Rheological behavior of suspensions of modified and unmodified cellulose nanocrystals in dimethyl sulfoxide

The rheological behavior of cellulose nanocrystal (CNC) and modified CNC (mCNC) suspensions in dimethyl sulfoxide (DMSO) was investigated. The efficiency of the surface modification of CNCs by grafting an organic acid chloride to produce hydrophobic CNCs has been verified by X-ray photoelectron spectroscopy (XPS). The thermal degradation temperature of the mCNCs was found to be 165 versus 275 °C for CNCs. The CNC suspensions in DMSO at 70 °C underwent gelation at very low concentration (1 wt%) after 1 day. The network formation was temperature sensitive and did not occur at room temperature. For gels containing 3 wt% CNCs, the complex viscosity at 70 °C increased by almost four decades after 1 day. For the mCNCs in DMSO, a weak gel was formed from the first day and temperature did not affect the gelation. Finally, the effect of adding 10 wt% of polylactide (PLA) to the solvent on the rheological properties of CNC and mCNC suspensions was investigated. The properties of suspensions containing 1.9 wt% CNCs and mCNCs increased during the first and second days, and PLA did not prevent gel formation. However, the reduced viscosity and storage modulus of the CNC and mCNC gels with PLA were lower than those of samples without PLA.     

Über N1- und N2-substituierte 2-Amino-5,6-dihydro-4(1H)-pyrimidinone

The reactions of the monosubstituted guanidines2 b-h with methyl acrylate in dimethylformamide or ethanol as solvent preferentially afford 1-substituted 2-amino-5,6-dihydro-4(1H)-pyrimidinones6 b-h. The structures of 1-hexyl- and 1-benzyl-4-pyrimidinones6 c, e and of the picrate of 1-phenylpyrimidinone6 g were proved by comparison with authentic samples, which were prepared from N-substituted ethyl 3-amino-propionates14 c, e andg and cyanamide. Accordingly,6 g is not identical with authentic 2-phenylaminopyrimidinone7 g (prepared from 2-methylthio-4-pyrimidinone10 and 2-thioxo-4-pyrimidinone12 respectively, compare¹⁰).N,N-Disubstituted guanidines2 i-m react with methyl acrylate in dimethylformamide as solvent to afford N²,N²-disubstituted 2-amino-5,6-dihydro-4-(1H)-pyrimidinones7 i-m. Action of morpholine-4-carboxamidine (21) on methyl acrylate in ethanol yields 2-morpholinopyrimidinone71 as byproduct and 3-ethoxy-N-[morpholino(amino)methylene]propionamide (91) as mainproduct.

Herrn Prof. Dr.Robert Ott mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Phenol‐urea‐formaldehyde cocondensed resol resins: Their synthesis,curing kinetics,and network properties

Several phenol‐urea‐formaldehyde (PUF) cocondensed resol resins were synthesized by different procedures. The curing kinetics and network properties of these PUF resins were examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). A kinetic study indicated that the activation energy values of PUF resins are generally higher than those of phenol‐formaldehyde (PF) resins during curing processes, but the curing rates of PUF resins are faster than those of PF resins. The pH values of PUF systems have a significant influence on the rate constants, although they affect the activation energy very slightly. Moreover, the dependence of activation energy on the conversion showed that there are more individual reactions with different activation energies occurring during the curing processes in PUF resins than in PF resins. The decomposition of methylene ether bridges to form methylene bridges probably occurs at high temperature in PUF resins. DMTA data indicated that the network rigidity of PUF resins is slightly lower than that of PF resin. The gel point and T_{tan δ2} transition measured by DMTA were consistent with the kinetic results obtained from the DSC data, but they were also related to the physical and mechanical properties of the network, especially with regard to the T_{tan δ2} transition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1929–1938, 2003     

Zur Reaktionsweise von Enaminen mit Cyclopropenonen IV. Einsatz von Ketenacetalen

A new interpretation – based on a reevaluation of the spectroscopic properties of products 16 to 27 – is proposed for the reaction of diphenyl-cyclopropen-one 14 and -thione 15 with ketene-A, N-diacetals 8 to 13 (A ? R₂N, RO and RS) originally reported by Sauer & Krapf. It is concluded that the previous structural assignments (see the a-structures), made on the assumption of a prevailing “C,C-insertion” reaction, must be rcplaced as follows: (1) All the “secondary adducts” are, in fact, derivatives (amides and lactams) of 2,3-diphenyl-penta-2, 4-dienoic acid and thioacid (structures 16b to 24b ); (2) the “isomerization products”, differ from the latter only in the configuration of the α,β-double bond (structures 25b and 26b ); (3) the common “hydrolysisproduct” is α,β-diphenyl-γ-methyl-γ-hydroxy-Δ^α-butenolide ( 27b ), The above cyclopropenone-ketcneacetal reactions represent, therefore, cases of “C, N-insertion”. This is rationalized with a reaction scheme, in which the “acylide” structure of the “primary adducts” plays a role.     

Synthesis of novel 1-methyl-1H-pyridazino[3,4-b]indoles

New synthetic pathways have been elaborated to 1-methyl-1H-pyridazino[3,4-b]indoles starting from halopyridazin-3(2H)-ones. Suzuki cross-coupling reaction of chloro, iodo, dichloro, and dibromo substituted pyridazin-3(2H)-ones with 2-pivaloylaminophenylboronic acid followed by hydrolysis of the amide and subsequent ring closure via condensation gave fused indoles. Some of these compounds showed biological activity as antitrypanosomal agents.     

Kinetics of adsorption of poly(vinylimidazole) (PVI) onto copper surfaces investigated by quartz crystal microbalance studies

Organic corrosion inhibitors offer a huge potential of lowering product cost and manufacturing complexity in printed circuit board industry. Up to now, there is no reliable and fast method available to classify materials according to their ability to prevent copper from corrosion based on kinetic data of adsorption. We investigated the potential of the recently presented fast impedance-scanning quartz microbalance (FIS-QCM) to perform such studies. We selected poly(vinylimidazole) (PVI) that is known for its excellent ability to prevent copper from corrosion. However, kinetics and free energy of adsorption of PVI were never investigated. This paper presents the results of these studies. Reliable kinetic data were obtained, and the measurements show also the excellent frequency stability of this device that enables the detection of very small changes in resonance behaviour of the sensor quartz crystal, even below 1?Hz.