Salt resistivity of poly (4-vinyl benzoic acid) gel

Salt resistivity of poly (4-vinyl benzoic acid) (P4VBA) gel was investigated to compare with the super salt-resistivity that was found for poly (4-vinyl phenol)(P4VPh) gel containing an acidic proton and π-electron system. Poly(acrylic acid) (PAA) gel was also prepared and used as a reference gel containing only an acidic proton. P4VBA gel showed a moderate salt resistivity, which was less significant than that for P4VPh gel, in many kinds of inorganic salt solutions (MgCl₂, LiCl, NaCl, KCl, CsCl, KI, KSCN, Na₂SO₄). On the other hand, PAA gel showed a drastic deswelling in the presence of concentrated MgCl₂, LiCl, Na₂SO₄, and (NH₄)₂SO₄ solutions, and a significant swelling for KSCN solution. These contrastive behaviors between P4VBA and PAA gels strongly suggest that the combination of acidic proton and π-electron system is essential and necessary for polymer gels to be endowed with the salt resistivity.     

Physico-chemical study of ionic equilibria for poly-2 and poly-4-vinylpyridines in alcohol-water solutions

The ionic equilibria for poly-4-vinyl pyridine (P4VP) and poly-2-vinyl pyridine (P2VP) were studied by physico-chemical techniques such as potentiometry, viscosity and NMR-¹H. The mixture of ethanol (45 per cent w.p.) and water was used as solvent to obtain the total range of ionization (0–1). It was found that the dissociation constants of pyridine residue of polymers in the absence of electrostatic interaction (pK₀ = 3·3–3·9) are lower than for the monomer analogues 4-ethylpyridine and 2-ethylpyridine (5·02) and depend on ionic strength (NaCl).A sharp decrease of pK_app at the beginning of titration and increase of specific viscosity for P4VP and P2VP are both explained by electrostatic interactions between positive charges forming during titration of the macromolecules. Most probably, these interactions act through the organic part of the macromolecule. On the other hand, it is shown by NMR-¹H that sharp changes in pK_app and specific viscosity at the beginning of the titration are not associated with changes in the average conformation of the monomer unit in the polymer. This conformation can be destroyed only when the energy of electrostatic interactions is large enough and this occurs when the mean distance between positive charges is relatively short.     

Aqueous biphasic systems formed by nonionic polymers I. Effects of inorganic salts on phase separation

The effect of salts KSCN, KI, KBr, KCl, KClO₄, KF, K₂SO₄ and NH₄Cl, LiCl, NaCl, KCl, CsCl on the binodials of the phase diagrams for aqueous biphasic dextranpolyvinylpyrrolidone, dextran-polyvinyl alcohol, dextran-ficoll and dextran-polyethylene glycol systems was studied. It is established that the K-salts present at the concentrations of 0.1 and 0.5 mol/kg alter the binodials of the phase diagrams for the above systems. The effect of a salt is found to be related to the lyotropy of the salt quantified by the salt molal surface tension increment. It is assumed that phase separation in an aqueous polymer biphasic system is affected by the presence of a salt mainly due to the effect of the salt on the structure and/or state of water in the system.     

Balance of hydrophobic and electrostatic forces in the pH response of weak polyelectrolyte capsules

A detailed study of the role of solution pH and ionic strength on the swelling behavior of capsules composed of the weak polyelectrolytes poly(4-vinylpyridine) (P4VP) and poly(methacrylic acid) (PMA) with different numbers of layers was carried out. The polyelectrolyte layers were assembled onto silicon oxide particles and multilayer formation was followed by zeta-potential measurements. Hollow capsules were investigated by scanning electron microscopy and atomic force microscopy. The pH-dependent behavior of P4VP/PMA capsules was probed in aqueous media using confocal laser scanning microscopy. All systems exhibited a pronounced swelling at the edges of stability, at pHs of 2 and 8.1. The swelling degree increased when more polymer material was adsorbed. The swollen state can be attributed to uncompensated positive and negative charges within the multilayers, and it is stabilized by counteracting hydrophobic interactions. The swelling was related to the electrostatic interactions by infrared spectroscopy and zeta-potential measurements. The stability of the capsules as well as the swelling degree at a given pH could be tuned, when the ionic strength of the medium was altered.     

Copolymer of poly(4-vinylpyridine)-g-poly(ethylene oxide) respond sharply to temperature, pH and ionic strength

The stimuli-responsive copolymers with poly(ethylene oxide) (PEO) as side chain were prepared by free-radical copolymerization of methacrylamide end-capped PEO macromonomer and 4-vinylpyridine (4VP). Phase transition behavior of these copolymers of poly(4-vinylpyridine)-g-poly(ethylene oxide) (P4VP-g-PEO) was investigated as a function of polymer concentration, temperature, pH and ionic strength by monitoring the turbidity of the polymer solutions. The copolymers displayed sharp response to temperature and pH. The LCST of P4VP-g-PEO copolymer increased with the increase of PEO content and decreased with increasing pH due to the deprotonation of the pyridine ring, indicating well-tunable LCST. In addition, the LCST of P4VP-g-PEO9 presented a unique phase transition behavior with varying salt concentration, showing a minimum with 1 M NaCl solution at pH 6.0.     

Aqueous biphasic systems formed by nonionic polymers II. Concentration effects of inorganic salts on phase separation

Concentration effects of KSCN, KClO₄, KI, KBr, KNO₃, KCl, KF and K₂SO₄ on the compatibility of dextran with ficoll, polyvinylpyrrolidone and poly(ethylene glycol) at fixed polymer concentration ratios were studied in aqueous solution. The results obtained are considered in terms of the Patterson theory of-effect. It is assumed that phase separation in an aqueous solution of two nonionic polymers results from the appearance of two different water structures in the vicinity of the phase polymers. The data obtained are considered in terms of the concept of salting-in-salting-out effects of neutral salts on aqueous solubility of biopolymers. The salt effects observed are attributed to two antagonistic influences of salts on the electrostatic (dipole-dipole) polymer-water interactions and on the water-water interactions in the vicinity of the phase polymers.     

Kinetics and equilibria associated with the absorption and desorption of water and lithium chloride in an ethylene—vinyl alcohol copolymer

Sorption and desorption equilibria and kinetics for LiCl and H₂O in an ethylene—vinyl alcohol copolymer film containing 70 mole percent vinyl alcohol were investigated at 25°C. The swelling behavior of water in the polymer was characterized by vapor and liquid sorption experiments over a range of water activities. p]The effects of LiCl content on the water sorption kinetics and equilibria in the films are presented and discussed. The kinetics and mechanism of LiCl sorption have also been studied. The amount of salt sorbed into the polymeric films increases linearly with the salt concentration in the external aqueous solutions. Both the rate and the amount of sorbed water increase significantly as the LiCl content increases. p]The desorption of LiCl, previously sorbed into the polymer, was characterized for different salt loadings. The rate of fractional salt release is independent of LiCl concentration in the film. Initially, the salt release is controlled by the nearly constant-rate absorption of water. The salt release, at long times, lags behind the swelling-controlled water uptake, indicating that the salt release is not completely controlled by the water sorption and that diffusion in the swollen polymer matrix contributes significantly to the long term elution of LiCl. Independent thermal analysis experiments suggest the formation of a metal salt—poly(ethylene—vinyl alcohol) complex.     

Complexation behaviour of radiation synthesized poly(vinylbenzyltrimethylammonium chloride) and its gel with potassium hexacyanoferrates (II, III) and potassium persulfate in aqueous medium

High energy gamma radiation has been used to synthesize linear poly(vinylbenzyltrimethylammonium chloride) (PVBT) as well as crosslinked PVBT gels. Complexation behaviour of linear and crosslinked PVBT with K₂S₂O₈, K₃[Fe(CN)₆] and K₄[Fe(CN)₆] have been studied by viscometry, turbidity and equilibrium swelling measurements. The stoichiometry of the complex formed was found to be a function of charge on the anions of complexing species. Crosslinked poly(vinylbenzyltrimethylammonium chloride) gels were found to desorb some of the embedded water when swollen gels were placed in these salt solutions. Existence of strong ionic interactions between polymer chains and complexing salts was confirmed by changes in equilibrium swelling of complexed crosslinked matrices as well as in the stoichiometry of linear PVBT complexes in presence of strong electrolytes like NaCl.     

Rheology of cellulose/KSCN/ethylenediamine solutions and coagulation into filaments and films

Dissolution of cellulose in ethylenediamine/potassium thiocyanate (KSCN) was studied as a function of cellulose and KSCN concentration. Concentrations of up to 9% (w/w) cellulose were obtained. Large variations in solution rheology with salt and cellulose concentration were observed, and phases including flowing solutions and gels were identified visually. Rheological data indicated that viscosity decreased with increasing salt or cellulose concentration in certain composition ranges. Viscosity decrease with concentration increase is associated with either onset of liquid crystalline ordering or phase separation in the system. Both of these are quite likely in the cellulose/ethylenediamine/KSCN system, depending on composition. Additionally, comparison of loss (G′′) and storage (G′) moduli confirmed that compositions that exhibited gel behavior at zero shear became liquid at shear rates as low as 1 Hz. Solutions were coagulated into filaments and films using ethanol (CH₃CH₂OH) and methanol (CH₃OH). Infrared spectroscopy (FTIR) indicated that significant quantities of KSCN salt remained in the fibers and films after coagulation. Subsequent washing removed residual KSCN and improved physical properties. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2013–2022, 2005     

Effects of chemical modifications on the swelling behaviors of poly (4-vinyl phenol) gel

Poly (4-vinyl phenol) (P4VPh) gels were prepared by crosslinking with a hydrophilic crosslinker [ethyleneglycoldiglycidylether (EGDGE)] and a hydrophobic one [diglycidyl 1,2-cyclohexane dicarboxylate (DGCHDC)], and the former gel was further modified by CH₃I or C₂H₅I to partially convert the hydrogen of phenol OH to the corresponding alkyl groups. Swelling behaviors of P4VPh gels, thus modified, were investigated to see how the hydrophobic groups introduced to the crosslinker and the polymer substrate affect the super salt resistivity to inorganic ions and the high water content (>90%) that have been observed for the original P4VPh gel. Water content and salt resistivity were unexpectedly preserved even for the modified gels. Effects of the chemical modifications on the gel swelling were only observed in the presence of hydrophobic solutes, i.e., tetrabutyl ammonium chloride and ionic surfactants. All these results strongly suggest that hydration around the polymer substrate in the gel phase is specifically stabilized, probably because of the coexistence of the hydrophobic hydration and the π-hydrogen-bonding hydration around the phenol ring.     

New neutral and ionic poly(ethylene oxide) networks by radical polymerization

New opportunities resulting from a turn to radical polymerization in the synthesis of poly(ethylene oxide) (PEO) networks are discussed and exemplified. Several series of such networks have been prepared by radical homo‐ and copolymerization in aqueous media of “macromonomers”, i.e. partly methacrylated poly(ethylene glycol) (PEG) of varied molecular weight (MW ≅ 2000‐12000) and functionality (f_n ≅ 1.25‐1.8). This family of gels as a whole has the volume swelling degree Q in the range of 10 to 200 ml/ml. The hydrogels are characterized by means of Q, elastic modulus, swelling pressure, and with the use of some probes. The swelling behaviour of neutral hydrogels of this kind is briefly resumed. The multifunctional junctions formed in the propagation reaction of methacrylate end groups determine their main peculiarity. Anomalous elastic behaviour of the swollen networks prepared at high concentration of polymer has been observed and attributed to the network chains stretching of the same nature as in polymer stars or brushes. The junctions' functionality (F ≈ 20‐300) is evaluated from these data as well as from MW of the soluble models of network junctions. The PEO networks with charged units in junctions have been obtained by copolymerization of macromonomers with some ionic (meth)acrylic monomers. These gels display all the polyelectrolyte features, e.g. enhanced Q values in water (up to 50‐70) and, contrary to neutral PEO gels, the strong dependence on salt content. However, the osmotic contribution of mobile ions into swelling is shown to be low due to localization of charges in the junctions. The hydrogels that combine PEO and polymethacrylic acid chains capable of interpolymer complexation have been prepared and studied. They show much higher swelling in pure water (Q up to 200), strong deswelling by NaCl, and very sharp drop in swelling (ca. two order in Q) at pH ≈ 4.5‐5.5 due to complexation.     

Conductivity of molten LiCl–KF–ZrF<Subscript>4</Subscript> mixtures

Specific conductivity of molten LiCl–KF–ZrF₄ mixtures was measured for the first time by the reference capillary method using an ac bridge. In the ternary salt systems, the study was performed at a molarfraction ratio between the alkali metal halides of 1: 3, 1: 1, and 3: 1. The temperature dependences of specific conductivity were determined for all melt compositions. The calculated molar conductivities λ of studied LiCl–KF–ZrF₄ ternary melts and their relative deviations from the ideal values enable us to infer the processes that proceed during mixing of the melt components.     

Poly(oxyethylene methacrylate)–poly(4-vinyl pyridine) comb-like polymer electrolytes for solid-state dye-sensitized solar cells

Poly(oxyethylene methacrylate)–poly(4-vinyl pyridine) (POEM–P4VP) comb-like copolymers with 3:7, 5:5, and 6:4 wt ratio were synthesized via atom transfer radical polymerization and confirmed by ¹H-NMR and FT-IR spectroscopy. The copolymers were quaternized with 1-iodopropane to convert the pyridine groups into pyridinium ions, i.e., POEM–qP4VP. Transmission electron microscopy showed that strongly segregated microphase separation in POEM–P4VP was less prominent upon quaternization due to interactions between the ether oxygens of POEM and the quaternized pyridine groups of qP4VP, as confirmed by FT-IR spectroscopy. The energy conversion efficiencies of dye-sensitized solar cells (DSSCs) with quaternized polymer electrolytes were always greater than those with pristine electrolytes due to greater ionic conductivity and concentrations of free iodide ions. The maximum energy conversion efficiency of a DSSC employing POEM–qP4VP electrolyte reached 3.0% at 100 mW/cm² when a 6:4 wt.% of POEM–qP4VP was used.     

Swelling behaviour of crosslinked hydrogels based on (2-hydroxyethyl methacrylate) with a zwitterionic comonomer (1-3-sulfopropyl-2-vinyl-pyridinium-betaine)

Copolymeric hydrogels were prepared by the chemically initiated free radical copolymerization in aqueous solution of mixtures of [1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (SPV) and (2-hydroxyethyl methacrylate) (HEMA) in the presence of a crosslinking agent N,N′-methylene-bis-acrylamide (MBA). The hydrogels were swollen to equilibrium in water and aqueous KSCN at 298 K and their swelling behaviour has been investigated using gravimetric measurements. The effects of the concentration of KSCN and the mole fraction of SPV in the feed (F_s) have been noted and discussed. The main findings are:(a) In water, the water content (W₁) of copolymeric hydrogels is insensitive to SPV content at F_s ? 0.45. In contrast, W₁ decreases sharply with decreasing F_s within the range of 0 < F_s < 0.45. (b) In aq. KSCN, the degree of total swelling (W) exceeds the value in pure water, the enhancement in swelling being most marked at low values of [KSCN]. The content of water within the hydrogel increases with KSCN concentration in the swelling medium for low values of [KSCN], but thereafter falls with further increase in salt concentration. In contrast, the salt content within the swollen hydrogel displays a continuous increase with increasing [KSCN]. All these results of item (b) are for copolymeric hydrogels within the full range of F_s (0 < F_s < 1). (c) at a fixed aq. KSCN concentration, both W and W₁ increase sharply with increasing F_s over the entire range of copolymer composition.     

Anti-Hofmeister series properties found for a polymer having a π electron system and acidic protons

Anti-Hofmeister series properties have been found for a polymer (PVA-T) having a π electron system and acidic protons, which were prepared by introducing trimellitic anhydride to poly(vinyl alcohol) (PVA). Aqueous dispersion of PVA-T became clear in the presence of 1 M Na₂SO₄, a typical kosmotrope, due to dissolution of the solid polymer sample, while the turbidity in the presence of 1 M KSCN, a typical chaotrope, hardly changed. Being consistent to the salt effects, PVA-T hydrogel, which was prepared by chemical cross-linking, showed marked swelling in sulfate solutions, whereas the swelling degree was only marginal in thiocyanates.     

Swelling behavior of ionically cross-linked polyampholytic hydrogels in varied salt solutions

Ionically cross-linked polyampholytic hydrogels were synthesized by redox copolymerization of acrylamide and an ionic complex of (N,N-diethylamino)ethyl methacrylate and acrylic acid (designated as PADA hydrogel). The swelling behavior of the hydrogels in water indicated that a minimal equilibrium swelling ratio is found when the molar ratio of anionic/cationic monomers was 1.55. In NaCl solution, the hydrogels exhibited the typical swelling behavior of conventional polyampholytic gels. Their equilibrium swelling ratios increased with an increase in the NaCl concentration. In solutions of multivalent ions (CaCl₂ and trisodium citrate solutions), the equilibrium swelling ratios of the hydrogels increased first and were then followed by a decrease with an increase in salt concentration. Interestingly, an unexpected abrupt swelling phenomenon was observed when the fully swollen hydrogels in salt solution were transmitted to pure water. The unique swelling behavior of PADA hydrogels depends not only on the molar ratio of the anionic/cationic monomers but also on the valency of the ions.     

Specific swelling behaviors of poly(4-vinyl phenol) gels in tetraalkylammonium chloride solutions

Swelling behaviors of poly(4-vinyl phenol) (P4VPh) gel in aqueous tetraalkylammonium chloride (TAACl) solutions were investigated to find a very specific swelling behavior. Especially for the tetrabutylammonium chloride (TBACl) system, P4VPh gel remarkably deswelled with increasing salt concentration (/= ca. 2.1 M). A similar swelling profile was also observed in the swelling time-course; upon immersion of a water-swollen P4VPh gel into 2.5 M TBACl solution, the gel first deswelled in an early stage (approximately 0.1 h) and then remarkably reswelled with time. Relative amounts (mol/mol) of TBA cation and water per monomer residue were estimated as ca. 1 and 0 for the deswollen state and 5 and 50 for the reswollen state, respectively. This result, together with those of attenuated total reflection Fourier transform infrared measurements performed for the gels swollen in various kinds of TAACl and inorganic salt solutions, suggested that in the highly deswollen and almost dehydrated state, phenol rings aggregated with intervening TBA cations, while the aggregation reswelled upon further binding with TBA cations.     

离子键交联的聚两性电解质凝胶在不同pH和不同电解质溶液中溶胀行为研究

以丙烯酸(AA)和甲基丙烯酸二乙氨基乙酯(DEAM)形成的离子复合物与丙烯酰胺(AAm)共聚,合成了一种新型的离子键交联的聚两性电解质凝胶(PADA).由于分子之间的氢键作用,PADA凝胶并不是在A/C(负正离子单体摩尔比)为1,而是在A/C为1.55处有最大消溶胀.与共价键交联的聚两性电解质凝胶相比,PADA凝胶的溶胀行为具有更强的pH敏感性.PADA凝胶在不同pH缓冲溶液中的溶胀行为表明,在pH 3~4之间消溶胀程度最大.在偏离该pH区域时凝胶均发生溶胀.但凝胶的溶胀程度在pH<3的酸性溶液中随A/C的增加而降低;而在pH>4的偏碱性溶液中随其增加而增加.在不同价数的离子溶液中,离子浓度对于PADA凝胶的平衡溶胀有着不同的影响.对于一价的NaCl溶液,PADA凝胶有典型的反聚电解质效应.但对于高价的CaCl2和柠檬酸三钠溶液,只在较低的浓度下,才表现出反聚电解质效应.而在较高盐浓度时,随盐浓度的增加其溶胀比反而降低.这可能与高价离子形成的离子键交联有关.与pH对PADA凝胶溶胀程度的影响相似,在CaCl2溶液中,PADA凝胶的溶胀程度随A/C的增加而降低;而在柠檬酸三钠溶液中则刚好相反.这种独特的溶胀行为似乎与高价离子电荷的正负性有关.     

Synthesis of pH-responsive particles with shape anisotropy

Seeded emulsion polymerization is used to produce large quantities of shape anisotropic, amphoteric particles in a size range of about 1 μm. Copolymer dicolloids (CDCs) containing pyridine groups are synthesized by swelling spherical, lightly cross-linked polystyrene seeds with a mixture of styrene and pH-responsive monomer 2-vinyl pyridine followed by secondary polymerization to contrast with their analogue homopolymer dicolloids (HDCs) where the swelling step is carried out with styrene alone. After the particles are coated with a nonionic surfactant to minimize van der Waals attractions, surface potentials and aggregation properties of dilute suspensions are studied as functions of pH and ionic strength. Compared to HDCs, which remain stable at all pH values studied (3 < pH < 9) up to an ionic strength of 5 M, the CDC particles show amphoteric behavior with strong attractions under conditions where dipolar interactions are expected to dominate.     

Isomer‐dependent properties of poly(vinyl pyridine)‐based films grown on copper surfaces

The effect of poly(2‐vinyl pyridine) (P2VP) and poly(4‐vinyl pyridine) (P4VP) isomers on the growth of surface films on copper substrates was studied by electrochemical, spectroscopic, thermogravimentric, and microscopic methods. In acid environment (3% v/v acetic acid) and in the presence of KSCN, electrochemically generated copper cations reacted rapidly with SCN^? and P2VP or P4VP, yielding coordination compounds, which deposited onto copper surfaces as films. The characteristics of such polymer–metal complexes (films) were markedly isomer‐dependent. Cu(I)/P2VP/SCN^? complexes with monovalent cations and sulfur‐coordinated thiocyanate were obtained in the presence of P2VP, whereas the formation of Cu(II)/P4VP/SCN^? complexes with divalent cations and nitrogen‐coordinated thiocyanate was observed in the presence of P4VP. Interestingly, similar physical–chemical properties (electronic structure, stoichiometry, and thermal behavior) were observed for materials synthesized by electrochemical and chemical methods. These results suggest, therefore, that control over the surface properties of copper substrates can be achieved using electrosynthesized films based on different PVP isomers. Besides acting as effective protective barriers against aggressive media and thus reducing the metal dissolution (corrosion) kinetics, these materials are potentially attractive for other applications in which surface properties are paramount, such as in catalysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 215–225, 2009