bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of degree of crosslinking in natural rubber vulcanizates. Part VI. Evidence for chain scission during the crosslinking of natural rubber with organic peroxides
Authors: Moore C. G. , Scanlan J. 
Published: April 2003

AbstractThe possible scission of natural rubber chains during their crosslinking by organic peroxides at 140°C. has been examined: (1) by comparing the kinetics of crosslinking and of peroxide decomposition and (2) by measuring the relaxation in stress of an extended sheet of a peroxide vulcanizate subjected to further crosslinking by di‐cumyl peroxide in nitrogen. The former method is too insensitive to establish the occurrence of chain scission, but the latter method indicates that degradation of the primary network occurs during the formation of the secondary network, an effect which is ascribed to the unimolecular scission of polysoprenyl radicals competing with their bimolecular combination to from crosslinks. Under the reaction conditions prevaling in (2) it is calculated that degradation of the primary network occurs equivalent to about 10% of the new elastically effective crosslinks formed. These findings suggest that minor revision of the existing calibrations1,4 relating the physical and chemical degrees of crosslinking of a natural rubber vulcanizate is necessary, since the basis of the original chemical estimate1 was that the sole fate of polyisoprenyl radicals, derived from the reaction of natural rubber with alkyloxy‐, aralkyloxy‐ and methyl radicals, is bimolecular combination. However, the available data, coupled with the present status of stress relaxation theory, are inadequeate to permit precise corrections of the existing calibrations to be made at this stage.
Radiation crosslinking of rubber. III. Chain fracturen
Authors: Mullins L. , Turner D. T. 
Published: April 2003

AbstractPurified natural rubber has been exposed in vacuo to the 4‐M.e.v. electron beam from a linear accelerator and attempts have been made to estimate the ratio of fractures of the main chain of carbon atoms to crosslinks, using three different methods. Measurements of the sol fraction (S) as a function of the radiation dose (R) did not conform to a linear relationship between S + S1/2 and R−1 reported by Charlesby and Pinner for a number of other polymers. It appeared that in the present experiments there was little consummated random fracture, and it was found that the sol fraction tended towards zero at radiation doses above about 50 Mrad. The stress in rubbers maintained at constant elongation decreased continuously on irradiation, and it was found that rigorous exclusion of traces of air and impurities was of critical importance. Deficiencies of previous analyses of stress‐relaxation data are discussed and an attempt made to provide an internally consistent treatment of the data. In one treatment which made no allowance for the possible contribution of chain entanglements a value for β of 0.18 was obtained. In another treatment an attempt was made to allow for entanglements and a much lower value for β of 0.03 was obtained. This very low value may be due to the inadequacy of the assumption made that fracture inevitably releases entanglements under conditions where a much higher rate of concurrent crosslinking may serve to lock them into the network. Further work is required to establish a reliable basis for the interpretation of stress‐relaxation data. In a third method stress‐strain measurments of irradiated rubber provided estimates of the number‐average molecular weights of both (1) the chain segments between adjacent crosslinks and (2) the primary molecular chains. Comparison with similar data for vulcanizates prepared by thermal decomposition of di‐tert‐butyl peroxide gave a value for β of 0.11. This value was calculated on the assumption that no fracture occurs on formation of the peroxide vulcanizates and is, therefore, likely to be an underestimate. The nominal G(X) value of 0.9 is increased to 1.05 when an allowance is made for fracture.
Linear phenol–formaldehyde polymers. Synthesis of partially substituted polymers
Authors: Burke W. J. , Short Glen A. , Higginbottom Harold P. 
Published: April 2003

AbstractReaction of 2,6‐bis‐(chloromethyl)‐4‐chlorophenol withp‐cresol provided a convenient synthesis of 2,6‐bis‐(2‐hydroxy‐5‐methylbenzyl)‐4‐chlorophenol. Condensation of formaldehyde with this trimer alone and in the presence of controlled amounts ofp‐cresol made possible the synthesis of linearp‐cresol–p‐chlorophenol–formaldehyde polymers having 1,2, and 4p‐chloro substituents per 12 phenolic residues. Treatment with sodium in liquid ammonia gave the corresponding dehalogenated polymers. Crosslinking of the latter with hexamethylenetetramine was studied. Both series of polymers were characterized by infrared spectra.
Vulcanization of butadiene/styrene rubber in a thermal neutron field
Authors: Anderson Herbert R. 
Published: April 2003

AbstractVulcanization of butadiene/styrene rubber in a thermal neutron field is described. Tread type vulcanization produced from highly ionizing particles resulting from the nuclear reactions B10(n, α)Li7* and Li6(n,α)H3 (where Li7* denotes Li7 left in excited state to yield ultimately a 0.4 m.e.v. gamma ray) have negligible residual radioactivity and possess physical properties comparable with those produced by other means, e.g., gamma rays and peroxides. Swelling and stress‐strain properties indicate that the response of the tread type compound to analogous nuclear reactions have pronounced differences. The vulcanizates also differ markedly. Values of G, the crosslinking efficiency of energy utilization, of the tread‐type compound in a helium atmosphere was found to have an average value of 3 for promotion by lithium methoxide and 0.9 in the case of boron nitride. Such values decrease 30% with lithium methoxide promotion and increase by a factor of 2 for boron nitride promotion when air is substituted for helium as an irradiation atmosphere.
Infrared spectra of crystalline polysaccharides. IV. The use of inclined incidence in the study of oriented films
Authors: Liang C. Y. , Marchessault R. H. 
Published: April 2003

AbstractThe infrared spectra (tilting spectra) obtained with the incident beam inclined to oriented films are discussed. Various experimental settings for obtaining the tilting spectra are studied. It is pointed out that quantitative interpretations (to determine the direction of the transition moment of a normal mode) of the tilting spectra are not possible at present. Qualitative interpretations, however, are usually possible. The tilting spectrum of a uniaxially oriented film of chitin crysallites at various settings is presented for the purpose of demonstrating different tilting effects. The tilting spectra of 101 and 101 uniplanarly oriented films of cellulose I materials and of doubly oriented films of cellulose I and cellulose II crystallites are presented. A number of interesting tilting effects in these spectra are discussed in terms of crystal structure.
Polymerization of α‐piperidone by alkali metal and certain acyl compounds
Authors: Yoda Naoya , Miyake Akihisa 
Published: April 2003

AbstractIt has been shown that the resonance‐stabilized, six‐membered lactam, α‐piperidone, is polymerized by alkali metal and acyl compounds to form poly‐5‐valeramide, melting point 259°C., [r] = 0.25, d = 1.243. A mechanism is proposed for the polymerization of α‐piperidone with alkali metal and acyl compound which involves chain propagation by the stepwise addition of piperidone ring at the end of the molecules leading to the formation of poly‐5‐valeramide. This mechanism is supported by experimental results obtained in the presence of alkali metal salts of α‐piperidone, data on deuterium exchange reactions, and infrared analytical evidence. The conditions for polymerization have carefully been investigated. A maximum conversion of 76% was obtained. As the concentration of alkali metal and acyl compound increases, the conversion increases. On the other hand, the conversion decreases when the concentration of alkali exceeds 3.0 mole‐% and the concentration of N‐acetyl piperidone is over 1.0 mole‐%. As the reaction temperature increases, both conversion and the degree of polymerization diminish. Furthermore, the polymerization with other useful catalysts has been reported.
Hydrogen bond chains and dielectric relaxation of polyvinyl alcohol
Authors: Kurosaki Shigehiko , Furumaya Toshihiko 
Published: April 2003

AbstractThe dielectric constant ϵ′ and the loss factor ϵ″ of untreated and heat‐treated polyvinyl alcohol and of a deuterated polyvinyl alcohol were observed over the frequency range of 30–106 cycles/sec. at several temperatures. For comparison, ϵ′ and ϵ″ of two normal long‐chain alcohols were also measured. Polyvinyl alcohol has its ϵ″ peak at a frequency of 104−105 cycles/sec., and activation energies E* for dielectric dispersion are quite small (6–18 kcal./mole), despite the large relaxation time. This finding cannot be explained by the theory of restricted rotation of dipoles, but can be explained by the use of the concept introduced by Sack of the chain mechanism of dielectric relaxation in hydrogen‐bond chains. It is concluded that hydrogen‐bond chains in the amorphous regions of polyvinyl alcohol have a mean length of about 1350 A. and are shortened only very slightly by deuteration.
Theory of viscoelasticity of amorphous polymers. III. Dispersion of dynamic bulk modulus
Authors: Nakada Osamu 
Published: April 2003

AbstractThe origin of the relaxation phenomena associated with volume deformation in amorphous polymers is attributed to the configurational relaxation of the three‐dimensional extension of the chain molecule. A diffusion equation of chain configuration is formulated with the use of the model of a chain molecule which is composed of beads connected by Hookian springs. A dynamic relation between varying pressure and volume is derived by integration of the diffusion equation for sinusoidal pressure change, and thus the real and imaginary parts of the bulk modulus are calculated. The dispersion of bulk modulus is specified by two characteristic time constants, τβ and τΓ, the former relating to the rubberlike elasticity of a chain, and the latter to the elasticity of the energetic nature which comes from the distorsion of chemical bonds and also from the change of cohesive energy. A preliminary comparison of the theory with experiment is made.
Isotope effects in polymerizations of carbon‐14‐labeled styrenes
Authors: Hodnett Ernest M. , Jensen Arnold W. 
Published: April 2003

AbstractStyrene‐β‐C14 has been polymerized (1) thermally at 99°, (2) with benzoyl peroxide at 51°, and (3) with stannic chloride at 25°. The C14‐labeled monomer was found to react (1) 91.8%, (2) 91.5%, and (3) 95.0% as fast as the nonradioactive styrene under these conditions. When styrene‐α‐C14 was polymerized (1) thermally at 99° and (2) with stannic chloride at 25°, the radioactive monomer reacted 97.0% and 100% as fast as nonradioactive styrene. These results are interpreted in terms of the propagation step of the reaction.
The kinetics of the polymerization of methyl methacrylate. I. The bulk reaction
Authors: Hayden P. , Melville Harry 
Published: April 2003

AbstractA thermocouple method of following the nonstationary state of chemical reactions has been used to study the changes which occur in the velocity coefficients and energies of activation for the propagation and termination reactions over the whole range of the conversion of methyl methacrylate to polymer. After about 10% conversion the rate and lifetime of the kinetic chain increase as conversion proceeds. These changes are accompanied by a decrease in the overall energy of activation and an increase in the temperature coefficient of the reciprocal of the lifetime. During this stage of the reaction, the intensity exponent falls from an initial value of 0.5 to 0.25. These results are believed to be due to an increase in the activation energy for the diffusion of polymeric radicals in the increasingly viscous medium. Beyond 40% conversion the activation energy for the propagation increases while the corresponding velocity coefficient decreases, possibly due to the monomer addition step becoming diffusion controlled. Simultaneously the intensity exponent increases toward unity.
On the thermodynamical interpretation of osmotic and of Donnan equilibria in salt‐containing polyelectrolyte solutions. Part I
Authors: Alexandrowicz Z. 
Published: April 2003

AbstractA formal treatment is proposed for the interpretation of Donnan and osmotic equilibria in a three component solution which consists of a polyelectrolyte, a simple salt, and a solvent. To this end a scheme is outlined for the measurement of the activity coefficients of the permeating components; namely the salt and the solvent. According to this scheme, these coefficients are measured in a way which facilitates their graphical differentiation in respect to the concentration of the polyelectrolyte and of the salt. As a second stage, the use of a thermodynamical cross relation and of the Gibbs‐Duhem equation leads to the evaluation of the partial derivatives, in respect to the above mentioned variables, of the activity coefficient of the polyelectrolyte itself. The numerical integration of the latter is also discussed. The above calculation of the various activity functions provides a complete thermodynamical description of the three component system. Such a description suffices to correlate in a formal way, without the introduction of any theoretical models, the results of various methods of measurement (e.g., osmotic pressure, light scattering, the transport phenomena). Since it is considered that the socalled “osmotic concentration method” (a previously described differential osmotic technique) is best adapted for the execution of the requisite measurements, the calibration of this method is given for solutions which contain a freely permeating salt.
Apparent activation energy of hydrolysis of some cellulosic materials
Authors: Nelson Mary L. 
Published: April 2003

AbstractApparent activation energies for heterogeneous acid hydrolysis of four samples of cellulose which differed in crystallinity were calculated separately for the amorphous and crystalline regions, from data obtained under drastic hydrolytic conditions. Some approximate activation energies were also calculated for hydrolysis of the amorphous fraction of cotton and a viscose rayon, using data obtained with a range of dilute acid concentrations. These values are discussed in relation to hydrolytic conditions. The relations between the hydrolysis rate, the acidity function (H0), and the hydrogen‐ion concentration, as well as the values of activation entropy were examined for evidence with respect to reaction mechanism. Data from the literature were used to show that the activation energy probably is temperature dependent.
Calculation of nonbonding forces as applied to stereospecific polymerization
Authors: Ferstandig L. L. , Goodrich F. C. 
Published: April 2003

AbstractThe nonbonding interactions were calculated for four models resembling types of propylene polymerization. The calculations predict syndiotactic polymerization for a radical or carbonium ion model and suggest isotactic polymerization for anionic‐type reaction.
A kinetic study of the oxygen‐initiated polymerization of ethylene
Authors: Ehrlich Paul , Pittilo Robert N. 
Published: April 2003

AbstractThe kinetics of the oxygen‐initiated polymerization of ethylene show some features previously unrecorded in vinyl polymerizations. Preceding formation of polyethylene, there is an induction period which depends strongly on temperature and pressure but only slightly on oxygen concentration. During the induction period the rate of oxygen consumption increases exponentially with time and approximately one‐half of the oxygen is consumed prior to polymerization which can take place only if certain critical conditions depending primarily on pressure and oxygen concentration are exceeded (critical boundary). A formal reaction mechanism with degenerate kinetic chain branching is postulated from which the most important experimentally observed relations can be deduced. The induction period for polymerization then becomes the reciprocal branching factor for the oxidation of ethylene and the critical boundary a kinetic limit familiar in hydrocarbon oxidations with degenerate branching. The shape of the critical boundary can be derived by postulating, in addition, a sequence of reaction steps similar to those frequently used to represent the low temperature oxidation of hydrocarbons. Under the conditions investigated, the initiation mechanism dominates the polymerization, and an interpretation of the propagation and termination steps cannot be made.
Crystal structure of d,l‐poly(propylene oxide)
Authors: Stanley E. , Litt M. 
Published: April 2003

AbstractPowder and oriented fiber photographs of crystalline poly(propylene oxide) were taken and indexed. An orthorhombic unit cell with space group P212121 of dimensions a = 10.40 A., b = 4.64 A., and c = 6.92 A. was found. The polymer has a sinuous, zig‐zag backbone, with the methyl group falling between the oxygen and methylene groups of the neighboring chain. The oxygen and methylene groups are almost interchangeable, and it is possible that both optically active and d,l unit cells are present at the same time.
Copolymerizability of vinylpyridines
Authors: Tamikado Takashi 
Published: April 2003

AbstractThe copolymerizations of 2‐vinylpyridine (2‐VP), 4‐vinylpyridine (4‐VP), and 5‐ethyl‐2‐vinylpridine (5‐Et‐2‐VP) with styrene (St), methyl methacrylate (MMA), and methyl acrylate (MA) have been investigated. The copolymer compositions have been determined by visual titration with crystal violet indicator of the copolymers in the 20:80 glacial acetic acid‐acetonitrile mixture with N/10‐perchloric acid in glacial acetic acid. It has been proved that this titration method is consistently successful. The monomer reactivity ratios, r1 and r2, were calculated for the systems St‐2‐VP (0.56 ± 0.02 and 0.9 ± 0.2, respectively), MMA–2‐VP (0.439 ± 0.002 and 0.77 ± 0.02, respectively), MA–2‐VP (0.168 ± 0.003 and 1.58 ± 0.05, respectively), St–4‐VP (0.54 ± 0.03 and 0.7 ± 0.1, respectively), MMA–4‐VP (0.574 ± 0.004 and 0.79 ± 0.05, respectively), MA‐4–VP (0.22 ± 0.01 and 1.7 ± 0.2, respectively), St–5‐Et‐2‐VP (0.79 ± 0.03 and 1.2 ± 0.2, respectively), MMA–5‐Et‐2‐VP (0.395 ± 0.003 and 0.69 ± 0.03, respectively), and MA–5‐Et‐2‐VP (0.179 ± 0.006 and 1.16 ± 0.08, respectively). The alternating tendencies of the pyridines with the comonomers measured by the reactivity ratio products have been discussed in connection with styrene and, further, the Q‐e values have been calculated. On the basis of these data, it has been concluded that the pyridyl groups of these monomers act as electron donors to the double bond, as does the phenyl group in the styrene molecule; these groups show comparable resonance stabilization to styrene, and thus the copolymerizabilities of these vinylpyridines are analogous to that of styrene.
The effect of network flaws on the elastic properties of vulcanizates
Authors: Scanlan J. 
Published: April 2003

AbstractA treatment is given of the effect of network flaws due to the finite chain length of the primary elastomer molecules on the elastic properties of rubber vulcanizates. In this treatment full allowance is made for the elastically inactive material which exists either as sol or as loose ends of the network. The cases of linear primary molecules with either a random distribution of lengths or with uniform lengths are considered, and the results are compared with those of earlier theoretical treatments.
Melt viscosity of polymers: Effect of polydispersity
Authors: Bueche F. 
Published: April 2003

AbstractThe author's theory for the melt viscosity of high polymers is extended to include the effect of molecular weight polydispersity. It is found that if one describes the viscosity by the relation η = (const.)Mt3.5, the molecular weight average appropriate for Mt lies between the weight and z average. For molecular weight distributions with Mw/Mn less than about two, Mt is best represented by Mw. Above that value, Mz is a better approximation. These latter statements are not precise because of the fact that Mt appears sensitive to the exact form of the distribution. Reasonable agreement with available experimental data is found.
Molecular weight of ethyl cellulose
Authors: Scherer P. C. , Tanenbaum A. , Levi D. W. 
Published: April 2003

AbstractLight‐scattering and viscosity measurements were made on six ethyl cellulose fractions in methanol at 25°C. The relation [η] = 5.23 × 10−4M̄w0.65 was found to hold over the molecular weight range of 0.98 × 105 to 4.10 × 105. Second virial coefficients for this system were found to be essentially zero at 25°C. The dependence of dielectric dispersion of ethyl cellulose solutions on molecular weight was confirmed.
Poly(2‐ethylbutyl methacrylate). VI. Dilute solution properties by viscosity and light scattering
Authors: Didot F. E. , Chinai S. N. , Levi D. W. 
Published: April 2003

AbstractPoly(2‐ethylbutyl methacrylate) was prepared by emulsion polymerization and fractionated. Light‐scattering and viscosity techniques were used to study eight fractions in a good solvent, methyl ethyl ketone, and in an ideal solvent, isopropanol. Relations between viscosity and molecular weight are shown. The effect of the size of pendant groups on the degree of chain extension of a series of alkyl methacrylate polymers in ideal solvents is discussed. It was found that the degree of chain extension of the polymers thus far studied follows the order: poly(n‐lauryl methacrylate) > poly(n‐hexyl methacrylate) > poly(2‐ethylbutyl methacrylate) ≥ poly(n‐octyl methacrylate) > poly(n‐butyl methacrylate) > poly(ethyl methacrylate) ≥ poly(methyl methacrylate).
Proton magnetic resonance in irradiated and unirradiated polyvinyl alcohol
Authors: Fujiwara Shizuo 
Published: April 2003

AbstractCrystalline and amorphous components in PVA were investigated by the analysis of the line shapes of the NMR spectra of several samples being different in the degree of polymerization and in the forms. Measurements of the temperature dependence of the line shape, the line width, and the second moments were also performed for the irradiated and unirradiated samples. In the samples bombarded in the air by the deuteron beam, marked irradiation effects were observed by the measurements of the humidity dependence of the NMR intensity of the motional component, of the temperature dependences of the line shape and the second moment, and of the behavior of the line shapes at the higher temperature range, suggesting the occurrences of the destruction of the amorphous part, the degradation of the less‐motional part, and the crosslinking of the amorphous part with the less‐motional one. Investigations were also made with the samples irradiated by gamma rays in vacuum. The NMR features of the gamma‐irradiated samples showed the optimum point of about 106 rad, which would refer to thedestruction of the amorphous component and the initiation of crosslinking.
Dynamic mechanical measurement of M̄n
Authors: Cox W. P. , Isaksen R. A. , Merz E. H. 
Published: April 2003

AbstractA procedure is described for the measurement of number‐average molecular weight M̄n on a specimen in bulk form, utilizing a dynamic torsion pendulum. For both atactic and isotactic polystyrenes it has been found that the minimum value of the damping logarithmic decrement, δm, (above the glass temperature) is related to an measured osmometrically in dilute solution by M̄n = δ × 105. The M̄v/M̄n ratio can also be estimated directly from the δ vs. temperature curve. A four‐element spring‐and‐dashpot model yields similar 6 vs. T curves when the Williams‐Landel‐Ferry temperataure dependence is assigned to the viscosity of the dashpots.