bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of radiation‐induced addition reaction of carbon tetrachloride onto liquid 1,2‐polybutadiene accompanied by cyclization
Authors: Okamoto Hidemasa , Adachi Shoichi , Takada Kiyoshi , Iwai Tadashi 
Published: April 2003

AbstractEffects of irradiation conditions were investigated in the γ‐ray‐induced addition reaction of carbon tetrachloride onto liquid 1,2‐polybutadiene. The rate of addition reaction was proportional to the dose rate, and its apparent activation energy was 1.4 kcal/mole in the range of ca. 20–80°C; the G values for the addition of carbon tetrachloride and vinyl consumption were high. The addition reactions of methyl isobutylate, isopropyl amine, and bromotrichloromethane to liquid 1,2‐polybutadiene by γ rays were studied to compare with carbon tetrachloride. Methyl isobutylate and isopropyl amine were added much more slowly. On the other hand, in bromotrichloromethane the rate of addition reaction was much faster but cyclization was less pronounced than in carbon tetrachloride. On the basis of these results a mechanism of a radical chain reaction which includes the addition of carbon tetrachloride, cyclization, and crosslinking, is proposed.
Copolymerization of 1,6‐anhydro‐ß‐D‐galactopyranose and 1,6‐anhydro‐ß‐D‐mannopyranose derivatives
Authors: Ito Hiroshi , Marousek Vladimir , Schuerch Conrad 
Published: April 2003

Abstract1,6‐Anhydro‐2,3,4‐tri‐O‐(p‐methylbenzyl)‐ß‐D‐galactopyranose (TXGal,M1) has been copolymerized with 1,6‐anhydro‐2,3,4‐tri‐O‐benzyl‐ß‐D‐mannopyranose (TBMan,M2), the products characterized by NMR, specific rotation, and viscosity, and the reactivity ratios calculated. The reactivity ratios r1 = 0.37 ± 0.15 and r2 = 38 ± 4 indicate that the anhydromannose derivative is about 100 times as reactive as that of anhydrogalactose. A comparison of glucose, mannose, and galactose copolymerizations suggests that the reactivity differences of the three propagating cations are comparatively small and the reactivity differences of the monomers large. This result is consistent with a mechanism proposed earlier. Methyl substitution on the aromatic rings of the p‐xylyl groups inhibits the initiation process significantly relative to benzyl, but propagation only slightly.
Kinetics of the copolymerization of styrene with small quantities of divinylbenzenes
Authors: Kwant P. W. 
Published: April 2003

AbstractThe study of copolymerization of styrene with small amounts (≤0.04 wt %) of divinylbenzenes (DVB) offers advantages over similar studies made at high DVB concentrations. A simple set of equations can be used to describe the kinetics of copolymerization at low DVB concentrations. Experimental data show that the copolymerization constants (r2) for the copolymerization of the first double bonds of m‐ and p‐DVB (monomer 1) with styrene (monomer 2) are 0.85 and 0.43, respectively. In contrast to findings at higher DVB concentrations these constants do not change during the first half of the polymerization. After 50% conversion an autoacceleration effect reduces the selectivity of the growing polystyrene radical. The copolymerization constants for the second double bonds of m‐ and p‐DVB during the first half of the polymerization are estimated as 1.
Thermal decomposition products of a chlorinated aromatic polyamide
Authors: Chatfield D. A. , Einhorn I. N. , Mickelson R. W. , Futrell J. H. 
Published: April 2003

AbstractProducts from the thermal decomposition of a chlorinated aromatic polyamide fabric are described for conditions of pyrolysis and flaming and nonflaming oxidative degradation. Volatile degradation products were identified by gas chromatography‐mass spectrometry (GC‐MS) and the condensible fraction, by infrared (IR) spectroscopy, high‐pressure liquid chromatography (HPLC), and MS. Nonvolatile char was characterized by IR and elemental analysis. Twenty‐one compounds were identified as volatile products from pyrolysis at 550°C; the condensible material contained ammonium chloride and at least 22 organic compounds. From volatile compounds produced in flaming oxidative degradation 21 compounds were identified, of which CO, CO2, and H2O were prominent. Nonflaming oxidative degradation at 400 and 550°C produced 11 and 21 volatile identifiable compounds, respectively, and results from experiments at the higher temperature compared favorably with results from the flaming experiments. By comparison of data from this work with those from unchlorinated analogs (described in an earlier article), it is concluded that the incorporation of chlorine into the polymeric structure lowers the temperature for the onset of thermal degradation and alters the type and concentration of thermolytic products. The major degradation products can be explained by a mechanism similar to that proposed for aromatic polyamides with the exception of the formation of substantial amounts of ammonium chloride. It is proposed that the latter is formed by an initial acid‐catalyzed hydrolysis reaction which is followed by deammoniation or by an intermolecular process that involves an isoimide intermediate.
Analysis of the products of thermal decomposition of an aromatic polyamide fabric
Authors: Chatfield D. A. , Einhorn I. N. , Mickelson R. W. , Futrell J. H. 
Published: April 2003

AbstractThe thermal degradation of an aromatic polyamide was studied under conditions of pyrolysis and oxidative degradation at 550°C and of flaming combustion. Techniques described elsewhere were used to determine the volatile compounds quantitatively by gas chromatography‐mass spectrometry (GC–MS). The condensible material and the solid residue were characterized by infrared spectroscopy and MS, and in pyrolysis experiments 28 compounds were identified (CO, CO2, H2O, and C6H5CN were the primary products). Collectively, these compounds accounted for 79% of the sample weight loss. The remaining 21% was a condensible material that contained at least 17 compounds; the two major components were 1,3‐dicyanobenzene and 3‐cyanobenzoic acid. Most of the nitrogen content of the polymer remained as involatile residue. This study was sufficiently detailed to obtain a mass balance between the composition of the original polymer and the sum of the observed pyrolysis products. The major products observed in pyrolysis experiments supported a mechanism that involved the cleavage of an aromatic‐NH bond and the loss of H2O to form aromatic nitriles. Hydrolysis of the amide linkage, followed by decarboxylation of the product acid, accounted for the high concentrations of CO2 observed. Oxidative degradation at 450°C yielded ten identifiable compounds and an additional 19 volatile compounds were formed at 550°C. The condensible fraction, which contained at least 20 compounds, was similar in composition to the fraction collected from the pyrolysis experiments. The sum of the carbon content from the two major volatile products of oxidative degradation (CO and CO2) and from the solid residue quantitatively accounted for the carbon content in the original sample. Flaming combustion studies revealed a markedly different product distribution than was observed under nonflaming conditions, especially in regard to the higher‐molecular‐weight species.
Polymerization of t‐butyl thiirane. II. Polymerization of enantiomerically enriched monomer. Mechanism of stereoelective process
Authors: Dumas Philippe , Spassky Nicolas , Sigwalt Pierre 
Published: April 2003

AbstractThe kinetics of enantiomerically enriched t‐butyl thiirane was studied. The stereoelectivity and the kinetic behavior are not changed when a monomer of an initial enantiomeric composition lower than a defined limit value is used. When the enantiomeric composition is higher than this value, the stereoelectivity increases. In agreement with kinetic results, a mechanism is proposed involving, in a first step, the complexation of monomer on preexisting sites of the initiator with formation of highly selective chiral active species on which propagation occurs.
Synthesis and properties of polyurethanes derived from bis‐N‐hydroxyimides and diisocyanates
Authors: Kurita Keisuke , Imajo Hidetomo , Iwakura Yoshio 
Published: April 2003

AbstractPolyurethanes were synthesized by polyaddition reaction of bis‐N‐hydroxyimides and diisocyanates. The reactions were carried out in an aprotic polar solvent such as dimethylacetamide or N‐methyl‐2‐pyrrolidone, and the polymers with inherent viscosities of up to 1.32 dl/g were obtained. These polyurethanes were found to exhibit high reactivity toward nucleophiles such as water and amines, which brought about rapid reduction of viscosity. The stabilities against heat and exposure to sunlight were also studied.
Polymerization of diacetylenes in multilayers
Authors: Tieke B. , Lieser G. , Wegner G. 
Published: April 2003

AbstractA series of amphiphilic diacetylene monocarbonic acids was synthesized, and their ability to form monolayers at the air–water interphase was investigated. Acids with total number of C atoms ≥20 and mp >45°C form surface states suitable to be used for buildup of multilayers by the Langmuir–Blodgett technique. Using the LB technique, multilayers of defined thickness were built up on quartz substrates. The multilayers were polymerized by exposure to a UV light source according to the mechanism of solid‐state polymerization of diacetylenes without destruction of the layer structure and with retention of the packing in the individual layers. Thus well‐defined polymer multilayers were obtained. The monomer and polymer multilayers were characterized by UV spectra, x‐ray small‐angle diffraction, and interference microscopic and electron microscopic techniques. The polyconjugated backbones of the polymer chains are all stretched out in the plane of the substrate but not over macroscopic dimensions because the multilayers have a crystalline domain structure. The polymer multilayer films are quite stable under ambient conditions.
2,4‐Dimethyl‐3‐pentanone‐sensitized photopolymerization of vinyl monomers
Authors: Encina M. V. , Lissi E. A. 
Published: April 2003

AbstractThe initiation quantum yield in the bulk photopolymerization of vinyl monomers sensitized by 2,4‐dimethyl‐3‐pentanone has been measured for several monomers. The results obtained were interpreted in terms of a mechanism that considers singlet and triplet photocleavage of the ketone, competing with the quenching by the monomer. The quenching process does not lead to free radicals that can initiate the polymerization.
Thermotropic liquid crystalline polymers. I. Cholesterol‐containing polymers and copolymers
Authors: Shibaev V. P. , Platé N. A. , Freidzon Ya. S. 
Published: April 2003

AbstractAn approach to the creation of thermotropic cholesterol‐containing liquid crystalline polymers by the chemical binding of cholesterol molecules with side chains of comblike polymers is presented. This type of structure permits a decrease in the steric hindrances provided by the backbone chains for the purpose of realizing the liquid crystalline state. A number of new cholesteric esters of poly(N‐methacryloyl‐ω‐aminocarbonic acid)s (PChMAA‐n) with different side‐chain lengths (n = 2–11) as well as a series of copolymers of ChMA‐n with n‐alkylacrylates and n‐alkylmethacrylates have been synthesized. The experimental evidence of liquid crystalline structure formation in these polymers in glass, viscoelastic, and fluid states is discussed. Molecular and supermolecular structures of cholesterol‐containing comblike polymers have been studied and the model of macromolecular packing in the liquid crystalline state is proposed. It is shown that the existence of a layered order of side methylene groups together with ordering of cholesterol groups is necessary to the production of the liquid crystalline state in these polymers.
Photooxidation of polybutadiene: Quenching of excited triplet states of αβ‐unsaturated carbonyls
Authors: Hargreaves J. S. , Phillips D. 
Published: April 2003

AbstractThe quenching of the triplet states of several model αβ‐unsaturated ketones and that produced by thermal oxidation of polybutadiene by the triplet quencher cyclooctadiene at low temperatures has been studied by quantum yield and phosphorescence decay‐time methods. Both the Perrin and Inokuti–Hirayama relationships were tested and a typical exchange interaction distance for half‐quenching of R0 = 12 ± 1 Å was obtained for both models on all compounds studied.
Polymerization of acetylenes catalyzed by rhenium carbonyl halides
Authors: Tsonis Christos P. , Farona Michael F. 
Published: April 2003

AbstractThe homogeneous catalyst Re(CO)5X (X = Cl, Br) was found to promote the homopolymerization of terminal alkynes at elevated temperatures. Detection and structure characterization of low‐molecular‐weight products provided evidence of the formation of a metal–acetylide species as the initiator of polymerization, and propagation occurs by a series of insertion reactions of coordinated alkynes into metal–carbon bonds of the growing chain. Evidence of the active forms of the catalyst comes from studies on gas evolution, catalyst derivatization, and copolymerization reactions. The final polymers have a linear, polyconjugated macrostructure, and the formation of aromatic species was not detected in these reactions.
Small‐angle x‐ray scattering from solution of rodlike particles with length distribution
Authors: Ishimuro Yoshitaka , Hamada Fumiyuki , Nakajima Akio 
Published: April 2003

AbstractThe scattering function of rods with a constant radius, 8 Å, and a length distribution of the Schulz–Zimm type was calculated on a computer as a model of helical synthetic polypeptide. The influence of length and length distribution on the scattered intensity of small‐angle x‐ray scattering was clarified. As length grows and length distribution broadens it is difficult to obtain reliable values of molecular weight and radius of gyration from a Zimm plot. The influence of length distribution on the mass per unit length, Mq, and the radius of gyration of the cross section, 〈S〉1/2, from the Guinier plot of the cross‐sectional factor decreases as the length increases, and reliable values of Mq and 〈S〉1/2 can be obtained even for rods with wide distribution for rods more than 600 Å long. In particular, it is pointed out that the value of 〈S〉1/2 is little influenced by length and length distribution.
Radiation crosslinking of polymethylhydrogensiloxane containing methoxy groups
Authors: Nishide Shinko , Shimizu Harumichi 
Published: April 2003

AbstractThe bulk viscosity of polymethylhydrogensiloxane containing methoxy groups (PMHS‐A) was measured before and after irradiation. The gel point was then determined from the variation of viscosity by irradiation by comparing it with methoxy‐free polymethylhydrogensiloxane (PMHS‐B) and polydimethylsiloxane blocked by methoxyldimethylsilyl (PDMS‐C) or trimethylsilyl (PDMS‐D). The following results were obtained: (1) The G value of crosslinking by irradiation is 167, 52, 25, and 3 for PMHS‐A, PMHS‐B, PDMS‐C, and PDMS‐D, respectively. (2) The scission of the SiOCH3 bond is easier than that of the SiH, SiCH3, or SiCH2H bond. The SiOCH3 bond is PMHS‐A is severed from SiO· and ·CH3 to induce chain reactions at the initial stage by irradiation. (3) It was confirmed that the commercial PMHS is at present free of methoxy groups. To replace the hydrogen of SiH in the commercial PMHS with methoxy groups heat treatment with methanol was performed by which the G value of crosslinking was increased.
High‐conversion polymerization. IV. A definition of the onset of the gel effect
Authors: Dionisio J. , Mahabadi H. K. , O'Driscoll K. F. , Abuin E. , Lissi E. A. 
Published: April 2003

AbstractThe gel effect in free radical polymerization of vinyl monomers has been recognized as the result of the increased viscosity of the reaction solution of polymer in monomer, which causes a decrease in the rate of the termination reaction. This effect manifests itself as an increase in the rate of polymerization over that rate to be expected in its absence. Definition of the onset of the gel effect has become necessary for several purposes. Previously, it has been common to define the onset phenomenologically, i.e., in terms of the increase in the rate of polymerization. It is proposed here that the onset of the gel effect is best defined on a fundamental basis, i.e., as occurring at that conversion at which the rate of segmental diffusion of the polymeric radicals equals the rate of their translational diffusion. Experimental evidence is presented that shows that the small minima predicted by this definition do exist for both rates and degrees of polymerization. Measurements of the viscosities of solutions of polymers in their monomers suggest that the polymer concentrations at which the “chain‐entanglement” phenomena are observed are the same as those for the onset of the gel effect for styrene, methyl methacrylate, and butyl methacrylate.
Kinetics of the hydrolysis of linear poly[(acylimino)‐ethylenes]
Authors: Kem Kenneth M. 
Published: April 2003

AbstractThe kinetic variables associated with the hydrolysis of linear poly[(acylimino)ethylenes] by acid and base have been studied. As anticipated, both reactions follow conventional second‐order rate laws and are essentially irreversible. This stoichiometry and the unexpectedly rapid rate of the acid hydrolysis have been useful in the preparation of partly deacylated poly[(acylimino)ethylenes]. The desired degree of deacylation can be accurately obtained by the relative amount of acid and hydrolyzable amide functionality. The effects of the reaction temperature and nature of the acyl group on the reaction rate have been determined and an unusual relationship between rate and molecular weight was uncovered. The reactions are compared with the hydrolyses of corresponding monomeric tertiary amides and the potential utility of the products is discussed.
Polymer morphology and random chain scission of nylon 66
Authors: Kachi H. , Jellinek H. H. G. 
Published: April 2003

AbstractNylon 66 films with varying spherulite size but almost constant percentages of crystallinity were prepared (melt method). These films were degraded by NO2 over a range of temperatures from 35 to 65°C. Random chain scission took place except in the initial stages at low temperatures at which some crosslinking occurred. Observation of the films with the extent of degradation under polarized light revealed that dark bands developed around and also inside spherulite boundaries that became wider with the extent of degradation. This indicates that amorphous material is formed during random chain scission; the spherulites remained practically intact, however. The experimental chain scission rate constants did not change essentially with spherulite diameter until small diameters were reached, at which time the rate constants increased noticeably. Degradation can be accounted for by chain scission in amorphous and interfacial regions; in the latter the rate constants increased with this area and in addition main chain links were weaker in fold regions, due to strain energy, than normal ones in amorphous regions. The energy of activation for chain scission was compatible with a predominantly diffusion‐controlled process.
Thermally reversible polymer systems by cyclopentadienylation. I. A model for termination by cyclopentadienylation of olefin polymerization
Authors: Kennedy Joseph P. , Castner Kenneth F. 
Published: April 2003

AbstractThe reaction between tert‐butylchloride (t‐BuCl) and dimethylcyclopentadienylaluminum (Me2AlCPD) was studied as a model for initiation by the tert‐butyl cation (t‐Bu⊕) and termination by cyclopentadienylation by the Me2Al(CPD)Cl⊖ counteranion of isobutylene polymerization. All reaction products formed in this model system have been identified and quantitatively determined. A comprehensive scheme that indicates pathways to these products was developed (scheme III). It is proposed that the predominant product, tert‐butylcyclopentadiene (t‐BuCPD), arises in the collapse of the t‐Bu⊕‐Me2Al(CPD)Cl⊖ ion pair, mainly by CPD⊖ transfer to the tert‐butyl cation. The minor products are neopentane (t‐BuMe) and isobutylene (i‐C4H8), which are probably formed, respectively, by Me⊖ transfer to and proton loss from the t‐butyl cation. Cyclopentadienylation selectivity increases by lowering the temperature and extrapolation of results suggests 100% cyclopentadienylation at −55°C. The t‐BuCl/Me2AlCPD ratio strongly influences the overall reaction pathway. The reaction is first order in t‐BuCl with ΔEa of ca. 7 kcal/mole (1,2‐dichloroethane or chlorobenzene solvents, +24 to −29°C). Indirect evidence indicates that the kinetic product of cyclopentadienylation is 5‐t‐BuCPD and that this isomer cannot be tert‐butylated; that is, the initiation of 5‐t‐BuCPD polymerization by t‐Bu⊕ is sterically unfavorable. Detailed analysis of the chemistry and kinetics of the t‐BuCl/Me2AlCPD model system holds important clues to the controlled polymerization of olefins leading to macromolecules with cyclopentadiene (CPD) termini.
Studies on the optical active alternating copolymer of benzofuran or 1,3‐cyclooctadiene with acrylic monomers
Authors: Kobayashi Eiichi , Furukawa Junji , Nagata Shiro 
Published: April 2003

AbstractIn the presence of an optical active amyloxyaluminum or menthoxyaluminum chloride the asymmetric‐induction alternating copolymerization of benzofuran or 1,3‐cyclooctadiene and acrylonitrile or methacrylonitrile was investigated. The sign of optical rotation of copolymers was positive or negative, depending on the kind of catalyst used. The optical activity of copolymers of benzofuran and acrylonitrile attains a maximum value at an equimolar composition. The highest specific rotation [α]D of copolymers of benzofuran and acrylonitrile prepared in the presence of stoichiometric amount of (—)‐menthoxyaluminum dichloride with respect to acrylonitrile was about −8°. The stereo‐structure of acrylonitrile unit may be controlled by the optical active aluminum compound onto which a strong coordination of acrylonitrile may occur.
Photopolymerization of methyl methacrylate using hydrogen peroxide as the photoinitiator
Authors: Ghosh Premamoy , Sengupta Pranab Kumar , Mukherjee Nikhileswar 
Published: April 2003

AbstractPhotopolymerization of MMA with the use of H2O2 as the photoinitiator under visible light at 30°C was studied. Kinetic features in bulk monomer and in the presence of different diluents differ significantly. Usual free radical kinetics with square‐root dependence of rate on initiator, indicating bimolecular termination of chain radicals, were observed for bulk polymerization. On dilution with various solvents polymerization was found to be retarded to different (usual and more than usual) extents, the observed monomer exponent value being much higher than unity in many cases. This deviation from normal kinetics has been interpreted in terms of the predominance of degradative initiator transfer in the diluted systems.
A study of the cationic solid‐state polymerization of 1,3,5‐trithiane
Authors: Żuk Aleksander , Jȩczalik Jerzy 
Published: April 2003

AbstractThe effect of various reaction parameters, such as temperature, catalyst, and concentration, on the cationic‐initiated polymerization of 1,3,5‐trithiane in solid state was studied and the apparent activation energies were estimated. A simple mathematical formula to describe the observed kinetic curves is proposed. The features observed are interpreted in terms of disordering a crystal structure during polymerization.
Volume and conformation. II. Homopolypeptide chains
Authors: Zanotti G. , Spadon P. , Del Pra A. 
Published: April 2003

AbstractA conformational analysis of two homopolypeptides, poly‐L‐proline and polyglycine, has been carried out with a method based on the van der Waals molecular volume change as a function of internal rotation angles about the nonrigid bonds. The results indicate that the structures with large van der Waals volume are all reasonable structures.