bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of the molecular weight distribution of polyisoprenes from the sol dependence on crosslinking
Authors: Calderon Nissim , Scott Kenneth W. 
Published: April 2003

AbstractA polyisoprene with a narrow molecular weight distribution was prepared with a polyisoprenyl lithium catalyst by the “seeding” technique. Dicumyl peroxide was shown to be a quantitative crosslinking agent for this polyisoprene. The dependence of the sol fraction on the amount of crosslinking introduced by dicumyl peroxide vulcanization was determined and found to give excellent agreement with gel network formation theory. Two procedures for estimating the breadth of the molecular weight distribution from the sol dependence on crosslinking yield the value of 1.05 ± 0.05 for the ratio of the weight‐average to number‐average molecular weight for this polyisoprene. These results demonstrate that it is possible to determine the molecular weight and molecular weight distribution of polyisoprenes, containing cis‐1,4, trans‐1,4, or moderate amounts of 3,4 addition structures, from the sol dependence on the amount of dicumyl peroxide used in crosslinking. Temporary or permanent molecular chain scission that might accompany the crosslinking by dicumyl peroxide was negligible, as there was no evidence of broadening of the molecular weight distribution due to scission. For the most likely set of recombination reactions that might occur it is estimated that less than 0.3% of the dicumyl peroxide is used in reactions leading to temporary molecular chain scission.
Surface energetics, adhesion, and adhesive joints. III. Surface tension of molten polyethylene
Authors: Schonhorn Harold , Sharpe Louis H. 
Published: April 2003

AbstractThe surface tension of polyethylene has been measured by the ring method over the temperature range 125–193°C. Because of problems with the viscousness of the liquid polyethylene, it was found convenient to use an Instron testing apparatus instead of the usual du Nouy torsion balance. The surface tension of the polyethylene decreased from a value of 28.5 dynes/cm. at 125°C. to 23.3 dynes/cm. at 193°C. with an average temperature coefficient of −0.076 dynes/cm./°C.
Copolymerization of secondary fumarates with styrene
Authors: Burgh L. F. Vander , Brockway C. E. 
Published: April 2003

AbstractReactivity ratios for the copolymerization of styrene (M1) with some secondary butyl fumarates (M2) indicate that the r1 values are more dependent on the inductive effect of the alkyl groups than on the steric effect and that the r2 values approach zero. Copolymerization rates of the secondary dialkyl fumarates with 65 mole‐% styrene were found to be consistent with the r1 values and the rate of styrene homopolymerization. However, mono(1‐methylpropyl) fumarate copolymerized with styrene at a rate more than twice that of styrene homopolymerization; this agrees very well with the modified copolymer equation which is obtained when the terms of the general copolymerization equation which contain r2 are set equal to zero.
Modification of polymers via the Wittig reaction
Authors: Mallavarapu L. X. , Ravve A. 
Published: April 2003

AbstractRepresentative macromolecules containing either aldehyde or ketone groups were subjected to the Wittig reaction. As expected, the carbonyl content of the reaction products was drastically decreased, with concomitant increase in unsaturation. This is shown by spectral and chemical evidence. However, the molecular weights of the polymers before and after reaction showed significant differences; some degree of crosslinking was also noted.
Vinyl polymerization. XCII. Polymerization of propenyl chloride isomers
Authors: Otsu Takayuki , Shimizu Akihiko , Imoto Minoru 
Published: April 2003

AbstractThe effect of the substituent on polymerization of isopropenyl chloride (IPC), cis‐propenyl chloride (CPC), and trans‐propenyl chloride (TPC) has been investigated. These monomers homopolymerized only very slightly in the presence of radical or ionic catalyst, and only a low molecular weight polymer of IPC was isolated. However, these monomers copolymerized with radical initiator with vinyl acetate, vinyl chloride, and acrylonitrile, and their reactivities towards the poly(vinyl acetate) radical decreased in order of IPC ≫ TPC ≥ CPC. The Q, e values for the monomers were estimated as follows: for IPC, Q = 0.06, e = −0.85; for CPC, Q = 0.005, e = −1.66; for TPC. Q = 0.009, e = −1.33. Further results on copolymerization with maleic anhydride indicated that the steric effect of the substituent for these monomers increased in order IPC ≪ TPC ≤ CPC. On radical polymerization of IPC, its degradative chain transfer reactivity was suggested to be also significant.
Rubber elasticity of preswollen polymer networks: Highly crosslinked vinyl–divinyl systems
Authors: Shen M. C. , Tobolsky A. V. 
Published: April 2003

AbstractThe rubber elasticity of highly crosslinked, preswollen network polymers is studied. Copolymers of tetraethylene glycol dimethacrylate with ethyl acrylate, n‐butyl acrylate, methyl methacrylate, and styrene covering the whole range of composition are investigated. Dioctyl phthalate is used to preswell the polymers up to 50% by volume. Both shear moduli and front factors are found to increase with increasing crosslink concentration but to decrease with increasing diluent content. Crosslinking efficiencies are determined by a modified Loshaek‐Fox method. They are relatively invariant with the degree of preswelling. Factors contributing toward these observations are discussed.
Effect of constraints on the equilibrium swelling of rubber vulcanizates
Authors: Southern E. , Thomas A. G. 
Published: April 2003

AbstractThe swelling of natural rubber vulcanizates under equal two‐dimensional compression has been investigated. The degree of crosslinking of the vulcanizate and the nature of the swelling liquid have both been varied. The reduction in equilibrium swelling produced by the stresses is found to agree well with theoretical predictions, except for high degrees of swelling. This divergence from theory has been explained on the basis of surface instability, which takes the form of wrinkles of the rubber surface.
Application of transmission electron microscopy to polymer thin sections. I. Observations on nylon 66, bulk and filament forms
Authors: Rusnock John A. , Hansen David 
Published: April 2003

AbstractA study was made on the internal morphology of molding pellets and filaments of nylon 66 by using transmission electron microscopy on ultrathin sections and polarized light microscopy. Nylon specimens embedded in an epoxy–phenolic resin alloy were sectioned to below 500 A. in thickness on an ultramicrotome with a 48° diamond knife. This resin combined good sectioning properties with strong adhesion to the nylon due to the interaction between the phenolic and the nylon. It was established that success in sectioning depended on embedding in a medium with proper wetting characteristics (to permit floating sections away from the knife edge) and obtaining a strong adhesive bond between specimen and embedding material. Contrast in the electron micrographs was enhanced by staining the nylon sections with phosphotungstic acid. Observations on nylon 66 molding pellets resolved the fibrillar structure of spherulites at the 100 A. level. Observations on undrawn monofilaments indicated a cylindrical rather than spherical symmetry of spherulitic crystallization. When the filaments were cold‐drawn, these spherulites retained their radial symmetry but were reduced in diameter.
Comparison of some mechanical and flow properties of linear and tetrachain branched “monodisperse” polystyrenes
Authors: Wyman D. P. , Elyash L. J. , Frazer W. J. 
Published: April 2003

AbstractThe strength and flow properties of narrow distribution polystyrenes have been studied as functions of molecular weight and branching (tetrachain star‐type molecules). Most of the mechanical properties of linear and branched narrow distribution polystyrenes were essentially the same as those for a broad distribution general‐purpose polystyrene. For the narrow distribution linear polymers the value of a given property increased rapidly with molecular weight until ca. M = 1.6 × 105. Thereafter the magnitude of the property increased only slightly for rather large increases in M and asymptotically approached a maximum. The same was true of the branched polymers except that certain properties, e.g., tensile strength, were found to level off in value at higher molecular weights than for the corresponding linear polymers. Studies of apparent melt viscosity, η, made with a capillary rheometer showed that at low shear rates (\documentclass{article}\pagestyle{empty}\begin{document}$ (\dot \gamma < 10) $\end{document} sec.−1), the branched polymers exhibited much lower apparent values of η than linear polymers of the same total molecular weight. At high shear rates (\documentclass{article}\pagestyle{empty}\begin{document}$ (\dot \gamma \sim 2000) $\end{document} sec.−1), this difference essentially disappeared and η approached a constant value independent of \documentclass{article}\pagestyle{empty}\begin{document}$ \dot M(1.5 \times 10^5 - 4.5 \times 10^5) $\end{document} and branching. Melt viscosity data for both the linear and branched narrow distribution polymers when plotted in the form of reduced viscosities versus a function of \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} (as suggested by Bueche) fell upon one master curve.
Kinetics of alternating copolymerization
Authors: Baldwin M. G. 
Published: April 2003

AbstractThe rates of copolymerization of three monomer pairs which form only alternating copolymers have been studied. The monomer pairs were vinyl isobutyl ether–diethyl fumarate, vinyl isobutyl ether–maleic anhydride, and 1‐octene–maleic anhydride. It was shown that the maximum copolymerization rate occurs at [M1]/[M2] ratios which differ significantly from unity, for a fixed total monomer concentration ([M1] + [M2]). An equation for the rate of copolymerization for alternating systems is given and the results are discussed in terms of the equation.
Stereospecific polymerization of 1,3‐butadiene. I. New catalysts based on TiCl4, AlI3, and some aluminum hydride derivatives
Authors: Marconi W. , Mazzei A. , Araldi M. , De Maldé M. 
Published: April 2003

AbstractSome ternary catalytic systems used in the polymerization of butadiene to a prevailingly 1,4‐cis product are described. They make use of some aluminum hydride derivatives, aluminum iodide, and titanium tetrachloride. For each catalytic system we have adopted conditions to obtain the maximum yield of polymer and the highest content of 1,4‐cis units. Such optimum conditions are achieved at certain molar ratios of aluminum hydrides/TiCl4 and AlI3/TiCl4. In particular, for a constant amount of AlI3 and TiCl4, the choice of the optimum ratio of hydride/TiCl4 depends on the quantity of active hydrogens present in the aluminum compounds while it does not depend on the type substituents, e.g., chloro, amino groups, etc. The presence of Lewis bases, which tend to stabilize some aluminum hydrides and make them soluble in the reaction medium, does not influence the course of polymerization provided such bases are present in stoichiometric amount with respect to the aluminum. If, however, these complexing agents are in excess, a decrease of the catalytic activity and 1,4‐cis content is noticed. This is more so, the stronger the basicity of the complexing Lewis base added. The results obtained in the polymerization of butadiene by means of numerous laboratory runs were confirmed by pilot‐plant runs.
Preparation and characterization of some cellulose graft copolymers. Part III. The role of concurrent degradation during radiation grafting
Authors: Wellons J. D. , Stannett V. 
Published: April 2003

AbstractThe radiation degradation of cellulose acetate has been studied both in the dry state and in solution. The rate of degradation was greater in the solid state and was unaffected by oxygen. Conjugated solvents such as pyridine, toluene, and α‐methylstyrene were shown to exert considerable protection against the radiation degradation of cellulose acetate when in solution or as swollen films. α‐Methylstyrene has been used as a model for styrene to study the amount of degradation accompanying the grafting process. Matching experiments have been carried out by using both the mutual and the preirradiation methods of grafting. Considerably greater chain cleavage was found to accompany the grafting in the preirradiation case. With both methods the number of chain cleavages has been measured when α‐methylstyrene was present in the “grafting” solution and the number of grafted side chains when styrene was used. It was shown that at least twice as many grafted chains as cleavages occur with the mutual technique, but in the case of preirradiation the number of cleavages is comparable to the number of grafted chains. The G (grafted chain) value for cellulose acetate with styrene was determined and was about 1.1 in all cases. The G (chain cleavage) values varied, however, from 0.2 to 1.3, approximately. The proportion of grafted chains attached to the ester groups was determined by extraction with benzene after cold alkaline hydrolysis. About half of the grafts were found to be attached in each case, including the preirradiation product. In general, it can be said that in every case at least 50% of the graft copolymers are side‐chain grafts; this figure is probably considerably higher in the case of the mutual radiation preparations.
Distribution of short‐chain branching in low‐density polyethylene
Authors: Shirayama Kenzo , Okada Takayuki , Kita Shin‐Ichiro 
Published: April 2003

AbstractThe distributions of short‐chain branching in some commercial low‐density polyethylenes have been investigated by measuring the degree of short‐chain branching of their fractionated samples. The results obtained on the fractions which were fractionated with respect to molecular weight showed that some polyethylenes have broad distributions and others have narrow distributions, and these results have been considered to depend mainly on the polymerization conditions. These fractions of which the molecular weight is considered to be approximately uniform were further refractionated with respect to degree of short‐chain branching, and thus cross‐fractionations were accomplished. The distributions of short‐chain branching in those parent fractions were also examined, and it was found out that the parent fractions have fairly broad distributions, and the distribution is broader when the molecular weight is lower, but the difference of distribution is not so great in the different samples. The distributions in those parent fractions showed close agreement with the theoretical distributions which were calculated on the basis of statistical branch formation.
Chain stiffness in polyisocyanates
Authors: Schneider N. S. , Furusaki S. , Lenz R. W. 
Published: April 2003

AbstractLight‐scattering measurements of the molecular conformation of n‐hexyl polyisocyanate (PIC) in tetrahydrofuran (THF) show that the ratio of the root‐mean‐square end‐to‐end distance to the maximum extension exceeds 25% even at a molecular weight of 3 × 105 and that the effective bond length in the equivalent freely linked chain is 23 A., corresponding to about 17 links per statistical segment. These results are at least twice as high as the values of cellulose trinitrate in acetone at a comparable degree of polymerization. Although a significant variation in intrinsic viscosity occurs in different solvents, the recently reported viscosity‐ and sedimentation coefficient–molecular weight exponents of 1.18 and 0.16 for n‐butyl PIC in THF indicate that the polymer behavior lies outside the Gaussian region and must result from the short range structure rather than from strong interactions with the solvent. In fact, by using a form of the Kirkwood‐Riseman theory, modified to take account of the expansion factor, a viscosity–molecular weight exponent of 0.9 is calculated for theta conditions. It is proposed that the chain is stiffened by restrictions to rotation imposed by resonance effects in the peptide bonds that make up the polymer backbone.
Homopolymerization of hydronopyl vinyl ether and 2‐hydronopoxyethyl vinyl ether
Authors: Marvel C. S. , Malzahn R. A. , Comp J. L. 
Published: April 2003

AbstractThe effectiveness of several free radical, cationic, and coordination initiators for the polymerization of hydronopyl vinyl ether and 2‐hydronopoxyethyl vinyl ether has been examined. The most effective initiator found for polymerization of hydronopyl vinyl ether is a coordination catalyst prepared from triisobutylaluminum and titanium tetrachloride. Generally, cationic initiators are less effective and free radical initiators much less effective with this monomer. Of the initiators investigated for polymerization of 2‐hydronopoxyethyl vinyl ether, only one, boron fluoride etherate, proved to be effective. This initiator yielded a rubbery polymer of high molecular weight.
Cyclic distribution in dimethylsiloxanes
Authors: Carmichael Jack B. , Winger Robert 
Published: April 2003

AbstractGas–liquid chromatography was used to determine the amounts of cyclic molecules present in an equilibrium polymerization mixture of high polymer and cyclic dimethylsiloxane molecules. The study was carried out as a function of polymerization temperature. For [(CH3)2SiO]4–10 the equilibrium concentration is shown to be independent of temperature. The change in cyclic concentration as a function of n for [(CH3)2SiO]4–10 does not follow the theoretical Stockmayer‐Jacobson distribution. The concentrations of [(CH3)2SiO]3,4 are qualitatively predictable by the Stockmayer‐Jacobson theory and by the model proposed by Carmichael and Kinsinger. For [(CH3)2SiO]4, Kexp = 0.74 mole SiO/l. The model calculations yield 0.12 (Stockmayer‐Jacobson) and 0.36 Carmichael‐Kinsinger. For [(CH3)2SiO]3, Kexp = 0.024 mole SiO/l. Model calculations yield 0.017–0.16 (Stockmayer‐Jacobson) and 0.056–0.52 (Carmichael‐Kinsinger). The range of values rises because of uncertainty in the cyclic strain energy.
Stress‐cracking of polyethylene examined from the viewpoint of critical strain
Authors: Tung L. H. 
Published: April 2003

AbstractStress‐cracking in polyethylene has been examined from the viewpoint of critical strain based on a proposed theory for the formation of the cracks. Stress‐cracking under constant load and constant strain was determined experimentally at 60°C. on a 3.5 melt index high‐density polyethylene. A critical strain of 1.95% associated with a critical relaxation time of 90 min. was found for the sample. Good agreement was found between the theory and experiments made in Igepal CO 630. Some disagreements between the theory and experiments made in air were attributed to the rate of propagation of the cracks.
Rates of sulfonation of polystyrenes crosslinked with pure p‐, 2:1/m:p‐, and commercial divinylbenzenes
Authors: Wiley Richard H. , Venkatachalam T. K. 
Published: April 2003

AbstractData for the rates of sulfonation of polystyrene crosslinked with 2, 4, and 8% pure p‐, 2:1/m:p‐, and commercial divinylbenzenes at 60 and 80°C. have given activation energies varying from 11,520 to 40,190 cal./mole. Rates are lowest and activation energies highest for the p‐divinylbenzene crosslinked structures. This is attributed to differences in rates of diffusion through the different types of network structures and is consistent with previously noted decreased swelling ratios for the para crosslinked types.
Dye‐sensitized photopolymerization. III. Structural effects of thiazine dyes
Authors: Chen Catherines S. Hsia 
Published: April 2003

AbstractPhotopolymerization of aqueous acrylamide was investigated by use of mixtures of thiazine dyes with different structural features and triethanolamine as sensitizers. New methylene blue N (I), with two electron‐donating methyl group in the 2‐ and 10‐ positions, and methylene green (III), with an electron‐withdrawing nitro group in the 2‐position of methylene blue (II, 3,9‐bisdimethylaminophenazothionium chloride) were employed. Induction periods for polymerization were observed for both I and III: the kinetics thereafter were of similar nature to those reported for II.1 The lengths of the induction period were in the order of III > II > I. The rate of polymerization and the quantum yield were in the order of III > II > I. In combination with an anionic dye (eosin Y) in an equivalent ratio of 7:6, spectroscopy indicated interaction between both I and eosin Y and III and eosin Y, III–eosin Y interaction was of similar nature to II–eosin Y interactions, but to a lesser extent. Interaction between I and eosin Y, however, was of a different nature. Results in polymerization showed that enhancement in rate was observed for III–eosin Y but not for I–eosin Y. The order of enhancement was thus II > III > I.
Graft copolymerization onto cellulose by the ceric ion method
Authors: Iwakura Yoshio , Kurosaki Toshikazu , Imai Yohji 
Published: April 2003

AbstractStyrene was polymerized in ceric salt–alcohol redox systems and hydroxyl endgroups on the polystyrene obtained were characterized quantitatively by the spectrophotometric determination of the polymer treated with p‐phenylazophenyl isocyanate. A series of polymerization of acrylamide initiated in redox systems of ceric salt and various alcohols was studied as a model system for graft copolymerization onto cellulose. From studies of the rate of polymerization it was shown that the grafting was likely to occur at hemiacetal and 1,2‐glycol units. The cellulose–styrene graft copolymer was isolated from the reaction products by a selective extraction technique and characterized by acetolysis of the cellulose backbone. The graft copolymers obtained were found to be a mixture of block and graft copolymers.
Study of hydrocarbon‐soluble organometallic catalysts. I. Correlations between catalytic activity and electric conductivity of Al(C2H5)3–Ti(OC4H9)4 catalysts in the synthesis of stereoregular polyacetylene
Authors: Nicolescu I. V. , Angelescu Em. 
Published: April 2003

AbstractThe correlation between the catalytic activity of the system Al(C2H5)3–Ti(OC4H9)4 and its electrical conductivity in stereospecific polymerization was investigated. The activity of the catalyst was evaluated for varying molar ratios of Al/Ti (in the range of 0.75–6) and reaction temperatures (in the range of −78 to +70°C.) by means of the velocity of absorption of the acetylene. The ionic state of the catalytic complex may be assessed on the basis of electrical conductivity measurements. The electrical conductivity of the pure state of the two catalyst components is in the range of 10−12 or 10−10 (ohm‐cm.)−1 while that for the catalyst complex is of the order of 10−8 (ohm‐cm.)−1. The experimental data prove the existence of a correlation between the velocity of reaction, the composition of the catalyst complex, and the electrical conductivity. The values obtained for the activation energy of the electrical conductivity correlate with the energy required to break the complex ion aggregate of the catalyst and therefore with the activity of the catalyst.