Klaus Dirnberger

Pseudo-Jahn–Teller and TICT-models: a photophysical comparison of meta- and para-DMABN derivatives

Spectra and photophysical properties of a series of meta- and para-substituted aniline derivatives are compared. The radiative rate constant kf decreases strongly whenever the anomalous charge transfer fluorescence band is observed. In another case, a strong increase of kf is observed, independent of a second fluorescence band. These results are discussed within the pseudo-Jahn–Teller and the TICT model.

Ring‐Opening Metathesis Polymerization Based Pore‐Size‐Selective Functionalization of Glycidyl Methacrylate Based Monolithic Media: Access to Size‐Stable Nanoparticles for Ligand‐Free Metal Catalysis

Monolithic polymeric supports have been prepared by electron-beam-triggered free-radical polymerization using a mixture of glycidyl methacrylate and trimethylolpropane triacrylate in 2-propanol, 1-dodecanol, and toluene. Under appropriate conditions, phase separation occurred, which resulted in the formation of a porous monolithic matrix that was characterized by large (convective) pores in the 30 μm range as well as pores of <600 nm. The epoxy groups in pores of >7 nm were hydrolyzed by using poly(styrenesulfonic acid) (Mw = 69,400 g mol(-1), PDI=2.4). The remaining epoxy groups inside pores of <7 nm were subjected to aminolysis with norborn-5-en-2-ylmethylamine (2) and provided covalently bound norborn-2-ene (NBE) groups inside these pores. These NBE groups were then treated with the first-generation Grubbs initiator [RuCl2 (PCy3 )2 (CHPh)]. These immobilized Ru-alkylidenes were further used for the surface modification of the small pores by a grafting approach. A series of monomers, that is, 7-oxanorborn-5-ene-2,3-dicarboxylic anhydride (3), norborn-5-ene-2,3-dicarboxylic anhydride (4), N,N-di-2-pyridyl-7-oxanorborn-5-ene-2-carboxylic amide (5), N,N-di-2-pyridylnorborn-5-ene-2-carboxamide (6), N-[2-(dimethylamino)ethyl]bicyclo[2.2.1]hept-5-ene-2-carboxamide (7), and dimethyl bicyclo[2.2.1]hept-5-en-2-ylphosphonate (8), were used for this purpose. Finally, monoliths functionalized with poly-5 graft polymers were used to permanently immobilize Pd(2+) and Pt(4+), respectively, inside the pores. After reduction, metal nanoparticles 2 nm in diameter were formed. The palladium-nanoparticle-loaded monoliths were used in both Heck- and Suzuki-type coupling reactions achieving turnover numbers of up to 167,000 and 63,000, respectively.

Gold Catalysis: AuCl-induced Polymerization of Styrene and n-Butylvinylether

Polymerization of styrene, 4-methoxystyrene, and n-butylvinylether was achieved using simple AuCl as catalyst and AgPF6 as cocatalyst. High molecular weights and low polydispersity indices were obtained. Evidence for a cationic mechanism was obtained by reactions with nucleophiles. The mechanistic study also indicates a living polymerization with the gold(i)–alkene complex as the resting species.

Modification of surface properties of polypropylene films by blending with poly(ethylene-b-ethylene oxide) and its application

The possibility of improving the interfacial adhesion between polypropylene (PP) and polyamide layers (PA) has been investigated by means of addition of commercially available amphiphilic poly(ethylene-b-ethylene oxide) (P(E-b-EO)) block copolymers. These block copolymers were added to the PP matrix polymer in a twin screw extruder as integral additive. The change in surface properties of PP films upon incorporating P(E-b-EO) was investigated in model studies of blends prepared by casting PP/P(E-b-EO) solutions in 1,2-dichlorobenzene onto glass and Teflon Petri dishes, by melt pressing of PP/P(E-b-EO) blends between Teflon foils and glass substrates, or by melt extrusion of PP/P(E-b-EO) mixtures. The surfaces of the blend films were analyzed by attenuated total reflection Fourier transform infrared spectroscopy and water contact angle measurements. It was shown that an enrichment of the block copolymer at the surface of the blend depends highly on the conditions of film preparation and is driven by reducing the interfacial energy between the blend and the contacting medium. Effects of shear rate and residence time during normal processing conditions were also revealed. Blown film experiments with PP/P(E-b-EO) blends and PA were carried out for evaluating the effect of the integral P(E-b-EO) additive on the interfacial adhesion.

Synthesis and properties of hydrophobically modified water-borne polymers for pigment stabilization

Abstract Some aspects of the molecular design of pigment stabilizers are discussed. The approach of employing copolymers with pigment-affine segments and matrix-affine segments will be particularly addressed. First experimental results obtained with amphiphilic block copolymers and amphiphilic graft copolymers with similar overall composition with regard to polar and relatively non-polar blocks of, e.g. polar backbone and relatively non-polar grafts will be presented. The comparison between the poly(acrylic acid)-polystyrene block copolymer and the graft copolymer with poly(acrylic acid) backbone and polystyrene grafts showed a similar stabilization of TiO 2 in water.

Stabilization of carbon black with ionic-hydrophobic polyelectrolytes

The mode of action and efficiency of amphipolar copolymers of different molecular architectures with copolymers consisting of ionic (acrylic acid) and hydrophobic (styrene) constitutional units and sequences (segments, blocks, grafts) as stabilizers of carbon black dispersion are discussed. The pigment-copolymer interactions were investigated by the ESA method as well as lumifuge and rheological measurements. The results indicate that there are distinctive differences in the stabilization behavior depending on the molecular architecture with better results being achieved for block and graft copolymers.

Synthesis of Polyolefin-g-Poly(ethylene oxide) by Reacting Maleic Anhydride Modified Polypropylene or Poly(propylene-co-ethylene) with Hydroxy-terminated Poly(ethylene Oxide) in the Melt

The synthesis of amphipolar graft copolymers by reactive extrusion of maleic anhydride modified polypropylene or poly(propylene-co-ethylene) and α, ω-dihydroxy-poly(ethylene oxide) or α-hydro-ω-oxymethyl-poly(oxyethylene) was studied. The graft copolymers were characterized by Fourier transform infrared spectroscopy. Residence time of 30 min at 160°C was established to be sufficient for graft copolymer formation by melt extrusion.

Determination of thermorheological phase diagram of poly(propylene)/poly(ethylene-b-ethylene oxide) blends

Abstract The phase diagram of the polypropylene (PP)/poly(ethylene-blockethylene oxide) (P(E-b-EO) blends exhibiting upper critical solution temperature (UCST) was experimentally established by using small amplitude oscillatory shear rheology, in which the binodal line was obtained by dynamic temperature ramps and the spinodal temperatures were quantitatively estimated on the basis of the theory developed by Ajji et al. The measurements were carried out in the linear viscoelastic regime in which the material functions are sensitive to phase separation.