bluuebunny/crossref_metadata_2025 huggingface dataset:
γ–α Solid–solid transition of isotactic polypropylene
Authors: Pae K. D.
Published: April 2003

X‐ray diffraction patterns have been taken as a function of time and temperature on a sample of polypropylene held under high pressure (4.14 kbar) for 180 hr. at a temperature of 248°C. and subsequently cooled to room temperature. The molded sample initially crystallizes in the triclinic γ–phase but transforms to the γ–phase at elevated temperatures. The rate of conversion from γ to α is a function of time and temperature and tends to approach a constant value with increasing time. The nature of the thermal changes occurring in the sample was also studied by differential scanning calorimetry. It appears that at low scan speeds, there is a solid–solid transformation from the α‐phase to the γ–phase, but at high scan speeds, the γ–phase melts without conversion to the α‐phase.
Temperature dependence of the bulk crystallization rate of polymers
Authors: Kim H. , Mandelkern L.
Published: April 2003

Data already existing in the literature for the overall crystallization kinetics of a variety of polymers have been analyzed according to different possible nucleation mechanisms. The conclusions reached are similar to those previously deduced from an examination of ata for spherulite growth rates. It is demonstrated that, if allowed a reasonable choice for the equilibrium melting temperature, no unbiased selection of a unique nucleation process can be made. Moreover, a set of universal parameters exists for each of the nucleation and growth processes considered which allows the data for all polymers to be represented by a single straight line. The only quantities that are unique to a given polymer are the equilibriun melting temperature and the activation energy for transport.
Phase relationships and thermodynamic interactions in isotactic polypropylene–diluent systems
Authors: Nakajima Akio , Fujiwara Hiroshi
Published: April 2003

Phase relationships of isotactic polypropylene in various organic diluents were investigated. The diluents used were aliphatic alcohols, alkyl phenols, aryl phenols, diphenyl derivatives, alkyl aryl ethers, esters, and others. Among the diluents examined, n‐butyl alcohol, p‐tert‐butyl phenol, p‐tert‐amyl phenol, diphenyl, diphenyl ether, benzyl phenyl ether, dibenzyl ether, and benzyl propionate were found to be theta solvents for isotactic polypropylene at temperatures in the range 120–190°C. For these theta solvents, the thermodynamic interaction parameters were determined. The results are discussed in relation to the type of diluent.
Viscoelasticity of oriented poly(ethylene terephthalate)
Authors: Murayama Takayuki , Dumbleton John H. , Williams Malcolm L.
Published: April 2003

Time–temperature superposition can be successfully applied to both the stress relaxation and dynamic mechanical properties of oriented PET fibers. Two curves result; one is the time dependence of the modulus at constant temperature, while the other is the shift, log aT, of this curve along the time scale as a function of temperature. This temperature dependence is less than that for both unoriented PET and typical amorphous polymers above Tg. It is about the same as that for oriented nylon 66 and unoriented glassy poly(methyl methacrylate). The isothermal modulus has the same time dependence as that of the unoriented PET; however, it is a factor of 3.3 larger. The modulus curve is almost identical in both shape and magnitude with that of oriented nylon 66. However, a temperature of 82°C. is required to place the viscoelastic dispersion region of PET at the same time scale as nylon 66 at 25°C. This temperature increase is the major difference in viscoelasticity between these two oriented polymers.
Phase equilibria in polymer–liquid–liquid systems
Authors: Suh K. W. , Liou D. W.
Published: April 2003

The phase equilibria in polymer–liquid 1–liquid 2 ternary systems have been calculated on the basis of the Flory‐Huggins theory of polymer solutions. A new approximation method based on the “cluster” concept has been introduced for mixed solvents comprising a solvent and a nonsolvent. This concept has been verified with polystyrene–solvent–methanol systems.
Melting of polycaprolactam
Authors: Liberti F. N. , Wunderlich Bernhard
Published: April 2003

Highly crystalline polycaprolactam was prepared by zone polymerization of ε‐caprolactam. Folded‐chain crystallized and annealed, melt‐crystallized, and solution‐crystallized polycaprolactam was produced from commercial polycaprolactam. All samples were characterized by x‐ray diffraction, electron microscopy, density measurement, and heat of fusion measurement. The determination of the time‐dependent melting by DTA and scanning calorimetry revealed that all the different morphologies show different melting behavior. Zone‐polymerized polycaprolactam superheats, and the other morphologies reorganize on heating to different degrees. Densities and heat of fusion vary in the same manner—from highest to lowest—in the order: zone‐polymerized, solution‐crystallized, annealed, and melt‐crystallized. An estimate of heat of fusion, equilibrium melting point, and surface free energy was obtained from the melting points.
Some rheological properties of molten polypropylene
Authors: Adamse J. W. C. , Janeschitz‐Kriegl H. , Den Otter J. L. , Wales J. L. S.
Published: April 2003

The following measurements were carried out on the melts of two samples of polypropylene, one with a narrow and one with a broad molecular weight distribution: viscosity in steady shear flow, dynamic storage and loss moduli, total normal thrust in cone‐and‐plate apparatus, and flow birefringence. The validity of various theoretical interrelations between the measured quantities is checked. The influence of molecular weight distribution is qualitatively discussed.
NMR studies of polymer solutions. III. Conformational transition study of oligomeric polyethylene in mixed solvents
Authors: Liu Kang‐Jen
Published: April 2003

The intramolecular structure of oligomeric polyethylene (PE) in solvent mixtures of α‐chloronaphthalene and carbon tetrachloride, α‐chloronaphthalene and deuterated octane, and α‐chloronaphthalene and deuterated hexadecane was studied at 35°C. by a high‐resolution nuclear magnetic resonance technique. It was clearly shown that the n‐alkanes show no detectable selective solvent absorption in these systems. The conformational structure (Pp), which was formed in “bulky” aromatic solvents when the chain length was greater than 16, was significantly destroyed by the presence of carbon tetrachloride, octane, or hexadecane in the above‐mentioned solvent mixtures. Therefore, the “bulky” aromatic solvents, such as α‐chloronaphthalene and 9‐chloroanthracene, can be classified as Pp‐structure‐promoting solvents, in which the PE remains in the Pp conformation. In contrast, carbon tetrachloride and linear alkanes are Pm‐structure‐promoting solvents, in which the PE does not exhibit any Pp structure but is in the disordered Pm conformation. It is speculated that the Pp structure is caused by a “chain‐fold” mechanism.
Viscoelastic properties of 1,2‐polybutadiene—comparison with natural rubber and other elastomers
Authors: Sanders James F. , Ferry John D. , Valentine Robert H.
Published: April 2003

Viscoelastic properties of uncrosslinked 1,2‐polybutadiene (91.5% vinyl, 7.0% cis, 1.5% trans, number‐average molecular weight 99,000) were studied by dynamic shear measurements between 0.15 and 600 cps (torsion pendulum and Fitzgerald transducer) and shear creep measurements over time periods up to 3.7 × 104 sec., in the temperature rang from 5 to 50°C. More limited dynamic measurements were made on a sample of unvulcanized natural rubber with number‐average molecular weight 350,000 at frequencies from 0.4 to 400 cps and temperatures from 13 to 48°C. All data were reduced to 25°C. by shift factors calculated from equations of the WLF form with the following coefficients: 1,2‐polybutadiene, c1 = 6.23, c2 = 72.5; natural rubber, c1 = 5.94, c2 = 151.6. In the transition zone, the relative positions of the loss tangent curves on the logarithmic frequency scale for these and other rubbers (1,4‐polybutadiene with 50% trans configuration; styrene–butadiene rubber with 23.5% styrene content; and polyisobutylene) provided relative measures of local segment mobility. At 25°C., these ranged over a factor of 3700 with 1,2‐polybutadiene and polyisobutylene the lowest and 1,4‐polybutadiene the highest. When the frequency scale of each rubber was reduced to a temperature 100°C. above its glass transition temperature, however, the loss tangent curves for all except polyisobutylene were nearly coincident; the latter still showed a lower mobility by a factor of about 1/800. The terminal relaxation time and steady‐state compliance for the 1,2‐polybutadiene calculated from the Rouse theory were larger than those observed experimentally. The level of compliance corresponding to the entanglement network of 1,2‐polybutadiene, JeN, was calculated by integration over the loss compliance, J″, to be 1.62 × 10−7 cm.2/dyne; integration over G″ to obtain the corresponding modulus gave reasonable agreement. From such JeN, values, the average number of chain atoms between entanglement points, jZe, was estimated as follows: 1,2‐polybutadiene, 132; natural rubber, 360; 1,4‐polybutadiene, 110; styrene–butadiene rubber, 186; polyisobutylene, 320. Values of jZe were also estimated from the minimum in the loss tangent and compared with those reported from the molecular weight dependence of viscosity. The three sources were in generally good agreement.
Vibrational analysis of chain folding in polyethylene crystals
Authors: Tasumi M. , Krimm S.
Published: April 2003

The vibration frequencies of a polyethylene crystal lattice have been computed for various structures in which a fully deuterated chain is mixed with a normal chain. Intermolecular potential functions previously developed by the authors were used in the calculation. It is shown that such structures make it possible to distinguish experimentally between chain folding in the (110) plane and folding parallel to the (100) plane. Calculations have also been done for a regular polymer of (CH2CD2). Such a structure would permit the determination of the parity of the number of methylene groups in the fold.
Quantitative characterization of deformation in drawn polypropylene films
Authors: Samuels Robert J.
Published: April 2003

The submicroscopic morphology of uniaxially deformed isotactic polypropylene films has been examined by small‐angle light scattering (SALS), electron microscopy, optical microscopy, small‐angle x‐ray scattering (SAXS), wide‐angle x‐ray diffraction, birefringence, sonic modulus, and density methods. Several new interpretations and extensions of existing theories are developed and verified experimentally as follows. (1) The Vv SALS pattern is shown to be a new tool for the identification of the sign of the birefringence of spherulites too small to be seen in the optical microscope. The theoretical dependence of the Vv SALS pattern is developed and verified experimentally with patterns from isotactic polypropylene, polyethylene, Penton, nylon 6,6, poly(ethylene terephthalate), and nylon 6,10. (2) Intraspherulitic lamellar behavior during deformation can be identified from the SAXS pattern. This includes quantitative evaluation of the long spacing between lamellae and their average orientation. (3) The two‐phase sonic modulus theory is valid over the wide range of deformations, crystallinities, processing temperatures, and molecular weights used in this study. The deformation of isotactic polypropylene films drawn at 110 and 135°C. has been characterized quantitatively in terms of an integrated picture of mass movement on all morphological levels: the molecular, the interlamellar, and the spherulitic. At both temperatures, the spherulites deform affinely with extension, whereas the deformation mechanisms within the spherulite depend on the location of the radii with respect to the applied load. During spherulite deformation, lamellar orientation and separation processes predominate, whereas at high extensions, fibrillation occurs and crystal cleavage processes predominate. The noncrystalline region orients throughout the draw region. At 135°C. non‐orienting relaxation processes appear in the noncrystalline region which retard the rate of molecular orientation with extension.
Temperature dependence of photoelastic properties of crosslinked amorphous polyethylenes
Authors: Saunders D. W. , Lightfoot D. R. , Parsons D. A.
Published: April 2003

Crosslinked samples of polyethylene were prepared by electron irradiation of both high‐ and low‐density polymers in the crystalline state. A further crosslinked sample was obtained by curing a high‐density polyethylene by reaction with dicumyl peroxide at 180°C. The stress–strain–birefringenece relations were obtained on specimens cut from these samples at temperatures between 130 and 250°C. All samples showed a substantial decrease in stress‐optical coefficient with increasing degree of crosslinking and with increasing temperature. The stress‐optical properties at each temperature were extrapolated to zero degree of crosslinking to give quantities characteristic of the Gaussian network. Comparison of these properties with the theory of networks of rotational isomeric chains with both independent and interdependent rotation allows estimates to be obtained for (1) the trans–gauche energy differences in rotation around skeletal bonds and (2) the difference in principal optical polarizabilities for the CH2 group in the elastomeric state. This latter quantity is shown to be more nearly given by Denbigh's than by Bunn and Daubeny's bond polarizability values.
Dielectric relaxations and electrical conductivities of poly(alkyl methacrylates) under high pressure
Authors: Sasabe Hiroyuki , Saito Shogo
Published: April 2003

Dielectric properties of four methacrylate polymers (methyl, ethyl, n‐butyl and n‐octyl) were studied in the frequency range 0.0001 cps–300 kcps at temperatures above and below the glass transition temperature and at various pressures up to 2500 atm. At temperatures well above Tg a single relaxation peak (α′ peak) was observed in the case of the higher n‐alkyl methacrylates. However, this peak was split into two peaks, α and β, with decrease in temperature or increase in pressure. The molecular motions corresponding to the α and the β relaxation processes are the micro‐Brownian motions of amorphous main chains and of flexible side chains, respectively. From the temperature and the pressure dependence of the average dielectric relaxation time of these polymers the single relaxation process (the α′ process) was attributed to the micro‐Brownian motion of the main chain coupled with that of the side chain. The effects of temperature and pressure on the d.c. conductivity of these polymers were also studied.
Fast passage dispersion signals in inhomogeneously broadened electron spin resonance spectra: Application to the measurement of the spin‐lattice relaxation times of free radicals derived from esters and salts of poly(methacrylic acid)
Authors: Bullock A. T. , Griffiths W. E.
Published: April 2003

The shape of the first derivative of the dispersion mode of an inhomogeneously broadened electron spin resonance spectrum changes markedly on saturation. This behavior provides a convenient and rapid technique for estimating the spin latice relaxation time of the paramagnetic species involved. The technique is described together with the relevant theory. Values for the relaxation times of free radicals derived from poly(methyl methacrylate) and from poly(sodium methacrylate) have been obtained by this method and are found to be in good agreement with those obtained by the progressive saturation technique. A series of salts of polymethacrylic acid have been γ‐irradiated, and the spin lattice relaxation times of the resulting trapped radicals were determined at 77 and 299°K. For a given polymer the relaxation times show little variation with temperature. This is attributed to a broad distribution of correlation times.
Sedimentation transport method for determination of molecular weight distributions
Authors: Kotaka Tadao , Donkai Nobuo
Published: April 2003

The sedimentation of the system polystyrene‐cyclohexane at the Flory temperature has been studied with emphasis on the effects of pressure as well as concentration. The relation between the molecular weight M and the limiting sedimentation coefficient s00, is found to be s00 = 1.50 × 10−15 M1/2 (sec.) The concentration dependence parameter ks has the form, ks = k′M1/2 = k″s00 with k′ = 4.5–5.5 × 10−4. However, a rather unexpected dependence of ks on the rotor speed is also found. A procedure is proposed for deducing solute molecular weight distributions from boundary spreading data in sedimentation transport experiments, a so‐called “single concentration” method, requiring only one sedimentation run. Application to several polystyrenes (in cyclohexane at 35°C) with narrow, broad, and very broad distributions demonstrates the feasibility of the procedure. Comparisons are made with data from elution chromatography and gel permeation chromatography. The GPC method predicts somewhat broader distributions than those obtained by the other two methods.
Tensile strength of rubbers
Authors: Tobolsky A. V. , Lyons P. F.
Published: April 2003

A current theory of the tensile strength of rubbers invokes large‐scale crosslink interchange at room temperature to explain the high tensile strengths of networks crosslinked with weak linkages. This mechanical lability of certain crosslinks has been assumed from their known thermal lability at higher temperatures. Relaxation of stress experiments at various elongations have been performed at room temperature on networks crosslinked with both weak and strong linkages. Our purpose was to detect mechanically induced crosslink slippage. We have found no evidence of any mechanical lability of weak crosslinks at room temperature. A hypothesis is presented which explains the high tensile strengths of rubbers crosslinked with weak linkages as resulting from an internally relaxed network formed by the thermal lability of the crosslinks at the vulcanization temperature. This theory is shown to be consistent with some previously unexplained experimental results.
Variation of crystallite orientation with degree of crystallinity: Isotactic polystyrene
Authors: Krigbaum W. R. , Maruno Shigeo
Published: April 2003

The orientation of the crystallographic c axis (chain axis) was followed by x‐ray diffraction during the crystallization of four samples of isotactic polystyrene differing in elongation ratio. The crystallite orientation can be expressed by 〈cos2 χc〉, where χc is the angle between the c axis and the stretching direction. The degrees of crystallinity w were estimated from the diffraction data by using density for calibration. It was found that 〈cos2 χc〉 decreases in a linear manner with crystallinity, the rate of decrease being very small when the elongation ratio α is 5, but becoming progressively larger as α is decreased toward unity. A qualitative measure suggests that amorphous orientation decreases during crystallization at a rate which is nearly independent of α. The variation of 〈cos2 χc〉 with w is therefore governed by the orientation of the statistical chain segments prior to crystallization. If the elongation ratio is small, the supply of well oriented statistical segments is limited, and 〈cos2 χc〉 will decrease at a rapid rate during crystallization. A treatment due to Krigbaum and Roe permits evaluation of the ratio, ν/N, where ν and N are the average numbers of statistical segments in the crystallization nucleus of critical size, and in a network chain, respectively. Our polystyrene samples were not crosslinked, so chain entanglements must serve as junction points. Values of ν could not be obtained, since N was unknown. However, the (ν/N) ratio for isotactic polystyrene decreases slowly with α, and the values agree reasonably well with those obtained in a previous study of oriented polychloroprene networks. After nearly complete crystallization (ω ca. 0.30), the long period spacing measured by low angle diffraction was approximately 135 Å, and varied only slightly with elongation ratio in the range α = 1 to 5. It therefore appears that chain folded lamellae are present in both drawn and undrawn samples of isotactic polystyrene.
Dynamic mechanical properties of cross‐linked rubbers. V. An approximate analysis of the modulus contributions of trapped and untrapped entanglements
Authors: Mancke Ralph G. , Dickie Ray A. , Ferry John D.
Published: April 2003

Using the criterion that a coupling entanglement in a polymer network is trapped if all four strands radiating from it terminate in chemical cross‐links (an approximation to a more rigorous treatment of Langley), an equation is derived relating the equilibrium modulus to the magnitude of the compliance in the frequency region where all coupling entanglements, whether trapped or not, contribute to the elasticity. The latter value is estimated from the storage compliance at the frequency where the storage compliance of the uncross‐linked polymer corresponds to the entanglement compliance derived from integration over the loss compliance. The theory agrees rather well with data on vulcanizates of natural rubber. For 1,4‐polybutadiene and styrene–butadiene rubbers, the agreement is somewhat less satisfactory, but the results support the hypothesis that the low‐frequency losses observed in lightly cross‐linked rubbers are due to relaxation of untrapped entanglements.
Bubble formation in vulcanized rubbers
Authors: Denecour R. L. , Gent A. N.
Published: April 2003

A theoretical treatment is given for the formation of visible holes in an elastic solid. It differs from previous treatments of bubble formation in liquids by neglecting the problem of hole nucleation altogether. Instead, a small spherical hole is assumed to be present initially. The inflation of such a hole by a dissolved gas is then considered. A critical internal pressure is deduced, at which the hypothetical hole would become infinitely large. This pressure is given by 5G/2; where G is the shear modulus of the rubber. Some model experiments are described in which swollen rubber vulcanizates were rapidly heated to bring the dissolved liquid into a superheated conditions. The temperatures of rapid bubble formation were determined for a number of vulcanizates having different degrees of crosslinking and hence different values of shear modulus, and for different swelling liquids. The results are shown to be in reasonably good quantitative agreement with the theoretical predictions.
Viscosity and normal stresses in branched polydisperse polymers
Authors: Graessley William W. , Prentice James S.
Published: April 2003

The steady‐flow behavior of five samples of branched poly(vinyl acetate) has been studied with the Weissenberg rheogoniometer. The branching densities and molecular weight distributions were known from an analysis of the polymerization kinetics. Measurements were made on concentrated diethyl phthalate solutions (0.170 and 0.225 g/ml) at temperatures of 30 and 70°C. The viscosities of all solutions at zero shear rate were less than of solutions of linear poly(vinyl acetate) with the same weight‐average molecular weight. The amount of decrease was in excellent agreement with Bueche's theory of melt viscosity in branched systems. The viscosity versus shear rate curves were surprisingly independent of molecular weight distribution, the data from all samples being superimposable on the same master curve. Relaxation times derived independently from the viscosity behavior and the normal stress data were of similar magnitude and always close to the Rouse relaxation time of each solution.
Analysis of the random configuration of the polycarbonate of diphenylol‐2,2′‐propane
Authors: Williams A. D. , Flory P. J.
Published: April 2003

The structure of the polycarbonate chain has been analyzed from the point of view of the spatial configurations it may assume. The carbonate group is certainly planar, and the trans,trans configuration probably is strongly preferred. Rotations about the aryloxygen bonds are subject to symmetric, twofold potentials. It follows that the molecule can be treated as a freely rotating chain consisting of a succession of virtual bonds 7.0 Å in length, joined at angles of ca. 112°. Calculations carried out on this basis yield 〈r2〉0/M = 0.85 Å2/g‐mole wt for the unperturbed random coil, in excellent agreement with the experimental results of Berry, Nomura, and Mayhan. The effect of occurrence of some of the carbonate groups in cis, trans configurations is investigated using more elaborate methods.
Polarization of fluorescent light from a uniaxially oriented rubber
Authors: Stein R. S.
Published: April 2003

The polarization of fluorescence from a polymer characterizes two segment orientation functions, fs(2) and fs(4). These may be calculated as a function of elongation using the kinetic theory of rubber elasticity. Three cases are considered: (a) the transition moment direction lies parallel to the segment axis and does not change its orientation during the lifetime of the excited state, (b) the transition moment direction lies at an angle γ to the segment axis, and (c) the transition moment changes its orientation during the lifetime of the excited state.
Poly(1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate). III. Adsorption on a crystalline silica
Authors: Shyluk W. P.
Published: April 2003

With low‐shear mixing, a portion of a high molecular weight poly(DMVPMS) is immediately adsorbed, and fairly stable aggregates are formed by the polymer bridging mechanism. The adsorption equilibrium is not established after several weeks because of a very slow liberation of the partly covered surface that is trapped within the aggregates. At a high ionic strength, or when the polymer is degraded to a low molecular weight, the adsorption equilibrium is quickly established because of a weaker bridging in the aggregates. It is proposed that poly(DMVPMS) adsorbs from water in a flattened conformation by an ion exchange mechanism. The saturation level increases and then becomes constant as the ionic strength is increased. Simple electrolytes show a specific effect on the adsorption of poly(DMVPMS) that is analogous to their effect on the interaction of other colloidal particles.
Quantitative characterization of deformation in polypropylene fibers
Authors: Samuels Robert J.
Published: April 2003

A modus operandi is developed for characterizing, in quantitative morphological terms, the structural changes occurring during the preparation (spinning, drawing, and heat setting) and testing (tensile modulus) of isotactic polypropylene fiber. This involves the application of the following eight different physical techniques: wide‐angle x‐ray diffraction, birefringence, density, sonic modulus, small‐angle x‐ray diffraction, dark‐field microscopy, small‐angle light scattering, and tensile modulus. Structural changes on several organizational levels, the spherulitic, the interlamellar, and the molecular, are determined in this manner and related to the processes involved.
Thermostable organic polymers devoid of hydrogen and other pendent groups
Authors: Hirsch Stephen S.
Published: April 2003

Aromatic hydrogen atoms in thermostable polymers can be surprisingly labile at relatively low temperatures and may participate extensively in degradative reactions. If hydrogen were eliminated from the polymer chain, a number of degradative pathways would be excluded. Replacement of hydrogen with other pendent groups such as fluoride or trifluoromethyl still leaves a potential “handle” to enter into unwanted reactions, therefore, all bonds not required to create the chain were eliminated. The polyimide devoid of hydrogen from pyrazinetetracarboxylic dianhydride and 2,5‐diamino‐1,3,4‐thiadiazole was synthesized. This polymer exhibits extraordinary high temperature
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oxidation stability. Films of this composition support weight in air up to 592°C, and rupture at this temperature is accompanied by no charring whatever. By comparison, the corresponding polymer from pyromellitic dianhydride, with two hydrogen atoms per repeating unit begins to char at 320°C.
Synthesis, reactivity, and polymerization of vinylureas
Authors: Overberger C. G. , Montaudo G. , Ishida S.
Published: April 2003

The syntheses of N,N′‐divinylureas and some related compounds are reported. Polymerization of these monomers and determination of the structures of the resulting polymers are described. Evidence is presented which supports the tendency of vinylureas to react through their tautomeric form.
Triptycene polymers
Authors: Hoffmeister E. , Kropp J. E. , McDowell T. L. , Michel R. H. , Rippie W. L.
Published: April 2003

New, bifunctional, bridgehead‐substituted triptycenes were synthesized and used to prepare a series of triptycene polymers, including polyesters, polyamides, polyurethanes, and a polyoxadiazole. Certain of these partially aliphatic polymers were thermally stable. Clear and colorless films were obtained in some instances.
Synthesis of 4‐vinylbiphenyl–isoprene block copolymers and their characterization by gel‐permeation chromatography
Authors: Heller J. , Schimscheimer J. F. , Pasternak R. A. , Kingsley C. B. , Moacanin J.
Published: April 2003

4‐Vinylbiphenyl–isoprene ABA block copolymers were prepared by initiating 4‐vinylbiphenyl with n‐butyllithium in benzene, adding isoprene, and coupling the resulting AB anion with phosgene. Preliminary coupling experiments with a polyisoprene anion have shown that virtually quantitative coupling could be achieved provided the phosgene was added extremely slowly. The block copolymers could be quantitatively analyzed by gel‐permeation chromatography from a knowledge of the ratio of the refractive index increments of the two homopolymers and the overall composition.
Polymerization of aromatic nuclei. XV. Polymerization of 2,5‐di‐ and 2,3,5‐trichlorothiophenes with aluminum chloride–cupric chloride
Authors: Ramsey J. S. , Kovacic Peter
Published: April 2003

2,5‐Dichlorothiophene was polymerized to a solid in 93% yield on treatment with aluminum chloride–cupric chloride in carbon disulfide under mild conditions. The product is believed to be poly‐5‐chloro‐2,3‐thienylene on the basis of elemental analysis and infrared and NMR spectral data. Hydrogen chloride was collected in 90% of the theoretical amount. Dimer‐ and tetramer‐type fractions were isolated from the polymer. 2,3,5‐Trichlorothiophene underwent an analogous transformation in trichlorobenzene at 90–100°C. Polythienylenes coupled through the 2,3‐positions have not been reported previously. The net effect of the reaction is nuclear coupling by dehydrohalogenation. We believe that the mechanism involves cationic polymerization accompanied by loss of hydrogen chloride. 2‐Chlorothiophene and thiophene gave products of complex make‐up.
Molecular structure parameters in certain semiconducting polymers
Authors: Kho J. H. T. , Pohl Herbert A.
Published: April 2003

The condensation polymers formed by condensing aromatic hydrocarbons or their derivatives with aromatic acids are quite conductive. The room temperature resistivities of 42 polymers studied here range from 102 to 1012 ohm‐cm. It is found that the resistivities are inversely related to the number of fused rings in the hydrocarbon portion of the monomer for either the homopolymers or copolymers. The resistivities are strongly dependent, inversely, upon the acid strength of the acid monomer reactants. For all the polymers studied, the conductivity σ depended upon the pressure P as ln(σ/σ0) = (b*/k)P1/2 where b* is seen to be an inverse function of the number of fused rings in the monomer in accord with theory. The resistivity ρ varied with absolute temperature T, as ln ρ ∞ (1/T) for all polymers. Thermoelectric powers were determined, and the various relationships established among energy interval, resistivity at “infinite temperature,” carrier concentrations and mobility ratios, number of fused rings, and pressure coefficients are discussed. The polymers are p‐type. Doping by Be++ or Cu++ has a small effect, increasing the conductivity slightly. Electron spin concentrations and carrier concentrations are directly related among the polymers, being found nearly equal for the most conductive but differing by up to nine orders of magnitude in the least conductive polymers.
Synthesis and properties of self‐protecting polyarylates
Authors: Korshak V. V. , Vinogradova S. V. , Siling S. A. , Rafikov S. R. , Fomina Z. Ya. , Rode V. V.
Published: April 2003

Self‐protective polyesters were synthesized in two ways: by polymer analog transformations on polymers obtained and by introduction of inhibiting groups into the polymer during synthesis. It is shown that the Fries rearrangement takes place in the aromatic polyesters in the presence of the Friedel‐Crafts catalysts and on ultraviolet irradiation as well. Thermogravimetric analysis of the rearranged polymers and investigations of the influence of the ultraviolet irradiation on their properties show that the rearrangement markedly increases the photochemical and thermal stability of the polymers. Photostabilization may also be accomplished by the introduction of inhibiting groups, such as hydroxyl, sulfur, or phosphorus into the polymer molecule.
Free‐radical copolymerizations of 1,2‐dichloroethylenes. Evidence for chain transfer by chlorine atom elimination
Authors: Dawson T. L. , Lundberg R. D. , Welch F. J.
Published: April 2003

Trialkylboron–oxygen, an active, low‐temperature free‐radical initiator, has been employed to investigate the effects of very low temperatures on the copolymerizations of vinyl acetate with cis and trans‐1,2‐dichloroethylenes. The low temperatures favor the propagation rate relative to the transfer rate, such that high molecular weight copolymers containing substantial quantities of 1,2‐dichloroethylene can be prepared. The molecular weights of the copolymers depend only on the amounts of 1,2‐dichloroethylene in the copolymers, regardless of the isomer which takes part in the copolymerization. Since the double bond of the trans isomer is about six times as reactive as that of the cis isomer, this indicates that the dominating chain transfer reaction occurs by chlorine atom elimination subsequent to the addition of the dichloroethylene unit to the growing free radical chain. It is suggested that a similar chain‐transfer mechanism occurs in the polymerization of vinyl chloride, wherein an infrequent head‐to‐head placement of monomer unit is followed by ejection of a chlorine atom to form an olefinic bond and termination of that growing chain. The presence of the 1,2‐dichloroethylene unit in the copolymer increases the glass transition temperature approximately 1°C per weight per cent copolymerized with the vinyl acetate.
Polymerization by crystallization of trioxane from cyclohexane solutions in presence of 1,3‐dioxolane
Authors: Baccaredda M. , Giorgini M. , Lucchesi A. , Morelli F. , Tartarelli R.
Published: April 2003

Trioxane–1,3‐dioxolane copolymers of high molecular weights and good thermal stability are obtained with high yields by a crystallization‐polymerization method. The feed consists of concentrated solutions of trioxane in cyclohexane in the presence of dissolved 1,3‐dioxolane. The 1,3‐dioxolane/trioxane molar ratio in the feed lies in the range 2 to 10%. The results are compared with those obtained from isothermal copolymerizations.
Proton magnetic resonance investigation of structure of ω‐alkyl‐α‐olefin/SO2 copolymers
Authors: Bacskai R. , Lindeman L. P. , Ransley D. L. , Sweeney W. A.
Published: April 2003

The 100 MHz proton magnetic resonance (PMR) spectra of free radical alternating ω‐alkyl‐α‐olefin/SO2 copolymers has been investigated. The data obtained from the quantitative evaluation of the spectra are consistent with a copolymer structure containing unrearranged olefinic monomer units. The 4‐methyl‐1‐pentene/SO2 copolymer shows a quadruplet resonance in the CH3 proton region. This multiplicity, observed also in the analogous 1,2‐dichloro‐4‐methylpentane and 1,2‐dibromo‐4‐methylpentane, arises from the presence of magnetically nonequivalent CH3 protons located in the vicinity of the asymmetric carbon atoms of the main chain. There is no detectable nonequivalency of CH3 protons in the 5‐methyl‐1‐hexene/SO2 copolymer, probably because the center of asymmetry is further removed from the isopropyl group. In poly‐4‐methyl‐1‐pentene, prepared with Ziegler‐Natta catalyst, the polymer structure around the main chain tertiary carbons is fairly symmetrical; and, as expected, the CH3 protons of the isopropyl group are magnetically equivalent.
Poly(Vinyl 2‐furylacrylate), a new photosensitive polymer
Authors: Tsuda Minoru
Published: April 2003

Poly(vinyl 2‐furylacrylate), a new photosensitive polymer, was prepared, and its photosensitivity was investigated. The polymer cannot be synthesized by the usual procedure, condensation of poly(vinyl alcohol) and 2‐furylacrylyl chloride in hot pyridine, but is easily prepared by the aqueous alkaline process, regardless of the degree of polymerization. Poly(vinyl 2‐furylacrylate) is remarkably highly photosensitive and is spectrally sensitized by aromatic nitro compounds and aromatic carbonyl compounds. The mechanism of photochemical reaction is considered to involve the dimerization of the furylacrylyl group, and the quantum yield appears to be constant.
New high‐temperature polymers. VIII. Ordered benzoxazole‐ and benzothiazole‐imide copolymers
Authors: Preston J. , Dewinter W. F. , Black W. B.
Published: April 2003

Ordered heterocycle copolymers of high thermal stability were prepared from aromatic dianhydrides reacted with aromatic diamines containing preformed benzoxazole or benzothiazole units. These ordered benzoxazole‐imide and benzothiazole‐imide copolymers were prepared in the form of their soluble precursor polyamic‐acids, which, after fabrication to desired shapes, were converted to the thermally stable polymer. In general, these polymers are more resistant to air oxidation at elevated temperatures than are simple aromatic polyimides, and their thermoöxidative stability is equal to or greater than that reported for benzoxazole or benzothiazole homopolymers. Unlike the o‐hydroxyamide precursors to simple polybenzoxazoles, the amic acid precursors to benzoxazole‐imide ordered copolymers do not require temperatures above 300°C to complete ring closure nor inert atmospheres to prevent polymer degradation during ring formation. Excellent self‐supporting films and film coatings for metals were prepared. Selected compositions were readily spun to excellent fiber.
Dielectric properties of stereoregular poly(methyl methacrylates)
Authors: Shindo Heisaburo , Murakami Ichiro , Yamamura Hitoshi
Published: April 2003

To obtain more useful information about the effect of the degree of stereoregularity on the motion of the polymer chain, the dielectric and dilatometric measurements were made for a series of stereoregular poly(methyl methacrylates) (PMMA). The α‐ and β‐absorptions were observed in each sample, of which the dielectric behaviors of the α‐process are discussed. The temperature dependence of the relaxation time of the α‐process was sufficiently represented by the WLF equation and the resulting values of the parameters fg and B in the modified WLF equation were found smaller for isotactic‐rich PMMA than those values for syndiotactic PMMA. It may be deduced from these results that the chain mobility of the isotactic PMMA is larger than that of the syndiotactic. The dielectric increment of the α‐process in the isotactic PMMA is much larger than that in the syndiotactic PMMA, increasing rapidly with temperature, and taking its maximum in the temperature range of 55 to 60°C. The dielectric transition was clearly observed in the case of isotactic‐rich PMMA.
Nature of the active component in the catalytic system prepared from titanium(III) chloride(AA), ethylaluminum dichloride, and tetrakis(dimethylamino)silane, in the polymerization of propylene
Authors: Matsumura Kiichiro , Atarashi Yuji , Fukumoto Osamu
Published: April 2003

The chemistry of the titanium(III) chloride(AA)–ethylaluminum dichloride–tetrakis‐(dimethylamino)silane system for the polymerization of propylene was studied. A complex of ethylaluminum dichloride with tetrakis(dimethylamino)silane was isolated. It was shown that this complex contains ethylaluminum dichloride and tetrakis(dimethylamino)silane in the ratio of 2:1. This complex with titanium(III) chloride is responsible for the polymerization activity.
The cupric sulfate–hydrazine system as an initiator of vinyl polymerization. I. The polymerization of methyl methacrylate in aqueous solution in the presence of oxygen
Authors: Bond Joan , Lee P. I.
Published: April 2003

The cupric sulfate–hydrazine system has been used to initiate the aqueous solution polymerization of methyl methacrylate at pH 9.25 in the presence of oxygen. At cupric sulfate concentrations greater than the saturation solubility of cupric hydroxide, hydrazine is adsorbed on, and decomposes on, the surface of the hydroxide. The kinetics of the decomposition are zero‐order both in the absence and the presence of monomer. The initiation of the polymerization occurs both at the surface of the cupric hydroxide on to which some monomer is adsorbed and also in solution. Below the saturation solubility of cupric hydroxide, the initiation reaction between cupric ions and hydrazine occurs in solution.
Polycondensation rate of poly(ethylene terephthalate). II. Antimony trioxide–catalyzed polycondensation in static thin films on metal surfaces
Authors: Stevenson Robert W.
Published: April 2003

In the catalyzed polycondensation reaction of poly(ethylene terephthalate), defined by

equation image

rates of polymerization in thin films under vacuum are orders of magnitude greater than those observed in an equilibrating system. Such behavior is consistent with a mechanism in which a volatile component of the reaction mixture reacts reversibly with the catalyst to render it unreactive in polycondensation; removal of this component is facilitated as polymerizing melt thickness is decreased. In accord with such a mechanism polycondensation rates for polymerizations carried out on metal surfaces at thicknesses of 1 to 5 mils of polymerizing melt are observed to increase with decreasing thickness, provided a catalyst is present. In the absence of a catalyst there is no tendency of rate to increase with decreasing thickness. A number of metal surfaces were found to dissolve in the polymerizing melt. On rhodium and silver, which were found to be inert to such dissolution, uncatalyzed polycondensation rate constants kp of 0.03 and 0.04 liter mol−1 min−1 were found. These values of kp are low and identical within experimental error. This behavior is in accord with the assumption that no catalysis occurs at the interface of the polymerizing melt and the metal surface. A typical value for the catalyzed rate constant kp (uncorrected for catalyst concentration) was 0.6 liter mol−1 min−1 in a 1‐mil thickness of polymerizing melt at 275°C and in the presence of 0.025 wt‐% antimony trioxide. The activation energy for the antimony trioxide–catalyzed polycondensation was found to be 14 kcal; for the uncatalyzed polycondensation it was 45 kcal.
Determination of the number of particles/unit volume of latex during the emulsion polymerization of styrene
Authors: Robb I. D.
Published: April 2003

The variation of the number of particles/unit volume of latex (N) with conversion was determined during the emulsion polymerization of styrene. The results showed that, contrary to what is required by the Smith‐Ewart theory, N increased during the constant rate period. This conclusion was supported by the variation of the particle size distribution with conversion. Further evidence that latex particles could form in the absence of micelles was given by using systems in which the soaps were below the CMC. The chain length of the soaps used had a marked effect on the rate of polymerization. This effect was shown not to be due to the variation of the CMC with chain length, but possibly to the stronger adsorption of the longer chain length soaps at the polymer–water interface.
The preparation and characterization of some cellulose graft copolymers. V. ESR study of preirradiation grafting of styrene to cellulose acetate
Authors: Campbell D. , Williams J. L. , Stannett V.
Published: April 2003

Previous studies have shown a two‐peak molecular weight distribution of the grafted polystyrene side chains from preirradiation‐grafted cellulose acetate. ESR has been used to investigate this grafting system in further detail. It was found that the rate of decay of the trapped radicals on adding the monomer solution was quite slow and a substantial proportion remained after 3 days at 25°C. The G value for radicals lost was, however, in good agreement with the G (grafted side chains) produced during the same period. The ESR spectrum does not change on addition of the monomer solution. The explanation offered is that the side chains grow and terminate rapidly compared with the slow overall rate of decay. The grafting yield and the molecular weight of the grafted side chains continue to grow until the reaction is terminated, leading perhaps to the high molecular weight narrow distribution fraction.
Copolymerization of butadiene and styrene by initiation with alkyllithium and alkali metal tert‐butoxides
Authors: Wofford C. F. , Hsieh H. L.
Published: April 2003

Combinations of the various alkali metal tert‐butoxides with organolithium initiators give homogeneous copolymers of butadiene and styrene. The unprecedented flexibility of this initiator system allowed preparation of random copolymers with various amounts of vinyl unsaturation and various degrees of randomness. The butyllithium–potassium tert‐butoxide initiator system was more efficient than phenylpotassium.
Polymerization of aromatic aldehydes. II. Cationic cyclopolymerization of phthalaldehyde
Authors: Aso Chuji , Tagami Sanae , Kunitake Toyoki
Published: April 2003

Phthalaldehyde was found to undergo cyclopolymerization with ease by several cationic catalysts and by γ‐ray irradiation. The polymer was composed entirely of the dioxyphthalan unit, as confirmed by infrared spectroscopy and ready decomposition to monomer. The enhanced polymerizability of phthalaldehyde as compared with other aromatic aldehydes was explained in terms of the intermediate‐type or, preferably, concerted propagation scheme. The conversion reached a saturation value of 87% in about 1 hr in methylene chloride at −78°C, indicating an equilibrium polymerization. The ceiling temperature of the polymerization was −43°C, as estimated from the relation between the saturation yield and polymerization temperature. The enthalpy and entropy of propagation were −5.3 kcal/mole and −23.0 eu, respectively. Since the molecular weight of the polymer was proportional to conversion, the propagating chain end was considered to be “living” in this system. The rate constant for propagation was calculated to be 0.18 1/mole‐sec in methylene chloride at −78°C with BF3OEt2 catalyst.