unchlorinated units or at one end of a sequence of chlorinated units. Since among the unchlorinated units more racemic units are present than expected for a completely random chlorination, it can be suggested either that chlorination is affected by stereoregularity or that it does not take place in the crystalline regions of the polymer.
Radiation‐induced emulsion polymerization of vinyl acetate and styrene
Authors: Stannett V. , Gervasi J. A. , Kearney J. J. , Araki K. 
Published: April 2003

AbstractStudies have been made of the γ‐induced emulsion polymerization of styrene and comparisons made with chemically initiated emulsion polymerization. The polymerization proceeded smoothly to high conversions at 0 and 60°C, the reaction showing a high G (monomer) value. Complete conversions were obtained with total doses of less than 0.05 Mrad. In accordance with the behavior expected of systems having a constant rate of initiation, the molecular weight was found to decrease with decreasing temperature. The molecular weight and particle size distributions were narrower than those obtained in chemically initiated emulsion polymerizations at the same temperature. The radiation‐induced emulsion polymerization of vinyl acetate proceeded smoothly at temperatures in the range 0–50°C to give polymers of much higher molecular weight than these obtained from chemically initiated polymerizations at the same temperature. Complete conversion was attained after a dose of 0.02 Mrad for latices approaching 50% solids. The elimination of ionic endgroups in the poly(vinyl acetate) radicals tends to drive the polymerization from the aqueous phase, resulting in faster rates and higher molecular weights than are obtained from chemically initiated systems. Rates of polymerization were found to be independent of temperature and the molecular weight of the polymer to be independent of dose rate. Latices of poly(vinyl acetate) of high solids content were evaluated for latex and film properties and found to have improvements over commercially available samples in both areas, especially in clarity of film and scrub resistance. A number of acrylate and maleate esters were copolymerized with vinyl acetate in a radiation‐initiated emulsion system. High molecular weight copolymers were produced after low dose.
Structural characterization of vulcanizates part X. Thiol‐disulfide interchange for cleaving disulfide crosslinks in natural rubber vulcanizates
Authors: Campbell D. S. 
Published: April 2003

AbstractThe thiol‐disulfide exchange reaction is shown to be applicable to cleavage of disulfide crosslinks in accelerated sulfur vulcanizates of natural rubber. The reaction, in conjunction with the previously reported selective cleavage of polysulfide crosslinks, is used to determine the distribution of crosslink types for several accelerated sulfur vulcanization systems as a function of cure time. Discrepancies between the results and published results obtained using the reagent sodium di‐n‐butyl phosphite for disulfide crosslink cleavage are discussed.
The cupric sulfate‐hydrazine‐oxygen system as an initiator for the emulsion polymerization of methyl methacrylate
Authors: Bond Joan , Lee P. I. 
Published: April 2003

AbstractThe kinetics of the emulsion polymerization of methyl methacrylate initiated by the cupric sulfate‐hydrazine system in the presence of oxygen have been evaluated.A maximum rate of polymerization occurs at a cupric sulfate concentration of 1.8 × 10−4 mole liter−1. The adsorption of cupric ion on the micelles and the adsorption of soap on cupric hydroxide are discussed as an explanation of this effect.A reaction between hydrazine and methyl methacrylate produces a surface active agent which enhances the rate of polymerization and increases the number of particles at high ratios of monomer concentration to soap concentration.The kinetics follow the mechanism of Gershberg rather than that of Smith and Ewart, and the initiation of the emulsion polymerization appears to take place inside the micelle rather than in the aqueous phase as was proposed by van der Hoff for styrene.The activation energy for the complete process is 23.7 kcal mole−1.
The mechanical properties of films and their relation to paint chipping
Authors: Bender Howard S. 
Published: April 2003

AbstractA correlation has been made between dynamic mechanical properties and impact resistance of a multicoat paint system. It has been determined that the shear or rigidity modulus and damping of free primer films are some of the parameters that control the impact characteristics of the system. Those films of low modulus and high damping show the best chip resistance. A series of physical and chemical modifications were made on the primer and chipping results were compared with dynamic mechanical properties of free paint films. It was found that increasing cure temperature, addition of catalysts, decreasing the oil length of the resin, increasing the amount of pigmentation and increasing the tension and strain rate all led to increased paint chipping and increases in the modulus of rigidity. Two new primers were synthesized which incorporated the above results and were found to give increased gravel impact resistance.
Thermal conductivity of some electron transfer polymers
Authors: Jenkins Robert K. , Byrd Norman R. , Lister James L. 
Published: April 2003

AbstractA number of electron transfer polymers were prepared by reacting various α, ω‐alkanediamines with benzoquinone. The resulting polymers, through the formation of inter and intramolecular complexes, displayed high thermal conductivity with a strong temperature dependency. The mechanism contributing to the increased thermal conductivity was attributed to strong interchain complexing.
The thermal analyses of polymers. II. Thermomechanical analyses of segmented polyurethane elastomers
Authors: Miller G. W. , Saunders J. H. 
Published: April 2003

AbstractThe development of new and more sensitive techniques in thermal analyses aids in a more complete understanding of the contributions of individual components in urethane elastomers regarding their mechanical and thermodynamic behavior. The behavior of various segments of the elastomers reported in this work illustrates a clearer interpretation of reasons for changes in mechanical behavior caused by changes in heat capacity, volume and tensile properties; the gross changes previously reported for polyurethane properties as a function of temperature are also confirmed with a more exact definition of their origin.The sub‐ambient temperature behavior and response of physical measurements near the melting point of the backbone polyol are largely a function of the so‐called “soft block.” The soft block does not contribute to the mechanical properties above the melting point of the polyol unless some urethane segments from the diisocyanate and extender are structured into the soft block, that is, excess diisocyanate and extender are added to build in the “hard” block. The extender and isocyanate influence for both low and high temperature properties is observed by the lack of molecular fit imparted to the backbone polyol as well as some crystallinity in the polymer hard block. The usual Tg transition reported in urethane elastomers corresponds to a first‐order transition in the polyester or polyether backbone.
Kinetics of autoxidation of isotactic polybutene‐1 by infrared spectroscopy
Authors: Stivala S. S. , Yo G. , Reich Leo 
Published: April 2003

AbstractThe autoxidation of a film of isotactic polybutene‐1 (IPB) containing a relatively large amount of metallic ash (≈0.2%) was studied by means of infrared spectroscopy. Reaction temperatures were varied from 105 to 120°C and oxygen concentrations from 25 to 100% by volume. A reaction scheme previously reported for the autoxidation of atactic polybutene‐1 (APB) was utilized for the IPB. Various results obtained for IPB were compared with those previously reported for APB.
Stress softening in elastomer blends
Authors: Meluch William C. 
Published: April 2003

AbstractCompressive stress softening (Mullins effect) in black‐filled vulcanizates of the blended system natural : nitrile : brominated butyl rubber has been investigated. The results are expressed in terms of parameters derived from successive stress‐strain cycles. The ratio of the work done on loading in the first and second cycles is called the load work ration, Rw. A similar quantity, Rh, is defined for the loss or hysteresis work. Both load and loss work ratios show a compositional dependence similar to other properties of blends. The variation of Rw and Rh with composition agrees with the recent thesis of Mullins, Harwood, Payne and others that the Mullins effect is a property of the elastomer. Sudden variation of Rh with elongation has been interpreted in light of recent results of R. W. Smith as indicative of vacuole formation.
The continuous synthesis of addition polymers with a pricesely controlled average molecular weight and minimum polydispersity
Authors: Kenat Thomas A. , Kermode Richard I. , Rosen Stephen L. 
Published: April 2003

AbstractA novel technique for the control of continuous synthesis of addition polymers with precisely controlled average molecular weight and minimum polydispersity has been developed. A control system adjusts the concentration of chain‐transfer agent in the reactor feed to compensate for all other upsets, in the reactor inputs: initiator and monomer concentrations, temperature and feed rate. The technique has been evaluated quantitatively on a digital computer using a kinetic model of homogeneous, free‐radical solution polymerization. In computational tests, the modeled control system generally held the instantaneous number‐average chain length within 1%, and quickly returned it to the desired value in response to a wide variety of upsets. By generalizing the Schulz distributions to include termination by disproportionation, combination and chain‐transfer, it is shown that changes in the molecular‐weight distribution resulting from the action of the control system are minor.
Rate effects in the measurement of polymer transitions by differential scanning calorimetry
Authors: Strella S. , Erhardt P. F. 
Published: April 2003

AbstractDepending on heating rate, differences as large as 15°C in polymer transition temperatures may be observed in DCS measurements. A heat transfer analysis of the method shows that this rate dependence is a result of a lag in the heat path to the test sample and lag in heat transfer within the sample. Experiments confirmed the analysis. Methods for obtaining the correct values of transition temperatures are given.