Conformational changes of pyrene-labeled polyelectrolytes with pH: effect of hydrophobic modifications

Structural changes of pyrene-labeled and unlabeled poly(maleic acid/octyl vinyl ether) (PMAOVE) and poly(maleic acid/methyl vinyl ether) (PMAMVE) with changes in pH have been investigated in this study. The changes in the photophysical properties of pyrene are interpreted to investigate uncoiling or swelling of the polymeric chains with pH. The vibrational fine structure of the pyrene fluorescence (I(3)/I(1)) and the ratio between excimer and monomer fluorescence (I(e)/I(m)) of both pyrene-labeled and unlabeled PMAMVE and PMAOVE suggest that, at pH 4, the polymers are in the coiled form and PMAOVE forms hydrophobic nanodomains. An increase in pH ionizes a number of COOH groups on both PMAMVE and PMAOVE, which leads to the stretching or swelling of the polymers.     

Complexation of hydrophobically modified polyelectrolytes with surfactants: anionic poly(maleic acid/octyl vinyl ether)/anionic sodium dodecyl sulfate

Interactions of surfactants with hydrophobically modified polyelectrolytes in aqueous solutions are important in several applications such as detergents, cosmetics, foods, and paints. Fundamental questions arise on the mechanisms of complexation of the polyelectrolyte and surfactant that control their behavior. In this work, the complexation was studied by examining interactions in aqueous solutions of a hydrophobically modified polymer, poly(maleic acid/octyl vinyl ether) (PMAOVE), with sodium dodecyl sulfate (SDS) by monitoring viscosity, pyrene solubility, light scattering, and analytical ultracentrifugation. When the anionic surfactant SDS was added to aqueous solutions of the similarly charged polymer PMAOVE, the surfactant was incorporated into the hydrophobic nanodomains of PMAOVE even far below the cmc of the surfactant. On the basis of viscosity, pyrene solubility, and analytical ultracentrifugation data, it is proposed that PMAOVE undergoes structural unfolding and at higher SDS concentrations mixed micelles are formed.     

Interpolymer complexes of copolymers of vinyl ether of diethylene glycol with poly(acrylic acid)

 The complex formation reactions of poly(vinyl ether of diethylene glycol) as well as vinyl ether of diethylene glycol–vinyl butyl ether copolymers with poly(acrylic acid) have been studied in aqueous and alcohol solutions. The formation of interpolymer complexes which were stabilized by hydrogen bonds was shown. The effects of molecular weight of poly(acrylic acid) and the nature of the nonionic polymer on the composition and stability of interpolymer complexes were clarified. The critical pH values of complexation were determined for different systems with various molecular weights and hydrophobic–hydrophilic balances. The stability of the interpolymer complexes formed in aqueous and alcohol solutions with respect to dimethylformamide addition was evaluated. The role of hydrophobic interactions and the presence of active groups on stability of the interpolymer complexes is discussed. Received: 23 July 2001 Accepted: 27 September 2001     

Reversible flocculation of silica across the phase boundary of poly(vinyl caprolactam) in aqueous solution

The colloid stability of silica dispersions in water in the presence of poly(vinyl caprolactam) (PVCAP) has been studied below and above the lower consolute temperature (LCT) of its solutions. The dispersion sediments slowly without PVCAP in the temperature range studied (26-40 degrees C) or with PVCAP below the LCT ( approximately 30 degrees C). In contrast, with PVCAP above the LCT, rapid flocculation occurs at acid pH, with re-dispersal on cooling. Reversible flocculation is also obtained above the LCT by cycling the pH from alkaline to acid and back. The flocculation observed above the LCT may also be regarded as heterocoagulation between the silica particles and the aggregates of the polymer.     

Improved oxygen barrier performance of poly(vinyl alcohol) films through hydrogen bond complex with poly(methyl vinyl ether-co-maleic acid)

Hydrogen bonding between poly(methyl vinyl ether-co-maleic acid) (PMVE-MA) and poly(vinyl alcohol) (PVOH) has resulted in films with lower oxygen transmission rates (OTR) than pure PVOH. In the range 20-30% (w/w) PMVE-MA, complexation between the two polymers in the blend was maximized, as shown by viscometry, Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) analysis. OTR measurements have shown that the maximum interpolymer complexation ratio also correlates with the lowest OTR values of the resulting film. The improved oxygen barrier properties are believed to be a combination of the relatively intact PVOH crystalline regions as shown with X-ray diffraction (XRD) and a higher degree of hydrogen bonding in the amorphous regions of the PVOH and PMVE-MA films as indicated by glass transition temperature (T_g) shifts. This leads to denser amorphous regions that reduces the rate of gases diffusing through the polymer film, hence the reduced OTR.     

Compatibility of binary systems of poly(methyl methacrylate), poly(vinyl chloride) and poly(vinyl acetate)

The influence of the thermal treatment on the stability in time of the dispersion degree of films containing binary polymer mixtures, poly(vinyl chloride)/poly(methyl methacrylate), poly(vinyl chloride)/poly(vinyl acetate) and poly(vinyl acetate)/poly(methyl methacrylate), was studied by thermogravimetry and optical microscopy with phase contrast. The dispersion degree depends particularly on the composition of the polymer mixture and can be improved by thermal treatment at temperatures above the glass temperatures of both homopolymers. It seems that this thermal treatment yields exclusively metastable structures with a general tendency to phase separation in a short time after thermal treatment, the heterogeneity mixtures (as film) being more pronounced.     

pH effects on the complexation, miscibility and radiation-induced crosslinking in poly(acrylic acid)-poly(vinyl alcohol) blends

The effect of pH on the complexation of poly(acrylic acid) with poly(vinyl alcohol) in aqueous solution, the miscibility of these polymers in the solid state and the possibility for crosslinking the blends using gamma radiation has been studied. It is demonstrated that the complexation ability of poly(vinyl alcohol) with respect to poly(acrylic acid) is relatively low in comparison with some other synthetic non-ionic polymers. The precipitation of interpolymer complexes was observed below the critical pH of complexation (pH(crit1)), which characterizes the transition between a compact hydrophobic polycomplex and an extended hydrophilic interpolymer associate. Films prepared by casting from aqueous solutions at different pH values exhibited a transition from miscibility to immiscibility at a certain critical pH, pH(crit2), above which hydrogen bonding is prevented. It is shown here that gamma radiation crosslinking of solid blends is efficient and only results in the formation of hydrogel films for blends prepared between pH(crit1) and pH(crit2). The yield of the gel fraction and the swelling properties of the films depended on the absorbed radiation dose and the polymer ratio. [Diagram: see text] SEM image of an equimolar PAA-PVA blend cast from a pH 4.6 solution.     

Interactions of hydrophobically modified polyelectrolytes with nonionic surfactants

Interactions of surfactants with hydrophobically modified polyelectrolytes in aqueous solutions are important in several applications such as detergency, cosmetics, food, and paints. Complexes formed in these systems raise some fundamental questions about the polymer-surfactant interactions that control their behavior. In this work, the interactions of a nonionic surfactant, penta-ethyleneglycol mono n-dodecyl ether (C(12)EO(5)), with a hydrophobically modified anionic polymer, poly(maleic acid/octyl vinyl ether) (PMAOVE), in aqueous solutions were studied using surface tension, viscosity, electron paramagnetic resonance (EPR) spectroscopy, light scattering, and fluorescence spectroscopic techniques. When the nonionic surfactant C(12)EO(5) was added to aqueous solutions of the anionic polymer PMAOVE, it was incorporated into the hydrophobic nanodomains of PMAOVE far below the the critical micelle concentration (cmc) of the surfactant. Two inflection points were observed corresponding to the critical complexation concentration (formation of mixed micelles composed of C(12)EO(5) and the octyl chains of PMAOVE) and the saturation concentration (saturation of the polymer with C(12)EO(5) molecules). Above the saturation concentration, the coexistence of pure C(12)EO(5) micelles and mixed micelles of PMAOVE and C(12)EO(5) was observed. Such a coexistence of complexes has major implications in their performance in colloidal processes.     

Heterotactic poly(vinyl alcohol)

Bulky substituents in vinyl trialkylsilyl ethers and vinyl trialkylcarbinyl ethers led to heterotactic polymers (H = 66%). The polymers were converted into poly(vinyl alcohol) (PVA) and further to poly(vinyl acetate), and tacticity was determined as poly(vinyl acetate). Vinyl triisopropylsilyl ether in nonpolar solvents yielded a heterotactic polymer with a higher percentage of isotactic triads than syndiotactic triads (Hetero-I). Vinyl trialkylcarbinyl ethers in polar solvents gave a heterotactic polymer with more syndiotactic triads than isotactic (Hetero-II). Heterotactic PVA was soluble in water and showed characteristics infrared absorptions. Interestingly, Hetero-I PVA showed no iodine color reaction, but Hetero-II showed a much more intense color reaction than a commercial PVA. The mechanism of heterotactic propagation was discussed in terms of the Markóv chain model.     

Stereoregularity of poly(vinyl ether)

α-Methylvinyl isobutyl and methyl ethers were polymerized cationically and the structure of the polymers was studied by NMR. Poly(α-methylvinyl methyl ether) polymerized with iodine or ferric chloride as catalyst was found to be almost atactic, whereas poly(α-methylvinyl isobutyl ether) polymerized in toluene with BF₃OEt₂ or AlEt₂Cl as catalyst was found to be isotactic. In both cases, the addition of polar solvent resulted in the increase of syndiotactic structure as is the case with polymerization of alkyl vinyl ether. tert-Butyl vinyl ether was polymerized, and the polymer was converted into poly(vinyl acetate), the structure of which was studied by NMR. A nearly linear relationship between the optical density ratio D₇₂₂/D₇₃₆ in poly(tert-butyl vinyl ether) and the isotacticity of the converted poly(vinyl acetate) was observed.     

Colloidal complexes from poly(vinyl amine) and carboxymethyl cellulose mixtures

The phase behaviors of polyelectrolyte complexes formed from dilute solutions of poly(vinyl amine) (PVAm) and carboxymethyl cellulose (CMC) were determined as a function of overall composition and pH. The phase diagram included regions with soluble complexes, colloidal complexes, and macroscopic precipitates. Colloidal complexes were stable when either polymer was in sufficient excess to give electrosteric stabilization. The polymer mixing ratios giving complexes with an isoelectric point of 7 could be predicted from a simple model using the degree of ionization vs pH data for PVAm and CMC. The model failed at extreme pH values because not all added polymer was incorporated into the complexes. At pH 7, essentially all the added polymer was incorporated into the colloidal complex or precipitate, as long as the mixing ratio was within +/-10% of charge stoichiometry. The interaction of PVAm and CMC at pH 7 was endothermic, supporting the generally accepted viewpoint that the interaction of oppositely charged polyelectrolytes is entropy-driven. Although the colloidal complexes had a broad particle size distribution, the average particle size was rather insensitive to mixing ratio. By contrast, complex size was sensitive to electrolyte concentration with no complex formation when the NaCl concentration was > or =2 M.     

Synthesis of poly(vinyl alcohol)-based poly(crown ether)s and permeability of their polymeric membranes

Polymers that contain crown ether moieties at the side chain and are capable of forming rather tough film were synthesized by the polymer reaction of poly(vinyl alcohol) with formyl derivatives of aliphatic crown ethers such as 12-crown-4, 15-crown-5, and 18-crown-6. In the passive transport of alkali metal picrates across the poly(crown ether) membranes the permeation, particularly of alkali metals which tend to form intramolecular sandwich-type complexes with the crown ether rings, was retarded, compared with a poly(vinyl alcohol) membrane. The cation selectivities in the permeation of poly(crown ether) membranes differed significantly from those of poly(vinyl alcohol).     

Thermal degradation of poly(vinyl butyral) in alumina,mullite and silica composites

Thermal degradation of poly(vinyl butyral) (PVB) and its mixtures with alumina, mullite and silica was investigated by non-isothermal thermogravimetry in the temperature range of 323 to 1273 K. The analysis of the data was carried out using a three-dimensional diffusion model. Results showed that the kinetic parameters (activation energy and pre-exponential factor) of the PVB degradation are different for polymer alone, and ceramic/polymer composites. The overall weighted mean apparent activation energy showed an increasing reactivity in the order of PVB<alumina+PVB<mullite+PVB<silica+PVB. This shows that the acidic and basic surface characteristics of the ceramics promote the thermal degradation of PVB and, the more acidic silica affects the degradation more than mullite and alumina. The effect of pellet compression pressure in the range of 4000 to 8000 psig is also investigated.     

Reversible association of thermoresponsive gold nanoparticles: polyelectrolyte effect on the lower critical solution temperature of poly(vinyl methyl ether)

Thermoresponsive gold nanoparticles (GNPs) have been prepared by the borohydride reduction of gold salt in the presence of water-soluble polymer, poly(vinyl methyl ether) (PVME). The PVME-coated GNPs (PVME-GNPs) have been assembled into large aggregates in the presence of polyelectrolytes, viz., poly(sodium-4 styrene sulfonate) and sodium salt of carboxymethylcellulose at low pH by raising the solution temperature from 20 to 40 degrees C. Increase of temperature triggers the interparticle association due to hydrophobic interaction of pendent methyl group of the surface adsorbed PVME. This assembly process is reversible with respect to temperature and pH of the medium and was studied by monitoring the change in surface plasmon resonance band of PVME-GNPs. Three-dimensional assemblies of various architectures, depending on the concentration of polyelectrolytes, were observed through transmission electron microscopy. A mechanistic model has been suggested for the reversible assembly formation that suits well with the experimental observations. The changes in optical properties of the PVME-GNPs due to their aggregation/disaggregation enabled us to use it as an effective tool to monitor the change in lower critical solution temperature (LCST) of PVME in the presence of polyelectrolytes due to interpolymer complexation at low pH. This result agrees well with the variation of LCST of pure aqueous PVME solution in the presence of polyelectrolytes measured by conventional turbidimetric technique.     

Mixed films of poly(n-hexyl isocyanate) and poly(vinyl acetate) at the air-water interface

We study interfacial properties of rigid-rod-like poly(n-hexyl isocyanate) (PHIC), flexible poly(vinyl acetate) (PVAc), and mixed films of PHIC and PVAc spread at the air-water interface as a function of the molar fraction of PHIC by surface pressure measurements and fluorescence microscopy. From the plots of the experimental mean area of the mixed polymer films at a constant surface pressure as a function of the molar fraction of PHIC in the mixed films, the binary mixtures of PHIC/PVAc were concluded to be compatible at the air-water interface. This means that the hydrophobic hexyl group of PHIC takes a horizontal orientation to the air-water interface rather than a perpendicular one, leading to PHIC and PVAc having the same interfacial orientation. Compatibility of the binary mixtures of PHIC/PVAc at the air-water interface is also confirmed by their fluorescence microscopic images, since PHIC proves to be inhomogeneous and PVAc is homogeneous with the aid of a fluorescence probe, respectively.     

Synthesis and characterization of novel photoactive polymer poly(vinyl alcohol)‐graft‐poly(vinyl naphthalene)

A copolymer of poly(vinyl naphthalene) grafted onto poly(vinyl alcohol) has been synthesized with nitroxide‐mediated controlled radical polymerization. By separating the processes of the generation of grafting sites and polymerization, we can avoid the formation of the homopolymer. Because of its architecture, the polymer is soluble in water, despite the high content of hydrophobic groups. The naphthalene chromophores tend to aggregate, forming hydrophobic microdomains in an aqueous solution. Those aggregates exist in a very constrained environment that leads to extraordinarily large redshifts of both the absorption and emission of the polymer. The polymer acts as an efficient photosensitizer in photoinduced electron transfer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2675–2683, 2006     

Miscibility and morphologies of poly(arylene ether phenyl phosphine oxide/sulfone) copolymer/vinyl ester resin mixtures and their cured networks

Nonreactive bisphenol A‐based poly(arylene ether triphenyl phosphine oxide/diphenyl sulfone) statistical copolymers and a poly(arylene ether triphenyl phosphine oxide) homopolymer, each having a number‐average molecular weight of about 20 kg/mol, were synthesized and solution‐blended with a commercial dimethacrylate vinyl ester resin. Free‐radical cured systems produced morphologies that were a function of both the amount of phosphonyl groups and the weight percentage of the copolymers. For example, highly hydrogen‐bonded poly(arylene ether phenyl phosphine oxide) homopolymer/vinyl ester resin mixtures were homogeneous in all proportions both before and after the formation of networks. Copolymers containing low amounts (≤30 mol %) of the phosphonyl groups displayed phase separation either before or during cure. The phase‐separated cured materials generally had phase‐inverted morphologies, such as a continuous thermoplastic copolymer phase and a particulate, discontinuous vinyl ester network phase, except for systems containing a very low copolymer content. The resin modified with a copolymer containing 30 mol % phosphine oxide comonomer showed improved fracture toughness, suggesting the importance of both phase separation and good adhesion between the thermoplastic polymer and the crosslinked vinyl ester filler phase. The results suggested that the copolymers with high amounts of phosphine oxide should be good candidates for interphase sizing materials between a vinyl ester matrix and high‐modulus carbon fibers for advanced composite systems. Copolymers with low amounts of phosphonyl groups can produce tough, vinyl ester‐reinforced plastics. The char yield increases with the concentration of bisphenol A poly(arylene ether phosphine oxide) content, suggesting enhanced fire resistance. The incorporation of thermoplastic copolymers sustains a high glass‐transition temperature but does not significantly affect the thermal degradation onset temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2409–2421, 2000     

Molecular dynamics simulations of atomistic hydration structures of poly(vinyl methyl ether)

Molecular dynamics simulations have been performed on the aqueous solutions of poly(vinyl methyl ether) (PVME) at various concentrations. Both radial and spatial distribution functions are used to investigate the detailed hydration structures. The structures of water are found to get increasingly concentrated when polymers are introduced and the water motions are severely hindered by the polymer matrix. At low concentrations, larger populations of tt conformers in meso dyads than those at higher concentrationsare found and this phenomenon is believed to be due to the increasing in bonding of water molecule to two ether oxygens in meso dyad. At higher concentrations, the size and conformations of polymers are quite similar to those in bulk. A transition of hydrogen bond fractions between PVME and water at around the concentration of 0.3 is observed and this value is perfectly in agreement with the results of conformational analysis and Raman spectra. Second neighbor hydrogen bond statistics revealed the domination of complicated hydrogen bond networks at low concentrations, but single hydrogen bonds as well as isolated clusters composed of 2-4 water molecules are usual around each polymer repeat unit.     

From linear side-chain functionalized poly(vinyl ether)s to functional macrocycles

This paper deals with the synthesis of functional polymers of controlled chain dimensions and architecture from poly(chloroalky1 vinyl ether)s. The living polymerization of chloroalkyl vinyl ethers initiated by HX/ZnX₂ systems, and the chemical substitution of the pendant chlorines by various organic functions and groups, in order to generate specific polymer properties are first discussed. Also based on the living character of the polymerizations, the preparation of poly(chloroethyl vinyl ether) with monomacrocyclic and plurimacrocyclic architectures as well as their characterization are then reported. Some evidence for specific host–guest interactions between large organic molecules and polymacrocycles is also presented.     

Effect of copolymer composition on interpolymer complex formation of (co)poly(vinyl ether)s with poly(acrylic acid) in aqueous and organic solutions

The complex formation between vinyl ether of poly(ethylene glycol‐co‐vinyl butyl ether) with poly(acrylic acid) has been considered in aqueous and isopropanol solutions. The effect of copolymer composition on the complex formation process was clarified. It has been shown that the incorporation of hydrophobic fragments into macromolecules enhances the hydrophobic stabilization of polycomplexes in aqueous solutions. In organic media this effect disappears. The stability of polycomplexes formed both in aqueous and in organic solutions in respect to the addition of dimethylformamide has been studied.