Initial Polymer Solution Research Articles

Ion Conduction and Water Transport in Polyphosphazene-Based Multilayers

Layer-by-layer (LbL) assembled films of poly[bis(methoxyethoxyethoxy) phosphazene] (MEEP) and poly (acrylic acid) (PAA) are demonstrated by utilizing the hydrogen bonding between these two polymers. These films show controlled thickness growth, high ionic conductivity, and excellent hydrolytic stability. The ionic conductivity of these films is studied by changing the assembly pH of initial polymer solutions and thereby controlling the hydrogen bonding characteristics. MEEP/PAA LbL films assembled at higher pH values have enhanced water uptake and transport properties, which play a key role in increasing ion transport within the films. At fully humidified conditions, the ionic conductivity of MEEP/PAA is 7 × 10−4 S cm−1, more than 1 order of magnitude higher than previously studied hydrogen-bonded LbL systems. Finally, free-standing films are isolated from low-energy surface substrates, which allows for bulk characterization of these thin films.

Sulfasalazine release from alginate-N,O-carboxymethyl chitosan gel beads coated by chitosan

In the present study, spherical beads were prepared from a water-soluble chitosan (N,O-carboxymethyl chitosan, NOCC) and alginate with ionic gelation method. Then, swollen calcium–alginate–NOCC beads were coated with chitosan. To prepare drug loaded beads, sulfasalazine (SA) was added to the initial aqueous polymer solution. The effect of coating, as well as drying procedure, on the swelling behavior of unloaded beads and SA release of drug loaded ones were evaluated in simulated gastrointestinal tract fluid. The rate of swelling and drug release were decreased for air-dried and coated beads in comparison with freeze-dried and uncoated ones, respectively. No burst release of drug was observed from whole tested beads. Chitosan coated beads released approximately 40% of encapsulated drug in simulated gastric and small intestine tract fluid. Based on these results, the chitosan coated alginate–NOCC hydrogel may be used as potential polymeric carrier for colon-specific delivery of sulfasalazine.

Influence of fibrous and solid fillers on the rheological and surface properties of polymer compositions

The influence of fibrous and solid granulated fillers on the rheological and surface properties of polymer compositions on the basis of poly(vinyl alcohol) and carboxymethyl cellulose is demonstrated. The effect of the concentration of initial polymer solutions and the time of complex formation on the properties of polymer complexes upon the addition of various fillers is revealed.

Effects of parameters on nanofiber diameter determined from electrospinning model

In this paper the effects of 13 material and operating parameters on electrospun fiber diameters are determined by varying the parameter values in an electrospinning theoretical model. The complexity of the electrospinning process makes empirical determination of the effects of parameters very difficult. The results show that the five parameters (volumetric charge density, distance from nozzle to collector, initial jet/orifice radius, relaxation time, and viscosity) have the most significant effect on the jet radius. The other parameters (initial polymer concentration, solution density, electric potential, perturbation frequency, and solvent vapor pressure) have moderate effects on the jet radius. Parameters relative humidity, surface tension, and vapor diffusivity have minor effects on the jet radius. Knowing the relative effects of parameters on jet radius should be useful for process control and prediction of electrospun fiber production.

Radiation-chemical synthesis of crown-containing poly(ethylene oxide) hydrogels. Swelling behavior and crown ether retention

Poly(ethylene oxide) hydrogels containing physically immobilized dicyclohexano-18-crown-6 (DCH18C6) were synthesized by radiation-chemical cross-linking. DCH18C6 concentration in initial polymer solution has insignificant effect on the gelation dose at the weight ratio of crown ether to polymer lower than 0.2. The higher molecular weight of PEO results in lower gelation dose and higher gel fraction. An increase in absorbed dose leads to a noticeable decrease in the swelling ratio corresponding to a denser hydrogel network. At the same time the absorbed dose in the range of 5–100 kGy has no pronounced effect on the DCH18C6 retention.

Formation of Parallel Strips in Thin Films of Polystyrene/Poly(vinyl pyrrolidone) Blends via Spin Coating on Unpatterned Substrates

Patterns of parallel strips, consisting of alternating polystyrene (PS) and poly(vinyl pyrrolidone) (PVP) regions, were observed in thin films spin cast from a PS/PVP/chloroform solution on unpatterned substrates. The formation of anisotropic patterns, manifested not only in thickness variation but also in composition variation, was found to be driven by Marangoni instability, with the PS and PVP streams flowing toward the preferred regions as the phase separation induced by solvent evaporation proceeded. The initial viscosity of the polymer solution and the thickness of the spin-cast films were lumped into one single parameter to study the phase morphology development at various initial polymer solution concentrations. Interestingly, the ratio of the square of the film thickness to the viscosity, a parameter loosely related to the Marangoni number, was found to reach a maximum value at the concentration where the strip patterns were most well-developed.

Viscosity of polymer solution phase and other factors controlling the dissolution of theophylline microspheres prepared by the emulsion solvent evaporation method

The objectives of this investigation are to evaluate the effect of the viscosity of polymer solution phase on microsphere properties, especially the drug release characteristics since no studies on this formulation variable have been reported. Also, since it is known that polymer molecular weight affects both the viscosity of the polymer solution and the release properties of microspheres, the interaction of these factors was studied. Microspheres with 33% theoretical drug loading of anhydrous theophylline core material were prepared by the emulsion solvent evaporation method. Two cellulose acetate butyrate polymers, (CAB381-2, CAB381-20), chemically similar but having different molecular weights, were used to prepare different polymer solutions having different apparent viscosities in acetone. A Brookfield viscometer was used to evaluate the viscosities of polymer solutions. Dissolution rates of microspheres prepared from the polymer solutions were inversely related to the initial polymer solution viscosities for both CAB381-2 and CAB381-20. The times for the release of 30 and 50% of the drug from the microspheres have a linear relationship with initial polymer solution viscosity. Initial release was significantly decreased with increasing polymer solution viscosity. Unlike CAB381-2 microspheres which follow Higuchi spherical matrix release kinetics, microspheres prepared from the higher molecular weight polymer (CAB381-20) showed extended release dissolution profiles with near zero order kinetics. It is evident that both the polymer solution viscosity and the molecular weight have an effect on the drug release from microspheres. These results suggest that release rates of matrix microspheres could be predictably optimized by adjusting the viscosity of polymer solutions.

Viscosity of polymer solution phase and other factors controlling the dissolution of theophylline microspheres prepared by the emulsion solvent evaporation method

The objectives of this investigation are to evaluate the effect of the viscosity of polymer solution phase on microsphere properties, especially the drug release characteristics since no studies on this formulation variable have been reported. Also, since it is known that polymer molecular weight affects both the viscosity of the polymer solution and the release properties of microspheres, the interaction of these factors was studied. Microspheres with 33% theoretical drug loading of anhydrous theophylline core material were prepared by the emulsion solvent evaporation method. Two cellulose acetate butyrate polymers, (CAB381-2, CAB381-20), chemically similar but having different molecular weights, were used to prepare different polymer solutions having different apparent viscosities in acetone. A Brookfield viscometer was used to evaluate the viscosities of polymer solutions. Dissolution rates of microspheres prepared from the polymer solutions were inversely related to the initial polymer solution viscosities for both CAB381-2 and CAB381-20. The times for the release of 30 and 50% of the drug from the microspheres have a linear relationship with initial polymer solution viscosity. Initial release was significantly decreased with increasing polymer solution viscosity. Unlike CAB381-2 microspheres which follow Higuchi spherical matrix release kinetics, microspheres prepared from the higher molecular weight polymer (CAB381-20) showed extended release dissolution profiles with near zero order kinetics. It is evident that both the polymer solution viscosity and the molecular weight have an effect on the drug release from microspheres. These results suggest that release rates of matrix microspheres could be predictably optimized by adjusting the viscosity of polymer solutions.

Adsorption of heavy metal ions from aqueous solutions by porous polyacrylonitrile beads

AbstractThe adsorption of Cu(II), Ni(II), Zn(II), and Pb(II) from aqueous solutions on acrylonitrile copolymer sorbents was studied. We prepared five types of sorbents from polyacrylonitrile by varying its concentration in the initial polymer solution and the composition of the coagulation bath, aiming to achieve a different porous structure. The specific area, pore volume, and pore radius of the sorbents were determined on a porosimeter. The porous structure was studied by scanning electron microscopy. Modification of sorbents with sodium hydroxide and hydroxylamine was carried out to form amidooxyme and carboxylic groups with proven complex‐forming properties toward heavy metal ions. The optimal pH of the sorption of metal ions was found. The adsorption kinetics were investigated. The order of polymer sorbents toward the sorption of Pb(II), Cu(II), Ni(II), and Zn(II) ions, and the order of heavy metal uptake were determined for all types of sorbents. The effectiveness of heavy metal desorption and the coefficient of recovery of sorption ability were determined. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3036–3044, 2002; DOI 10.1002/app.2334

Study of cryostructuration of polymer systems. XX. Foamed poly(vinyl alcohol) cryogels

Foamed poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze–thaw treatment of whipped PVA water solutions (polymer with MW of 69,000 Da and DD ∼99 mol % was used), were obtained and their properties were studied. The rheological characteristics and macrostructure of these gel materials were controlled by the same factors as for the ordinary nonfoamed PVA cryogels (initial polymer concentration and freezing–thawing regimes) and also by the conditions of generation of fluid PVA foams. The study of the kinetics of the freeze–thaw-induced gel formation of these foams revealed that the temperature dependence of the efficiency of cryotropic gelation showed a maximum at about −1.5°C. The presence of low molecular weight admixtures in the initial polymer solution appears to be a rather important factor because the admixtures were capable of decreasing the stability of fluid PVA foams and weakening both foamed and nonfoamed cryogel samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1609–1619, 2001

Study of cryostructuration of polymer systems. XX. Foamed poly(vinyl alcohol) cryogels

AbstractFoamed poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze–thaw treatment of whipped PVA water solutions (polymer with MW of 69,000 Da and DD ∼99 mol % was used), were obtained and their properties were studied. The rheological characteristics and macrostructure of these gel materials were controlled by the same factors as for the ordinary nonfoamed PVA cryogels (initial polymer concentration and freezing–thawing regimes) and also by the conditions of generation of fluid PVA foams. The study of the kinetics of the freeze–thaw‐induced gel formation of these foams revealed that the temperature dependence of the efficiency of cryotropic gelation showed a maximum at about −1.5°C. The presence of low molecular weight admixtures in the initial polymer solution appears to be a rather important factor because the admixtures were capable of decreasing the stability of fluid PVA foams and weakening both foamed and nonfoamed cryogel samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1609–1619, 2001

Water-absorbing properties of hydrogels based on polymeric complexes

Colloidal and chemical properties of polymeric complexes based on polyacrylamide and polyvinyl alcohol have been investigated. Several factors affecting water absorption by polymeric complexes have been studied: concentration of initial aqueous polymer solutions; components ratio in the mixture; temperature and duration; sorbed aqueous solutions properties (pH; kind of ions).Macromolecular globules of polyacrylamide in aqueous solutions upon addition of polyvinyl alcohol exhibit interactions of hydroxyl and amide groups. The heat treatment of polycomplexes aqueous solutions leads to formation of cross-linked products (hydrogels) which are not soluble in water and show superabsorbents properties.Variation of conditions of polycomplex formation allows to regulate the properties of the resulting products such as hydrogel strength and the water absorption in wide ranges. This gives us possibilities for optimal use of the hydrogels in function of their specific applications.

Electrical conductance of CHCl3 solutions of polyethylene oxide doped with KCI

CHCl3 solutions containing a few percent polyethylene oxide PEO (MW = 200 000) or the low-molecular model dioxane are stirred at 50°C during more than 100 h in the presence of small amounts of KCl. The specific conductance, the viscosity and the density of the solutions are measured at 25°C as a function of time. Both PEO and dioxane act as ligands improving the solubility of KCl. The relaxation times are of the order of several hours. After 40 h or more the viscosity of the solutions increases in a spectacular way. However, the most striking observation is that the specific conductance of the polymeric solutions at 25°C is systematically 5% higher than the value measured with the same sample at 45°C, just as for metals. The effect of the dilution of the primary stirred solutions either in the pure solvent or in the initial polymer solution is investigated. These results are discussed in terms of a three-step mechanism in the polymer systems: (1) Loading of the coils to polymeric cations with a full elementary charge, as a consequence of charge transfer interactions of the crown-ether type with numerous K+ ions penetrating into the coils; (2) Electron tunnelling conduction of the Hamill—Ceulemans type from one positive coil to the neighbouring one; (3) Alteration of the structure of the coils and of their hydrodynamic radius by the motions of K+ in the coils. These ‘brachiation’ motions by a hopping mechanism result from an increased mobility of the complexed K+ ions, which is also the origin of the Zundel effect. They do not directly contribute to the conductance but are responsible for the delayed increase of the viscosity.

Effects of order and disorder on field-effect mobilities measured in conjugated polymer thin-film transistors

The morphology of conjugated polymer thin films has been controlled by exploiting the processes giving rise to solvatochromism in the initial polymer solutions from which the polymer films were deposited by spin coating. The material used was the substituted polythiophene, 3[2(S2-methylbutoxy)ethyl]-polythiophene. Starting with polymer dissolved in ‘‘good’’ solvent, various quantities of ‘‘bad’’ solvent when added lead to the reorganization of the solubilizing side chains attached to the conjugated polymer backbone. Ordering of these side chains increases with addition of bad solvent decreasing the flexibility of the backbone, yielding more rigid rodlike polymer chains. This in turn causes aggregation and finally precipitation. It is found that this molecular order can be transferred from solution to solid film during the spinning process, ascertained from optical spectroscopy. With these films acting as the active layer in a field-effect transistor structure, the mobility of the carriers injected into the films can be measured. It is found that as the molecular order and aggregation increases, carrier mobility decreases from ∼10−5 cm2 V−1 s−1 to ≤10−8 cm2 V−1 s−1 in films displaying the highest degree of molecular order. This is ascribed to the increased interchain separation in the ordered systems along with effects due to macroscopic aggregate grain boundaries.

Intramolecularly crosslinked polystyrene as model of a supercrosslinked network

Globular soluble intramolecularly crosslinked polystyrene (PS) was prepared both by reaction of individual PS coils with monochlorodimethylether in the presence of tin chloride, and by reaction of chloromethyl groups in previously chloromethylated coils with the phenyl rings of the same macromolecule. The concentration of the initial polymer solution subjected to intramolecular crosslinking was 0.1–0.5%. By viscometric, electron microscopic and GPC methods it was established that the globules represent individual PS macromolecules strengthened by a large number of intramolecular crosslinks. The globules of intramolecularly crosslinked PS exhibit the same properties as supercrosslinked PS networks: their internal specific surface reaches 800–1000 m 2/g and they can swell in methanol. The equivalence of these unusual properties directly proves that they result from the specific features of supercrosslinked structures at molecular level.

Formation de gels de poly ( N-vinylpyrrolidone) par l'action des rayons gamma sur des solutions aqueuses de poly( N-vinylpyrrolidone)

The gamma radiolysis of aqueous solutions of PNVP was investigated. Solutions containing 1–30 g PNVP per 100 ml were subjected to doses of up to 8 KGy (8 Mrad). The increase of the viscosity of the solutions was determined during the pre-gel stage. The respective values of sol and gel fractions were measured at doses higher than the critical dose for gel formation D∗. It was found that D∗increases with the concentration of the initial polymer solution and that it was independent of dose-rate. The experimental values of sol fractions are in good agreement with the equation of Charlesby and Pinner. The radiation chemical yields of cross-linking G(cross-links) were derived from the experimental values of D using two methods. It was found that G(cross-links) is very small for the 1% PNVP solution and that it increases steadily with the concentration of polymer. The various competing processes which account for the observed relationships are considered.