bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization and copolymerization of trioxane: Factors influencing molecular weight and end groups
Authors: Chen Catherine S. Hsia 
Published: April 2003

AbstractIn bulk polymerization and copolymerization of trioxane with ethylene oxide, it has been shown that p‐chlorophenyldiazonium hexafluorophosphate
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is a superior catalyst as compared to boron trifluoride dibutyl etherate (BF3 · Bu2O). Polymers and copolymers of significantly higher molecular weight have been obtained. The higher molecular weight has been attributed primarily to less inherent chain transfer during propagation, which in turn can be attributed to the superior gegenion PF6−.The polymerization proceeds via a clear period followed by sudden solidification. Faster polymerization and higher molecular weight polymers have been observed for homopolymerization than for copolymerization. The polymer yield obtained after solidification is determined by both rate of polymerization and rate of crystallization of polymers. These rates, in turn, are dependent on the catalyst concentration. The molecular weight is determined both by polymer yield and extent of inherent chain transfer. In the range of monomer to catalyst mole ration [M]/[C] = (0.5–20) × 104 investigated, it has been found that in the higher range, the polymer yield is independent of the catalyst concentration and the extent of inherent chain transfer is inversely proportional to the half power of catalyst concentration: [M]/[C] = (0.5–8) × 104 for homopolymerization and (0.5–3) × 104 for copolymerization with 4.2 mole % ethylene oxide. In the lower range, the yield decreases with catalyst concentration and the extent of inherent chain transfer is inversely proportional to higher power of catalyst concentration. The dependence of molecular weight of polymers on catalyst concentration has been shown to be a complex one. The molecular weight goes through a maximum as the catalyst concentration is decreased. The maximum molecular weights have been obtained at [M]/[C] ≈ 8 × 104 for homopolymerization and ∼3 × 104 for copolymerization with 4.2 mole % ethylene oxide. Prior to reaching maximum the molecular weight is inversely proportional to the half power of catalyst concentration indicating it is primarily controlled by inherent chain transfer. Upon further decrease of catalyst, molecular weight decreases as a result of both a decrease in polymer yield and an increase in inherent chain transfer.In copolymerization of trioxane and ethylene oxide, it has been ascertained that methylene chloride exhibits a favorable solvating effect. Although higher inherent chain transfer takes place in copolymerization than in homopolymerization, the extent of chain transfer is independent of ethylene oxide concentration. The difference in polymer yield and molecular weight a t different ethylene oxide concentrations is attributed primarily to the difference in kp/kt ratio. It also has been demonstrated that end capping of polymer chains can be accomplished by the use of a chain transfer agent—methylal.
Autoxidation of poly‐4‐methylpentene‐1. I. The role of diffusion in autoxidation kinetics
Authors: Billingham N. C. , Walker T. J. 
Published: April 2003

AbstractAn apparatus is described for the measurement of oxygen uptake into a polymer sample at constant oxygen pressures in the range 20–1000 mm Hg. Measurements of the rate of oxygen uptake into poly‐4‐methylpentene‐1 show that the rate is accurately first‐order in oxygen pressure over the range 50–800 mm pressure for temperatures ranging from 122 to 154°C and film thickness in the range 0.001–0.025 cm. A theoretical treatment of the kinetics of a reaction in which oxygen diffuses into both faces of a thin film, in which it is consumed by a first‐order reaction shows that the oxidation rate ρ per unit area of film surface is given by ρ = ρ∞ tanh ßL/2 where ρ∞ is the limiting oxidation rate for a thick film, L is the film thickness, and ß = (k/D)1/2, k being the oxidation rate constant and D the diffusion constant. Values of D and the activation energy for diffusion calculated from autoxidation data are in good agreement with values determined directly.
Dependence of structure of dehydrated PVA on the crystallinity of the original PVA
Authors: Nakanishi Yoichiro 
Published: April 2003

AbstractPoly(vinyl alcohol) (PVA) films having different crystallinities were prepared by elongating PVA films to different degrees and heating the films with and without elongation treatment at several temperatures between 60 and 200°C. Then, they were dehydrated by heating from 80°C to 230 or 330°C in hydrogen chloride gas. Infrared spectral measurements were made on the dehydrated PVA films obtained. Absorbances of the absorption bands due to several groups seen in the infrared spectra depended only on the density of original PVA films, regardless of its degree of elongation. From these dependences, it was found that the dehydration reaction progressed more easily in the crystalline region than in the amorphous region, that the aromatic rings with four or five adjacent hydrogen atoms were formed mainly in the amorphous region and those with two adjacent hydrogen atoms in the crystalline region, and that the aromatic rings with two isolated hydrogen atoms were formed in both the amorphous and crystalline regions. Relative concentrations of the groups of which the dehydrated PVA were composed were estimated. Comparison of the numbers of carbon atoms among the composing groups indicated that the main groups were the methylene group and the aromatic ring.
Determination of rate constants for polymerization of styrene initiated by 2,2′‐azobisisobutyronitrile by utilizing steady‐state population densities
Authors: Scamehorn J. F. , Timm D. C. 
Published: April 2003

AbstractA theoretical description of chain‐growth polymerization is presented in terms of a distributed parameter model. Analysis of molecular distributions of macromolecular materials results in graphical procedures capable of yielding absolute values for kinetic constants. A steady‐state analysis of styrene polymerizations initiated with 2,2′‐azobisisobutyronitrile in toluene yielded the following rate information, which is in qualitative agreement with previously published results: f = 0.4; Ki = 1.58 × 1015 exp {−30,800/RT} Ktc/K2p = 1.10 × 10−5 exp {13,200/RT}.
Studies of the photooxidation mechanism of polymers. III. Role of tetrahydrofuran in the photooxidative degradation of poly(vinyl chloride)
Authors: Rabek Jan F. , Shur Young J. , Rårnby B. 
Published: April 2003

AbstractThe influence of tetrahydrofuran (THF) on photooxidative degradation of poly(vinyl chloride) in films cast from THF solution was studied. THF is partially retained in the polymer matrix in amounts of 6–8% after casting and drying the film. The last 2–3% is very difficult to remove. By use of thermogravimetric analysis, density measurements, and gas permeability measurements, it was shown that THF residues can be removed by preheating the PVC samples to 80°C. THF forms a charge‐transfer complex with oxygen which is easily photolyzed. During this reaction hydroperoxide radicals are formed. Molecular weight distribution curves by gel‐permeation chromatography (GPC) show that THF in the presence of air promotes the photodegradation of PVC. Attention has been given to the correct interpretation of the infrared absorption spectra of PVC films containing THF residues and ultraviolet‐irradiated in air.
Study on radiation‐induced polymerization of vinyl monomers adsorbed on inorganic substances. II. Radiation‐induced polymerization of methyl methacrylate adsorbed on several inorganic substances
Authors: Fukano Kazuyuki , Kageyama Eiichi 
Published: April 2003

AbstractThe radiation‐induced polymerization of methyl methacrylate (MMA) absorbed on such inorganic substances as silica gel, white carbon, silicic acid anhydride, zeolite, and activated alumina was carried out to compare with the case of styrene. The rate of radiation‐induced polymerization adsorbed on inorganic substances was high compared with that of radiation‐induced bulk state polymerization, as was the case with styrene. Inorganic substrates which contain aluminum as a component element are more likely to be grafted than those which consist of SiO2 alone, as with styrene. The molecular weight distribution of unextractable polymer and extractable polymer differs, depending on the type of inorganic substance. Experiments by a preirradiation method were carried out in case of silica gel, white carbon, and silicic acid anhydride. GPC spectra of the polymer obtained were different from those of polymer formed by the simultaneous irradiation method. It appears that all the unextractable polymer is grafted to the inorganic surface with chemical bond.
Photopolymerization of vinyl fluoride
Authors: Raucher Daniel , Levy Moshe 
Published: April 2003

AbstractThe photopolymerization of vinyl fluoride, in the presence of peroxide, was studied in dimethyl sulfoxide (DMSO) solution and in bulk. It was found that high rates of reaction could be obtained in spite of the fact that the polymer precipitates at an early stage. By continuous supply of monomer the precipitated polymer was converted into a transparent bulk polymer.
Pyrolysis–gas chromatographic analysis of chain branching in polyethylene
Authors: Seeger Michael , Barrall Edward M. 
Published: April 2003

AbstractA system with flash pyrolysis and gas chromatography (PGC) which includes in‐line hydrogenation and packed columns is described. Under optimal conditions of temperature programming and flow rate, a high degree of resolution was obtained over a broad range of fragment lengths. The system has been applied to the analysis of side groups and long branches in polyethylene. It was found that, for low concentration of branches, yield and distribution of the isoalkanes is very sensitive to the type of polymerization used to form the polyethylene. A great number of the single‐branched isoalkanes have been identified by comparing their retention time with the scale of respective boiling points and by pyrolyzing well characterized ethylene‐propylene copolymers. The pyrograms of the ethylene‐propylene copolymers demonstrated that a CC bond in an α‐ or β‐position to a tertiary carbon cleaves about two times more readily than a CC bond in a linear chain. It was further found that the branch length of the side chain is indicated by the identity of the fragments produced, and the probability of formation of these fragments is directly related to the possibility of a cyclic decomposition mechanism. From the high yields of 3‐ and 5‐methylalkanes it was possible to detect about 20 ethyl and 10 n‐butyl branches per thousand in a low‐density polyethylene. Thus, pyrolysisgas chromatography has to be considered seriously as a method for the determination of branches, even when in present in low concentration (Ziegler‐type polyethylene).
α‐amidoalkylation of polystyrene
Authors: Swiger R. T. 
Published: April 2003

AbstractCrystal polystyrene was alkylated with N‐methylolacetamide (CH3CONHCH2OH), boron trifluoride being used as the catalyst. A linear relationship between degree of N‐methyleneacetamide substitution and the glass transition temperature Tg of the polystyrene was observed. The Tg values ranged from 104°C for 0% amidization to 125°C for 20% amidization. The critical strain εc of these materials was measured at room temperature in air, hexane, and oil (50–50, a cottonsed oil–oleic acid) and an increase in the εc above which crazing occurs was observed as the degree of alkylation increased. Thermogravimetric analysis (TGA) of the amidized polystyrenes in air at 250°C showed these materials to become more stable as the amount of N‐methylene substitution increased. Tensile data show that the amidized polystyrene, although stronger than the unsubstituted material, exhibits the same elongation at break and tensile modulus.
Monomer‐isomerization polymerization. XI. Monomer‐isomerization copolymerizations of 2‐butene with 2‐pentene and 2‐hexene with Ziegler‐Natta catalyst
Authors: Otsu Takayuki , Shimizu Akihiko , Itakura Keisuke , Endo Kiyoshi 
Published: April 2003

Abstract2‐Pentene and 2‐hexene were found to undergo monomer‐isomerization copolymerizations with 2‐butene by Al(C2H5)3–VCl3 and Al(C2H5)3–TiCl3 catalysts in the presence of nickel dimethylglyoxime or transition metal acetylacetonates to yield copolymers consisting of the respective 1‐olefin units. For comparison, the copolymerizations of 1‐pentene with 1‐butene and 1‐hexene with 1‐butene by Al(C2H5)3–VCl3 catalyst were also attempted. The compositions of the copolymers obtained from these copolymerizations were determined by using the calibration curves between the compositions of the respective homopolymer mixtures and the values of D766/D1380 in the infrared spectra. The monomer reactivity ratios for the monomer‐isomerization copolymerizations of 2‐butene (M1) with 2‐pentene and 2‐hexene, in which the concentrations of both 1‐olefins calculated from the observed isomer distribution were used as those in the monomer feed mixture, and for the ordinary copolymerizations of 1‐butene (M1) with 1‐pentene and 1‐hexene by Al(C2H5)3‐VCl3 catalyst were determined as follows: 2‐butene (M1)/2‐pentene (M2): r1 = 0.14, r2 = 0.99; 1‐butene (M1)/1‐pentene (M2): r1 = 0.30, r2 = 0.74; 2‐butene (M1)/2‐hexene (M2): r1 = 0.11, r2 = 0.62; 1‐butene (M1)/1‐hexene (M2): r1 = 0.13, r2 = 0.90.
Radiation induced copolymerization of chlorotrifluoro ethylene with butenes
Authors: Tusche R. , Seyhan M. , Schneider Ch. 
Published: April 2003

AbstractThe radiation induced copolymerization of chlorotrifluoro ethylene (CTFE) with various butenes was studied at temperatures between −20°C and +40°C using 60Co‐γ rays.In the case of isobutene (IB) an almost alternating crystalline copolymer is formed in a heterogeneous reaction. At high IB‐concentrations a cationic homopolymerization of this olefin occurs simultaneously to the radical copolymerization. The copolymerization rate increases with increasing temperature and degree of conversion. The highest rates are obtained for monomer mixtures with about 80 to 90 mole % CTFE. The decrease in rate for monomer mixtures with still higher CTFE concentrations is assumed to be partly due to the low IB‐concentration and partly to degradative chain transfer by the isobutene. In support of this assumption molecular weights and melting points of the copolymer have been determined.Similar results were obtained for butene‐1 but in this case, no cationic homopolymerization was observed and the reaction proceeded homogeneously.Cis‐ and trans‐butene‐2 only acted as polymerization inhibitors.
Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). V. Kinetics of initial template polymerization
Authors: Gons J. , Vorenkamp E. J. , Challa G. 
Published: April 2003

AbstractThe influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between −11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ Sp†) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ Et†) of complexed growing chain radicals.
Charge‐transfer polycondensation of diethyl chelidonate with hexamethylenediamine
Authors: Ogata N. , Shimamura K. 
Published: April 2003

AbstractPolycondensation of diethyl chelidonate (DEC) with hexamethylenediamine (HMD) took place very rapidly under mild conditions to form a corresponding polyamide. The polycondensation reaction proceeded through the formation of a charge‐transfer complex between DEC and HMD, which transformed rapidly into polyamide. Various reaction conditions to form polyamide from DEC and HMD were investigated in terms of solvents, concentration, and temperature. Model reaction of DEC with primary or tertiary amines confirmed the formation of a charge‐transfer complex which transformed into chelidonamide except tertiary amine. The polycondensation of DEC with HMD was accelerated by irradiation with light.
Polymerization of α‐amino acid N‐carboxy anhydrides initiated by histamine in N,N‐dimethylformamide
Authors: Tsuchida Eishun , Hasegawa Etsuo , Honda Kenji 
Published: April 2003

AbstractThe polymerization of α‐amino acid N‐carboxy anhydrides (NCAs) initiated by 4‐aminoethylimidazole (histamine) was studied in order to synthesize poly(amino acids) containing an imidazole nucleus at the end of polymer chain. On the basis of the kinetical measurements, it was found that the rate of polymerization is proportional to the first order in both NCA and initiator concentrations and that the initiation reaction is predominantly caused by the primary amine with the highest basicity in a histamine molecule. Binding of the histamine fragment to the end of polymer chain was confirmed by elementary analysis, nuclear magnetic resonance spectroscopy, and measuring the number‐average molecular weight of the resulting polymers. It was thus possible to prepare poly(amino acids) with a pendant histamine. In addition, the lowering of the number‐average degree of polymerization of the polymers prepared was observed under the condition that the initial molar ratio of NCA to histamine was larger. It was caused by the reinitiation of polymerization by the imidazole nucleus at the chain end.
Photocrosslinkable resins with benzylideneacetophenone (chalcone) structure in the repeat units
Authors: Panda S. P. 
Published: April 2003

AbstractSyntheses, characterization and photoreactions of six diglycidyl ethers obtained by condensing 2,2′, 2′,4, and 4,4′‐dihydroxychalcones with epichlorohydrin in two different molar proportions have been reported. It has been observed that the well known cyclodimerization and trans‐cis isomerization of the chalcone moiety under photoirradiation could be significantly affected to the extent of completely supressing the isomerization in 2,2′, and 2′,4‐chalconic resins by steric factors. Increase in molecular weight made the photodimerization difficult in the 2,2′, and 2′,4‐chalocnic resins whereas the 4,4′‐chalconic resin remained unaffected. It has been suggested that the chalconic resin could be used in photomechanical processes mixed with aryldiazonium fluoroborates. These additives are known to decompose under photoirradiation yielding BF3 which is a crosslinking agent for the epoxide group.
Polymérisation anionique des diènes. IV. Contribution aux etudes des mécanismes de propagation stéréospécifique des isoprène et butadiène par les organo‐alcalins
Authors: Essel Alain , Salle Robert , Pham Quang‐Tho 
Published: April 2003

AbstractBy taking into account different possible interactions between the living end, the counterion and the nature of the solvent used on the one hand, and the influence of the temperature on the kinetics and the microstructures of polydienes on the other hand, it has been possible to suggest some new explanations concerning the mechanisms of the anionic propagation of butadiene and isoprene. In hydrocarbon media, the stereospecificity of the 1,4 propagation initiated by lithium should be considered as the consequence of the coordination of the counterion by both of the two bonds of the diene molécule. The stereospecificity of the vinyl propagation by the same counterion in dioxane solvent should be the consequence of the competition between the (Li+, dioxane) and (Li+, diene) coordination complexations. In this case, the Li+ counterion should only be coordinated by only one of the two double bonds of the diene molecule. With isoprene, the π‐electron donation should originate mainly from the C3C4 double bond. The decrease of the stereospecificity is due to the increasing size of the alkali counterion and the separation or the dissociation of the growing ion‐pairs.
Influence of the reaction medium on the composition and the microstructure of styrene–acrylic acid copolymers
Authors: Toppet S. , Slinckx M. , Smets G. 
Published: April 2003

AbstractTwo series of acrylic acid‐styrene copolymers of various composition have been prepared in benzene and dimethylformamide in order to study their sequence distribution by using 13C NMR spectroscopy. The reactivity ratios in benzene were rA = 0.13, rA = 0.30 and in dimethylformamide rA = 0.05, rS = 1.60. Copolymers with the same overall composition but prepared in different media display marked differences in sequence distribution, the copolymers obtained in dimethylformamide always having longer sequences. For the series of copolymers prepared in dimethylformamide, the experimental percentages of acrylic acid‐centered triads (SAS, SAA, AAA) disagree with the values calculated from the monomer reactivity ratios.
Polyene sequence distribution in thermally degraded poly(vinyl chloride)
Authors: Abbås K. B. , Laurence R. L. 
Published: April 2003

AbstractA kinetic model for the formation of polyene sequences during the thermal degradation of poly(vinyl chloride) in nitrogen is proposed. The model includes a propagation step of the “zipper” type and termination by crosslinking. The initiation can occur randomly or at weak links in the polymer chain. The rate of polyene growth increased with increasing polyene sequence length and passed through a flat maximum at n = 7. The average polyene sequence length was almost constant up to about 0.5% conversion, but then slowly decreased with increasing conversion. This was the result of a larger extent of termination reactions (crosslinking) at higher conversions. At 0.2–0.5% conversion an average polyene sequence length of about 6 was observed. The degradation was carried out in nitrogen at 190°C. The experimental results were obtained from ultraviolet‐visible spectrophotometric measurements.
Crosslinking and pyrolytic behavior of natural and man‐made cellulosic fibers
Authors: Rodrig H. , Basch A. , Lewin M. 
Published: April 2003

AbstractPyrolysis rates, energies of activation, and DSC data were obtained for cellulosic fibers crosslinked with increasing amounts of formaldehyde. Pyrolysis rates are affected by the reduction in degree of polymerization, the breaking of intermolecular hydrogen bonds, and the introduction of covalent linkages that accompany the crosslinking process. Thermal stabilization of cellulose is related mainly to the formation of interchain crosslinks. The influences of the crystallinity and orientations of the polymers upon changes in thermal stability and pyrolytic behavior due to crosslinking are demonstrated.