bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dimensions of branched and linear polymer chains in solution: Modifications of flory's theory
Authors: Casassa Edward F. 
Published: April 2003

AbstractIt is pointed out that a theory proposed by Vrij for the expansion of a linear polymer chain in solution beyond its unperturbed size is also applicable formally to branched chains. The theory predicts the temperature at which the chain obeys random‐flight statistics to be lower for a branched chain than for a linear one (for a polymer–solvent system exhibiting the usual upper critical consolute point). Vrij's derivation follows a well‐known procedure of Flory, but refines it to take account of the variation of the time‐averaged segment density with distance from the center of mass of the chain. This modification in combination with a somewhat different derivation is shown to lead to a similar result. Yet another scheme for “correcting” Flory's theory is outlined. Some reasons are advanced for questioning the physical significance of these small modifications of Flory's theory, all of which depend on the retention of previously ignored terms in power series expansions.
Local deformation in stretched polybutene‐1 spherulites
Authors: Yee R. Y. , Stein R. S. 
Published: April 2003

AbstractThe orientation of crystals in spherulites of modifications I and II of polybutene‐1 was studied by micro‐x‐ray diffraction. Changes in such micro‐x‐ray diffraction patterns were measured in various regions of the spherulites as a function of strain and time. The relationship between micro‐x‐ray diffraction from parts of spherulites and macro‐x‐ray diffraction from entire spherulites is discussed. Changes are resolved into contributions arising from (1) deformation of spherulites with change in crystal orientation and (2) transformation of crystals from modification II to modification I.
Polymorphic forms of nylon 3
Authors: Masamoto Junzo , Sasaguri Kiichiro , Ohizumi Chihiro , Kobayashi Hidehiko 
Published: April 2003

AbstractThe crystal structure of nylon 3 was studied, and four crystalline modifications were observed. Modification I, as determined from the x‐ray diffraction pattern of drawn fibers, is similar to the α crystal structure of nylon 6. The unit cell is monoclinic; a = 9.33 Å, b = 4.78 Å, (fiber identity period), c = 8.73 Å, and β = 60°. The theoretical density for nylon 3 with four monomeric units in the unit cell is 1.39 g/cm3, and the observed density is 1.33 g/cm3. The space group is P21. The nylon 3 chains are in the extended planar zigzag conformation. Although other odd‐numbered nylon form triclinic or pseudohexagonal crystals when oriented, drawn nylon 3 crystals are monoclinic. In addition to modification I, modifications II, III, and IV were studied. Lattice spacings of modifications II and III are equal to those of modification I. However x‐ray diffraction intensities are different. Infrared spectra of those forms indicate an extended planar zigzag conformation of the chains. Modification IV is thought to correspond to the so‐called smectic hexagonal form. No γ crystals were found, and it appears that polyamide chains with short sequences of methylene groups cannot form crystals of this type.
Plastic deformation of polyethylene. I. Change of morphology during drawing of polyethylene of high density
Authors: Meinel G. , Morosoff N. , Peterlin A. 
Published: April 2003

AbstractThe transformation of microspherulitic quenched and annealed polyethylene film into highly oriented drawn material with the characteristic fiber structure was investigated by small‐angle and wide‐angle x‐ray measurements and by a study of the thermograms after the fuming nitric acid treatment. With the details of deformation depending slightly on the crystallinity, one observes generally a preferential tilt of the platelets against draw direction at draw ratios below 2. At least in annealed material, an increasing tilt of the molecule within the lamella is also observed, which leads at higher draw ratios to slipping of blocks in the crystallites. With further drawing a new fiber structure appears, which is practically independent of the thermal history of the original film. This fact is established by investigation of the crystal thickness by three different methods; investigations of small‐angle scattering, study of the width of the (002) reflection, and investigation of the debris after treatment with fuming nitric acid.
Quantitative analysis of gaseous diffusion in glassy polymers
Authors: Petropoulos J. H. 
Published: April 2003

AbstractThe current theoretical treatment of diffusion of gases in glassy polymers is based on the “dual sorption” model, but also includes certain other important assumptions, at least some of which cannot be fully justified a priori. They require experimental validation, which, however, is not possible by the procedures used or proposed so far. Methods suitable for this purpose are discussed here.
Thermal analysis of polysiloxanes. II. Thermal vacuum degradation of polysiloxanes with different substituents on silicon and in the main siloxane chain
Authors: Thomas T. Howard , Kendrick T. C. 
Published: April 2003

AbstractThermogravimetric (TG) investigations of various substituted polysiloxanes of the type \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm R}_1 {\rm R}_2 {\rm SiO\rlap{--} )}_n $\end{document} have been carried out in vacuo and the activation energies for the depolymerization processes calculated from the resulting thermograms. (R1 and R2 are methyl, ethyl, n‐propyl, trifluoropropyl, or phenyl.) It is postulated that the activation energy is mainly a function of the inductive effect of the substituent group and that electron‐withdrawing groups attached to silicon increase the activation energy, whereas electron‐donating groups decrease it. A linear relation is found between the Taft constant σ* for the substituent on silicon and the calculated activation energy for depolymerization. Product analysis results from isothermal degradations indicate that the degradation mechanism in a silmethylene siloxane polymer and a silethylene‐siloxane polymer
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is very similar to that in polydimethylsiloxanes (PDMS). For the \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm R}_1 {\rm R}_2 {\rm SiO\rlap{--} )}_n $\end{document} polymers, the amount of cyclotrisiloxane in the degradation products increases with the size of the substituent on silicon, and it is postulated that the rate of depolymerization is mainly influenced by short‐range steric interactions between the substituents on the silicon atoms of the siloxane chain.
Use of numerical methods in the prediction of polymer adsorption
Authors: Hoffman Robert F. , Forsman W. C. , Lovering Edward G. 
Published: April 2003

AbstractAverage polymer segment densities and thermodynamic properties of polymer adsorbed at liquid–solid interfaces were computed by extension of the polymer adsorption theory of Forsman and Hughes. Expressions were derived for the total free energy of adsorbed polymer chains by using the Flory‐Huggins theory to represent free energy of mixing. A square‐well potential was used to represent segment–surface interaction, and configurational entropy was calculated from the probability density function for the radius of gyration of random‐flight chains. For each specified amount of surface coverage the free energy of the adsorbed polymer was minimized by varying the density of segments normal to the adsorbing surface and using a modified gradient search algorithm on a digital computer. Two different segment densities were considered, and they both gave qualitatively the same results. The two densities were (1) the sum of two Gaussian distributions and (2) a two‐step density distribution. Isotherms were then calculated by equating the partial molal free energy of polymer at the surface to that of polymer in bulk solution for each specified amount of surface coverage. The results showed that for the initial region of the isotherms the distribution of polymer segments normal to the surface consisted of a high‐density layer adjacent to the surface and a low‐density “tail” extending far out into the solution. At higher amounts of adsorbed polymer, i.e., in the general concentration range of the pseudo‐plateau, the tail of the polymer density distribution was predicted to thicken, and a single Gaussian distribution best described the segment density. Predicted adsorptions were in good agreement with reported experimental values.
Use of numerical methods in the prediction of polymer adsorption
Authors: Hoffman Robert F. , Forsman W. C. 
Published: April 2003

AbstractAverage polymer segment densities and thermodynamic properties of polymer adsorbed at liquid–solid interfaces were computed by extension of the polymer adsorption theory of Forsman and Hughes. Expressions were derived for the total free energy of adsorbed polymer chains by using the Flory‐Huggins theory to represent free energy of mixing. A square‐well potential was used to represent segment–surface interaction, and configurational entropy was calculated from the probability density function for the radius of gyration of random‐flight chains. For each specified amount of surface coverage the free energy of the adsorbed polymer was minimized by varying the density of segments normal to the adsorbing surface and using a modified gradient search algorithm on a digital computer. Two different segment densities were considered, and they both gave qualitatively the same results. The two densities were (1) the sum of two Gaussian distributions and (2) a two‐step density distribution. Isotherms were then calculated by equating the partial molal free energy of polymer at the surface to that of polymer in bulk solution for each specified amount of surface coverage. The results showed that for the initial region of the isotherms the distribution of polymer segments normal to the surface consisted of a high‐density layer adjacent to the surface and a low‐density “tail” extending far out into the solution. At higher amounts of adsorbed polymer, i.e., in the general concentration range of the pseudo‐plateau, the tail of the polymer density distribution was predicted to thicken, and a single Gaussian distribution best described the segment density. Predicted adsorptions were in good agreement with reported experimental values.
Flow behavior of narrow‐distribution polydimethylsiloxane
Authors: Lee C. L. , Polmanteer K. E. , King E. G. 
Published: April 2003

AbstractThe flow behavior of α,ω‐dihydroxypolydimethylsiloxanes, having a weight‐average number‐average molecular weight ratio of 1.1–1.2, was studied with a Cannon‐Manning viscometer and an Instron rheometer. Comparison of the flow behavior of samples with narrow and broad molecular weight distributions indicated that the onset of non‐Newtonian behavior occurred at a much higher shear rate for narrow‐distribution polydimethylsiloxanes than for polydisperse polydimethylsiloxanes. A plot of reduced viscosity versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma \eta _0 {M \mathord{\left/ {\vphantom {M T}} \right. \kern-\nulldelimiterspace} T} $\end{document} gave two experimental master curves, one for polymer of narrow distribution and the other for polydisperse polymer. The experimental master curve obtained from the narrow‐distribution polymer was found to fit the theoretical master curve derived from Graessley's entanglement theory. The viscosity–molecular weight relationship for the higher molecular weight polydimethylsiloxanes was found to be the same for both hydroxydimethylsilyl‐ and trimethylsilyl‐endblocked polymers. However, at low molecular weight, the viscosity–molecular weight curve deviated from linearity because of the association of polydimethylsiloxanols, which apparently is not significant at higher molecular weights. The critical molecular weight of entanglement, Mc, was found to be about 30,000.
Dynamic mechanical properties of two copolymers of styrene and n‐hexyl methacrylate
Authors: Nigmankhodjaev Abralkhodja S. , Bi Le‐Khac , Wong Chiu‐Ping , Schrag John L. , Ferry John D. 
Published: April 2003

AbstractThe storage (J′) and loss (J″) shear compliances have been measured for two random copolymers of styrene and n‐hexyl methacrylate with styrene contents of 18% and 30% (by weight) in the frequency range 45–4400 Hz and the temperature range 31–107°C. The data at different temperatures were combined by the method of reduced variables, and the WLF coefficients were calculated from the temperature shift factors by the method of Pierson and Kovacs. The data were compared with earlier data for the two homopolymers. The thermal expansion coefficient of the fractional free volume, and the free volume at the glass transition temperature, varied monotonically with composition, but the fractional free volume at a reference temperature of 100°C appeared to pass through a maximum as a function of concentration. Comparison of isothermal plots of J′ at 100°C, plots of the relaxation spectrum at 100°C, the monomer friction coefficient and its temperature dependence, and isochronal plots of the storage shear moduls at 100 radians/see all show that the properties of poly(n‐hexyl methacrylate) are very slightly affected by incorporation of 18% styrene and only moderately affected by 30% styrene. By contrast, comparison of styrene–butadiene rubber with 1,4‐polybutadiene shows a very large effect of incorporation of 23.5% styrene. These differences may be associated with local packing relations of the comonomer residues and suggest that copolymer properties cannot be readily predicted from those of the component homopolymers.
Effect of birefringence on the scattering of light. II. Oriented polymers
Authors: Legrand D. G. 
Published: April 2003

AbstractIt has been considered for some time that the presence of birefringence in an oriented polymer must affect the light‐scattering behavior. Previous analyses of this phenomenon are restricted to single‐particle scattering. A more complete theory of the effect of birefringence on the scattering of light from correlated systems is presented. The measured scattering intensity is shown to be dependent upon the optical properties of the sample as well as the experimental technique and conditions.
The effect of interference between anisotropic scattering entities on the light scattering from polymer films. I. Case of no impingement
Authors: Stein Richard S. , Picot Claude 
Published: April 2003

AbstractEquations are developed for describing the effect of interspherulitic interference on the scattering of light by anisotropic spherulites. These are used to account for the variation in VV and HH scattered intensity during the course of spherulitic crystallization. The scattering depends upon the number of spherulites, their size, their anisotropy, the difference between one of their polarizabilities and that of the surroundings, and the radial distribution function of spherulite centers.
Physical structure and properties of 3‐methylbutene‐1 polymer and fiber
Authors: Quynn R. G. , Sprague B. S. 
Published: April 2003

AbstractIsotactic 3‐methylbutene homopolymers and copolymers (of low 1‐olefin content) exhibit a major transition between 50 and 100°C, which dilatometric, density, and NMR observations indicate is not a glass transition, but rather a crystal–crystal transition occurring within the crystalline phase, the only phase present in significant amount. Fibers prepared from these polymers show a very high degree of orientation and crystallinity, have measured densities close to the theoretical crystal densities, and exhibit abrasion debris and electron microscopic evidence of crystalline lamellae. The fibers have a quasistatic initial modulus equivalent to the sonic modulus and exhibit very low stress relaxation and very high elastic recovery from large extensions. The fact that the fiber is highly crystalline and fully oriented, with a comparatively low initial modulus, high elastic recovery, and an extensibility of about 40%, indicate that the crystalline lamellae themselves, joined together in stacks, are able to deform (probably bend) elastically, and that the aggregate is able to undergo large elastic deformations.
Isotope effect in gas transport. I. Measurement of the free volume element in four polymers above the glass transition temperature
Authors: Ziegel K. D. , Eirich F. R. 
Published: April 2003

AbstractThe experimental observation of an isotope effect in diffusive gas transport across polymeric films is reported. The differences in energies of transport between hydrogen and deuterium are used to estimate the effective dimensions of characteristic minima or “wells” in the potential energy surface of rubbery polymers. The size of a well, determined by assuming it to be a cubical cavity, is interpreted as the effective free volume element vf, as measured by the hydrogen molecule probe. Estimations are made of the entropy of activation and “jump distance” for the hydrogen diffusion process based on vf values and experimentally determined pre‐exponential factors.
Solution of Fujita's equation for equilibrium sedimentation by applying Tikhonov's regularizing functions
Authors: Gehatia Matatiahu , Wiff D. R. 
Published: April 2003

AbstractThe Fujita equation relating molecular weight distribution to concentration of solution subjected to centrifugal forces in equilibrium proved to be an improperly posed problem in the Hadamard sense. Application of Tikhonov's regularizing functions leads to a good approximate solution of Fujita's equation. Such functions have been applied to a monomodal and a bimodal molecular weight distribution, and approximate results have been computed.
Proton magnetic relaxation times and molecular motions in polydimethylsiloxane
Authors: Cuniberti Carla 
Published: April 2003

AbstractThe NMR relaxation times T1 and T2 have been measured for fractionated samples of polydimethylsiloxane with different molecular weights in the amorphous state and in tetrachloroethylene solutions. The results are interpreted on the basis of the anisotropic reorientation model proposed by Woessner for small molecules. A correlation time characteristic of the diffusional rotation of chain segments is calculated and shown to be proportional to the square root of the bulk viscosity.
Structure and properties of a styrene–butadiene–styrene block copolymer
Authors: Miyamoto T. , Kodama K. , Shibayama K. 
Published: April 2003

AbstractElectron‐microscopic texture and physical properties of a styrene–butadiene–styrene (SBS) block copolymer obtained by casting from toluene, carbon tetrachloride, ethyl acetate, and methyl ethyl ketone are discussed. Two peaks are observed in the mechanical loss (tan delta;) curve at −70 and 100°C which are attributed to segmental motion of polybutadiene and polystyrene, respectively. The polybutadiene peak heights are in the order of solubility in the solvent used; the polystyrene peak heights are in converse order. In addition to these peaks, a third peak is observed at 10°C for specimens cast from ethyl acetate or methyl ethyl ketone. A transition corresponding to this peak is also noticed in thermal analysis. It is proposed that aggregation of styrene blocks is relatively incomplete in specimens cast from solution in poor solvents.
Molecular weights in polymerization as a function of conversion
Authors: Litt Morton 
Published: April 2003

AbstractA relatively novel method of calculating molecular weight changes and broadening during a polymerization is proposed. It differs from others in that the distribution is considered implicitly rather than explicitly. This allows direct use of kinetic rate equations in the derivation of weight‐average and number‐average degree of polymerization etc.; the mathematics simplifies to simple integration rather than sums of complicated series. The method is illustrated by applying it to several cases. These range from various models where only monomer concentration changes, to where both monomer and initiator or monomer and chain transfer agent are changing. Cases previously unsolvable can now be handled.
Small‐angle light scattering by random assemblies of incomplete spherulites. I. Sheaflike textures
Authors: Picot C. , Stein R. S. , Motegi M. , Kawai H. 
Published: April 2003

AbstractThe calculation of the scattering from a sheaflike sector of a two‐dimensional spherulite has been carried out as a function of the apex angle of the sector. It is found that while for a complete spherulite the Hv scattered intensity is zero at zero scattering angle, there is an increasing intensity of scattering at 0° as the sector angle narrows. For very small values of the sector angle, the scattering becomes similar to that of a rod, with the exception that a scattering maximum is still seen at an angle close to that at which the spherulite scattering maximum occurs. The predictions of the model compare favorably with the scattering patterns observed for polymers in early stages of spherulitic growth.
Cleavage of branched polyethylene by chemical filling
Authors: Hoffman H. T. 
Published: April 2003

AbstractBranched polyethylene, melt‐crystallized in commercial fabrication processes, cleaves into two layers when exposed to a prolonged “chemical filling” treatment (i.e., formation of filler in situ by interdiffusion of two reactive permeants). Cleavage has been observed in film and blown bottles. With film, progressive changes in experimental conditions from one sample to another, shifted the cleavage plane from near the surface to deeper lying planes. Separation of a thin surface layer requires more filler deposit than does separation into layers of more equal thickness. These observations suggest that a well defined layer structure may exist in branched polyethylene and that cohesive bonding is stronger between layers near the surface of the film than it is between deeper lying layers. Linear polyethylene showed slight layer separation after prolonged chemical filling, but clean cut separation of large areas was not achieved. This behavior may indicate that the cohesive bonding between layers is much stronger in linear polyethylene than in branched polyethylene.
Infrared photoelectric effects in polyethylene
Authors: Vermeulen L. A. , Wintle H. J. 
Published: April 2003

AbstractWe have observed a flow of charge on illumination of low‐density polyethylene with infrared light in the wavelength range 1.6–0.7 μ by using silver electrodes. This flow is reversed on removal of the light, is proportional to the light intensity, and varies little with wavelength in this spectral region. There is no significant response to light of visible wavelengths. The effect decreases as the temperature is increased up to 60°C, though the time constant remains fixed. There are qualitative differences between the responses obtained with gold and with silver electrodes, and quantitative changes when the ambient air pressure is altered. The behavior suggests that during illumination, the dynamic equilibrium between carriers in the electrodes and those in the material close to the electrodes undergoes a reversible adjustment.
Morphospecific polymerization: Polyoxymethylene copolymers
Authors: Chen Catherine S. H. , Wenger Franz 
Published: April 2003

AbstractHomopolymerization and copolymerization of trioxane by use of various catalysts have been investigated. When MoO2(AcAc)2 is employed, crystalline homopolymers and copolymers as formed from polymerization exhibit significantly higher melting points than corresponding polymers prepared by use of ordinary cationic catalysts. The higher melting points are attributed to different morphology of the polymer chains formed during polymerization. We now call this phenomenon morphospecific polymerization. This communication describes our results in the copolymerization of trioxane and 1,3‐dioxolane and some outstanding properties of the copolymers. A polymerization mechanism is also proposed.