bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crosslinking of copolymers of N‐methylolacrylamide and ethyl acrylate induced by heat treatment
Authors: Kamogawa Hiroyoshi , Sekiya Toshii 
Published: April 2003

AbstractThe effects of crosslinking by N‐methylolacrylamide in emulsion copolymers with ethyl acrylate under heat treatment in acid medium was investigated, and various methods for calculating the effective density of crosslinking were compared. It was found that stress‐strain relationships of copolymer films showed marked dependence both on the temperature of cure and on the methylolamide group content of the polymer; these dependences can be attributed to the formation of crosslinkages between polymer chains. The effective densities of crosslinking (ρ) of the cured copolymer films were calculated according to three methods: (1) stress‐strain measurement in dry state (ρe); (2) stress‐strain measurement in acetone (ρe′); (3) measurement of the degree of swelling in acetone (sρe). Values of ρe must be corrected with values for polymer with an infinite degree of swelling by use of the empirical equation of Mooney and Rivlin, in order to eliminate such steric factors as polymer chain entanglements; this method was found to be the most rational of the three, since ρe′ and sρe had their respective faults. The effective densities of crosslinking were found to be proportional to the squares of the methylolamide contents of the polymers, and there was a linear relationship with −5/3 slope between the logarithms of the stress and the degree of swelling, satisfying the theoretical expression.
The fractionation and molecular weight distribution of polypropylene
Authors: Davis Thomas E. , Tobias Robert L. 
Published: April 2003

AbstractThe application of the sand columm extraction, fractional coacervation, and coacervate extraction methods to the molecular weight fractionation of polypropylene is described. Extremely reproducible results are given by the sand column method, and ten fractions taken by this method are adequate for characterization of the usual polypropylene distribution. The variation between the molecular weight distributions derived from six fractionations of a test polypropylene by the three methods was small and indicates that fraction polydispersity probably contributes negligibly to any deviation of the experimental distributions from the true distribution. Polypropylenes made with aluminum triethyl‐transition metal trichloride catalysts contain relatively large amounts of low molecular weight polymer and have broad distributions similar to that of low‐pressure polyethylene. All such polypropylene samples had distributions which were described well by a logarithmic normal equation with a constant standard deviation. The distribution was not altered when the aluminum triethyl in the catalysts was replaced by aluminum triisobutyl. Catalysts containing vanadium as the transition metal, however, produced polypropylenes with distributions distinctively different from those made with titanium trichloride.
Gas and free radical measurements in irradiated polyvinyl chloride
Authors: Loy B. R. 
Published: April 2003

AbstractSimultaneous gas and electron‐spin resonance measurements of HCl evolution and free radical decay in irradiated PVC support Atchison's conclusion that three species of radicals are trapped. In accordance with first‐order rates, each radical decays to yield a different but constant ratio of [HCl] to [R.] over its respective reaction period. Optical measurements indicate that each species yield a constant distribution of conjugated chain lengths. An explanation is offered whereby the dehydrochlorination process is restricted to isolated radical‐pair systems. By this mechanism the average chain lengths are 26, 51, and 126 units for the short‐, medium‐ and long‐lived radicals, respectively.
High polymer chelates. I. Structure and stability of polymethacroylacetone chelates
Authors: Teyssié M. T. , Teyssié P. 
Published: April 2003

AbstractThe chelates formed by polymethacroylactone (PMA) with several divalent cations were studied by spectrophotometric and potentiometric methods, and their behavior was compared to that of chelates formed by a low molecular weight diketone of similar structure, pivaloylacetone. The structure of the chelates formed by both types of diketones is identical, as indicated by the elementary analyses as well as the absorption spectra in crystalline state and in solution (these spectra are further indicative of resonance phenomena and orbital distribution in the chelate rings). The stability of these chelates was also investigated. A calculation based on the usual two‐step chelation process seems to indicate a higher stability of the high polymeric chelates over the low molecular weight ones, but the values of the constants become identical when taking in account the specific structure of the polymeric ligand: the metal ion, when fixed on a diketo group of the chain, is practically always in the nearest vicinity of a second chelating group, reacting immediately with it to form the chelate species MA2. The process will accordingly be dependent on the molar concentrations in the ligand only for the first step, but not for the second one as for monofunctional diketones. Finally, a linear relationship was found between the logarithms of the stability constants of the various chelates and the electronegativities of the corresponding metals. The behavior of both types of diketones is again identical. On the basis of this parallel in the behavior of low and high molecular weigh ligands of similar structure, a method is proposed to predict the selectivity of synthetic selective ion exchangers, and its validity is confirmed by absorption experiments in aqueous media.
The use of high‐energy irradiation in an investigation of the mechanism and kinetics of emulsion polymerization
Authors: Vanderhoff J. W. , Bradford E. B. , Tarkowski H. L. , Wilkinson B. W. 
Published: April 2003

AbstractThe emulsion polymerization of styrene initiated by γ‐rays was studied using competitive particle growth and conventional techniques. With γ‐rays, the rate of free‐radical generation is independent of temperature, and the absorption of energy is uniform throughout the system. From the competitive growth experiments, the particle growth rates were similar to those of persulfate ion‐initiated systems and quite different from those of benzoyl peroxide‐initiated systems. From the conventional experiments, the number of particles increased approximately as the square of the emulsifier concentration for both γ‐ray and persulfate ion‐initiated polymerizations. With γ‐rays, the number of particles decreased with increasing temperature; the opposite was observed for persulfate. This may be explained by the relative rates of free‐radical generation of each system; for γ‐rays this rate is independent of temperature, while for persulfate, the activation energy for initiator decomposition is greater than that for polymerization propagation. For the γ‐ray system, the calculated values of kp increased with increasing particle size; the activation energy was 7.2 (σ = 0.59) kcal./mole. The calculated values of kt at 50°C. were 104–105 l./mole/sec.
Crosslinking efficiency in the reaction of dicumyl peroxide with dimethyloctadiene
Authors: Parks C. R. , Lorenz O. 
Published: April 2003

AbstractThe crosslinking efficiency of dicumyl peroxide was investigated with the use of 2,6‐dimethyl‐2,6‐octadiene as a model polyisoprene. High‐temperature gas chromatography was used to determine quantitatively the amount of crosslinked products as well as the decomposition products of the peroxide, α,α‐dimethylbenzyl alcohol and acetophenone. The crosslinked products were found to be almost exclusively a mixture of isomeric dimers when the molar ratio of dimethyloctadiene to dicumyl peroxide was 40:1 or higher. When larger amounts of peroxide were used, higher molecular weight crosslinked products were also formed. The dimethylbenzyl alcohol and acetophenone formed accounted for 90–95% of the peroxide decomposed. The results are consistent with a mechanism according to which the radicals formed by decomposition of the peroxide react exclusively with polyisoprenes by hydrogen abstraction. The polyisoprenyl radicals formed are then used up exclusively by combination. One molecule of decomposed dicumyl peroxide should then form one crosslink, and this was confirmed by experiment. Kinetic data showed that the crosslinking reaction followed a first‐order law. The activation energy was found to be 32 kcal./mole.
The crosslinking efficiency of some vulcanizing agents in natural rubber
Authors: Lorenz O. , Parks C. R. 
Published: April 2003

AbstractThe crosslinking efficiencies of several curing agents have been determined from swelling measurements. The results indicate that dicumyl peroxide is a quantitative crosslinking agent for natural rubber, as was previously found to be true of dimethyloctadiene. As one molecule of dicumyl peroxide is able to form one crosslink, 3.2 to 4.0 molecules of tetramethylthiuram disulfide or 9–10 sulfur atoms in a sulfur‐sulfeneamide system are needed for the same purpose. A comparison is made between the number of chemically introduced crosslinks and a corresponding value obtained from swelling measurements with the help of the Flory‐Rehner equation. It was found that a filler can effect the properties of a vulcanizate through a filler‐curing agent interaction as well as through a filler‐rubber interaction. When a filler‐curing agent interaction takes place, a certain amount of curing agent or accelerator becomes unavailable for cure. This lowers the number of crosslinks introduced by the curing agent. If the filler‐curing agent interaction is insignificant and can be neglected, the swelling value Q for a filled stock can be related to that of an unfilled, analogous gum vulcanizate, Qgum, by the simple equation Q = kQgum; k is a function of the nature and amount of the filler and the elastomer, but is independent of the curing agent.
Electron spin resonance studies of the radicals produced in high polymers by γ‐irradiation and their reaction with sulfur dioxide
Authors: Kuri Zenichiro , Ueda Hisashi 
Published: April 2003

AbstractReactivities of free radicals formed in irradiated polymers were investigated. Procedures utilizing the electron spin resonance technique showed the behavior of free radicals with sulfur dioxide. Radicals from polymers containing an intramolecular having hydrogen bond in themselves, such as cellulose, starch, polyvinyl alcohol, etc., showed no reactivity following either irradiation in a sulfur dioxide atmosphere or irradiation in vacuo with subsequent introduction of sulfur dioxide. Other polymer radicals were classified into three groups according to the effects of sulfur dioxide on them.
Flow of gases through polyethylene
Authors: Michaels Alan S. , Bixler Harris J. 
Published: April 2003

AbstractDiffusion and permeability constants for twelve permanent gases have been measured in a linear and a branched polyethylene, hydrogenated polybutadiene, and natural rubber over the temperature range 5–55°C. The Barrer time lag apparatus has been used in these determinations. For all gas–polymer pairs investigated, a linear plot of the logarithm of the diffusion or permeability constants versus the reciprocal absolute temperature is observed, indicating activated diffusion is occurring. Arguments have been presented supporting the hypothesis that natural rubber is a completely amorphous analog of polyethylene with respect to the diffusion process. It has been possible, as a result, to quantitatively express the reduction in diffusion constants in going from natural rubber to hydrogenated polybutadiene (29% crystalline), to the branched polyethylene (43% crystalline), and to the linear polyethylene (77% crystalline). These reductions were strongly dependent on gas molecular size, increasing as the molecular size increases. A geometric impedance factor and a chain immobilization factor have been introduced to account for the effect of crystallinity. The former is assumed to be independent of molecular size and accounts for the necessity of the diffusing molecule to by‐pass crystallites which have been shown to be impenetrable. The latter size‐dependent factor reflects the reduction in amorphous chain segment mobility brought about through the proximity of crystallites. Analysis of the geometric impedance factor supports the existence of thin, highly anisometric sheets of crystalline polymer in polyethylene. The anisometry of the crystallites was observed to increase with increasing crystallinity consistent with the chain folding mechanism for crystal growth in polyethylene. Nucleation and growth kinetics also qualitatively accounted for the variation in crystal anisometry observed in polymers prepared by different methods of polymerization. The apparent activation energies for diffusion determined in polyethylene include not only the energy required for chain segment separation but also the effect of thermal expansion and crystalline melting. Correlations have been presented which permit the estimation of gas diffusion constants in a wide variety of polyethylenes.
Studies of the ethylenediamine–cellulose complex. III. Some factors in the formation of the complex
Authors: Segal Leon , Creely J. J. 
Published: April 2003

AbstractComplete conversion of the cellulose crystal lattice to that of the ethylenediamine‐cellulose complex can be attained with aqueous ethylenediamine solutions of 60% and greater. Cellulose in the form of loose cotton yarn or woven fabric immersed in 98% ethylenediamine solution for as little as 1 minute is as completely complexed as that immersed 4 hours. Removal of ethylenediamine in excess to that required by the diamine‐cellulose complex is accomplished as effectively by hexane extraction as by evaporation under reduced pressure (8 mm. Hg at 95–100°C.). Using the latter procedure, a period of 2 hr. is sufficient to reduce the diamine content to that which has been obtained after longer periods, i.e., about 20%. The x‐ray diffractograms of the complexes prepared from celluloses I, II, and III suggest that the starting material influences the interplanar spacings of the crystal lattice of the complex. They also show that water‐extraction of the complex prepared from cellulose II restored the cellulose II lattice, while cellulose I is obtained when cellulose III is used. The infrared absorption spectra of the complexes prepared from celluloses II and III are similar and show slight differences from that of the cellulose I complex. After water extraction of the diamine, the spectrum of the material from the cellulose III complex closely resembles that of the cellulose I material.
Optically active polymers. I. Polymerization of 4‐methyl‐7‐isopropyl‐2‐oxohexamethyleneimine
Authors: Imoto Minoru , Sakurai Hideki , Kono Tadao 
Published: April 2003

AbstractPolymerization of 4‐methyl‐7‐isopropyl‐2‐oxohexamethylèneimine (I) initiated by K ou Li was carried out at 150°C. in the presence of benzoyl chloride or the N‐benzoyl derivative of I (II). The yield of the polymer was 11–25% over the course of 8–70 hr. The values of [η] in formic acid were 0.047–0.075. Optical activities of I, II, the polymers and the open chain monomer (III) were measured in formic acid.
The nature of acid‐sensitive linkages in cellulose
Authors: Michie R. I. C. , Sharples A. , Walter A. A. 
Published: April 2003

AbstractExperiments with s:tmples of cellulose regenerated in various ways confirm the earlier observation that their initially high rate of acidic hydrolysis under heterogeneous conditions is considerably greater than that calculated for the normal glucosidic bonds. The presence of such weak bonds appears to be a general phenomenon, and the process by which they are formed does not seem to be associated with any specific chemical reaction. It is thus suggested that the enhanced rate a t which these bonds degrade may be a physical effect, resulting either from strains set up in the chain molecules in the amorphous regions or from local variations in the normal state of hydrogen bonding.
On the acetalization of regenerated cellulose with dialdehydes
Authors: Fujimura Toshikazu , Okamoto Shin'Ichi 
Published: April 2003

AbstractThe effects of acetalization with the divalent aldehydes glyoxal and glutaraldehyde on rayon staples of various structures were studied. The swelling in aqueous 25% sodium hydroxide was measured after centrifuging. The knot strength was taken as a measure of the fiber brittleness. The acetalized glyoxal was determined by Head's method, and the amount of glutaraldehyde liberated by hydrolysis of the acetalized fiber with acid was determined polarographically. The results were as follows: (1) The amounts of acetalized glyoxal formed increased with increasing steeping liquor concentration, curing temperature, and curing time, but the percentage of glyoxal reacted did not exceed 65% of that applied. (2) For a constant amount of aldehyde applied to the fibers, more acetalized glyoxal was obtained (a) with lower moisture in the fiber after predrying, (b) by treatment with a higher concentration of aldehyde in a single step rather than at lower concentrations in many steps, and (c) with lower pickup at higher concentration. Therefore, the aldehyde concentration in the fiber at the final stage of curing may determine the acetalization reaction equilibrium. (3) The amounts of free and semiacetals formed increased initially and then decreased with higher total amounts of acetalized glyoxal. (4) The fine structure of all‐skin rayon may be favorable to the reduction of water imbibition and also to the prevention of brittleness at the same degree of acetalization. (5) Glutaraldehyde was more reactive than glyoxal and more favorable to prevention of brittleness in the fiber. (6) Super rayon crosslinked with glutaraldehyde had relatively high strength, including knot strength, and resistance to alkali, so that blending it with cotton, which benefits from mercerization, is a possibility.
The cellulose–butadiene diepoxide reaction and its effect on the crease resistance of cotton
Authors: McKelvey John B. , Benerito Ruth R. , Webre Beverly G. , Berni Ralph J. 
Published: April 2003

AbstractButadiene diepoxide (BDE), the meso‐1,2,3,4‐diepoxybutane, may be added to cotton cellulose with a variety of catalysts and conditions at room temperature. A slow addition of BDE from nonpolar solvents to yarns pretreated with alkali resulted in weight gains which were proportional to the activity of hydroxyl ions used in pretreatment. For a given hydroxyl ion activity, percentage weight gains of BDE varied directly with time of reaction. Add‐on of BDE has been shown to be proportional to the product of hydrolyzed BDE and molarity of the hydroxyl ion in the dilute alkali. It has been shown that slow addition of epoxide from carbon tetrachloride solution to cotton fabric impregnated with dilute alkali, natural salts, or alkaline salt solutions produces a fabric of good dry and wet crease recovery. Rapid addition of epoxide to fabric by the use of more concentrated alkali or elevated temperature showed excellent wet, but no dry, crease recovery. Hydrogen ion catalysis of the BDE–cotton reaction is very slow and, in the case of acetic acid, is without effect. With sulfuric acid, only mediocre wet crease recovery is produced a t room temperature. Catalysis with zinc fluoborate, methanolic solutions of BDE, and curing temperatures of 75–125° resulted in excellent wet and dry crease resistance a t weight gains of less than 2%. All methods of BDE addition to cotton fabric that produce good dry crease recovery cause a lowering of tearing and breaking strengths. There is little change in tensile properties when only wet. crease resistance is imparted. This suggests that profound physical changes in the fine structure of cellulose result from mild chemical action with a water‐soluble diepoxide. Recovery from deformation of cotton fibers in the wet and dry states (crease recovery) has been attributed to intermolecular covalent crosslinking of anhydroglucose unit hydroxyls by the diepoxide and, in particular, to crosslinking of hydroxyls on carbons 2 or 6, with a resultant diminution of interchain slippage. Fibers that exhibit only wet crease recovery are believed to have a minimum of covalent crosslinks and to be hydroxy cellulose monoethers of the epoxide or graft polymers of the same, which prevent slippage of chains only when wet and swollen (possibly by entanglement).
Crystallization of cellulose and cellulose derivatives from dilute solution. I. Growth of single crystals
Authors: Rånby B. G. , Noe R. W. 
Published: April 2003

AbstractCellulose triacetate and triethyl cellulose have been crystallized from dilute solution into regular compact lamellar crystals of microscopic size (10–20 μ) and of the same type as the single crystals previously obtained from linear synthetic polymers The shape of the cellulose acetate crystals (pyramids with square base) conforms with the crystal lattice of cellulose triacetate II (pseudo‐orthorhombic unit cell) when the chains are at right angle to the base planes. Compact platelike crystals of pure cellulose containing the lattice of cellulose II (mercerized cellulose) have been prepared from aqueous solutions by slow saponification of water‐soluble cellulose acetates. At 90°C. the crystals can be grown to a regular diamond (lozenge) shape (15 × 30 μ in cross section) with a lattice order as good as or better than that of purified dried native cotton fiber or bacterial cellulose. The shape of the crystals conforms with the crystal lattice of cellulose II (monoclinic unit cell with the angle 60°) if the chains are a t right angle to the base planes. It is concluded that the crystals of cellulose and cellulose derivatives are single crystals of a structure analogous to that of synthetic polymers. This would require chain folding also for the cellulose molecules. From studies of molecular models of cellulose chains, a 180° fold is considered possible with about four glucose residues‐provided the consecutive units are rotated around the glycosidic bonds.
Crosslinking of cellulosics by high energy radiation. II
Authors: Leavitt Frederick C. 
Published: April 2003

AbstractNonionic water‐soluble cellulose ethers have been crosslinked by irradiation with high energy electrons in aqueous solution. This unexpected behavior of cellulosics toward radiation is reproducible. Crosslinking and chain scission are competitive reactions; nevertheless, conditions are described for obtaining one or the other as the predominant reaction. It is proposed that the mechanism is free radical in nature. High beta radiation dose rates (Van de Graaff generator) are necessary to crosslink substantial amounts of polymer. Low dose rates, such as usually administered with gamma radiation, fail to yield crosslinked products. Degradation, oxidation, and cleavage of substituent groups occur over a wide range of radiation dose rates. The viscosity of the medium also plays a major role in determining whether crosslinking will take place. Highly viscous solutions with limited freedom of chain motion are degraded until the viscosity is sufficiently low to allow free bimolecular coupling reactions; then a gelled system forms immediately. Carboxylated cellulosics have not been crosslinked by this method. Samples examined were degraded at all levels of radiation. The crosslinked cellulose derivatives included methyl cellulose, hydroxyethyl cellulose, methyl hydroxypropyl cellulose, and methyl hydroxybutyl cellulose.