László Garamszegi

Synthesis of thiol end-functional polystyrene via atom transfer radical polymerization

Polymers obtained by Atom Transfer Radical Polymerization (ATRP) possess an ω-halogen end-group that may be converted to other functional groups by appropriate chemical transformations. Here we report a versatile new method for end-functionalizing polymers with a thiol. The bromine end-group of the polystyrene obtained from ATRP is converted into an isothiouronium salt by reaction with thiourea. Subsequent treatment of this salt with a base permits the cleavage to a thiol. This method allows the preparation of thiol functional polystyrene of narrow polydispersity with a high degree of functionalization and control of the molecular weight.

Durability of hybrid PECVD-based coatings on semicrystalline polymers

The present work analyses silicon oxide coated polyester films, with attention paid to the effect of substrate process additives on the coating defect population, and on the coated film mechanical properties. The defect population is characterized by means of reactive ion etching, and the mechanical properties are determined from the analysis of uniaxial fragmentation tests. The coating crack onset strain is decreased by the presence of substrate additives, due to a broadening of the Weibull defect distribution. Moreover, finite element analysis of stress concentrations resulting from additive-induced roughness shows that local stress concentrations are negligible. It is the critical defects, such as microcracks that are the most detrimental to the coating effective cohesive properties.

Characterization of Hyperbranched Aliphatic Polyesters and their Trimethylsilylated Derivatives by GPC-Viscometry

Abstract Gel permeation chromatography (GPC) viscometry with universal calibration (UC) has been assessed as a means of characterizing the absolute molecular weight distribution of hydroxyl terminated hyperbranched aliphatic polyesters (HBPs) of aliphatic compounds. To generate a valid UC curve, it is necessary to work under conditions of strict size‐exclusion separation. This requirement was met when both dimethyl formamide (DMF) and tetrahydrofuran (THF) were used as eluants. All the HBPs were highly soluble in DMF at room temperature, but its use may necessitate special columns. Dissolution of the HBPs in THF, on the other hand, which is compatible with a variety of stationary phases, was relatively difficult, requiring prolonged heating above 50°C. As an alternative to direct characterization, the HBP hydroxyl end‐groups were end‐capped with trimethylsilane prior to the GPC measurements. Near quantitative replacement of the hydroxyl groups was achieved and the modified HBPs remained stable for several weeks under dry nitrogen. This permitted straightforward GPC analysis in THF at room temperature, giving results consistent with those obtained for the unmodified HBPs.

Silylation and sulfonation of structured supported catalysts active in the decoloration of azo-dyes under visible light

Structured silica woven fabrics have been derivatized with functional groups able to anchor by exchange of Fe3+-ions and TiO2 showing a stable performance during the visible light induced decoloration of the Orange II azo-dye. The kinetics and efficiency of the decoloration mediated by the catalytic loaded silica fabrics with Fe3+-ions were seen to be much higher than found with homogeneous Fenton reagents (Fe3+/H2O2) with the equivalent Fe3+ content. The same was observed for derivatized membranes where TiO2 has been anchored as the active catalyst surface species. In the case of the silica Fe3+-ions loaded fabrics, the decoloration was studied as a function of the amount of H2O2 oxidant added in solution, the intensity of the applied visible light and the concentration of the initial Orange II. In the case of the silica-TiO2 fabrics the decoloration kinetics was observed to be a function of the O2 present in solution. In the case of the derivatized Fe3+ and TiO2 loaded silica fabrics, the decoloration process presented three common features: (a) the decoloration process was observed only in the presence of light pointing to a photo-induced process in both cases, (b) the decoloration was also observed to be truly catalytical following repetitive cycles for Orange II, and finally (c) the decoloration processes were limited by the mass transfer kinetics taking place at the surface of both derivatized fabric catalyst and proceeded with about the same kinetics in both cases. The numerical values for the diffusion distance of the radicals species OHradical dot and HO2radical dot as well as the decrease in the concentration of radicals away from the silica fabric during the photodegradation of Orange II is estimated by the Smoluchowski diffusion equation.

Templating porosity in polymethylsilsesquioxane coatings using trimethylsilylated hyperbranched polymers

A series of trimethylsilyl end-functionalized aliphatic hyperbranched polymers has been used to template porosity in polymethylsilsesquioxane films prepared by heat treatment of a spin cast methylsilsesquioxane precursor. By varying the extent of the end-functionalization, closed pore foams with controlled pore sizes and pore contents of up to 40 vol% were obtained by chemically-induced phase separation and thermal degradation of the hyperbranched polymers during the heat treatment.

Fluorescent labeling of a narrow polydispersity high molecular weight polystyrene

Narrow polydispersity polystyrene with a molecular weight of 1.03 x 10 6 has been functionalized with anthracene groups using the metallocene technique. Side reactions such as chain coupling and bond scission can be limited by working in THF at -75 °C. Gel permeation chromatography combined with on-line viscometric, refractive index and fluorescence detection allows us to verify that degradation did not exceed 1 bond scission/ 180000 monomer units. The degree of grafting increases with the reaction time but remains modest (< 5% after 7 h) at low temperature.

Grafted Poly(acrylic acid) Brushes for Cell-Surface Interactions

Poly(acrylic acid) (PAA) was grafted onto RF plasma treated PET films and onto SiO 2 covered glass surfaces. PET films with various amounts of grafted PAA (0.4, 5, 11 and 19 μm/cm 2 ) were immersed into a solution of collagen to allow for polyionic complex formation as a method for protein immobilization. It was found that the amount of complexed collagen was close to proportional to the amount of PAA. A closer investigation of the optical density of the PAA brushes close to the glass surface wa was performed using Reflectometric Inteference Spectroscopy. The supression of possibilities of extension and collaps of the brushes upon variation in pH is suggested to be caused by polyionic crosslinking between protonated collagen and deprotonated PAA. Such PAA-collagen surfaces with PAA concentrations lower that 10 μm/cm 2 were shown to be suitable substrates for growth of human bladder smooth muscle cells.