Nursel Pekel

Radiation synthesis, characterization and amidoximation of N-vinyl-2-pyrrolidone/acrylonitrile interpenetrating polymer networks

Abstract Interpenetrating polymer networks (IPNs) were synthesized by irradiating acrylonitrile solutions of poly(N-vinyl-2-pyrrolidone) with 60Co-γ rays. The conversion to insoluble IPN structure was characterized using FT-IR and thermal analysis methods. The amidoximation of polyacrylonitrile moieties of IPN was carried out in aqueous solutions of NH2OH·HCl–NaOH at 50°C. The conversion of amidoximation was followed by using FT-IR spectrophotometer and conversion of nitrile groups to amidoxime was determined as percentage. The structure of amidoximated IPN was characterized by FT-IR and thermal methods as well.

Synthesis and characterization of N-vinylimidazole–ethyl methacrylate copolymers and determination of monomer reactivity ratios

Abstract Radical-initiated copolymerization of N-vinylimidazole (VIM) and ethyl methacrylate (EMA) was carried out with 2,2′-azobisisobutyronitrile (AIBN) as an initiator in benzene at 70°C in nitrogen atmosphere. Structure and composition of copolymers for a wide range of monomer feed were determined by elemental analysis (content of N for VIM-units) and by Fourier transform infrared spectroscopy through recorded analytical absorption bands for VIM (667 cm−1 for C–N of imidazole ring) and EMA (1729 cm−1 for CO of ester group) units, respectively. Monomer reactivity ratios for VIM (M1)–EMA (M2) pair were determined by Fineman–Ross and Kelen–Tudos (KT) methods. They are r1=0.35±0.02 and r2=3.47±0.2 as determined by KT method. Parameters of Q1=0.14 and e1=−0.61 for VIM monomer were calculated by using the Alfrey–Price scheme. Observed relatively high activity of EMA growing radical was explained by effect of complex formation between carbonyl group and imidazole fragments in chain growth reactions. Thermal behaviors of copolymers with various compositions were investigated by differential scanning calorimetry and thermogravimetric analysis. It was observed that glass transition temperature and thermal stability of copolymers increased with increasing of VIM content in copolymers.

Development of new chelating hydrogels based on N-vinyl imidazole and acrylonitrile

Copolymers derived from the binary mixture of N-vinyl imidazole (VIm) and Acrylonitrile (AN) monomers have been synthesized by the irradiation of their solution with 60 Co-g rays. Gelation percent‐dose graphs were formed, and 80% of gelation (maximum percentage) has been reached at around 14kGy dose. To impart metal ion adsorption properties, the hydrogels were amidoximated by the reaction of cyano groups on AN with hydroxylamine in aqueous media. Swelling behaviors of hydrogels were investigated before and after amidoximation. Hydrogels had 54% of swelling originally, this ratio reached 220% of swelling after amidoximation. The degree of amidoximation was followed by FT-IR spectroscopy. The structures of copolymers were analyzed spectroscopically and thermally before and after the amidoximation reaction. # 2000 Elsevier Science Ltd. All rights reserved.

Separation of uranyl ions with amidoximated poly(acrylonitrile/N-vinylimidazole) complexing sorbents

Abstract Acrylonitrile (AN)/N-vinylimidazole (VIm) copolymeric hydrogels were synthesized by irradiating their binary mixtures. The AN moieties of copolymers were amidoximated using hydroxylamine hydrochloride in basic medium. The amidoximated hydrogels were used for separating uranyl ions from aqueous solutions by a complexation process. Uranyl ion adsorption studies were conducted from different UO22+ ion solutions (650–1850 ppm). The result of all UO22+ ion adsorption studies complied with the L-type isotherm. The adsorption capacity was found as high as 0.64 g UO22+ g−1 dry amidoximated copolymer.

Radiation synthesis of n-vinyl 2-pyrrolidone/acrylonitrile interpenetrating polymer networks and their use in uranium recovery from aqueous systems

Abstract Interpenetrating Polymer Networks (IPNs) based on Poly n-vinyl 2-pyrrolidone (PVP) and Acrylonitrile (AN) were prepared by irradiating PVP solutions prepared in AN. PVP/AN mixtures were irradiated by 60 Co-γ rays at room temperature at a dose rate of 0.5 kGy/hour. IPNs were characterized by using FT-IR and Thermal Analysis techniques. The chelating adsorbents containing amidoxime groups were prepared by the reaction of these IPNs with hydroxylamine in aqueous NaOH solution at 50°C. These amidoxime containing adsorbents were used in adsorption studies for the recovery of uranium from aqueous systems. The adsorption capacity of an IPN with equivolume fraction of PVP and amidoximated PAN was found to be 750mg UO 2 2+ /g dry amidoximated IPN.

AMIDOXIMATION AND CHARACTERIZATION OF NEW COMPLEXING HYDROGELS PREPARED FROM N-VINYL 2-PYRROLIDONE/ACRYLONITRILE SYSTEMS

Solutions, obtained from the mixture of different mole ratios of N-vinyl 2-pyrrolidone and acrylonitrile, were irradiated in a 60Co-γ source to produce copolymers. The swelling percentage curves were formed, and a diffusion exponent was calculated. For the uranyl ion adsorption, these copolymers were reacted with hydroxylamine hydrochloride to convert C≡N groups to ─C˭N-OH (amidoxime) groups. The optimum amidoximation time was determined by uranyl ion adsorption. The structure of copolymers, before and after amidoximation, was analyzed with spectroscopic and thermal methods.

Preparation of poly(vinyl alcohol) hydrogels with radiation grafted citric and succinic acid groups

Ternary mixtures of PVA/Citric acid (CA)/water and PVA/Succinic acid (SA)/water were gamma irradiated to various doses in air at ambient temperature. Gelation % vs dose curves were constructed and swelling behavior of gels with maximum conversions was studied. In maximum gelled systems 80% of CA used in the feed composition was retained in the gel structure whereas this was only 20% for SA. The volume of swelling of ionic PVA gels increased from 230% to 530% for PVA/CA systems when pH was increased from 2.6 to 7.5. Less significant increase in swelling was observed for PVA/SA gels, from 250% to 330% in the same pH interval. The incorporation of SA and CA groups onto PVA networks improved remarkably the affinity of these structures for Co2+ and Ni2+ ion uptake.

Enhancement of stability of glucose oxidase by immobilization onto metal ion-chelated poly(N-vinyl imidazole) hydrogels.

Poly(N-vinylimidazole), PVIm, gels were prepared by γ-irradiation polymerization of N-vinylimidazole in aqueous solutions as an affinity gel for glucose oxidase (GOx). These affinity gels with a water swelling ratio of 1800% for plain polymeric gel and between 30–80% for Cu(II) and Co(II)-chelated gels at pH 6.0 in phosphate buffer were used in the GOx adsorption studies. Maximum metal ion adsorption capacity of these hydrogels was found to be 3.64 mmol/g dry gel for Cu(II) and 1.72 mmol/g dry gel for Co(II) leading to GOx adsorption capacities of 343 and 528 mg enzyme/g dry gel, respectively, as compared to 228 mg for the plain dry PVIm gel. Activity studies were carried out using plain and the metal ion-chelated form of this hydrogel to investigate the stability and retained activity of the GOx in different buffer solutions and at different temperatures. Activity of the enzyme, either in free or immobilized form on the gel, decreased dramatically in acetate buffer solutions. In phosphate buffer solution, however, stability of enzyme has been found to be significantly high reaching 90% retained activity at the end of a 40-day period at 4°C for Co(II) chelated systems. After immobilization of the enzyme onto metal-chelated hydrogel, the thermal stability of enzyme was enhanced significantly showing 23% activity, even at 75°C.

A new specific metal ion chelated-poly(N-vinylimidazole) gel sorbents for albumin adsorption-desorption

Poly (N-vinylimidazole) (PVIm) hydrogels were prepared by γ-irradiating binary mixtures of N-vinylimidazole-water in a 60 Co-γ source having 4.5 kGy/h dose rate. These affinity gels having different swelling ratio of Cu(II)-chelated, Co(II)-chelated and plain PVIm in acetate buffer were used in the albumin adsorption studies. Bovine serum albumin (BSA) adsorption on these gels from aqueous solutions containing different amounts of BSA at different pH adjusted with acetate and phosphate buffer was investigated in batch reactors. The adsorption capacities of BSA on/in the gels were decreased dramatically by increasing the ionic strength (I) adjusting with NaCL BSA adsorption capacities of the metal ion-chelated gels were higher than the plain PVIm gel even if the swelling ratio of the metal ion-chelated gels was very low comparing to the PVIm gel. The rigidity of the metal ion-chelated gel is very high and it can be used for the column applications. More than 95% of BSA were desorbed in 3 h in the desorption medium containing KSCN for PVIm gel and EDTA for metal ion-chelated gels. These results indicate that PVIm and metal ion-chelated PVIm gels are very efficient to remove BSA and the different metal ion-chelated PVIm gels show different affinity for BSA or biomolecules.

Radiation synthesis and characterization of N‐vinyl‐2‐pyrrolidone/N‐allylthiourea hydrogels and their use in the adsorption of invertase

N-Vinyl-2-pyrrolidone/N-allylthiourea (VP/ATU) copolymeric hydrogels were prepared by γ-irradiating ternary mixtures of VP/ATU/water. The influence of the ATU on the gelation of VP, on the network structure and on the adsorption of invertase was investigated. VP/ATU copolymeric hydrogels were found to swell in the range of 950 – 2 500%. The water diffusion to the hydrogels is a non-Fickian type diffusion and the diffusion coefficients varied from 15.4·10–8 to 1.5·10–8 m2 s–1. The adsorption capacity of the hydrogels was found to increase from 8.0 to 380.0 μg invertase/g dry gel with increasing amount of ATU, and loss in activity with adsorption is approximately threefold. N-Vinyl-2-pyrrolidon(VP)/N-allylthioharnstoff(ATU)-Copolymerhydrogele wurden durch γ-Bestrahlung von ternaren Mischungen von VP/ATU/Wasser hergestellt. Hierbei wurde der Einflus von ATU sowohl auf die Gelbildung von VP als auch auf die Netzwerkstruktur und die Adsorption von Invertase untersucht. Es zeigte sich, das die VP/ATU-Copolymerhydrogele in einer Grosenordnung von 950–2 500% quellfahig sind. Bei der Wasserdiffusion zum Hydrogel hin handelt es sich um eine nicht-Ficksche Diffusion; der Diffusionkoeffizient variiert von 15,4·10–8 bis zu 1,5·10–8 m2 s–1. Mit steigendem Anteil an ATU nimmt die Adsorptionskapazitat des Hydrogels von 8,0 auf 380,0 μg Invertase/g trockenen Gels zu, und die Adsorptionaktivitat nimmt ungefahr um den Faktor 3 ab.