bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent and salt effects on reaction of Na amalgam with acrylonitrile and methacrylonitrile
Authors: Arad Y. , Levy M. , Rosen H. , Vofsi D.
Published: April 2003

The reaction of acrylonitrile (AN) and methacrylonitrile (MeAN) with Na amalgam was studied in diglyme solution. It was shown that addition of dimethyl sulfoxide (DMSO) increases only the rate of hydrodimerization of AN to adiponitrile, while addition of water increases only the rate of hydrogenation of AN to propionitrile. The proposed mechanism assumes two separate intermediates for these two simultaneous reactions. The reaction of MeAN with Na amalgam was found to be 100 times slower than that of AN. DMSO increases the rate of both the hydrodimerization and hydrogenation reactions via the same intermediate. Addition of quaternary ammonium salts to AN in diglyme has an effect similar to that of DMSO. The salts, however, react at very low concentrations due to accumulation of the cations on the charged amalgam surface. The effect of the size and structure of the quaternary cations was studied and is discussed.
Self‐condensation reaction of aromatic tetraamines in polyphosphoric acid
Authors: Banihashemi A. , Fabbro D. , Marvel C. S.
Published: April 2003

Ladder and partial ladder polymers have been obtained by self‐condensation reactions of 1,2,4,5‐tetraaminobenzene, 3,3′,4,4′‐tetraaminodiphenyl ether, 3,3′‐diaminobenzidine and 3,3′,4,4′‐tetraaminodiphenyl sulfone in polyphosphoric acid. The products thus obtained are highly colored compounds with good thermal stability. They seem to be made up of polyquinoxaline or dihydrophenazine or a mixture of these two recurring units. They are slightly soluble in methanesulfonic acid and concentrated sulfuric acid and have inherent viscosities in the 0.2 to 0.4 range.
Polyperfluorobutadiene. II. Fractionation and crosslinking
Authors: Toy Madeline S. , Newman J. Melford
Published: April 2003

Perfluorobutadiene was polymerized in bulk under low pressure and temperature in the presence of diisopropyl peroxydicarbonate, bis(trifluoromethyl) peroxide, and benzoyl peroxide. Fractional solvent extraction of polyperfluorobutadiene by n‐hexane and hexafluorobenzene into three polymeric fractions was described. The hexafluorobenzene‐soluble fraction was used for crosslinking studies. Direct fluorination of solid polyperfluorobutadiene required no catalyst. The fluorine–polyperfluoropolyene reactions furnished a mechanism for crosslinking the unsaturated chains. Fluorination by gaseous fluorine formed free radical sites on the polymer chains besides saturation reactions. The presence of excess monomer in contact with these partially fluorinated solid polyperfluorobutadienes under controlled conditions were capable of crosslinking and grafting to the linear chains. Direct fluorination of solid polyperfluorobutadiene tends to involve reaction with the internal double bonds rather than the pendant perfluorovinyl group; the converse is true for crosslinking with hexamethylenediamine. The mechanisms are discussed.
Studies on the polymerization of ethyl acrylate. II. Chain transfer studies
Authors: Raghuram P. V. T. , Nandi U. S.
Published: April 2003

Transfer constants for different solvents representing hydrocarbons, halogenated compounds, alcohols, ketones, acids, and esters were determined in the thermal polymerization of ethyl acrylate at 80°C and they are compared with the available data on methyl acrylate and ethyl methacrylate. It was observed from the values of transfer constants that ethyl acrylate radicals are a little more effective than methyl acrylate or ethyl methacrylate in abstracting hydrogen atom from hydrocarbons and alcohols. In acetic and n‐butyric acid media, it has been found, by the aid of endgroup analysis, that the derived solvent radicals from transfer reactions are not too efficient to start a new chain.
Block polymers of isocyanates and vinyl monomers by homogeneous anionic polymerization
Authors: Godfrey R. A. , Miller G. W.
Published: April 2003

The “living” polymer method was used to prepare block polymers of vinyl monomers and isocyanates at low temperatures in toluene–tetrahydrofuran mixtures. Vinyl monomers and diisocyanates, which have one hindered isocyanate group, as in 2,4‐toluene diisocyanate, form block polymers which contain pendant reactive isocyanate groups. These block polymers can be crosslinked with water, diols, diamines, etc. The polymerization is apparently limited to block polymer formation, since the polyisocyanate anion is incapable of initiating the polymerization of common vinyl monomers.
Grafting of poly(ethylene oxide) on poly(methyl methacrylate) by transesterification
Authors: Twaik Menahem A. , Tahan Menashe , Zilkha Albert
Published: April 2003

The grafting of the potassium alkoxide derivative of poly(ethylene oxide) on poly(methyl methacrylate) in homogeneous solution in toluene was studied. The alkoxide was prepared by reaction with potassium metal with methanolic potassium methoxide, or with potassium naphthalene. The last was the most suitable for the systematic investigation of the grafting process. Soluble graft polymers were formed, and essentially the initial poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) participated in the production of graft polymer. The composition of the graft polymers and the frequency of grafting of the side chains were determined by NMR. The solubility of the graft polymers in methanol and water increased with increasing PEO contents, while the melting ranges decreased. Fractionation of the crude graft polymers showed that the grafting reaction was random, and graft polymers containing one PEO side chain per about 10–170 MMA units were obtained.
Polymers with quinoxaline units. V. Polymers with quinoxaline and dioxin units
Authors: Wolf Rainer , Marvel C. S.
Published: April 2003

Ladder or partly ladder polymers have been prepared by condensation of tetraphenols with tetrachloroquinoxaline compounds in melt, or in pyridine, naphthalene, and nitrobenzene reaction media. The polymers are dark‐colored, powdery materials with good thermal stability. Some of the samples are slightly soluble in sulfuric acid, while others are completely insoluble. No other solvents were found.
Block copolymerization with trapped radicals
Authors: Minoura Yuji , Ogata Yayoi
Published: April 2003

Acrylonitrile–styrene, vinyl chloride–styrene and vinyl chloride–methyl methacrylate block copolymers were obtained by employing trapped radicals in polyacrylonitrile or poly(vinyl chloride) formed in a heterogeneous system by tri‐n‐butylboron in air as initiator. The trapped polymer radicals were activated on addition of dimethylformamide as solvent. Confirmation of block copolymers was carried out with solvent extractions, elementary analysis, and turbidimetry. In block copolymerization, the polyacrylonitrile trapped radical was more active than the poly(vinyl chloride) radical. Results of kinetic studies were used to consider the mechanism of polymerization.
Calorimetric investigation of polymerization reactions. II. Copolymerization of diethyl fumarate with styrene
Authors: Horie Kazuyuki , Mita Itaru , Kambe Hirotaro
Published: April 2003

The bulk copolymerization of diethyl fumarate with styrene initiated by benzoyl peroxide or azobisisobutyronitrile was investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of copolymerization decreased almost linearly with the increase in diethyl fumarate content in the copolymer. The heat of homopolymerization for diethyl fumarate was equal to 15.5 ± 0.3 kcal/mole. Monomer reactivity ratios at 100°C were also determined. The rate of copolymerization was followed over the whole range of conversion. A gel effect was noticed in copolymerizations at lower but not at higher temperatures. The initial rate of copolymerization exhibited a maximum at an intermediate monomer feed composition, differing from the previously reported tendency. The difference was found to be due to the method used for determining the rate of copolymerization, and the superiority of the DSC method was proved. The mechanism of the radical‐radical termination process was discussed. From the viewpoint of chemically controlled termination, the cross‐termination factor ϕ was estimated to be 2.0, which is reasonable considering the steric hindrance; assumption of the predominance of a diffusion‐controlled termination reaction was also consistent with the results.
Crosslinking polyferrocenylenes by polymethylol compounds
Authors: Bilow N. , Landis A. L. , Rosenberg H.
Published: April 2003

Polyferrocenylenes with mean molecular weights of 500–4 000 have been converted into thermosetting polymers by reaction with xylylene glycol and telomers thereof. The prepolymers have been used successfully as molding materials and laminating resins. Glass fiber‐reinforced laminates have been made with flexural strengths of 63 × 103 psi and flexural moduli of 4–5 × 106 psi. Ferrocene–xylylene glycol copolymers were also prepared, and 1,1′‐bis(hydroxymethyl)ferrocene was used as a polyferrocenylene crosslinking agent. Laminates were also made from the 1,1′‐bis(hydroxymethyl)ferrocene‐based polymers.
Importance of the diamine reactant in the production of polyphosphonamides by the interfacial technique
Authors: Carraher Charles E. , Winthers D'Orsay , Millich Frank
Published: April 2003

The stirred interfacial polycondensation of phenylphosphonic dichloride and 1,6‐hexanediamine has been studied as a function of several reaction variables. The reaction is rapid, being completed in less than 1 min. When organic solvent is varied and reactant molar ratio is varied with an excess of the acid chloride, yield is constant. When reactant molar ratio is varied polymer yield increases with increase in amine concentration. When reactant concentration is increased yield increases. With the addition of a soluble salt in the aqueous phase yield is increased. The above indicates that the diffusion of the amine to the reaction zone is of primary importance in determining polymerization rate and that the diffusion of the acid chloride is relatively unimportant. Polymer yield was found to be dependent on the pH of the amine in the aqueous phase. The observed trend is related to the apparent solubility of the amine in the aqueous phase such that the greater the apparent solubility of the amine, the less the polymer yield. Polymer molecular weight is found to be independent of reaction variables tested. Polymer was also formed from the condensation of phenylphosphonic dichloride with p‐phenylenediamine, H2N‐D‐NH2 (where D is a 36‐carbon hydrocarbon chain), 1,3‐di‐4‐piperidylpropane, and 4‐aminomethylpiperidine; phenyl phosphorodichloridate with 1,6‐hexanediamine; chloromethyl phosphonic dichloride with 1,6‐hexanediamine.
Anionic polymerization of styrene in the presence of different anisoles
Authors: Geerts J. , Van Beylen M. , Smets G.
Published: April 2003

The butyllithium‐initiated polymerization of styrene has been studied in toluene solution at 20°C in the presence of anisole, o‐ethylanisole, and p‐ethylanisole. The concentration of styrene was 0.16 mole/1.; the concentration of ether varied from 0.8 to 0.33 mole/1. The rates of initiation were followed spectrophotometrically at γmax 330 mμ; they increased with increasing concentration of ether. The rates of propagation were measured dilatometrically. In the presence of anisole and p‐ethylanisole, the rate expression is Rp = [M][PLi]1/2(k1 + k2 [ether]), where k1 is the propagation rate constant in pure hydrocarbon, k2 that of the ether solvated chain end, and [PLi] denotes the concentration of polystyryllithium. On the contrary, o‐ethylanisole did not affect the rate of propagation of styrene, possibly on account of the steric hindrance of the o‐ethyl group. The apparent first‐order termination rate constants were also determined spectrophotometrically at 20°C and compared to those of poly‐o‐ and p‐methoxystyryllithium. The following decreasing order of rate constant was found: poly‐p‐methoxystyryllithium > polystyryllithium‐anisole > polystyryllithium–4‐ethylanisole > polystyryllithium‐2‐ethylanisole > poly‐o‐methoxystyryllithium.
Cyclopolycondensation. XII. Polymerization mechanism of polybenzoxazinones in polyphosphoric acid medium
Authors: Kurihara Masaru , Saito Hazime , Nukada Kenkichi , Yoda Naoya
Published: April 2003

The polymerization mechanism of polyphosphoric acid (PPA) solution polymerization of an aromatic diaminodicarboxylic acid with aromatic dicarboxylic acid derivatives was studied. By means of NMR methods, the initiation process for the polymerization of polybenzoxazinone in PPA medium was elucidated. The NMR spectra of a series of compounds were taken, and the salt formation of amino groups of monomer with PPA and the equilibrium between the salt and the free amino group were determined. It was established that the polymerization proceeded through the formation of phosphorylated intermediates to give the salt of amino groups of monomer with PPA. In the second step, the amine–PPA salt dissociates into the free amino group and PPA at the polymerization temperature above 140°C. Polymerization proceeds through the attack of “free” amino on phosphorylated carbonyl compounds to form polyamide acid of high molecular weight, and on subsequently being heated in PPA at higher temperatures, it undergoes an intramolecular cyclodehydration along the polymer chain to form polybenzoxazinones.
Lactone polymers. III. Polymerization of ε‐caprolactone
Authors: Lundberg R. D. , Koleske J. V. , Wischmann K. B.
Published: April 2003

Polymerization of ε‐caprolactone catalyzed by dibutylzine and triisobutylaluminum has been examined. Monomer conversion and polymer molecular weight increase simultaneously during the polymerization suggesting a living polymer system. Also, molecular weight is proportional to the reciprocal of catalyst concentration. However, the polymer molecular weights are three to five times that which would be calculated from the catalyst concentration assuming a living polymer system. In addition, fractionation of poly‐ε‐caprolactone prepared with dibutylzinc revealed that the distribution is considerably broader than expected for a Poisson distribution. While no mechanistic explanation for the broad molecular weight distribution observed has been defined, examination of the metal alkyl‐catalyzed polylactones shows that the molecular weight distributions can and do change with time. This change is due to an ester interchange process occurring subsequent to polymerization. This phenomenon can be used to change the molecular weight distribution from very broad to the most probable distribution.
Bond structure in the alkaline ferric–tartrate system
Authors: Hanby John E. , Johnson Donald C.
Published: April 2003

The bond structure of the complex in the alkaline ferric–tartrate system (FeTNa) was examined and related to the cellulose‐dissolving ability of the system. The subject of bonding was approached by magnetic susceptibility and absorption spectrophotometric techniques. The magnetic moment of the Fe(III) in the iron–tartrate system was found to depend on the pH of the system. With an iron molarity of 0.1 an iron/tartrate mole ratio of 1 : 3, and 2 moles of NaOH/mole of tartaric acid, a minimum magnetic moment of 3.9 BM was observed. In alkaline media the magnetic moment depended on the Fe(III) concentration and the iron/tartrate ratio. The Fe(III) in the cellulose–solvent FeTNa was found to be in a high–spin state (5.9 BM). With a large excess of tartrate, the absorption spectrum of the alkaline FeTNa was recorded and analyzed in terms of the Tanabe–Sugano determinants. Values of 13200 cm−1 and 0.66 were obtained for the parameters Δ and β, respectively. In addition, it was shown that the Fe(III) in the cellulosesolvent FeTNa is coordinated with less than the maximum possible amount of tartrate. This tartrate deficiency is apparently responsible for the solvent properties of the system. From the use of glycerol as a model for cellulose, it appears that cellulose coordinates with the iron in the solvent FeTNa in much the same manner as does additional tartrate.
Relationship between chain termination rate constant and conversion in radical polymerization
Authors: Ito Katsukiyo
Published: April 2003

At low and high conversions, the chain termination rate constant for bimolecular termination between polymeric radicals given by kt = AtDs, where At is a constant and Ds is the diffusion constant of radical chain end, is completely correct. This termination rate constant does not depend on solution viscosity, but conversion.
Monomer‐isomerization polymerization. VI. Isomerizations of butene‐2 with TiCl3 or Al(C2H5)3–TiCl3 catalyst
Authors: Shimizu Akihiko , Itakura Keisuke , Otsu Takayuki , Imoto Minoru
Published: April 2003

A study of the isomerization of butene‐2 with TiCl3 or Al(C2H5)3–TiCl3 catalyst in n‐heptane has been investigated at 60–80°C to elucidate further the mechanism of monomer‐isomerization polymerization. It was found that positional and geometrical isomerizations in the presence of these catalysts occurred concurrently with activation energies of 14–16 kcal/mole. The presence of Al(C2H5)3 with TiCl3 catalyst could accelerate the initial rates of these isomerizations and initiate the monomer‐isomerization polymerization of butene‐2. From the results obtained, it was concluded that the isomerization of butene‐2 proceeds via an intermediate σ‐complex between the transition metal hydride and butene isomers.
Polymerization of aromation amines with ferric chloride to produce thermally stable polymers
Authors: Bingham A. , Ellis Bryan
Published: April 2003

Simple aromatic amines have been polymerized by use of ferric chloride as a combined Friedel‐Crafts catalyst and oxidant to yield polymers which are both thermally and oxidatively stable. Under certain reaction conditions a polydiphenylamine was prepared which was stable in air up to 465°C as shown by thermogravimetric analysis. This polymer has a softening point of ca. 80–100°C and is soluble in some organic solvents. Such a polydiphenylamine and other polymers with similar properties are regarded as useful for conversion to thermally stable Phillips‐type resins by crosslinking with conventional difunctional agents.
Polymerization of methyl methacrylate with dimethylbenzylanilinium chloride
Authors: Otsu Takayuki , Sato Tsuneyuki , Ko Munan
Published: April 2003

In order to clarify the mechanism of initiation by dimethylbenzylanilinium chloride (DMBAC), the polymerization of methyl methacrylate with DMBAC has been investigated at 60–80°C. From the results of kinetic and tracer studies, it was found that this polymerization proceeded via a radical mechanism and benzyl radical was not an initiating species. However, it was also noted that DMBAC easily dissociated into dimethylaniline and benzyl chloride under the present conditions, and the overall activation energy for the methyl methacrylate polymerization was 14.6 kcal/mole. These observations indicate that initiating radicals other than benzyl radical, i.e., phenyl or methyl radicals, may be produced through a redox interaction between DMBAC and dimethylaniline dissociated from DMBAC.
Studies on the biaxial stretching of polypropylene film. V. Orientation mechanism of the one‐step biaxially stretched film
Authors: Tanaka Hiroshi , Masuko Tōru , Okajima Saburo
Published: April 2003

The molecular orientation behavior during one‐step biaxial stretching in air of a quenched, low crystalline film differs from that of a slightly crystallized, highly crystalline film. In the case of a quenched film a plot of −Δnss versus \documentclass{article}\pagestyle{empty}\begin{document}$ 1/\sqrt {va} $\end{document} is composed of three intersecting straight lines with different slopes, −Δnss and vA being the birefringence with respect to the normal to the film surface and the degree of stretching in area, respectively. On the other hand, −Δnss of crystalline film changes somewhat differently. It does not increase up to fairly high stretching ratio. When a film with surface layers of different crystallinity was stretched biaxially, the relations between −Δnss and \documentclass{article}\pagestyle{empty}\begin{document}$ 1/\sqrt {va} $\end{document} for the two surface layers differ, that is, a surface layer of low crystallinity shows a change of −Δnss for the two surface layers differ, that is, a surface layer of low crystallinity shows a change of −Δnss like that of a quenched film type and the surface layer of higher crystallinity, follows the behavior typical of highly crystalline film. However, a commercial film having different crystallinites on the two surface layers exhibits another type of −Δnss change, which may be ascribed to the stress remaining frozen in the film in the manufacturing process. In addition, it is found that an Abbé refractometer can give the refractive indices of both the upper and lower surface layers of a film when the film structure is not the same on both surface layers.
Nylon 66 polymers. I. Molecular weight and compositional distribution
Authors: Burke J. J. , Orofino T. A.
Published: April 2003

Results from characterization of melt‐polymerized nylon 66 by various solution property measurements are reported and employed in analysis of typical molecular weight and compositional distributions for these systems. Critical attention is paid to application of standard procedures including light scattering, viscosity, membrane osmometry and other colligative property measurements in arriving at satisfactory specification of polymer molecular weight averages. Particular consideration is given to polymers extending appreciably beyond the lower and higher limits in molecular weight normally encountered. The conclusions drawn are: (1) in the range of number‐average molecular weights less than about 25 000, nylon 66 as ordinarily prepared by melt condensation consists principally of linear species approximating the “most probable” distribution; (2) small amounts of cyclic oligomers are present in all samples: (3) increase in the extent of the melt polycondensation to progressively higher stages is accompanied by secondary reactions and the formation of branched components terminating ultimately in crosslinked, insoluble gels. Intrinsic viscosity–molecular weight relationships in seven solvents, applicable to nylon polymers meeting the requirements of (1) above, are derived.
Poly(1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate). IV. Flocculation of crystalline silica
Authors: Shyluk W. P. , Smith R. W.
Published: April 2003

Silica flocculated with a high molecular weight poly(DMVPMS) contains aggregates that are stable enough to permit size measurement with a Coulter counter. The average size of these aggregates increases up to a critical level of added polymer; the primary particles reappear at higher levels of added polymer. The aggregate size is reduced by continued mixing and the particle size distribution before flocculation is approached. Subsidence rates, equilibrium sediment volumes, and refiltration rates give somewhat different estimates of the degree of flocculation. Additional aggregation beyond that measured by the Coulter counter must be considered in the interpretation of these data. The decrease in floc strength during continued agitation is attributed to a disaggregation of the bridging polymer, to a decrease in the interparticle bonding of the bridging polymer, and to an increase in the surface coverage with polymer.
Weight distribution approach to the theory of random depolymerization of heterogeneous chains
Authors: Lee Sung Won
Published: April 2003

The random depolymerization model of Montroll and Simha for originally homogeneous polymers is derived analytically by utilizing a weight distribution function approach not requiring the use of any approximations. The model is then extended to consider heterogeneous initial chains having an arbitrary chain length distribution. The probabilities for breakage are assumed to be identical for all bonds joining monomeric elements in the system and to be independent of chain length and position in the chain, assumptions also used in the model of Montroll and Simha. An expression is found for estimating the probability of bond breakage.
Morphology of poly(vinylidene chloride) and of the carbons resulting from its pyrolysis
Authors: Bailey A. , Everett D. H.
Published: April 2003

This paper reports an electron microscopy study of the morphology of crystals of poly(vinylidene chloride) prepared under a variety of conditions and of the carbons resulting from the pyrolysis of the polymer. The structure of the polymer carbons prepared under conditions such that the polymer does not pass through a plastic phase is closely related to the morphology of the original polymer. The shapes of the crystals and of the crystal pseudomorphs are indexed in terms of the unit cell proposed by Narita and Okuda. Morphological studies of this kind are important in discussing the graphitizability of polymer carbons, their mechanical properties and pore structure, and the kinetics of the dehydrochlorination reaction.
Form birefringence in biaxially oriented polypropylene
Authors: Normandin L. M. , Legrand D. G.
Published: April 2003

The birefringence of several biaxially oriented polypropylene films swollen with a number of fluids has been measured and found to exhibit a minimum when plotted against the fluid refractive index, as predicted by the theory of Wiener. However, a discrepancy in the form birefringence behavior is observed when samples of different degrees of crystallinity but the same total birefringence are compared. These results are interpreted in terms of Bullough's theory and suggest that this discrepancy arises because of different morphologies. A refractometric technique was employed that makes possible the simultaneous determination of birefringence and the volume fraction of fluid.
Unperturbed dimension of poly‐N‐vinylcarbazole
Authors: Kuwahara Nobuhiro , Higashida Shiro , Nakata Mitsuo , Kaneko Motozo
Published: April 2003

Osmotic‐pressure, viscosity, and light‐scattering measurements have been carried out on dilute solutions of poly‐N‐vinylcarbazole fractions (4 < 10‐4M < 230) in toluene, dioxane, and benzene. The theta temperature for poly‐N‐vinylcarbazole in toluene solutions has been found to be 37 ± 1°C. The intrinsic viscosity of poly‐N‐vinylcarbazole in toluene at 37°C is represented by [η]θ = 76.2 × 10−3M̄n0.50. Values of the characteristic ratios (〈L2〉0/M)1/2 and σ = (〈L2〉0/〈L2〉0f)1/2 have been obtained as 633 × 10−11 and 2.85, respectively. It appears that the large σ value is due to the steric repulsion between large side groups.
A new method for determination of intrinsic viscosity
Authors: Maron Samuel H. , Reznik Richard B.
Published: April 2003

The Huggins and Kraemer equations generally used to determine intrinsic viscosity frequently do not yield identical results, and their constants often do not add up to 1/2 as is mathematically required. To overcome these difficulties an equation has been deduced which through linear plots gives unambiguous intrinsic viscosities, constants which meet the 1/2 condition, as well as two other flow constants. Extensive tests of the equation with precise data on solutions of poly(methyl methacrylates) and polystyrenes in benzene and toluene confirm the validity of the new equation in every respect. It is further shown that the four constants involved are interrelated, and that it is possible to express the values of three of these in terms of the fourth.
Thermodynamics of swelling of polymer‐network gels. Analysis of excluded volume effects in polymer solutions and polymer networks
Authors: Mijnlieff P. F. , Jaspers W. J. M.
Published: April 2003

The assumed analogy between polymer solutions and polymer‐network gels as regards the thermodynamics of swelling—a fundamental assumption implicit in all previous analyses of swelling measurements on gels, aimed at checking the statistical theories of rubber elasticity—is shown in fact to be rather limited. In particular, excluded volume effects, which play a dominant role in both solutions and gels, are quite different in the two types of systems. A new thermodynamic description of swelling equilibria, taking account of differences in excluded volume effects, is given, and analogies and differences between gels and solutions are pointed out.
Observation of optical modes in polyethylene by neutron scattering
Authors: Chang Y. I. , Summerfield G. C.
Published: April 2003

Multiphonon contributions to the directional phonon frequency functions are calculated for crystalline polyethylene. These results are compared to previously calculated one‐phonon frequency functions.
Study of low‐frequency molecular motions in polydimethylsiloxane polymers by neutron inelastic scattering
Authors: Henry A. W. , Safford G. J.
Published: April 2003

The intrachain and interchain vibrations below 900 cm−1 of polydimethylsiloxane (PDMS) have been studied by slow neutron inelastic scattering. A composite motion observed at +25°C for the methyl groups corresponds to nearly free rotation about the threefold axis of symmetry together with a large‐amplitude rotation of the entire methyl group. At −123°C, rotation about the threefold axis evolves to a torsional oscillation. The large‐amplitude rotation evolves to the skeletal vibrations of a helical conformation. Vestiges of the cooperative skeletal vibrations of the conformation at −123°C persist into the 25°C spectrum. The results indicate the presence of interrupted helical conformations at 25°C, which result from thermal disordering of the low temperature helices. The effects of crosslinking, low molecular‐weight oils, and silica filler on the freedom of the methyl group motions and on skeletal vibrations have been determined. The effects of different crosslinking agents and different relative amounts of filler and oil on both the macroscopic physical properties and the observed molecular motions of PDMS can also be interpreted in terms of an interrupted helix.
Energy transfer in polymer films: The nylon 66–proflavine system
Authors: Dearman H. H. , Lang F. T. , Neely W. C.
Published: April 2003

Triplet → singlet energy transfer in nylon 66 film (donor) dyed with proflavine (acceptor) is demonstrated by a decrease of the nylon phosphoresence lifetime and an increase in the proflavine delayed fluorescence/nylon phosphoresence ratio with increasing proflavine concentration. Although the observed donor phosphorescence decay is apparently exponential, the transfer is probably via a long‐range dipole–dipole (Förster) interaction, rather than by triplet exciton migration. Arguments are advanced to support this view. Proflavine delayed fluorescence produced by a direct excitation process is also observed. The decay time for this process is roughly an order of magnitude less than that for the sensitized process. All emission intensities are shown to vary linearly with exciting light intensity. Finally, temperature dependence of proflavine delayed fluorescence under different excitation conditions is shown. The efficiency of direct excitation process increases markedly near −50°C as the temperature is increased; the sensitized delayed fluorescence intensity follows that of the nylon phosphorescence with increasing temperature, as expected.
Thermal analysis of polydimethylsiloxanes. I. Thermal degradation in controlled atmospheres
Authors: Thomas T. Howard , Kendrick T. C.
Published: April 2003

Thermogravimetric analyses (TGA) of catalyst‐free polydimethylsiloxanes (PDMS) have been carried out in controlled atmospheres and a kinetic analysis of the results has enabled the various decomposition processes to be separated and identified. The calculated activation energy for thermal depolymerization is 42 ± 3 kcal/mole, while thermo‐oxidation has an apparent activation energy of 30 ± 2 kcal/mole. Quantitative analyses of the major degradation products and molecular weight distribution studies of the residues from degradation studies under isothermal conditions have shown that in vacuo, PDMS fractions depolymerize to cyclic dimethylsiloxanes and low molecular weight linear residues by a randomly initiated mechanism which, it is postulated, involves the formation of an intramolecular, cyclic, four‐centered transition state followed by siloxane bond rearrangement. This mechanism is a basic property of linear PDMS fractions and is independent of molecular weight. Molecular weight distribution (MWD) changes observed from further isothermal investigations on hydroxy endblocked PDMS fractions, have shown the presence of a chain‐lengthening process in vacuo below the depolymerization temperature. This process, with an apparent activation energy of 8.6 ± 1 kcal/mole, is attributed to the intermolecular condensation of terminal hydroxyl groups.
Ultimate tensile properties of elastomers. V. Rupture in constrained biaxial tensions
Authors: Smith Thor L. , Rinde James A.
Published: April 2003

The strength and extensibility of an unfilled styrene‐butadiene rubber vulcanizate were determined in constrained biaxial tension (essentially pure shear) by stretching thinwalled cylindrical specimens in the axial direction with an Instron tester while gas pressure was admitted to maintain constant the outside diameter of a specimen. The rupture stress, λ1b, and the extension ratio, λ1b, in the axial direction and the rupture stress, σ2b, in the circumferential direction were determined at extension rates from 0.0031 to 3.1 min−1 and temperatures from 25 to 90°C. Rupture data in simple tension were also obtained by testing ring specimens under similar test conditions. The time‐temperature shift factor, aT, obtained by superposing rupture data at different temperatures, gives a constant activation energy of 35 kcal. Doubly logarithmic plots were prepared showing the dependence of σ1b/λ1b, σ2b, and λ1b from the biaxial tensile tests and of σb/λb and λb from the simple tensile tests on the temperature‐reduced extension rate, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \lambda a_T $\end{document}. (The quantities σ1b/λ1b, σ2b, and σb/λb are rupture stresses based on the dimensions of undeformed specimens.) At equal values of \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \lambda a_T $\end{document}, the extension ratios λ1b and λb are sensibly identical. The ratios σ1b/σb and σ2b/σb, as well as λbσ2b/σb, were obtained from rupture data read from the composite curves at selected values of \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \lambda a_T $\end{document}. Also, similar ratios were derived from stress data at equal extensions in biaxial and simple tension for 1.25 ≤ λ ≤ 3.0, the range comparable to that in which rupture data were obtained. A consideration of the ratios given by both the rupture and the stress data shows that the von Mises failure criterion is not applicable, although the departure is small except at the larger values of λb.
Ultimate tensile properties of elastomers. VI. Strength and extensibility of a styrene–butadiene rubber vulcanizate in equal biaxial tension
Authors: Dickie Ray A. , Smith Thor L.
Published: April 2003

The ultimate properties of an unfilled styrene‐butadiene rubber vulcanizate in equal biaxial tension were determined by inflating a circular membrane into a bubble. Tests were made at several extension rates (evaluated at the pole) from about 0.15 to 4 min−1 and at temperatures from −43 to 90°C. The stress in the vicinity of the pole when rupture occurred was evaluated from the pressure, the radius of curvature, and the extension ratio λ, the latter two quantities being obtained from photographic data. Below 70°C, the ultimate extension ratio λb is approximately 5.2 and is essentially independent of extension rate and temperature, in striking contrast to the behavior in simple and constrained biaxial tension (pure shear). Likewise, the rupture stress is manyfold greater than in either simple or constrained biaxial tension. From the extremum points of failure envelopes, the maximum extension ratio (λb)max in equal biaxial tension is 5.7 and in simple tension is 7.2. An examination of ruptured membranes showed that, except at 70 and 90°C, rupture began away from the pole in a region where the stress state is unequal biaxial tension. Hence, values of the ultimate properties in truly equal biaxial tension are no doubt somewhat greater than those obtained from the membrane tests. However, it is shown that (λb)max in truly equal biaxial tension must be lower than that in simple tension by at least 10%. A consideration of rupture data in simple, constrained biaxial, and equal biaxial tension leads to the conclusion that no simple failure criterion is applicable for interrelating data obtained under the several states of combined stress. The rupture patterns and factors that affect the site of rupture initiation and the mode of crack growth are also discussed.
General description of optical (dichroic) orientation factors for relating optical anisotropy of bulk polymer to orientation of structural units. Part II. Fourth moments of orientation distribution and polarized fluorescence
Authors: Kimura Itsuro , Kagiyama Mitsuyasu , Nomura Shunji , Kawai Hiromichi
Published: April 2003

A general description is given for relations among the optical quantities obtained from fluorescence polarization measurements on bulk polymer stained by fluorescent groups: the moments of distribution of orientations of the fluorescent groups, and those of the structural units of the polymer (chain segments) on which the groups are adsorbed. Two assumptions as to the biaxial symmetry of the bulk polymer and the cylindrical symmetry of the optical anisotropy of the fluorescent element, both for the absorption and emission processes, reduce the intensities of the polarized fluorescence to a 3 × 3 matrix L which is asymmetric (Lij ≠ Lji), as has frequently been observed in experiments. The components of the L matrix are related to those of the J matrix which is so defined as to describe the fourth moments of the distribution of orientations of the structural units on the basis of a random distribution of the rotational angle of the unit about the segment axis. It is found that the use of the method of fluorescence polarization combined with absorption dichroism and/or emission gives the values of the optical anisotropy ratios of the fluorescent unit, and that the effects of the thermal agitation of the structural unit can be separated from the moments of the orientation distribution for the simplest case.
Stress relaxation of natural rubber during irradiation
Authors: Evans D. , Morgan J. T. , Sheldon R. , Stapleton G. B.
Published: April 2003

The site of chain scission and crosslinking in vulcanized natural rubber irradiated with 4 MeV electrons has been determined by analysis of stress relaxation data. Sulfur and peroxide vulcanizates of different crosslink densities were prepared and the crosslink densities determined from stress‐strain measurements. Stress relaxation was measured during irradiation using modified commercial relaxometers. The specimens were maintained in an atmosphere of nitrogen to minimize oxidative side effects. Scission is deduced to take place in the vicinity of crosslinks, since the rate of continuous stress relaxation is independent of crosslink density. Scission may be associated both with crosslinks initially present and with those subsequently introduced by irradiation. Crosslinking by radiation is largely a random process. However, there is a crosslinking reaction dependent to a slight extent on crosslink density as well as a small contribution from random scission reactions. G values for the random reactions are given.
Yielding of oriented poly(vinyl chloride)
Authors: Rider J. G. , Hargreaves E.
Published: April 2003

Poly(vinyl chloride) sheet was oriented by hot drawing. The yield behavior of the oriented sheet was then investigated under uniaxial tension at room temperature as a function of the angle between the tensile axis and the molecular alignment direction. The onset of yield was localized in deformation bands. The variation of yield stress with direction and the direction in which the deformation bands formed were found to be satisfactorily accounted for in terms of a yield criterion based on that of von Mises, provided that a term representing internal compressive stress in the molecular alignment direction was included. The internal stress was found to increase from zero with increasing draw ratio of the prior hot drawing. It is pointed out that other workers have found polymers to obey the yield criterion of Coulomb rather than that of von Mises.
Diffusion in glassy polymers. II
Authors: Frisch H. L. , Wang T. T. , Kwei T. K.
Published: April 2003

The Fickian diffusion coefficient of methylene chloride in a glassy epoxy polymer is calculated with the use of Crank's model of discontinuous change of D with concentration C. The diffusion constant is obtained as 1.93 × 10−6 cm2/sec. The swollen layer behind the advancing solvent front is essentially in the rubbery state of the same polymer. The case II swelling by benzene is discussed in terms of a convective transport arising from the partial stress (internal) tensor of the penetrant. The superposition of Fickian and case II diffusion found with mixtures of methylene chloride and benzene is also discussed briefly.
Diffusion and solubility of methane in polyisobutylene
Authors: Lundberg J. L. , Mooney E. J. , Rogers C. E.
Published: April 2003

Diffusion coefficients and solubilities of methane in polyisobutylene have been measured at four temperatures between 102 and 188°C. in the pressure range 23–341 atm. Diffusion coefficients extrapolated to atmospheric pressure range from 1.72 × 10−6 cm.2/sec. at 102°C. to 1.5 × 10−5 cm.2/sec. at 188°C. corresponding to an activation energy for diffusion of 8.7 ± 0.4 kcal./mole. Solubilities are small, about one molecule of methane for every forty carbon atoms in the polyisobutylene at 300 atm. partial pressure of methane. Solubilities vary little with temperature, but show an apparent minimum between 127 and 188°C. With improved methods of data analysis, diffusion coefficients and solubilities have been recalculated from previously reported studies on nitrogen in branched polyethylene and methane in branched polyethylene, linear polyethylene, and polystyrene. Recalculated diffusion coefficients are essentially the same as those reported previously, but the recalculated solubilities are decreased from 2 to 30%. The solubilities of all five systems show strong deviations from Henry's law, i.e., increases in partial pressure of methane and nitrogen with respect to solubility exceed linearity. The partial pressure (or fugacity)—solubility data may be interpreted in terms of a sorption model in which sorbed molecules are accommodated in widely dispersed, unoccupied volumes or sites in the polymer. An almost equivalent, solution model in which the first sorbed molecules to enter the polymer are accommodated to a large extent in existing volumes in the polymer, with successively sorbed molecules swelling the polymer to a greater extent (i.e., partial molal volume of sorbed molecules, V1, increasing with concentration) can also account for these data.
Effect of the internal field on the birefringence of polymer crystals
Authors: Stein Richard S.
Published: April 2003

The discrepancy between the values of the anisotropy of methylene groups determined from crystal refractive indices, stress‐optical data, and gas and liquid light‐scattering depolarization is explained on the basis of the effect of the internal field on the polarizability of the isolated molecule. The internal field may arise from intermolecular or intramolecular interactions which depend upon molecular conformation and state of aggregation. A simple continuum calculation based upon an extension of the calculation of the Lorenz‐Lorentz field is shown capable of accounting for the discrepancy.
Relations between dynamic mechanical properties and melting behavior of nylon 66 and poly(ethylene terephthalate)
Authors: Bell James P. , Murayama Takayuki
Published: April 2003

Nylon 66 films exhibiting form I melting behavior show the γ mechanical relaxation at −140°C. Samples which have form II melting behavior do not show this relaxation. The γ relaxation disappears when material having form I behavior is converted to material having form II behavior by annealing or by cold drawing. The form I and form II types of melting behavior are also found in poly(ethylene terephthalate); the interconversions and thermal behavior of the forms are analogous to the nylon 66 case. In poly(ethylene terephthalate), the β relaxation at −40 to −60°C is present only when form I melting behavior is found. Conversion to form II melting behavior by annealing or drawing (80°C) again causes the relaxation to disappear. No β relaxation was found in amorphous polymer. The γ dispersion in nylon 66 and the β dispersion in poly(ethylene terephthalate) can therefore be associated with the crystalline structure responsible for form I melting behavior. Form I melting behavior has been associated with foldedchain crystals based on previous work. It is therefore postulated that the γ dispersion in nylon 66 and the β dispersion in poly(ethylene terephthalate) are associated with motions in the chain folds. This assignment is not inconsistent with the change in the γ dispersion of nylon 66 with the number of backbone CH2 units, since these will affect the fold structure.
Typical fiber structure
Authors: Ishikawa Kinzo , Miyasaka Keizo , Maeda Masahiko , Yamada Mitsuo
Published: April 2003

Model fibers of polyethylene and nylon 6 were strained in the direction of the fiber axis and the internal deformation of the samples was studied by large‐angle and small‐angle x‐ray diffraction. The compression of samples along the fiber axis was successfully carried out, and the results obtained by x‐ray methods yielded more interesting information on the structure of the fibers than was obtained in extension. A model for the structure of the fiber was constructed on the basis of the results on compressed fibers. In this model, crystals are distributed in cylindrical symmetry around the fiber axis keeping a crystal axis tangential to circles in the section normal to the fiber axis. The characteristic crystal axis is the b axis in polyethylene and the a axis in nylon 6. The chain axis of the crystals varies in orientation with respect to the fiber axis. In compression of fibers with such a structure, the crystals rotate around the characteristic axis indicated above. In the case of nylon 6 fiber, only this simple rotation seems to occur, while additional changes occur in polyethylene fibers. However, the simple rotation predominates even in polyethylene fibers. This fiber structure is correlated with the structure of thin films of the materials. This similarity proves the existence of a common mechanism for the origin of the structure of fibers and films.