bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural transformations in poly‐L‐hydroxyproline and poly‐o‐acetyl‐L‐hydroxyproline
Authors: Sasisekharan V. 
Published: April 2003

AbstractThe structural modifications in poly‐L‐hydroxyproline and poly‐O‐acetyl‐L‐hydroxyproline as revealed by x‐ray diffraction and optical activity studies are discussed. Like the proline polymer these also exhibit polymorphism. The possible structures of the various forms in relation to the various forms of poly‐L‐proline are also mentioned.
Interpolymerization of acrylonitrile and vinylidene chloride in tert‐butyl alcohol
Authors: Hill E. H. , Caldwell J. R. 
Published: April 2003

AbstractTrue interpolymers of acrylonitrile and vinylidene chloride were prepared with the use of tert‐butyl alcohol or a mixture of tert‐butyl alcohol and water as the polymerization solvent. Analysis of the polymers showed that the ratio of the two monomers in the copolymers was very close to the initial monomer ratio. The polymers were tested for homogeneity by their solubility in acetone or acetonitrile.
Size distribution and gelation in condensation polymers with one unsymmetric reactant
Authors: Giacomo Armand Di 
Published: April 2003

AbstractEquations are derived which give the molecular weight distribution and the gelation characteristics of a condensation polymer which involves four kinetically different (but otherwise equivalent) polymerization steps in its preparation. Their use is illustrated by application to the system, toluene‐2,4‐diisocyanate and a polymeric primary glycol. Comparison is made with the published expressions for the case of “equal reactivity of all functional groups.”
Dilute solution study of poly(n‐lauryl methacrylate) in an ideal solvent
Authors: Lee H. T. , Levi D. W. 
Published: April 2003

AbstractDue to abnormally small root‐mean‐square end‐to‐end distances for poly(n‐lauryl methacrylate) fractions in an ideal solvent reported previously, investigation of this polymer in another ideal solvent was carried out. Phase separation studies indicated that in n‐amyl alcohol the θ‐temperature is 29.5°C., and viscosity and light‐scattering measurements were made in this temperature. Dimensions in this solvent were found to be in the expected range. K values in the two ideal solvents are compared.
Viscosity‐temperature relationships for dilute solutions of cellulose derivatives. III. Solutions of an incompletely substituted cellulose nitrate
Authors: Moore W. R. , Edge G. D. 
Published: April 2003

AbstractViscosities of dilute solutions of six fractions of a 12.2% N cellulose nitrate, covering a molecular weight range of 68,000 to 224,000, in representative solvents have been determined at temperatures between 18 and 60°C. Values of Q in the expression η =AeQ/RT vary with concentration c and molecular weight M in a manner similar to that previously observed with solutions of ethyl cellulose, but the variation of A with c and M appears to be rather more complex in most cases. Intrinsic viscosities can be related to Q, A, the absolute temperature T, and M. With good solvents negative temperature coefficients of [η] are similar in magnitude to those obtained with cellulose trinitrate, but with poorer solvents the temperature coefficients are smaller. Negative temperature coefficients appear to be primarily due to decreases in the value of (ro2/M) where ro2 is the mean square unperturbed end‐to‐end distance of the chains. The contribution of the swelling factor α appears to be greater with acetone as solvent, and in all cases values of α3 are greater than those obtained with the trinitrate, suggesting that the chains are less stiff. Values of the exponent a in the expression [η] = KMa decrease with increasing temperature suggesting decreasing chain extension, except in the case of nitrobenzene in which association is probable. The values of a also suggest that the chains are less extended than those of the trinitrate.
Quaternization kinetics of poly‐4‐vinylpyridine
Authors: Fuoss Raymond M. , Watanabe Masamoto , Coleman Bernard D. 
Published: April 2003

AbstractThe quaternization of poly‐4‐vinylpyridine by n‐butyl bromide in tetramethylene sulfone and in propylene carbonate at 25, 50, and 75°C. begins as a simple second‐order reaction with a rate constant approximately equal to that for 4‐picoline. As the quaternization proceeds, the rate decreases due to the charge which is being built up on the polymer, and the quaternization of the last half of the pyridine side groups occurs at about one‐tenth the initial rate. The kinetics can be summarized by the equation:

where x is concentration of bromide ion at time t, A is initial concentration of butyl bromide, B is initial concentration of polymer in monomoles per liter, k0 is the initial rate constant for quaternizing isolated pyridine groups, k2 is the rate constant for quaternizing pyridine groups both of whose neighbors are already quarternized, and α is a parameter which depends on temperature, initial concentrations, and on the intrinsic rate constants. A simple graphical method is described which permits evaluation of k0, k2, and α from the data. At 25° in tetramethylene sulfone, k0 = 5.0 × 10−4 l./mole min., k2 = 5 × 10−5, and α/A = 2 × 10−4.
Molecular distributions in polycondensations involving unlike reactants. VII. Treatment of reactants involving nonindependent groups
Authors: Case L. C. 
Published: April 2003

AbstractThe molecular distributions involving the use of reactants with nonindependent groups are considered in this paper. The distributions are shown to depend on the relative amounts of reactant in the unreacted state, the once‐reacted state, and the twice‐reacted state. The kinetic considerations determining these relative amounts are reviewed for several different types of reactants, including cyclic acid anhydrides and certain diisocyanates. The general linear distribution for a condensation polymerization of two reactants is derived. The calculations for nonindependent groups in other types of distributions are briefly indicated. The molecular distributions arising in polyurethane condensations, particularly those of chain extension, are slightly specialized forms of the general distribution. The methods of this paper are the only available tools to deal with these distributions. It is shown that a diacid or glycol can be treated as a reactant having nonindependent groups. The kinetic calculations for such a unit are seen to be the same as for a cyclic acid anhydride. Somewhat improved distributions for polymers of such units are thus made available.
Polymerization in the solid and near‐solid states
Authors: Bamford C. H. , Jenkins A. D. , Ward J. C. 
Published: April 2003

AbstractSome recent observations on the behavior of radicals in solid and near‐solid media are reviewed. Polymerization in a matrix of swollen polymer molecules is first discussed, and this is followed by a consideration of the photochemical polymerization of crystalline methacrylic acid as studied by electron spin resonance, optical microscopy, and kinetics methods. The behavior of radicals produced on crystal faces was also investigated, and it is suggested that their behavior may be explained by assuming that their energies of interaction with the surface cover a wide range and that, on raising the temperature, propagation and termination reactions occur. Two types of polymer were produced by bulk polymerization of the crystals, one clear and glassy, the other fibrous or granular; both were amorphous and not oriented, and it was concluded that the crystal lattice exerted no influence on the configuration of the polymer produced from it. The reaction seems to proceed by a phase boundary process rather than by propagation through the lattice.
Macromolecules with groups of high reactivity
Authors: Kern W. , Schulz R. C. , Braun D. 
Published: April 2003

AbstractReactions on the reactive groups of macromolecular substances (e.g., cellulose) have long been known, even since before the structures of macromolecules were understood. H. Staudinger carried out numerous reactions with macromolecules, maintaining the degree of polymerization constant, in order to substantiate the macromolecular structure of the substances investigated (polymeric‐analogous reactions). During the last fifteen years reactions with macromolecules have been investigated because it was desirable to compare the chemical diversity of low molecular weight compounds with the corresponding chemical diversity of macromolecular compounds. These endeavors bring forth materials which supplement the numerous macromolecular substances which are produced and used as materials for plastics, and therefore these materials should have as low reactivity and high stability as possible. Objectives are given for the preparation of macromolecules with a large variety of groups. From these objectives it is evident that, as in low molecular weight chemistry, macromolecular substances which possess functional groups of high reactivity are suitable as starting materials. Some of these which have been known for a long time but have been investigated only in recent years are polyaldehydes (polyacroleins and polymethylacroleins), polyacyl halides such as polyacryl chlorides and polyvinylsulfonyl chlorides and fluorides, and, most recently, polymeric organometallic compounds such as poly‐p‐lithiumstyrene. The reactions with these macromolecules are described and the properties of the resulting new polymeric substances are given.
Synthèse des copolymeres greffés à partir des polymères ayant subi l'action des radiations ionisantes. III. Etude comparée du greffage sur le polyéthylène et sur le polypropylène
Authors: Chapiro Adolphe 
Published: April 2003

AbstractOn a comparé les cinétiques du greffage de l'acrylonitrile sur un polyéthylène basse pression et sur un polypropylène, tous deux prépaés à l'aide du même catalyseur. Les deux polymères étaient préirradiés avec des rayons gamma en présence d'air et chauffés ensuite sous vide dans le monomère à différentes températures. La cinétique du greffage sur le polyéthylène présente les mêmes caractères que ceux qui avaient été décrits dans les deux premières parties de cette étude relatives au greffage sur le polyéthyléne haute pression. Avec le polypropylène par contre, la cinétique est trè différente. La forme des courbes de conversion varie avec la dose de préirradiation. Pour les doses élevées, la réaction de greffage est d'abord très rapide mais s'arrête rapidement pour un taux de greffage limite. Ce taux limite est d'autant plus petit que la dose de préirradiation est plus élevée. Les relations entre la vitesse de greffage d'une part et la dose et l'intensité de la préirradiation d'autre part sont différentes pour le polyéthylène et le polypropylène. II en est de m6me de l'influence de la température de greffage sur la réaction. Par ailleurs la quantité d'homopolymkre (polyacrylonitrile) formee au cours de la réaction est beaucoup plus importante dans le cas du greffage sur le polypropylène. On montre que ces résultats peuvent être interprétés en admettant que la peroxydation radiochimique conduit principalement à des hydroperoxydes POOH dans le polypropylène et à des biperoxydes POOP dans le polyéthylène. Dans le cas du polypropyène, la réaction est en outre contrôlée par la vitesse de diffusion du monomère dans le film de polymére. D'autre part la différence entre les températures de fusion des cristallites du polyéthyène et du polypropylène respectivement permet de comprendre l'effet de la température de greffage sur la cinétique observée dans ces deux systèmes.
Quelques aspects de la cinétique de formation des copolymerères greffés
Authors: Sebban‐Danon J. 
Published: April 2003

AbstractDans la plupart des méthodes permettant la synthèse des copolymères greffés (ou ǎ blocs) ǎ partir d'une solution d'un polymère An déjà formé dans un monomère B, on produit simultanément le copolymère greffé AnBm et l'homopolymère Bm, dans un milieu contenant l'homopolyměre An. Lorsque les deux homopolyměres An et Bm sont incompatibles—ce qui est la règle pour la plupart des polymères—la réaction de greffage est perturbée. En effet, une séparation en deux phases se produit alors. Dans le présent travail, on a étudié les modifications cinétiques, introduites par cette séparation en deux phases, au cours du greffage radiochimique du styrolène sur le polyisobutylène. On discute les résultats obtenus par d'autres auteurs avec d'autres couples polymère‐monomère qui conduisent également à une séparation en deux phases.
Grafting onto cellulosic macromolecules through chain transfer to mercaptoethyl side chains. I. Experimental procedure and results
Authors: Chaudhuri D. K. Ray , Hermans J. J. 
Published: April 2003

AbstractCellulose acetate films, cellophane, and cellulose model fibers are mercaptoethylated by an addition reaction with ethylene sulfide. A monomer is polymerized in the presence of the cellulose derivative obtained, so that chain transfer to SH groups can take place. Evidence for grafting is presented. The effect of reaction time, catalyst concentration, and monomer concentration is given in the form of tables and graphs. The initial rate of grafting is shown to be proportional to the square root of the catalyst concentration, and, roughly, to the concentration of the monomer. Rates of grafting of the order of 10–15 wt.‐%/hr. are easily obtained.
Quelques observations sur la polymérisation radiochimique de l'acrylonitrile
Authors: Bernas A. , Bodard M. 
Published: April 2003

AbstractOn sait que certains des caractères de la polymérisation en masse de l'acrylonitrile disparaissent quand la réaction est conduite en phase homogène et que l'occlusion des radicaux macromoléculaires n'intervient pas. Nous avons voulu examiner si ces mêmes caractères pouvaient s'atténuer ou disparaître par une élévation de température, vitesse d'initiation constante. Nous avons observé: (1) que l'exposant α de la relation V1 = KV'1 diminue régulièremcnt quand la tempèrature augmente et (2) que l'énergie d'activation globale décroit notablement an‐dessus de 60°C. Ces résultats s'interprètent bien en supposant qu'au dessus de cette température I'occlusion devient beaucoup plus faible; cependant elle n'est pas encorc négligeable à 100°C ainsi qu'en atteste le post‐effet observé.
The mechanism of free radical polymerization in the solid state
Authors: Adler G. , Ballantine D. , Baysal B. 
Published: April 2003

AbstractThe solid state polymerization of acrylamide and related monomers has been studied using the tools of electron spin resonance and optical microscopy. The data indicate that the reaction involves free radicals which do not terminate in the usual fashion. The reaction apparently involves a nucleation mechanism in which crystalline defects and the buildup and release of internal stresses affect the rate of reaction.
Recent developments in polymerization by an alternating intra‐intermolecular mechanism
Authors: Butler George B. 
Published: April 2003

AbstractRecent developments in polymerization by an alternating intra‐intermolecular mechanism are summarized and discussed briefly. The methods used to prove the structure of typical polymers, which in turn established the mechanism of polymerization, are reviewed. A study of larger ring formation by Marvel and Garrison is also summarized. Ring of sizes from 7 to 21 members were formed from α‐diolefins in yields of from 4 to 25%. A study of certain unsymmetrical dienes has shown that cyclization occurs in yields up to 60%, but that gelation eventually occurs because of the difference in relative reactivities of the two olefinic double bonds. Copolymerization of certain 1,4‐dienes with certain olefins to produce linear copolymers containing six‐membered rings is discussed. In an effort to explain the strong driving force to close a six‐membered ring during polymerization of 1,6‐diolefins, a pronounced interaction between the double bonds, which can be represented by several resonance forms of the molecule, is proposed.
Photochemical modifications of high polymers by visible light
Authors: Oster Gisela K. , Oster Gerald 
Published: April 2003

AbstractMethods have been developed in our laboratory to induce oxidation—reduction reactions with visible light using dyes as sensitizers. Applying this general technique to high polymers one can photochemically crosslink or decrosslink a polymer by changing the oxidation state of certain groups. Thus, gelatin containing dichromate ion, a dye, and a compound which serves as an electron donor for the light‐excited dye only becomes crosslinked by visible light. This is due to the photoreduction of chromate ion to chromic ion, the latter crosslinking the polymer. Similarly polyacrylamide which is crosslinked by complexation with mercuric ion and which is sensitized will decrosslink rapidly with visible light due to photoreduction of mercuric ion to mercurous ion. Mercaptans are photooxidized in the presence of sensitizing dyes. Hence polymers containing thiol groups can be crosslinked by dye‐sensitized photooxidation. This process can be reversed by far ultraviolet light.
The effect of high pressure on the individual steps of free radical polymerization
Authors: Walling Cheves 
Published: April 2003

AbstractA study of the effect of pressure on the emulsion polymerization of styrene gives a value of ΔV‡ for chain propagation of −11.5 cc./mole, close to the value for the peroxideinitiated bulk reaction. Chain initiation and termination are both somewhat pressureretarded, the latter presumably because the reaction becomes diffusion‐controlled. Pressure has little effect upon the chain‐transfer constant of styrene–CCl4 or upon transfer with monomer in allyl acetate polymerization. However, the overall rate of allyl acetate polymerization is greatly accelerated, indicating that transfer is no longer degradative. Pressure retards the unimolecular decomposition of both di‐tert‐butyl peroxide and benzoyl peroxides, and some complications in these reactions are discussed as well as the principles governing the effect of pressure on radical reactions in general.
Synthesis and polymerization of epiperchloratohydrin
Authors: Radell Jack , Connolly Joseph W. 
Published: April 2003

AbstractEpiperchloratohydrin (I) was synthesized and polymerized. Although covalent perchlorates are known to be hydrolytically unstable, I dissolved in benzene could be rapidly washed with water without causing major hydrolysis. A simple method for dehydrating silver perchlorate by an azeotropic distillation was used. Compound I before and after polymerization was explosive and required special care.
Stereospecific polymerization of some polar vinyl monomers
Authors: Butler K. , Thomas P. R. , Tyler G. J. 
Published: April 2003

AbstractAnionic polymerization of N,N‐disubstituted acrylamides in hydrocarbon media is stereospecific and yields a new series of crystalline tactic polymers containing polar groups. These tactic polymers melt above 300°C. and have different solubilities from the atactic isomers. There are also differences in the rates of hydrolysis and infrared spectra. The presence of ethers in the polymerization lowers both the tacticity of the product and its molecular weight. A heterogeneous surface is not necessary for stereospecificity, and, in cases where monomer and initiator are soluble in hydrocarbons, the reaction is homogeneous throughout.
Principles of lignin growth
Authors: Freudenberg Karl 
Published: April 2003

AbstractSpruce wood lignin has molecular weight of the order of magnitude of 10,000–100,000. Furthermore, it is bonded, to a large extent, if not completely, with the polysaccharides of the wood. It is formed by enzymatic dehydrogenation of coniferyl alcohol I. The mesomeric forms II–IV of the radical produced stabilize themselves by combining together to form dimers, the largest proportion of which—owing to the preponderant occurrence of the form III—are quinone methides. The latter stabilize themselves intramolecularly, steric arrangements permitting, forming ethers like V and VI. In the case of the quinone methide VIII alone, an intramolecular stabilization is impossible; this methide is stabilized by addition of water or of a hydroxyl group of the carbohydrates. In the latter case, an etherlike carbohydrate compound is formed which contains a phenolic group and which can hence be incorporated into lignin on further dehydrogenation. Substance VIII can also add on coniferyl alcohol, substance V, or other phenols, and hence it condenses units without further loss of hydrogen (XII and XIII). All of the processes described thus far proceed automatically after the formation of the radicals. The new building units thus formed (V, VI, and other similar units) can also be welded together by renewed dehydrogenation or by the formation of more quinone methides which give rise to addition reactions. By means of this combination of dehydrogenative condensation with addition of phenols and alcohols to quinone methides formed intermediarily, lignin grows to a polymolecule, grafting itself in the process onto the polysaccharides. The path of formation of the molecule also explains the extraordinarily great differences between the oligomeric building units, although in the case of conifer lignin they all proceed from the one substance, coniferyl alcohol. The branching of lignin is explained by the addition reaction. The sequence of the units is fully random, since no matrix provides for a definite order.
Influence des rayonnements ionisants sur les systèmes polymérisables
Authors: Magat M. 
Published: April 2003

AbstractAprés un bref rappel des résultats essentiels concernant la polymérisation des monomères vinyliques induite par les rayonnements ionisant.s et procédant par un mécanisme radicalaire, on examine les trois domaines de recherches plus récents, à savoir: la production de polymères greffés, la polymérisation ionique et la polymérisation à l'état solide. C'est dans ce domaine que les progrès sont les plus spectaculaires et les problèmes à résoudre les plus complexes. Si au début, la possibilité de polymérisation à l'état solide paraissait restreinte à quelques monomères particuliers, il s'est révélé plus récemment que presque tous les monomères courants pouvaient être polymérisés à l'état solide, même à de basses températures. On examine successivement les preuves que la polymérisation a effectivement lieu à l'état solide, l'influence de l'état solide tant sur la vitesse globale que sur les vitesses partielles de propagation et de terminaison, ainai que les difficultés que soulève la détermination du mécanisme (ionique ou radicalaire) de ces polymérisations. Pour conclure, on examine le cas de polymérisations “explosives” des monomères solides et l'on montre qu'elles peuvent être interprêtées à l'aide de la théorie de Semenoff des explosions thermiques.
Polymerization and the low‐frequency electromagnetic field
Authors: Piccardi Giorgio , Cini Renato 
Published: April 2003

AbstractIn the present work, the effect of a low‐frequency electromagnetic field, 10kHz (in hertzian units), on the polymerization of acrylonitrile in aqueus solution is studied with a differential method. The experiments are performed on three standard acrylonitrile series of samples respectively placed: (1) in electromagnetic field; (2) in a screened space; (3) in unscreened space. The results, obtained by comparing the masses of the solid polymer in standard conditions, show: (1) an appreciable effect on the polymerization of acrylonitrile in an electromagnetic field of 10 kHz; (2) an effect due to the screen's acting on the natural electromagnetic field; (3) a significant correlation between the data obtained in the present work and the data of the chemical test P collected at the same time.