bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of cyclopolymerization. Conformational analysis of cis‐1,3‐diisocyanatocyclohexane
Authors: Corfield G. C. , Crawshaw A. 
Published: April 2003

AbstractIn 1,3‐disubstitued cyclohexanes, in general, the diaxial conformation of the cis isomer is, energetically, the least favored conformation. An interspacial electronic interaction in the ground state of a cis‐1,3‐disubstituted cyclohexane would be expected to increase the proportion of this conformer in the equilibrium mixture. Such an interaction would provide an energetically favorable pathway for cyclopolymerization. From nuclear magnetic resonance studies on cis‐and trans‐1,3‐diisocyanatocyclohexane the conformational equilibrium in the cis isomer was determined. It is shown that cis‐1,3‐diisocyanatocyclohexane exists in the diequatorial conformation; this is taken as evidence that a ground‐state interaction between isocyanato groups in this monomer, which readily cyclopolymerizes, is not a significant factor in the cyclopolymerization mechanism. The value of the free energy barrier, ΔG‡, for trans‐1,3‐diisocyanatocyclohexane was calculated as 11.1 kcal/mole.
Selective reactivities and accessibilities of the hydroxyl groups in cotton cellulose based on equilibrium data from a reversible chemical reaction
Authors: Cirino V. O. , Bullock A. L. , Rowland S. P. 
Published: April 2003

AbstractIn order to determine the relative equilibrium constants for reactions of the hydroxyl groups at C2, C3, and C6 of the D‐glucopyranosyl units, methyl vinyl sulfone was reacted with cellulose dissolved in benzyltrimethylammonium hydroxide. The reaction was carried to constancy in distribution of substituents between the 2–0– and 6–0–positions. The distributions of substituents in the D‐glucopyranosyl units were measured by gas‐liquid chromatographic analysis of the products from hydrolysis of the modified cellulose. Relative equilibrium constants were then evaluated, assuming complete accessibility of all three types of hydroxyl groups of the cellulose in solution. For determination of the relative accessibilities of the individual types of hydroxyl groups in heterogeneous reactions of cotton cellulose with methyl vinyl sulfone, the reactions were carried to equilibrium distributions in media of various normalities of sodium hydroxide (i.e., media of various swelling strength). The distributions of substituents in the D‐glucopyranosyl units were measured. From these values and the ratio of equilibrium constants, the relative accessibilities of the hydroxyl groups at C2 versus those at C6 were calculated. Apparent accessibilities of the hydroxyl groups at C2 are approximately double those at C6 when the reaction is carried out in 1N sodium hydroxide and about triple those at C6 when the reaction is carried out in 0.5N sodium hydroxide.
Electron‐transfer polymers. XXXIX. Redox polymers based on duroquinonyl glycol
Authors: Nakabayashi Nobuo , Wegner Gerhard , Cassidy Harold G. 
Published: April 2003

AbstractRedox polyurethanes, polyesters, and alternate copolyurethanes and copolycarbonates from two kinds of benzoquinonyl glycol were prepared based on 2‐(duroquinonyl)‐propan‐1,3‐diol. The oxidized polymer is stable. When the fully reduced polymer in solution is exposed to air the durohydroquinonyl residues are oxidized to the quinone form while the less substituted hydroquinonyl glycol residues remain stable in the reduced form. There is thus prepared polymer with oxidized and reduced groups alternating along the chain.
Effects of substituents on chain‐transfer reactivities of p‐substituted cumenes in radical polymerization of p‐substituted styrenes
Authors: Yamamoto Tadahiro , Otsu Takayuki 
Published: April 2003

AbstractIn order to study the effects of the substituents in both substrate and attacking radical on the chain‐transfer reactivities of nuclear‐substituted cumenes toward substituted polystyryl radicals, the polymerizations of p‐substituted styrenes in the presence of p‐substituted cumenes were carried out with α,α′‐azobisisobutyronitrile as an initiator at 60°C, and their chain‐transfer constants were determined. The relative chain transfer reactivities of p‐substituted cumenes toward given p‐substituted polystyryl radicals did not follow the Hammett equation, but were correlated with the modified Hammett equation, log(k/k0) = pρ + γER, which was proposed by the present authors for evaluating the substituent effects in radical reactions. On the other hand, the relative reactivities of poly‐(p‐substituted styrene) radicals toward given p‐substituted cumenes were correlated by the Hammett equation. Thus, it was concluded that the effects of the substituents in substrate cumene depended upon the contributions of both polar and resonance factors, while those in attacking polystyryl radical depended upon only a polar factor.
Polymerization of β‐cyanopropionaldehyde. IV. Polymerization by the adducts of β‐cyanopropionaldehyde with triethylaluminum
Authors: Kobayashi Kazukiyo , Sumitomo Hiroshi 
Published: April 2003

AbstractAdducts (X, Y, and Z) between triethylaluminum and β‐cyanopropionaldehyde (CPA) have been prepared and characterized. It was found that an equimolar amount of triethylaluminum undergoes Grignard type addition reaction with aldehyde group of CPA to give aluminum alkoxide and that another equimolar quantity of triethylaluminum undergoes coordination with the nitrile group of CPA (adduct X, in which the molar ratio of CPA to aluminum is 1:2). The coordinated triethylaluminum in adduct X may be changed to aluminum alkoxide by the addition of further equimolar amount of CPA (adduct Y, molar ratio = 1:1); on the other hand, heating at 130°C affords mixtures of aluminum aldimine and aluminum ketenimine structures (adduct Z, molar ratio = 1:2). From the cryoscopic measurement, adduct Z may be regarded as a coordinated polymer joined through bridged structures I and II.
magnified imageIn the polymerization of CPA at −78°C, the stereoregularity of the resulting poly‐(cyanoethyl)oxymethylene was found to increase in the order: X < triethylaluminum < Y < Z. The polymerizations with triethylaluminum, X, and Y are considered to be initiated by NCCH2CH2CH(C2H5)OAl(C2H5)2. The degree of association of the species may influence the stereoregularity of the polymer.
Syntheses and reactions of functional polymers. XLII. Preparation and use of polymers having N‐hydroxy‐succinimide unit in the chain
Authors: Akiyama Masayasu , Narita Mitsuaki , Okawara Makoto 
Published: April 2003

AbstractStyrene‐maleic anhydride alternating copolymer was converted to N‐hydroxymaleimide‐styrene copolymer by reaction with hydroxylamine in pyridine at room temperature. The conversion was more than 90%. From this copolymer, N‐acetoxy‐ or N‐benzoyloxymaleimide‐styrene copolymers were derived by action of acetic anhydride or benzoyl chloride in dimethylformamide at room temperature. Acylation of several primary amines was carried out effectively by use of these N‐acyloxyimide‐styrene copolymers. The reaction of the acetylated copolymer with diethylamine at room temperature afforded N‐hydroxyimide copolymer.
Polymerization of β‐cyanopropionaldehyde. V. Anionic polymerization initiated by benzophenone–alkali metal complexes
Authors: Sumitomo Hiroshi , Hashimoto Kazuhiko 
Published: April 2003

AbstractAnionic polymerization of β‐cyanopropionaldehyde was studied with use of benzophenone‐monosodium, ‐disodium, and ‐dilithium complexes as initiators. The resulting poly(cyanoethyl)oxymethylene was compared with that obtained by cationic and coordinated initiators previously reported. Polymer of higher stereoregularity but lower molecular weight was formed in the present system. The marked influence of the initiator concentration on the polymer yield and stereoregularity is explained on the basis of the difference in the degree of association of the alcoholate ion pair, i.e., the associated ion pair may form stereoregular polymer and the nonassociated or less‐associated ion pair may form a large amount of amorphous atactic polymer. The initiation with benzophenone‐dialkali metal complex was found to be bond‐formation type. Chain transfer with active hydrogen of β‐cyanopropionaldehyde frequently occurs.
Graft polymerization of styrene on lithiated poly(2,6‐dimethyl‐1,4‐phenylene ether)
Authors: Chalk A. J. , Hoogeboom T. J. 
Published: April 2003

AbstractStyrene has been grafted onto poly(2,6‐dimethyl‐1,4‐phenylene ether) (I) with the use of lithiated I as an initiator. In benzene solution, solvent metalation resulted in some polystyrene homopolymer. In tetrahydrofuran, however, only graft copolymer was formed. By forming a derivative with trimethylchlorosilane and examining by NMR, it was possible to establish the proportion of lithium scavenged by impurities, the amount of polymeric lithium which reacted with styrene, and the amount which did not. The chain length of the grafted polystyrene was also calculated. No crosslinking was found, except where a high ratio of lithium to styrene resulted in some unreacted ring‐metalated polymer. In this case only, reaction with trimethylchlorosilane causes some crosslinking.
Photodegradation of copolymers of methyl methacrylate and methyl acrylate at elevated temperatures
Authors: Grassie N. , Torrance B. J. D. , Colford J. B. 
Published: April 2003

AbstractFour methyl methacrylate—methyl acrylate copolymers with molar ratios, MMA/MA, of 112/1, 26/1, 7·7/1, and 2/1 have been photodegraded at 170°C by 2537 Å radiation. The changes which occur in the molecular weight of the copolymers are typical of a random scission process and from these and volatilization data the extent of chain scission during the course of the reaction has been calculated. The pattern of volatile products is the same as that previously obtained in the thermal reaction at 300°C although there are a number of differences in detail. For example, only one in ten of the methyl acrylate units is liberated as monomer compared with one in four in the thermal reaction and the ratio CO2/chain scissions is considerably greater than the strict 1/1 ratio observed in the thermal reaction. Zip lengths are also very much greater in the photo reaction. These minor differences between the two reactions have been accounted for in terms of the mechanism previously presented to account for the thermal reaction, bearing in mind the differences in the temperature (170 and 300°C) at which the two investigations were carried out.
Relationship between reduction of ceric ion with poly(vinyl alcohol) and graft copolymerization
Authors: Ogiwara Yoshitaka , Uchiyama Masahiro 
Published: April 2003

AbstractVarious poly(vinyl alcohol) samples were preliminarily subjected to oxidation treatment with sodium hypochlorite, and the reduction of ceric ion and subsequently initiation in the graft copolymerization in the system containing methyl methacrylate were investigated. The reduction behavior of ceric ion could be subdivided into three parts, each of different reaction rate. In the initial stage of the reaction, there was observed rapid cleavage of the backbone chain of poly(vinyl alcohol) with ceric salts. The amount A of cleavage was proportional to the amount of ceric ion reduced at the initial fastest rate for various samples of different extents of oxidation; cleavage of 1 mole required ca. 10 moles of reduction of ceric ion. Higher carbonyl contents of the sample caused increased A. Graft polymerization was carried out in the same system with the addition of the monomer. The amounts of grafted chains produced were determined, and approximately one mole of grafted chains was obtained for per mole of cleavage. The copolymer is concluded to be blocklike in structure. The contribution of the carbonyl groups in poly(vinyl alcohol) sample to the initiation of the polymerization should be emphasized.
High‐pressure studies of polymerization in sulfur
Authors: Vezzoli Gary C. , Dachille Frank , Roy Rustum 
Published: April 2003

AbstractBy x‐ray and optical studies of thermally quenched products and by differential thermal analysis under pressure the effect of high pressure on the melting and polymerization of sulfur has been investigated to 31 kb and 500°C. At least four different liquid fields have been identified. DTA experiments indicate that pressure shifts the 159°C polymerization transition first toward higher temperatures and then toward lower temperatures until it finally coincides with the melting point at a pressure of about 0.7 kb. The depolymerization temperature was found by the same technique to increase with increasing pressure up to 0.4 kb. A liquid P—T boundary that may constitute the higher‐pressure extension to the depolymerization transition has been traced up to 7.5 kb and 480°C. A very sharp, practically temperature‐independent reaction in the liquid state has been located at about 9 kb extending from the liquidus to at least the limits of the apparatus at about 450°C. Evidence has been found for a possible second‐order phase transformation extending from about 10 kb at 400°C to the liquidus at approximately 360°C.
Alternating copolymerization of polar vinyl monomers in the presence of zinc chloride. I. Propagation and initiation of the copolymerization of acrylonitrile with styrene copolymer
Authors: Yabumoto Shigeru , Ishii Kiyoshi , Arita Koichiro 
Published: April 2003

AbstractCopolymerization of acrylonitrile with styrene spontaneously occurred on addition of zinc chloride without addition of any other radical initiator. The composition of the copolymer approached that of strictly alternating copolymer as zinc chloride added to the copolymerization system increased. The significance of the apparent monomer reactivity ratios of this copolymerization system was studied from a kinetic point of view, and it was shown that the monomer sequence distribution is indicated by the apparent monomer reactivity ratios. Further, equations which represent the relation between the apparent monomer reactivity ratios and Q,e values at a given salt concentration were derived. These equations reasonably accounted for the decrease of the apparent monomer reactivity ratios of the copolymerization of acrylonitrile with styrene in the presence of zinc chloride and the behavior of the other acrylonitrile copolymerization systems in the presence of zinc chloride. The initiation step of the spontaneous radical copolymerization of acrylonitrile with styrene in the presence of zinc chloride was explained by a cross‐initiation mechanism.
Radiation‐induced solid‐state polymerization of derivatives of methacrylic acid. II. Postirradiation polymerization of octadecyl methacrylate
Authors: Bowden M. J. , O'Donnell J. H. 
Published: April 2003

AbstractOctadecyl methacrylate (mpc ≈ 12°C.) polymerized readily in the solid state in the temperature range −30 to +12°C. after gamma irradiation at −196°C. The initial rate of polymerization and the “limiting” conversion increased with radiation dose and temperature. The temperature dependence of the rate corresponded to an “apparent” activation energy of 20 kcal./mole. Difficulties were experienced with polymerization during separation of the polymer from residual monomer, but these were minimized by using low radiation doses and a hot, selective solvent. The maximum conversion achieved was 70%. The polymer was crosslinked, even at low conversions.
Dehydration kinetics and glass transition of poly(acrylic acid)
Authors: Eisenberg A. , Yokoyama T. , Sambalido Emma 
Published: April 2003

AbstractThe kinetics of dehydration and decarboxylation as well as the glass transition temperature as a function of anhydride content were measured for poly(acry1ic acid). It was found that the glass transition of PAA is of the order of 103°C and increases with increasing anhydride content, reaching an extrapolated value of 140°C for the pure linear anhydride. Anhydride formation is a firstsrder reaction, as is also decarboxylation, the latter being much slower than the former. The rate constants are for dehydration, ka = 2.5 × 109 exp {−26000/RT}; for decarboxylation, kd = 2.9 × 108 exp {−27000/RT}. Anhydride formation occurs primarily by an intramolecular process.
Properties of swollen block copolymer elastomers
Authors: Cooper Stuart L. 
Published: April 2003

AbstractThe linear polyester—urethane block copolymer Estane is soluble in solutions having a solubility parameter of about 10.5. In benzene—methanol mixtures having solubility parameters sufficiently above and below 10.5, it is possible to swell this polymer to a quasi‐equilibrium state. For samples swollen to the same swelling ratio, those in the more polar swelling medium display lower tensile properties. This indicates that, although swelling involves solvation of both the associated rubbery polyester and aromatic urethane segments, the aromatic segments function primarily as quasi‐crosslinks which lead to enhanced physical properties. This is in agreement with previous observations on the mechanical properties of the unswollen elastomer.
Anionic graft polymerization of methacrylonitrile on potassium starch alkoxide
Authors: Tahan Menashe , Zilkha Albert 
Published: April 2003

AbstractThe anionic graft polymerization of methacrylonitrile on potassium starch alkoxide in dimethyl sulfoxide was studied. Factors affecting the graft polymerization such as monomer and alkoxide concentrations as well as temperature were investigated. The yield of the graft polymers was found to increase with alkoxide concentration, and it was possible to incorporate all the starch into graft polymer. On increasing the monomer concentration the graft polymer yield increased to a flat maximum. At the higher monomer concentrations, the efficiency of monomer in giving graft polymer decreased due to increased homopolymer formation. The composition of the graft polymers varied with increasing monomer concentration, graft polymers having about 40–65% of grafted starch were obtained. With increasing temperature (10 to 60°C), the yield of graft polymer decreased, there was more homopolymerization, but the amount of starch incorporated in the graft remained constant. The structure of the graft polymers was deduced from hydrolysis of the starch backbone of the graft polymers by dilute mineral acid and the determination of the molecular weights of the grafted side chains, and from oxidation by periodic acid, which showed the extent of grafting at the secondary hydroxyl groups. These results have shown that by anionic graft polymerization it is possible to obtain graft polymers having more densely packed grafted side chains of relatively low molecular weights than those obtained previously by free‐radical graft polymerization.
Dilute solution studies of nitrogen‐substituted polyurethanes
Authors: Beachell H. C. , Buck Jean C. Peterson 
Published: April 2003

AbstractA high molecular weight linear polyurethane was prepared by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4‐phenyl isocyanate). Varying amounts of the labile carbamate protons of the polyurethane backbone were substituted by a number of groups of varying length and composition. The resultant grafted or nitrogen‐substituted polyurethanes were then studied viscometrically in both polymer solvent and in a polymer solvent—nonsolvent mixture. The configuration of the nitrogen‐substituted polyurethane was found to be dependent upon the number and length of pendent branches.
Anionic graft polymerization of methyl methacrylate on starch and dextrin
Authors: Cohen Eliahu , Zilkha Albert 
Published: April 2003

AbstractThe anionic graft polymerization of methyl methacrylate on the potassium alkoxide derivative of starch or dextrin in DMSO was studied. The effects of monomer and alkoxide concentrations as well as temperature were investigated. The yield of graft polymer increased with increasing alkoxide concentration. With increasing monomer concentration and with increasing temperature the extent of homopolymer formation increased. The composition of the graft polymers was found to depend on the reaction conditions. Graft polymers having about 10–40% poly(methyl methacrylate) were obtained. There were quantitative differences in yield of isolated graft polymer between starch and dextrin and these were ascribed to differences in the solubility properties of the carbohydrates. Evidence on the structure of the graft polymers and on the mechanism of the graft polymerization was obtained from acid hydrolysis of the graft polymers and determination of the molecular weights of the cleaved side chains.
Properties of PVC. I. Properties of PVC films prepared by casting and by precipitation
Authors: Maláč Jiří , Šimu̇nková Eva , Zelinger Jiří 
Published: April 2003

AbstractThis investigation compares the properties of PVC films prepared both by casting from tetrahydrofuran solution and from samples obtained by precipitation with properties of samples from the original PVC. The differences in properties are explained on the basis of solvent residues remaining in the samples even after tempering at higher temperatures and after extremely long times of drying. Attention was given to the difficulties caused by this fact, namely, in observing the influence of molecular weight and of distribution of molecular weights of fractions on PVC properties. Reasons were given for the retention of the tetrahydrofuran by PVC.
Sulfur modification of polyethylene surfaces. II. Modification of polyethylene surfaces with fuming sulfuric acid
Authors: Olsen Douglas A. , Osteraas A. Jean 
Published: April 2003

AbstractPrevious work has shown that atomic sulfur irreversibility modifies polyethylene, presumably through an insertion reaction into carbon—hydrogen bonds with formation of surface thiol groups. The thiol groups were then oxidized to sulfonic acid surface groups, which were further reacted chemically as shown by wettability measurements. In this work the thiol group was bypassed and the surface sulfonic acid groups were obtained by exposing the polyethylene surface directly to fuming sulfuric acid. The sulfonic acid groups were reacted further. Critical surface tension values identical with those in the previous work with atomic sulfur were obtained, thus substantiating the previous work.
Silyl celluloses: A new class of soluble cellulose derivatives
Authors: Klebe J. F. , Finkbeiner H. L. 
Published: April 2003

AbstractTwo general methods for the silylation of cellulose have been developed. Silyl amides undergo silyl—proton exchange reactions with cellulose in polar solvents leading to displacement of 80–90% of the hydroxyl protons by silyl groups. The same products are obtained by reaction of the corresponding chlorosilanes with cellulose in pyridine; however, di‐ and trifunctional impurities present in commercial chlorosilanes have to be removed by scavenging with a carbohydrate in order to avoid crosslinking. Cellulose derivatives with trimethylsilyl, dimethylphenylsilyl, methyldiphenylsilyl, and γ‐cyanopropyldimethylsilyl substituents have been prepared by both methods. The properties of the new soluble polymers are largely dependent on the nature of the silyl substituents. The silyl celluloses exhibit a relatively high degree of hydrolytic stability; methyldiphenylsilyl cellulose is hydrolytically stable even under severe conditions.
Anionic polymerization of cyanoacetylene (propiolnitrile)
Authors: Wallach J. , Manassen J. 
Published: April 2003

AbstractCyanoacetylene can be polymerized into linear polymers at low temperatures by anionic initiators. The polymers are brown to black amorphous powders, soluble in polar organic solvents. Their molecular weights are of the order of several thousands and the presence of the acidic acetylenic hydrogen does not seem to be an inhibiting factor in polymerization. Some general features of the polymerization and the products obtained are discussed. It is possible to synthesize copolymers with acrylonitrile, which show spectral and solution properties intermediate between those of the two homopolymers. The difference in structure between the materials obtained after pyrolysis of polyacrylonitrile and polycyanoacetylene is discussed.