bluuebunny/crossref_metadata_2025 huggingface dataset:
Aromatic Poly‐1,3,4‐Thiadiazole Fibers
Authors: Frazer A. H. , Fitzgerald W. P.
Published: June 2010

It has been shown that aromatic poly‐1,3,4‐thiadiazole fibers can be prepared in a manner analogous to that of the aromatic poly‐1,3,4‐oxadiazole via the thermal cyclode‐hydration of an aromatic polyoxathiahydrazide fiber. These fibers exhibited the same high level of thermal and hydrolytic stability observed for the aromatic poly‐1,3,4‐oxadiazole fibers. The oxathiahydrazide‐thiadiazole conversion was found to occur at lower temperatures and much faster rates than the hydrazide‐oxadiazole conversion.
Boron nitride fibers
Authors: Economy J. , Anderson R. V.
Published: June 2010

The structure and properties of boron nitride fibers were examined. The fibers are polycrystalline consisting of a major phase of turbostratic boron nitride and a three‐dimensional ordered phase which is not hexagonal. The density of the fibers is determined by the amount of internal microporosity and crystal interlayer spacing. The existence of internal defects and necking‐down defects is described. The resistance of the fibers to refluxing water is shown to be closely related to the interlayer spacing. This effect of the crystal structure on the high thermal stability of the fibers is discussed. The mechanical properties are interpreted in terms of the microcrystalline structure. The electrical resistivity of BN fibers is compared to other insulators and arguments are presented to explain the difference between the conductivity of graphite and boron nitride.
A molecular theory of polymer chain folding
Authors: Lindenmeyer P. H.
Published: June 2010

A molecular theory is proposed to account for the regular folding of polymer chains during crystallization. It predicts that an isolated polymer chain greater than some critical length can lower its energy by crystallizing into a regular folded‐chain conformation. Similarly, a single molecular chain crystallizing upon an infinitely large substrate will also lower its free energy by regular folding. In a crystal composed of polymer molecules all having the same length the lowest free energy occurs when all chains are completely extended; however, there also exists a whole series of metastable states corresponding to one, two, three, etc. folds per molecules. When the crystal is composed of a distribution of molecular lengths, the lowest free energy corresponds to a folded‐chain crystal whose thickness is a sensitive function of the distribution. If the low end of the molecular length distribution is assumed to be truncated at the observed length of extended‐chain crystals, the theory satisfactorily predicts the observed thicknesses of folded‐chain crystals obtained by melt crystallization of both fractions and whole polymer.

I never saw a folded chain.

I never hope to see one

But I can tell you anyhow.

I'm damn near sure there be one.
The efficiency of gel permeation chromatography
Authors: Meyerhoff G.
Published: June 2010

The resolution power of gel permeation chromatography (GPC) columns and their combinations is tested as a function of the pore sizes of the gels and as a function of the elution velocity. The efficiency of GPC is characterized by the ratio UG/UT, where UG is the experimental, and UT the theoretical, inhomogeneity. The latter quantity is obtained from absolute measurements of Mw, and Mn. The ratio passes through a minimum for a series of columns with increasing pore sizes. The minimum occurs at that column or column set which is best suited to resolving a given polymer. UG/UT for any column decreases with decreasing elution velocity. At a certain velocity UG/UT becomes 1. This velocity is usually smaller than v = 1 ml./min., but for some columns appreciably greater. Columns with low UG/UT values allow an unexpectedly good separation of mixtures of two polymers with Mw/Mn = 2 and Mw(I)/Mw(II) = 2. A compression effect toward the peaks of the two components is observed.
Measurement of functional group and molecular weight interrelations by GPC/IR
Authors: Terry Stuart L. , Rodriguez Ferdinand
Published: June 2010

When the effluent from a gel permeation chromatograph is analyzed by infrared absorbance on a continuous basis (GPC/IR), individual functional groups can be followed. Successive analyses at different characteristic wavelengths permit the estimation of group distribution within a molecular weight distribution. The use of low molecular weight internal standards that combine the functional groups of interest is shown to enhance the reliability of the method. A mixture of polymers of styrene and methyl methacrylate and a copolymer of the two have been analyzed with phenyl benzoate as an internal standard. It is demonstrated also that the relative concentration of hydroxyl and ether groups can be monitored in a mixture of poly(ethylene oxide) homologs. Among the polymer substituent groups successfully analyzed in GPC/IR with trichloroethylene as solvent are OH, COC, SiOSi, CF, CH2, carboxyl, and phenyl.
Simultaneous measurement of oil content and molecular weight distribution of oil‐extended elastomers by gel permeation chromatography
Authors: Mate R. D. , Lundstrom H. S.
Published: June 2010

This paper describes the successful application of gel permeation chromatography to the measurement of both molecular weight distribution and oil content in oil‐extended elastomers with a single analysis. In this investigation, different solvents and column sequences were employed to study several typical aromatic, naphthenic, and paraffinic oils. Two out of the three oils studied were completely separated from both high polymer and solvent impurity regions. Calibration techniques and data obtained therefrom are discussed herein.
Gel permeation chromatography in the analysis of surface coating vehicles
Authors: Bartosiewicz R. L.
Published: June 2010

Surface coatings are usually generated in situ from complex systems often containing two or more phases. The film‐forming phase, called the vehicle, is in itself complex. There is usually a chemical composition distribution superimposed upon the molecular size distribution. The principal film‐forming component of the vehicle is in turn quite complex: it is usually a resin or blend of resins quite heterogeneous in molecular size, shape, and composition distributions. The determination of an absolute molecular weight for the resins incorporated into vehicles is thus difficult and may be meaningless. However, both vehicles and their film‐forming resin components can be fractionated quite well by gel permeation chromatography. In addition to providing fractions for further analysis by other techniques, the chromatogram obtained simultaneously yields much information concerning the vehicle or vehicle component not easily obtainable by former analysis schemes.
Polymerization of nitrogen‐containing and oxygen‐containing monomers by Ziegler‐Natta catalysts
Authors: Giannini U. , Brückner G. , Pellino E. , Cassata A.
Published: June 2010

The polymerization of oxygen‐ and nitrogen‐containing monomers by Ziegler‐Natta catalysts is described. In particular, the results obtained in the polymerization of unsaturated tertiary amines are reported. The polymerization is possible when both the nitrogen atom of the monomer and the aluminum atom of the organometallic compound used in the catalysis are shielded by branched alkyl groups. The influence of the distance of the nitrogen atom from the double bond is also studied. The polymerization of monomers containing siloxanic or silazanic groups are described. By hydrolysis of the polymers in an acid medium crystalline polymers of primary alcohols and an amorphous polymer of a secondary amine have been isolated.
Photochromic polymers
Authors: Vandewijer P. H. , Smets G.
Published: June 2010

Photochromic spiropyran copolymers have been prepared by radical copolymerization of 5‐methacrylamino‐3,3′‐diméthyl‐6′‐nitrobenzthiazo‐linospiropyran (R is CH2=C(Me)‐CO‐NH) with different vinyl monomers, as methyl methacrylate, methacrylonitrile, styrene, and 2‐vinylnaphthalene. Their solution behavior has been examined in different solvents and compared to that of the corresponding 5‐isobutyraminoderivatives (R is i‐C3H7‐CO‐NH). magnified image In a strong solvating medium the copolymers display a strong negative solvatochromism and behave similarly to the model substance; their decoloration reaction kinetics follow a first‐order relationship. The decoloration activation energy in DMF varies from 24.9 to 25.6 for the different copolymers instead of 22.1 for the model. In less polar solvents, the λmax of the copolymers show a large hypsochromic shift when compared to the model, while the decoloration reactions deviate strongly from first‐order kinetics. These deviations are interpreted by assuming the existence in the copolymers of two photocolored isomeric components, in slow equilibrium with each other, and with optical densities a and b and agree with following equation where the optical density can be related to the time of decoloration t.

The ratio a/b i s equal to 0.57, 2.00, and 2.06 in acetone, dichloromethane, and tetrahydrofuran, respectively. It is assumed that the steric hindrance resulting from the macromolecular environment raises the potential barriers between these different stereoisomers. On addition of a polar nonsolvent as t‐butanol, first‐order kinetics are, however, restored up to a degree of conversion of 60%. The rate of decoloration of methyl methacrylate copolymers decreases with increasing spiran content. Finally, it was observed that an increase of the solution viscosity also provokes a deviation from first‐order kinetics.
Reactivities and structural aspects in the cationic polymerization of mono‐ and diolefinic norbornanes
Authors: Kennedy J. P. , Makowski H. S.
Published: June 2010

To evaluate the various factors operative in carbonium ion polymerization of ring structures, in particular monoolefinic and diolefinic norbornane derivatives, the polymerization of select monomers was effected: 2‐methylene norbornane, 2‐methylene‐5‐norbornene, norbornene, 2‐vinyl‐5‐norbornene, 2‐isopropenyl‐5‐norbornene, 2,5‐norbornadiene, 2‐vinyl norbornane, and 2‐isopropenyl norbornane. The relative reactivities of these monomers and the structures of the polymers produced therefrom were rationalized on the basis of well‐documented organic‐chemical principles. Steric compression during propagation was considered to be a critical determinant in the polymerizability of methylene cycloalkanes. The relative polymerizabilities of cycloalkenes were explained on the basis of the ability of the first‐formed secondary cation to undergo a hydride shift to a nonpropagating tertiary cation. Similarly, the structures of polymers derived from vinyl cycloalkanes were explained on the basis of hydride shifts and steric compression during propagation.
The oxidative coupling of 2,6‐disubstituted phenols with PbO2 and other metal oxides
Authors: Van Dort H. M. , De Jonge C. R. H. I. , Mijs W. J.
Published: June 2010

The main product in the oxidative coupling of 2,6‐dimethyl phenol with PbO2 and other metal oxides is poly‐2,6‐dimethyl phenylene oxide (Mn up to 20,000). The influence of the temperature, the solvent, and the addition of small amounts of various substances on the course of the reactions is discussed. The addition of an amine to the reaction mixture suppresses the diphenoquinone formation, and polymers with much higher molecular weights may be obtained. Infrared and NMR endgroup analyses show that the polymers prepared with PbO2 and in the absence of amines are branched. On the addition of increasing amounts of amines to the reaction mixtures the degree of branching gradually decreases. Mechanisms for the branching reaction are suggested. The effect of soluble onium salts, such as trimethylcetylammonium bromide, on the course of the oxidative coupling is mentioned (slow reactions giving polymers with high molecular weights). Aromatic polyethers are also obtained in the metal oxide oxidations of 2,6‐disubstituted phenols with bulky substituents, such as: 2,6‐diethyl phenol, 2,6‐diisopropyl phenol, and 2,6‐dimethoxy phenol. Some properties of the polymers are given. There are indications that the reactions go by way of metal phenolates.
Ueber einige makromolekulare Halbleiter mit Porphyrazinstruktur
Authors: Manecke G. , Woehrle D. , Kossmehl G.
Published: June 2010

Polymers with a structure similar to phthalocyanine were made by melting of tetracyanothiophene (I), tetracyanofuran (II), octacyano‐P.P.P‐triphenylphospholidine (III), tetramethyl‐bis(maleonitriledithiolato)cuprate (IVa), and copper bis(maleonitriledithiolato)cuprate (IVb) with copper acetylacetonate and with other metal acetylacetonates in different molar ratios and with o‐phthalodinitrile (V). The conductivities at a pressure of 1,500 kp‐cm.−2 were in the range of 5.7 × 10−5 to 10−14 ohm−1 cm.−1. The conductivities decreased with decreasing aromatic character of the starting nitriles. In some cases of polychelates with two different incorporated metals higher conductivities were found than were expected from the two unimetallated polychelates. For various metal polychelates of (I) there seems to be a relationship between the conductivities and the ionization potentials and the ionic radii of the metals. Measurements of the thermal EMF showed p‐conduction. Seebeck coefficients were independent of the temperature for the polychelates made from (I) and (II) and were dependent on the temperature for the polychelates made from (III). A certain polychelate made from (III) had a thermal EMF of 40 mv. for ΔT × 30°. Polymers with a structure similar to tetraazadiarylene‐diisoindolenine were obtained by fusing of (I) with p‐phenylenediamine, and of (I), (IVa), (IVb), and nickel bis(maleonitriledithiolato)cuprate (IVc) with 2,6‐diaminopyridine and by melting of 2,5‐diamino‐3,4‐dicyanothiophene with or without CuCl2. The structure was proved by elementary analysis and by IR spectroscopy. The conductivities were in the range of 7.1 × 10−3 to 1.0 × 10−9 ohm−1 cm.−1. The polymers made from (IVb) and (IVc) showed smaller conductivities than did those from (IVb) and (IVc).
Viscosity of chain polymers in solution
Authors: Isihara A.
Published: June 2010

A theory is developed for the intrinsic viscosity of chain molecules in solution. The molecules are assumed to be composed of many repeating units called segments, which are distributed spherically around the center of each molecule. An integral equation similar to, yet different from, that of Kirkwood and Riseman is set up. This equation does not require the replacement of the Oseen hydrodynamical interaction tensor by its diagonal element and yields a new viscosity formula. This formula is rather general and is characterized by the Fourier transform of the segment distribution function and the eigenvalue λ(k) of the Oseen tensor expressed in momentum space. In the absence of hydrodynamical interactions between segments the formula is reduced to the Debye formula for the Staudinger empirical law. In the presence of interactions the eigenvalue λ(0) characterizes the viscosity. This eigenvalue is related to the average characteristic length of a chain molecule, through which the molecular‐weight dependence of the viscosity comes in.
The effect of solvent on the unperturbed dimensions of polystyrene
Authors: Cowie J. M. G.
Published: June 2010

The unperturbed root‐mean‐square radius of gyration of a polystyrene sample was measured in ten critical consolute mixtures encompassing solubility parameters ranging from 8.1 to 11.4 (cal./cm.3)1/2. The values of the intrinsic viscosity and coil size were found to reach a maximum in the vicinity of δp, the polymer solubility parameter. Preferential adsorption of the solvent component in the mixture, by polystyrene, was observed in each of the ternary systems examined. The variations in coil size and intrinsic viscosity were found to be mainly a function of solvent polarity and were not caused primarily by preferential adsorption, which was comparatively small in most of the mixtures.
The mechanism of polymer permeation through polymer gel membranes
Authors: Meyerhoff G. , Stannett V.
Published: June 2010

Polymer gels are capable of producing separation effects on polymers. Applications for fractionation and for osmotic measurements are possible. Investigations are reported concerning the separation properties of polystyrene layers grafted onto a supporting cellulose basis. The permeation for pure solvents and the separating molecular limit for different solvents are tested. Their size depends uniquely on the interaction between the grafted polystyrene and the solvent.
Organized polymerization of vinyl pyridinium salts
Authors: Kabanov V. A. , Patrikeeva T. I. , Kargina O. V. , Kargin V. A.
Published: June 2010

The study of the spontaneous polymerization of quaternary vinyl pyridinium salts in concentrated aqueous solutions showed that the process occurred by the specific ionic mechanism. The results of kinetic measurements made for 1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate are interpreted in terms of chain propagation in aggregates of regular monomeric salts existing in solutions at concentrations close to saturation. The aggregates of activated monomeric molecules also exist in dilute solutions when the formation of salts from vinylpyridine and polymeric organic acids takes place. In this case the polyacid macromolecules act as activating polymeric “matrices”.
Polysiloxane‐s‐triazinyl ethers
Authors: Bettelheim Frederick A. , D'Amelia Ronald
Published: June 2010

Polysiloxane‐s‐triazinyl ethers were prepared by condensing silanediols in dimethylformamide with cyanuric chloride in dioxane. Dry or aqueous base was used as catalyst and dimethylsulfoxide as promoter. Some structural and physical properties of these compounds are reported. The inclusion of the triazine ring in the silicones provides additional thermal stability with polyphenylsiloxane chains but only slight thermal improvement with bis(p‐chlorophenyl) siloxane chains.
Graft copolymerization onto proteins by the ceric ion method. II. Grafting onto bovine serum albumin
Authors: Iwakura Yoshio , Imai Yohji
Published: June 2010

Graft copolymerization of methyl methacrylate onto bovine serum albumin (BSA), trypsin, and α‐amylase was carried out by the ceric ion method. The grafted polymer chains were separated by selective hydrolysis of the backbone proteins with hydrochloric acid. The number of grafting sites were 0.02 to 0.3 moles/mole. Graftings were greatly affected by denaturation of the protein molecule. It is concluded that the grafting onto BSA is likely to occur at cysteine and cystine residues.
Volume–temperature relation of epoxy resin–acid anhydride mixtures with different degrees of crosslinking
Authors: Shimazaki Akio
Published: June 2010

Volume‐temperature relations of six kinds of epoxy resin‐acid anhydride composite and different curing times are discussed on the basis of free‐volume and occupied‐volume concepts. The specific volume Va at a fixed temperature above Tg decreases linearly with increasing Tg, but the specific volume Vb below Tg increases linearly. The specific volume Vg at Tg increases linearly with increasing Tg. The relation between Tg and log crosslinkage is linear except in the final stage of the curing process. The slope B of the Vg‐Tg relation is obtained from the iso‐free‐volume theory of glass‐transition phenomena as B = Voαb(1 – ΔVo/Vf · Vf/Vo · αa – αb/αb), where Vo is the occupied volume, Vf the free volume, αa – αb the thermal expansion coefficient of free volume, αb the thermal expansion coefficient of occupied volume; Vo is the sum of the two components Vo and Vo, where Vo is the occupied volume in the strict sense and ve is the empty volume into which polymer chains cannot flow. The equation predicts qualitatively the observed value of B.
Optical rotatory dispersion of synthetic polymer: Conformational aspects of N‐substituted poly‐2‐ethylethylenimine
Authors: Tsuboyama Sei , Yanagita Masaya
Published: June 2010

N‐Benzoylated poly‐2‐ethylethylenimines of different stereoregularities were prepared, and their optical rotatory dispersions (ORD) were measured in various solvents. The ORD behavior of the regular polymer in cyclic ethers was anomalous, and that of the irregular one changed to a simple dispersion. The result and general optical rotatory properties suggest that the regular polymer exists in a specific conformation, perhaps as a helix, in the solvents.
The formation reaction of a phenylmethylene polysulfone
Authors: Tokura Niichiro , Nagai Toshikazu , Shirota Yasuhiko
Published: June 2010

Polysulfones with a unit of magnified image have not yet been prepared. By the reaction of benzylsulfonyl halide with phenyllithium, oligomers with a unit of phenylmethylene sulfone magnified image were prepared, which include a disulfone, a trisulfone, and polysulfones with molecular weights of 850–970. The disulfone and the trisulfone were identified as α‐benzylsulfonyl‐α‐benzenesulfonyl toluene and α‐benzylsulfonyl‐α′‐benzenesulfonyl dibenzyl sulfone respectively, and the polysulfones were characterized as phenylmethylene polysulfones magnified image on the basis of the infrared and NMR spectra, elemental analysis, and the pyrolysis results. It has been observed that in ether solvent polysulfones were formed only at a low temperature (−70°C.), together with the trisulfone and the disulfone. However, in THF solvent polysulfones formed exclusively. Some factors exerting an influence on the formation of polysulfones and their formation mechanism are discussed.
An X‐ray study of cellulose triacetate
Authors: Watanabe Sadayoshi , Takai Mitsuo , Hayashi Jisuke
Published: June 2010

Cellulose triacetate I is yielded from cellulose II of mercerized cellulose and rayons in heterogeneous acetylation with lower swelling pretreatment. Both cellulose triacetates I and II with highly ordered structure substantially are converted into cellulose II on saponification. It is possible to obtain transformation of triacetate I to triacetate II without any dissolving process by a comparatively simple treatment with superheated steam. These three points are discussed.
Comparative chemical reactions between α,β‐unsaturated polyesters and monomeric maleic and fumaric esters. I. Nucleophilic addition
Authors: Lee Sung Ki
Published: June 2010

The noncatalytic nucleophilic addition of ammonia and amines with α,β‐unsaturated polyesters at temperatures between 20 and 80°C. was investigated. The mode of reaction is shown to be to a large degree dependent upon the nature of the solvent used. In a protonic solvent poly(hexamethylene glycol maleate) readily reacts with primary or secondary amines to give a normal 1,4 addition product as final product. In a nonprotonic solvent it undergoes rapid isomerization to poly(hexamethylene glycol fumarate). The behavior of these α,β‐unsaturated polyesters is compared with that of monomeric, unsaturated esters, such as dialkyl maleate and dialkyl fumarate. A reaction mechanism is suggested to account for the products of reaction, and the possible driving forces of the reaction is discussed. The comparative rates of reaction between polymeric and monomeric compounds were conveniently followed by using NMR, infrared, and polarographic methods.
The oxidation of ethylene–propylene copolymers with hexavalent chromium compounds
Authors: Burgert Bill E.
Published: June 2010

The oxidation of solutions of ethylene–propylene copolymers with chromic acid, chromyl chloride, and t‐butyl chromate has been studied. The efficacy of these reagents in producing crosslinking sites has been determined by curing with toluene diisocyanate. The presence of hydroxyl and carbonyl groups has been demonstrated by the preparation of soluble derivatives of the oxidized copolymers.
A computer program for the visualization of stereoregular polymers
Authors: Price Fraser P.
Published: June 2010

This paper describes a computer program that is useful in the elucidation and visualization of particular stereoregular polymer chains. The input is the fractions of isotactic, syndiotactic, and heterotactic triplets in a real polymer as determined by some technique such as NMR. The program calculates a matrix of conditional transition probabilities from these fractions. This matrix in conjunction with a random‐number generator is used with Monte Carlo techniques to calculate a specific sequence of 0's and 1's. The sequence contains 101 elements. This is the generated polymer chain. The number of various kinds of doublet, triplet, etc., is then counted for this particular generated chain, and compared with that calculated from the matrix for the chain of infinite length. Comparisons among these sets of figures show that the generated polymer chains are usually quite typical of the infinite chain.

The application of NMR techniques to the determination of the relative numbers of isotactic, heterotactic, and syndiotactic triplets in synthetic polymers was pioneered by Bovey (1) several years ago. The data thus obtained can be used in a straightforward manner to calculate various average properties of the polymer chain. Although these average properties may be used to describe the polymer, frequently it is difficult to visualize exactly what a typical polymer chain might look like from a stereoregularity point of view. This paper describes a computer program that calculates various sequence averages for an infinite polymer chain and that generates by Monte Carlo techniques a polymer chain typical of the NMR data. In addition the program, by calculating various sequence averages for the generated polymer chain, permits evaluation of just how representative the generated polymer is.
Polymer reactors and molecular weight distribution. Part V. Free‐radical polymerization in a transient stirred‐tank reactor train
Authors: Hui A. W. , Hamielec A. E.
Published: June 2010

The transient behavior of both batch and continuous stirred‐tank reactors for free‐radical polymerization of styrene have been studied. For the batch reactor a high‐conversion model was developed, based on experimental investigations measuring the conversion and molecular weight distribution. Significant improvement over the low‐conversion model was obtained when the viscosity or gel effect was accounted for by allowing the termination constant and catalyst efficiency to vary with viscosity. A transient model was also developed for a continuous stirredtank reactor based on batch reactor kinetics. This model was employed in the simulation of a system of stirred‐tank reactors operating under transient conditions.
Morphology and mechanical behavior of block polymers
Authors: Beecher James F. , Marker L. , Bradford R. D. , Aggarwal S. L.
Published: June 2010

The morphology of solution cast films of butadiene and styrene block polymers in both stretched and unstretched state has been studied by electron microscopy, and has been related to the mechanical behavior of these materials. These micrographs confirm the indications from dynamic properties that this material consists of a two‐phase system in which the relationship between the phases is sensitive to the solvent system used in casting. Although the basic morphological unit is a polystyrene sphere of 100 Å diameter dispersed in a matrix of polybutadiene, the interaction between spheres is complex. These spheres are more deformable than would be predicted from their glass transition temperature. The dynamic mechanical properties, stress‐strain properties, and stress relaxation properties of block polymers of styrene and dienes can be explained in terms of the morphology and changes of morphology on stretching in the electron microscope.
The stress‐strain‐birefringence properties of styrene‐butadiene block copolymers
Authors: Fischer E. , Henderson J. F.
Published: June 2010

The stress‐strain‐optical properties of three elastomeric styrene‐butadiene block copolymers containing 31, 40, and 49 wt‐% styrene were studied as a function of temperature. The mechanical and the optical properties indicate that these materials are two‐phase systems in which the polybutadiene chains form an elastomeric phase and the polystyrene a glassy phase with the latter providing physical crosslinks. Birefringence measurements indicate that the decrease in modulus and strength of these materials is associated with a decrease in the concentration of elastically effective network chains. The independence of the stressoptical coefficient on temperature suggests that the decrease in concentration of elastically effective chains is not due to the onset of rubber‐like behavior of flow within the polystyrene regions themselves, at least for temperatures below about 70°C. Rather, the decrease seems to be associated with the increased mobility of the polybutadiene chains at higher temperatures which also leads to an increase in the rate of stress relaxation. Birefringence measured during extension and retraction showed that the stress‐strain hysteresis is due to restricted mobility of the polybutadiene chain segments rather than to permanent viscous flow or to a change in the effective network structure of the block copolymers. The ultimate properties of these rubbers correlated well with the effective network structure in undeformed samples.
Kinetics and mechanism of the emulsion polymerization of ethylene
Authors: Stryker H. K. , Mantell G. J. , Helin A. F.
Published: June 2010

During the emulsion polymerization of ethylene the solubility of the monomer at 85°C and 4500 psig is 0.3–0.6 mol/1 in the aqueous phase and about 5 mol/1 in the monomer‐polymer particle. Hence, ethylene, like vinyl acetate, can be considered a water‐soluble monomer. The rate of polymer formation is proportional to the square root of the initiator concentration. The polymers contain a large amount of low molecular weight polymer that contributes to their characteristic lack of elongation at break. They also contain emulsifier covalently bound in the polymer by a chain‐transfer reaction. Because chain transfer occurs with emulsifier adsorbed on the particle surface and retards the rate of polymer formation, the molecular weight of the polymer is proportional to the particle diameter and the rate of polymer formation is inversely proportional to the emulsifier concentration. Based on similarities in dependence of density and branching on temperature, the propagation step in emulsion polymerization resembles that in the high pressure synthesis of polyethylene. In the absence of chain transfer, however, the structure of emulsion polyethylene becomes complex.
A kinetic investigation of the emulsion polymerization of vinyl chloride
Authors: Ugelstad J. , Mork P. C. , Dahl P. , Rangnes P.
Published: June 2010

An investigation of the kinetics of the emulsion polymerization of vinyl chloride has been performed. The effect on the rate of reaction of such variables as concentration of initiator (K2S2O8), amount and type of emulsifier and number of latex particles has been investigated at 50°C. The order of reaction with respect to initiator was found to be 0.5. The rate of reaction was found to increase with increasing conversion. The number of latex particles was found to be constant during the polymerization, between 10 and 90% conversion, and also found to be independent of the concentration of initiator. The order of reaction with respect to the number of particles was found to increase from 0.05 to 0.15 in the range investigated (Nw = 1016‐1019 per liter H2O). The order decreases slightly with increasing conversion. A mechanism involving a rapid desorption and reabsorption of radicals in the latex particles is proposed. A marked increase in rate was observed at about 70–80% conversion. A closer investigation of this phenomenon was performed by a continuous addition of vinyl chloride at a pressure below the saturation pressure of vinyl chloride corresponding to the reaction temperature. It appeared that under such conditions reaction rates of about twice those of the ordinary runs might be obtained. No change in the number of particles was observed, either during the polymerization or compared to the ordinary run at the same concentrations of emulsifier and initiator. The effect of the degree of reduction in the pressure of vinyl chloride was also investigated. It was found that the rate of reaction passed through a maximum at a pressure of about 6.75 atm, as compared to 7.75 atm in an ordinary run (Saturation pressure of vinyl chloride at 50°C).
The application of continuously uniform latices to kinetic studies of “ideal” emulsion polymerization
Authors: Williams D. J. , Grancio M. R.
Published: June 2010

In kinetic studies of emulsion polymerization, the use of latices which are completely uniform through all stages of growth offer a marked improvement in analytic accessibility over their polydispersed counterparts. This paper first reports recent developments in the technique of generating such model systems and their utility in studying the “ideal” period in emulsion polymerization. Special precautions are necessary in the use of the slow soap addition techniques since soap starvation can sometimes lead to agitation‐controlled reaction rate, and/or latex instability. A convenient‐to‐use, single‐charge formulation for styrene was developed, based on a combination of anionic and nonionic surfactants; this formulation eliminated the mixing problem and produced stable, continuously uniform latices suitable for generalized kinetic studies. Also, data on the development of both Mv and Mv in these systems give some insight into the nature of the reaction. Current steady‐state theories and the rationale associated with them predict for the “ideal” period the generation of polymer with constant molecular weight, but a substantial increase in both Mv and Mv is observed. These results suggest that either an unsteady‐state mechanism prevails or that our knowledge of the mechanism of initiation is inadequate.
Determination of latex particle size by light scattering. VIII. Forward angle ratio method
Authors: Maron Samuel H. , Pierce Percy E.
Published: June 2010

Although dissymmetry of light scattering is a simple and attractive method for determination of latex particle size, it is limited in application to values of D/γm below 0.60 for monodisperse systems, and practically inapplicable to polydisperse ones. Further, its use requires Fresnel corrections, and a knowledge of the refractive index ratios of the systems investigated. To obviate some of these difficulties, a method is described which utilizes the intensity ratios for two forward angles differing by 10°, such as 45°/35°. With such forward angle ratios Mie calculations show, and experiment confirms, that particle diameters up to D/γm = 2.00 or higher can be measured for monodisperse systems. Again, no Fresnel corrections are required, and the results are practically independent of refractive index ratio between 1.15 and 1.20. However, like the dissymmetry method, the forward angle ratio method is very sensitive to polydispersity, and results are obtained here which vary with the distribution of the systems, the angle ratio, and the wavelength of light used.
Particle size and molecular weight distributions of various polystyrene emulsions
Authors: Krackeler J. J. , Naidus H.
Published: June 2010

Three different emulsion polymerization techniques, the batch (B), monomer addition (M Add), and emulsion addition (E Add) procedures were studied. Rates of polymerization indicated that the B reacted more rapidly than either the M Add or E Add. This was related to the lower monomer concentration present in the M Add and E Add systems. This is described as monomer starvation. MW and MW distributions were compared for these polymers. The B polymer had a significantly higher MW than either the M Add or E Add polymer. This could also be related to monomer starvation in the latter systems. However, the MW distribution of these polymers gave comparable values of Mw/Mn = 3.1. This indicates a similar molecular growth phenomena which appears to result from polymerization occurring near the particle surface for the addition systems. Particle size distribution measurements showed the B latex to have the narrowest distribution while the E Add latex had the widest. Also, the M Add had a particle diameter distribution which was approximated by a normal distribution. This is explained by use of the monomer starvation concept. Additional polymerizations were carried out called “hybrids” which were variations of the polymerizations discussed above. Significant differences result from the various techniques of emulsion polymerization. These differences manifest themselves not only in average particle size and MW, but also in particle size distribution. No significant differences were obtained in MW distributions.
Packing efficiency in sediments of monodisperse latexes and bimodal latex mixtures
Authors: Hiemenz Paul C.
Published: June 2010

The packing efficiency of monodisperse polystyrene latexes stabilized by the sodium salt of 2‐sulfoethylmethacrylate was studied by centrifuging the dialyzed latexes. The solids level of the sediments were examined for 0.6 and 3.4 μ particles alone and in mixtures of various proportions. Monodisperse latexes produced sediment densities in the range of 54 to 64 vol‐%, and binary mixtures ultimately produced residues showing maximum sediment densities of about 80 vol‐% at some optimum mixture composition. Both the uniform and bimodal samples thus showed packing efficiencies somewhat less than the theoretical maxima, about 74 and 86 vol‐%, respectively. Colloidal instability and particle solvation are discussed as explanations for the deviations from maximum packing efficiency.
Investigation of the disposition of surfactant in a latex by the “rate of dialysis method.” Mechanism of detergent dialysis
Authors: Edelhauser Helmut A.
Published: June 2010

The initial rate of dialysis across a cellophane membrane for sodium dodecylsulfate and dodecylbenzenesulfonate proved to be dependent on surfactant concentration without a break at the critical micelle concentration (cmc) and could, therefore, be used to determine free surfactant concentration in latices over a wide range. Equilibrium dialysis is not a suitable tool, because, if the cmc is exceeded in the dialyzate, diffusion comes practically to a dead stop long before equilibration, at least with ordinary detergents. (Dialysis is, however, resumed at a substantial rate if dialyzate and dialyzed solution are replaced by newly prepared solutions of the same concentration.) An explanation for these phenomena is suggested. Free surfactant concentrations measured by rate of dialysis were far below the cmc in a polystyrene latex and far above the cmc in a comparable poly(vinyl acetate) (PVA) latex. When increasing the surfactant‐polymer ratio in a PVA dispersion by post‐addition complete solubilization of the polymer is observed eventually. Concentrations of free surfactant and of solubilized polymer were measured for the intermediate stages. The experimental data indicate a twofold mechanism for the solubilization process: Surfactant penetrates into the interior of PVA particles taking water with it and causing swelling to the point of disintegration, parallel to which single chains from the outer parts of the particles are already disentangled and solubilized. It is concluded that in a PVA latex only a comparatively small portion of the anionic surfactant will be at the particle surface, a relatively large part being in the aqueous phase and in the particle interior, which may account for this surfactant being a poor stabilizer in vinyl acetate emulsion polymerization at high total solids content.
Chitin and its association with other molecules
Authors: Rudall K. M.
Published: June 2010

Chitin or poly‐N‐acetyl‐D‐glucosamine occurs in three crystallographic forms α, β and γ. The α form is the most stable and consists of antiparallel chains. The β form (parallel chains – one chain per unit cell) and the γ form (probably two chains up and one down per unit cell) are both converted to the antiparallel arrangement (α form) on treatment in strong HCl. Chitin in the cuticles, apodemes and chaetae of animals occurs together with a considerable quantity of protein. X‐ray diffraction diagrams of the intact structures show repetition along the fiber axis corresponding to six NAG residues, or (more rarely observed) to eight NAG residues. The structural studies of Phillips and his colleagues on the reaction of lysozyme with NAG oligomers are taken as a relevant model for those chitin/protein complexes showing a repetition of six NAG residues/protein unit. In the case of locust tibia cuticles, evidence is presented for the existence of corpuscular protein units along chitin microfibrils and these repeat at 31 Å i.e. every six NAG residues. It is suggested that these protein units are basically a chitin synthetase but serving also as a “plasticiser” to modify the mechanical and water‐holding properties of the chitin.
The wetting of cellulose and wood hemicelluloses
Authors: Luner P. , Sandell M.
Published: June 2010

The wetting properties of wood polysaccharides were characterized by Zisman's empirical parameter, the critical surface tension of wetting, γc. Cellulose was tested in the form of cellulose films regenerated from viscose and cellulose acetate. It was found that the source of cellulose (cotton, wood and hydrolyzed cellulose), the method of film preparation (single‐bath, two‐bath, dry‐cast, orientation), and consequently the physical state of the cellulose surface, influenced the wettability of the samples. Contact angles were also measured on hemicellulose films derived from hardwoods and softwoods. The critical surface tension γc ranged from 35.5 to 49.0 erg cm−2 for cellulose and from 33 to 36.5 erg cm−2 for hemicellulose films. The hemicellulose samples showed the smallest hysteresis effects which may be related to its energetically more uniform surface or lower porosity. The effect of moisture on contact angle measurements is discussed. Finally, the wetting of cellulose is evaluated in terms of recent theories relating surface energies and intermolecular forces.
Conformational analysis of polysaccharides. III. The relation between stereochemistry and properties of some natural polysaccharide sulfates (1)
Authors: Rees D. A. , Steele I. W. , Williamson F. B.
Published: June 2010

The sol → gel → sol transformation of aqueous K‐carrageenan occurs with complex changes in optical rotation which may be explained qualitatively in terms of the double helix model for junction zones. Evidence is given that the double helices in the gel are normally aggregated but can be kept separate within a narrow temperature range, and that gelation is a kinetic rather than an equilibrium process. An attempt has been made to predict the preferred conformations of irregular carrageenans by joining segments of simpler polysaccharides; the effect of certain structural variations on gel properties may then be explained. Model building in the computer does not exclude the possibility of double helices for the following polysaccharides which are structurally related to K‐ and i‐carrageenan: hyaluronic acid, chondroitin, chondroitin 4‐sulfate, chondroitin 6‐sulfate, dermatan sulfate, keratan sulfate, agarose, porphyran, μ‐carrageenan and furcellaran.
A short history of superconductivity
Authors: Bloch Felix
Published: June 2010

Shortly after its discovery the electron was recognized as the carrier of electricity in metals. The difficulties encountered in treating the conduction electrons as a classical ideal gas was removed upon the advent of quantum mechanics and led to a satisfactory explanation of normal metallic conductivity. Although superconductivity was discovered more than fifty years ago, however, the first phenomenological theory did not come until the middle thirties and it took another twenty years before the first microscopic theory was presented. It was based upon the assumption that the conduction electrons formed a degenerate Bose gas but was soon replaced through the recognition that the pairing of electrons in a Fermi gas furnished a more realistic and quantitative explanation of superconductivity. The striking manifestation of superconductivity as a quantum phenomenon on macroscopic scale was demonstrated in the early sixties through the discovery of flux‐quantization in a closed superconductive ring and led shortly afterwards to the interesting related effects which arise from the introduction of a dividing barrier.
The exciton mechanism: Studies in model compounds
Authors: Schneider Richard S.
Published: June 2010

The “Little” model for a macromolecular high temperature superconductor can be discussed in terms of its component parts. Studies on molecules designed to serve as the polyene and the polyene spine indicate that polymeric metallocenes, in which planar aromatic hydrocarbon rings and meatal atmos alternate, may be suitable. Toward this end the hydrocarbon dicyclopentanaphthalene, and various substituted derivatives were synthesized, and the polymerization of the corresponding dianions with ferrous chloride were investigated.
Electron delocalization in anion‐radicals of permethylcyclopolysilanes
Authors: West Robert
Published: June 2010

The family of cyclic permethylpolysilanes, [(CH3)2Si]n, has been synthesized. Compounds in which n = 5, 6 and 7 undergo reduction at low temperatures to form anion‐radicals. The five‐ and six‐membered rings give the parent anion‐radicals [(CH3)2Si]5− and [(CH3)2Si]6− when reduced electrolytically, but all three compounds give [(CH3)2Si]5− when reduced with alkali metals. The ESR spectra of the anion‐radicals show that the unpaired electron contacts all of the methyl protons equally, and so is fully delocalized over all the silicon atoms in the ring. The permethylpolysilanes have electron affinities similar to that of benzene; the ease of reduction is in the order [(CH3)2Si]5 > benzene > [(CH3)2Si]6. These findings suggest that electron mobility and delocalization is not limited to “conjugated” molecules but can also be observed in systems not normally considered as “unsaturated.” Implications for the design of organic conducting elements will be mentioned.
Inelastic electron scattering from organic compounds
Authors: Gerber Sheldon H.
Published: June 2010

In calculations of possible superconductivity in a system, knowledge of certain matrix elements determines whether or not bound electron pairs can exist and thus lead to superconductivity. These matrix elements involve ground and excited state wave functions. We are presently attempting to experimentally determine such matrix elements in certain organic compounds by measuring differential cross sections for inelastic electron scattering. Such cross sections involve the square of the matrix elements of interest. To do this we are using a crossed beam technique with an electrostatic electron spectrometer for the production of the incident electron beam and analysis of the scattered beam. The apparatus is described, as well as the present status of the experiment.
The effect of molecular weight on frictional coefficients of poly‐α‐methylstyrene
Authors: Cowie J. M. G. , Bywater S.
Published: June 2010

The frictional coefficients. [f] of a wide range of poly‐α‐methylstyrene samples ranging in molecular weight from dimer to polymers of M ∼ 106 have been measured in a good solvent (toluene) and under θ conditions (cyclohexane, 37°C). All products were prepared anionically, and the very low molecular weight samples were initiated with phenyl‐isopropyl potassium to ensure that the end‐groups were not significantly different from the polymer chain. [f] was measured using both diffusion and sedimentation techniques. At molecular weights below ∼ 104, [f] is independent of solvent and proportional to M0.5 to quite low molecular weight. Divergences only occur at the very lowest part of the range. Above M∼ 104, [f] continues to be proportional to M0.5 in cyclohexane as expected, but the values in toluene become greater because of greater chain expansion in the better solvent. The results are discussed in terms of current theories of conformations of polymers in solution and its effect on flow properties.