Bohumil Bednář

Micellization of three-block copolymer poly[styrene-b-(ethene-co-butene)-b-styrene] in mixed solvents of tetrahydrofuran/ethanol

Abstract The behaviour of dilute solutions of a three-block copolymer poly[styrene-b-(ethene-co-butene)-b-styrene] in mixtures of tetrahydrofuran (THF)/ethanol was studied using viscometry, osmometry and light scattering. In solutions with a lower ethanol content the copolymer dissolved, but in solutions with a higher ethanol content it became associated, to form spherical micelles with cores composed of middle (aliphatic) blocks. Between the molecular and micellar solutions a region of the so-called anomalous micellization was described. Micelles in mixtures with a higher ethanol content were stabilized by means of fast electrons, isolated and characterized in THF solutions.

Preparation and properties of polypyromellitimides prepared from 1,n-bis(4-aminophenoxy)alkanes

Abstract Polyamic acids, polyimides and polyisoimides have been prepared from pyromellitic acid dianhydride and 1,n-bis(4-aminophenoxyalkanes). The synthesized polymers were characterized by physical and physico-chemical methods. The prepared polyimides and polyisoimides were found to be insoluble in common solvents and can only be dissolved in sulphuric acid. Compared with highly aromatic polyimides, their thermal stability is lower by 120–140°.

Light scattering and fluorescence studies of block copolymer micelles of polystyrene-block-poly(hydrogenated isoprene) in the selective solvent 1,4-dioxane-n-heptane

Abstract Diblock polystyrene- block -poly(hydrogenated isoprene) was fluorescence labelled by random covalent attachment of anthracene at the polystyrene block (the average number of anthracenes per copolymer chain was 0.88). Micellization of the labelled copolymer was studied in a broad composition range of the solvent mixture 1,4- dioxane heptane . Micelles with polystyrene cores are formed in heptane-rich solvents (0–30 vol% 1,4-dioxane). In mixtures with 30–50 vol% 1,4-dioxane, the sample dissolves molecularly in the form of individual copolymer coils and in dioxane-rich solvents (more than 50 vol% 1,4-dioxane), micelles with polystyrene shells are formed. Micellar solutions were characterized by static and quasielastic light scattering and by sedimentation velocity measurements. The mobility of pendant fluorophores and polymer segments in micellar cores and shells in selective solvents and in individual copolymer coils in good solvents was studied by time-resolved fluorescence-anisotropy measurements.

Behavior of Reversibly Associating Systems in Size Exclusion Chromatography. Interpretation of Experimental Data Based on Theoretical Model

Abstract The shape of the SEC chromatogram of a reversibly associating system in the SEC is a result of several competing processes: (a) SEC mechanism, (b) re-equilibration of the perturbed association equilibrium, and (c) the axial dispersion of individual components in the mobile phase. In some associating (micellizing) block copolymer systems in selective solvents, other secondary processes (e.g. temporary trapping of a polymer in pores of the stationary phase) may influence the chromatogram shape and complicate the analysis of experimental data. In this paper, general aspects of the interpretation of experimental data is discussed on the basis of theoretical models.

i.r. and 13C-CP-MAS-NMR spectra of pyromellitide and of its precursor based on 4,4′-diaminodiphenylmethane

i.r. and 13C-CP-MAS-NMR spectra were recorded for polyamidocarboxylic acid, polyimide and polyisoimide based on pyromellitic acid dianhydride (PMDA) and 4,4′-diaminodiphenylmethane (MDA), and of polyimide based on PMDA and 4,4′-diaminodiphenylether. The 13C-NMR spectra were interpreted and bands in solid state 13C-NMR spectra suitable for characterizing the structure of the PMDA/MDA polyimide were found. By measurement of i.r. spectra, the applicability of i.r. spectroscopy for monitoring the imidization of polyamidocarboxylic acid in PMDA/MDA was verified. Bands indicating the occurrence of precursor side reactions have not been observed in any of the studied spectra.

Chromatographic behaviour of reversibly associating macromolecules. Part 1.—Theoretical model

Block copolymers in selective precipitants form multimolecular micelles via closed association, which is characterized by an equilibrium between a unimer (molecularly dissolved copolymer) and micelles. A theoretical model is developed which accounts for: (i) relatively fast equilibration of the unimer between mobile and stationary phases, (ii) continuous perturbation and re-establishment of unimer ⇌ micelles equilibrium, and (iii) axial dispersion in the mobile phase during the passage of a solute through a column. This model describes quantitatively the behaviour of micellizing systems in size-exclusion chromatography. Chromatograms have been calculated for a wide range of association numbers and rates of association and dissociation. The results are compared with qualitative predictions of Colls theory and Gilberts theory of associating systems.

Size exclusion chromatography of associating systems. I: The theoretical model

Abstract Block copolymers in dilute solutions in selective solvents form micelles via closed association which is characterized by equilibrium between unimer and n-mer. A simple theoretical model has been proposed describing the behavior of such a system in the size exclusion chromatography (SEC). Chromatograms have been calculated varying association number and relative rates of association and dissociation. The results are compared with those of Colls theory for SEC of surfactants and Gilberts theory of associating systems.