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The oxidability of low density polyethylene stabilized with several antioxidants was investigated by oxygen uptake. The radiosterilization doses (5, 10 and 20 kGy) were applied for characterization of antioxidant activity of calix[4]arene, Santonox R, Ionox 220, Irganox 1076, Irganox 1081, tri-t-butylphenol and elementary selenium. Their contribution to the radiostability of LDPE is discussed in comparison with control sample. The order of increasing the oxidation induction time was established for depicting the evolution of oxidative degradation in stabilized polyethylene. Keywords: low density polyethylene, stabilization, radiosterilization

Controlled/living radical polymerization (CLRP) is a field that has been expanding continuously during the last 15 years, as the method allows for the synthesis of well-defined polymers under mild conditions. Many CLRP systems have been developed, all of them relying on an equilibrium between a minute concentration of radicals and a large amount of dormant species. Among them, atom transfer radical polymerization (ATRP) has evolved as one of the most versatile techniques for the production of well-defined materials. This paper briefly reviews the fundamentals of ATRP, while a future paper will be discussing the applications. Keywords: controlled/living radical polymerization, atom transfer radical polymerization, transition metal catalysis

By replacing polystyrene hard blocks with poly-á-methylstyrene ones, the service temperature of thermoplastic elastomers can be considerably enhanced, because the glass transition temperature of the latter is about 170°C. The thermodynamics of polymerization of á-methylstyrene is well-known (ÄH and ÄS are -35.1 kJ.mol-1 and -104 J.mol-1 K-1, respectively) so that the “ceiling” (equilibrium) concentration of AMS at various temperatures may be calculated. The living polymer molecules can attain a state of dynamic chemical equilibrium with the monomer molecules. If the temperature is subsequently raised above the ceiling temperature, the Gibbs free energy again favors the monomer. The higher the á-methylstyrene concentration and the lower the polymerization temperature, the higher is the achievable monomer conversion, but never hundred percent. Using n-butyllithium initiator alone, at low reaction temperature, when the maximum achievable theoretical conversion is the highest, the polymerization of á-methylstyrene occurs very slowly in hydrocarbon reaction media. Sasol Germany GmbH developed a high performance living anionic polymerization active center modifier, the purity of which is in agreement with those imposed by the highly sever conditions imposed by these reactions: 2-(2-ethoxyethoxy)-2-methylpropane. The purpose of this paper is to establish a regression model in order to determine the optimal conditions (temperature, reaction time, active center modifier concentration) of á-methylstyrene anionic polymerization in toluene (melting point – 93°C), initiated by n-butyllithium – 2-(2-ethoxyethoxy)-2-methylpropane system, using the factorial design of experiments. Keywords: polystyrene, poly-á-methylstyrene, n-butyllithium

The samples of type EPDM (ethylene-propylene-dienmonomer) rubber and elastoplastic mixtures obtained with either polyethylene or polypropylene in various weight percentages were studied using IR spectroscopy, thermal analysis as well as optical microscopy. The analyses proved the compatibility between EPDM elastomers and investigated plastic materials. The results could be used for choosing the suitable compositions, processing and fields for application of these composites. Keywords: EPDM (ethylene-propylene-dienmonomer) rubber, polyethylene, polypropylene, IR spectroscopy, thermal analysis

The possibility of obtaining thermally stable epoxy compositions by modifying composition of epoxy resins at 100-130°C with 6-20 phr 1,1’-(methylene-1,4-phenylene)bismaleimide and using 9-10 phr 4,4’-diaminodiphenylmethane as curing agent was studied. The cure behavior of these systems was studied using differential scanning calorimetry (DSC) and the thermograms indicated a unimodal exothermic peak for blends. The thermal stability as studied by thermogravimetric analysis (TGA) of the cured DGEBA resin was found to improve with polyaminobismaleimide blending. Keywords: epoxy resins, differential scanning calorimetry, polyaminobismaleimide

New polyesters with maleimide pendent groups have been synthesized by direct solution polycondensation reaction between 4-42 - dihydroxy- biphenyl and two functional bismaleimides containing carboxylic functionalities. The products were characterized by infrared and proton nuclear magnetic resonance spectroscopy. Thermal properties of the new synthesized copolymers were studied by thermogravimetric analyses and differential scanning calorimetry. Keywords: bismaleimides, polyesters, thermal stability

The ways leading to the increase of the flowrate of an extruder of a given geometry are examined, while considering the real situation: screw is rotating and the barrel is stationary; the granules slide onto the surface of the screw; in the granules’ relatively thick layers, relative motion takes place, equivalent to a velocity gradient. Reference was made to the granular material in the feeding zone, to the parameters specific to the feeding zone and their influence on the flowrate, through the values of the friction coefficients onto the barrel and screw (flowrate is proportional with the term , hence an increase in this term in a given case will lead to an increase in the flowrate value). The influence of both the grooves in the feeding zone and of the angle between the direction of movement of the granules and the position of grooves onto the interior surface of the barrel was analysed. There was also considered the posibility of increasing the flowrate through the increase in the bulk density of the granules in the feeding zone, while considering the influence of pressure as well as the ratio between the depth of the screw channel in the feeding zone (adjustable using grooves) and the granules’ diameter. Keywords: extruder floerate, friction coefficient, bulk density, pressure

This paper investigates the rheological properties of some o-sec-butyl-phenoxyacetic esters as a function of temperature, shear rate, and type of the polyol used to prepare the ester. The curves viscosity-temperature and viscosity-shear rate in loop tests at 20, 40, 60, 80oC were obtained and interpreted, and the activation energies of viscous flow and the creep curves were determined. Also, physical and phase changes were analyzed using differential scanning calorimetry (DSC) and correlations between the rheological and thermal behavior were established. Keywords: ester, rheology, DSC

The effect of an organophosphoric insecticide on the thermooxidative degradation of the diglycidil ether-bisphenol A epoxy resin was investigated, using infrared spectroscopy, thermogravimetric and thermodifferential analysis, pyrolysis-gas chromatography and elemental analysis. The results indicated that studied organophosphoric insecticide exercises an influence upon the degradative process of uncured resin by catalysing its decomposition in the lower temperature region. At the same time, the tested insecticide promotes the formation of a phosphorus containing thermostable solid residue. Keyword: epoxy resin, organophosphoric additive, thermooxidative degradation

An experimental study of local heat transfer at the melting of single spherical particles into a flowing liquid is presented in this paper. Local heat transfer coefficient at the particle surface, and local Nusselt number were determined using the photographical technique. Ice-spherical particles having 0,045 m in diameter, and distillated water were used in experiments. The investigations were carried out at the temperature of 303 K at 1 atm pressure, and at several values of water flow velocity ranging from 0,0971 to 0,2279 m/s. The results outline the influence of Reynolds number and proces duration on local Nusselt number. Keywords: heat transfer, local heat transfer coefficient, liquid – solid heat transfer