Dilute solution properties of a polyurethane. I. Linear polymers

A linear polyurethane of high molecular weight was prepared in solution by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). The polymer was fractionated by using a direct sequential extraction procedure, with a solvent–nonsolvent system consisting of N,N′-dimethylformamide (DMF) and acetone (A). The resulting fractions were characterized by viscosity and lightscattering measurements. The relationship between the intrinsic viscosity and molecular weight was found in DMF at 25°C. to be [η] = 3.64 × 10^?4M^0.71. The unperturbed polymer chain dimensions were determined from intrinsic viscosity measurements carried out under experimentally determined theta conditions.     

Dilute-solution properties of ring polystyrenes

The temperature Θ_A2 at which the second virial coefficient A₂ is zero for ring polystyrenes is 28.5°C in cyclohexane, independent of molecular weight in the range 2 × 10⁴ to 4.5 × 10⁵. This cannot be explained solely by the Candau–Rempp–Benoit theory, which takes into account the effect of segment density on Θ_A2 The radius of gyration of a ring is found to be approximately one-half that of a linear polymer with the same molecular weight. The intrinsic viscosities [η] and intrinsic translational friction coefficients [f] of ring polystyrenes with molecular weights ranging from 7 × 10³ to 4.5 × 10⁵ have been measured in cyclohexane at 34.5°C (Θ, the Flory theta temperature for linear polystyrenes) and in toluene (a good solvent). The results are compared with those for linear polystyrene. It is found that the Mark–Houwink exponent is less than one-half in cyclohexane at Θ. In toluene it is 0.67 compared to 0.73 for linear polystyrene. The hydrodynamic measurements suggest that large rings are less expanded than the linear polymers with the same molecular weight, contrary to many predictions.     

Dilute solution properties of anionic polystyrene in ternary mixture toluene-2-butanone-2-methyl-1-propanol

Several polystyrene samples with relatively narrow molecular weight distributions have been prepared by anionic polymerization. Dilute solution properties of these samples in binary and ternary liquid mixtures were investigated by light scattering and viscometry, using toluene and 2-butanone as solvents and 2-methyl-1-propanol as non-solvent. At 25° experiments were performed to find a set of compositions of the mixed solvent where the second virial coefficient of the osmotic pressure expansion equals zero for the polymer solution, and a set of compositions of the mixed solvent where the intrinsic viscosity of the polymer solution equals the value for polystyrene a theta solvent, such as cyclohexane at 34.5°. The results suggest that these sets of compositions are not identical. The specific effects of sorption and preferential sorption which give rise to the difference between the sets of compoisitions are qualitatively discussed in terms of the Flory-Huggins theory.     

Effect of the solvent nature on the course of quaternization of 3,5-diethoxycarbonyl-2,6-dimethyl-4-(3-pyridyl)-1,4-dihydropyridine

The effect of the solvent nature and temperature on the quaternization of 3,5-diethoxycarbonyl-2,6-di- methyl-4-(3-pyridyl)-1,4-dihydropyridine by lipophilic alkyl bromides has been investigated. By comparison of the solvent effect (acetone, acetonitrile, and 2-butanone) on the alkylation of the pyridine fragment of 3,5-diethoxycarbonyl-2,6-dimethyl-4-(3-pyridyl)-1,4-dihydropyridine it was established that conducting the reaction in acetonitrile at 81 °C is the most optimal.     

The conductance of electrolytes in acetone-2-propanol and acetone-1,1,1,3,3,3-hexafluoro-2-propanol mixtures at 25°C1

Precise conductance measurements are reported for tetrabutylammonium chloride, bromide, iodie, and perchlorate and lithium chloride in acetone-2-propanol (2-PrOH) and acetone-1,1,1,3,3,3-hexafluoro-2-propanol (HFP) mixtures at 25°C. Densities, viscosities and dielectric constants of the mixtures were determined. The dielectric constant vs mole % acetone curve for the acetone (ε=19.4)-2-propanol (ε=20.5) goes through a minimum at 40% acetone (ε=17.4), while that for acetone-HFP (ε=16.8) goes through a maximum at 50% acetone (ε=26.87). The variations ofK _A with ε in acetone-HFP are in accord with the predictions of electrostatic theory, while those for acetone-2-PrOH show more complex behavior. Ionic association in these mixtures is discussed in terms of an interplay between solvent structure and a multiple-step association process.     

Unperturbed dimensions of poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly(2,6-diphenyl-1,4-phenylene oxide) chains

The unperturbed chain dimensions of unfractionated poly(2-methyl-6-phenyl-1,4-phenylene oxide) and poly-(2,6-diphenyl-1,4-phenylene oxide) have been measured by combining molecular weight data from light scattering with intrinsic viscosity data in chloroform. The unperturbed chain dimensions of the former polymer were also measured directly by light scattering dissymmetry in a critical consolute solvent mixture (methyl cyclohexane: 1,4-dioxane 50:50 by volume). The results of these measurements and of measurements reported by other investigators are satisfactorily explained by postulating no dimension-expanding prejudice in azimuthal angle in chain conformers of the 2,6-substituted-1,4-phenylene oxide polymers. This corresponds to equal population of the two chain rotation energy minima at azimuthal angles 90° and 270°. Accepting this postulate, one calculates from the observed chain dimensions that the C? O? C bond angle is 118–120° in these aromatic polyethers in solution.     

Matched ring diblock and linear triblock copolymers in dilute solution

A unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12–35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light-scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 10⁴ for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (D_c) and linear triblock copolymer (D₁) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are D_c/D_l = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.     

Sorption of vapors of organic solvents with cyanoethyl hydroxyethyl cellulose

The interaction of cyanoethyl hydroxyethyl cellulose with acetone, methylene chloride, and trifluoroacetic acid in the temperature range 10–50°C was studied by the solvent vapor sorption technique. The temperature and concentration dependences of the Flory-Huggins parameter for polymer-solvent interaction Z₁ and the mechanism of the structural rearrangement in the systems were determined.     

Solution Properties and Chain Stiffness of Poly(Acenaphthylene)

Abstract

Solution properties of poly(acenaphthylene) (PACN) were investigated in a theta solvent (1,2-dichloroethane) and a good solvent (chloroform). The viscosity exponent α was found to be 0.50 at both 35 and 41 °C in 1,2-dichloroethane. Unperturbed dimensions found from viscometric measurements were compared with those of other vinyl aromatic polymers. Calculation of the chain flexibility parameters led to the conclusion that PACN is a rather stiff chain compared to other vinyl polymers with its characteristic ratio C∞ of 18.2 and chain flexibility parameter λ of 7.     

Development of an enantioselective membrane from cellulose acetate propionate/cellulose acetate,for the separation of trans-stilbene oxide

This paper reports the characterization of new synthesized chiral polymeric membranes, based on a cellulose acetate propionate polymer. The flux and permselective properties of the membrane were studied using 50 % ethanol solution of (R,S)-trans-stilbene oxide as feed solution. Scanning electron microscopy revealed the asymmetric structure of these membranes. The roughness of the surface was measured by atomic force microscopy. The resolution of over 97 % enantiomeric excess was achieved when the enantioselective membrane was prepared with 18 wt% cellulose acetate and 8 wt% cellulose acetate propionate in the casting solution of dimethyl formamide/N-methyl-2-pyrrolidone/acetone, at 20 °C and 55 % humidity, and a water bath at 10 °C for the gelation of the membrane. The operating pressure and the feed concentration of the trans-stilbene oxide were 275.57, 345.19, and 413.84 kPa and 2.6 mM, respectively.     

Ion association of lithium bromide,chloride and picrate and of sodium picrate in 2-propanol at 25°C. I. Conductance measurements

The molar conductances of lithium bromide, chloride and picrate, and of sodium picrate have been determined as a function of salt concentration in 2-propanol solvent at 25°C. Values of the limiting molar conductance, Λ₀, and ion pair formation constant K_A have been calculated for each of these salts using both the Fuoss 1978 and the Lee and Wheaton conductance equations. Both of these equations yield comparable results for the present systems. The limiting conductances found here are compored with those reported for lithium chloride in 1-propanol and acetone and with those for the picrates in acetone and 2-butanone, all solvents of comparable dielectric constants. The Rasaiah-Friedman square mound potential, h_+?/kT, has been calculated for each salt using the approach of Justice and Justice. These values for 2-propanol have been compared with those for lithium chloride in 1-propanol and in acetone and for the picrates in acetone and 2-butanone.     

Gravimetric analysis of membrane casting : I. Cellulose acetate — acetone binary casting solutions

Solvent evaporation from cellulose acetate solutions cast to a thickness of 100–500 μ m is followed gravimetrically at 12–28°C. The desolvation curves include a region in which ω (solvent/polymer weight ratio) decreases almost exponentially with time. The exponential decrease lasts, at 28°C, until 75–85% solvent has evaporated, whereas below 19°C, upward bending in the log w vs. t relation is observed after evaporation of about half the solvent. The time constant of desolvation, τ, increases with the initial acetone weight per unit area, d, as τ α d^γ, where γ = 1.4–1.6. About a threefold increase in τ is observed on decreasing temperature from 28 to 12°C. Numerical solutions of the diffusion equation are obtained by taking time-dependence of surface solvent concentration and movement of the solution/air interface into account. The experimental facts are shown to be explicable by comparison with calculations. The effectiveness of the gravimetric approach to an understanding, characterization, and control of membrane casting processes is discussed.     

Relaxation and Miscibility of the Blends of a Poly (Ether Imide) (Ultem™) and a Phenol-A-Based Copolyester (Ardel™) by Inverse Gas Chromatography

Inverse gas chromatography (IGC) was used to analyze the secondary transition temperatures and the miscibility of binary mixtures of poly (ether imide) (Ultem™) and a copolyester of bisphenol-A with terephthalic and isophthalic acids (50/50) (Ardel™) in three compositions (25/50, 50/50 and 75/25). Retention diagrams of the mixtures of Ultem™ and Ardel™ for n-nonane, n-decane, n-butyl acetate and isoamyl acetate were obtained at temperatures between 60 and 285 °C. Second-order transition temperatures of the mixtures were determined according to the slope change in retention diagrams of the solvents. The glass transition temperatures of the mixtures suggested the miscibility of the polymers. Polymer–polymer interaction parameters of binary mixtures of the polymers were determined at temperatures between 260 and 285 °C by Flory–Huggins theory. The polymer–polymer interaction parameters were dependent on the solvent used. The small values of polymer–polymer interaction parameters close to zero suggest some weak interactions between the polymers in the mixture. It was concluded that it was possible to obtain more meaningful information related to the interactions of polymers in a mixture from IGC measurements, if binary polymer–solvent interaction parameters of the used solvent probes were around 0.5.

     

Synthesis and characterization of palladium–tin bicolloids prepared by chemical liquid deposition

Palladium–tin bicolloids have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with ethanol, 2-propanol, 2-methoxyethanol, 2-butanone and acetone. The distribution of particle sizes was determined by transmission electron microscopy of the stables dispersions. The sizes ranged from 3.8 nm for 2-methoxyethanol to 8.3 nm for acetone colloids. Electrophoretic measurements such as colloid charge and zeta potential were achieved. lt was found that the colloids possess electrical charge; therefore, it is postulated that their stability is by simple solvatation. The colloids showed stability over 1 week at room temperature. The zeta-potential values are in agreement with the stability and electrophoretic mobility. The highest zeta potential was obtained for PdSn–2-methoxyethanol colloids with 379 mV and the lowest for 2-butanone with 114 mV. The colloids exhibit absorption bands in the UV region. In the visible region no plasma absorption was found. Active solids obtained by evaporation of the solvent contain a certain amount of the solvent incorporated, and owing to their reactivity they produce a mixture of tin oxide with palladium and tin. The presence of solvents can be observed by Fourier transform IR incorporation in the finely divided solids. Characteristic bands for each solvent were measured. By means of thermogravimetric analysis and differential scanning calorimetry the thermal stability of the solids and the transition heat give us the carbonaceous residues in the films. The elemental analysis of the powders was carried out.     

Polystyrene in cyclopentane: Dilute solution properties from the upper critical to the lower critical solution temperature

Dilute solutions of polystyrene in cyclopentane are studied with four narrow-distribution polymer fractions ranging in molecular weight from 1.6 × 10⁵ to 1.8 × 10⁶. Light scattering (total intensity) and viscosity measurements cover a temperature range spanning both “theta” temperatures: the limiting upper critical solution temperature (19.6°C) and the limiting lower critical temperature (154.5°C). Within experimental uncertainty, chain dimensions are the same at the two theta temperatures. Correlations among second virial coefficients, mean-square molecular radii of gyration, and intrinsic viscosities, are analyzed. Temperature and molecular-weight dependences are correlated satisfactorily in terms of the excluded-volume parameter z that is central to the “two-parameter” theories of dilute solution behavior. The data can also be correlated in the framework of the newer renormalization theories.     

Cellulose membranes grafted with vinyl monomers in a homogeneous system

The homogeneous grafting of hydrophilic monomer onto cellulose derivatives was carried out in an aqueous system at 30, 50, 70 and 90 °C during reaction periods of 30 to 180 min. The graft polymer was isolated by ethanol from the reaction mixture, dried, and weigh. The grafted polymer was characterized by IR spectroscopy as well as microscopic sample morphology detected by electron scanning microscopy. The water absorption capacities and grafting values of grafted cellulose derivatives were also determined. The maximum grafting yield was obtained at 30 °C. Copyright © 2002 John Wiley & Sons, Ltd.     

Unperturbed dimensions of poly(ethylene oxide)

The intrinsic viscosities of fractions of poly(ethylene oxide) in the molecular weight range 1.5 × 10³ to 10⁶ have been measured at 25°C in benzene, carbon tetrachloride, and acetone; at 35°C in 0.45M aqueous potassium sulfate; and at 50°C in methyl isobutyl ketone and diethylene glycol diethyl ether. The latter three are practically theta solvents. The value of (r₀² /M)^1/2 for poly(ethylene oxide) is calculated to be 0.84 Å from the molecular weights of the high molecular weight fractions, and their intrinsic viscosities in the theta solvents and acetone. Erroneous values result if the usual methods of determination are applied to the data obtained for the low molecular weight (<10⁴) fractions or to the intrinsic viscosities in the very good solvents, benzene and carbon tetrachloride.     

Interval kinetic gravimetric sorption of acetone in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Interval sorption kinetics of acetone in solvent cast films of random poly(ethylene terephthalate)-co-(ethylene 2,6-naphthalate) (PET-co-PEN) are reported at 35°C and at acetone pressures ranging from 0 to 7.3 cm Hg. Polymer composition is varied systematically from 0% to 50% poly(ethylene 2,6-naphthalate). Equilibrium sorption is well described by the dual-mode sorption model. Interval sorption kinetics are described using a two-stage model that incorporates both Fickian diffusion and protracted polymer structural relaxation. The incorporation of low levels of PEN into PET significantly reduces the excess free volume associated with the glassy state and, for these interval acetone sorption experiments in ∼ 5 μm-thick films, decreases the fraction of acetone uptake controlled by penetrant-induced polymer structural relaxation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2973–2984, 1999     

Raman depolarization measurements over the entire miscible range for polystyrene–cyclohexane and polydimethylsiloxane–benzene solutions: Determination of upper theta temperatures

Raman depolarization ratio measurements (ρ) have been made for 20% polydimethylsiloxane (PDMS) solutions in benzene and 10% Polystyrene (PS) solutions in cyclohexane over the temperature range 20 > T > 200°C. The bands studied were the 2907 cm^?1 methyl stretch in PDMS and the 1002 cm^?1 ring breathing mode in PS. The measured ρ are related to rotational isomeric state populations and a qualitative picture of the polymer conformation changes over much of their miscible ranges is described. Measurements of ρ for PDMS gum over the temperature ranges 20 < T < 200°C have been obtained and the upper theta temperature has been determined to be 171 ± 3°C for PDMS/benzene. Quantitative information about the variation of the polymer solvent interaction parameter χ can in principle be obtained.     

Lithiated cyclopropanone ketals

The ketene acetal I reacted with dibromocarbene yielding the dibromocyclopropanone ketal II, which was reduced to the monobromide III by treatment with tri-n-butyltin hydride. Reaction of III with n-butyllithium at ?78°C yielded the lithiated cyclopropanone ketal IV, which yielded adducts with acetone, cyclohexanone, cyclohexenone, 3,3,3-trimethoxybutan-2-one, 2-butanone, and 3-pentanone.