bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of propagation and degenerate chain branching in the oxidation of polypropylene and polyethylene
Authors: Zolotova N. V. , Denisov E. T. 
Published: April 2003

AbstractSamples of polypropylene with adjacent and isolated hydroperoxide groups have been prepared. The rate constants of free‐radical formation from solid hydroperoxides were measured by the inhibitor method. It was found that the free radicals yielded by adjacent hydroperoxide groups are formed more rapidly. The main reaction of free‐radical formation in oxidized polypropylene is of the type: ROOH + ROOH → RO + H2O + RO2˙. The average yield of free radicals from polypropylene hydroperoxide is 2–4%. Oxygen has no effect on the yield of free radicals. However, the pressure of oxygen Po2 affects the rate of degenerate chain branching in polypropylene. The number of adjacent hydroperoxide groups and the rate of initiation increase with Po2. Consequently, a reaction of the type, R˙, + RH → RH + R˙, plays an important part in transport of free valence through solid polymer. This reaction is very fast in polyethylene, and no adjacent hydroperoxide groups are formed. The free radicals from polyethylene hydroperoxide are found to form by a reaction of the type: ROOH → RO˙ + HO˙.
Low‐temperature polyesterification in the presence of tertiary amines
Authors: Vinogradova S. V. , Vasnyev V. A. , Mitaishvili T. I. , Vasil'yev A. V. 
Published: April 2003

AbstractSeveral variations of catalysis (nucleophilic and general basic) responsible for the lowtemperature polyesterification in solution have been investigated. The type of catalysis which predominates depends on the chemical structure of the initial reagents and the reaction conditions. Increasing basicity of the tertiary amine and increasing acidity of the bisphenol promote the general base catalysis.
Side‐chain crystallinity. III. Influence of side‐chain crystallinity on the glass transition temperatures of selected copolymers incorporating n‐octadecyl acrylate or vinyl stearate
Authors: Jordan Edmund F. 
Published: April 2003

AbstractThe influence of side‐chain crystallinity on the glass transition temperatures of selected copolymers was investigated. The copolymers were selected, in part, from those whose crystallinity was treated in the preceding paper. These included the lower amorphous acrylate esters, such as methyl, ethyl, n‐butyl, and 2‐ethylhexyl acrylates, together with methyl methacrylate and acrylonitrile, each copolymerized with n‐octadecyl acrylate over the range of composition. The decline in the glass transition temperature was linear with increasing weight fraction of n‐octadecyl acrylate for all systems in the composition range where the copolymers were essentially amorphous. The extrapolated Tg for the amorphous state of poly(n‐octadecyl acrylate), and for amorphous poly(oleyl acrylate), was close to −111°C. This coincided with a value previously obtained by an extrapolation of data on homologs. Beyond a critical fraction of octadecyl acrylate (0.3 to 0.5), developing side‐chain crystallinity in n‐octadecyl acrylate raised the glass temperature steadily for all systems, up to a value of 17‐C, obtained for the crystalline homopolymer. Crystallinity did not develop in stiff copolymers until Tg was about 30°C below the melting point of the most perfect crystals. In compositionally heterogeneous copolymers incorporating vinyl stearate, blocks of crystalline units appeared to be dispersed in a glassy matrix of amorphous co‐units. An empirical equation was derived which fitted the experimental data for random copolymers, over all composition ranges, with fair accuracy.
Analysis of polymerization rates in radical polymerization with primary radical termination of some methacrylates
Authors: Ito Katsukiyo 
Published: April 2003

AbstractPolymerization rates in polymerizations with primary radical termination of ethyl methacrylate, β‐phenylethyl methacrylate, β‐methoxyethyl methacrylate, and phenyl methacrylate initiated by 2,2'‐azobis‐(2,4‐dimethylvaleronitrile) at 60°C were analyzed by using a simple linear equation. The values obtained of kti/kikp (where kti is the primary radical termination rate constant, ki is the rate constant of addition on to monomer of primary radical, and kp is the propagation rate constant) on these analyses are discussed on the theoretical base.
Stereospecific polymerization of butadiene in the presence of isobutylene
Authors: Veruović Budimír 
Published: April 2003

AbstractThe polymerization of isobutylene–butadiene monomer mixtures by a cobalt‐containing catalytic system (cobaltous acetylacetonate–diethylaluminum chloride–water) yields a homopolymer mixture consisting of polyisobutylene and polybutadiene. It is assumed that the polymerization of both monomers proceeds according essentially identical reaction mechanisms, i.e., isobutylene polymerizes cationically and butadiene follows a coordination‐cationic mechanism.
Anionic bulk polymerization of α‐methylstyrene. Stopping of polymerization due to vitrification and equilibrium in bulk
Authors: Mita Itaru , Okuyama Hiroshi 
Published: April 2003

AbstractAnionic living polymerization of α‐methylstyrene containing a small amount of THF (less than 10%) was studied at temperatures between −30°C and 50°C. At any temperature studied, a certain quantity of monomer remained without further polymerization. The effect of temperature and THF content on the final state was completely different in low and high temperature regions; at temperatures lower than ca. 20°C, the final monomer concentration decreased with increasing polymerization temperature and THF content. This is explained by the concept of “stopping of polymerization due to vitrification” of the polymerizing mixture. In fact, the final reaction mixture is really glassy in most cases and the red color of living polymer buried in the glass is discolored only very slowly when exposed to air. Detailed analysis of the results showed that the vitrification stopping holds only approximately. At temperatures higher than ca. 30°C, a normal equilibrium between propagation and depropagation holds, and the final monomer concentration increased with temperature. It is, however, far less than the equilibrium monomer concentration obtained in solution polymerization at the same temperature, and it increased appreciably with the increase in THF content. It is shown that the behavior of the equilibrium for the whole concentration range can be explained satisfactorily by a thermodynamic theory of ternary mixture.
Aminimides. XII. Synthesis, homo‐ and copolymerization studies of trialkylamine N‐acryloyl or N‐methacryloyl glycinimides and β‐aminopropanimides
Authors: Culbertson B. M. , Freis R. E. , Grote D. 
Published: April 2003

AbstractSome representative examples of a new family of aminimide monomers, i.e., trialkylamine N‐acryloyl or N‐methacryloyl glycinimides and β‐aminopropanimides have been prepared and studied. These are the first examples of a possible large family of primary aminimide monomers. With radical initiators, the acryloyl and monosubstituted methacryloyl monomers readily homopolymerize. The disubstituted methacryloyl aminimides do not homopolymerize under the same conditions. All of the new monomers copolymerize with styrene, methyl methacrylate, and n‐butyl acrylate. The various polymers were characterized by IR, DTA, TGA, GPC and inherent viscosities. When heated (160°C) the polymers liberate amine and crosslink in the presence of active hydrogen moieties to give resins with carbamate, urea, allophonate, etc., residues. When no active hydrogens are available during heating, polymers can be prepared with pendent primary isocyanate groups. This preliminary work shows these monomers to be highly useful for preparing a wide variety of reactive copolymers.
Thermodynamic properties of epoxy reaction systems
Authors: Aleman J. V. 
Published: April 2003

AbstractEnthalpy, entropy, and Gibbs free energy of epichlorhydrin, bisphenol A, and epoxy resins from specific heat data obtained experimentally in a DuPont 900 differential thermal analyzer are described. The epoxy resin used has a second‐order transition temperature around −15°C and a chain rigidity of 50.6 cal/g.
60Co‐initiated copolymerization of styrene with vinyl acetate
Authors: Niezette Joseph , Desreux Victor 
Published: April 2003

AbstractThe kinetic behavior of the 60Co‐initiated copolymerization at 25°C of styrene with vinyl acetate at 1100 and 2000 rad/hr was studied. As in the case of thermal and photochemical copolymerizations of these monomers, the growing chains are particularly rich in styrene units, and the overall rate is affected by a diluent effect due to the vinyl acetate monomer. However, in the case of the radiation copolymerization, this effect is partially counterbalanced by an increase of the initiation rate with the vinyl acetate concentration; the polymerization rate curve shows a maximum at a vinyl acetate molar fraction of 0.25. This effect is due to the very different free radical yields of these two monomers. The experimental results may be understood on the basis of a kinetic scheme which involves an energy transfer process from the excited vinyl acetate molecules to the styrene monomer and a termination reaction of the growing chains by very short styrene radicals when the mixture is rich in vinyl acetate.
Polymerization of vinyl chloride by the Ti(O‐n‐Bu)4–AlEt3–epichlorohydrin catalyst system
Authors: Suzuki Yuji , Saito Mitsutaka 
Published: April 2003

AbstractThe polymerization of vinyl chloride was carried out by using a catalyst system consisting of Ti(O‐n‐Bu)4, AlEt3, and epichlorohydrin. The polymerization rate and the reduced viscosity of polymer were influenced by the polymerization temperature, AlEt3/Ti(O‐n‐Bu)4 molar ratios, and epichlorohydrin/Ti(O‐n‐Bu)4 molar ratios. The reduced viscosity of polymer obtained in the virtual absence of n‐heptane as solvent was two to three times as high as that of polymer obtained in the presence of n‐heptane. The crystallinity of poly(vinyl chloride) thus obtained was similar to that of poly(vinyl chloride) produced by a radical catalyst. It was concluded that the polymerization of vinyl chloride by the present catalyst system obeys a radical mechanism rather than a coordinated anionic mechanism.
Studies on formaldehyde condensation resins. XII. Gelation theory for tetrafunctional amino resins
Authors: Uragami Tadashi , Oiwa Masayoshi 
Published: April 2003

AbstractGeneral kinetic equations for the gelation reaction of tetrafunctional amino monomer with formaldehyde are formulated according to Case's gelation theory. The ratio of the rate constant of the condensation reaction to that of the addition reaction is evaluated by applying a theoretical kinetic equation to the experimental measurements. The ratio of the rate constant for addition of an imino group to that for an amino group is also determined by combining the kinetic equation, stoichiometric relation, and expression for the gel point. The total yield of resin, the yield of sol, and the number‐average molecular weight of the sol fraction are discussed.
Studies on formaldehyde condensation resins. XIII. Gelation of acetoguanamine–formaldehyde resin
Authors: Uragami Tadashi , Oiwa Masayoshi 
Published: April 2003

AbstractThe gelation reaction of acetoguanamine with formaldehyde was investigated in the light of the gelation theory for tetrafunctional amino resins described in the previous paper. The gel time and extents of reaction of formaldehyde, amino groups, and imino groups varied with the molar ratio in the feed, but values of K (the ratio of the rate constant for condensation to that for addition) and k (the ratio of the rate constant for addition of the imino group to that of the amino group) were nearly constant. When the catalyst concentration was increased, the gel time, extents of reaction of each functional group, and the values of K and k varied; in particular K increased markedly. From the results of varying the molar ratio and concentration of acidic catalyst, it was found that the number of methylol groups per molecule of acetoguanamine at the gel point was influenced by the reaction conditions but the number of methylene linkages per molecular of acetoguanamine was nearly constant at about 0.6, regardless of reaction conditions. The number‐average molecular weights up to the gel point varied with the reaction conditions, but at the gel point they were all nearly constant at about 385.
Lamellar and interlamellar structure in melt‐crystallized polyethylene. II. Lamellar spacing, interlamellar thickness, interlamellar density, and stacking disorder
Authors: Kavesh S. , Schultz J. M. 
Published: April 2003

AbstractMeasurements of the small‐angle scattering power and the degree of crystallinity in melt‐crystallized high‐density polyethylene have been used to evaluate the “amorphous” density in situ by the relation,

where V is the irradiated volume and ḡ(S) is the “slit‐smeared” absolute intensity. The amorphous density is a function of sample history and is always higher than the extrapolated melt density. After slit‐height correction, and within the experimental error, the ratio of the two observed long periods is 2:1 at all temperatures (25‐‐126°C). The lamellar thickness and the average interlamellar spacing are obtained from the degree of crystallinity and the first corrected long period. At increasing temperatures between 25°C and 110°C, the lamellae become thinner while the interlamellar zone expands by almost half. Over this range the changes are reversible with temperature. Above 110°C, both the lamellae and the interlamellar region expand with temperature. The thickening is partially reversible upon recooling. Other results obtained include measurements of stacking disorder and of microstructural changes with crystallization temperature and with time at ambient temperature.
Structure and optical activity of a crystalline modification of isotactic poly‐(S)‐4‐methyl‐1‐hexene
Authors: Bassi I. W. , Bonsignori O. , Lorenzi G. P. , Pino P. , Corradini P. , Temussi P. A. 
Published: April 2003

AbstractThe results of an x‐ray and polarimetric study of a crystalline modification (form I) of isotactic poly‐(S)‐4‐methyl‐1‐hexene are reported and discussed. The x‐ray fiber spectra of this polymer are practically indistinguishable from those of isotactic poly‐(R)‐(S)‐4‐methyl‐1‐hexene. Although the crystal structure of the latter can be described on the basis of helices of different screw sense packed in a P4 space group, the crystal structure of poly‐(S)‐4‐methyl‐1‐hexene is better described on the basis of a P1 space group. The conclusion of the x‐ray investigation, that in the crystals of the optically active polymer an equal number of right‐handed and left‐handed helices must be present, is supported by the polarimetric measurements, which have shown that the polymer in the crystalline form I possesses a rather low rotatory power.
Side‐chain relaxation in stereoregular poly(isobutyl methacrylate)
Authors: Ochiai Hiroshi , Shindo Heisaburo , Yamamura Hitoshi 
Published: April 2003

AbstractThe effects of stereoregularity on the low‐temperature relaxation processes were studied by dynamic mechanical measurements on isotactic and syndiotactic polyisobutyl methacrylates (iso‐PiBMA and syn‐PiBMA). The α, β, and γ relaxation processes were observed in both stereoregular forms. Both the α, and β loss peaks were at lower temperatures for iso‐PiBMA than for syn‐PiBMA. The γ loss peak was observed at about −155°C at 30 Hz for both forms, and the apparent activation energy of this process was same for both samples within experimental error (6.7 ± 0.5 kcal/mole). It was reduced from these results that the α and β processes are both considerably influenced by the isotactic configuration but the γ process is not.
Occurrence of rippling during the deformation of oriented polyethylene
Authors: Robertson Richard E. 
Published: April 2003

AbstractRippling is another mode, in addition to kink‐band formation, by which oriented polyethylene can deform and results in a profuse and irregular waviness in the fibrils. For the medium‐density and high‐density polyethylenes investigated, rippling tended to occur only at strain rates below about 1 min−1 at 25°C. Above this rate, kink bands tended to form. It is suggested that rippling results from easy slip between the fibrils of the oriented polymers and from the resistance of the fibrils to shortening under a compressive stress. The applied shear stress is reduced by the easy slip to a simple compression along the fibrils, and this distorts the fibril into the series of waves that constitutes rippling. Stress–strain measurements confirm that fibril slip is considerably easier under the rates at which rippling occurs than at the rates at which kink bands form.
Effect of pressure in capillary flow of polystyrene
Authors: Penwell Richard C. , Porter Roger S. 
Published: April 2003

AbstractSeveral corrections possibly required for capillary flow are based on the existence of a linear relationship between the pressure drop along the capillary and the length‐to‐diameter ratio at a given temperature and shear rate. Recently, the appearance of nonlinearities in this relationship has created some concern as to the cause of this behavior. The occurrence and an explanation of the nonlinearities for polystyrene form the basis of this study. A narrow‐distribution, low molecular weight (20,400) polystyrene was tested in eight capillaries at temperatures of 140 and 160°C to initiate the discussion of the nonlinearity in a ΔP (pressure) versus L/D (length/diameter of capillary) plot. The sample exhibits negligible extrudate swelling at all pressures which reinforces the idea that pressure is influencing the flow. The pressure dependence of viscosity is determined using the equivalent expression of the WLF equation derived from free volume theory. Justification for its use is presented. A pressure correction, representing the increased shear stress necessary for flow of the higher viscosity material, is found to linearize the ΔP versus L/D data. A narrow‐distribution, high molecular weight polystyrene (670,000) is subjected to a similar analysis at 165°C by using nine capillaries. The situation is quite different, as the high molecular weight sample is not nearly as ideal as the low molecular weight polystyrene.
Dielectric and rheo‐optical properties of some ethylene‐carbon monoxide copolymers
Authors: Phillips P. J. , Wilkes G. L. , Delf B. W. , Stein R. S. 
Published: April 2003

AbstractStudies were made on films of copolymers of ethylene with 0.5 and 1.0 mole‐% carbon monoxide. The carbon monoxide appeared negligibly to affect the degree of crystallinity, melting point, morphology, and dynamic mechanical spectra. Infrared dichroism showed that the orientation of the carbonyl groups was comparable with that of the crystalline CH2 groups and indicated that the carbonyl groups are at least partially within the crystals. This is confirmed by x‐ray measurements which indicate an expansion of the a‐axis spacing and by an appreciable increase in the height of the α dielectric loss peak which has been assigned to crystalline motion. This α loss peak moves to a lower temperature with increasing carbonyl content, while the γ dielectric loss peak moves to higher temperatures. Activation energies of 25, 35, and 15 kcal/mole for the α, β, and γ peaks, respectively, were independent of carbonyl content and comparable with values for oxidized polyethylene.
Segmental motion in polyoxymethylene
Authors: Crist B. , Peterlin A. 
Published: April 2003

AbstractThe proton spin‐lattice relaxation times (T1) of melt‐crystallized, solution‐crystallized, and solid‐state‐polymerized polyoxymethylene (POM) were measured between −60 and +150°C. The three types of samples each have a pronounced T1 minimum near room temperature which is a high‐frequency manifestation of the γ process. From the quantitative dependence of the relaxation intensity on crystallinity as well as from the absolute magnitude of the relaxation times, it is concluded that the γ process in POM arises from hindered rotation of noncrystalline chain segments. The relation between the relaxation times and the long period indicates that these noncrystalline segments constitute disordered lamellar surface layers, the thickness of which depends on thermal history of the material. The temperature dependence of the motion of the relatively thin surface layers of solution crystallized POM is quite straightforward. The γ process in the bulk‐crystallized material involves cooperative motion, however, leading to temperature‐dependent kinetic parameters.
Size‐distribution analysis of polymer latex systems by use of the extrema in the angular light‐scattering pattern: II. The polarization ratio
Authors: Wallace Thomas P. 
Published: April 2003

AbstractPreviously, the angular positions of the extrema of the polarization ratio have been utilized in light‐scattering studies as a method of particle‐size analysis under the assumption of monodisperse, spherical particles. Since the consequences of the existing finite polydispersity on this method of analysis was not assessed, the results are questionable. This work is concerned with (1) reporting the quantitative effects of a finite polydispersity on the method of analysis, (2) pointing out previous misuse of the method, and (3) revising the method of analysis to include polydispersity and the exact Mie calculations. The method will then permit the characterization of a scattering system in terms of a modal diameter and a distribution‐width parameter by utilizing prepared diagrams for a particular relative refractive index.
Polymerization mechanisms and stereosequence distributions: A monomer–dimer model
Authors: Pyun Chong Wha , Fox Thomas G 
Published: April 2003

AbstractA polymerization mechanism in which monomers and dimers add to a growing polymer chain with different rate constants and different stereospecificity is considered. A fraction of the dimers are in isotactic placement internally, and low conversion to polymer is assumed. The stereosequence distribution generated by this monomer–dimer model is calculated and found to be non‐Markovian in general. A method of determining kinetic parameters of the mechanism from experimentally obtained placement sequence probabilities and related experimental tests for the applicability of the mechanism are also described. A few ramifications of the general monomer–dimer model are then discussed. A case of special interest is the one in which all the dimers have a single internal tacticity, a model recently proposed by Blumstein, et al., for a polymerization involving the surface of certain aluminosilicate minerals. For the case where all dimers are isotactic, it is found that although the propagation of consecutive syndiotactic placements alone is simple Markovian, the overall stereosequence distribution is non‐Markovian. Another special case of interest is the limiting case with dimers only in the feed. This case turns out to correspond to a special case of the cyclopolymerization mechanism proposed previously by Reinmöller and Fox. Although the tacticity distribution of the placements created by the head (or tail) monomer units alone of the dimers is Bernoullian, the composite stereosequence distribution is again non‐Markovian.