Solvent Molecular Weight Research Articles

The transient extensional behavior of polystyrene‐based Boger fluids of varying solvent quality and molecular weight

The behavior under transient uniaxial elongation of a homologous series of variable extensibility polystyrene‐based Boger fluids has been investigated in an apparatus similar to that developed by Sridhar and co‐workers. The test fluids are dilute solutions of either 2.0×107 or 2.0×106 g/mol monodisperse polystyrene dissolved in poor, dioctyl phthalate‐based or good, tricresyl phosphate‐based solvents. This rational manipulation of Boger fluid solvent quality (assessed based on previously reported light scattering and intrinsic viscometry measurements) and chain length yields a unique opportunity to correlate viscoelastic extensional response to finite extensibility and molecular interactions: here we search for such effects in transient filament extension between parallel plates, an approximation of purely extensional flow. The test device, which can impart a maximum Hencky strain, ε, of 4.5 at rates, ε̇, between 0.3 and 3.0 s−1, is similar to that reported by Sridhar et al. (1991). In agreement with results communicated there and in Tirtaatmadja and Sridhar (1993), large strain hardening is observed for these polymer solutions, as well as certain deviations of the experimental flow from ideal uniaxial extension. As opposed to Tirtaatmadja and Sridhar (1993), no steady‐state extensional viscosities are obtained for the comparatively small strains of our experiment. The transient experimental results are roughly consistent with simple one‐dimensional FENE–P calculations. However, uncertainties due to the nonideal nature of the flow at short times and the sensitivity of the measured extensional stress growth coefficient to the details of the imposed elongation make it difficult to unambiguously assign L based solely on short time filament stretching results. These results are considered in light of the substantial effects solvent quality and molecular weight have on the measured drag in flow past a sphere [Chmielewski et al. (1990); Solomon and Muller (1996b)].

Liquid - liquid phase separation in linear low density polyethylene - solvent systems

In this contribution the results of an investigation on the influence of pressure, solvent type and polymer structure on liquid - liquid phase separation in LLDPE - solvent systems is reported. Lower solution temperatures (LST) in LLDPE + solvent systems were determined experimentally as a function of pressure at 400–600 K and at pressures up to 13 MPa. The solvent type and the presence of ethylene in the LLDPE - solvent mixture appear to be the most important factors that govern the solubility of LLDPE, while the structure of the LLDPE itself is of minor importance. It is shown that the Perturbed Hard Chain Theory predicts a priori the right type of phase behaviour. Moreover the experimental trends in solubility with changing solvent type and molecular weight of the polymer are equally well predicted.

A correlation of diffusion coefficient at infinite dilution based on dense fluid theory

In this paper a new correlation of the Schmidt number is proposed as a function of solvent molar volume and molecular weight for predicting binary molecular diffusion coefficients in reservoir fluids and self-diffusion coefficients of dense and liquid carbon dioxide. The feature of this new correlation is that the model is derived from the Chapman and Enskog theory as well as computer simulation results for self-diffusion coefficients of dense fluids. In the correlation from experimental data, the cubic simplified perturbed hard-chain equation of state has been used to predict the molar volumes of the solvent as well as the molecular parameters in the new correlation. The newly-developed semi-theoretical liquid viscosity model of Du and Guo has been used in predicting the viscosities of solvents. Extensive comparisons of the calculated and experimental diffusion data have been carried out to ensure that the new model is applicable for predicting the self- and binary diffusion coefficients, particularly for carbon dioxide-alkane and alkane-alkane systems.

Measurement and Correlation of Binary Diffusion Coefficients in Near Critical Fluids

The binary diffusion coefficients of benzoic acid, oleic acid, α-tocopherol, and glycerol trioleate were measured in near critical carbon dioxide over the temperature range 298-318 K and pressure range 71-251 bar. A correlation based on an extensive literature database was developed which can be used to estimate both self and binary diffusion coefficients in a range of near critical solvents over the solvent reduced density range 1-2.5, with an average error of ±10%. The correlation is not suitable for estimating binary diffusion coefficients at the binary mixture critical point. The only input data required for the correlation are the solvent molecular weight, reduced temperature, and density, the solute molecular weight, and an estimate of the solute critical volume

Triglyceride Content of Supercritical Carbon Dioxide Extracted Fractions of Beef Fat

ABSTRACTBeef fat was fractionated using supercritical carbon dioxide at 40°C and pressures from 10.3–27.6 MPa. Extractions followed by one or two stage separation were collected at atmospheric pressure and ambient temperature. Triglyceride analysis of extracts using HPLC and evaporative light scattering detection resolved 15 major peaks. Triglyceride content (mg/g extract) was influenced by extraction conditions. Extraction at 27.6 MPa and separation at 20.7 MPa resulted in highest triglyceride concentration, while 13.8 MPa resulted in the lowest. Saturated and monounsaturated triglycerides were selectively extracted based on solvent density and molecular weight. Little selectivity of polyunsaturated triglycerides was observed for fractionating beef fat.

Characterization of Polymers and Their Surfaces Using Ultra-Soft X-Ray Absorption Spectroscopy

AbstractIn this paper we illustrate the use of Ultra Soft X-ray Absorption Spectroscopy (USXAS) for the characterization of polymeric materials by highlighting three novel applications of the technique. The surface sensitivity of electron yield (3 nm) and the bulk information available from fluorescence yield USXAS (200 nm) provide unique information on the chemistry of polymer surfaces and interfaces. USXAS is sensitive to both concentration and orientation of functional groups in polymers. The systems highlighted here include the characterization of flame treated model acrylic automotive coatings, ultra-low surface energy crosslinked fluorocarbon films, and spin cast polystyrene films. The chemical and surface sensitivity of the technique are emphasized by the ability of USXAS to detect an increase in the trigonally coordinated carbon at the surface after treatment with a reducing flame. The sensitivity to functional group orientation at the surface is demonstrated by the characterization of the crosslinked flurocarbon polymer films. The results show that the pendant fluoroalkyl moieties of these polymers are strongly oriented perpendicular to the film surface. Spin coated polystyrene films were characterized as a functionv of molecular weight, film thickness and casting solvent. The pendant phenyl groups were found to be preferentially oriented towards the normal to the surface plane, independent of casting solvent, molecular weight, and film thickness

Processing of poly(amide imides) as matrices for high‐performance composites

AbstractPoly(amide imide) (PAI) has proven to be an excellent engineering thermoplastic. Injection and compression molding processes are currently used to produce poly(amide imide) parts when superior toughness, solvent resistance, and high‐temperature heat performance are required. The objective of this work was to determine the essential features necessary to use these systems as matrices for carbon‐fiber‐reinforced composites. The principal steps utilized were: impregnation of the carbon fibers with a PAI solution, drying the solvent from the individual plies, stacking the plies for final consolidation, and a postcure. A processing cycle was developed applicable to resins with different solvent concentration and molecular weight, giving special attention to the solvent evaporation step. A model capable of predicting the rate of evaporation as a function of temperature was developed using the principle of time–temperature superposition. A viscosity model similar to that for a curing thermoset was developed by combining Arrhenius expressions for the temperature and concentration effects. Collectively, this work then provided insight for matrix requirements in the formulation of PAI composites by solvent impregnation.

Poly(4‐methylstyrene‐co‐chloromethylstyrene): A negative electron beam resist—synthesis and lithography evaluation

AbstractSynthesis and lithographic characterization of a series of negative acting electron sensitive resists based on poly(4‐methylstyrene‐co‐chloromethylstyrene) are reported. The sensitivity and contrast of these resists were found to depend on the chloromethylstyrene (CMS) content and an optimum value of 5 wt% was determined from consideration of parameters associated with the reproducibility of the synthetic method and also the lithographic performance. Both the sensitivity and resolution were found to depend on the molecular weight and CMS content of the copolymer. Several methods of scale up for the synthesis were explored, the route having a very significant influence on the film formation characteristics of the resists. The reactivity ratios of the monomers were measured in order that the compositional drift, which occurs during the synthesis, could be quantified. The effect of solvent composition and molecular weight of the copolymer were explored in relation to the quality of the resulting lithography. These studies have indicated that the copolymer has the potential of being used as a VLSI sub‐micron resist with good plasma etch resistance.

Novel thermoplastic elastomer triblocks of a soft polyisobutylene midblock connected to two hard PMMA stereocomplex outer blocks

The preparation of PMMA stereocomplexes as outer blocks of the thermoplastic elastomer were prepared by blending isotactic PMMA (iPMMA) with the syndiotactic PMMA (sPMMA) blocks. The melting temperature of the iPMMA/sPMMA stereocomplexes is affected by the relative amounts of the i- and sPMMA in the outer blocks and is much higher than either of the T g of the i- and sPMMA components. The blending solvent, i- and sPMMA molecular weights and annealing affect stereocomplexation.

Solubility studies on a paraffin wax in base oils

The solubility of a paraffin wax with m.p. 43 °C in various base oils was experimentally investigated. A general empirical correlation for the prediction of paraffin wax solubility in various base oils was developed using the solvent molecular weight and the solubility temperature values. The results were compared with experimental data. The correlation was found to reproduce the experimental data with an average absolute deviation of 9.0% and a maximum absolute deviation of 19.7%.

Characterization of the active centers in the cationic polymerization of p‐substituted α‐methylstyrenes

AbstractPolymer tacticity, molecular weight and molecular weight distribution were used as the basis for characterizing the type of active centers present in the cationic polymerization α‐methylstyrene monomers. The affect of reaction solvent polarity and the resonance effects of para‐substituents were used to deduce the nature of, and changes in, the ion pair character of the carbocation active center. For this purpose, the polymer yield, tacticity and molecular weight parameters were determined in the cationic polymerization reactions of p‐chloro and p‐fluoro‐α‐methylstyrene. The dielectric constant of the reaction medium was varied by using mixtures of methylene chloride and either hexane, a non‐solvent for the polymers, or toluene, a good solvent for the polymers. For both solvent systems, the yields and molecular weights of the polymers from both of the monomers were strongly effected by reaction time and solvent composition. Also, for both monomers, tacticity did not change with reaction time, and for the p‐fluoro monomer tacticity was constant with changes in reaction solvent composition in both mixed solvent systems. In contrast, the tacticities of the polymers from the p‐chloro monomer decreased with increasing amounts of the non‐polar solvent in the mixture. The tacticity effects induced by reaction solvent changes are interpreted on the basis of the electronic effects of the para‐substituents on changing the ion pair character of the carbocation active center. The effect of solvent composition on polymer yield and molecular weight may be a function of changes in the rates of initiation, propagation and monomer transfer, with the latter two also determined by the ion pair character of the carbocation active end group.

The importance of the motion of water for magnetic resonance imaging.

Since the water content of all soft tissues is about the same, contrast in magnetic resonance imaging depends principally on the parameters that govern nonequilibrium behavior of the nuclear spin system of the water protons of tissue, the longitudinal and transverse relaxation rates 1/T1 and 1/T2. A fundamental understanding of the determinants of both 1/T1 and 1/T2 at a cellular level, and ultimately at a molecular level (so that contrast can be optimized and perhaps manipulated), will require a model of the behavior of water that describes the dynamics of the motion of water molecules throughout tissue. A particular model is presented here, one in which tissue water is relatively free to diffuse randomly throughout the intracellular and extracellular regions of tissue, colliding with cellular and subcellular constituents along the way; this motion dominates 1/T1 at higher fields. When not in actual contact with interfaces, ie, within about 5 A of a macromolecular surface, the thermal motion of the water molecules is not influenced by the interfaces, but is altered slightly by the presence of solute macromolecules. However, this small difference is amplified 10(6)-fold, roughly the ratio of the macromolecular to solvent molecular weights, by a mechanism previously named the "slosh effect"; this effect dominates 1/T1 at low fields, and 1/T2 at all fields. It is shown how the foregoing view of tissue water follows quite naturally from NMRD profiles (measurements of the magnetic field dependence of 1/T1 of water protons) of a wide variety of protein solutions and samples of tissue, both native and containing added paramagnetic (Mn2+)ions.(ABSTRACT TRUNCATED AT 250 WORDS)

An investigation of the structure of micelles formed by a polystyrene-b-poly(ethylene/propylene) block copolymer in paraffinic solvents using 1H and 13C-nuclear magnetic resonance

The dynamic structure of micelles formed by a polystyrene-b-poly(ethylene/propylene) block copolymer in paraffinic solvents has been studied by electron microscopy, photon correlation spectroscopy and 1H and 13C-nuclear magnetic resonance. In n-octane below 50°, the polystyrene core has two components, a “rigid” component exhibiting the same NMR linewidth as bulk glassy polystyrene and a “mobile” component attributed to a plasticised surface layer. The “rigid” component undergoes a sharp linewidth transition at 50° attributed to segmental motions. In n-octane, the micelles dissociate significantly above 80°. In higher alkanes, the dissociation occurs at increasing temperature with increasing solvent molecular weight.

Diffusion in organic liquids. 4. An evaluation of the influence of solvent viscosity and molecular weight on the isotope mass effect for tracer diffusion

Diffusion in organic liquids. 4. An evaluation of the influence of solvent viscosity and molecular weight on the isotope mass effect for tracer diffusion

Concentrated solutions of SBS block copolymers in solvent mixtures

The viscosities of 10% and 20% solutions of linear and non-linear SBS block copolymers were measured in various solvent pairs comprising ethyl acetate/toluene, ethyl acetate/cyclohexane, ethylacetate/carbon tetrachloride, ethyl acetate/n-hexane, ethyl acetate/cyclohexanone, methyl ethyl ketone/cyclohexanone and methyl ethyl ketone/n-hexane. Addition of the second solvents to 10% solutions of the polymers in ethyl acetate or methyl ethyl ketone gave rise to peaks around 10% to 14% added solvents. These peaks are caused by phase separation involving micelles and their occurrence depends on the interplay of composition of solvent mixtures, molecular weight and solution concentration and not on polymer architecture, styrene content or state of shear.

The viscosity of polycapramide solutions as a function of chemical non-uniformity, molecular weight, concentration and solvent type

The possibility of formulating the general characteristics of the viscosity as a function of the solvent type, concentration, temperature, molecular weight and chemical non-uniformity of the macromolecules has been shown on the solutions of a number of polycapramide samples with diverse non-uniformities of their macromolecules. The preferred methods of generalizing the concentration dependence of the viscosity of polycapramide solutions are those based on the Budtov theoretical equation and the Schultz-Blaschke empirical equation.

ChemInform Abstract: THE SOLVENT EFFECT ON DI‐TERT‐BUTYL NITROXIDE. A DIPOLE‐DIPOLE MODEL FOR POLAR SOLUTES IN POLAR SOLVENTS

New measurements of the solvent effect on the nitrogen hyperfine coupling constant of di‐tert‐butyl nitroxide are reported. These, together with literature data, are used to test various models for the solvent effect. At the Huckel level of approximation, aN is a linear function of the applied electric field. Thus various reaction field theories may be considered. The widely used Onsager reaction field does not account for the effects of the more polar solvents or for the differences between polar and nonpolar solvents. The Wertheim and Block–Walker reaction fields are better, especially for very polar solvents. However none of these continuum reaction fields is entirely satisfactory theoretically or experimentally. We propose a dipole–dipole model for polar solvents which is superior to the continuum models. From the dipole–dipole model, we suggest that the quantity μρ/M is a convenient linear parameter for polar solvent effects, the factors being solvent dipole moment, density, and molecular weight. The...

The solvent effect on di-t e r t-butyl nitroxide. A dipole–dipole model for polar solutes in polar solvents

New measurements of the solvent effect on the nitrogen hyperfine coupling constant of di-tert-butyl nitroxide are reported. These, together with literature data, are used to test various models for the solvent effect. At the Hückel level of approximation, aN is a linear function of the applied electric field. Thus various reaction field theories may be considered. The widely used Onsager reaction field does not account for the effects of the more polar solvents or for the differences between polar and nonpolar solvents. The Wertheim and Block–Walker reaction fields are better, especially for very polar solvents. However none of these continuum reaction fields is entirely satisfactory theoretically or experimentally. We propose a dipole–dipole model for polar solvents which is superior to the continuum models. From the dipole–dipole model, we suggest that the quantity μρ/M is a convenient linear parameter for polar solvent effects, the factors being solvent dipole moment, density, and molecular weight. The dipole–dipole model should apply to a wide range of polar solutes. Some special situations are not explained by the model, including hydrogen-bonding solvents, halogenated aromatics, and solvents with more than one conformation. The temperature dependence of the solvent effect is also considered.

The rheological properties of carbopol gels I. Continuous shear and creep properties of carbopol gels

The effect of physical and chemical variables on consistency of Carbopol 940 and 941 gels was investigated by continuous shear rheometry. Gels provided plastic flow curves with negligible hysteresis. Continuous shear properties were not greatly affected by centrifuging, milling, temperature cycling, and ageing. Initial addition of neutralizing agent (0–6% w/w for 3% gels) markedly increased consistency; further addition caused a more gradual increase. Daylight reduced consistency. Apparent viscosities varied exponentially with concentration. Increased temperature gradually decreased apparent viscosity. Solvents had a variable effect on apparent viscosities which could not be correlated with solvent viscosity nor molecular weight. Apparent viscosities for gels neutralized with different bases were independent of type of base used.Small strain testing investigated fundamental properties of Carbopol gels and determined the effect of polymer concentration, temperature, neutralization, different solvents and neutralizers. Gels were linear viscoelastic and to a first approximation were elastic solids. Creep compliance varied exponentially with concentration and showed no correlation with solvent or neutralizer type.

Parameters, affecting the sensitivity of poly(methyl methacrylate) as a positive lithographic resist

AbstractThe contribution of parameters such as molecular weight, molecular weight distribution and stereochemistry to electron beam sensitivity of poly(methyl methacrylate), PMMA, has been investigated. The sensitivity is interpreted here as the minimum radiation dose required to obtain a predetermined solubility rate ratio, S/So = SR, of the exposed, S, and unexposed, So, material. The G‐value was foam be independent of molecular weight, molecular weight distribution, and stereochemistry. Data indicate that the weight average molecular weight ratio correlates better with SR than the number average molecular weight ratio. The tacticity of the resist and the developer solvent molecular weight or size have a large effect on solubility rate. Although the solubility rate pf isotactic PMMA is much greater than the syndiotactic and heterotactic stereoforms, the sensitivity appears to be independent of tacticity. In a homologous series of n‐alkyl acetate developer solvents, the molecular size of the solvent has a greater effect on the solubility rate than the molecular weight of the resist. A developer solvent has been selected from the n‐alkyl acetates which enhanced the sensitivity of PMMA.