bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oligomerization of styrene over molybdenum oxide on silica‐alumina catalyst
Authors: Kumar V. G. , Rao M. Rama , Ravindran P. V. , Rao K. V. C. 
Published: April 2003

AbstractStyrene was found to yield saturated and unsaturated linear oligomers in the presence of a surface‐supported catalyst, molybdenum oxide on silica‐alumina. The reaction rates, the structure, and the molecular weight distribution of the products were found to be controlled by the choice of the solvent. Higher‐molecular‐weight fractions were favored in isooctane, whereas low‐molecular‐weight oligomers were preferred in dioxane. The reaction followed first‐order kinetics with respect to the monomer. End‐group analysis suggests a probable cationic mechanism. Approximate transfer constants KtrKp were deduced from product distribution data. The behavior of the surface‐supported catalyst was compared with other cationic catalyst systems.
Conformational aspects of a “very simple” chain: Polyacetylene
Authors: Cernia Enrico , D'Ilario Lucio 
Published: April 2003

AbstractPotential energy calculations of the isolated chains of trans‐ and cis‐polyacetylene (PA) were made to obtain information on the most probable conformations. Different sets of van der Waals potential functions, different values for the barrier height to the bond rotation, and different geometries for the repeating unit were used. Calculations were also made of the seven‐atom chains of PA for which independent rotations were allowed around three consecutive “quasi‐single” bonds. The deepest minima on the potential energy map of the trans three‐atom chain were consistent with an all‐trans conformation (the most stable one) and with a “distorted cis” conformation, which deviated from the planarity because of the repulsion between hydrogen atoms 1 and 4. The energy maps of the cis polymer showed two minima, both of which corresponded to nonplanar conformations. From the seven‐atom chain analysis of trans‐ and cis‐ PA, in addition to the stable conformations obtained for the three‐atom chains, other minima corresponded to triplets formed from both conformers.
Degradation of PVCs obtained by controlled chemical dehydrochlorination
Authors: Iván Béla , Kennedy Joseph P. , Kelen Tibor , Tüdõs Ferenc , Nagy Tibor Tamás , Turcsányi Béla 
Published: April 2003

AbstractThermal and thermo‐oxidative degradation of poly(vinyl chloride)s (PVCs) containing increased concentrations of allylic chlorines, PVC(A)s, prepared by controlled chemical dehydrochlorination with potassium‐t‐butoxide (t‐BuOK) have been studied. The introduction of small amounts of internal allylic chlorines into PVC significantly decreases the thermal and thermo‐oxidative stability of the resin. A linear relationship exists between the initial rates (VHCl)0 of thermal and thermooxidative dehydrochlorination of solid PVC(A)s and the concentration S of internal allylic chlorines. Both the slope and the intercept of the thermo‐oxidative (VHCl)0 vs. S plot are higher in oxygen than those obtained in nitrogen at the same temperature; this finding is attributed to fast oxidation of polyenes, and to peroxy radicals formed during polyene oxidation, which initiate subsequent HCl loss by attacking normal repeat units in PVC. The extent of HCl loss as a function of time during thermal degradation of PVC(A)s in intert solvent shows a rapid initial phase followed by a slower stationary phase. The first phase is due to dehydrochlorination involving the labile chlorines, while the stationary phase indicates random initiation of HCl loss at normalCH2CHCl repeat units. Initial rates of HCl loss increase with S, while the rates of HCl loss during the stationary phase are independent of S. The rate constant of initiation of HCl loss at internal allylic chlorines is almost four orders of magnitude higher than that of random initiation; however, the former is still orders of magnitude lower than that of chain propagation. Quantitative analysis of UV‐visible spectra of PVC(A)s degraded in solution suggests geometric polyene distribution. The average length of polyenes decreases as the extent of HCl loss increases and reaches a constant value of ca. 3 at ca. 1% HCl loss for all the investigated PVC(A) samples.
ESR study of free radicals produced from the reaction of o‐substituted phenyl methacrylates with tert‐butoxy radical
Authors: Yamada Bunichiro , Matsumoto Akikazu , Otsu Takayuki 
Published: April 2003

AbstractESR spectra of radicals produced from the reactions of phenyl methacrylate (PMA) and four o‐substituted PMAs, 2,4,6‐trimethyl‐, 2,6‐diisopropyl‐, 2,6‐di‐tert‐butyl‐, and 2,6‐di‐tert‐butyl‐4‐methyl‐PMAs, with tert‐butyoxy radical were measured in 2‐methyltetrahydrofuran over the temperature range of −53 to −15°C. The coupling constants of the β‐methylene protons observed varied with the bulkiness of the o‐substituents, whereas the p‐substitution did not affect the pattern of the spectra. 2,6‐Diisopropyl‐ and 2,4,6‐timethyl‐PMAs, which can form homopolymers, gave 5‐ and 13‐line spectra, respectively. For the radicals from 2,6‐di‐tert‐butyl‐ and 2,6‐di‐tert‐butyl‐4‐methyl‐PMAs, the same 8‐line spectrum was observed, indicating that the coupling constant of one of the β‐methylene protons was too small to detect. Conformations of the radicals were deduced from the coupling constants of the β‐methylene protons. Variation of the ESR spectrum according to the bulkiness of the o‐substituent was interpreted as a consequence of steric interactions between the polymer chain bound to the β carbon and the substituents, and the α‐methyl group.
Effect of active‐group position in polymeric interactions
Authors: Worsfold D. J. 
Published: April 2003

AbstractThe effect of the position of a substituent along a polymer chain on the equilibrium constant in interpolymer interactions has been determined for equilibria involving the substituent. Polymers containing single dimethylamino groups have been equilibrated with coupling bidentate dinitro phenols, and the excluded‐volume effect determined. The magnitude of the hindrance to complex formation was found to be considerably greater for centrally substituted polymers than for end‐substituted polymers. However, for all polymers the measured effect is less than those expected from previous theoretical treatments of interpolymer reactions. Also, the size of the effect is less in the equilibria than found previously for interpolymer reactions. This suggests that the theoretical treatments that deal only with the effect of excluded volume on the transition complex may be oversimplifications.
New polymer synthesis. IX. Synthesis of poly(ether sulfone)s from silylated diphenols or hydroxybenzoic acids
Authors: Kricheldorf Hans R. , Bier Gerhard 
Published: April 2003

AbstractThe condensation polymerizations of bis(4‐flurophenyl) sulfone with the bistrimethylsilyl derivates of bisphenol‐A, 4,4′‐dihydroxydiphenyl sulfone, 1,5′‐dihydroxynaphthalene, 3‐hydroxybenzoic acid, and 4‐hydroxybenzoic acid were investigated. These polycondensations were only successful when potassium or cesium fluoride was used as catalyst. The yields were in the range of 91–98% and the number molecular weights in the range of 2,500–17,500 depending on the reaction conditions. Viscosity and GPC measurements were conducted and glass transitions were determined. Crystallization was never observed.
Free‐radical identification by ESR in polyethylene and nylon
Authors: Igarashi M. 
Published: April 2003

AbstractIdentification of the free radicals in polyethylene and nylon produced by irradiation, grinding, and pulling to fracture was carried out by comparing the experimentally observed spectra with the spectra constructed from theoretical consideration with the aid of a computer. It was demonstrated that the various primary and secondary radicals are produced and formed in the materials depending upon means of degradation, degradation processes, orientation of materials, and conditions of ESR measurement.
Exciplex formation in aromatic copolymers and photoinduced electron transfer from exciplex to acceptor
Authors: Iwai Kaoru , Itoh Yoshihiro , Furue Masaoki , Nozakura Shun‐Ichi 
Published: April 2003

AbstractThe exciplex formation in 9‐vinylphenanthrene‐p‐N,N‐dimethylaminostyrene copolymers, its characteristics, and the electron transfer process in polar solvents were studied. The copolymer exhibited a more intense intramolecular exciplex fluorescence than the low‐molecular‐weight model system, phenanthrene‐N,N‐dimethylaniline, in which the intermolecular exciplex formation occurred. Intensities of the exciplex fluorescence, which were unchanged regardless of the copolymer composition, led us to speculate that the efficient energy migration takes place from an excited phenanthrene unit to an exciplex forming site on the polymer chain. The electron transfer in the copolymer‐p‐dicyanobenzene system was studied in polar media. The formation of p‐dicyanobenzene anion radical was measured by flash photolysis and electron spin resonance (ESR). p‐Dicyanobenzene anion radical was generated by the electron transfer process via exciplex and the direct electron transfer process from the excited phenanthrene unit in the copolymer.
Kinetic and mechanistic studies of the copolymerization of bis‐4‐substituted‐1,2,4‐triazoline‐3,5‐diones with styrenes
Authors: Lai Yu‐C. , Butler G. B. 
Published: April 2003

AbstractHighly reactive 4‐substituted‐1,2,4‐triazoline‐3,5‐diones (TDs) have been studied extensively as dienophiles, but little work has been done on their role as enophiles and particularly on their use as propagating species in polymerization studies. The copolymerization between bis‐4‐substituted‐1,2,4‐triazoline‐3,5‐diones (bis‐TDs) and styrene has been reported. The purpose of the present work was to synthesize new copolymers derived from a variety of substituted styrenes and bis‐TDs and to study the mechanism and kinetics of this novel polymerization. Three bis‐TDs were prepared: 3,3′‐dimethyl‐4,4′‐bis[3,5‐dioxo‐1,2,4‐triazoline‐4‐yl] biphenyl (8), t‐1,4‐bis[3,5‐dioxo‐1,2,4‐triazoline‐4‐yl] methyl cyclohexane (9), and 4,4′‐bis[3,5‐dioxo‐1,2,4‐triazoline‐4‐yl] phenyl ether (10). Their structures were fully established by spectroscopic studies, elemental analyses, and indirectly, their quantitative ene reactions with 2,3‐dimethyl‐2‐butene. Copolymerization between bis‐TDs and substituted styrenes was carried out in dimethylformamide (DMF), tetrahydrofuran (THF), or dichloroethane (DCE). Polymers formed were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and viscometry. Molecular weights of polymers range from 5000 to 16,000 in most cases. They were stable up to 250°C and higher. Polymers derived from bis‐TDs and p‐t‐butylstyrene, α‐methylstyrene, p‐nitrostyrene, and p‐acetoxystyrene contained only Diels‐Alder‐ene (DAe) repeating units, whereas those derived from styrene, p‐chlorostyrene, p‐bromostyrene, p‐methylstyrene, p‐methoxystyrene, and 4‐vinylbiphenyl contained both DAe and double Diels‐Alder (dDA) repeating units. A kinetic study of the copolymerization of 4,4′‐bis‐(3,5‐dioxo‐1,2,4‐triazoline‐4‐yl) phenyl ether with α‐methylstyrene, p‐t‐butylstyrene, styrene, p‐chlorostyrene, and p‐nitrostyrene in DCE was carried out; the copolymerization rate constants were 60.9, 49.8, 8.4, 5.5, and 0.8 (1 mol−1s), respectively.
Synthesis and thermal analysis of some oligomeric silicon derivatives of ferrocene
Authors: Asatiani L. P. , El‐Agamey A. A. , Diab M. A. 
Published: April 2003

AbstractThis article reports a study of the catalytic addition reaction of ferrocene containing dihydrosilane to diacetylenic silicon derivatives. A hypothetical structure based on reaction kinetics and spectral data is presented. The oligomers obtained were studied by TG and DTA from ambient temperature to 1000°C in oxygen atmosphere (80 mL/min). The existance of phenyl groups in the structure of the oligomers makes them less stable than those with derivatives.
Synthesis and properties of polythienylenes
Authors: Hotz Charles Z. , Kovacic Peter , Khoury Issam A. 
Published: April 2003

AbstractAlthough polymerization of 2,5‐dibromothiophene via coupling of the Grignard reagent with organonickel salts was reported in two earlier communications, a detailed examination of reaction variables was not done. This report provides results from variation in the following: time, amount of magnesium, amount of iodine, dilution, and variation in the halide of the monomer. The highest yield was obtained for reactions with 1:1 molar ratio of monomer to magnesium in more concentrated solutions of tetrahydrofuran for a reaction time of 4 h. For variation in the halogen of the monomer the following yield sequence was obtained: I > Br > Cl. The results are compared with the corresponding benzenoid system investigated by Yamamoto. In addition, polymerization studies were carried out with other brominated thiophene monomers. Use of an organic promoter (cis‐1,4‐dichloro‐2‐butene) in place of a nickel salt proved successful in the generation of poly(2,5‐thienylene).
Head‐to‐head polymers. XXIV. Synthesis of head‐to‐head polyisobutylene by Grignard coupling reaction
Authors: Malanga Michael , Vogl Otto 
Published: April 2003

AbstractHead‐to‐head polyisobutylene of molecular weight 3000 to 10,000 was prepared in about 30% yield by Grignard coupling polymerization of 2,2,3,3‐tetramethyl‐1,4‐dibromobutane with copper(I) tris(triphenylphosphino)bromide as the catalyst. Head‐to‐head polyisobutylene is crystalline, with a Tm of 187°C and a Tg of 87°C and still has bromine end groups left. The polymers have been characterized by their infrared, 1H‐, and 13C‐NMR spectra and compared to the corresponding head‐to‐tail polymers of similar molecular weight. A substantial portion of the reaction product of the Grignard coupling polymerization is not polymeric but was identified as cyclized product, 1,1,2,2‐tetramethylcyclobutane.
Aqueous polymerization of methyl methacrylate. III
Authors: Shukla J. S. , Tiwari R. K. , Sharma G. K. , Shukla S. K. 
Published: April 2003

AbstractThe aqueous polymerization of methyl methacrylate (MMA) initiated by potassium persulfate (I)‐thiomalic acid (TMA) redox couple has been studied at 30 ± 0.2°C under nitrogen atmosphere. The rate of polymerization is given by

up to 20.0 mmol/L TMA concentration, where x = 0.52 for the I concentration 0.6–10 mmol/L and x = 0.27 for higher I concentrations. The temperature had a marked effect on initial rate and maximum conversion. The overall energy of activation was found to be 11.79 kcal/mol (49.31 kJ/mol). Injection of more initiator (I) at intermediate stages enhanced both the initial rate and maximum conversion. Ag (I) and Fe (III) depressed initial rate as well as maximum conversion, while Cu (II) activated the polymerization. The effect of solvent was also studied.
Thermal conversions of polymers with macroheterocycles in the chain
Authors: Siling S. A. , Gribkova P. N. , Ponomarev I. I. , Balykova T. N. , Vlasova I. V. , Pavlova S.‐S. A. , Korshak V. V. , Vinogradova S. V. 
Published: April 2003

AbstractThermal conversion of polyhexazocyclanes and compound modeling the fragments of polymers were explored within 300–600°C under vacuum (10−5 torr) and in water vapor. At temperatures below 450°C, the hydrolytic degradation plays a key role in the thermal degradation of polyhexazocyclanes. At a higher temperature, the homolytic processes prevail, water, strongly retained by the macroheterocycle, is most important in the hydrolysis process. It was shown that the increase in the thermohydrolytic stability of polymers with the system of condensed cycles in the macroheterocycles and that of polyhexazocyclanes modified by polymer analogous conversion at the secondary amino groups of the isoindole cycle was caused by the absence of bound water.
Radical polymerization in the presence of complexing agents. V. Effect of low concentration of ZnCl2 on the radical copolymerization of methyl methacrylate with ethyl acrylate
Authors: Madruga E. L. , Román J. San , Rodriguez M. J. 
Published: April 2003

AbstractReactivity ratios for the free‐radical copolymerization of methyl methacrylate with ethyl acrylate in the presence of low concentrations of ZnCl2 are analyzed at different polymerization temperatures, 35,50, and 65°C. The different tendencies of the two monomers toward the formation of molecular complexes with the metal halide modify the homopropagation and cross‐propagation coefficients and the results obtained seem to indicate a conventional cross‐propagation mechanism in which both free and complexed species of acrylic monomers participate.
Functional monomers and polymers. CVIII. Photodimerization of pendant thymine bases in thymine containing poly‐lysine derivatives
Authors: Suda Yasuo , Inaki Yoshiaki , Takemoto Kiichi 
Published: April 2003

AbstractThe photodimerization reaction of pendant thymine bases in thymine‐containing poly‐lysine derivatives was studied over a wide range in aqueous solution. It was found that the quantum yield of the photodimerization of pendant thymine bases is affected mainly by the conformation of the polymers in solution. The differences in photoreaction behavior were discussed for poly‐D‐, poly‐L‐, and poly‐DL‐lysine derivatives.
The effect of filler shape on the mechanical properties of a reinforced vulcanizate: The SBR‐ground asbestos system
Authors: Papirer Eugène 
Published: April 2003

AbstractGrinding chrysotile under controlled conditions results in microfibers with the dimensions of carbon black or silica agglomerates used in the reinforcement of rubber. The mechanical properties of SBR reinforced with ground asbestos are similar to those of SBR filled with a silica of equivalent surface area.
The investigation of cancerous human bone (osteoclastoma) by small‐angle X‐ray scattering
Authors: Patel A. , Khanduala B. Ch. , Thakur G. B. , Labischinski H. 
Published: April 2003

AbstractSmall‐angle X‐ray scattering methods were applied to provide a pore analysis of cancerous human bone (osteoclastoma). For experimental measurements of the scattering intensities a small‐angle Kratky camera, equipped with a counterattachment and a programmable step‐scanning device, was used. By applying the theories of Kratky, Porod, Debye, and Bueche, applicable to a densely packed two‐phase system belonging to a general micelle system, macromolecular parameters such as specific inner surface, length of coherence, range of inhomogeneity, void percentage, and transversal lengths l̄1 and l̄2 were evaluated and found to be 4.69 × 10−4 Å−1, 21.39 Å, 18.01 Å, 0.21%, 18.01 Å and 8.53 × 103 Å, respectively. A comparison of these parameters with those of pure human bone revealed a macromolecular dissociation in osteoclastoma.
Radical‐initiated homo‐ and copolymerization of cyanomethyl methacrylate
Authors: Ueda Mitsuru , Suzuki Toshiyuki , Imai Yoshio , Pittman Charles U. , Wallace Easley 
Published: April 2003

AbstractThe kinetics of cyanomethyl methacrylate (CyMA) homopolymerization was investigated in acetonitrile with azobisisobutyronitrile as initiator. The rate of polymerization Rp was expressed by Rp = k[AIBN]0.49[CyMA]1.2 and the overall activation energy was calculated as 72.3 kJ/mol. Kinetic constants for CyMA polymerization were obtained as follows: kp/k = 0.10 L1/2s−1/2; 2fkd = 1.57 × 10−5s−. The relative reactivity ratios of CyMA(M2) copolymerization with styrene (r1 = 0.15, r2 = 0.29) and methyl methacrylate (r1 = 0.43, r2 = 0.75) in acetonitrile were obtained. Applying the Q‐e scheme (in styrene copolymerization) led to Q = 1.64 and e = 0.98. The glass transition temperature Tg of poly(CyMA) was observed to be 91°C by thermomechanical analysis. Thermogravimetry of poly(CyMA) showed a 10% weight loss at 265°C in air.
Photoinitiated polymerization of vinyl monomers by benzophenone t‐butyl peresters
Authors: Abu‐Abdoun Ideisan. I. , Thijs L. , Neckers D. C. 
Published: April 2003

AbstractBenzophenone peresters undergo efficient photodecomposition when irradiated at 366 nm. This article reports peresters derived from benzophenone p,p′‐dicarboxylic acid 1 which may produce radicals at two different centers in the same molecule. These peresters represent a unique new example of an efficient photoinitiator for acrylate and styrene polymerization.
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Phase‐transfer‐catalyzed free‐radical polymerization: Kinetics of polymerization of methyl methacrylate using ammonium peroxydisulfate/hexadecyl pyridinium chloride in ethyl acetate/water
Authors: Jayakrishnan A. , Shah D. O. 
Published: April 2003

AbstractThe kinetics of phase‐transfer‐catalyzed free‐radical polymerization of methyl methacrylate using the system ammonium peroxydisulfate/hexadecyl pyridinium chloride have been investigated in the temperature range of 50–60°C in ethyl acetate/water two‐phase systems. The superior efficiency of the phase‐transfer‐catalyzed reaction in comparison with polymerization initiated by oil soluble initiators such as 2,2′‐azobisisobutyronitrile and benzoylperoxide has been demonstrated. Rate of polymerization increased with increase in concentration of the quaternary salt but showed a tendency to level off at higher concentrations. Increase in the peroxydisulfate concentration also resulted in an increase in the rate at lower concentrations, but was found to decrease at higher concentrations. The order with respect to the monomer was found to be approximately unity. The title reaction has been found to be not truly phase‐transfer catalyzed in character as claimed by previous workers. A suitable kinetic scheme has been proposed to account for the experimental data and its significance discussed.
Ionic species in irradiated poly(methyl methacrylate). A pulse radiolysis and ESR study
Authors: Tabata M. , Nilsson G. , Lund A. , Sohma J. 
Published: April 2003

AbstractPoly(methyl methacrylate) free of initiators was synthesized by γ‐irradiation and cast into transparent films. The samples were investigated by ns pulse radiolysis at various temperatures, and by ESR spectroscopy after γ irradiation at 77°K. Short‐lived transients with optical absorptions at 440 and 725 nm were observed. The 440 nm absorption has been ascribed to the cation and the 725 nm absorption (εG = 3000 M−1 cm−1 (100 eV)−1, τ1/2 = 190 ns at −13°C, Ea = 6.5 kcal/mol) to the anion. These assignments are based on ESR data of samples of poly(methyl methacrylate) and pivalic acid methyl ester deuterated at the ester deuterated at the ester and α‐methyl groups, respectively, and subjected to thermal annealing and photobleaching. The anion decomposes on photobleaching by loss of the ester ·CH3 radical, and the cation is proposed to decay by loss of the ·CH3 radical from the α‐methyl group. The thermal decay of the anion is discussed.
Termination in radical copolymerization: Correlation of experimental data
Authors: Procházka Ondřej , Kratochvíl Pavel 
Published: April 2003

AbstractVarious termination models in the radical copolymerization are compared on the basis of available experimental data for the dependence of the initial rate of copolymerization on the composition of the monomer mixture. A diffusion‐controlled model seems to be more adequate for the majority of reported data than a chemically controlled one. The potential effect of activity coefficients in calculations of the initial rate of copolymerization is discussed.
The skewness of polymer molecular weight distributions
Authors: Chen Show‐An , Hu Hsing‐Chung 
Published: April 2003

AbstractA new parameter α3 for characterization of the skewness of a polymer's molecular weight distribution (MWD) based on the statistics is introduced. For α3 > 0, the skewness is positive, characterizing the MWD with a tail at higher‐MW side. For α3 = 0, the MWD is symmetric. For α3 < 0, the skewness is negative, characterizing the MWD with a tail at the lower‐MW side. A relationship between α3 and the first four (from zeroth to third) moments of the MWD is developed which allows calculation of the skewness without detailed calculation of the MWD. An example of polymerization of styrene with n‐butyllithium is given to demonstrate the characteristics of α3.