bluuebunny/crossref_metadata_2025_split huggingface dataset:
Emulsion polymerization. VII. Effects of instantaneous chain termination during the interval of particle nucleation
Authors: Gardon J. L. 
Published: April 2003

AbstractIn the Smith‐Ewart treatment of particle nucleation all particles were assumed to grow as if they contained exactly one radical. Modification of particle growth rate by chain termination in growing particles and reinitiation of nongrowing particles by radicals entering them was neglected in this interval although such effects were taken into account after the particle number became constant. The present theory eliminates this inconsistency for the case where chain termination is instantaneous. This refinement does not change previous predictions for the final number of particles, the steady state rate or the particle radius. Unlike the old theory, the present theory predicts continuous decay of the average number of radicals per particle from the initial value of unity to the steady‐state value of one half. It also provides new theoretical predictions for the shape of the conversion‐time curve at the initial stages of the reaction. Experimental data are reviewed in the context of the theory. Experimental particle sizes, steady‐state conversion rates, and conversions at completion of particle nucleation were often in good quantitative agreement with the theoretical predictions. The predicted maximum in the conversion rate at the time when particle nucleation became completed was observed in a few instances. The theoretically predicted initial shape of the conversion‐time curve may not be always observable due to experimental difficulties mainly associated with induction effects.
Synthesis and characterization of poly‐β‐hydroxybutyrate. I. Synthesis of crystalline DL‐poly‐β‐hydroxybutyrate from DL‐β‐butyrolactone
Authors: Agostini D. E. , Lando J. B. , Shelton J. Reid 
Published: April 2003

AbstractThe polymerization of β‐butyrolactone was investigated as a possible monomer for a proposed synthesis of the naturally occurring polyester, D‐poly‐β‐hydroxybutyrate (D‐PHB). The racemic DL‐monomer was used in this initial study to determine the best conditions and catalyst system for use in a subsequent study of the polymerization of optically active β‐butyrolactone. In so doing it was found that certain organometallic catalysts (Et2Zn and Et3Al) plus a cocatalyst of water produced highly crystalline samples of polyester from the racemic monomer. This paper describes the synthesis and characterization of the racemic polymer obtained using these catalyst systems, and compares the results obtained with certain other catalysts that were also investigated for this purpose. Examination of the DL‐PHB by infrared, NMR, x‐ray, and electron microscopy shows that it is possible to synthesize a crystalline racemic polymer that is virtually identical (excepting optical activity) to the naturally occurring polymer, D‐PHB.
Radiation‐induced reaction of ethylene–cyclohexane–carbon tetrachloride system
Authors: Yamabe Masamori , Shimizu Harumichi 
Published: April 2003

AbstractThe γ‐ray‐induced reaction of ethylene with carbon tetrachloride in cyclohexane was carried under a pressure of 30 kg/cm2 and at a temperature of 20°C. The liquid and the solid products were obtained. Their structures were discussed on the basis of infrared absorption spectra and differential thermal analysis curves. The liquid product is considered to be ethylene–carbon tetrachloride telomer. The solid product consists of three components, differing slightly in molecular structure and molecular weight. To clarify the reaction process, some runs with the ethylene–cyclohexane–(ethylene–carbon tetrachloride telomer) system were also carried out. In this system, only solid product was obtained. Thus, it is concluded that the reaction proceeds stepwise, the first step being the telomerization reaction and the second the graft polymerization of ethylene onto the telomer produced in the first step.
Initiation of polymerization of alkyl 2‐cyanoacrylates in aqueous solutions of glycine and its derivatives
Authors: Kulkarni R. K. , Bartak D. E. , Leonard F. 
Published: April 2003

AbstractThe polymerization of methyl 2‐cyanoacrylate and heptyl 2‐cyanoacrylate was carried out with the use of aqueous solutions of 14C‐tagged glycine, methyl glycine, and acetyl glycine as initiators. When glycine and methyl glycine were used, radioactive polymers were formed. When acetyl glycine was used, the polymer formed was not radioactive. The data seem to indicate that free NH2 groups appear to be necessary for the incorporation of the glycine initiator in the polymer. A possible mechanism for the polymerization is presented.
Organometallic polymers. XIV. Copolymerization of vinylcyclopentadienyl manganese tricarbonyl and vinylferrocene withN‐vinyl‐2‐pyrrolidone
Authors: Pittman Charles U. , Grube Paul L. 
Published: April 2003

AbstractN‐Vinyl‐2‐pyrrolidone(I) has been copolymerized with vinylferrocene(II) and vinylcyclopentadienyl manganese tricarbonyl(III) in degassed benzene solutions with the use of azobisisobutyronitrile (AIBN) as the initiator. The polymerizations proceed smoothly, and the relative reactivity ratios were determined asr1= 0.66,r2= 0.40 (for copolymerization of I with II, M1defined as II) andr1= 0.14 andr2= 0.09 (for copolymerization of I with III, M1defined as III). These copolymers were soluble in benzene, THF, chloroform, CCl4, and DMF. Molecular weights were determined by viscosity and gel‐permeation chromatography studies (universal calibration technique.) The copolymers exhibited values of M̄nbetween 5 × 103and 10 × 103and M̄wbetween 7 × 103and 17 × 103with M̄w/M̄n< 2. Upon heating to 260°C under N2, copolymers of III underwent gas evolution and weight loss. The weight loss was enhanced at 300°C, and the polymers became in creasingly insoluble. Copolymers of vinylferrocene were oxidized to polyferricinium salts upon treatment with dichlorodicyanoquinone (DDQ) oro‐chloranil (o‐CA) in benzene. Each unit of quinone incorporated into the polysalts had been reduced to its radical anion. The ratio of ferrocene to ferricinium units in the polysalts was determined. The polysalts did not melt at 360°C and were readily soluble only in DMF.
Organometallic polymers. XV. Synthesis and characterization of some ferrocene‐containing oxysilane polymers from bis(dimethylamino)silanes
Authors: Pittman Charles U. , Patterson William J. , McManus Samuel P. 
Published: April 2003

AbstractThree bis(dimethylamino)silane monomers have been polymerized with 1,1'‐bis‐(hydroxymethyl)ferrocene to give ferrocene‐containing polyoxysilanes I and II. They were bis(dimethylamino)dimethylsilane (III), bis(dimethylamino)diphenylsilane (IV), and 1,4‐bis(N,N‐dimethylaminodimethylsilyl)benzene (V). Mixing of the diol and III or IV at O°C followed by heating resulted in polymerization to higher molecular weights than when the monomers were initially mixed at higher temperatures. At higher temperatures the formation of monomeric cyclic products seriously competed with polymerization, and the five atom bridged derivative, 3‐sila‐2,4‐dioxa‐3,3diphenyl[5]ferrocenophane (VI) was isolated in good yield. The use of silane V, where cyclization is not expected to compete, led to higher polymer yields and molecular weights. The polymers were low melting and I (R = C6H5) could be cast into films and weak fibers were drawn from its melt. The polymers were sensitive to hydrolytic decomposition; those containing Si‐CH3 linkages were completely hydrolyzed in refluxing THF‐H2O (10:1) in 1 hr. The polymers were characterized by viscosity studies, gel‐permeation chromatography, and infrared and NMR spectroscopy.
Transparent ultraviolet‐barrier coatings
Authors: Cohen S. M. , Young R. H. , Markhart A. H. 
Published: April 2003

AbstractA number of phenyl polyesters have been synthesized to furnish molecules whose backbones rearrange under ultraviolet irradiation to ano‐hydroxybenzophenone structure. This photochemical Fries rearrangement produces ultraviolet opacity in the irradiated film while maintaining visual transparency. Thin coatings of these polyesters completely protect substrates ordinarily sensitive to ultraviolet light. Spectroscopic analysis of various rearranged films and coatings clearly shows that theo‐hydroxybenzophenone polymer formed is concentrated at the irradiated surface of the original polyester coating as a “skin”. Such a skin, formedin situduring the irradiation, functions to protect both the original polyester coating as well as the coated substrate from degradation by ultraviolet irradiation. Furthermore, a significant “healing” mechanism appears inherent in these coatings, for as the exposed skin ultimately degrades under extended ultraviolet irradiation, more of the underlying polyester layer apparently rearranges to compensate for the loss. Thus the clear coating functions both as a protective skin and a rearrangeable reservoir. Modified structures of the polyesters have been prepared which possess, in addition to their protective film properties, a useful solubility spectrum and a good solution shelf life.
Side‐chain crystallinity. II. Heats of fusion and melting transitions on selected copolymers incorporating n‐octadecyl acrylate or vinyl stearate
Authors: Jordan Edmund F. , Artymyshyn Bohdan , Speca Anthony , Wrigley A. N. 
Published: April 2003

AbstractThe heats of fusion and the melting transitions of the crystallinity present in the side chains were determined for selected copolymers incorporating n‐octadecyl acrylate or vinyl stearate. A major purpose of this investigation was to ascertain the effect of interrupting the long ordered 18‐carbon side chains by randomly interspersed amorphous side chains of various lengths. For this purpose the lower acrylate homologs (C1 through C8 and including oleyl, C8) were copolymerized over the composition range with n‐octadecyl acrylate. It was found that simple dilution of the crystalline component (from comonomer b) by the amorphous component (from comonomer a) governed the decline in the heats of fusion and the fraction of crystallinity present. High crystallization rates were encountered because equilibrium crystallinity was nearly achieved for most of the copolymers. Melting point depression was less than theory in copolymers having short amorphous comonomer side chain lengths, but approached the theoretical depression as these side chains became very long. Thus the outer methylene sequences (the crystalline sequences) of the fatty co‐units could bridge the smaller amorphous a units, giving rise to larger crystal sizes than theory specified. Main‐chain stiffness, when present in the melt, had a small effect on the distribution of crystallite sizes but exhibited a much larger influence in preventing the attainment of equilibrium crystallinity, especially at high amorphous comonomer compositions. However, crystallinity was still high compared with that of copolymers described in the literature crystallizing through their main‐chain units. When long blocks of crystalline segments were present (as in compositionally heterogeneous vinyl stearate copolymers), melting point depression was small and followed the theoretical probability sequence function.
Temperature effects in γ‐initiated polymerization of styrene. II
Authors: Sood S. P. , Hodgins J. W. 
Published: April 2003

AbstractExperimental data are presented for the γ‐initiated polymerization of commercial styrene at a series of temperatures above ambient. Examination of the early stages of polymerization (up to 10% conversion) has led to the following conclusions. For this system, there exists a critical temperature (109°C) above which the rate of polymerization is independent of dose rate, over a wide range of γ‐intensities. This dose rate independence is ascribed to a “limiting rate of initiation,” characteristic of the intensity range. A consequence of this is that at a given temperature above the critical temperature the degree of polymerization is also dose rate‐independent. The above phenomena can be expected in any vinyl monomer where the monomer is fairly active and produces relatively stable radicals. Experimental procedure is described, and kinetic analysis presented to substantiate the conclusions.
Effect of the polymeric ligand on electron‐transfer reactions: Iron(II) reduction of cis‐chloropoly‐4‐vinylpyridinebis(ethylenediamine)‐cobalt(III) complexes
Authors: Kurimura Yoshimi , Yamada Kazuo , Kaneko Masao , Tsuchida Eishun 
Published: April 2003

AbstractWater‐soluble Co(III)–PVP complexes (where PVP = poly‐4‐vinylpyridine) were prepared, and the specific rates and activation parameters for the iron(II) reductions of cis‐Co(en)2XCl2+ (where X = PVP or pyridine and en = ethylenediamine) were determined in dilute sulfuric acid solutions. Under the conditions [H2SO4] = 0.50M, Σ[SO42−] = 1.25 M at 25°C, the second‐order rate constants and activation entropies, respectively, for the cis‐Co(en)2−XCl2+ are (4.10 ± 0.05) × 10−3l./mole‐sec and −14 ± 0.6 eu for × = pyridine, (2.1 ± 0.1) × 10−3l./mole‐sec and −6.0 ± 1 eu for × = PVP (Pn = 19), and (2.42 ± 0.08) × 10−3 l./mole‐sec and −2.5 ± 0.8 eu for × = PVP (Pn = 98), where Pn is the degree of polymerization of the PVP. The main feature of the polymer effect in the electron‐transfer reactions of the PVP complexes in which uncoordinated pyridine rings are present may be attributed to greater activation entropy. Such a greater entropy for the PVP complex may be partly ascribed to the intricate structure of the PVP ligand in the solution.
Optical rotatory properties of synthetic polymers. II. Optical rotatory dispersion of poly(propylene sulfide)
Authors: Tsunetsugu Toshiyuki , Furukawa Junji , Fueno Takayuki 
Published: April 2003

AbstractOptically active propylene sulfide was polymerized in the presence of potassium hydroxide as catalyst to give optically active poly(propylene sulfide). Rotatory dispersion curves of the polymer thus obtained were measured in benzene and chloroform media. In both cases, the curves were anomalous in shape with the same sign, having troughs at 290 and 275 mμ, respectively. (–)‐1,2‐Diethylthiopropane was prepared as an optically active model compound of poly(propylene sulfide) in optical rotatory properties. It was found that the model compound also shows anomalous rotatory dispersion both in benzene and chloroform with the same sign. Thus it may be concluded that the anomalous dispersion of poly(propylene sulfide) must be attributed to an additional Cotton effect caused by the absorption of sulfide bonds, which are generally admitted to have absorptions at 200 and 230 mμ (shoulder).
Radiation chemistry of aqueous poly(ethylene oxide) solutions. II. Highly purified samples
Authors: Ward J. A. 
Published: April 2003

AbstractThe radiation chemistry of highly purified, rigorously degassed aqueous solutions of poly(ethylene oxide) is markedly different from solutions not so treated. Gelation doses are lower in the purified samples by almost two orders of magnitude. Degradation is unimportant in dilute solutions. The very broad molecular weight distribution as well as the very high molecular weight of these polymers makes the interpretation of the results difficult. Neither gel dose measurements nor solubility measurements give valid crosslinking yields. The crosslinking yield is highly concentration‐dependent.
Simulation of degradation processes. II. Testing some relations for random crosslinking without cyclization
Authors: Maláč J. 
Published: April 2003

AbstractBy use of a Monte Carlo method the course of crosslinking without cyclization was simulated. For the simulated case the following was determined: number‐average molecular weight and degree of polymerization of the system; weight‐average molecular weight and degree of polymerization of the system; number of molecules of a given degree of polymerization; quantity of gel; number‐average degree of polymerization of sol and branching. The values obtained by simulation were compared with some equations published to date. It was shown that the dependence of weight‐average polymerization degree and, consequently, of the weight‐average molecular weight on time and the dependence of the number of molecules of a given polymerization degree on time is probably more complicated than hitherto supposed.
Characterization of diene polymers. I. Infrared and NMR studies: Nonadditive behavior of characteristic infrared bands
Authors: Tanaka Yasuyuki , Takeuchi Yasumasa , Kobayashi Masamichi , Tadokoro Hiroyuki 
Published: April 2003

AbstractExtinction coefficients of the characteristic infrared bands due to isomeric structural units were measured for polybutadiene and polyisoprene in CS2 or CCl4 solutions and were compared with the isomer composition determined by NMR. The NMR signal assignments were made on the basis of the spectra of deutero derivatives of the polymers. In the case of polyisoprene, linear relations were obtained between the extinction coefficients and the isomer contents determined by NMR for the absorption bands at 1385 cm−1 (characteristic of trans‐1,4 units), 1376 cm−1 (cis‐1,4 units), and 889 cm−1 (3,4 units). However, for the absorption bands at 840 cm−1 (characteristic of cis‐1,4 and trans‐1,4 units), isomerized polyisoprenes did not give such a linear relationship. In polybutadiene, the extinction coefficient for the atactic 1,2 units was found to be lower than that of the syndiotactic 1,2 unit. These experimental facts lead to the conclusion that additivity of the extinction coefficients does not always hold for diene polymers. The deviation from the linear relation may be associated with regular sequences of one isomeric conformation in the chain.
Planar organosilicon polymers
Authors: Linsky John P. , Paul Thomas R. , Kenney Malcolm E. 
Published: April 2003

AbstractWork on two sheet organosilicon polymers, one derived from the mineral chrysotile and the other from the mineral apophyllite, is described. This work provides direct evidence that both these polymers are composed of sheets. In addition, it shows that in the chrysotile‐derived polymer the sheets curl into scrolls, and that in the apophyllite‐derived polymer the sheets are essentially flat.
Equilibrium melting points of the low‐melting and high‐melting crystalline forms of trans‐1, 4‐polyisoprene
Authors: Lovering Edward G. , Wooden David C. 
Published: April 2003

AbstractEquilibrium melting points in trans‐1,4‐polyisoprene were calculated from plots of crystallization temperature versus the experimentally measured melting points. The melting points were found to be 78 ± 1.7°C for the low‐melting crystalline form and 87 ± 1.3°C for the high‐melting form. Within the experimental error, melting points were independent of molecular weight above a number‐average weight of 33,000.
Axial dispersion of solute zones in gel permeation chromatography
Authors: Halvorson Herbert R. , Ackers Gary K. 
Published: April 2003

AbstractThe two essential aspects of axial dispersion in gel permeation chromatography have been studied: (1) the relationship of axial dispersion to the continuity equations of chromatographic transport, and (2) the relationship to molecular size and the system parameters of an individual column. Theoretical analyses are presented for both of these problems and are applied to an experimental study of axial dispersion by both zonal (small‐zone) and frontal (large‐zone) experiments with a series of macromolecular species having discrete, precisely known molecular weights. Theoretically predicted non‐Gaussian elution profiles were observed for the small‐zone experiments, and axial dispersion coefficients for each molecular species were determined as a function of flow rate. Resulting values were found to be in good agreement with the theoretical equation relating axial dispersion to molecular size, flow rate, and two “calibration constants” of the column. These results provide a rational basis for axial dispersion effects in terms of the fundamental processes and system parameters of gel columns. Extension of the analysis to multicomponent systems is discussed.
Adhesion of viscoelastic materials to rigid substrates. II. Tensile strength of adhesive joints
Authors: Gent A. N. 
Published: April 2003

AbstractMeasurements have been made of the tensile force required to pull a disk of a model viscoelastic adhesive away from an inert rigid substrate. Over a wide range of temperature and rate of deformation of the adhesive the results were found to yield a single master relation in terms of deformation rate by means of the Williams, Landel and Ferry rate—temperature equivalence for viscous materials. Thus, the strength of adhesion is due mainly to dynamic effects in the adhesive of a viscous nature, in a similar way to the cohesive strength of viscoelastic materials. This similarity is attributed to a common failure mechanism: initial failure at a highly stressed point, followed by spreading of the failure zone under local stresses which are governed by the dynamic response of a compliant material. An increase in the strength of adhesion is observed with decreasing thickness of the adhesive layer. This is also explained by the proposed failure mechanism if failure starts at a critical amount of local deformation energy, a form of Griffith's fracture criterion.
Adsorption of polydimethylsiloxanes from solution on glass
Authors: Ashmead B. V. , Owen M. J. 
Published: April 2003

AbstractThe adsorption of polydimethylsiloxane polymers from solution on glass has been studied. The amount of polymer adsorbed depends markedly on the solvent because of specific solvent—surface interactions. The presence of silanol groups in the polymer, particularly as endgroups, markedly increases the amount of polymer adsorbed. Large differences are shown between the adsorption of the commercially available, and fully trimethylsilylated polydimethylsiloxanes of narrow molecular weight distribut on. Possible adsorption mechanisms are discussed.
Normal stress and shear stress in a viscoelastic liquid under steady shear flow: Effect of molecular weight heterogeneity
Authors: Endo Hiroshi , Fujimoto Teruo , Nagasawa Mitsuru 
Published: April 2003

AbstractUnder steady shear flow, the normal stress and the shear stress in both dilute and concentrated solutions of monodisperse poly‐α‐methylstyrenes and their blends were measured. It was confirmed that the molecular theories of Rouse and Zimm extended to concentrated solutions can explain the relation between the zero‐shear normal stress coefficient and the zero‐shear steady‐flow viscosity for both monodisperse and polydisperse systems. Shear‐rate dependence of steady‐flow viscosity can be understood fairly well by the molecular entanglement concept proposed by Graessley so long as the polymer is monodisperse or the amount of the higher molecular weight component is high. However, zero‐shear viscosity of blended systems cannot be explained quantitatively by the theory of Graessley. The shear‐rate dependence of steady‐state compliance of blended systems was also observed, and it can well be explained by the theory of Tanaka, Yamamoto, and Takano which interpreted the shear rate‐dependent steady‐state compliance in terms of the relaxation time spectrum and its variation with shear rate.
Dispersion and polar contributions to surface tension of poly(methylene oxide) and Na‐treated polytetrafluoroethylene
Authors: Kaelble D. H. , Cirlin E. H. 
Published: April 2003

AbstractAverage values for dispersion γsd and polar γsd contributions of the solid surface tension γs γsd + γsp for poly(methylene oxide) (PMO) and Na‐treated polytetrafluoroethylene (PTFE) are determined by a new computational analysis of wettability data. PMO displays γsd equals; 21.8 ± 0.9 and γsp = 11.5 ± 1.5 dyn/cm while Na‐treated PTFE displays γsd = 36.1 ± 3.0 and γsp = 14.5 ± 2.9 dyne/cm. These surfaces present the highest fractional surface polarity ps = γsp/γs = 0.29‐0.35 yet encountered for organic polymers or oriented monolayers. These unusual surface tension properties are correlated with surface chemistry and adhesion phenomena.