Karel Jeřábek

Mechanism of hypercrosslinking of chloromethylated styrene–divinylbenzene copolymers

Abstract Hypercrosslinked polymers are remarkable materials exhibiting extremely high apparent surface area and exceptional sorption properties. Their special morphology is a result of the fixation of expanded position of polymer chains in a good (swelling) solvent by methylene crosslinking bridges created by the Friedel–Crafts reaction of chloromethyl groups. We have performed a detailed investigation of the formation of the crosslinking bridges in the reaction starting from the swollen, already chloromethylated polymer. Conversion of the chloromethyl groups was determined from the residual chlorine content. The total chlorine content determined after burning a sample of the polymer in oxygen and the content of reactive, accessible chlorine determined by reaction of the chloromethyl groups with pyridine were differentiated. Changes in the content of both types of chlorine were monitored for varying reaction conditions (time, catalyst content, etc.) and were correlated with the development of the microporous texture resulting from the hypercrosslinking of the swollen polymer matrix.

Catalysis and polymer networks: the role of morphology and molecular accessibility

Catalysis and polymer networks — the role of morphology and molecular accessibility B. Corain a, M. Zecca a, K. Jeřabek b,∗ a Universita’ di Padova, Dipartimento di Chimica Inorganica, Metallorganica e Analitica and Centro di Studio sulla Stabilita’ e Reattivita’ dei Composti di Coordinazione, C.N.R., via Marzolo 1, 35131 Padova, Italy b Institute of Chemical Processes Fundamentals, Academy of Sciences of the Czech Republic, Rozvojova 135, 165 02 Praha 6 Suchdol, Czech Republic

Solvent impregnated resin (SIR) containing dialkyl dithiophosphoric acid on Amberlite XAD-2: extraction of copper and comparison to the liquid-liquid extraction

Abstract The extraction of Cu(II) from chloride solutions at 0.19 M Cl − ionic strength by solvent impregnated resins (SIR) containing di-(2-ethylhexyl) dithiophosphoric acid (DEHTPA) on the Amberlite XAD-2 polymeric support has been studied. The distribution of DEHTPA between the aqueous phase and the resin phase was determined as a function of both pH and loading of DEHTPA ligand (HL) on the resin. The Cu(II) extraction are presented as plots of log distribution coefficient versus pH and DEHTPA concentration in the resin phase. Graphical and computer, analysis showed that the extraction of Cu(II) can be explained by the formation of metal complexes in the resin phase of CuCl 2 (HL) 8 and CuCIL(HL) 8 composition with values of equilibrium extraction constants K ′ = 9.19 max 9.41 and K ″ = 7.69 max 7.99, respectively.

Ring opening metathesis polymerisation of emulsion templated dicyclopentadiene giving open porous materials with excellent mechanical properties

Surfactant stabilized emulsions of dicyclopentadiene and 50%, 60%, 70% or 80% of water were cured using ring opening metathesis polymerisation. All formulations gave open porous architectures featuring excellent mechanical properties which change upon oxidation.

Metal palladium dispersed inside macroporous ion-exchange resins: the issue of the accessibility to gaseous reactants

Abstract Commercial macroporous ion-exchange resins (Lewatit SPC 118 and UCP 118) were used to support Pd metal by a two step ion-exchange and reduction procedure. The textural features of the resins were determined by Inverse Steric Exclusion Chromatography (ISEC) measurements. TEM characterization of the obtained Pd/resin composite showed the presence of uniformly sized Pd crystallites located at the macropore “surface”. Pulse chemisorption analysis gave evidence for the lack of accessibility of the crystallites when the resin composite is in the dry state. This suggests that the metal particles are in fact embedded in a gel-type resin layer at the “surface” of the macropores and therefore practically unaccessible to the molecules of a gaseous phase unless the support is in the swollen state.

Polybenzimidazole as a promising support for metal catalysis: morphology and molecular accessibility in the dry and swollen state

Polybenzimidazole (PBI) in beaded form (250-500 microm) has been characterized in the dry state by scanning electron microscopy (SEM), BET, and nitrogen porosimetry. In the swollen state, it has been characterized by inverse steric exclusion chromatography (ISEC) in tetrahydrofuran, toluene, and water, by ESR of TEMPONE (2,2,6,6-tetramethyl-4-oxo-1-oxypiperidine), and pulse field gradient spin echo (PGSE) NMR spectroscopy, toluene, in tetrahydrofuran, ethanol and water. The dry-state results are in good agreement with the ISEC results obtained in tetrahydrofuran, toluene, and water with regard to the 40-80 nm macroporosity. The swelling-dependent surface area and pore volume detected by ISEC in toluene and water reveal the amphiphilic nature of PBI.

Highly Chemoselective Hydrogenation of 2-Ethylanthraquinone to 2-Ethylanthrahydroquinone Catalyzed by Palladium Metal Dispersed inside Highly Lipophilic Functional Resins

Most hydrogen peroxide is currently produced by the selective hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ), followed by treatment with dioxygen; this produces hydrogen peroxide and regenerates 2-ethylanthraquinone. We have developed novel catalysts for this process that are based on palladium supported on very lipophilic functional resins and that are able to promote a chemoselectivity for EAHQ slightly but definitely superior to that provided by an industrial catalyst under identical conditions. This finding demonstrates the potential of variations of the lipophilic/hydrophilic character of the support as a tool for the improvement of the chemoselectivity of resin-based metal catalysts.

Post-crosslinked polymer adsorbents and their properties for separation of furfural from aqueous solutions

Abstract Polymer adsorbents have been prepared by post-polymerization crosslinking of the swollen chloromethylated gel-type and macroreticular copolymers of styrene and divinylbenzene. Their morphology has been studied in the dry state by nitrogen adsorption/desorption method and in the swollen state by inverse steric exclusion chromatography. Their sorption properties were tested for the separation of furfural from aqueous solutions. Obtained data were compared with properties of conventional commercial polymer adsorbents Amberlite XAD-2 and XAD-4. At low concentrations of the sorbate in the surrounding solution the highly microporous post-crosslinked materials are much more efficient adsorbents than the conventional commercial polymers. However, their sorption capacity is restricted by limited pore volume and at higher equilibrium concentrations the high surface area macroporous polymers like Amberlite XAD-4 can be more efficient adsorbents.

Characterisation of Solute Mobility in Hypercross-Linked Resins in Solvents of Different Polarity: Two Promising Supports for Catalysis

Two hypercross-linked resins stemming from a gel-type poly-chloromethylated styrene-divinylbenzene resin (GT) in beaded form are investigated with a combination of spectroscopic techniques (EPR and time-domain (TD)-NMR spectroscopy) to evaluate their use as supports for the development of operationally flexible heterogeneous metal catalysts, suitable to be employed in liquid and gas phase. The first resin (HGT) is the direct product of the hypercross-linking reaction, whereas the second one (HGS) is the sulphonated analogue of HGT obtained by exchanging approximately 3 wt % of the chloromethyl groups with sulphonic groups. HGT and HGS absorb both polar and apolar solvents in the permanent nanoporosity created by the hypercross-linking, and NMR data highlight that the pore size is not affected by the different properties of the investigated liquid media. The EPR analysis of the dry resins reveals that during the hypercross-linking process paramagnetic species are formed in the HGT beads, which persist in the sulphonated resin. The mobility of solutes inside the polymers framework was investigated with EPR spectroscopy upon soaking the resins with solutions of two spin probes (2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL)) in THF, toluene, n-heptane and water. The EPR spectra show that, depending on the solvent, the two resins can act as sorbents, able to trap the solutes in the polymer framework, or as simple supports that allow free diffusion of the solutes. Our results suggest that HGT and HGS are promising supporting materials for metal catalysts, provided one chooses carefully the solvent to be employed for the catalysed reaction as this choice strongly affects the mobility of the substrates and, thus their effective reactivity.

Relations between morphology and catalytic activity of ion exchanger catalysts for synthesis of bisphenol A

Swollen-state morphology of a series of ion exchanger catalysts was analyzed by inverse steric exclusion chromatography. Correlation of the obtained information with data on activities of the catalysts for synthesis of bisphenol A (BPA) served for quantitative assessment of usefulness of various fractions of polymer mass of the examined ion exchangers for bisphenol A synthesis.