Effects of solvent adsorption on solution properties of poly(vinyl alcohol)/dimethylsulfoxide/water ternary systems

In this study, the solvent adsorption phenomena of poly(vinyl alcohol) (PVA) in cosolvent mixtures of dimethylsulfoxide (DMSO; solvent 1) and water (solvent 2) were investigated. Typically, this cosolvent mixture could form hydrogen‐bonded DMSO/(water)₂ complexes, involving one DMSO and two water molecules. Because of the complex formation in the cosolvent mixtures, PVA chains preferentially adsorb water molecules at DMSO mole fraction X₁ < 0.33, but preferentially adsorb DMSO molecules at X₁ > 0.33. The preferential adsorption of DMSO (a good solvent for PVA) could cause the relatively extended conformation of PVA chains in solutions because of the increase in excluded volume effect. Because of various interactions between PVA chains and cosolvent mixtures, the aggregation and gelation behaviors of PVA solutions were significantly affected by the composition of cosolvent mixture. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3211–3217, 2004     

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.     

Effects of poly(vinyl alcohol) suspension medium on critical current density of Ba2Y1Cu3 oxide superconducting filaments produced by suspension spinning method

Superconducting Ba₂Y₁Cu₃ oxide filament was produced by means of the suspension spinning method. The effects of poly(vinyl alcohol) (PVA) suspension medium on structure and critical current density (Jc) of the filament sintered were explored with PVA of various degrees of polymerization (DP) in dimethyl sufoxide (DMSO), hexamethylphosphoric triamide (HMTA) and the mixed solution of DMSO and HMTA (1 : 1). Although the PVA was removed as a volatile component by heating treatment of the filament, the dispersion behavior of the oxide powder in the filament was dependent on the suspension medium, hence the microstructure and superconducting properties of the filament obtained was affected by the suspension medium. The filament spun through the mixed solution of DMSO and HMTA had a high Jc of 77 K more than 100 A/cm² at the wide range of DP and powder content. The crystal grains of the oxide in the sintered filament grew finer with increasing the DP of PVA. On the other hand, the Jc of the filament produced by pure solution of DMSO and HMTA was not detected at DP of 3000 and 2450, respectively, due to the influence of entanglement of the molecular chains of PVA.     

Characteristic rheological features of PVA solutions in water-containing solvents with different hydration states

Two organic solvent systems containing equimolar ratio of water but different association strenght, 8/2 by wt mixture of dimethyl sulfoxide (DMSO) and water and 86.7/13.3 by wt mixture of N-methyl morpholine N-oxide and water (NMMO monohydrate), were chosen and the rheological properties of polyvinyl alcohol (PVA) solutions in the solvents were investigated and compared. The associated state of water in the solvent systems had a significant effect on the rheological properties of the solutions. In dilute concentration regime, NMMO monohydrate gave higher intrinsic viscosity than DMSO/water although two solvents gave similar values of the Mark-Houwink exponent. More noticeable difference was observed on the viscosity curve in high concentration regime. DMSO/water exhibited near a Bingham behavior and gave much lower power-law index than NMMO monohydrate. On the logarithmic plot of storage modulus (G′) against loss modulus (G″), both solutions exhibited slight decrease in slope with increasing concentration. Of two solvent systems DMSO/water gave lower values of slope than NMMO monohydrate. In addition, NMMO monohydrate gave greater than one at low frequency whereas DMSO/water gave much less than one over the entire frequency range examined. Further, the frequency to cause gelation was decreased with increasing concentration in the case of NMMO monohydrate. This indicates that PVA/DMSO/water system is more heterogeneous because weakly bonded water molecules produce hydrogel structure.     

3D gel printing of magnetic hydrogel scaffolds assisted by in-situ gelation in a water level-controlled crosslinker bath

Polyvinylalcohol/chitosan (PVA/CS) is an excellent dual-network hydrogel material, but some significant challenges remain in fabricating composites with specific structures. In this study, 3D gel printing (3DGP) combined with a water-level controlled crosslinker bath was proposed for the rapid in-situ prototyping of PVA/CS/Fe₃O₄ magnetic hydrogel scaffolds. Specifically, the PVA/CS/Fe₃O₄ hydrogels were extruded into the crosslinker water to achieve rapid in-situ gelation, improving the printability of hydrogel scaffolds. The effect of the PVA/CS ratio on the rheological and mechanical properties of dual-network magnetic hydrogels was evaluated. The printing parameters were systematically optimized to facilitate the coordination between the crosslinking water bath and printer. The different crosslinking water baths were investigated to improve the printability of PVA/CS/Fe₃O₄ hydrogels. The results showed that the printability of the sodium hydroxide (NaOH) crosslinker was significantly better than that of sodium tripolyphosphate (TPP). The magnetic hydrogels (PVA: CS= 1: 1) crosslinked by NaOH had better compressive strength, swelling rate, and saturation magnetization of 1.17 MPa, 92.43%, and 22.19 emu/g, respectively. The MC3T3-E1 cell culture results showed that the PVA/CS/Fe₃O₄ scaffolds promoted cell adhesion and proliferation, and the scaffolds crosslinked by NaOH had superior cytocompatibility. 3DGP combined with a water-level controlled crosslinker bath offers a promising approach to preparing magnetic hydrogel materials.     

Modification of polypropylene through intercrosslinking graft copolymerization of poly(vinyl alcohol): Synthesis and characterization

Modification of polypropylene (PP) has been successfully carried out through intercrosslinking of poly(vinyl alcohol) (PVA), by chemical graft copolymerization method using benzoyl peroxide (BPO) as radical initiator. Prior to grafting, PP was irradiated by gamma rays at a constant dose rate of 3.40 kGy/h to introduce hydroperoxide groups. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters. Maximum percentage ofgrafting of PVA (75%) was obtained at [BPO] = 5.51 × 10^?2 mol/L in 120 min at 70°C using 15 mL of water. Characterization of pristine PP and PP‐g‐PVA was carried out by FTIR, thermogravimetric analysis, and scanning electron micrography. Swelling studies were carried out in pure, binary, ternary, and quaternary solvent systems comprising of water, ethanol (EtOH), dimethylsulfoxide (DMSO) and N, N‐dimethylformamide (DMF) in different ratios. Maximum swelling values of PP‐g‐PVA (both composite and true graft) was observed in pure DMSO followed by DMF, EtOH, and water and it was also higher than that observed in mixed solvent system. Water retention studies of pristine PP and PP‐g‐PVA (both composite and true graft) were investigated at different time periods, temperature, and pH. Maximum % water retention of PP‐g‐PVA (composite) (108%) was observed in 8 h at 50°C in neutral medium (pH = 7). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and mechanical and electrical properties of oriented PVA-VGCF and PVA-MWNT composites

The composites poly(vinyl alcohol) (PVA) and vapor growth carbon fiber (VGCFs) and multi wall carbon nanotubes (MWNTs) were prepared by gelation/crystallization from the mixture of dimethyl sulfoxide (DMSO) and water (H₂O). The composite films were elongated to 5-10-fold uniaxially. The mechanical properties of PVA composites were improved significantly by introduction of VGCFs and MWNTs and also by the orientation of fillers. Compared to VGCFs, MWNTs was more effective to improve the electric conductivity of the composites because of its network structure. The change in the electrical conductivity for the PVA/MWNT composites containing 5 wt% MWNT was independent of the draw ratio up to eight-fold indicating no disruption of the network formation. A certain high level of filler content was proved to be necessary for the promotion of both mechanical and electrical properties in oriented composite.     

Preparation of high molecular weight poly(vinyl alcohol) with high yield using low‐temperature solution polymerization of vinyl acetate

Vinyl acetate (VAc) was solution‐polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) having low chain transfer constant at 30, 40, and 50°C, using a low temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl acetate) (PVAc) and corresponding poly(vinyl alcohol) (PVA) obtained by saponification with sodium hydroxide. The polymerization rates of VAc in TBA and in DMSO were proportional to the 0.49 and 0.72 powers of ADMVN concentration, respectively. For the same polymerization conditions, TBA was absolutely superior to DMSO in increasing the molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VAc in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration calculated using initial rate method and by an activation energy difference of polymerization obtained from the Arrhenius plot. Low‐temperature solution polymerization of VAc in TBA or DMSO by adopting ADMVN proved successful in obtaining PVA of high molecular weight (number–average degree of polymerization (P_n): 4100–6100) and of high yield (ultimate conversion of VAc into PVAc: 55–80%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum P_n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P_n and lightness were higher, and the degree of branching was lower with PVA prepared from PVAc polymerized at lower temperatures in TBA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1003–1012, 2001     

Preferential solvation of pomalidomide,an anticancer compound,in some binary mixed solvents at 298.15 K

Preferential solvation of pomalidomide (PMD) was explored in dimethyl sulfoxide (DMSO)-dimethylformamide (DMF), DMSO-tetrahydrofuran (THF), DMSO-methanol (MeOH), DMSO-isopropanol, DMSO-water, water-DMF, water-THF, water-MeOH, and water–isopropanol binary mixed solvents at 298.15 K. Bosch-Rose model was utilized to determine the electronic transition energies (E_T) and other preferential solvation parameters, describing solute-solute and solute-solvent interactions. We found that λ_max situation shifted with dielectric constant of the pure solvents meaningfully. According to the obtained results, E_T enhanced and λ_max shifted to the lower wavelengths as the percentage of DMSO decreased in the binary mixtures, remarking the important role of DMSO for stabilizing the excited state (π^⁎) of PMD chromophore via efficient intermolecular solute-solvent interactions. In addition, the aqueous binary systems showed an optimum point for the E_T values as the percentage of water changed in the solutions. The local mole fraction of the solvents in the cybotactic region was also estimated to describe the specific and non-specific interactions in the systems.     

Synthesis of poly(vinyl benzal) from poly(vinyl alcohol) in nonaqueous medium

Poly(vinyl alcohol) (PVA) is soluble only in water and so some important derivatives like esters cannot be prepared from PVA. The 100% conversion of PVA to acetal is also elusive as there is strong intermolecular and intramolecular hydrogen bonding. However, PVA can be dissolved in a nonaqueous medium in the presence of a small amount of C₂H₅NO₃ · DMSO(EN · DMSO) and so a maximum extent of conversion may be possible. Here, we report the preparation of poly(vinyl benzal) (PVB) by acid-catalyzed homogeneous acetalization of PVA with benzaldehyde in a nonaqueous medium. The formation of PVB was confirmed by IR and ¹H-NMR spectra. The molecular mass of the polymer was determined by the GPC method. The PVB prepared had a degree of acetalization of 95 mol%. The glass transition temperature, T_g was measured from differential scanning calorimetric (DSC) thermograms. Thermal stabilities were checked by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG). A possible mechanism of three-step thermal decomposition of PVB is proposed. © 1996 John Wiley & Sons, Inc.     

Preparation of ultrahigh molecular weight syndiotactic poly(vinyl alcohol) microfibrillar fibers by low‐temperature solution polymerization of vinyl pivalate in tertiary butyl alcohol and saponification

Vinyl pivalate (VPi) was solution polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) with a low chain transfer constant using a low temperature initiator, 2,2′‐azobis(2,4‐ dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl pivalate) (PVPi) and its saponification product poly(vinyl alcohol) (PVA). TBA was absolutely superior to DMSO in increasing the syndiotacticity and molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VPi production in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration, calculated by the initial rate method. Low‐temperature solution polymerization of VPi in TBA or DMSO by adopting ADMVN proved to be successful in obtaining PVA of ultrahigh molecular weight [maximum number‐average degree of polymerization (P_n): 13,500–17,000] and of high yield (ultimate conversion of VPi into PVPi: 55–83%). In the case of bulk polymerization of VPi at the same conditions, maximum P_n and conversion were 14,500–17,500 and 22–36%, respectively. The P_n and syndiotactic diad content were much higher and the degree of branching was lower with PVA prepared from PVPi polymerized at lower temperatures in TBA. Moreover, PVA from the TBA system was fibrous, with a high degree of orientation of the crystallites, indicating the syndiotactic nature of TBA polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1992–2003, 2002     

Rheological and rheo-optical properties of high molecular weight syndiotactic and atactic polyvinylalcohol solutions

The rheological and rheo-optical properties of solutions of high molecular weight polyvinylalcohol (PVA) with different syndiotactic diad contents in dimethylsulfoxide (DMSO) were investigated in terms of tacticity, molecular weight, and degree of saponification. Tacticity played a significant role in rheological behavior. Over the frequency range of 10^?1 to 10² rad/s PVA with syndiotactic diad content of ～53% (atactic PVA) exhibited almost Newtonian flow behavior whereas PVA with syndiotactic diad content of ～63% (syndiotactic PVA) exhibited Bingham flow behavior. On the plot of storage modulus (G′) against loss modulus (G″) atactic PVA gave slopes of ～2 while syndiotactic PVA gave slopes of ～1. With syndiotactic PVA, an increase of shear rate notably increased flow birefringence (Δn_f) at shear rates higher than 5 sec^?1. On the other hand, only a slight increase in Δn_f was observed in the case of atactic PVA. The effects of molecular weight and degree of saponification were discussed as well.     

Characterization of strong polyelectrolyte hydrogels based on poly(vinyl alcohol)

Maleic anhydride (MA) was grafted onto both partially and fully hydrolyzed poly(vinyl alcohol) (PVA) in the presence of an initiator. Strong polyelectrolyte polymers were prepared by sulfonation of PVA–MA grafts. The sulfonation was completed by reaction of hydroxyl groups of PVA–MA grafts with two different sulfonating reagents (chlorosulfonic acid and pyridine sulfonic acid). The sulfonation degree was evaluated by acid–base titration and ¹H NMR analysis. The solution behaviour of the prepared grafts was evaluated from viscosity measurements. Four kinds of water‐insoluble PVA–MA and PVA–MA‐SO₃H hydrogels were prepared by heat treatment, physical gelation and chemical crosslinking with different weight ratios of N,N‐methylene bisacrylamide (MBA) crosslinker. The swelling parameters were measured for all prepared gels in deionized water and aqueous solutions at different pH values from 2 to 12 having constant ionic strength (I = 0.1). All gels exhibit a different swelling behaviour upon environmental pH changes. Copyright © 2004 Society of Chemical Industry     

Gelation of a new hydrogel system of atactic‐poly(vinyl alcohol)/NaCl/H2O

a‐PVA/NaCl/H₂O hydrogels have been prepared by gelation of aqueous atactic‐poly(vinyl alcohol) (a‐PVA) solutions in the presence of NaCl. The gelling temperature, melting temperature and the preservation of water of the hydrogels have been measured. The effect of the addition of NaCl to the hydrogels on gelling temperature and melting temperature is marked when the NaCl concentration is over a certain value. High NaCl concentration favours high‐melting‐point hydrogels. When the NaCl concentration is high enough (such as 11%), high‐melting‐point and white turbid opaque a‐PVA/NaCl/H₂O hydrogels can be prepared, regardless of the PVA concentration. Similarly, the low gelling temperature of a‐PVA/NaCl/H₂O solutions comes from low NaCl concentration, while high gelling temperature ranges from 50 to 70 °C when the NaCl concentration is 11%. In appearance, the types of syneresis of a‐PVA/NaCl/H₂O are χ‐type or a mixture of χ‐ and n‐types; water release of the hydrogels is slowed down by the addition of NaCl. © 2002 Society of Chemical Industry     

Cooperative behavior of poly(vinyl alcohol) and water as revealed by molecular dynamics simulations

An aqueous poly(vinyl alcohol) (PVA) model has been extensively studied by using the molecular dynamics (MD) simulation method. The employed molecular and force field models are validated against the available data in the literature. In particular, the glass transition temperature (T_g) is determined from the specific volume versus temperature, which compares well with the experimental observations. The diffusion coefficients of water (H₂O) through the PVA matrix follow the Arrhenius equations at both temperature regions separated by T_g, indicating the existence of free and bound water defined by hydrogen bonds (HBs). It has also been confirmed that HBs occur between PVA and H₂O, between PVA and PVA, between H₂O and H₂O, and all of them play the key roles in the glass transition. The local dynamics suggested by the decorrelations of various bond vectors can be well described by the Williams-Landel-Ferry (WLF) equation. This work demonstrates the cooperative behavior of PVA and H₂O which is responsible for the glass transition of the whole binary system.     

Preparation and characterization of membranes obtained from blends of acrylonitrile copolymers with poly(vinyl alcohol)

New microfiltration and ultrafiltration membranes were obtained using acrylonitrile‐vinyl acetate copolymers in mixture with poly(vinyl alcohol) (PVA). Thus, a blend polymer solution was prepared in dimethylsulfoxide (DMSO) and used to obtain bicomponent polymer membranes by phase inversion. The rheological behavior of the DMSO polymer solutions was, mostly, dilatant at low shear gradients and pseudo plastic with quasi Newtonian tendency at higher gradients. Membranes were characterized by Fourier transform infrared spectrometry (FTIR), optical microscopy, atomic force microscopy, thermal gravimetric analysis‐differential thermal gravimetry, and pure water flux (PWF). FTIR spectra displayed the characteristic bands for acrylonitrile, vinyl acetate, and PVA. The morphology and the porosity can be tailored by the preparation conditions. PVA allows controlling the size of the pores and enables, in principle, to use the resulted membranes as supports for enzyme immobilization. PVA content influences the thermal stability. PWF values depend on the copolymer, on the content in PVA, but also on the coagulation bath composition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41013.     

Effects of poly (vinyl alcohol) (PVA) content on preparation of novel thiol-functionalized mesoporous PVA/SiO2 composite nanofiber membranes and their application for adsorption of heavy metal ions from aqueous solution

Thiol-functionalized mesoporous poly (vinyl alcohol)/SiO₂ composite nanofiber membranes and pure PVA nanofiber membranes were synthesized by electrospinning. The results of Fourier transform infrared (FTIR) indicated that the PVA/SiO₂ composite nanofibers were functionalized by mercapto groups via the hydrolysis polycondensation. The surface areas of the PVA/SiO₂ composite nanofiber membranes were >290 m²/g. The surface areas, pore diameters and pore volumes of PVA/SiO₂ composite nanofibers decreased as the PVA content increased. The adsorption capacities of the thiol-functionalized mesoporous PVA/SiO₂ composite nanofiber membranes were greater than the pure PVA nanofiber membranes. The largest adsorption capacity was 489.12 mg/g at 303 K. The mesoporous PVA/SiO₂ composite nanofiber membranes exhibited higher Cu²⁺ ion adsorption capacity than other reported nanofiber membranes. Furthermore, the adsorption capacity of the PVA/SiO₂ composite nanofiber membranes was maintained through six recycling processes. Consequently, these membranes can be promising materials for removing, and recovering, heavy metal ions in water.     

Electrochemical formation and characteristics of aluminium hydroxide on a platinum substrate from dimethylsulphoxide and water mixtures

Results obtained with Al(ClO₄)₃ in DMSO solutions with different water content at a Pt substrate are presented. Different negative potential perturbations produce the reduction of water molecules from the aluminium ion coordination sphere yielding hydrogen gas and a film of aluminium hydroxide solvated by water and DMSO molecules. The inhibiting effect of the electroformed film and its water content depend on the negative potential value reached. Potentiodynamic i/E profiles present two main cathodic current peaks which are related to [Al(DMSO)_6-iH₂O_i]³⁺ complexes with i = 1 and 2, through the current dependences with water and aluminium ion concentrations. Bulk diffusion of the complexes, charge-transfer reactions and the inhibiting nature of the film formed were thoroughly investigated. Molecular hydrogen is oxidized at positive potentials yielding hydrogen ions which in turn produce a partial recovery of the electrode activity.     

Alginate–poly(vinyl alcohol) core–shell microspheres for lipase immobilization

A lipase [triacylglycerol ester hydrolase (EC 3.1.1.3)] was encapsulated in sodium alginate (AlgNa)/poly(vinyl alcohol) (PVA) microspheres. Spherical AlgNa/PVA beads were prepared by the ionotropic gelation of an AlgNa/PVA blend in the presence of calcium tetraborate (CaB₄O₇). The particles were spherical and had an average diameter of 400 μm. The microspheres were studied with differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, and water transport by the equilibrium degree of swelling. The elevation of the glass‐transition temperature of the microspheres indicated specific crosslinking reactions of the component polymers (AlgNa/PVA). FTIR spectra showed no evidence of a strong chemical interaction changing the nature of the functional groups of both AlgNa and PVA in the AlgNa/PVA blends. The water diffusion coefficients increased with increasing PVA content in the microspheres, indicating a decrease in the resistance to mass transfer through the AlgNa/PVA microsphere wall. The AlgNa/PVA microspheres were characterized by the Michaelis constant (K_M) and the maximum reaction velocity (V_max), which were determined for both free and immobilized lipases. The enzyme affinity for the substrate (K_M/V_max) remained quite good after immobilization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1553–1560, 2006     

Thermo-electrical properties of PVA-nanotube composite fibers

We present in this work an experimental study of the resistivity of composite nanotube fibers made of polyvinyl alcohol and multiwalled carbon nanotubes. These fibers which exhibit exceptional mechanical properties could be used for new conductive and multifunctional textiles or composites. We report on their electrical properties and draw two main conclusions: (i) when the fibers contain a large fraction of amorphous polymer, a substantial decrease of the resistivity is observed in the vicinity of the glass transition temperature (T_g) of the pure PVA. On the basis of X-ray diffraction characterizations, we believe that this behavior results from the relaxation of stress in the polymer-nanotube composite. Slight structural modifications and partial loss of nanotube alignment at T_g could yield an increase of the density of intertube contacts and thereby to a decrease of the electrical resistivity. (ii) Annealing the fibers at high temperature reduces the fraction of amorphous PVA which becomes more crystalline. As a result, the conductivity becomes more stable and does not exhibit any abrupt variation at T_g. Instead the conductivity is non-metallic with an effective semi-conductor type behavior as observed in other nanotube composites or even in pure nanotube assemblies.