bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

Precise 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

Dilatometric 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

Optical 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

The 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

A 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

The 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

The 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

The 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

L'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

The 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

Melanin 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

The 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

In 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

The 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

On 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.
Viscoelastic properties of branched whole polymers. I. Calculation of relaxation times
Authors: Peticolas Warner L.
Published: April 2003

The calculations of the relaxation times of whole polymers has been extended to include the effect or branching. These relaxation times depend upon the weight average of the mean‐square radii, 〈R〉w, of the branched polymer molecules. It is proposed that this quantity may be obtained in a θ solvent from the equation [η] = 61/2ΦC〈R〉w, where [η] is the limiting viscosity number, Φ is a universal constant, and C = Kb, where b is the root‐mean‐square of the end‐to‐end distance of a submolecule and K is the ratio of the number of submolecules to the molecular weight. The constant C may be obtained from measurements of [η] and 〈R〉 on linear, monodisperse polymers. Equations are given by which the effect of branching and molecular weight distribution on rheological measurements may be calculated.
A study of the mechanism of interfacial polyamidation and polyesterification
Authors: Hodnett Ernest M. , Holmer Donald A.
Published: April 2003

The interfacial polyamidation reaction between phthaloyl chloride and piperazine and the interfacial polyesterification reaction between phthaloyl chloride and 4,4′‐isopropylidenediphenol were found to be second‐order at 0°C. Studies with C14‐labeled phthaloyl chloride and with piperazine in one case and with 4,4′‐isopropylidenediphenol in the other case showed no isotope effect. However, the interfacial monoamidation reaction between carboxy C14‐labeled benzoyl chloride and morpholine gave an isotope effect of 0.950. These results are interpreted, and a mechanism is proposed for the interfacial polycondensation reactions.
Statistische methoden zur ermittlung der verteilung der molekülgrössen in hochpolymeren polymolekularen systemen aus experimentalergebnissen der fraktionierten fällung. II. Mitteilung: Auswertungsmethoden
Authors: Hosemann R. , Schramek W.
Published: April 2003

Die messtechnisch bedingte Unkentnis des in polymolekularen Systemen vorkommenden höchsten Polymerisationsgrades Pe bedingt bei der konventionellen Auswertungsmethode nach der sogenannten summierenden Stufenkurve in der Errechnung der Standardabweichung ΔP eine grosse Unsicherheit. Diese Unsicherheit wird abgeschätzt und auf den aus ihr abzuleitenden Fehler in der Polydispersität g hingewiesen. Dieser Fehler wird als “Abbrucheffekt” bezichnet. Er wird in der III. Mitteilung ausführlich behandelt. Dahingegen vermittelt eine halbgraphische Auswertungsmethode nach Funktionstyp bei sachkundiger Anwendung gelegentlich schon Informationen, die auf wenige Prozent genau sein können. Dies wird an dem Beispiel einer realen Fraktionierung erläutert. Schliesslich wird eine neuartige statistische Auswertungsmethode unter Anwendung der Dirac'schen δ‐Funktion beschrieben, bei welcher die hypothesenfreien Informationen des Fraktionierungsexperimentes klar getrennt sind von obigen Unsicherheiten. Dies Methode verwendet ausschliesslich die 2k Informationen des Experimentes und eine wichtige Beziehung über die Natur der Fraktionen. Zur Erläuterung wird das Beispiel der nach der Gleichgewichtstheorie von Schulz vollständig durchgerechneten theoretischen Fraktionierung eines hochpolymeren, polymolekularen Systems mit acht annähernd äquidistanten Fraktionen discutiert.
Thermooxidative degradation of polyesters. A contribution to the study of degradation reactions of some types of linear polyesters
Authors: Gömöry I. , Mlejnek O. , Štímeľ J.
Published: April 2003

This report is part of an extensive investigation on thermal and thermooxidative degradation. The results of an analysis of the products formed during degradation of the glycol esters of phthalic, maleic, adipic and sebacic acids are discussed. The experiments were carried out in an apparatus especially devised for this purpose. The specimens were subjected to heat treatment at 200, 250, and 300°C. in a current of air for periods varying between 4 and 200 hr. The degradation products were selectively trapped and analyzed by classical methods and by paper chromatography. Some of the degradation products were determined quantitatively, others only qualitatively. Among the degradation products of all types of the polyesters studied were found the monomers, formaldehyde, acetaldehyde, formic and acetic acids, carbon dioxide, carbon monoxide, water and compounds of the type of hydroxyaldehydes, hydroxyacids, and aldehydic acids, which were not identified closer. Furthermore, among the degradation products of glycol adipate and glycol sebacate acids and aldehydes were found with three and more carbon atoms to the molecules. Benzoic acid is a specific product of the degradation of glycol phthalate, as well as cyclopentanone of glycol adipate. The qualitative composition of the degradation products changes little with change in temperature and duration of the experiment. The change in quantity with these factors is greater. From the quantitative standpoint the main degradation products are the monomers, carbon dioxide, carbon monoxide and water. A mechanism for the degradation is proposed which includes consecutive reactions (hydrolysis, esterification, and ressterification) leading to the formation of free endgroups and monomers on the one hand, and radical reactions of which the products are mainly oxidized substances of the structural units of the polymer, on the other.
Thermal stability of polydimethylsiloxane. II. Formation of stable complexes on basic active centers
Authors: Kučera M. , Láníková J.
Published: April 2003

Amphoteric hydroxides are found to possess a great ability to deactivate the “living” ends of polydimethylsiloxane molecules. They not only prevent depolymerization but also suppress the formation of crosslinks between polymer molecules (which is due to the oxidation of methyl groups). Deactivation of active centers can also be carried out by benzoic acid; however, this acid attacks siloxane bonds at elecated temperatures and promotes decreased molecular weight of polydimethylsiloxane. This undesirable decrease in molecular weight is not caused by benzoic acid only in polymers which originally contained basic active centers; it is found also in polymers without any “living” ends, whether these were removed by transformation into stable complexes or decomposed by heating at 150°C. (as in the case of SiOPBu4).
Elastic moduli of oriented polymers. II. (A1A2)n‐type polymers
Authors: Asahina M. , Enomoto S.
Published: April 2003

We have calculated the elastic moduli for (A1A2)n type polymers. Polyvinyl chloride is a model of a planar zigzag structure for the (A1A2)n type polymer, and the calculated value for E is of the magnitude of 1012 dyne/cm.2. As polyisobutylene, isotactic polypropylene and polyoxymethylene have helical structures, their E values are of the magnitude of 1011 dyne/cm.2. A polymer having a helical structure shows a smaller calculated value of E than that of polymers having planar zigzag structures.
Cyanoethyl and aminopropyl ethers of polyvinyl alcohol
Authors: Alexsandru L. , Opris M. , Ciocǎnel A.
Published: April 2003

The presence of free hydroxyls in polyvinyl alcohol presents a multitude of opportunities for changing the properties of this polymer, a fact which is of considerable theoretical and practical interest. The results are presented of a study of the incorporation of nitrile and amino groups in polyvinyl alcohol. Despite the fact that the cyanoethylation reaction has been described in the literature it is still insufficiently elucidated. The reaction was carried out in an organic medium. The present investigation is concerned with the effect on the extend of cyanoethylation of the chemical nature of the substance used as reaction medium, of the preliminary swelling of the polymer, of the molar ratio of the reactants, and of the reaction time. The relation between the degree of crystallinity of polyvinyl alcohol and its reactivity in the cyanoethylation reaction has been determined. It was found that with growth in crystallinity there is a fall in reactivity and in exent of cyanoethylation. It follows from this that the reaction takes place predominately in amorphous regions. Depending upon the degree of cyanoethylation, polyinyl alcohol changes its structure, being transformed into a rubberlike mass. The solubility of polyvinyl alcohol in water also falls with increasing cyanoethylation. Polyvinyl alcohol with 35–40% cyanoethylated hydroxyl groups is insoluble in water even on heating. On reducing the cyanoethylated Polymer, the polyaminopropyl vinyl ether is obtained.

The effect of the reaction medium, pressure, temperature, concentration, type of catalyst, etc. on the degree of reduction has been investigated. The greatest influence is exerted by the degree of cyanoethylation of the initial polymer. Polyvinyl alcohol having 30–35% of the hydroxyl group sin ether linkage with propanolamine has been synthesized. The polymer is insoluble in water and methanol, is partially soluble in acetone, benzene, and dimethylformamide and has the appearance of a rubbery mass.
Regarding the change of crystallinity and average crystallite size occurring at polycaprolactam filaments by the cold drawing process
Authors: Urbańczyk G. W.
Published: April 2003

Changes of crystallinity and average crystallite size which occur in polycaprolactam filaments during the cold drawing process are analyzed. The estimation of fiber crystallinity was carried out by use of the differential‐filtration x‐ray method. The crystallite size was evaluated on the basis of the broadening effect of Debye lines from x‐ray powder‐method diagrams and from the large identity period interferences obtained by small‐angle scattering patterns. The results obtained show that with the change of draw ratio the crystallinity and the average crystallite size also change. The highest values of crystallinity and average crystallite size were found at 375% nominal draw (315% real elongation). The total increase in crystallinity in comparison with the undrawn state of a filament is approximately 27%.
The chemistry of xylylenes. XIV. The moldability and thermal stability of poly(p‐xylylene) and related polymers
Authors: Errede L. A. , Knoll N.
Published: April 2003

Freshly prepared α‐poly(p‐xylylene) softens at 220–260°C. and then rehardens as it forms β‐poly(p‐xylylene). Consequently, homogeneous objects can be fabricated at this temperature range by simultaneous application of heat and pressure. This “moldable” poly(p‐xylylene), however, becomes nonmoldable within a week if allowed to age at room temperature. It is speculated that this change in moldability with aging at room temperature may be due to formation of tiny areas of crystalline α‐polymer which serve as seeds for rapid conversion from α‐ to β‐polymer before melt‐flow can occur in the critical temperature range of 220–260°C. of the heating cycle. The shelf life of the moldable polymer is increased considerably, however, by polymerization of the monomer in the presence of a molar equivalent of trialkylphosphines of trialkylphosphites. In vacuum, poly(p‐xylylene) has excellent thermal stability below 400°C., but in air, oxidative degradation is serious even at about 225°C. The moldability of p‐xylylene polymers is improved by copolymerization with a variety of olefinic and inorganic molecules, but the thermal stability, thermal oxidative stability, and sometimes the electrical properties of the resultant product are inferior to those of unmodified poly(p‐xylylene). These polymers appear to be resistant to degradation by γ‐irradiation.
Absolute rates in anionic copolymerization
Authors: Morton Maurice , Ells F. R.
Published: April 2003

A study has been carried out to determine the absolute values of the rate constants in the homogeneous anionic copolymerization of butadiene and styrene, initiated by alkyllithium. The approach used was to measure the rate of formation of disappearance of the styryl anion spectrophotometrically, using the absorption peak at 436 mμ. The solutions of butadienyl and styryl anions (in benzene) were prepared by reacting butyllithium with small amounts of butadiene or styrene, in a preliminary step, until the initiation reaction was complete. Subsequently, each of the anionic solutions was mixed with the opposite monomer, and the cross‐propagation reaction measured spectrophotometrically. It was found that the rate of the reaction of the styryl anion with butadiene was extremely rapid, being virtually completed in less than one minute at room temperature. On the other hand, the rate of reaction of the butadienyl anions with styrene was easily measurable at room temperature, being of the same order as the previously measured homopolymerization rates for butadiene. These measurements enabled a calculation of the following reactivity ratios: rB = 3, rS = .06. This very large difference in cross‐propagation rates can easily account for the “anomalour” behavior previously found by several investigators, wherein butadiene polymerized preferentially in a mixture with styrene, and which had been attributed to special “solvation” effects by the butadiene.
Analysis and properties of ethylene–propylene copolymers
Authors: Smith W. E. , Stoffer R. L. , Hannan R. B.
Published: April 2003

Copolymers of ethylene and C14‐labeled propylene were prepared with a metal‐oxide catalyst which polymerizes ethylene to a high density polymer. Methyl branches arising from the propylene were counted radiochemically and then related to the infrared absorption of films at 8.7 μ. This band was then used independently to determine methyl branching of a series of ethylene‐propylene copolymers that differed in density and stiffness. Both properties decrease in value with an increase in branching.
Relaxation phenomena in homopolymers and copolymers of ethylene and propylene
Authors: Kontos E. G. , Slichter W. P.
Published: April 2003

The physical properties of ethylene–propylene copolymers depend partly on the overall proportions of the monomers and on the arrangement of the two monomers within the polymer. The effect of composition upon the glass transition and related relaxation is reported, with comparisons drawn from dilatometry, dynamic mechanical loss, and measurements of nuclear magnetic resonance absorption. The relaxation times ranged from about 103 sec. to about 10−7 sec. The copolymers varied in composition from an ethylene: propylene mole ratio of 85:15 to a ratio of 16:84, and the homopolymers were also studied. The relaxation phenomena are interpreted qualitatively in terms of the expected temperature dependence of the spectra of frequencies of molecular motion.
Properties of ethylene–propylene copolymers and of terpolymers containing unsaturation
Authors: Natta G. , Crespi G.
Published: April 2003

The elastomeric properties of amorphous ethylene–α‐olefin copolymers have been described in previous papers, as well as the importance of both the homogeneity of composition of each macromolecule forming the raw polymer and the statistical distribution of the two comonomers. It has been observed that a narrow distribution of the molecular weights is very important with regard to the mechanical properties of the cured synthetic rubbers obtained from the ethylene–propylene copolymers, whereas a not too high average molecular weight is important as far as the processability is concerned. One of the most interesting properties of the ethylene–propylene copolymers is their good aging resistance which is due to the saturated nature of the polymeric macromolecules. It has been observed that these properties are substantially shown also by those terpolymers consisting predominantly of ethylene and propylene (or other α‐olefins), and in addition a small amount of a monomer whose molecule contains more than one double bond; on polymerization these last monomers yield monomeric units still containing a double bond. A great number of monomers are well suited for the production of terpolymers with a low degree of unsaturation, which is sufficient for the conventional vulcanization methods adopted for other rubbers, particularly for those containing a low degree of unsaturation. It is quite essential, in order to obtain good vulcanizable products, that the unsaturation is regularly distributed in all the macromolecules, and that in each of these they are distributed at random. Probably, the differences observed with various monomers depend primarily on the ability of each monomer and of the copolymerization system adopted to meet to these requirements. This is the reason why we shall discuss the properties of those products in which a considerable homogeneity of distribution has been achieved. The mechanical and dynamic properties will be related to the degree of unsaturation. The results obtained from the use of such terpolymers for the production of elastomers have demonstrated that the elastic, dynamic, and aging properties remain essentially the same as those for the ethylene–propylene copolymers when the degree of unsaturation does not exceed 2–3%, expressed as number of double bonds per hundred monomeric units.
Studies on grafting glycidyl methacrylate on polyvinyl chloride backbones
Authors: Ravve A. , Khamis J. T.
Published: April 2003

Graft copolymers of glycidyl methacrylate on polyvinyl chloride backbones were prepared by the free radical technique. Three types of backbones were used: (1) vinyl chloride homopolymer; (2) copolymer of vinyl chloride–vinyl acetate, 87:13; (3) copolymer of vinyl chloride–vinylidene chloride, 89:11. The grafting reactions resulted in products with lower intrinsic viscosities than the unreacted backbones. The graft copolymers were fractionated with the separation of glycidyl methacrylate homopolymers from the rest of the graft products. Unreacted backbones were separated through gelation of all the epirane‐bearing chains. Structure proof was conducted by chemical cleavage of the grafted side chains by reduction with LiAlH4 and through acid hydrolysis.
The hypochlorite oxidation of polyvinylacetophenone
Authors: Merrill Stewart H.
Published: April 2003

Polyvinylacetophenone can be oxidized by a special two‐step technique to poly(vinylbenzoic acid). The product is soluble in alkali and in many common organic solvents. Analytical studies on the product indicate that extra oxygenated functions and some scission occur along the chain. An explanation is offered for the crosslinking reaction which occurs when strong alkalinity is not maintained during the oxidation. A portion of the carboxyl groups can be converted to acid chloride for preparation of derivatives.
The role of symmetry in crystallization and polymerization phenomena
Authors: Ham George E.
Published: April 2003

Crystallization mechanisms are interpreted as processes in superimposition of molecules from random positioning in space. It is shown that at the melting point there are substantial restrictions on the number of configurations (i.e., ordering) available to molecules, and that this preordering is an important factor in crystallization, influencing melting point, entropy of fusion, and heat of fusion. The interpretation of the melting behavior of nylon 6, nylon 66, polypropylene, and linear polyethylene proceeds from these considerations. The polynuclear hydrocarbons are also considered in detail as prototypes for preordering effects in the melt.
Electron spin resonance studies of irradiated acrylamide and methacrylamide
Authors: Ueda Hisashi , Kuri Zenichiro
Published: April 2003

Electron spin resonance spectra of the irradiated monomers and polymers of both acrylamide and methacrylamide were studied. On thermal treatment, the spectra are changed both in their patterns and in intensity. The polymerization yield of these monomers after irradiation followed by the same thermal treatment as with that used for ESR samples was also studied. The radicals existing in the irradiated acrylamide are concluded to be a mixture of two kinds of radicals, one at the ends and the other in the middle of the polymer chain.
Investigation of the protective ultraviolet absorbers in a space environment. II. Photochemical studies
Authors: Schmitt Richard G. , Hirt Robert C.
Published: April 2003

Compounds which are effective in protecting materials from terrestrial ultraviolet radiation may, in the high vacuum of space, suffer loss both by evaporation and by photochemical degradation. The photochemical stability of the protective ultraviolet absorbers has been studied under extraterrestrial and terrestrial conditions using an AH‐6 high‐pressure mercury are to simulate sunlight above the earth's atmosphere. It was determined that the ultraviolet absorbers are considerably less stable in a space environment and that the loss in stability is due primarily to a higher quantum yield for the short wavelength ultraviolet radiation (below 3000 A.).
Proposed structures and models for polymers crystallized in bulk
Authors: Gruenwald G.
Published: April 2003

Since many publications have been concerned with polymers which have been crystalized in single crystals where chain‐folding represents the only way for explaining the arrangement of the long chain molecules, there are appearing increasingly more publications referring to chain‐folding also on polymers crystallized in bulk. Assuming that a polymer molecule is randomly coiled whether in solution or in bulk where actually sister molecules represent the “solvent,” then on crystallization of polymers in bulk, like chain sections will aggregate whether belonging to the same molecule or to a nearby sister molecule. In the latter case, regular chain‐folding should be very unlikely to occur. Using woolen yarn as a model substance which simulates both covalent and van der Waals binding forces (the latter by means of the fuzzy fibers), it is illustrated how bulk crystallization may be nicely imitated by parallel combing of randomly arranged yarn. This concept is also applied to explain changes in long‐period as occurring on annealing and the formation of macrostructures, mainly spherulites.
Theories for the flow of dilute solutions of polymers and of nondiluted liquid polymers
Authors: Pao Yoh‐Han
Published: April 2003

The formulation of two theories for the flow of polymeric systems and some of the principal results are presented in this paper. The theory for the flow properties of dilute solutions of polymers is related to the work of Kirkwood and Riseman, and Rouse, Bueche, and Zimm. The combined effects of long‐range excluded volume, hydrodynamic shielding and branching are considered in computations for intrinsic viscosity. The dependencies of solution viscosity on velocity gradient and frequency of oscillation are derived. The continuum theory is adequate for describing the combined effects of finite deformation and viscoelastic flow of molten polymers.
Study of the treatment of polymer fractionation data
Authors: Tung L. H.
Published: April 2003

The fractionations of a hypothetical 250‐component system and an actual polymer were simulated by computations on a digital computer. The results indicated that Schulz's method of treating polymer fractionation data is acceptable if the fractions obtained are reasonably sharp. When extremely low molecular weight materials are present in the polymer, the computation shows that one must be very careful in computing the M̄u/M̄n ratio. A comparison of the computation result with the experimental result of a linear polyethylene fractionation indicates that the Flory‐Huggins' theory describes the liquid‐liquid phase separation of polymer solutions well.
Irradiation of crystalline polyethylene
Authors: Salovey Ronald
Published: April 2003

Measurements of crosslinking, unsaturation, and hydrogen evolution following electron bombardment are similar for bulk polyethylene and fast‐filtered single crystals. Slow‐filtered single crystals evidence a unique irradiation behavior. It is suggested that irradiation‐induced crosslinking is preferentially between the layers of polyethylene single crystals if the lamellae are in close contact. Following slow filtration the lamellae are separated while fast filtration of single crystal preparations brings the lamellae into contact. Moreover, it is possible that the bulk polymer is composed of folded molecules in compacted lamellae.
Synthesis of graft copolymers by a transesterification method
Authors: Kolesnikov H. S. , Khan'‐Min Tsen
Published: April 2003

It is shown for the first time that mutual transesterification between carbochain polyesters (polymethyl methacrylate) and heterochain polyesters may be used for synthesizing graft copolymers. The graft copolymers obtained from polymethyl methacrylate and crystalline polyesters are crystalline have high softening temperatures. The grafting of amorphous polyesters yields amorphous graft copolymers. An increase in the number of graft side chains is accompanied by a decrease in intrinsic viscosity of the copolymer and by a rise in value of the Huggins constant. The decrease in the intrinsic viscosity is not the result of a degradation process, since polymethyl methacrylate may be regenerated by methanolysis of the graft copolymers. The intrinsic viscosity of the regenerated polymethyl methacrylate is equal to that of the initial polymer. Graft copolymers from polymethyl methacrylate and heterochain polyesters possess a lower tensile strength and higher ultimate elongation than polymethyl methacrylate. It was also established that on heating mixtures of methyl methacrylate and ω‐hydroxyacids in the presence of a catalyst graft copolymers form by simultaneous polymerization, polycondensation, and mutual transesterification reactions. Some correlations in this process and the properties of the resultant graft copolymers have been studied.