Reversible selectivity of water/organic solvent mixtures in poly(lactic acid) film

The separation properties of water/organic solvent mixtures in poly(lactic acid) (PLA) films were investigated. The organic solvent flux increased linearly as the feed concentration increased, whereas the water flux was almost constant up to a feed concentration of 30 wt %. Interestingly, the permselectivity of PLA films was reversed from organic solvent selectivity to high water selectivity depending on the type of organic solvent. The permselectivity was strongly correlated with the solution concentration at which the solvent‐induced crystallization of the PLA films occurred. The selectivity of permeation, solution, and diffusion in water/organic solvent mixtures was determined by the expanded free volume of the PLA films as a result of the interaction between PLA and the water/organic solvent mixture. The permeability behavior of water/organic solvent mixtures in PLA films was very complex. However, it was found that this behavior could be predicted through immersion tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43822.     

Orientation of merocyanine dye in Langmuir-Blodgett films of mixtures of poly(γ-benzyl l-glutamate)/poly(ethylene oxide)/ poly(γ-benzyl l-glutamate) block copolymer and dye

Summary Merocyanine dye(MD) can be spread with poly(γ-benzyl L-glutamate)/poly(ethylene oxide)/poly(γ-benzyl L-glutamate)(PBLG/PEO/PBLG) onto the air-water interface from a solvent in which the copolymer assumes a helical conformation. The expanded isotherm of the copolymer changed into compressed one with mixing of MD in the copolymer monolayer. Langmuir-Blodgett(LB) assemblies can be built up from copolymer/MD mixture layer when the helical axes of the polypeptide chains are oriented in the compression direction. The dichroic absorption of the copolymer/MD mixtures indicates that dyes are located with a preferential orientation of their molecular axes with regard to the director axis of the polypeptide.     

The solubility of poly(vinylidene chloride) in solvent mixtures

Effective solvents for poly(vinylidene chloride) (PVDC) were obtained by mixing a polar aprotic solvent with a less polar solvent of cyclic structure. The polar components included sulfoxides, N,N-dialkylamides, and N-alkyl lactams. The cyclic cosolvents included aliphatic and aromatic hydrocarbons, ketones, ethers, and thioethers. The problem of solubility of a crystalline polymer in a mixed solvent was analyzed by extending the Flory theory of melting point depression to three component mixtures. The results predict that favorable mixtures arise when at least one of the components interacts strongly with the polymer but is nearly incompatible with the cosolvent. This is in qualitative agreement with the observed behavior of PVDC.     

Development of poly(vinylidene fluoride) hollow-fiber membranes for the treatment of water/organic vapor mixtures

Attempts were made to spin hollow-fiber membranes from poly(vinylidene fluoride) (PVDF) material by the dry–wet phase inversion method. Hollow fibers so prepared were characterized for various parameters and by electron microscopic techniques. Membranes were also tested for the separation of water/1-propanol mixtures in vapor phase. It was found that the hollow fibers were water selective despite the fact that PVDF material is hydrophobic. Intrinsically organic selective property of PVDF material was proved by coating a porous polyetherimide membrane with a PVDF layer, which resulted in enhancement of 1-propanol permeation while suppressing the permeation of water. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1263–1270, 1997     

Gelation of poly(vinyl alcohol) in dimethyl sulfoxide/water solvent

Summary Gelation of poly(vinyl alcohol) (PVA) in dimethyl sulfoxide (DMSO)/water was observed at 23°C with viscometry, spectrophotometry, wide angle X-ray scattering and light scattering. Here transparent gel formation was found to take place prior to being turbid in some cases, whereas the solution became turbid prior to gelation in other cases. Whether transparent gel is formed at first or solution becomes turbid, depends on DMSO composition. PVA solution forms gel in the DMSO composition range from 20 to 80 wt.%. Below the boundary DMSO composition of 60–70 wt.%, gelation takes place at first (i.e. transparent gel is formed) and then becomes turbid eventually, while beyond this DMSO composition the solution becomes turbid and then opaque gel is formed.     

Upper critical solution temperature—type cononsolvency of poly(N,N-dimethylacrylamide) in water—organic solvent mixtures

The behaviour of linear poly(N,N-dimethylacrylamide) (PDMAM) chains was studied by turbidimetry and viscometry in mixtures of water with the polar organic solvents methanol, dioxane and acetone. The swelling-deswelling behaviour of PDMAM gels in the same solvent mixtures was also investigated. Contrary to the behaviour in water-methanol mixtures, in water-dioxane and water-acetone mixtures a significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, was observed for high organic solvent fractions. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon decreasing temperature. This upper critical solution temperature (UCST) phase separation behaviour in mixed solvents was studied by turbidimetry and compared to the well-known lower critical solution temperature (LCST) behaviour of poly(N-isopropylacrylamide) (PNIPAM) in similar solvents mixtures.     

Pervaporation of ethanol–organic solvent mixtures through poly(2,6-dimethyl-1,4-phenylene oxide) membrane

Homogeneous dense membranes of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were used to separate mixtures of ethanol—organic liquid by pervaporation. If the organic liquid had a strong affinity to PPO (e.g., toluene) and its concentration in the feed was low, smaller molecules of ethanol permeate preferentially through the membrane. When the concentration of this liquid in the feed was increased up to a certain value, the membrane was, on the contrary, permeated by it preferentially. When its concentration in the feed was further increased, flux through the membrane is dramatically increased and the membrane lost its selectivity. If the liquid in a binary mixture with ethanol in the feed had a low affinity to PPO (e.g., 1-propanol), the selectivity of the PPO membrane virtually did not depend on the feed composition, and the membrane was preferentially permeated by smaller molecules. © 1994 John Wiley & Sons, Inc.     

Reentrant conformation transition in poly(N,N-dimethylacrylamide) hydrogels in water-organic solvent mixtures

Conformational changes in poly(N,N-dimethylacrylamide) (PDMA) networks swollen in aqueous solutions of organic solvents are studied both experimentally and theoretically. PDMA hydrogels of various charge densities were prepared by free-radical crosslinking copolymerization. Swelling behavior of the hydrogels was investigated in aqueous organic solvent mixtures as functions of solvent species and the concentration. With increasing volume fraction ? of acetone, tetrahydrofuran, or 1,4-dioxane in the aqueous solution, PDMA hydrogels exhibit reentrant conformation transition. During this transition, the gel first deswells in the range of ? between 0.4 and 0.9, and then rapidly reswells if ? is monotonically increased. The reswelling of the collapsed PDMA gel occurs in a narrow of ? above ?=0.97. It was shown that the reentrant transition in PDMA gels requires moderate hydrogen bonding organic solvents, so that the hydrophobic interactions between PDMA and the organic solvent dominate the swelling process. The results were interpreted using the theory of equilibrium swelling. The interaction parameters in the gel system as well as the partition parameter of the organic solvent between the gel and the solution phases were calculated.     

Investigation of organic solvent/oil sorption capabilities of phenylene-bridged cross-linked poly(alkoxysilane)s

Phenylene-bridged cross-linked poly(alkoxysilane)s produced by the condensation of 1,4-bis(triethoxysilyl) benzene (BTEB) with different lengths of aliphatic diols in proper stoichiometric ratios were successfully prepared. The synthesized phenylene-bridged poly(alkoxysilane)s were characterized by Fourier transform infrared spectroscopy (FTIR), solid-state ¹³C and ²⁹Si cross polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR), and thermal gravimetric analysis (TGA). The oil and organic solvent uptake capacity, reusability, absorption and desorption kinetics of cross-linked polymers were examined. The effect of chain length of the linear diol monomers on the polymer-solvent interaction was also investigated. The swelling experiments were conducted in oils such as gasoline, euro diesel and organic solvents such as dichloromethane, tetrahydrofuran, benzene and toluene. All the synthesized polymers have high and fast swelling properties in oils and organic solvents. The reutilize properties of polymer in organic solvents were also investigated.     

Self-assembly of C60 containing poly(methyl methacrylate) in ethyl acetate/decalin mixtures solvent

[60]Fullerene (C₆₀) was mono-substituted with well-defined poly(methyl methacrylate) (PMMA-b-C₆₀) using the atom transfer radical polymerization (ATRP) technique. The self-assembly behaviors of PMMA-b-C₆₀ in ethyl acetate (EA) and decalin mixtures were studied using laser light scattering (LLS) and transmission electron microscopy (TEM). Homogeneous solutions of PMMA-b-C₆₀ can be obtained in the solvent mixtures containing more than 40 wt% EA, where the molar ratio of decalin to EA is close to 1. For each solvent mixture, unimers coexist with micelles and large aggregates. The sizes of PMMA-b-C₆₀ micelles and aggregates are independent of polymer concentration, confirming that they are produced via the closed association mechanism. For the various solvent mixtures, the weight-averaged molecular weights, M_w of the PMMA-b-C₆₀ aggregates range from 4.1×10⁷ to 12.5×10⁷ g/mol. The hydrodynamic radii of the large aggregate, R_h, vary from 90 to 136 nm, while the z-averaged radii of gyration, R_g, range from 210 to 311 nm. The R_g/R_h value for each solvent mixture is ∼2.3, which is independent of decalin contents in the mixed solvents. The morphological study using the transmission electron microscope suggests that the large aggregates are composed of porous large compound micelles (LCM) in solution.     

Interpretation of the enhanced solubility of poly(vinylidene chloride) in certain solvent mixtures

The 3-component mixture poly(vinylidene chloride)—tetramethylene sulfoxide–tetrahydrophalene has been investigated by viscometric methods. This solvent pair shows an unusal affinity for the polymer. This can be attributed to the strong polar interaction between the acidic polymer and the basic sulfoxide which is enhanced by the presence of the nonpolar diluent.     

Influence of high-pressure on cononsolvency of poly(N-isopropylacrylamide) nanogels in water/methanol mixtures

We show that the temperature-induced collapse of poly(N-isopropylacrylamide) (PNiPAm) nanogels in water/methanol mixtures can be reversed by excess hydrostatic pressure. Small angle X-ray scattering (SAXS) results reveal that first a swollen surface layer is established and then the particles swell homogeneously. A threshold pressure needed for rewelling fully collapsed nanogels indicates that hydrophobic interactions inside the nanogel have to be compensated to form a swollen surface layer. The size change is related to a change in polymer solvation detected by infrared (IR) spectroscopy. Pressure favours polymer/water hydrogen bonds to the cost of methanol/polymer bonds so that water is enriched inside the nanogel.     

Measurement and modeling of poly(vinyl acetate)–solvent viscosity mixtures

The viscosities of various poly(vinyl acetate) (PVAc)–solvent mixtures (PVAc–toluene, PVAc–benzene, and PVAc–cyclohexanone) were measured at different temperatures with a Haake viscometer. The required molecular weight of a commercial‐grade PVAc sample was measured with an Ubbelohde viscometer. The measured viscosities were correlated with a previously proposed viscosity model, and the model parameters were calculated. The results indicated the applicability of the model to the viscosity calculations of PVAc–solvent mixtures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1244–1249, 2005     

Crystalline complex between poly(γ-methyl l-glutamate) and dimethyl phthalate

The crystalline complex between poly(γ-methyl l-glutamate) (PMLG) and dimethyl phthalate (DMP) has been formed in films cast from a solution in dichloroethane. It has the stoichiometry of 1 mol of DMP to three or four residues of PMLG and shows two definite characteristics in X-ray diffraction patterns; one is the large hexagonal unit cell with the edge of around 28 Å and another the ‘extra’ 5.07 Å meridional reflection which can not be interpreted by a PMLG α-helical conformation. The structural examination for the films with various DMP contents is carried out by X-ray, viscoelastic, and d.s.c. measurements and the following structure is proposed for the crystalline complex. Four PMLG are associated to form a group which is hexagonally packed and DMP molecules, located in the gaps between groups, form a specific favourable helical structure along PMLG chains in which the van der Waals stacking of benzene rings of DMP is significant.     

Measurement and correlation of solubility of meropenem trihydrate in binary (water + acetone/tetrahydrofuran) solvent mixtures

The solubility of meropenem trihydrate in water + acetone mixtures and water + tetrahydrofuran mixtures were determined from T =(278.15 to 303.15) K by static method under atmospheric pressure.Effects of solvent composition and temperature on solubility of meropenem trihydrate were discussed.To extend the applicability of the solubility data,experimental solubility data in two kinds of binary solvent mixtures were correlated by the Apelblat equation and NIBS/Redlich-Kister model.It was found that the two models could satisfactorily correlate the experimental data and the Apelblat equation could give better correlation results.     

Intrinsic birefringence of amorphous poly(bisphenol-A carbonate)

The birefringence of uniaxially oriented poly(bisphenol-A carbonate) (PC) samples stretched over a wide range of temperatures has been measured accurately with a combination of the compensator and the wedge methods. The Hermans' orientation function of anisotropic PC was calculated from the measured dichroic ratio of the infrared absorption band at 1364 cm^-1. Measurements using differential scanning calorimetry, X-ray diffraction, or infrared spectroscopy indicated no stress-induced crystallinity in stretched amorphous PC. At each state having a defined molecular orientation, samples stretched below the glass transition temperature (T_g) always exhibited excess birefringence and slightly higher density. This phenomenon is attributed to bond distortion during stretching, a result of the suppression of large-scale segmental motions of polymer chains below the T_g. The birefringence of samples stretched above the T_g arises exclusively from the orientation effect as a result of greater chain mobility. These measured birefringence values are proportional to Hermans' orientation functions, yielding a linear relationship which allows precise determination of the intrinsic birefringence of amorphous PC as 0.192 ± 0.006.     

Solubility in the binary and ternary system for poly(alkyl acrylate)-supercritical solvent mixtures

Experimental cloud-point data to 210 ‡C and 2,200 bar are presented for binary and ternary mixtures of poly(methyl acrylate)-CO₂-methy acrylate and poly(ethyl acrylate)-CO₂, propylene, and 1-butene-ethyl aerylate systems. The accuracy of the experimental apparatus was tested by comparing the measured pressure-temperature phase behavior data of the poly(ethyl acrylate)-CO₂ system obtained in this study with those of Rindfleisch et al. [1995]. The phase behaviors for the system poly(methyl acrylate)-CO₂-methyl acrylate were measured in changes of pressure-temperature slope, and with cosolvent concentrations of 0, 5.0, 13.7, 25.3, and 43.3 wt%, respectively. With 48.3 wt% methyl acrylate to the poly(methyl acrylate)-CO₂ solution significantly changes, the phase behavior curve takes on the appearance of a typical lower critical solution temperature (LCST) boundary. The impact of ethyl acrylate on the cloud-point for the poly(ethyl acrylate)-CO₂ system shows the change of slope of the phase behavior curves from negative to positive with ethyl acrylate concentration of 0, 8.2, and 25.0 wt%. The cloud-point behavior for the poly(ethyl acrylate)-CO₂-39.5 wt% ethyl acrylate system shows an LCST curve. The solubility curve to ∼150 ‡C and 1,650 bar for poly(ethyl acrylate)-propylene-ethyl acrylate system shows the change of pressure-temperature diagram and with ethyl acrylate concentration of 0, 7.2 and 21.0 wt%. Also, when 41.1 wt% ethyl acrylate was added to the poly(ethyl acrylate)-propylene solution, the phase behavior curve showed the LCST region. The high pressure phase behavior of poly(ethyl acrylate)-1-butene-0, 3.1, 8.1, 18.5 and 30.7 wt% ethyl acrylate system presented the change of pressure-temperature curve from the UCST region to U-LCST region as the ethyl acrylate concentration increased.     

High birefringence of poly(trimethylene terephthalate) spherulite

Poly(trimethylene terephthalate) (PTT) spherulite shows interference color under polarized light microscope without a sensitive tint plate. The fact indicates that the retardation of PTT spherulite is high, while it was reported that the birefringence in PTT fiber is low. In this study, the reason why the high birefringence is observed in PTT spherulite was discussed. By small area X-ray diffraction measurement, it was confirmed that a-axis of unit cell of PTT crystal was parallel to the radial direction of the spherulite. Based on the result, we calculated the refractive indices of parallel to a-axis and the other orthogonal directions. It was clarified that the refractive index of a-axis is much lower than the others and the intrinsic birefringence for a-axis orientation is high. It is the reason why the PTT spherulite shows high and negative birefringence.     

Elongational flow-induced birefringence of polyacrylamide and poly(acrylamide-co-sodium acrylate)

Aqueous solutions of poly(acrylamide-co-sodium acrylate), in up to 1M NaCl, exhibited a flow-induced negative birefringence above a critical elongation flow rate in a crossed-slot device. Aqueous polyacrylamide, on the other hand, exhibited a positive birefringent pattern just above a critical elongation rate. At slightly higher elongation rates a negative birefringent thin-line region centred in the positive birefringent region appeared. This phenomenon was observed for all polyacrylamide concentrations tested (0.001 to 0.5 wt%; 0.5 to 20 times the quiescent overlap concentration). This change in birefringence sign can be qualitatively mimicked using a simple coil deformation model which includes contributions from intrinsic, microform and macroform optical anisotropy terms. Evidence is also given for this alternating birefringence sign pattern possibly being due to an elongational flow-induced change in the microstructure of the polyacrylamide.     

Spectroscopic study of anthraquinone dye/amphiphile systems in binary aqueous/organic solvent mixtures

The absorption spectra of novel dye/amphiphile systems, in which the dye is a 1,5-bis-(R-phenylamino)anthraquinone [R = o-methoxy, o-ethoxy, H] and the solvents are either organic or H₂O/organic solvent mixtures, have been investigated. It was found that an abrupt λ_max shift of more than 80 nm occurred for the system containing dye having R = o-methoxy and the amphiphile (poly-bis-(2,2′-dimethyl-5,5′-disulphonate)naphthylmethane disodium salt) in pure solvents with a specific E_T(30) value or in H₂O/DMF (N,N-dimethylformamide) mixtures containing at least 38% water. This type λ_max shift was not observed when solvent mixtures containing the other two dyes were studied. The origin of the pronounced λ_max shift is discussed in detail. It is believed that this shift arises mainly from changes in the solvation state of hydrophobic dye having R = o-methoxy when water is introduced in the presence of a dispersing agent. In this regard, dye is converted from the monomolecular state to dispersed particles.