bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear magnetic resonance studies of polymer solutions. I. Poly(methyl methacrylates)
Authors: Liu Kang‐Jen 
Published: April 2003

AbstractThe microscopic interactions of solvent with the diastereoisomeric units of isotactic and syndiotactic poly(methyl methacrylate) have been studied by high‐resolution nuclear magnetic resonance. The changes in chemical shifts in various solvents were compared with those of low molecular weight analogs, methyl acetate, and methyl propionate. These changes are caused mainly by the ring‐current effect, which has been found to be larger for the low molecular weight analogs than for the polymer. This is especially true when the protons on the polymer backbone are compared with the corresponding ones in the low molecular weight compounds. As one changes from a chloroform solvent to an aromatic solvent, the displacements of the chemical shifts of the polymer can be expressed as percentages of the corresponding shifts of methyl acetate. For syndiotactic poly(methyl methacrylate) in chlorobenzene, benzene, and α‐chloronaphthalene, respectively, the percentages are 82, 93, 75 for ester protons; 35, 29, 17 for the backbone methylene protons; and 18, 6.7, 0 for the backbone α‐methyl protons. For isotactic poly(methyl methacrylate) in chlorobenzene and benzene, respectively, the percentages are 71, 76 for the ester protons; 41, 38 for the backbone methylene protons; and 41, 32 for the backbone α‐methyl protons. These results are discussed in terms of the local stereochemistry of the polymer systems. The exploitation of procedures of this sort in revealing details of polymer behavior in solution indicates dramatic possibilities for future investigations.
Theory of polymer fractionation efficiency
Authors: Huggins Maurice L. 
Published: April 2003

AbstractThe theory of the equilibrium distribution of a mixture of different size species of a polymer between two liquid phases is reviewed and used as a basis for the calculation of the dependence of fractionation efficiency on overall concentration, interaction coefficient (hence, choice of solvent and temperature), average molecular weight, and the spread of the molecular weight distribution in the polymer. The special case of a single type of polymer in a single solvent, for which the polymer–solvent interaction coefficient is independent of concentration, is dealt with quantitatively. The ultimate aim is to make it possible to determine systematically the optimum solvent (or mixture of solvents), temperature, and overall concentration for fractionation of a given type of polymer, having a given average molecular weight and molecular weight distribution, considering practical limitations, e. g., the total volume which can conveniently be handled and the time required to achieve a sufficiently close approach to equilibrium.
New initiator for the low‐temperature polymerization of vinyl chloride
Authors: Borsini Giancarlo , Nicora Carlo 
Published: April 2003

AbstractThe polymerization of vinyl chloride initiated by a mixture of tetraethyllead and ammonium ceric nitrate has been studied at low temperatures. As (NH4)2Ce(NO3)6 was insoluble in vinyl chloride, methanol was added. Methanol was found to be not only a solvent for the catalyst but also to affect the polymerization reaction by complexing the ceric ions. A reaction order of −0.4 with respect to methanol was calculated. Rate curves were shown to decrease fairly rapidly with time, suggesting a decrease of the rate of production of radicals during the polymerization. The apparent activation energy obtained from polymerizations carried out at different temperatures was 7.4 kcal./mole. A maximum in average polymerization rate on changing the ceric salt concentration was attributed to reactions of radicals with ceric ions. Orders of 1.2 with respect to (NH4)2Ce(NO3)6 and 0.9 with respect to Pb(C2H5)4 were obtained. An increase in molecular weight was observed during the polymerization; this could be accounted for by the decreasing rate of production of radicals and by the transfer process involving one component of the initiator system. The results indicate that the mechanism of formation of radicals is described by the equation:
Vinyl polymerization. 178. Copolymerizations of p‐substituted phenyl vinyl sulfides
Authors: Tsuda Kazuichi , Kobayashi Shigeru , Otsu Takayuki 
Published: April 2003

AbstractThe copolymerizations of p‐substituted phenyl vinyl sulfides (M2) having OCH3, CH3, H, Cl, and Br substituents with styrene and methyl methacrylate (M1) and their intercopolymerizations at 60°C. were studied. From the results of copolymerizations with styrene and methyl methacrylate, the monomer reactivity ratios and the Q2e2 values were determined. For example, the Q and e values for unsubstituted phenyl vinyl sulfide were 0.45 and −1.26 in the copolymerization with methyl methacrylate. This result indicated the importance of the 3d orbital resonance between the sulfur atom and the adjacent carbon atom in the transition state of copolymerizations. The relative reactivities of these monomers toward the polymer radicals were found to be correlated with the Hammett σ constants of the substituents. In the intercopolymerizations of these monomers, it was also found that the relative reactivities followed the Hammett equation approximately.
Statistische methoden zur ermittlung der verteilung der molekülgrössen in hochpolymeren systemen aus experimentalergebnissen der fraktionierten fällung. IV. Berücksichtigung der polydispersität der fraktionen
Authors: Hosemann R. , Schramek W. 
Published: April 2003

AbstractThe relation between the most important statistical parameters of the number frequency h(P) determining the kinetics of polymerization and the molecular weight distribution H(P) is explained. The polydispersity gw of H corresponds to the non‐uniformity of H(= U). For calculating gw, a correction formula (22) is derived which takes into account the averaged polydispersity α of the fractions. By this means, the asymmetry of h is also calculated. As explained in an earlier investigation, it is possible to determine the type of distribution function in the SWN step diagram. If this type is known, it is furthermore possible to calculate the correction quantity α according to the equilibrium theory of G. V. Schulz. The α unequivocally depends on the distribution function, the volume quotient φ of the sol and the gel, and on the parameter k of the function type, if the number X of the fractions lies between 5 and 20 and the single fractions show approximately the same mass. As an example, it is shown that then the quantity k, which is characteristic for the type of the reaction, can be calculated from the experimental data with an error of only a few per cent, and α2 has a value below 0.1. Although, with a fractionation column, α2 generally shows lower values, in favorable cases even down to 0.03, the uncertainty in the determination of the parameter k is, for many practical reasons, generally not lower compared with the uncertainty observed in precipitation fractionations using our new method.
Polymer reactions. III. Structure of polypropylene hydroperoxide
Authors: Chien James C. W. , Vandenberg E. J. , Jabloner H. 
Published: April 2003

AbstractOxidation of polypropylene introduces hydroperoxide groups into the polymer. Infrared spectroscopy has determined that more than 90% of these groups are intramolecularly hydrogen bonded. The sequential lengths and sequence distributions of these neighboring hydroperoxides were estimated from the electronic spectra of the polyenes derived from the polypropylene hydroperoxide by two methods: (1) reduction, acetylation, and pyrolysis, and (2) reduction and dehydration. The results indicate that all the hydroperoxide groups are present in sequences of length two and greater. Intramolecular hydrogen abstraction during oxidation could account for the formation of these neighboring hydroperoxides.
Thermal decomposition products of polyethylene
Authors: Tsuchiya Yoshio , Sumi Kikuo 
Published: April 2003

AbstractDecomposition products of polymers have been determined by many investigators, but the results are often conflicting because of difficulties in analyzing a large number of products. A comprehensive analysis of the volatile thermal decomposition products of high‐density polyethylene has been made with the latest techniques in gas chromatography. The formation of products is explained on the basis of free‐radical mechanism. The predominant process in the formation of volatiles appears to be intramolecular transfer of radicals, in which isomerization by a coiling mechanism plays an important role in determining the relative quantities of each product.
Cationic polymerization of formaldehyde in liquid carbon dioxide. Part I
Authors: Yokota Hisao , Kondo Masatsune , Kagiya Tsutomu , Fukui Kenichi 
Published: April 2003

AbstractA cationic polymerization of formaldehyde which gave a high molecular weight polymer was studied in liquid carbon dioxide at 20–50°C. In the polymerization without any catalyst both the rate of polymerization and the molecular weight of the resulting polymer increased rapidly with a decrease in the loading density of the monomer solution to the reaction vessel, and also increased with an increase in the initial monomer concentration. From these results it was concluded that the initiating species could be ascribed to an impurity contained in the monomer solution. Both the rate of polymerization and the degree of polymerization of the polymer also increased with rising temperature. The carboxylic acid added acted as a catalyst in the polymerization because of increase in the polymer yield, the molecular weight of polymer formed, and the number of moles of polymer chain with increasing dissociation constant of acid used. It was concluded that the polymerization in liquid carbon dioxide proceeded by a cationic mechanism. Methyl formate had no influence on the polymerization, but methanol and water acted as a chain‐transfer agent.
Infrared spectroscopic studies of polystyrene emulsion polymers: Effect of oxidation during polymerization
Authors: Shaw J. N. , Marshall M. C. 
Published: April 2003

AbstractInfrared spectroscopy was empolyed to study the nature of the structural changes which occurred through oxidation during the emulsion polymerization of styrene. Aliphatic carboxylic, amino, and phosphate emulsifiers and hydrogen peroxide and potassium persulfate initiators were empolyed for polymer preparation. In addition, a polystyrene dispersion prepared in the absence of any emulsifier or stabilizer was examined. Irrespective of the nature of the initiator–emulsifier combination employed, all of the polymer spectra revealed bands at 1705 and 1770 cm.−1. The band at 1705 cm.−1 was assigned in part to the carbonyl stretching mode of dimertic carboxylic acid, formed by oxidation, in the polystyrene chains. Absorption at 1770 cm.−1, which was very weak, was tentatively attributed to the carbonyl stretching mode of the monomeric form of this acid. The structure of the acid endgroup was not established, but the results obtained suggest that it was possibly a phenylacetic acid residue or a residue with a similar structure.
Effects of mercaptides on the butyllithium‐initiated polymerization of methyl methacrylate
Authors: Hirahara Takuji , Nakano Toyotoshi , Minoura Yuji 
Published: April 2003

AbstractThe effect of mercaptides on the butyllithium‐initiated polymerization of methyl methacrylate in toluene were investigated. The rates of polymerization were decreased by the addition of mercaptides, possibly owing to the formation of a relatively stabilized complex between the mercaptides and the active center of the polymerizing monomer. The stereoregularity was also affected by the addition of mercaptides. The effects increased in the order of increase in the bulk of the alkyl group of the mercaptides: n‐propyl < isopropyl < tert‐butyl < phenyl. The effects of mercaptides on the stereoregularity were larger than those of the analogous oxygen compounds. The concentrations of butyllithium and monomer had no effect on the stereoregularity.
Vinyl polymerization initiated by ceric ion reducing agent systems in sulfuric acid medium
Authors: Subramanian S. V. , Santappa M. 
Published: April 2003

AbstractPolymerization of the monomers, methyl acrylate (MA) and methyl methacrylate (MMA) was carried out in sulfuric acid medium at 15°C. With the redox initiator system, ceric ammonium sulfate–malonic acid. There was no induction period, and a steady state was attained in a short time. There was found to be no polymerization even after 1 hr. in the absence of the reducing agent R. The initiation was by the radical produced from the Ce4+–malonic acid reaction. The rate of monomer disappearance was proportional to [M]1.5, [R]0.5, and [Ce4+]0.3–0.5, and the rate of ceric disappearance was directly proportional to [R] and [Ce4+]. Chain lengths of the polymers were directly proportional to [M] and inversely to [R]1/2 and [Ce4+]1/2. The experimental results were explained by a kinetic scheme involving the following steps: (a) oxidation of the substrate to give the primary radical which reacts with Ce4+ to give the products, (b) initiation by the primary radical, (c) propagation, and (d) termination of the growing polymer radicals by the mutual type. For the polymerization of acrylonitrile (AN) by the redox system, ceric ammonium sulfate–cyclohexanone (CH), in sulfuric acid at 15°C., the scheme was modified to include linear type of termination by Ce4+, along with the mutual termination to explain the results especially under conditions with [Ce4+] ≥ [CH].
Polytetrazoles and polyaminotetrazoles
Authors: Dyer Elizabeth , Christie Peter A. 
Published: April 2003

AbstractPolyaminotetrazoles were obtained by the action of hydrazoic acid on solutions of polycarbodimides prepared from methylenebis(4‐phenyl isocyanate), toluene 2,4‐diisocyanate, 3,3′‐dimethoxy‐4,4′‐biphenylene diisocyanate, mesitylene diisocyanate, and hexamethylene diisocyanate. The polyaminotetrazoles, which were soluble only in concentrated sulfuric acid, had inherent viscosities of 0.12–0.78. Polymerization of the disodium salts of bistetrazoles with α,ω‐dihalides gave polytetrazoles without the secondary amine linkage in the chain. The bistetrazoles, used were methylenebis(5‐tetrazole) and 5,5′‐p‐phenylenebistetrazole, and the dihalides were α,α′‐dichloro‐p‐xylene, 1,2‐dibromoethane, and 1,4‐dibromobutane. The polytetrazoles were soluble in concentrated sulfuric acid and had low inherent viscosities, 0.08–0.17. Thermogravimetric analyses showed that marked degradation of both classes of polymers occured at 250–300°C.
Crystalline titanium dichloride—an active catalyst in ethylene polymerization. II. Polymer structure, polymerization variables, and scope
Authors: Benning C. J. , Wszolek W. R. , Werber F. X. 
Published: April 2003

AbstractPolymerization of ethylene with ball‐milled titanium dichloride leads to a completely linear polymer with terminal unsaturation corresponding to approximately one carbon–carbon double bond per molecule. Polymerization rate is first‐order in both monomer and catalyst concentration at 140°C. Due to a thermal deactivation of the catalyst, the polymerization rate falls sharply with temperature above 180°C. Propylene and butene‐1 will copolymerization with ethylene in this system, propylene more efficiently than butene‐1. Evidence for copolymerization of trans‐2‐butene, but not of the cis‐isomer or of isobutene, in trace concentrations is presented. Propylene is homopolymerized to a product low in isotactic content. The significance of the structural and (limited) kinetic data in terms of the mechanism of polymerization are discussed.
Effect of polymer structure on ease of hydrogen abstraction by cumyloxy radicals
Authors: Lal Joginder , McGrath James E. , Board Robert D. 
Published: April 2003

AbstractVulcanizates of five elastomers having different chemical structures were prepared with recipes comprising dicumyl peroxide. Cumyl alcohol/acetophenone molar ratios were determined by gas–liquid chromatography (GLC) on acetone extracts of vulcanizates. Diphenyl ether was used as the internal standard. The ease of hydrogen abstraction by cumyloxy radicals, reflected by the cumyl alcohol/acetophenone ratio, decreases in the following order: cis‐1,4‐polyisoprene > poly(propylene oxide) > poly(vinyl n‐butyl ether) > poly‐1‐heptene ≅ EPR. This order is in qualitative agreement with the order based on calculated relative rates of hydrogen abstraction by methyl and tert‐butoxy radicals and literature data on oxygen absorption of some of these polymers as a result of hydrogen abstraction by peroxy radicals.
Reactions of living polystyrene with difunctional nitriles to produce specifically placed grafting sites
Authors: Gervasi J. A. , Gosnell A. B. , Woods D. K. , Stannett V. 
Published: April 2003

AbstractGraft polymers have been synthesized with two equal length branches and one or two branches of a different length or composition. The first step was a coupling reaction of living polystyrene with a difunctional nitrile. The product was hydrolyzed to form a ketone‐containing backbone. Subsequently another sample of living polystyrene or of poly‐2‐vinylpyridine was added to the backbone to form the graft. Anionic polymerization was used for the synthesis of backbone and side chains, so all of the products are well defined. The products and reaction sequences also serve as models for a general synthesis of well‐defined comb‐shaped polymers, in which the length of the backbone, and the number, length, and spacing of the side chains may be controlled.
Polycondensation rate of poly(ethylene terephthalate). I. Polycondensation catalyzed by antimony trioxide in presence of reserve reaction
Authors: Stevenson R. W. , Nettleton H. R. 
Published: April 2003

AbstractThe technique of G. Challa was employed for following the reaction of oligomeric poly(ethylene terephthalate) in the presence of antimony trioxide. This technique is based on determining the changes in glycol and bishydroxyethyl terephthalate concentrations with time at a given temperature. The linear trimer of ethylene terephthalate, prepared from terephthaloyl chloride and bishydroxyethyl terephthalate, was employed as starting material. Rate constants were not corrected for catalyst concentrations. The reaction was studied over the temperature range 221–251°C. The equilibrium constant kp/k′ for the polycondensation reaction
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was found to be 0.36. Observed reaction rates were low but faster than in the uncatalyzed reaction studied by Challa. At 231°C. the values of the rate constants found in the presence of 0.025% by weight antimony trioxide were kp = 0.151.mole−1 hr.−1 and k′ = 0.33 l./mole‐hr., and the redistribution rate constant was kR = 0.11 l./mole‐hr. From data at four temperatures the estimated activation energies were Ep = 29 kcal. and ER = 24 kcal. The polycondensation rates were low compared with rates calculated from literature data. A mechanism to explain the difference requires that bishydroxyethyl terephthalate endgroups compete successfully with oligomer endgroups for antimony trioxide catalyst and that the bishydroxyethyl terephthalate catalyst product is unreactive in polymerization.
Study of Ziegler‐Natta catalysts. Part II. The liquid phase and polymerization activity of the catalyst
Authors: Kollár L. , Simon A. , Osváth J. 
Published: April 2003

AbstractThe polymerization activity of the Ziegler‐Natta catalysts is significantly affected by the aluminium alkyls in the liquid phase. These may be studied provided the solid phase of the catalyst remains unchanged. Part of these aluminum alkyls is adsorbed on the surface of the solid phase. It is possible to displace one type of alkyls by another one or to elute it from the adsorbed layer. This last affects the polymerization rate.
Preparation of ion‐selective membranes from crosslinked copolymers of styrene and p‐vinylbenzenesulfonic acid
Authors: Brydges T. G. , Dawson D. G. , Lorimer J. W. 
Published: April 2003

AbstractIon‐selective membranes similar to those described by Graydon and Stewart [J. Phys. Chem. 59, 86 (1955)] were prepared by improved methods involving copolymerization of styrene, n‐propyl‐p‐vinylbenzenesulfonate, and divinylbenzene (DVB) with subsequent hydrolysis of the ester. Both the highly reactive ester and DVB were purified by column chromatography and were well characterized by their infrared and proton magnetic resonance spectra. For preparation of membranes about 25% by weight of N,N‐dimethylformamide (DMF) was included with the vinyl monomers in the polymerization mixture. Thermal polymerization was initiated by benzoyl peroxide, and membranes were formed in special molds of two types. In one type a free surface of the mixture was exposed, while in the other the mixture filled the mold. The DMF in the fresh membranes was replaced with aqueous KOH by diffusion, and hydrolysis was then carried out. By this method hydrolysis times were decreased from several days to a few hours. Capacity, water content, and thickness were determined for all membranes, and density, swelling in salt solutions, and Young's modulus were measured for selected membranes. The Vermaas‐Hermans‐Flory theory of polyelectrolyte gels was found to account satisfactorily for the swelling properties and water content of these membranes, the solvent interaction parameter χ1 increasing with increasing volume fraction of polymer from 0.7 to 1.0 at zero external salt concentration and up to 1.8 for membranes deswollen in 1M KCl. No differences in average water contents for given densities of fixed charge and crosslinking were observed with (1) different molds, (2) commercial or pure DVB, and (3) a swelling agent (DMF) or no swelling agent. The results in general indicate that the state of the membrane at a given temperature and pressure can be specified by any two of the parameters: degree of ionization per unit volume of an average structural unit, concentration of crosslinking agent, and degree of swelling. Young's modulus decreased markedly with increasing water content, but data were not sufficiently extensive or precise to permit a quantitative treatment.
Studies of polymers from cyclic dienes. IV. Determination of the structure of polycyclopentadiene
Authors: Aso Chuji , Kunitake Toyoki , Ishimoto Yoshikazu 
Published: April 2003

Abstract3,4‐ and 3,5‐Dimethylcyclopentenes were prepared as model compounds of the structural unit in polycyclopentadiene. These two isomers give characteristic NMR spectra. The assignment based on the 60 Mc./sec. spectrum was further confirmed by decoupling experiments on the 100 Mc./sec. spectrum of 3,5‐dimethylcyclopentene. By comparing the NMR spectra of these compounds with that of polycyclopentadiene methods were developed for estimating the polymer structure from the relative peak area of the methine–methylene and olefinic protons. Polycyclopentadiene obtained with Friedel‐Crafts catalysts at lower temperatures was shown to be composed mostly of the 1,4 and 1,2 structures. Polycyclopentadiene obtained with several Ziegler‐type catalysts possessed comparable amounts of both structures, contrary to the earlier proposals.