Zs. László-Hedvig

Study of the thermal oxidation of polyolefins: Part XII—Thermal oxidation of isotactic and atactic polypropylene in the condensed phase and in solution

Abstract A study has been made of the oxidation of APP and IPP in the condensed phase and in 1,2,4-trichlorobenzene solution. The differences in the oxidation rates and hydroperoxide concentrations between the amorphous APP melt and the semi-crystalline IPP were attributed to the dissimilarities in the supermolecular structure, since those differences did not appear in solution. It was found that in the accelerating stage of the process, the oxidation in solution follows the kinetic rules of degenerate radical chain reactions under steady-state conditions, while in the condensed phase the condition of stationarity is not fulfilled. Solutions of IPP and APP behave similarly in many respects; significant differences were found, however, in the induction period of the process, as well as in the conversion dependence of the carboxyl group concentration and of the number of chain scissions.

DSC characterisation of urea/formaldehyde condensates, II. Experiences with high pressure DSC cell

At anisothermic thermograms registered when curing the urea/formaldehyde (UF) resins in high pressure DSC cell the endothermic effects, such as evaporation of water and elimination of formaldehyde shift to temperatures higher by about 40°C in comparison to the thermograms received using the cell without pressure. The temperature for the exotherma of curing remains unchanged. Due to the shift of decomposition temperature the elimination of formaldehyde takes place at more agreeable conditions: as the resin is more rigid the risk of additional endothermic effect connected with bubble blowing is diminished. The shift of water elimination temperature however disturbs at clear recognition of the base line of the endotherma. Preliminary treating of samples with inert gas before the measurements helps to improve the measurement conditions.ZusammenfassungDas thermische Verhalten beim Aushärten von UF-Harzen wurde unter hohem Druck in DSC-Meßzellen verfolgt. Es zeigte sich, daß die endothermen Effekte (Verdampfen von Wasser, Abgabe von Formaldehyd) unter Druck bei um 40°C höheren Temperature erfolgen. Dagegen bleibt der Temperaturbereich der exothermen Reaktionen unverändert. Aufgrund dieser Verschiebung erfolgt die Abgabe von Formaldehyd unter günstigeren Bedingungen als ohne Druck: das Harz ist in diesem Zustand fester und das Risiko zusätzlicher endothermer Effekte (z. B. Platzen von Dampfblasen) ist geringer. Dagegen wirkt sich die höhere Temperaturs der Wasserabspaltung störend aus für das eindeutige Erkennen der Basislinie. Eine vorangehende Behandlung mit Inertgasen verbessert die Versuchsbedingungen.

Crosslinking behaviour of diolmodified epoxies: 2. DSC measurements

SummaryDiglycidyl ether of bisphenol A (BADGE) reacts with aliphatic alcohols to form different products, depending on the type of accelerator. Using isothermal and dynamic DSC, magnesium perchlorate proved to be a more selective accelerator in comparison with N,N-Dimethylbenzylamine (DMBA). In the presence of DMBA, Arrhenius plots of log tc (tc-cure times) versus inverse cure temperature show a changing reaction order over a wide range of temperatures.

Effect of an inert solvent on the copolymerization of styrene/diethylmaleate

We studied the effect of an inert solvent (benzene) on the overall rate of copolymerization in the system styrene/diethylmaleate (ST/DEM), initiated with azo-bis-iso-butyro-nitrile (AIBN) at 50°C. The experimental results can be interpreted on the hot radical theory.

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.

Kinetics of radical polymerization. XLVI: Kinetic investigation of the polymerization of styrene in solution by gel permeation chromatography

Abstract Molecular mass distribution was investigated for the polymerization of styrene initiated by AIBN at 50° in the presence of various solvents. Two types of solvents were chosen; in one, there is no chain transfer to solvent (Bz, DMF) whereas in CCl 4 the chain transfer should be considered. The molecular mass distributions of the systems were determined by GPC and they were also calculated from kinetic data in terms of the hot radical theory. The agreement of MMD curves obtained by both methods (GPC and kinetic) are within experimental error, sufficient.