bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phenylene sulfide polymers. III. The synthesis of linear polyphenylene sulfide
Authors: Lenz Robert W. , Handlovits Carl E. , Smith Harry A. 
Published: April 2003

AbstractLinear polyphenylene sulfide has been synthesized by the condensation polymerization of alkali metal salts of p‐halothiophenols. The monomers investigated included the lithium, sodium and potassium salts of p‐bromothiophenol and the sodium salts of p‐fluoro‐, p‐chloro‐, p‐bromo‐, and p‐iodothiophenol. The mass polymerizations of these monomers were carried out below the melting points of the salts and appear to involve a solid state reaction. Rate measurements were made on the polymerization of these monomers in pyridine and on a model of the propagation reaction. In both cases, the order of reactivities of the sodium salts was I > Br > F ∼ Cl, and in the polymerization reaction, the order of reactivities of the alkali metal salts of p‐bromothiophenol was K < Na < Li. Comparison of the rates of the polymerization and model reactions indicates that the reactivities of all functional groups were essentially identical for the iodo and bromo derivatives. However, this comparison indicated that for the chloro and fluoro derivatives, the polymer chain endgroups were more reactive than the monomers. This effect, termed preferential polymer formation, has been verified for the polymerization of sodium p‐fluorothiophenoxide by the determination of unreacted monomer after the polymerization. Complete control of side reactions which lead to chain termination has not as yet been achieved for these condensation polymerization. Linear polyphenylene sulfide is kinetically stable in air and nitrogen up to 400°C. In nitrogen, a residue forms, representing approximately 50% of the original weight of the polymer, which is kinetically stable up to 900°C.
Polymerization induced by ionizing radiation at low temperatures. II. Effects of change of phase and heterogeneity on the polymerization of styrene and 2,4‐dimethylstyrene
Authors: Chen Catherine S. Hsia 
Published: April 2003

AbstractThe radiation‐induced polymerizations of undiluted styrene and of 2,4‐dimethylstyrene have been studied in the solid, partially solid, and completely liquid states. The results may be compared with solution polymerizations covering a similar temperature range reported in the previous paper.1 In addition to the interesting information obtained from the rate data for the solid phase, decidedly unusual effects of temperature on rate have been found by studying the systems in the vicinities of the melting points. For styrene, in the solid state (below −30.5°C.), the rate increases with temperature (ΔEa = 6–7 kcal./mole), having a maximum value when the system is partially solid. The rate drops rapidly above the melting point to a minimum, and then rises in a normal manner with temperature (ΔEa = 9–10 kcal./mole). For 2,4‐dimethylstyrene, in the solid monomer (−120 to −65°C.), the rate increases with temperature (ΔEa = 1 kcal./mole), having, like styrene, a maximum value at the melting point where the system is a solid–liquid mixture. The rate drops precipitously above the melting point. In the liquid state, the rate also increases with temperature (ΔEa = 1 kcal./mole). Similar effects have been observed in the polymerization of styrene–benzene and styrene–ethylbenzene mixtures. Enhanced rates have also been observed at the melting temperatures of these mixtures.
An experimental verification of gel network formation theories
Authors: Scott Kenneth W. 
Published: April 2003

AbstractPrecise sol fraction determinations over the range 0.07–1% have been made on milled natural rubber crosslinked with varying amounts of the quantitative crosslinker, dicumyl peroxide. The benzene‐soluble sol fraction was determined following an initial acetone extraction to remove the nonrubber, soluble reaction products of the crosslinking. The milled natural rubber had a viscosity‐average to number‐average molecular weight ratio close to that of a random or most probable distribution of molecular weights. The sol fraction dependence on the amount of crosslinking has been compared with the predictions of gel network formation theory. The agreement between theory and these experimental results is good, both as to the form of the molecular weight distribution and the number average molecular weight. This agreement establishes the validity of calculation of either the number of crosslinks or the molecular weight distribution from sol fraction measurements when the other is known. The extent of permanent molecular scission that might occur during the crosslinking reaction was also determined from these data. The ratio of permanent molecular scissions to crosslinked units introduced is not significantly different from zero, and at the 95% confidence level this ratio can be said to be less than 0.0048. A number of simple, rapid methods for estimating molecular weight distributions from sol fraction–crosslinking studies are described.
Higher‐order transitions in poly(4‐methyl‐1‐pentene)
Authors: Rånby B. G. , Chan K. S. , Brumberger H. 
Published: April 2003

AbstractDilatometric data for the glass transition temperature Tg of poly(4‐methyl‐1‐pentene) (PMP) have been extended to more crystalline samples and rendered more precise. Tg is definitely shown to decrease with increasing degree of crystallinity, an effect which tentatively is related to increasing free volume of the amorphous part of the polymer as the less dense crystalline phase increases and pulls apart the polymer chains in the amorphous regions. Tg is determined to be 14 ± 2°C. for 78% crystalline PMP, and 25 ± 2°C., for amorphous polymer. The existence of a higher‐order transition at 125 ± 10°C. is confirmed by x‐ray measurements and ascribed to transverse chain segment motion.
Diffusion in polymers: Optical techniques
Authors: Barker R. E. 
Published: April 2003

AbstractOptical techniques have been applied to study gas diffusion in poly(methyl methacrylate) and Lexan polycarbonate resin[poly(diphenyl‐2,2‐propane carbonate)] for temperatures ranging from 20°C. to the glass transition temperatures. One method consists of observing the movement of a sharp colored diffusion boundary which occurs when certain radical scavenging gases (e.g., O2, I2) penetrate a polymer which has been exposed to high energy irradiation. The theoretical basis and physical interpretation of the moving boundary are discussed. In essence, the color center concentration (produced by irradiation) is greater than the normal equilibrium concentration of scavenger molecules in the polymer so that the latter are trapped before they can move very far inward. The result is approximately a step‐function distribution of the remaining color centers. For O2 penetration into Lexan below Tg, D (cm.2/sec.) ⋍ 0.014 exp {7100 cal./mole/RT}. This relation accounts for the effect of O2 partial pressure on the penetration rate. For O2 penetration into PMMA, below Tg, an activation energy of 10 kcal./mole was observed. A spectrophotometric method was used to measure the uptake of J2 vapor in polycarbonate films. The data indicate a large change (∼50 kcal./mole) in apparent activation energy near 114°C. Several possible applications of the moving boundary technique are mentioned and the results of its use to investigate the effect of stress on the diffusion rate in the polycarbonate are presented. Tensile stresses near the yield point produce a two‐fold increase in D, whereas compressive stresses of comparable magnitude cause only a slight reduction.
Anionic polymerization of styrene (thermodynamics)
Authors: Bywater S. , Worsfold D. J. 
Published: April 2003

AbstractThe polymerization of styrene initiated by butyllithium in hydrocarbon solvents at elevated temperatures has been studied. Measurable amounts of monomer remained in equilibrium with the polymer in the temperature range covered (100–150°C.). The equilibrium concentrations were found to differ in the two solvents benzene and cyclohexane, but the calculated free energies of the polymer–monomer systems were the same after corrections had been applied for the different heats of solution. From the free energy data the heat and entropy of polymerization of styrene were calculated and found to agree with the calorimetric values.
Mechanical behavior of high polymers under deformations of different time function, type, and magnitude
Authors: Becker G. W. , Rademacher H.‐J. 
Published: April 2003

AbstractA report is given of some investigations of the mechanical behavior of high polymers under deformations of different time function, type, and magnitude. For a plasticized polyvinyl chloride the time‐dependent Young's modulus and the time‐dependent extension compliance were measured in the main relaxation region of the material. The relation between these two characteristic quantities given by the theory of viscoelasticity could be confirmed by using a simple approximation formula. The stress relation behavior of polystyrene under longitudinal and torsional strain was measured. From the corresponding time‐dependent moduli the Poisson ratio was calculated by use of the classical relationship and another one given by Schwarzl. Both calculations agree and give the expected monotonic increase of the Poisson ratio from 0.33 to 0.5 for the transition from the brittle to the rubbery state of the material. The relaxation behavior at larger extensions was investigated on polyethylenes of different crystallinities and on vulcanized rubbers having different filler contents. In the case of the filled rubbers measurements were carried out at strains up to 700%. For both series of materials the effects of strain and time were found to be factorable. In the case of the polyethylenes an appropriate strain function was developed on the basis of the Mooney‐Rivlin theory. For the filled rubbers the stress–strain equations given in literature are insufficient if the whole range of deformations is considered. An appropriate empirical function is given.
On the kinetics of propylene polymerization
Authors: Kohn E. , Schuurmans H. J. L. , Cavender J. V. , Mendelson R. A. 
Published: April 2003

AbstractThe kinetics of propylene polymerization catalyzed by a commercial sample of highly activated titanium trichloride and diethylaluminum chloride have been investigated. Polymerizations were carried out at various temperatures, pressures, and catalyst concentrations, and reaction rates were determined by a gasometric technique. The concentration of metal—polymer bonds was measured by quenching aliquots of the reaction mixture with methanol‐O‐t and radioassaying the polymer. The rates were found to decrease with time while the concentration of metal—polymer bonds increased. These results were interpreted in terms of two exchange reactions of the active sites, one which leads to an inactive site, and another which produces a different active site. With the aid of a kinetic model based on this mechanism, number‐average and weight‐average molecular weights were calculated and were compared with values obtained from fractionation, osmometry, and viscometry.
Measurements on the degree of crosslinking of high‐conversion post‐gelation methyl methacrylate—methylene dimethacrylate copolymers
Authors: Hwa Jesse C. H. 
Published: April 2003

AbstractThe degrees of crosslinking of three post‐gelation high‐conversion copolymers were measured by γ‐irradiation, extraction, and swelling experiments. The copolymers containing 0.2, 0.5, and 1.0 mole‐% of the crosslinker were prepared by suspension polymerization at 60°C. with a free‐radical catalyst. The degree of effective chemical crosslinking for the parent copolymers was calculated by correlating irradiation dose with extractables data after Shultz and the efficiencies of effective crosslinking were 40, 35, and 27% for the three copolymers, respectively. Based on related data by other workers, the low effective crosslinking efficiencies were due partly to incomplete polymerization of some crosslinkers on both ends and partly to wastage of crosslinks by intramolecular cyclization. On correlating the extractables data with the backbone molecular weight of the irradiated and extracted gels after Horikx, similar crosslinking efficiencies were obtained. A new technique has been shown to obtain the latter information by hydrolyzing the copolymer with 80% sulfuric acid under specific conditions and reesterifying the hydrolyzed intermediate with diazomethane. The effective chemical crosslinking of the irradiated and extracted gels, (ve)ir, were calculated from the crosslinking efficiency and extractables data. The degree of effective crosslinking, (ve)sw, for the parent as well as the irradiated gels were calculated from swelling data by means of Flory's swelling equation. It was found that the apparent value of (ve)sw for a given polymer decreased when a better solvent was used in the swelling. This finding was interpreted to be due to failure to correct the polymer‐solvent interaction parameter X1, that was used in the swelling equation, for concentration dependence. The aim of this work was to ascertain the validity of the swelling equation with respect to the prediction of (ve)sw. On comparing (ve)ir with (ve)sw, the latter being determined in benzene (X1 = 0.439), the ratios (ve)sw/(ve)ir for the three parent copolymers were between 9 and 10. A large part of the discrepancy was believed to be due to the presence of permanent chain entanglements which acted like physical crosslinks. (ve)sw/(ve)ir for the corresponding irradiated and extracted gels decreased sharply, and all appeared to approach an apparent common limit of about two at large irradiation doses. The theoretical limit should be one. Since the theory of rubber elasticity by James and Guth would require the limit of (ve)sw/(ve)ir to be 0.5 by the present scheme, Flory's theory on which the swelling equation was based seemed to be preferable. This work, however, could not distinguish Flory's theory from a slightly different theory by Hermans.
Role of polymer–catalyst bond in coordinated anionic polymerization of diolefins
Authors: Orr R. J. 
Published: April 2003

AbstractThe variations in the microstructure of polydiolefins made with alkali metal catalysts can be adequately explained in terms of the nature of the bond between the metallic catalyst and the growing polymer chain. This bond, in alkali metal polymerization, is not a resonance hybrid of ionic and covalent states, but is a tautomeric equilibrium of covalent bonds and ion pairs. The size of the equilibrium constant is one of the factors controlling the microstructure of the final polymer. An additional factor is the degree of p character of the covalent bond. Variations in microstructure between polyisoprene and polybutadiene can be attributed to differing proportions of ion pairs. Similarities between Ziegler‐Natta and alkali metal catalysis are shown. Some predictions of relative catalytic activity of alkali metals were shown to correspond to observed reactions.
Copolymeres séquencés obtenus par polymerisation anionique
Authors: Champetier Georges , Fontanille Michel , Sigwalt Pierre , Korn Anne‐Claudine 
Published: April 2003

AbstractL'amorçage de la polymérisation du 1–2 dihydronaphtalène et de la 2‐vinylpyridine par réaction de transfert électronique à partir de composés d'addition du sodium avec des carbures polycycliques a conduit à la formation de “polymères vivants.” Ceux‐ci pouvant amorcer en particulier la polymérisation du styrolène, et les ions polystyrolène(−) amorçant d'autre part la polymérisation de ces deux monomères, ceci permet d'obtenir des copolymères constitués par un grand nombre de séquences alternées pour les couples vinylpyridine/styrolène et 1–2 dihydronaphthalène/styrolène. Une purification très poussée des monomères, de l'initiateur et du solvant a été réalisée sous vide sur des hydrures métalliques et des films de sodium, ce qui a permis d'éliminer presque complètement les agents terminateurs de chaîne. Les polymérisations ont été effectuées sous la tension de vapeur du solvant dans un appareil soigneusement vidé et dégazé au préalable. Les homopolymères éventuellement présents ont été séparés par extraction sélective. Le rendement en copolymère séquencé n'est pas inférieur à 90% pour des copolymères renfermant cinq séquences. La viscosité intrinsèque des copolymères renfermant des proportions équivalentes des deux monomères est beaucoup plus faible que celle que l'on pourrait attendre, par suite d'une incompatibilité entre les polymères.
Specific heat of synthetic high polymers. X. Isotactic and atactic polypropylene
Authors: Wilkinson Raymond W. , Dole Malcolm 
Published: April 2003

AbstractThe specific heats of isotactic and atactic polypropylene have been measured over the ranges −14 to +211°C. and −55 to +204°C., respectively. In both cases, the samples were annealed at about 140°C. and the measurements repeated, but a slight thermal degradation prevented the results from the second heating from having additional significance. Isotactic polypropylene shows no glass transition in the range studied; the only transition observed is the melting transition. From the enthalpy—temperature curve for a measured fraction of crystallinity of 0.60, the heat of fusion of completely crystalline isotactic polypropylene was calculated to be 35 cal./g. This value is intermediate between previously published values of 15 and 62 cal./g. and in fair agreement with the value of 44 cal./g. calculated from pressure—melting point data. Atactic polypropylene shows a marked glass transition at −12°C. and two small first‐order transitions at 70°C. and at 155°C. The value for the Δcp per mole of chain atoms at the glass transition of 2.4 is in reasonable agreement with the theoretical value of 2.97 derived by Wunderlich from the Hirai‐Eyring theory of liquids. The small transition at 155°C. is attributed to an isotactic or syndiotactic content, either as impurity or as isotactic or syndiotactic segments in the atactic chains. The transition at 70°C. is tentatively attributed to the melting of heterotactic sequences. Infrared measurements indicate that the atactic polypropylene contained a few per cent of isotactic material while from the heat of melting about 1% was estimated.
Structure of melanins and melanogenesis
Authors: Nicolaus R. A. , Piattelli M. 
Published: April 2003

AbstractMelanin from Sepia officinalis is a natural high polymer present in the ink sack of the animal as calcium and magnesium salt. Sepiomelanin loses carbon dioxide on heating and reacts with diazomethane yielding a methylated compound. With methanol and hydrogen chloride an ester is obtained. Analytical data suggest that polymerization occurs with the participation of a compound containing more hydrogen than 5,6‐dihydroxyindole and carrying a carboxyl group, probably dopachrome. Furthermore, pyrrole nuclei resulting from the breakdown of the benzenoid part of some indolequinone units are present in the pigment.
Prediction of the conformation of the chain in the crystalline state of tactic polymers
Authors: Natta G. , Corradini P. , Ganis P. 
Published: April 2003

AbstractThe postulate of geometric equivalence of the monomeric units of a tactic chain with regard to an axis (I) and the postulate that the conformation is such that the internal energy of the chain, considered as not subjected to external forces, is the lowest (II), can be applied to the prediction of the conformation in the crystalline state of chains of unknown configuration, as demonstrated by the application of these postulates to known structures. Postulate (I) leads easily to the prediction of the possible linear chain repetition groups for a succession of monomeric units of given absolute configuration. In the case of polypropylene, for instance, it can be easily shown that isotactic polypropylene should have a helicoidal chain conformation, whereas syndiotactic polypropylene should have a glide plane or a helix (associated with two‐fold axes perpendicular to the chain axis) chain conformation. The angles of internal rotation defining the actual conformation of tactic polypropylene chains can be predicted on the basis of postulate (II) through semiquantitative methods of minimization of the internal energy content.
Alternating copolymers having a stereoregular polyester structure
Authors: Natta G. , Mazzanti G. , Pregaglia G. F. , Pozzi G. 
Published: April 2003

AbstractIn the presence of catalysts acting through an anionic mechanism (alkyls or alcoholates of lithium), it was possible to obtain alternating crystalline copolymers of dimethylketene with some aromatic and heterocyclic aldehydes (having the general formula RCHO) consisting of macromolecules in which the repeating unit corresponds to the formula:
magnified image
Owing to the presence of an asymmetric carbon atom in the repeating unit of the products obtained, this copolymerization represents the first example of stereospecific synthesis of polyesters. The chemical structures of the copolymers obtained have been demonstrated by chemical and infrared analyses and by the identification of the products obtained by hydrogenolysis with LiAlH4. The preparation of alternating copolymers of dimethylketene with various aldehydes and the properties of the products are described. Furthermore a possible reaction mechanism according to which the two monomers are simultaneously coordinated to a molecule of the catalyst is proposed.
Quantitative determination of carboxyl endgroups in vinyl polymers by the dye‐interaction method
Authors: Palit Santi R. , Ghosh Premamoy 
Published: April 2003

AbstractThe possibility of quantitative estimation of carboxyl groups in polymers by the dyeinteraction method developed in this laboratory has been investigated. The benzene extract of rhodamine 6Gx from a buffer of pH 10 under specified conditions has been used as the reagent. The estimation has been made by colorimetric measurement at 515 mμ of the color developed by mixing a solution of the polymer in benzene with the reagent. Copolymers of styrene (or methyl methacrylate of vinyl acetate) with acrylic acid, methacrylic acid, crotonic acid, itaconic acid, or maleic anhydride at varying M1:M2 ratios in the 100:1 composition range have been prepared, and the monomer reactivity ratio r1 (which under such conditions becomes equal to the ratio of the mole‐per cent of carboxyl in the feed to that in the copolymer) has been determined. The result agrees fairly well with the value of r1 reported in the literature. This indicates that the proposed method is capable of estimating fairly accurately the carboxyl groups or endgroups present in a polymer chain.
La polymérisation des allylsilanes par catalyse et sous l'effet des rayonnements
Authors: Topchiev A. V. , Nametkin N. S. , Polak L. S. 
Published: April 2003

AbstractOn a étudié la polymérisation d'hydrures d'alcénoylsilanes variés en présence d'initiateurs ou de catalyseurs et au moyen d'irradiation par photons gamma et d'électrons. On a réalisé également la copolymérisation des hydrures d'alcénoylsilanes avec l'alcool et l'acrylonitrile. Certains des polymères et des copolymères se forment avec des rendements élevés et présentent des caractéristiques physico‐chimiques intéressantes. On a montré qu'entre 20 et 250° la polymérisation des hydrures d'alcénoylsilanes en présence d'initiateurs et sous des rayonnements se déroulait suivant un mécanisme par radicaux. Dans tous les cas étudiés la polymérisation peut se dérouler dans deux directions: (a) suivant la double liaison du radical allyle; (b) par utilisation de la liaison SiH de l'hydrure d'alcénoylsilane. La vitesse de polymérisation croǐt avec le nombre de groupements allyliques dans les hydrures d'alcénoylsilanes et dépend, dans le cas des monoallylsilanes, de la nature des substituants à l'endroit de l'atome de silicium.