Ágnes Sáfrány

From microspheres to monoliths: Synthesis of porous supports with tailored properties by radiation polymerization

Abstract Advanced functional materials, both in shape of beads and monoliths, are in high demand for a variety of applications ranging from catalysis, chromatography, diagnostics, sensors to combinatorial chemistry. Here we report the synthesis of functional supports of different size and shape by radiation co-polymerization in organic solvents using diethylene glycol dimethacrylate (DEGDMA) and glycidylmethacrylate (GMA) as co-monomers. With the increase in the GMA content, the particle diameter increases from 0.9 to about 3 μm, while the yield decreases from 80% to 50%. The usefulness of the microspheres for immobilization was tested with histidine and lysosyme. Monoliths were prepared in situ as chromatographic columns. Our results showed that when a 30% monomer solution was irradiated, a 100% conversion of the monomer was obtainable with doses higher than 15 kGy. We showed the effect of dose and dose rate as well as the irradiation temperature on the pore size of the monoliths and the flux. The effect of such different solvents as tetrahydrofuran, ethylpropionate, acetone, methanol, ethanol, propanol and butanol is also discussed. Our results showed that radiation synthesis of porous polymer supports with epoxy functionality is a viable alternative to either thermally initiated or photo polymerization.

Radiation processing: Synthesis and modification of biomaterials for medical use

Abstract Hydrogels that show inverse thermo-response have been synthesized by simultaneous radiation polymerization and crosslinking. The polymerization mechanism was studied by pulsed radiolysis and pulsed NMR, and the swelling and mechanical properties were correlated to the synthesis conditions.

Synthesis and characterization of superclean thermo-reversible copolymer hydrogels

A series of hydrogels that show inverse thermo-response have been synthesized by simultaneous radiation polymerization and crosslinking. Superclean gels were obtained by irradiating the monomers (hydroxyethylacrylate and hydroxypropylacrylate) in bulk or in aqueous solutions without any additive. By variation of the monomer concentration, co-monomer ratio, irradiation temperature and absorbed dose, hydrogels with various swelling charactheristics were obtained. By increasing the ratio of the more hydrophilic ethylacrylate, the critical temperature of the gel can be shifted to higher temperatures, and by increasing the monomer concentration or the dose, gels with better mechanical characteristics albeit lower swelling degree could be obtained.

Radiolysis of hydroxy ethylacrylate in dilute aqueous solutions

Abstract The reaction of e - aq and OH radicals with hydroxy ethylacrylate was investigated, the intermediates formed were identified and their decay characteristics were established by pulse and steady state radiolysis. The electron adduct decays by protonation at the β carbon atom forming thus α-carboxyalkyl radical. The OH adduct also has the α-carboxyalkyl radical structure. The radicals under pulse radiolytic conditions, in the hydroxy ethylacrylate concentration range investigated (0.05–1 mmol dm -3 ) mostly disappear in bimolecular self termination reactions.

Pulse radiolysis of aqueous solutions of ethyl acrylate and hydroxy ethyl acrylate

Abstract Ethyl- and hydroxy ethyl acrylate show high reactivities with hydrated electron and hydroxyl radical intermediates of water radiolysis. The electron adduct reversibly protonate with pK values of 5.7 and 7.3. The adducts may take part in irreversible protonation at the β carbon atom forming α-carboxyl alkyl radicals. Same type of radical forms in reaction of acrylates with OH: at low concentration the adduct mainly disappear in self termination reactions. Above 5 mmol dm-1 the signals showed the startup of oligomerization.

Electron-beam initiated crosslinking in poly(N-isopropylacrylamide) aqueous solution

Abstract The reactions between the OH, H and e aq − transients of water radiolysis and a linear poly( N -isopropylacrylamide) were identified by the spectral and kinetic properties of intermediates. The radical responsible for crosslink formation is the isopropyl-centered radical that forms mainly in OH radical attack on the polymer. Below pH 3 this radical undergoes reversible protonation with p K a ≈2.1. The radical decay is composed of fast and slow parts. The initial fast decay is attributed to intramolecular reactions of radicals on the same chain (loop formation), the following slow decay to competition between further intramolecular and intermolecular (H-type crosslinks) termination processes. The differences in the network formation during irradiation of aqueous monomer and polymer solutions are discussed.

Surface modification by electron irradiation for improved immunoassay

Abstract Polystyrene microtitration (ELISA) plates modified by electron beam irradiation were used for a monoclonal antibody based sandwich immunoassay for quantitation of circulating anodic antigen levels in Schistosoma -infected individuals. The plates irradiated with 15 kGy showed 2–4-fold lower detection level compared to untreated plates, and a 10-fold lower antibody coating concentration than usually used was still detectable. These results were reproducible and the modified surfaces were stable even after 2 years when kept at room temperature.

Analytical followup of the gamma initiated synthesis of a molecularly imprinted polymer

A molecularly imprinted polymer (MIP) for the template phenytoin has been prepared by gamma initiated copolymerization of methacrylamide and ethylene glycol dimethacrylate. The progress of polymerization was studied by measuring the monomer conversions and the template binding properties of the resulting polymers, respectively. The consumption rate of the two monomers showed different course. There was no difference observed in the polymerization rates of the MIP and the control polymer (NIP). The template binding properties of the MIP and the NIP changed considerably with the progress of the polymerization process and became similar to those of the thermally initiated polymers after full conversion.