On the Hydrolytic Stability of Organic Ligands in Al-, Ti- and Zr-Alkoxide Complexes

The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated -diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and -ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and ¹³ C NMR spectroscopy and were found to be L:M 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H₂O : OR) = 0.5–2.0 decreases with increasing H$$₂O:complex ratio. Furthermore, the ligand stability depends on the type of metal in the complexes and decreases in the order Al- > Zr- > Ti-butoxide complexes at h=1. The ACAC ligand likewise shows in the Al-, Ti- and Zr-butoxide complexes a high hydrolytic stability (95–100%) at h=1 within 7 days. The Ti- and Zr-butoxide complexes with -ketoesters as ligand show at h=1> a release to a different extent e.g., up to 60% in the case of the MEAA-ligand in the Ti-butoxide complex after 2 days. In general, the hydrolytic stability of the ligands in the Ti-butoxide complexes (L:M = 1, h=1) decreases in the order ACAC > APD > AAA > EAA MEAA. The hydrolysis/condensation reaction of complexes having a weak ligand stability leads to larger particle sizes in the sols than those with stable ACAC ligands. The results contribute to a more controlled synthesis of sols and of new inorganic-organic hybrid polymers via the sol-gel process.     

Synthesis and MALDI-TOF-MS of PS-PMA and PMA-PS block copolymers

The synthesis of well-defined block copolymers from styrene and methyl acrylate via ATRP is discussed in this contribution. Kinetic studies on these block copolymerizations as well as characterization studies were performed to investigate the monomer composition in the respective PS and PMA blocks. MALDI-TOF-MS was performed to clarify the exact number of repeating units of each block and the total number of units in the block copolymer. Block copolymers up to 22 kDa could be analyzed by MALDI-TOF-MS, whereby polymers with PMA as first block showed a large second distribution corresponding to PMA homopolymers. However, SEC demonstrated that only a small amount of homopolymer was present indicating that care needs to be taken with interpreting MALDI-TOF-MS data, which is a qualitative rather than a quantitative technique.     

Determination of total attenuation cross section of carbon using secondary excitors in the energy range 4.5–60 keV

Experimental total attenuation coefficients of carbon in the photon energy range 4.5–60 keV have been measured. The total attenuation cross section of C rapidly decreased with energy in the range of 4.5–10 keV. The measured values are in agreement with the theoretical values.     

DX-center energy calculation with quantitative mobility spectrum analysis in n-AlGaAs/GaAs structures with low Al content

Experimental Hall data that were carried out as a function of temperature (60–350 K) and magnetic field (0–1.4 T) were presented for Si-doped low Al content (x=0.14) n–Al_xGa_1−xAs/GaAs heterostructures that were grown by molecular beam epitaxy (MBE). A 2-dimensional electron gas (2DEG) conduction channel and a bulk conduction channel were founded after implementing quantitative mobility spectrum analysis (QMSA) on the magnetic field dependent Hall data. An important decrease in 2DEG carrier density was observed with increasing temperature. The relationship between the bulk carriers and 2DEG carriers was investigated with 1D self consistent Schrödinger–Poisson simulations. The decrement in the 2DEG carrier density was related to the DX-center carrier trapping. With the simulation data that are not included in the effects of DX-centers, 17 meV of effective barrier height between AlGaAs/GaAs layers was found for high temperatures (T>300 K). With the QMSA extracted values that are influenced by DX-centers, 166 meV of the DX-center activation energy value were founded at the same temperatures.     

Synthesis and Characterization of Conducting Copolymers of Thiophene Derivatives

Electrochemical copolymerizations of N¹,N²-bis(thiophen-3-ylmethylene)benzene-1,2-diamine (TMBD), 4-methyl-N¹,N²-bis (thiophen-3-ylmethylene)benzene-1,2-diamine (MTMBD) and 4-nitro-N¹,N²-bis(thiophen-3-ylmethylene)benzene-1,2-diamine (NTMBD) with 3,4-ethylenedioxy thiophene (EDOT) were carried out in CH₃CN/LiClO₄ (0.1 M) solvent–electrolyte couple via potentiodynamic electrolysis. The resulting copolymers were characterized by cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The conductivity measurements of copolymers and PEDOT were carried out by the four-probe technique.     

Synthesis,electrochemical, and antibacterial activity of some novel N<Subscript>4</Subscript>O<Subscript>2</Subscript> ligand derivativies

A novel ligand has been synthesized by the condensation of 1,3-diaminoprophane (HL) wıth isonitroso-p-chloroacetophenone. The complexes of cobalt(II), nicel(II), cupper(II) and zinc(II) with HL were prepared. All compounds were characterized by spectroscopic techniques and its antibacterial activities were determined by the disc diffusion method used against to those gram-positive and-negative bacteria. All compounds were investigated by cyclic voltammetry at 25°C. The voltammograms were recorded with a potential scan of 100 mV s⁻¹. The text was submitted by the authors in English.     

Preparation of conductive polybenzoxazines by oxidative polymerization

Soluble and thermally curable conducting high molecular weight polybenzoxazine precursors were prepared by oxidative polymerization 3‐phenyl‐3,4‐dihydro‐2H‐benzo[e][1,3] oxazine (P‐a) alone and in the presence of thiophene (Th) with ceric ammonium nitrate in acetonitrile. The structure of the precursors was confirmed by FTIR, ¹H NMR, and DSC measurements, indicating the presence of a cyclic benzoxazine structure, together with small but varying amount of a ring opened phenolic structure. The resulting polymers exhibit conductivities around 10^?2 S cm^?1 and undergo thermal curing at various temperatures. Attempts to copolymerize P‐a with another electroactive monomer, pyrrole (Py), by a similar redox process were unsuccessful, which was attributed to the unfavourable oxidation potential of Py. The cured products exhibited high thermal stability but lower conductivity, than those of the precursors. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 999–1006, 2007     

Chemoenzymatic polymerization of hydrazone functionalized phenol

Hydrazone substituted oligophenol was synthesized via enzymatic oxidative polymerization of (E)-2-((2-phenylhydrazono)methyl)phenol. Enzymatic polymerization catalyzed by Horseradish peroxidase (HRP) enzyme and H₂O₂ oxidizer yielded oligophenol with hydrazone functionality on the side-chain. Effects of various factors including solvent system, reaction pH and temperature on the polymerization were studied. Optimum polymerization conditions with the highest yield (84%) and molecular weight (M_n = 8 × 10³, DP ≈ 37, PDI = 1.11) was achieved using MeOH/pH 6.0 buffer (1: 1 vol %) at 25°C in 24 h under air. Synthesized oligomer was characterized by ¹H and ¹³C NMR, FTIR, UV–Vis spectroscopy, GPC, cyclic voltammetry and thermogravimetric analyses. The polymerization involved hydrogen elimination from the monomer, and terminal units of the oligomer structure consisted of phenolic hydroxyl (–OH) end groups. The oligomer backbone possessed phenylene and oxyphenylene repeat units. The resulting oligomer was completely soluble in common organic solvents. The oligomer was thermally robust and exhibited 5% mass loss at 375°C and 50% mass loss at 440°C.