Ferenc Tüdős

DSC application for characterization of urea/formaldehyde condensates

Curing process was investigated for a variety of urea/formaldehyde (UF) resin adhesives suitable for particle boards and/or plywoods using DSC in anisothermal mode. In spite of the very different origins of the adhesives (both commercial and laboratory made) several common features in their thermal behaviour are noticed. The maximum curing reaction rate was detected in the range of 80–85°C. Elimination of formaldehyde was observed at 105–150°C. At temperatures higher than 150°C thermal decomposition of methylene linkage takes place which affects the mechanical properties of the adhesives. According to our results a good compromise can be found between product quality and curing rate (production efficiency) on the one hand, and environmental protection (low formaldehyd emission) on the other.ZusammenfassungDer Aushärtungsprozeß verschiedener UF-Harze für Spanplatten und Sperrholz wurde mit Hilfe der anisothermen DSC untersucht. Trotz der äußerst unterschiedlichen Herkunft der kommerziellen und im Labor synthetisierten Harze konnten ähnliche Reaktionen auf die thermische Behandlung festgestellt werden. Die maximale Aushärtungsreaktion lag zwischen 80 und 85°C. Freisetzung von Formaldehyd wurde zwischen 105 und 150°C beobachtet. Über 150°C zerfallen Methylenbindungen, wodurch die mechanischen Eigenschaften der Harze beeinträchtigt werden. Es läßt sich ein guter Kompromiß finden zwischen Produktqualität und Aushärtezeit (Produktivität) auf der einen Seite und Umweltschutz (geringe Formaldehydemission) auf der anderen.

Spin trapping reactions with nitric oxides IV. Reactions with olefins

Abstract Electron Spin Resonance spectra of nitroxide radicals formed in the nitrogen oxide olefin systems (isobutylene, styrene and α-methylstyrene) have been investigated. The primary reaction step is the formation of alkyl radicals by the addition of nitrogen dioxide to the methylene carbon of olefins. The nitric oxide scavenges two alkyl radicals. In styrene and α-methylstyrene nitroxide diastereomers with different rates of formation and termination have been observed.

Spin trapping reactions with nitric oxides II. Acylalkyl nitroxides

Abstract Radical trapping by nitric oxide in the presence of oxygen has been studied by ESR spectroscopy. The oxygen was found to react much faster with alkyl radicals than nitric oxide, it suppresses formation of dialkyl nitroxides and initiates creation of acyl nitroxides through reactions between peroxy radicals and nitric oxide.

Physico-chemical studies of polymeric carriers: 2. Molecular mass determination of poly(N-vinylpyrrolidone-co-maleic acid) fractions

SummaryCritical interpretation of the various conceptions concerning the problems in characterization of linear polyelectrolyte type polymers containing maleic acid as a comonomer is given. Proper conditions to avoid the fundamental experimental difficulties are proposed. Our conception is supported by molecular light scattering measurements of hydrolysed, fractionated poly (N-vinylpyrrolidone-co-maleic anhydride) samples. It was found that the problems were eliminated by the reduction of the degree of dissociation of carboxyl groups to a minimum value.

Spin trapping reactions with nitric oxides. III. Alkoxyalkylnitroxides and new nitrogen centered radicals

Abstract Subsequent trapping of photochemically generated alkyl and alkoxy radicals by nitric oxide yields alkoxyalkylnitroxide radicals. New types of nitrogen centered radicals have been detected and tentatively explained by reactions of nitrogen oxides N 2 O, NO, NO 2 , N 2 O 3 , N 2 O 4 with alkyl and peroxide radicals.

Spin trapping reactions with nitric oxides. V. Reactions with unsaturated macromolecular chains - a new spin labeling method

Abstract Formation of macromolecular nitroxides (i.e., spin labeled polymer chains) has been detected by Electron Spin Resonance spectroscopy in the reaction of nitric oxide gas with several unsaturated polymers/synthetic polyisoprene, polybutadiene , poly(isoprene-co-isobutylene), poly(butadiene-co-styrene)/dissolved in aromatic hydrocarbons. Spectroscopic evidences of gel formation, precipitation, and of solvent effect have been given.

Tracking of alkyd-resin condensation by GPC

SummaryCondensation process of pentaerythritol / phtalic-anhydride/ benzoic acid/synthetic fatty acid mixture was carried out according to two different schedules; the first was carried out in one step (I) at 210 °C, the other in two steps (II) feeding pentaerythritol into the mixture of the other components already preheated to 180 °C and then elevating the temperature to 210 °C. GPC chromatograms were taken during the process. It has been established that fractions with higher molecular mass are formed from fractions with lower molecular mass. It could be proved with a three-detector method that they become chemically homogeneous starting from molecular masses of about 10 000.

Reexamination of the Stereospecific Copolymerization of Butadiene with Isoprene

Summary14 systems of the stereospecific anionic butadiene/isoprene copolymerization were reinvestigated using the Kelen-Tüdős (KT) treatment of data. It was found that the classical binary copolymerization model holds for these systems, too; the level of error is relatively moderate and the reproducibility is better than in case of cationic copolymerizations.