J. Lukáš

Reactive polymers : XXV. Morphology of polymeric sorbents based on glycidyl methacrylate copolymers☆

Abstract Scanning electron microscopy was used to obtain basic data on the surface and internal morphology of macroporous copolymers based on glycidyl esters of methacrylic acid which are useful as chromatographic sorbents. The basic morphological units in beads consist of spherical microparticles (globules and nodules), hundredths to tenths of a micrometre in size. On the bead surface the globules are compactly arranged in the shell, owing to the surface tension in suspension copolymerization. The pores in the shell are an order of magnitude smaller than the macropores between the aggregates of globules inside the beads. With increasing content of the crosslinking agent in copolymers, the microparticles become finer and more individualized, which explains the increase in the specific surface area of the sorbents. In gas chromatography, the morphology of the sorbent preferentially determines the retention of non-polar compounds, while that of polar compounds is affected by the chemical composition of copolymers, that is, by the content of glycidyl epoxy groups in this instance.

Reactive polymers : XV. polar polymeric sorbents based on glydicyl methoacrylate copolymers

Abstract The basic chromatographic characteristics of a number of copolymers based on glycidyl esters of methacrylic acid have been determined. The individual samples are characterized by a broad range of specific surface areas (44–434 m 2 /g) and polarities, which have been evaluated by means of modified Rohrschneider constants. The retention times of adsorbates on these poymeric sorbents are very short, though the selectivity of separation remains intact, so that they can be used at working temperatures similar to those used in gas—liquid chromatography.

Reactive Polymers : XVI. Surface-modified polymeric sorbents based on glycidyl esters☆

Abstract Copolymers based on glycidyl methacrylate-co-ethylenedimethacrylate were modified by reaction with a number of amines, and by acid hydrolysis followed by cyanoethylation. The physical and chromatographic properties of the modified copolymers suggest that a single copolymer with reactive functional groups can yield a number of sorbents possessing various polarities and various sorption properties.

Modification of the Rohrschneider method for the classification of the polarity of polymeric sorbents based on methacrylic acid esters

Abstract In order to express the polarity of polymeric sorbents based on methacrylic acid esters, the Rohrschneider method has been modified by replacing squalane with a non-polar adsorbent, Carbopack B. Using ethanol sorption as an example, it was shown that the modified Rohrschneider constants may be correlated with the thermodynamic function ° Ha, describing the direct participation of specific adsorbatepolymeric sorbent interactions. Hence, by using the modified Rohrschneider constants it is possible to classify the polarity of these polymeric sorbents simply and with good accuracy.

Characterization of ion exchange membrane surfaces by means of X-ray photoelectron spectroscopy and SEM

Abstract By using X-ray photoelectron spectroscopy (XPS or ESCA), surfaces of two types of cationactive membranes based on the sulfonated copolymer of polystyrene and polyethylene were investigated. The first type of membrane was prepared by radiation grafting of polystyrene on polyethylene films followed by sulfonation; in the second type polystyrene was radiation-grafted to the polyethylene granulate, followed by kneading, film pressing, and sulfonation. Considerable differences were observed in the chemical composition of the surfaces of membranes of both types, which suggests also differences in their internal structure. The data regarding chemical structure explain also the different electrochemical and separation characteristics of both types of the membranes. SEM micrographs confirm the XPS results from the morphological point of view.

Reactive polymers : XXXI. Thermally treated polymeric sorbents based on glycidylmethacrylate copolymers

Abstract Heating of polymeric sorbents based on glycidylmethacrylate-ethylenedimethacrylate copolymers to 250–280 °C for short periods in an inert nitrogen atmosphere leads to pronounced morphological changes. The chromatographic properties of sorbents thus treated are mainly characterized by a considerable shortening of the retention times of sorbates. This makes possible rapid chromatographic analyses of mixtures at low working temperatures (as much as 60 °C lower than with Porapak T), which is advantageous for the separation of thermally less stable compounds. The selectivity of separation of polar compounds is also higher for thermally treated copolymers.

Reactive polymers: XL. Study of the internal structure of thermally treated polymeric sorbents based on glycidyl methacrylate copolymers

Abstract A decrease in the specific pore volume and specific surface area and an overall narrowing of the pore distribution are the main changes in the internal structure of thermally treated copolymers based on glycidyl methacrylate-ethylene dimethacrylate. They are also colsely connected with changes in the chromatographic properties of polymeric sorbents thus treated. The decrease in the pore volume may be directly correlated with the decrease in the retention volumes.

Reactive polymers : XLI. Effect of the content and distribution on polar groups on the polarity of glycidylmethacrylate polymeric sorbents

Abstract Photeelectron spectroscopy has revealed that the distribution of polar groups (carboxylic and epoxy groups) in macroporous copolymers based on glycidylmethacrylate (GMA)—ethylene dimethacrylate (EDMA) is not uniform, but that their concentration increases starting from the surface towards the centre of the globules. Heat treatment of these copolymers gives rise of conformational changes, which in turn cause an increase in the concentration of polar groups on the surface of the globules, and thus also a rise in polarity. Differences between the modified Rohrschneider constants on the copolymers GMA—EDMA and methyl methacrylate (MMA)—EDMA were used in order to evaluate the participation of epoxy groups in the overall polarity of glycidylmethacrylate polymeric sorbents.