Investigations of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) blends, 1. Compatibility

Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(N-vinyl-2-pyrrolidone) (PVP) made from aqueous solutions appear to be miscible in the whole composition range according to DSC results. A large negative value of the interaction parameter between the two polymers was found from melting point depressions. IR spectroscopy evidenced compatibility of the two polymers on a molecular level. DSC, density and IR results all show a proportion of pure PVA crystallites in blends, which decreases with increasing PVP content and becomes nil at about 50 wt.-% of PVP. However, close examination of the hydroxyl stretching region of the blends indicates the presence of organized regions of PVA beyond this limit. According to IR results, the sequence of decreasing hydrogen-bonding power should be the following: multiple hydroxyl-hydroxyl bonding in organized PVA regions, hydroxyl-carbonyl bonding between the two polymers, and simple hydrogen-hydrogen bonding in amorphous PVA regions. It appears that the PVA component can be held in the amorphous state by hydrogen bonding with the PVP component when there is a sufficient amount of the latter in the blend. The amorphous part of PVA is compatible with PVP, but the crystallizable part is not in its most stable form.     

Complexation of poly(monobenzyl itaconate) and poly(N-vinyl-2-pyrrolidone) in dilute solution

Upon mixing dilute solutions (10^?4 – 10^?2 mol/l) of poly(monobenzyl itaconate) (PMBI) and poly(N-vinyl-2-pyrrolidone) (PVP) in methanol, soluble polycomplex particles are formed. Here we report on the spectrophotometric determination of the turbidity of different solutions of PVP and PMBI as a function of polymer concentration and PVP molecular weight. Viscosity measurements were also performed. The polycomplex is weak. Polycomplex particles are more compact and much larger than separated chains of polyacid and polybase. No definite stoichiometry is observed and a microgel-like structure is proposed.     

Investigation of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) blends, 3. Permeation properties of polymer blend membranes

Dense membranes made of poly(vinyl alcohol) (PVA) and poly(N-vinyl-2-pyrrolidone) (PVP) blends of different compositions were studied in gas-sweeping permeation of a water-ethanol mixture containing 10 wt.-% of water. When the PVP content increases, the steady-state permeation flux and the water content in the permeate show sudden changes at ca. 30–40 wt.-% of PVP in the membrane: the flux increases drastically, while the water selectivity of the membrane falls to a much lower level. The diffusion coefficients of both water and ethanol, as determined from the permeation flux changes in the transient regime, exhibit a large increase when the PVP content exceeds 30 wt.-%, and this accounts for the flux increase. The fall in the permeation selectivity is shown to be due to a strong decrease in the sorption selectivity. The threshold of the change corresponds approximately to the PVP content at which PVA crystallites no longer exist in the blend. A further study on the states of water in the blend membranes by differential scanning calorimetry made it possible to relate these changes with a change in the interactions of water with hydrophilic sites in the polymer blend when the PVP content changes.     

Studies of crosslinked poly(N-vinyl-2-pyrrolidone) by calorimetry and by NMR

Aqueous solutions of poly(N-vinyl-2-pyrrolidone) are converted to gels by reaction with potassium peroxydisulfate K₂S₂O₈. The degree of crosslinking in the gel fractions depends on the amount of persulfate used. The degree of crosslinking is related to the amount of non-freezing bound water in the gels by means of differential scanning calorimetry in the temperature range from −50°C to + 170°C. The chemical nature of the bonds formed during gelation is studied by ¹H and ¹³C NMR Spectroscopy and by swelling tests. NMR measurements point to the formation of aliphatic sidechains as well as crosslinks in the gelation. The swelling tests give low values for the number of crosslinks, hence the formation of branched chains strongly influences the properties of the gels. In contrast to what was expected no carboxyl groups are found in the gels.     

Glass transition temperatures in blends of poly(N-vinyl-2-pyrrolidone) with a copolymer of bisphenol A and epichlorohydrin or with poly(vinyl butyral)

Blends of poly(vinyl butyral) (PVB) and of a copolymer of bisphenol A and epichlorohydrin (Phenoxy) with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared by solution casting. The glass transition temperatures T_g for different compositions of the blends were measured by differential scanning calorimetry (DSC). The T_g behaviour of PVB/PVP blends suggests the existence of a single phase for blends containing less than 50 wt.-% PVP, and of two phases in blends containing more than 50 wt.-% PVP. Phenoxy/PVP blends showed to be miscible over the entire composition range. It was found that the Gordon-Taylor equation predicts adequately the T_g-composition dependence with a K parameter equal to 0,5 and 1,25 for PVB/PVP and Phenoxy/PVP blends, respectively.     

Study of the miscibility of poly(N-vinyl-2-pyrrolidone) with poly[styrene-co-(4-hydroxystyrene)]

Poly(N-vinyl-2-pyrrolidone) (PVP) was blended with poly[styrene-co-(4-hydroxytyrene)] (PSH) which was obtained from the random copolymer poly[styrene-co-(4-acetoxystyrene)] (PSA). The miscibility of PVP/PSH blends in a composition 1 : 1 by weight was evaluated by differential scanning calorimetry (DSC), non-radiative energy transfer (NET) and Fourier transform infrared (FTIR) spectroscopy. It was found that the blends become miscible when the hydroxystyrene units (HS) in PSH exceed 11 mol-%. The driving force of miscibility may be attributed to hydrogen bonding between ? OH in PSH and in PVP. The experimental results of miscibility were compared with that estimated from a “miscibility parameter” (MP) concept, and we found that the general trend of MP values is in agreement with the experimental results.     

Molecular association in aqueous solutions of high molecular weight poly(N-vinyl-2-pyrrolidone)

A viscosimetric method was used to investigate the molecular association in aqueous solutions of poly(N-vinyl-2-pyrrolidone), (PVP), of molecular weight 700 000. Limiting viscosity numbers [η] and Huggins constants k_H of the polymer solutions were observed to decrease upon addition of denaturing agents such as thiourea and guanidinium sulfate. Guanidinium sulfate was found to be even more effective in its denaturing action as compared to urea and thiourea. The decrease in [η] and k_H values increased with increasing concentrations of the denaturing agents. This behaviour was explained on the basis of the rupture of bridges formed by water molecules among different PVP chains, hydrogen bonding being responsible for these intermolecular associations. While no change in the [η] values was observed for PVP in 2 M thiourea solutions upon increasing the temperature from 25°C to 35 and 45°C, for the same increase in temperature the [η] values of aqueous PVP solutions showed substantial decreases. This is also attributed to the breaking of hydrogen bonds existing between PVP molecules.     

Investigations of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) blends, 2. Influence of the molecular weights of the polymer components on crystallization

Blends of crystallizable poly(vinyl alcohol) (PVA) and poly-(N-vinyl-2-pyrrolidone) (PVP) of different molecular weights were prepared from aqueous solutions by evaporation and studied by Fourier-transform IR spectroscopy. When the molecular weight of one of the polymer components increases, the PVP content at which crystallinity in PVA is no longer observed decreases. The wide band representing hydroxyl stretching splits into four components at welldefined frequencies which are assigned to (1) multiple hydroxyl-hydroxyl bonding in organized PVA regions, (2) hydroxyls which are simply bonded to carboxyl, (3) hydroxyls doubly bonded to two carbonyls or to one carbonyl and one hydroxyl, and (4) simple hydrogen-hydrogen bonding in amorphous PVA regions. When the PVP content increases, the relative intensity of the bond of di-hydrogen-bonded hydroxyls remains quasi-invariant, while that of multiple hydrogen bonds in PVA decreases, and that of simple hydroxyl-carbonyl bonds increases correspondingly. It appears that the higher the molecular weight, the more effective the hindrance of PVP crystallization. An explanation of the mechanism leading to the formation of different structures in the blends is proposed on the basis of these results. It stresses the importance of the role of chain dynamics in an entangled chain network, which greatly affects the kinetics of crystallization of PVA during the drying step.     

Swelling behaviour of a non-ionic poly(N-vinyl-2-pyrrolidone) gel in a linear poly(acrylic acid) solution

The swelling behaviour of a non-ionic poly(N-vinyl-2-pyrrolidone) hydrogel in a linear poly-(acrylic acid) solution upon the influence of chain length, pH, ionic strength, and water/dimethyl sulfoxide composition was studied. The sharp shrinkage of the gel volume within a narrow range of polyacid concentration takes place as a result of the formation of an intermacromolecular gel-polymer complex on the base of hydrogen bonding. According to X-ray diffraction this complex is amorphous. The formation of the gel-polymer complex is a long term process and the system reaches equilibrium within 48 h. The swelling behaviour strongly depends on the chain length of the polyacid whereas it does not depend on the ionic strength. With increasing pH value and changing water/dimethyl sulfoxide composition the gel reswelling is induced. The complex formation with poly(acrylic acid) occurs in the same way for linear and crosslinked poly(N-vinyl-2-pyrrolidone).     

Platelet interactions with plasma-polymerized ethylene oxide and N-vinyl-2-pyrrolidone films and linear poly(ethylene oxide) layer

Dimethyldichlorosilane (DDS)-treated glass (DDS-glass) was modified with either poly(ethylene oxide) (PEO) films or poly(N-vinyl-2-pyrrolidone) (PNVP) films by plasma polymerization. The thickness of the plasma polymerized films was varied between 40 and 700 nm. The results showed that the hydrophilic plasma polymerized PEO and PNVP films on DDS-glass did not prevent platelet adhesion and activation. The film thickness had only marginal influence on the prevention of platelet activation. In contrast, platelet adhesion was prevented on DDS-glass adsorbed with a PEO-containing block copolymer (Pluronic® F-108 surfactant) even at a calculated thickness of the PEO layer of less than 40 nm. This study shows that surface hydrophilization is not sufficient for prevention of platelet adhesion and activation. The contrasting results in platelet adhesion between cross-linked plasma polymers and linear PEO-containing block copolymers may be explained qualitatively by a steric repulsion mechanism that is achieved by the conformational freedom of the linear PEO chains interacting with water.     

Raman spectroscopic study of hydrogen bonding of poly(N-vinyl-2-pyrrolidone) in heavy water and dimethyl sulfoxide

The Raman spectra of solutions of poly(N-vinyl-2-pyrrolidone) (PVP; M?_w = 1 000, 10 000, 40 000 and 360 000) in D₂O and dimethyl sulfoxide (DMSO) were measured at various concentrations. PVP is hydrated by D₂O in a manner different from N-ethyl-2-pyrrolidone (NEP) and N-methyl-2-pyrrolidone (NMP), monomer analogues of PVP. The self-association of DMSO molecules in the solution of PVP was found to be different from that in the solution of NMP by using difference spectroscopy. These phenomena were attributed to a net-like structure of concentrated solutions of PVP.     

Solvent effect on the formation of poly(methacrylic acid)-poly(N-vinyl-2-pyrrolidone) complex through hydrogen bonding

An interpolymer complex can be obtained by mixing the solutions of poly(methacrylic acid) and poly(N-vinyl-2-pyrrolidone). Three phase changes were observed on increasing the initial polymer concentration: namely, a homogeneous solution, a precipitate, and a gel. Such interpolymer complex formations were examined in several protic and aprotic solvents. The obvious relationship between the complex formation and the dielectric constant of the solvent was eludicated. The effect of hydrophobic interactions on the complex formation was also discussed as well as the role of the α-methyl group of poly(methacrylic acid).     

Embolized crospovidone (poly[N-vinyl-2-pyrrolidone]) in the lungs of intravenous drug users.

Crospovidone is an insoluble polymer of N-vinyl-2-pyrrolidone that is used as a disintegrant in pharmaceutical tablets. It can potentially embolize to the lung when aqueous tablet suspensions are injected intravenously. In this report, we identified embolized crospovidone in autopsy-derived lung tissue from three adult IV drug users, 1 man and 2 women, whose ages respectively were 27, 38, and 40 years. Suspected crospovidone was compared with pharmaceutical-grade crospovidone by means of histochemical stains, transmission electron microscopy, and infrared spectroscopy. Similar particles were also observed by light microscopy in a 4-mg tablet of hydromorphone, a preparation prescribed to two of the patients. Two patients had sickle cell disease and were taking methadone and/or hydromorphone for pain management; the third was receiving parenteral hyperalimentation after small bowel resection. Crospovidone appeared as deeply basophilic, coral-like particles within pulmonary arteries and in extravascular foreign-body granulomas. Intrapulmonary crospovidone stained similarly to the pure substance, including intense staining with mucicarmine, Congo red, and Masson trichrome. With Movat pentachrome stain, both intravascular and purified crospovidone appeared orange-yellow, whereas most interstitial particles associated with giant cells stained blue-green. Alcian blue failed to stain intravascular or purified crospovidone but strongly decorated some phagocytized particles. Ultrastructurally, both purified powder and tissue deposits of crospovidone appeared as irregular, electron dense, laminated, and finely granular material. Intrapulmonary crospovidone was associated with inflammatory cells and exhibited degenerative changes. By infrared spectroscopy, crospovidone in tissue had the same spectral characteristics as pharmaceutical grade crospovidone and the library reference, polyvinylpyrrolidone (PVP). We conclude that crospovidone contributes to pulmonary vascular injury in some persons who illicitly inject pharmaceutical tablets. It is readily identifiable histologically and distinguishable from other tablet constituents, such as cornstarch, talc, and microcrystalline cellulose. The variable staining with Alcian blue and Movat suggests that crospovidone is altered in vivo by the inflammatory response.     

Miscibility and specific interactions in blends of poly(vinyl acetate-co-vinyl alcohol) with poly(ethyloxazoline)

Miscibility of poly(ethyloxazoline) (PEOX) with poly(vinyl acetate) (PVAC), poly(vinyl alcohol) (PVAL) and poly(vinyl acetate-co-vinyl alcohol) (ACAL copolymers) has been investigated over a wide composition range. In some blends, due to the small difference between the glass transition temperatures of the components, the enthalpic relaxation method was used as miscibility criterion. Differential scanning calorimetry (DSC) results indicate that PEOX is immiscible with PVAC and PVAL but is miscible with ACAL copolymers in a certain range of compositions. The ACAL/PEOX phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with blend composition for miscible systems was found to follow the Kwei equation. Infrared spectroscopy studies of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups in vinyl alcohol units and the carbonyl group in the tertiary amide, which appear to be decisive for miscibility.     

The color reaction between partially saponified poly(vinyl acetate) and iodine-iodide in the presence of amylose

The color reaction between partially saponified poly(vinyl acetate), (P-PVAc), which is dissolvable in water and iodine-iodide was investigated in the presence of amylose. As the concentration of amylose increases, the absorbance at λ_max = 488 nm of the red-violet complex between P-PVAc and iodine-iodide decreases and, on the other hand, the absorbance at λ_max = 625 nm of the blue complex between amylose and iodine-iodide increases. The equation for the relationship between the decrease in the red-violet complex and the increase in the blue complex was derived. On the basis of this equation, the molar absorption coefficient per iodine molecule at λ_max = 625 nm for the blue complex of amylose with iodine-iodide was found to be 3,68·10⁴ l mol^?1 cm^?1 at 15°C.     

Poly(N-vinyl-2-pyrrolidone) elution from polysulfone dialysis membranes by varying solvent and wall shear stress

Some dialysis patients are treated with post-hemodiafiltration (HDF); the blood viscosity of the patients who undergo post-HDF is higher than that of the patients who undergo conventional hemodialysis. This study aims to evaluate poly(N-vinyl-2-pyrrolidone) (PVP) elution from PSf dialysis membranes by varying solvents and high wall shear stress caused by blood viscosity. We tested three commercial membranes: APS-15SA (Asahi Kasei Kuraray), CX-1.6U (Toray) and FX140 (Fresenius). Dialysate and blood sides of the dialyzers were primed with reverse osmosis (RO) water and saline. RO water, saline and dextran solution (2.9 and 5.8 mPa s) were circulated in the blood side. The amount of eluted PVP was determined by 0.02 N iodometry. The hardness and adsorption force of human serum albumin (HSA) on the membrane surfaces were measured by the atomic force microscope. When wall shear stress was increased using dextran, the amount of PVP eluted by the 2.9 mPa s solution equaled that eluted by the 5.8 mPa s solution with APS-15SA and CX-1.6U sterilized by gamma rays. The amount of PVP eluted by the 5.8 mPa s solution was higher than that eluted by the 2.9 mPa s solution with FX140 sterilized by autoclaving. The wall shear stress increased the PVP elution from the surface, hardness and adsorption force of HSA. Sufficient gamma-ray irradiation is effective in decreasing PVP elution.     

Optimization of solution fractionation of poly(vinyl acetate)

The theoretical assumptions to understand the elution mechanism of the discontinuous solution fractionation and complete elution method could be confirmed for the system poly(vinyl acetate)/butyl acetate/cyclohexane. In this case the process of complete elution, however, can only be carried out with an unfavorable high consumption of time and material. The complete elution method with all its advantages can be preserved, if the process is carried out as multistage process with a limited number of discontinuous steps. By means of such a multistage procedure improved separation results were achieved compared with the conventional single stage procedure. Furthermore some results are given which show a decrease of the separation effect of solution fractionation due to procedural limitations.     

The color reaction between partially saponified poly(vinyl acetate) and iodine-iodide in the presence of boric acid

The effect of the boric acid concentration on the color reaction between partially saponified poly(vinyl acetate), which is dissolvable in water, and iodine-iodide was investigated. As the concentration of boric acid increased, the absorbance at λ_max = 488 nm of the red-violet complex, which is due to a long sequence of vinyl acetate units distributed along the polymer chain, increased gradually, reached a maximum, and then decreased from the point in which the absorbance at λ_max = 656nm of the blue complex, based on the vinyl alcohol units in the polymer, was observed. The color complex in an excess of boric acid transferred from red-violet to red-tinged blue with time. From the color change, the molar absorption coefficient at λ_max = 656 nm for the iodine molecule in the blue complex was found to be 3,92.10⁴l/(mol cm).     

Controlled release of cytarabine from poly(2-hydroxyethyl methacrylate-co-N-vinyl-2-pyrrolidone) hydrogels

Controlled release of cytarabine (ara-C) from poly(2-hydroxyethyl methacrylate-co-N-vinyl-2-pyrrolidone) [p(HEMA-co-VP)] hydrogels cross-linked with ethylene glycol dimethacrylate (EGDMA) is reported. Three compositions of copolymer, each one with a different cross-linking degree, have been studied: H50/VP50, H75/VP25, and H80/VP20. Ara-C (5-25 mg by disc) was trapped in the gels by including it in the polymerization feed mixture. The ara-C release time was between 1 day from H50/VP50/E0.5 discs and 16 days from H80/VP20/E15 discs. In all cases there is a time period for which the drug release rate is constant.     

Release of gentamicin sulphate from a modified commercial bone cement. Effect of (2-hydroxyethyl methacrylate) comonomer and poly(N-vinyl-2-pyrrolidone) additive on release mechanism and kinetics

The influence of the (2-hydroxyethyl methacrylate) (HEMA) monomer addition as a comonomer to the cement liquid component and of a polymer, poly(N-vinyl-2-pyrrolidone) (PVP) to the solid component of a standard CMW-1 bone cement on gentamicin sulphate (GS) on its drug release properties have been studied. The addition of HEMA modifies the habit of the delivery curves. The incorporation of PVP into the cement matrix, apparently, did not very much modify the shape of the HEMA modified cement release curves, but led to a remarkable increase of the maximum amount of GS released. This effect was proportional to the PVP concentration incorporated. From the matrix composition and SEM data, a model based on the morphology of the matrix has been proposed. The cumulative amount of GS released by each slab Mt is most adequately fitted and represented by the equation Mt = c + at 1/2 + b[1 - exp(-nt)], which corroborates that the release occurs according to the model proposed. by means of three discrete mechanisms, namely: (i) a short-term initial elution due to the imperfections in the poly(methyl methacrylate) covering of the most external GS beads, burst effect by the buffer solution; (ii) followed by a fracture by stress cracking in an active media of the coated GS beads located on the external surface of the matrix where water molecules enter to dissolve GS molecules releasing them into the buffer solution by a diffusion-controlled process; and (iii) a third process in which the buffer solution penetrates into the internal voids and cracks creating a series of channels in a labyrinthic structure, which may facilitate the access of water molecules to the plastic-coated GS beads within the bulk matrix. This third process is enhanced by the incorporation of PVP beads as dissolved molecules within the matrix. This water-soluble additive is leachable, generating a highly porous structure in the cement. This HEMA and PVP modified cement may be used as a drug delivery system to modulate the GS release rate.